A high voltage direct current contact for a vacuum electron device (VED), including (a) an outer cathode line having a first hollow cylinder having a first VED connection end, (b) a contact block removably positioned within the outer cathode line, having a heater contact and a first threaded stem extending towards the first VED connection end, (c) an inner cathode line removably positioned within the first hollow cylinder and placed in contact with the contact block, the inner cathode line including a second hollow cylinder and a support plate having an opening removably receiving the first threaded stem, and (d) a heater contact line in contact with the heater contact, including a third hollow cylinder and a flange on an exterior thereof, the flange being in contact with the support plate, the third hollow cylinder having a threaded end removably coupled with the first threaded stem.

1. Field of the Invention
The present invention relates to vacuum electron devices (VEDs). More particularly, the present invention relates to input circuits for high power RF amplifiers which employ VEDs such as Klystrodes, Inductive Output Tubes (IOTs), and the like in the television broadcast service.
2. The Background Art
Vacuum tube amplifiers generally include an input circuit having three major components: the enclosure, the input resonator, and the socket. The enclosure houses the socket and the input resonator to which high voltage connections are made. Not only does the enclosure envelope the circuit, but its function is also to contain radio frequency (RF) energy within the RF compartment.
IOTs have limited life times and must be replaced from time to time. Existing IOT-based amplifier designs generally require complete removal of the amplifier input circuit from the transmitter in order to replace the VED. This process can be cumbersome and inconvenient. During tube replacement, electrical contact fingers in the socket may be easily damaged due to incorrect alignment. With damage to the contact fingers, RF energy may leak from the amplifier. RF leakage can also generate a substantial amount of heat or arcing which may damage wiring and components. In addition, misalignment may also cause RF leakage from the amplifier enclosure due to improper seating on an electro magnetic interference (EMI) gasket.
Even if the input circuit is properly seated, the high voltage leads can couple an undesirable percentage of the input RF into the transmitter's instrumentation. Due to spatial constraints, it is difficult to isolate the RF signals within the enclosure by loading it with ferrites (filter components, chokes and bobbins). Consequently, end-users currently place such RF isolation components in the transmitter output circuit. Despite the ability to combine RF components and high voltage components under the same cover, the spatial constraint limits the ability to improve the product. Aside from RF isolation, high voltage standoff issues make it difficult to incorporate a quick and easily accessible connection box.
FIG. 1 is an external perspective view of a conventional input circuit and enclosure of an amplifier employing a VED in accordance with the prior art. An enclosure cover 10 houses a radio frequency (RF) connection and high voltage connections to a VED (not shown). An air distribution system comprising a tree 12 and branches 14 access the VED enclosure through a separate entry 16 from cover 10.
FIG. 2 is a cross-sectional drawing of an input resonator and socket for a VED in accordance with the prior art. The input resonator comprises a parallel LC circuit. The inductance is provided by a shorting pin (not shown) located between the cathode 21 and grid 24 lines. The capacitance is generated by a cathode and grid structure (not shown) located in the VED. The input resonator is capacitively tuned such that the structure's parallel circuit resonant frequency matches the operational carrier frequency the VED is operated at. The cathode 21 and grid 24 lines also serve as socket collets which affix to their corresponding surfaces on the VED (not shown). The collets transfer the input RF energy to the input section of the VED. In addition, the cathode line delivers the DC beam voltage to the VED's cathode. The grid line distributes the bias voltage to the VED's grid. The socket is also comprised of a heater collet 25 and a vac-ion 31 contact. The heater collet delivers a DC voltage to the VED to provide power needed to operate the VED's cathode (not shown) at an elevated temperature. The vac-ion contact provides a DC voltage required to operate an appendage vacuum pump (not shown) located on the VED.
In operation, an alternating RF voltage is applied between the cathode 21 and grid 24 lines. The input RF voltage propagates to the input section of the VED (not shown) generating a RF voltage between the VED's grid and cathode (not shown). The VED's cathode emits electrons resulting in a bunched (density modulated) electron beam. An anode structure (not shown) operating at a high DC beam voltage accelerates the bunched beam through the anode's aperture.
The heater collet 25 is retained to cathode lines 21 and 22 through C-Clips 26 as heater collet 25 heats up cathode lines 21 and 22. Mounting screws 27 retain heater collet 25 against a high voltage insulator 28. When heater collet 25 needs to be removed for maintenance, mounting screws 27 along with C-clips 26 must be disassembled. Therefore, when a user needs to replace a component of the RF socket that houses the heater line, the entire RF socket needs to be completely removed. Such components can easily be damaged during assembly or installation of the RF socket.
Accordingly, a need exists for an improved input circuit for an RF amplifier providing a high power output which provides a good seat alignment for the VED with an EMI gasket to prevent RF leakage, an easy assembly and disassembly mechanism, a proper cooling system with RF isolation, and an easy socket interface.

High voltage connection for vacuum electron device

Communication and Power Industries, Inc.


A real-time spectrum analyzer for measuring time domain data sampled from an input signal includes a processing unit and a density histogram memory unit. The processing unit includes an FFT engine, a frequency mask detector and a frequency mask gate. The FFT engine performs FFTs on the sampled time domain data to provide FFT spectra, each FFT spectrum including multiple FFT points. The frequency mask detector determines whether each FFT point in each spectrum meets a trigger condition, and generates gate control signals corresponding to the FFT spectra based on the determinations. The frequency mask gate receives the FFT spectra and the gate control signals, and outputs only select FFT spectra that contain at least one FFT point that meets the trigger condition in response to the corresponding gate control signal. The density histogram memory unit stores the select FFT spectra for generating in a density histogram.

A conventional real-time spectrum analyzer generally receives a time domain input signal and displays corresponding frequency domain spectra, where each frequency domain spectrum represents a corresponding time interval. The spectra may be obtained by performing fast Fourier transforms (FFTs) on digital time domain data representing the time domain input signal. The display may be a density histogram display, which visually indicates the density of various frequencies. The density histogram display is periodically updated, where each update may be referred to as a "slice." Approximately 10,000 FFTs from multiple spectra form each slice.
A frequency mask trigger may be included in a conventional real-time spectrum analyzer to provide triggered measurements when used with a density histogram display. The frequency mask trigger is configured to detect a trigger condition in the spectra based on the frequency mask. When the trigger condition is detected, a fixed amount of data of the spectra is stored (and displayed), and then the trigger is re-armed. However, real-time gap free operation is lost during the data transfer, display, and re-arming processes. Further, using a conventional frequency mask trigger, all of the FFTs in the spectra of a histogram slice are displayed, regardless of how many of the FFTs actually meet the trigger condition. In other words, when the frequency mask trigger is turned on, if the trigger condition has been met for the slice, all of the FFTs of all of the spectra in that slice are displayed, even if only one FFT of one spectrum meets the trigger condition. This may be particularly problematic when the input signal is moving in and out of the trigger condition within a single slice, since the display of the slice will show FFTs that are both inside and outside the trigger condition. Although this feature may be desirable for batch mode stored data, it is not compatible with a continuous visual display of a gap-free density histogram in which a user wants to see only the domain spectra of the input signal that meet the trigger condition.

Real-time spectrum analyzer including frequency mask gate and method of operating the same


The present disclosure relates to compositions and methods for screening a plurality of polypeptide variants.

Methods for screening and identifying polypeptides having desired activities are useful in the preparation of new compounds such as enzymes, hormones, receptors and pharmaceutical compounds. Current methods for identifying novel polypeptides are often time-consuming and costly, requiring screening an enormous number of polypeptide variants, and it may take months or years to find a new polypeptide with the desired activity, if one is ever found. These limitations also make the known methods less than ideal for timely development of commercial products and processes. Thus, compositions and methods useful in accelerated identification of novel polypeptide variants having desired activities in a cost effective and time efficient manner would be highly desirable.


Aspects of the invention provide a switching power supply that exhibits an improved conversion efficiency. In aspects of the invention, a load condition detecting circuit sets a threshold voltage for determining the magnitude of the load on the DC-DC converter based on the maximum value of the output voltage of the power factor correction converter in a suspended period of the power factor correction converter. An operation permission signal is delivered when a feedback voltage that indicates the magnitude of the load of the DC-DC converter exceeds the threshold voltage. When the feedback voltage exceeds a threshold voltage that is set at a value higher than the threshold voltage, the operation permission signal is delivered.

1. Field of the Invention
Embodiments of the invention relate to switching power supplies, and, in particular, switching power supplies including power factor correction converters.
2. Description of the Related Art
Power factor correction is used for switching power supplies of power rating over 75 W to provide stability and safety in commercial power systems. Recently, a switching power supply has been proposed in Japanese Unexamined Patent Application Publication No. 2007-288855, for example, having a small-sized and highly efficient power factor correction converter (PFC) and a DC-DC converter that converts a DC voltage obtained by the PFC into an output DC voltage according to the specification of the load. The DC-DC converters employed in such switching power supplies are often quasi-resonance converters (QR) in the case of a rated load of about 100 W because of a little burden on a rectifying diode in the secondary side.
FIG. 7 shows a schematic construction of a switching power supply 1 having a power factor correction converter 2 and a DC-DC converter 3 that is a quasi-resonance converter. FIG. 7 also shows a rectifying circuit 4 that rectifies the AC power supplied by the commercial power supply 5 and delivers to the power factor correction converter 2, and a noise filter 6 interposed between the rectifying circuit 4 and the commercial power supply 5.
The power factor correction converter 2 comprises an inductor L1 connected to the rectifying circuit 4, a switching element Q1, and a diode D1. The switching element Q1 forms a current path from the rectifying circuit 4 through the inductor L1 in the ON state of the switching element Q1. The diode D1 forms a current path from the inductor L1 to an output capacitor C2 in the OFF state of the switching element Q1. The power factor correction converter 2 comprises a control circuit IC1 that ON/OFF drives the switching element Q1 to control the current flowing through the inductor L1 thereby obtaining a stable DC voltage Vb.
Resistors R1 and R2 divide the voltage Vb across the output capacitor C2. The divided voltage is fed back to the control circuit IC1. A shunt resistor R3 detects the current flowing through the load of the power factor correction converter 2. The operation and effects of the power factor correction converter 2 as described above are disclosed in detail in Japanese Unexamined Patent Application Publication No. 2010-220330, for example.
The DC-DC converter 3 that is a quasi-resonance converter basically comprises: an isolating transformer T having a primary winding P1, a secondary winding S1, and an auxiliary winding P2; a switching element Q2 connected to the primary winding P1, which receives the output DC voltage Vb of the power factor correction converter 2; a resonance capacitor C4 connected in parallel with the switching element Q2; and an output capacitor C5 connected through a rectifying diode D2 to the secondary winding S1 of the isolating transformer T. The DC-DC converter 3 comprises a control circuit IC2 that ON/OFF drives the switching element Q2 to generate quasi-resonance phenomenon with a leakage inductance of the transformer T and the resonance capacitor C4, thereby obtaining a specified output DC voltage Vo.
The resistances R5 and R6 divide the output DC voltage Vo across the output capacitor C5. The divided voltage is fed back to the control circuit IC2 through a feedback circuit. A shunt resistor R4 detects the current flowing through the switching element Q2. The DC-DC converter 3 detects a ZCD voltage developed on the auxiliary winding P2 of the isolating transformer T and controls the turn ON timing of the switching element Q2. The operation and effects of the DC-DC converter 3 that is a quasi-resonance converter as described above are disclosed in detail in Japanese Unexamined Patent Application Publication No. 2011-015570, for example.
The DC-DC converter 3 is provided with a load condition detecting circuit 7 that detects a load condition and delivers an operation permission signal EN for operation of the power factor correction converter 2 to permit or stop the operation of the power factor correction converter 2. The power factor correction converter 2 is provided with an operation control circuit 8 that permits or stops operation of the power factor correction converter 2 according to the operation permission signal EN. The load condition detecting circuit 7 suspends operation of the power factor correction converter 2 under a light load condition of an input power lower than 75 W, for example, to eliminate any power loss in the power factor correction converter 2. Thus, the overall power conversion efficiency of a switching power supply 1 is improved.
The load condition detecting circuit 7 is constructed as shown in FIG. 8, for example, and installed in the control circuit IC2. The load condition detecting circuit 7 comprises a comparator 7b, which is a light load detecting circuit, and a comparator 7c, which is a middle load detecting circuit. The light load detecting circuit 7b determines a light load condition and sets a flip-flop 7a when the feedback voltage FB, which is used for ON/OFF controlling the switching element Q2 in the DC-DC converter 3, falls below a preset first threshold voltage Vref1. The middle load detecting circuit 7c determines a middle load condition, which is with an ordinary load, and resets the flip-flop 7a when the feedback voltage FB exceeds a second threshold voltage Vref2, which is larger than Vref1 and explained later. The output of the flip-flop 7a is used for set/reset control of a flip-flop 7e after delaying processing through a delay circuit 7d utilizing charging and discharging of a capacitor Ct. Thus, the operation permission signal EN is obtained as a set output of the flip-flop 7e.
The delay circuit 7d comprises the capacitor Ct and a switching element S connected in parallel with the capacitor Ct. When the output of the flip-flop 7a is in an H level, the switching element S is in an OFF state to charge the capacitor Ct with a constant current source It. When the output of the flip-flop 7a is at an L level, the switching element S is in an ON state to discharge the charges accumulated on the capacitor Ct through the resistor Rt. The load condition detecting circuit 7 comprises comparators 7f and 7g. The comparator 7f resets the flip-flop 7e when the charged voltage Vd on the capacitor Ct exceeds a second reference voltage Vth2; and the comparator 7g sets the flip-flop 7e when the charged voltage Vd falls below a first reference voltage Vth1.
FIG. 9 illustrates waveforms in operation of the load condition detecting circuit 7 having the construction described above. When the load Po becomes lighter and the feedback voltage FB drops below the first threshold value Vref1, the flip-flop 7a is set. According to the setting of the flip-flop 7a, the switching element S in the delay circuit 7d turns OFF and the capacitor Ct is charged with a rate determined by the capacitance of the capacitor Ct and the magnitude of the constant current fed by the constant current source It. After a specified period of time Td-off when the charged voltage Vd of the capacitor Ct exceeds the reference voltage Vth2, the flip-flop 7e is reset and the operation permission signal EN turns to an L level to control the power factor correction converter 2 to stop.
After stop of operation of the power factor correction converter 2, the output voltage Vb of the power factor correction converter 2 gradually decreases and then settles down to a voltage determined by the AC voltage Vac supplied by the commercial power supply 5. The output voltage Vb of the power factor correction converter 2 changes periodically with a period of rectification of the AC voltage Vac and an amplitude determined by the magnitude of the load Po and the capacitance of the output capacitor C2.
In this suspended state of operation of the power factor correction converter 2, when the load Po becomes heavy, the feedback voltage FB in the DC-DC converter 3 rises. When the feedback voltage FB exceeds the second threshold voltage Vref2, the flip-flop 7a is reset and the charges accumulated on the capacitor Ct in the delay circuit 7d are discharged. After a specified period of time Td-on when the charged voltage Vd of the capacitor Ct falls below the reference voltage Vth1, the flip-flop 7e is set to turn the operation permission signal EN to an H level. Consequently, operation of the power factor correction converter 2 is permitted and the power factor correction converter 2 resumes operation.
In the suspended state of the power factor correction converter 2, the DC voltage Vb obtained at the output capacitor C2 of the power factor correction converter 2 changes periodically as described previously with an amplitude determined by the magnitude of the load Po and the capacitance of the output capacitor C2. Accordingly, it has been noted conventionally that the bottom voltage Vb-min of the DC voltage Vb varies depending on the magnitude of the load Po and thus, the second threshold voltage Vref2 for the feedback voltage FB has been set based on the minimum of the DC voltage Vb, the bottom voltage Vb-min.
When the AC voltage Vac is lower than the rated voltage, for example 100 V, or in the case of a small capacitance of the output capacitor C2, even through without large variation in the load Po, the feedback voltage FB rises with decrease in the DC voltage Vb as described earlier. Thus, a situation arises that the feedback voltage FB becomes higher than the second threshold voltage Vref2 that is set based on the minimum of the DC voltage Vb, the bottom voltage Vb-min. This situation causes erroneous detection of increase in the load Po. Thus there is a problem that distinct detection of the rise of the feedback voltage FB that is caused by the increase in the load Po cannot be assured.
FIG. 10 shows a relationship between the feedback voltage FB and the DC voltage Vb depending on the AC voltage Vac in the case of a load Po of a constant value of 30 W, for example. It is shown that the feedback voltage FB increases with decrease in the DC voltage Vb. When the output DC voltage Vb becomes below about 85 V, the feedback voltage FB is always higher than the second threshold voltage Vref2 despite the fact that the load Po is in a light load condition of 30 W constant.
The comparator 7c detects this state to reset the flip-flop 7a, which in turn sets the flip-flop 7e and turns the operation permission signal EN to an H level. Thus, the power factor correction converter 2 changes into an operating state according to the operation permission signal EN despite no change in the magnitude of the load Po. Therefore, it becomes impossible to perform the intended operation in which when the DC voltage Vb decreases with drop of the AC voltage Vac, the power factor correction converter 2 resumes operation thereof after detecting increase in the load Po in a suspended state of the power factor correction converter 2.
To cope with this problem, the second threshold voltage Vref2 could be set relatively high. A high value of the second threshold voltage Vref2, however, makes detection of increased load Po difficult. As a result, when the AC voltage Vac is stable at a sufficiently high value and the operation of the power factor correction converter 2 is suspended, increase in the load Po may not cause operation of the power factor correction converter 2 resume. As a consequence, the DC-DC converter 3 may also fail to adapt to and deal with the increase in the load Po, causing another problem of poor operation of the switching power supply itself. Thus, as has been discussed above, there is a need in the art for an improved switching power supply.

Switching power supply including threshold based permissions


A process for transalkylating a coal tar stream is described. A coal tar stream is provided, and is fractionated to provide at least one hydrocarbon stream having polycyclic aromatics. The hydrocarbon stream is hydrotreated in a hydrotreating zone, and then hydrocracked in a hydrocracking zone. A light aromatics stream is added to the hydrocracking zone. The light aromatics stream comprises one or more light aromatics having a ratio of methyl/aromatic available position that is lower than a ratio of methyl/aromatic available position for the hydrotreated stream. The hydrocracked stream is transalkylated in the hydrocracking zone.

Many different types of chemicals are produced from the processing of petroleum. However, petroleum is becoming more expensive because of increased demand in recent decades.
Therefore, attempts have been made to provide alternative sources for the starting materials for manufacturing chemicals. Attention is now being focused on producing liquid hydrocarbons from solid carbonaceous materials, such as coal, which is available in large quantities in countries such as the United States and China.
Pyrolysis of coal produces coke and coal tar. The coke-making or "coking" process consists of heating the material in closed vessels in the absence of oxygen to very high temperatures. Coke is a porous but hard residue that is mostly carbon and inorganic ash, which is used in making steel.
Coal tar is the volatile material that is driven off during heating, and it comprises a mixture of a number of hydrocarbon compounds. It can be separated to yield a variety of organic compounds, such as benzene, toluene, xylene, naphthalene, anthracene, and phenanthrene. These organic compounds can be used to make numerous products, for example, dyes, drugs, explosives, flavorings, perfumes, preservatives, synthetic resins, and paints and stains. The residual pitch left from the separation is used for paving, roofing, waterproofing, and insulation.
There is a need for additional processes for increasing the yield of desirable aromatics, such as xylenes, from hydrocarbons such as coal tar organic compounds.

Hydrocracking process for a hydrocarbon stream


A chip resistor (1) includes a chip substrate (2) a mutually separated terminal electrodes (3, 4) formed on the upper surface of the substrate (2), and a meandering resistor film (5) formed between the two terminal electrodes (3, 4). Each of the terminal electrodes (3, 4) includes an inner edge (3a, 4a) extending diagonally from one side surface (2a) toward the other side surface (2b) of the chip substrate (2). Each of the inner edges (3a, 4a) has a portion closer to the resistor film (5) that is electrically connected to a narrow portion (7, 8) formed integral with the resistor film (5). The narrow portion extends outward from an end (5a, 5b) of the resistor film (5).

Conventionally various types of chip resistors have been proposed. For instance, the Patent Document 1 listed below discloses a chip resistor having a structure as shown in FIG. 9 of the present application. The Patent Documents 2 and 3 disclose a chip resistor having a structure as shown in FIG. 11 of the present application. It should be noted here that the chip resistor shown in FIG. 10 of the present application is not presented as prior art, but as a comparative example only for better understanding of the present invention.
Patent Document 1: JP-A-H11-273901
Patent Document 2: JP-A-2000-216001
Patent Document 3: JP-A-2002-203702
Specifically, the conventional chip resistor R1 shown in FIG. 9 of the present application includes a substrate A1, a resistor film A2 and a pair of terminal electrodes A3 connected to the resistor film A2. The substrate A1 has a predetermined length L and a predetermined width W. The resistor film A2 is formed with a trimming groove A4 for resistance adjustment.
In the chip resistor R1, the single resistor film A2 is provided between the paired terminal electrodes A3. With this arrangement, when a voltage is applied between the paired terminal electrodes A3, current flows only through the resistor film A2. Therefore, when the chip resistor R1 is applied to a circuit for high power supply, the temperature of the resistor film A2 may become excessively high. In such a case, the circuit may fail to operate properly.
This problem may be solved by employing the structure shown in FIG. 10, for example. Specifically, the chip resistor R2 shown in the figure includes a substrate B1, a plurality of resistor films B2 and a pair of terminal electrodes B3. The length L and the width W of the substrate B1 are equal to those of the above-described substrate A1. Each of the terminal electrodes B3 is formed on a longitudinally-extending side surface of the substrate B1. The resistor films B2 are connected in parallel with each other with respect to the paired electrodes B3. In the chip resistor R2 of this structure, the current flows as dispersed into the plurality of resistor films B2. Thus, although the size of the chip resistor R2 is the same as that of the chip resistor A, the rated power of the chip resistor R2 is large.
However, in the chip resistor R2, the effective length (length of the portion which functions as a resistor element) of each of the resistor films B2 is shorter than that of the resistor film A2 of the chip resistor R1. Therefore, when the chip resistor R2 has the application of a surge voltage, its resistance tends to vary significantly (meaning that the resistor has a low surge resistance).
With reference to FIG. 11 of the present application, the chip resistor disclosed in the Patent Document 2 or 3 will be described below. The chip resistor R3 shown in the figure includes a substrate 31, electrodes 32 and 33 formed on the substrate and a resistor element 34. The left end 37 of the resistor element 34 is connected to a projection 35 of the electrode 32, whereas the right end 38 of the resistor element 34 is connected to a projection 36 of the electrode 33. The resistor element 34 extends in a meandering manner between the two electrodes 32 and 33. With this arrangement, the current path in the resistor element 34 is longer than that of a resistor element extending straight between the two electrodes. Thus, the surge resistance of the chip resistor R3 is enhanced.
Further, by connecting the opposite ends of the resistor element 34 to the projections 35 and 36 of the electrodes 32 and 33, a sufficient distance is secured between the inner edge 32a of the electrode 32 and the outer edge 34a of the resistor film 34 (or between the inner edge 33a of the electrode 33 and the outer edge 34b of the resistor film 34). Thus, in forming the resistor element 34 and the electrodes 32 and 33 on the substrate 31 by screen printing, the resistor element 34 and the electrodes 32, 33 are prevented from becoming too close to or coming into contact with each other (if the resistor element and the electrodes are too close, discharge occurs between them).
However, the structure shown in FIG. 11 has the following drawbacks.
As described above, the electrodes 32 and 33 (and the resistor element 34) can be formed by screen printing. Specifically, a screen for printing formed with holes corresponding to the shape of the electrodes 32 and 33 is prepared. Then, the screen is placed on the upper surface of the substrate 31. Then, material paste is applied from the upper surface side of the screen. Then, the material paste is loaded into the holes for electrode formation by using a squeegee. Finally, the screen is removed from the substrate 31. In this way, the electrodes 32 and 33 are formed.
In the above-described process, however, in removing the screen from the substrate 31, part of the material paste loaded in the holes may be removed from the substrate 31 together with the screen. In such a case, the projections 35 and 36 of the electrodes 32 and 33 cannot have a desired straight edge but have a round edge as indicated by the double-dashed lines α and β in FIG. 11. As a result, the distance L0 between the two electrodes 32 and 33 is larger than the proper distance L, which causes the resistance of the chip resistor R3 to deviate from the desired value.

Chip resistor and its manufacturing process


A digital data storage apparatus has primary, secondary and backing storage elements characterized by respectively longer access times. A level detector signals when the quantity of data in the secondary store exceeds a threshold amount. A data migrator responds by moving selected data files from the secondary store to the backing store. The apparatus also includes a baseline back-up element that stores archive copies of a set of selected data files. A full back-up element stores archive copies of those files that, (1) were originally copied to the baseline back-up set but have since changed, or (2) are not otherwise within the baseline back-up set. For those files which were originally copied to the baseline back-up set and which have not changed, the full back-up element stores pointers indicating locations of the respective files in the baseline back-up set.

This disclosure includes Appendices A, B and C, which have not been printed with the specification but are available in the application file. Appendices A and B are software for carrying out the invention. Appendix C is a copy of application Ser. No. 07/452,960, filed Dec. 19, 1989 and incorporated herein by reference.
This application relates to digital data processing and, more particularly, relates to methods and apparatus for improved data migration.
The use of storage-intensive computer applications such as high-performance, high-resolution graphics has grown significantly in recent years, with indications that it will continue to grow through the next decade. Fueling user demand has been the introduction of lower cost 32-bit workstations and an increase in the base of applications software available for those systems. Because of their computational and graphics power, these workstations are employed in data-intensive applications such as electronic publishing, computer-aided design (CAD) and scientific research.
Paralleling these developments has been the emergence of industry standard communication protocols which permit users to operate in a multi-vendor environment. Of particular interest is the Network File System (NFS) protocol, developed by Sun Microsystems, allowing users to share files across a local area network such as Ethernet.
Thus, over the past few years, available CPU power per site has grown by several orders of magnitude, due largely to the introduction of engineering workstations and personal computers. The growth in secondary storage capacity, however, has not kept pace. Data intensive applications such as mechanical CAD, electrical CAD, scientific visualization and computer generated animation are straining the data storage capability of existing file servers. The data storage requirements of professional work groups employing networked workstations can measure billions of bytes--i.e., Gigabytes--in size. Much of this results from users generating and accumulating large file sets which have aged, but which are considered valuable for future use.
Conventional options for increasing data storage capacity are often excessively costly or inconvenient to implement. Additional file servers can be incorporated into an existing computer network, but each additional server has a high incremental cost and adds to the administrative burden of managing the network.
Alternatively, the additional data can be stored offline on magnetic tape or other archival storage media. The economic costs associated with online storage of large data accumulations often compel system administrators to periodically remove apparently inactive data from online file server environment, archiving it to magnetic tape or an equivalent medium. This offline storage is much more economical than magnetic disk storage, and the use of such storage has grown commensurately with file server capacity. In 1987, a typical file server contained 105 Megabytes of data for each workstation it supported. In 1988, this typical storage level grew to 155 Megabytes, a 47% increase in one year. The typical number of archival data tapes grew from 47 to 65 per server in that same period.
While offline storage is economical, management of such offline tape libraries is often labor-intensive and error prone. Moreover, conventional archiving techniques share a number of deficiencies. For example, the selection of information to be archived is often arbitrary. Secondly, in many computing systems, such as those running under the UNIX operating system, no ready means is provided for cataloging information stored offline, requiring users to manually track their own information files. Related to these archival problems are those of migrating data--transferring computer data files, typically on off-line media, to an on-line medium, so that the files can be read and utilized by computers or processors in the network. Workstation users experience significant delays when it becomes necessary to retrieve information from the offline volumes. These delays are both frustrating and expensive.
In view of these and other problems presented by prior art data storage, the object of this invention is to provide digital data storage systems having the speed and convenience of online data storage, and the economy and large capacity of offline storage.
It is a further object of the invention to provide digital data storage systems that incorporate improved data migration methods.
Another object of the invention is to provide a data migration system that reduces the time associated with conventional data migration schemes, to the point that data migration occurs in a manner that is "transparent"--i.e., not discernable to the user.

Digital data storage system with improved data migration


Embodiments of the present invention disclose a method, computer program product, and system for user interface customization. A computer records activity of a first computer on a user interface. The computer determines one or more repetitive activities of the first computer utilizing the recorded activity of the first computer. The computer determines a customized user interface for the first computer corresponding to the one or more repetitive activities of the first computer. In another embodiment, the computer initiates display of the customized user interface to the first computer. In another embodiment, the recorded activity of the first computer includes navigation through links in the user interface, applying filters to data in the user interface, and accessing data on the user interface.

In an organization, a dashboard presents data relevant to a specific objective or business process (i.e. sales, production, and marketing) in an interactive user interface. Reporting data for business processes involves data corresponding to numerous relevant attributes. Dashboards primarily include a visual presentation of key performance indicators (KPIs), and allow an individual accessing the dashboard to navigate further into sections of the dashboard to see additional data. Individuals utilizing dashboards can have the ability to filter the data displayed on the dashboard (i.e. KPIs), and select attributes to display and compare data.
Business Intelligence (BI) involves analyzing data corresponding to a business and various processes associated with the business. This data can be presented in the form of a dashboard. Business Intelligence (BI) and dashboard applications can include logging capabilities that record and store actions of individuals utilizing dashboards. In some examples, the BI applications record and store the data corresponding to how individuals access a dashboard and utilize the dashboard (i.e. applying filters, navigation, and data comparisons).

Customizing a dashboard responsive to usage activity

International Business Machines Corporation


An electronic device has a physical port, and a control circuit coupled to the physical port. The control circuit is arranged to electrically sense the physical port, and operate the physical port as one of an Ethernet port and an RS-232 port based on electrically sensing the physical port. In some arrangements, the physical port operates as an Ethernet port at one time and an RS-232 port at another time. In some arrangements, the electronic device senses for Ethernet signals and RS-232 signals concurrently. In other arrangements, the electronic device senses for Ethernet signals and RS-232 signals at different times in an alternating manner.

A conventional router typically includes a set of Ethernet ports and a serial console port. Each Ethernet port typically includes an RJ-45 style female jack to receive a connecting end of an Ethernet cable (e.g., a Cat-3, Cat-5, Cat-5e or better). The serial console port typically includes a DB-9 or DB-25 connector or an RJ-45 jack to receive a connecting end of an RS-232 cable.
During operation, the conventional router sends and receives Ethernet communications signals through its Ethernet ports. Each Ethernet communications signal is a differential signal having a positive (+) signal component and a negative (−) signal component which is opposite the positive signal component and isolated from ground. Some router devices operate as PSE (power sourcing equipment) to provide power concurrently with communications signals through the Ethernet ports to PDs (powered devices) in accordance with established Power over Ethernet (PoE) standards.
In contrast to the above-described Ethernet ports which carry Ethernet communications signals and possibly power, the serial console port provides an administrative interface for a local "dumb" terminal. That is, the serial console port is a serial communication physical interface through which a user is able to carry out a number of local administrative functions that could not or should not be conducted over an Ethernet connection. For instance, the operating system of the router may treat a user login session through the local terminal, which is connected to the serial console port, as more trustworthy/secure.

Dual utilization of a physical port of an electronic device


Disclosed are a method for controlling a driving of a drum type washing machine preventing vibration and noise of a drum, reducing a usage of washing water, and reducing rinse time, and an apparatus thereof. To this end, the drum is rotated with a preset equilibrium speed faster than a speed that vibration of the drum is excessively generated accordingly as a rotation speed of the drum is decreased when a dewatering process of laundry is completed, and washing water is supplied into the drum type washing machine while maintaining the drum as the preset equilibrium speed.

1. Field of the Invention
The present invention relates to a washing machine, and more particularly, to a method for controlling a driving of a drum-type washing machine and an apparatus thereof.
2. Description of the Conventional Art
Generally, a washing machine is a mechanical apparatus for washing laundry by performing a washing process, a rinse process, and a dewatering process. The washing machine is divided into a pulsator method, an agitation method, a drum method, and etc. according to a washing method. Hereinafter, a general drum type washing machine will be explained with reference to FIG. 1.
FIG. 1 is a sectional view showing a construction of a drum type washing machine in accordance with the conventional art.
As shown, the drum type washing machine comprises a casing 12, a tub 17 arranged in the casing 12, and a drum 15 rotatably arranged in the tub 17.
Hereinafter, a construction of the drum type washing machine according to the conventional art will be explained in more detail.
The casing 12 has a rectangular parallelepiped shape, and an aperture 22 through which laundry is put in/out is formed at a front side of the casing 12. A door 23 for opening and closing the aperture 22 is disposed at a lateral surface of the aperture 22. The tub 17 for accommodating washing water is installed in the casing 12, and a supporting spring 11 and a damper 18 for shock-absorbingly supporting the tub 17 are respectively installed at upper and lower sides of the tub 17.
A spider 13 for rotatably supporting the drum 15 is coupled to a rear side of the tub 17, and a drum driving motor 14 for rotating the drum 15 is integrally coupled to a rear lateral surface of the spider 13.
A water supply pipe and a water supply valve (not shown) for supplying washing water into the tub 17 are installed at an upper portion of the tub 17, and a drain pump 19 for draining washing water through a drain pipe 16 is installed at a lower portion of the tub 17.
A cyclic water pipe 20 for taking out washing water inside the tub 17 and circulating the taken washing water into the upper portion of the tub 17 is installed at one side of the drain pipe 16, and a circulation pump 21 for pumping washing water is installed at the cyclic water pipe 20.
According to this, when laundry is received in the drum 15 and detergent and washing water are supplied thereto, a control unit (not shown) controls the drum driving motor 14 thus to rotate the drum 15 and drives the circulation pump 21 thus to circulate washing water.
Then, when the washing process is completed, the control unit controls the drain pump 19 and the drum driving motor 14 thus to perform a drain process and a dewatering process in turn and supplies washing water into the tub 17 thus to perform a rinse process several times. Herein, the rinse process is performed several times, and whenever the rinse process is performed one time, the drain process and the dewatering process are also performed one time.
When the dewatering process is performed in a state that laundry is arranged with eccentricity in the drum 15, the drum 15, the tub 17, and a supporting component for the drum 15 (not shown) are damaged and forcibly abraded. Accordingly, in order to prevent the damage and forcible abrasion, an amount of eccentricity of the drum 15 has to be detected before the dewatering process and when the amount of eccentricity is less than a preset reference value, the dewatering process has to be performed.
However, in the conventional drum type washing machine, when the dewatering process is completed after the washing process, or when the dewatering process is completed after the rinse process, a rotation speed of the drum is gradually decreased and the drum is stopped. According to this, vibration and noise are generated at a speed section where vibration of the drum 15 is drastically increased (for example, 150˜200 rpm (revolution per minute)).
Also, in the conventional drum type washing machine, an amount of eccentricity of the drum 15 is detected in a state that the drum 15 is rotated with a speed which is a little increased than a rotation speed of the drum 15 at the time of a washing process after the drum 15 is completely stopped after the washing process is performed, so that vibration and noise are generated at a speed section where vibration of the drum 15 is drastically increased (for example, 150˜200 rpm (revolution per minute)).
Besides, in the conventional drum type washing machine, when the detected amount of eccentricity exceeds the preset reference value (a reference value of an amount of eccentricity of the drum), the drum 15 is stopped and then is driven again, which is repeatedly performed several times or a dozen times According to this, it takes a lot of time to detect an amount of eccentricity of the drum 15 and then to proceed to a next step by making the amount of eccentricity be less than the preset reference value.
Besides, in the drum type washing machine according to the conventional art, an amount of eccentricity of the drum 15 is detected at a low speed and when the detected amount of eccentricity is less than the preset reference value, a rotational speed of the drum 15 is increased. According to this, the amount of eccentricity of the drum is again increased thus to cause vibration and noise.
In addition, in the drum type washing machine according to the conventional art, the time taken to rinse laundry with washing water is less than the time taken to supply washing water in order to rinse laundry, so that much washing water is put into the tub 17 and time for performing the rinse process is increased.
Minute explanations for the drum type washing machine according to the conventional art are also disclosed in U.S. Pat. Nos. 6,615,619 and 6,612,138.

Method for controlling driving of drum-type washing machine and apparatus thereof


A sensor is used to detect luminescent radiation that is radiated from a reflector as a result of state changes induced by a beam of radiation being incident on an area of the reflector. The intensity of the luminescent radiation at particular wavelengths can be used to determine the intensity of the beam of radiation.

1. Field of the Invention
The present invention relates to a lithographic projection apparatus and lithographic apparatus and device manufacturing method.
2. Description of the Related Art
The term "patterning device" as here employed should be broadly interpreted as referring to device that can be used to endow an incoming radiation beam with a patterned cross-section, corresponding to a pattern that is to be created in a target portion of the substrate. The term "light valve" can also be used in this context. Generally, the pattern will correspond to a particular functional layer in a device being created in the target portion, such as an integrated circuit or other device (see below). An example of such a patterning device is a mask. The concept of a mask is well known in lithography, and it includes mask types such as binary, alternating phase-shift, and attenuated phase-shift, as well as various hybrid mask types. Placement of such a mask in the radiation beam causes selective transmission (in the case of a transmissive mask) or reflection (in the case of a reflective mask) of the radiation impinging on the mask, according to the pattern on the mask. In the case of a mask, the support will generally be a mask table, which ensures that the mask can be held at a desired position in the incoming radiation beam, and that it can be moved relative to the beam if so desired.
Another example of a patterning device is a programmable mirror array. One example of such an array is a matrix-addressable surface having a viscoelastic control layer and a reflective surface. The basic principle behind such an apparatus is that, for example, addressed areas of the reflective surface reflect incident light as diffracted light, whereas unaddressed areas reflect incident light as undiffracted light. Using an appropriate filter, the undiffracted light can be filtered out of the reflected beam, leaving only the diffracted light behind. In this manner, the beam becomes patterned according to the addressing pattern of the matrix-addressable surface. An alternative embodiment of a programmable mirror array employs a matrix arrangement of tiny mirrors, each of which can be individually tilted about an axis by applying a suitable localized electric field, or by employing piezoelectric actuators. Once again, the mirrors are matrix-addressable, such that addressed mirrors will reflect an incoming radiation beam in a different direction to unaddressed mirrors. In this manner, the reflected beam is patterned according to the addressing pattern of the matrix-addressable mirrors. The required matrix addressing can be performed using suitable electronics. In both of the situations described hereabove, the patterning device can comprise one or more programmable mirror arrays. More information on mirror arrays as here referred to can be seen, for example, from U.S. Pat. Nos. 5,296,891 and 5,523,193, and WO 98/38597 and WO 98/33096. In the case of a programmable mirror array, the support may be embodied as a frame or table, for example, which may be fixed or movable as required.
Another example of a patterning device is a programmable LCD array. An example of such a construction is given in U.S. Pat. No. 5,229,872. As above, the support in this case may be embodied as a frame or table, for example, which may be fixed or movable as required.
For purposes of simplicity, the rest of this text may, at certain locations, specifically direct itself to examples involving a mask and mask table. However, the general principles discussed in such instances should be seen in the broader context of the patterning device as hereabove set forth.
Lithographic projection apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In such a case, the patterning device may generate a circuit pattern corresponding to an individual layer of the IC, and this pattern can be imaged onto a target portion (e.g. comprising one or more dies) on a substrate (silicon wafer) that has been coated with a layer of radiation-sensitive material (resist). In general, a single wafer will contain a whole network of adjacent target portions that are successively irradiated via the projection system, one at a time. In current apparatus, employing patterning by a mask on a mask table, a distinction can be made between two different types of machine. In one type of lithographic projection apparatus, each target portion is irradiated by exposing the entire mask pattern onto the target portion at once. Such an apparatus is commonly referred to as a wafer stepper. In an alternative apparatus, commonly referred to as a step-and-scan apparatus, each target portion is irradiated by progressively scanning the mask pattern under the beam in a given reference direction (the "scanning" direction) while synchronously scanning the substrate table parallel or anti-parallel to this direction. Since, in general, the projection system will have a magnification factor M (generally <1), the speed V at which the substrate table is scanned will be a factor M times that at which the mask table is scanned. More information with regard to lithographic devices as here described can be seen, for example, from U.S. Pat. No. 6,046,792.
In a known manufacturing process using a lithographic projection apparatus, a pattern (e.g. in a mask) is imaged onto a substrate that is at least partially covered by a layer of radiation-sensitive material (resist). Prior to this imaging, the substrate may undergo various procedures, such as priming, resist coating and a soft bake. After exposure, the substrate may be subjected to other procedures, such as a post-exposure bake (PEB), development, a hard bake and measurement/inspection of the imaged features. This array of procedures is used as a basis to pattern an individual layer of a device, e.g. an IC. Such a patterned layer may then undergo various processes such as etching, ion-implantation (doping), metallization, oxidation, chemo-mechanical polishing, etc., all intended to finish off an individual layer. If several layers are required, then the whole procedure, or a variant thereof, will have to be repeated for each new layer. It is important to ensure that the overlay (juxtaposition) of the various stacked layers is as accurate as possible. For this purpose, a small reference mark is provided at one or more positions on the wafer, thus defining the origin of a coordinate system on the wafer. Using optical and electronic devices in combination with the substrate holder positioning device (referred to hereinafter as "alignment system"), this mark can then be relocated each time a new layer has to be juxtaposed on an existing layer, and can be used as an alignment reference. Eventually, an array of devices will be present on the substrate (wafer). These devices are then separated from one another by a technique such as dicing or sawing, whence the individual devices can be mounted on a carrier, connected to pins, etc. Further information regarding such processes can be obtained, for example, from the book "Microchip Fabrication: A Practical Guide to Semiconductor Processing", Third Edition, by Peter van Zant, McGraw Hill Publishing Co., 1997, ISBN 0-07-067250-4.
For the sake of simplicity, the projection system may hereinafter be referred to as the "lens." However, this term should be broadly interpreted as encompassing various types of projection system, including refractive optics, reflective optics, and catadioptric systems, for example. The radiation system may also include components operating according to any of these design types for directing, shaping or controlling the projection beam of radiation, and such components may also be referred to below, collectively or singularly, as a "lens". Further, the lithographic apparatus may be of a type having two or more substrate tables (and/or two or more mask tables). In such "multiple stage" devices the additional tables may be used in parallel or preparatory steps may be carried out on one or more tables while one or more other tables are being used for exposures. Dual stage lithographic apparatus are described, for example, in U.S. Pat. Nos. 5,969,441 and 6,262,796.
In order to ensure that the resist receives the correct exposure dose, it is important that the intensity of the radiation beam at substrate level be controlled during exposure. Unfortunately, intensity measurement during exposure is very difficult to perform without either altering the intensity or altering the intensity distribution (uniformity). Therefore in conventional lithographic apparatus, a combination of sensors is typically used to minimize the disturbance: a first sensor normally attached to the substrate table such that it can be positioned in the beam for measurements between exposures, and a second sensor at a suitable position in the optical path, for example mounted on a portion of a reflector, to measure the intensity of a region of the beam during exposure. Using the first sensor between exposures, very accurate measurements may be made of the beam intensity and the beam intensity distribution, and the characteristics of the apparatus may be analyzed by measuring the relative intensities measured by the different sensors under different conditions. This data can then be used to predict the intensity at substrate level using only measurements by the second sensor. The disadvantage of this is that there will always be either a disturbance in the intensity due to the presence of the second sensor.
Alternatively, one of the reflectors in the apparatus may be partially silvered, allowing a portion of the incident radiation to pass through the reflector to a sensor behind the reflector, or may redirect a portion of the beam to a sensor. This arrangement intrinsically reduces the intensity of the beam, which in turn reduces the throughput of the apparatus. Apparatus using EUV radiation are especially sensitive to this problem since EUV reflectors are naturally very inefficient. High reflectivity mirrors for EUV radiation are not currently available. Furthermore, in lithographic projection apparatus employing EUV radiation, the beam is radiated in an evacuated system to prevent losses in intensity. Therefore the beam intensity sensors must also be located within the evacuated system and must therefore be designed to be vacuum tolerant and to not outgas when placed in the vacuum.

Lithographic apparatus and device manufacturing method


Computer-implemented methods, apparati, and computer-readable media for detecting malicious computer code in a file (2) associated with a computer (10). A method of the present invention comprises the steps of determining whether there is more than one hard link (1) to the file (2); and when there is more than one hard link (1), ascertaining the identities of all the hard links (1), and performing an antivirus scan on the file (2) based upon the hard link(s) (1) having the most restrictive scanning criteria of all the hard links (1), or upon the union of scanning criteria amongst all the hard links (1).

The invention will be illustrated in conjunction with NTFS (New Technology File System). NTFS is present in every NT and higher operating system manufactured by Microsoft Corporation. In NTFS, the attributes of a file 2 within a computer 10 (see FIG. 1) are stored in alternate data streams. A file 2 is a composition of many streams. In NTFS, any data stream can have multiple alternate data streams associated therewith.
NTFS 5.0 (and above) supports multiple hard links 1. A "hard link 1" is a pointer to the file 2 that comprises, at a minimum, the file name. The hard link may comprise the full path name including the file name. Since there can be multiple hard links 1, any file 2 can have multiple file names, even though there is but one physical version of the file 2. Two or more of the file names can point to the same file 2 data, but be located in the same or different directories. FIG. 1 shows an example in which there are three hard links 1 to file 2. Modifying file via any one of the hard links 1 changes the underlying data pointed to by all of the hard links 1.
NTFS considers all file names to be hard links 1 to the file in question, but most files 2 have just one hard link 1 associated with that file 2. An NTFS file 2 is deleted when all hard links 1 to it are removed, i.e., when the last hard link 1 is removed. This means that a first hard link 1 (1) could be created for file 2 in a first directory, a second hard link 1 (2) could be created for the file 2 in another directory, the first hard link 1 (1) could be deleted, and the second hard link 1 (2) would still exist.
Other operating systems also support hard links, e.g., UNIX (in which they are called hard links) and OS2 (in which they are called shadows).
Antivirus scanners often make optimization decisions based upon the path or extension of a file 2. For example, if an ostensibly temporary file having the extension .tmp is opened, the antivirus scanner may decline to scan the contents of the file 2, because a .tmp file is not deemed by the antivirus scanner to be executable. However, if that .tmp file name is actually a hard link 1 (2) to an existing .exe file 2, modifying the .tmp file actually modifies the .exe file as well. In this scenario, the antivirus scanner could be lulled into not scanning a file 2 for the presence of malicious code when it should be scanning the file 2. This can result in computer 10 being harmed by the malicious code. As used herein, "malicious code" means any computer code that enters the computer 10 without an authorized user's knowledge and/or without an authorized user's consent. Thus, "malicious code" can include viruses, worms, and Trojan horses. As used herein, the term "antivirus scanner" is used in the broad sense, so that such scanner can detect all types of malicious code, including worms and Trojan horses as well as viruses.
An NTFS file 2 contains the number of hard links 1 to the file 2, but it does not identify the hard links 1 any further. Thus, when a user accesses file 2 via the second hard link 1 (2), this user knows that there are two other hard links 1 (1) and 1 (3), but is not told what they are. The only way for the user to find the other hard links 1 (1) and 1 (3) is to note the serial number that is included in each NTFS file 2, and then to do a search for all of the files 2 in the computer 10 matching that serial number. That is an extremely time consuming and cumbersome operation, and is the problem addressed by the present invention.
Bolosky et al., "Single Instance Storage in Windows 2000", downloaded from the Internet on Oct. 11, 2002 at http://research.Microsoft.com/sn/Farsite/WSS2000.pdf, discloses the creation of backpointer tables in cases where a single file has multiple hard or symbolic links pointing to the file. Unlike the present invention, where the contents of file 2 do not change, an attempt to modify the contents of the target file in the reference results in a new version of the target file being created.

Antivirus scanning in a hard-linked environment


A housing for holding a disc-shaped information carrier having a bottom section including a holding device, and a cover section which is hingeably connected to the bottom section. The bottom section is box-shaped and has transparent front, side and rear walls. The bottom section contains an insert sheet having portions which extend adjacent each of these transparent walls, including substantially the length of the side walls. Each of these portions may be provided with readable data relating to the information stored in the information carrier.

The invention relates to a housing for holding a disc-shaped information carrier, and more particularly to such a housing which comprises a bottom section having a holding device for holding the information carrier, and a cover section which is hingeably connected to the bottom section at a back side of the housing. The bottom section has a bottom wall, a transparent front wall which faces the back side of the housing, two side walls, and an insert sheet arranged on the bottom wall. The insert sheet has an upright portion which extends adjacent the front wall, and contains printed information which is readable through the front wall.
Such a housing is known from DE-A 34 25 579 and is used for the storage of an optical information disc, particularly a Compact Disc. The known housing comprises a bottom section having a central clamping device for clamping the optical disc. The bottom section has raised side walls, of which one side wall forms an uninterrupted front wall and of which two opposite side walls have recesses for the removal of the information disc from housing. The bottom section generally contains an insert sheet which has a folded upright front portion which faces the transparent raised front wall. The front portion can accommodate readable data about the information stored digitally in the information disc. The central clamping device is retained in the bottom section by snap pins in the side walls at intermediate locations between the front and rear side walls, and the central portion of the side walls between the snap pins is interrupted by a space into which the disc extends. This space permits easy gripping of the edge of the disc so that a user can remove it.
A drawback of the known housing is that it has only limited possibilities to accommodate externally readable information.

Housing with readable side walls for a disc-shaped information carrier


A method and system for performing a quantum key distribution process in a quantum cryptographic system (200, 400) is provided. A first endpoint (405a) contributes a first set of random values to a quantum key distribution process. A second endpoint (405b) contributes a second set of random values to the quantum key distribution process. The first and the second endpoints (405a, 405b) derive a key based on at least some of the first set of random values and at least some of the second set of random values. In some implementations, the first endpoint (405a) may send each of the first set of random values using a basis (act 702, act 902) and the second endpoint (405b) may send an indication of received pulses and a basis for each of the received pulses (act 704, act 904).

Within the field of cryptography, it is well recognized that the strength of any cryptographic system depends, among other things, on the key distribution technique employed. For conventional encryption to be effective, such as a symmetric key system, two communicating parties must share the same key and that key must be protected from access by others. The key must, therefore, be distributed to each of the parties.
FIG. 1 shows one form of a conventional existing key distribution process. As shown in FIG. 1, for a party, Bob, to decrypt ciphertext encrypted by a party, Alice, Alice or a third party must share a copy of the key with Bob. This distribution process can be implemented using a number of known methods including the following: 1) Alice can select a key and physically deliver the key to Bob; 2) a third party can select a key and physically deliver the key to Bob; 3) if Alice and Bob both have an encrypted connection to a third party, the third party can deliver a key on the encrypted links to Alice and Bob; 4) if Alice and Bob have previously used an old key, Alice can transmit a new key to Bob by encrypting the new key with the old; and 5) Alice and Bob may agree on a shared key via a one-way mathematical algorithm, such as Diffie-Hellman key agreement.
All of these distribution methods are vulnerable to interception of the distributed key by an eavesdropper, Eve, or by Eve "cracking" the supposedly one-way algorithm. Eve can eavesdrop and intercept or copy a distributed key and then subsequently decrypt any intercepted ciphertext that is sent between Bob and Alice. In existing cryptographic systems, this eavesdropping may go undetected, with the result being that any ciphertext sent between Bob and Alice is compromised.
To combat these inherent deficiencies in the key distribution process, researchers have developed a key distribution technique called quantum cryptography. Quantum cryptography employs quantum systems and applicable fundamental principles of physics to ensure the security of distributed keys. Heisenberg's uncertainty principle mandates that any attempt to observe the state of a quantum system will necessarily induce a change in the state of the quantum system. Thus, when very low levels of matter or energy, such as individual photons, are used to distribute keys, the techniques of quantum cryptography permit the key distributor and receiver to determine whether any eavesdropping has occurred during the key distribution. Quantum cryptography, therefore, prevents an eavesdropper, like Eve, from copying or intercepting a key that has been distributed from Alice to Bob without a significant probability of Bob's or Alice's discovery of the eavesdropping.
An existing quantum key distribution (QKD) scheme involves a quantum channel, through which Alice and Bob send keys using polarized or phase encoded photons, and a public channel, through which Alice and Bob send ordinary messages. Since these polarized or phase encoded photons are employed for QKD, they are often termed QKD photons. The quantum channel is a path, such as through air or an optical fiber, that attempts to minimize the QKD photons' interaction with the environment. The public channel may comprise a channel on any type of communication network, such as a Public Switched Telephone network, the Internet, or a wireless network.
An eavesdropper, Eve, may attempt to measure the photons on the quantum channel. Such eavesdropping, however, will induce a measurable disturbance in the photons in accordance with the Heisenberg uncertainty principle. Alice and Bob use the public channel to discuss and compare the photons sent through the quantum channel. If, through their discussion and comparison, they determine that there is no evidence of eavesdropping, then the key material distributed via the quantum channel can be considered completely secret.
FIGS. 2 and 3 illustrate an existing scheme 200 for quantum key distribution in which the polarization of each photon is used for encoding cryptographic values. To begin the quantum key distribution process, Alice generates random bit values and bases 205 and then encodes the bits as polarization states (e.g., 0°, 45°, 90°, 135°) in sequences of photons sent via the quantum channel 210 (see row 1 of FIG. 3). Alice does not tell anyone the polarization of the photons she has transmitted. Bob receives the photons and measures their polarization along either a rectilinear or diagonal basis that is randomly selected with substantially equal probability. Bob records his chosen basis (see row 2 of FIG. 3) and his measurement results (see row 3 of FIG. 3).
Bob and Alice discuss 215, via the public channel 220, which basis he has chosen to measure each photon. Bob, however, does not inform Alice of the result of his measurements. Alice tells Bob, via the public channel, whether he has made the measurement along the correct basis (see row 4 of FIG. 3). In a process called "sifting" 225, both Alice and Bob then discard all cases in which Bob has made the measurement along the wrong basis and keep only the ones in which Bob has made the measurement along the correct basis (see row 5 of FIG. 3).
Alice and Bob then estimate 230 whether Eve has eavesdropped upon the key distribution. To do this, Alice and Bob must agree upon a maximum tolerable error rate. Errors can occur due to the intrinsic noise of the quantum channel and eavesdropping attack by a third party. Alice and Bob choose randomly a subset of photons m from the sequence of photons that have been transmitted and measured on the same basis. For each of the m photons, Bob announces publicly his measurement result. Alice informs Bob whether his result is the same as what she had originally sent. They both then compute the error rate of the m photons and, since the measurement results of the m photons have been discussed publicly, the polarization data of the m photons are discarded. If the computed error rate is higher than the agreed upon tolerable error rate (typically no more than about 15%), Alice and Bob infer that substantial eavesdropping has occurred. They then discard the current polarization data and start over with a new sequence of photons. If the error rate is acceptably small, Alice and Bob adopt the remaining polarizations, or some algebraic combination of their values, as secret bits of a shared secret key 235, interpreting horizontal or 45 degree polarized photons as binary 0's and vertical or 135 degree photons as binary 1's (see row 6 of FIG. 3).
Alice and Bob may also implement an additional privacy amplification process 240 that reduces the key to a small set of derived bits to reduce Eve's knowledge of the key. If, subsequent to discussion 215 and sifting 225, Alice and Bob adopt n bits as secret bits, the n bits can be compressed using, for example, a hash function. Alice and Bob agree upon a publicly chosen hash function ƒ and take K=ƒ(n bits) as the shared r-bit length key K. The hash function randomly redistributes the n bits such that a small change in bits produces a large change in the hash value. Thus, even if Eve determines a number of bits of the transmitted key through eavesdropping, and also knows the hash function ƒ, she still will be left with very little knowledge regarding the content of the hashed r-bit key K. Alice and Bob may further authenticate the public channel transmissions to prevent a "man-in-the-middle" attack in which Eve masquerades as either Bob or Alice.
Sifting is described in the paper, "Quantum Cryptography: Public Key Distribution and Coin Tossing," by Charles H. Bennett and Giles Brassard, International Conference on Computers, Systems & Signal Processing, December 1984. A known variation on sifting, called the Geneva protocol, provides protection against an eavesdropping attack, called a photon-number splitting attack. The Geneva protocol is described in, "Quantum Cryptography Protocols Robust Against Photon Number Splitting Attacks," by V. Scarani, A. Acin, G. Ribordy, N. Ribordy and N. Gisin, ERATO Conference on Quantum Information Science 2003, Sep. 4-6, 2003, Niijima-kaikan, Kyoto Japan. In existing sifting protocols, both parties select a 'basis' for each light pulse, but only one of the parties contributes a 'value.' For example, in the sifting protocols discussed above, a one-way system is described. In one-way systems and plug and play systems, one party may contribute the 'value.' In a typical quantum system based on entanglement, a source of entangled photons contributes the 'value' (automatically by the physical process that produces entangled pairs).
To ensure that the party contributing the 'value' does so in a random fashion, the contributing party must continually monitor its random sequences to check for bias. If bias is found, the contributing party either compensates for any observed bias or, when the bias is too severe for compensation, the contributing party may shut down the system. The bias monitoring, in general, is rather crude and it is quite possible that a party's random number generator may exhibit patterns of bias that are not detected by any checking procedure. Such patterns will degrade the quality of the cryptographic key produced by the system because any pattern to the randomness decreases the entropy of the key material. Furthermore, low-quality cryptographic key material may be produced for some time before subtle patterns of bias are detected.
Existing, non-quantum cryptographic systems perform a bias check. In addition, however, these non-quantum systems often obtain randomness by combining random number inputs from two different parties under the assumption that if one or both parties' random number generators are biased, in general, these problems will not be correlated. For example, in an existing Diffey-Hellman key agreement technique, each party (Alice and Bob) independently formulates a random number. A distributed calculation uses the two random numbers to determine a shared key. Thus, proper combination of two generators may lead to randomness of a higher quality than use of a single random number generator alone.
A quantum cryptographic system that allows multiple parties to contribute random values for the quantum key distribution process is needed in order to decrease the probability of generating biased cryptographic keys.

Quantum cryptography with multi-party randomness


A method of making a device using a lithographic system having a lens from which an exposure pattern is emitted. A conforming immersion medium can be positioned between a photo resist layer and the lens. The photo resist layer, which can be disposed over a wafer, and the lens can be brought into intimate contact with the conforming immersion medium. The photo resist can then be exposed with the exposure pattern so that the exposure pattern traverses the conforming immersion medium.

The formation of various integrated circuit (IC) structures on a wafer often relies on lithographic processes, sometimes referred to as photolithography, or simply lithography. As is well known, lithographic processes can be used to transfer a pattern of a photomask (also referred to herein as a mask or a reticle) to a wafer.
For instance, patterns can be formed from a photo resist layer disposed on the wafer by passing light energy through a mask having an arrangement to image the desired pattern onto the photo resist layer. As a result, the pattern is transferred to the photo resist layer. In areas where the photo resist is sufficiently exposed and after a development cycle, the photo resist material can become soluble such that it can be removed to selectively expose an underlying layer (e.g., a semiconductor layer, a metal or metal containing layer, a dielectric layer, a hard mask layer, etc.). Portions of the photo resist layer not exposed to a threshold amount of light energy will not be removed and serve to protect the underlying layer during further processing of the wafer (e.g., etching exposed portions of the underlying layer, implanting ions into the wafer, etc.). Thereafter, the remaining portions of the photo resist layer can be removed.
There is a pervasive trend in the art of IC fabrication to increase the density with which various structures are arranged. As a result, there is a corresponding need to increase the resolution capability of lithography systems. One promising alternative to conventional "dry" lithography is a next-generation lithographic technique known as immersion lithography. In the immersion lithography systems proposed to date, the wafer to imaged by a lithography system is placed in a flowable liquid medium, through which the patterned light is transmitted. Known immersion lithography mediums are purified de-ionized water for use in conjunction with a 193 nm light source 14 (e.g., an argon fluorine (ArF) laser) and polyfluoroethers for use in conjunction with a 157 nm light source 14. These readily flowable immersion mediums replace an air or gas gap that is conventionally present between the final lens of a conventional dry lithography imaging system and the wafer.
However, attempts to implement immersion lithography have encountered a number of challenges. For example, minor variations and/or nonuniformities in the index of refraction of the immersion medium can adversely affect the quality of the exposure pattern incident on the wafer. The cause(s) of changes in the index of refraction of the liquid immersion medium can include, for example, flow of the immersion medium, changes in density of the immersion medium, changes in temperature of the immersion medium and so forth. In dry lithography, several joules of energy can be absorbed by the wafer from the exposure dose. In immersion lithography, it is believed that at least some of the energy from the exposure dose will be absorbed by the immersion medium. Also, since the immersion medium is in contact with at least the wafer, heat may be transferred from the wafer to immersion medium. The absorption of energy by the immersion medium, even in small quantities, may be sufficient to create a variation and/or nonuniformity in the index of refraction of the immersion medium that could adversely affect the imaging pattern. Also, the wafer may be mounted on a stage that is moved relative to the imaging subsystem. For example, the wafer may be exposed, then moved about 30 mm to a new location and stopped for a second exposure and so forth. Wafer motion rates can be about 250 mm/second to about 500 mm/second. This movement may create non-uniform fluid flow (e.g., turbulence, laminar flow, vortex flow, etc.) or other changes to the properties of the immersion medium that could result in variations in the index of refraction of the immersion medium. In addition, it is contemplated that the immersion medium may be purposefully placed in motion (e.g., in a flow pattern over the wafer) or subjected to hydraulic pressure. These factors may also invoke variations in the index of refraction of the immersion medium.
Bubbles and/or contaminants in a liquid immersion medium can also disrupt imaging of the wafer. Fluid flow of the immersion medium may cause bubbles to form and/or become submersed in the immersion medium. During exposure, gases may be released from the photo resist. These gases could dissolve in the immersion fluid, ultimately leading to bubble formation. It is also contemplated that a foreign body may be carried on the wafer and brought into the immersion medium where the foreign body dislodges from the wafer and begins to "float" in the immersion medium. Liquid immersion mediums are used repeatedly for multiple wafers and are subjected to repeated application of radiation that could lead to a significant build up of bubbles, dissolved matter and/or contaminants over time.
Accordingly, there exists a need in the art for improved immersion lithography processes and systems.

Immersion lithographic process using a conforming immersion medium


An improved fast neutron x-y detector and radiographic/tomographic device utilizing a white neutron probe (4). The invention includes a multiple scattering filter (44), radiographic and tomographic imaging of the number densities of atoms in small volume increments through a sample 32 and the atomic, chemical and physical structure of a sample, (32), and neural net analysis techniques, where the neural net is trained through use of simulated volume increments. The invention detects fast neutrons over a two dimensional plane, measures the energy of the neutrons, and discriminates against gamma rays. In a preferred embodiment, the detector face is constructed by stacking separate bundles (6) of scintillating fiber optic strands (20) one on top of the other. The first x-y coordinate is determined by which bundle (6) the neutron strikes. The other x-y coordinate is calculated by measuring the difference in time of flight for the scintillation photon to travel to the opposite ends of the fiber optic strand 20. In another embodiment, the detector is constructed of discrete scintillator sections (48) connected to fiber optic strands (52) by couplers (50) functioning as lens. The fiber optic strands (52) are connected to a multi-anode photomultiplier (100) tube (56). The x-y coordinate of a neutron interaction is determined by the row and column of the affected scintillation section (48). Neutron energy for both detectors is calculated by measuring the flight time of a neutron from a point source (2) to the detector face.

1. Fast Neutron Radiographic and Tomographic Systems
A workable system for detecting explosives in airport luggage is urgently needed. A very small piece of modern explosive will destroy and airplane. These explosives are easy to hide and cannot be detected by current systems. For example, a plastic explosive hidden in a small radio apparently destroyed Pan American Flight 103 over Lockerbie, Soctland. The most accurate method would be a tomographic scan which could identify the elements which make up an explosive. For practical use in an airport, each scan would have to be completed in seconds. A system this advanced does not exist and is not possible under current technology.
Current methods for detecting explosives in airport luggage use uncharged particles such as X-rays and neutrons. X-rays are sensitive to differences in X-ray absorption coefficients in the luggage. However, explosives have absorption coefficients similar to many items commonly found in luggage. For this reason, detection systems using X-rays have high false alarm rates. X-ray computed tomography (CT) scanners are also used to inspect luggage. However, CT scanners are also sensitive to X-ray absorption coefficients, and so have the same problems as X-ray systems.
The most common nuclear based explosive detection methods are thermal neutron absorption (TNA) and n, gamma pulsed fast neutron spectroscopy. "Nuclear-Based Techniques for Explosive Detection", T. Gozani, R. Morgado, C. Seher, Journal of Energetic Materials, Vol. 4, pp. 377-414 (1986). The TNA detects the n, gamma reaction on nitrogen, and so searches only for nitrogen. "Airport Tests Of SAIC/FAA Explosive Detection System Based On Thermal Neutron Activation", P. Shea and T. Gozani, American Defense Preparedness Assoc. Proceedings, Cambridge, Mass., Oct. 26, 1988. TNA has an unacceptably high false alarm rate, since many materials other than explosives contain large amounts of nitrogen. Other problems with TNA include that the neutrons must be thermalized, the n, gamma cross section is in the millibarn range, it is difficult to obtain the spatial nitrogen concentration, and the background count is very high.
N, gamma pulsed spectroscopy detects the neutron inelastic scattered gamma rays from nitrogen, carbon, and oxygen. Zdzisaw Sawa and Tsahi Gozani, (PFNA Technique for the Detection of Explosives), Proc. of First Int. Sym. on Explosives Det. Technology, FAA Tech. Ctr., Atlantic City Int. Airport, N.J., Feb. 1992. Problems with n, gamma spectroscopy include that the cross sections are still in the millibarn range, the background counts are very high, determination of concentration as a function of position has large uncertainties, and it is difficult to make a gamma ray detector with adequate energy resolution and still maintain high count rate capability.
TNA and n, gamma spectroscopy search for explosives in an indirect way. Both cause a neutron interaction and then attempt to detect the resulting gamma rays. Neither method accurately pinpoints the location of an explosive in the luggage. A system is needed which can probe directly for explosives through first order interactions.
The most accurate method would be a tomographic scan which could identify the number densities of the dements which make up explosives in small volume increments through the luggage. Neutrons are an ideal probe, because neutrons interact directly with the atomic nuclie in the sample. A tomographic method which uses total cross sections rather than partial cross sections would be optimal. Current methods using neutron probes detect only second order effects such as gamma rays (partial cross sections) and do not provide tomographic images.
In conventional neutron tomography, neutrons are directed through a sample and the result are recorded on a detector. E. W. McFarland, R. C. Lanza and G. W. Poulos, "Multi-dimensional Neutron-computed Tomography Using Cooled, Charged-coupled Devices," IEEE Transactions on Nuclear Science, Vol. 38, No. 2, Apr. 1991. A number of runs at different angles are used to create a tomographic image. Conventional methods reconstruct the spatial distribitions of macroscopic interaction cross sections from the attenuation of radiation passing through the sample.
These conventional methods use monoenergetic neutron probes. Monoenergetic probes show macroscopic cross-section variations, while providing little information regarding atomic or chemical structure. In contrast, a white neutron probe (fast neutrons of multiple energies) would provide information not possible from a monoenergetic neutron probe. Light provides a simple analogy. Under a red light (single energy), all objects appear as shades of red. However, a white light (multiple energies) reveals different colors and other details. A tomographic system using a white neutron probe would be far more advanced than any system in operation. Unfortunately, under current technology, it cannot be built. Problems include multiple scattering of radiation, inability to detect and measure the energies of fast neutrons over an x-y plane, and difficult in reducing and analyzing data. These numerous problems would have to be solved in a single system.
Overly discussed that, under laboratory conditions, it is possible to identify different elements in a sample by using a white neutron beam. J. C. Overly, "Determinations of H, C, N and O content of Bulk Materials from Neutron Activation Measurements," Int J. Radiat Isot , Vol. 36, No. 3, pp. 185-191, 1985. Overly also discussed the scientific principle in deducing the number densities of elements along a neutron beam for a tomographic cut. "Element-Sensitive Computed Tomography With Fast Neutrons" by J. C. Overly, Nuc. Instr. and Meth. in Physics Research, B24/25 (1987) 1058-1062.
Overly required 23 hours for a single cut. A workable system for detecting explosives must reduce this time to seconds. Even after 23 hours, Overly obtained only an estimate of number densities at a single cut. A workable system must obtain a tomographic image of the number densities of atoms over the entire suitcase in a matter of seconds. As Overly acknowledged in his paper, current technology has not advanced to the point of applying these scientific principles in a workable system. The Federal Aviation Association ("FAA") recognized this critical need when requesting proposals for an invention using a white neutron probe for explosives. FAA "Guidelines for Preparing Responses to the Federal Aviation Administration's Broad Agency Announcement For Aviation Security Research Proposals,", p. 7, Nov. 1989. The FAA Guidelines acknowledge that the scientific principle has not been applied to airline security, even though it has been published for several years. In fact, the scientific principle has not been applied to any workable system. Neither the FAA, nor any other party, has found a way to address all of the problems which must be solved in order for a white neutron probe system to work. The following sections describe these problems.
2. Multiple-Scattering Correction of Radiation
Neutron tomographic systems must detect neutrons from the source while excluding neutrons scattered by the sample. If scattered neutrons reach the detectors, the tomographic image will not be accurate. X-ray systems use a detector located behind a shielded slot only a few millimeters wide. The slot is narrow enough to exclude most scattered radiation. This is one reason why a CAT scan takes so long. The detector row moves slowly across the body. A system using a large detector array could view the entire sample at once. However, such detectors (if they existed) could not be used for tomography until the multiple scattering problem is solved. The problem is even more critical when designing a system using a white neutron probe. The system must detect, measure the energies, and catalog the location of millions of neutrons passing through different parts of a sample each second. In order to provide meaningful data, the spatial resolution must be as small as several centimeters square. A workable system must eliminate multiple scattering while completing a scan in only a few seconds. There is a critical need for such a system.
Harding, Pat. No. 4,380,817 (1983) attempted to correct multiple scattering for purposes other than tomography. Harding's method measures electron density in a body through radiation which is "single scattered" from a narrow pencil beam of radiation. Harding's method shields the detector from the single scattered radiation, so that the detector measures only multiple scattered radiation. Then the multiple scattered radiation is subtracted from the sum of the single and multiple scattered radiation. This method is not workable for neutron tomography, which requires measuring neutrons which are not scattered (either single or multiple scattered). Harding's system would not work in a system using a white neutron probe for tomography.
3. X-Y Position Fast Neutron Detectors
A tomographic system using a white neutron probe must detect fast neutrons passing through a sample and pinpoint the location in the sample for each neutron. The system must perform these functions for millions of neutrons striking all portions of the sample each second.
One solution is to place the sample in front of an x-y detector which can record the two dimensional (x-y) coordinates of neutron interactions. The points of interaction on the x-y detector correspond to the locations in the sample. There are x-y neutron detectors, but most are for thermal neutrons. (Neutrons which have a kinetic energy of approximately 0.025 electron volts.) Many types of x-y detectors use an element that has a large fission cross section for thermal neutrons. The fission fragments are detected through the ionization they produce. McFarland, cited above, describes a detector using a sheet of .sup.6 Lif-ZnS. Lithium-6 has a large fission cross section for thermal neutrons. A fraction of the incident thermal neutrons interact with the Lithium-6 to produce Lithium-7. The Lithium-7 in turn fissions into a triton and an alpha particle, which cause a scintillation. A CCD camera records the scintillation and its position. Another variation uses an element that absorbs the thermal neutrons and emits X-rays or gamma rays.
The above types of detectors have a low detection efficiency for fast neutrons, since the fast neutron fission cross section is very small. Also, current x-y detectors cannot perform all of the functions needed for a tomographic system using a white neutron probe. These functions include measuring neutron energy, achieving high count rates, and collecting data in a way to facilitate tomographic imaging.
Fast neutron x-y detectors do exist, but have certain drawbacks. One type of x-y detector uses the multi-wire proportional counter with s proton radiator. B. Director, S. Kaplin and V. Perez-Mendez, "A Pressurized Multi-Wire Proportional Chamber for Neutron Imaging," IEEE Tr. on Nucl. Sc., Vol. NS-25, No. 1, Feb. 1978, 558-561. The proton radiator is a thin sheet of a hydrogen rich material such as polyethylene. A fraction of the incident neutrons scatter from the protons in the radiator. The resulting recoil protons enter the multi-wire proportional counter. The multi-wire proportional counter consists of thin gas filled cells with small wires running parallel throughout the cells. The wires are placed at high voltage. When a proton enters a cell close to a particular wire, a voltage pulse is created.
By recording the position of the voltage pulse, the position of the event is known in the direction perpendicular to the wires. By placing a second ionization chamber with wires running perpendicular to the first set of wires, the position in the other direction is known. The radiators must be very thin so that the recoil protons can escape. In order to achieve reasonable efficiency, many units must be placed in tandem. This setup cannot efficiently count neutrons below 3 MeV, since the radiator would require a width of nearly zero to allow the lower energy protons to reach the first cell. Efficiency would approach zero. These detectors do not allow measurement of neutron energy and would not provide the high count rates or neutron energy resolution required for a white neutron probe system.
An x-y detector for fast neutrons could be constructed from a large number of individual photomultiplier tubes. The applicant describes such a detector in "Contraband Detection Device", Ser. No. 07/635,996 filed on Dec. 31, 1990. One problem with this detector is that its electronics are very complex. A complete detector system is required for each photomultiplier tube. For example, a detector face of only 400 cm. by 400 cm., with a spatial resolution of 4 cm. by 4 cm., would require one hundred 4 cm. by 4 cm. detectors to form a single row 400 cm. long. One hundred rows of such detectors would provide a surface of 400 cm. by 400 cm. The system would require 10,000 individual detectors and 10,000 complete electronics systems. The system would be highly complex and expensive. Another problem is that the array is rigid and not capable of being geometrically configured for the optimal shape.
4. Collection, Reduction and Analysis of Data
Identifying contraband in sealed luggage is one of the most difficult tasks facing scientists. Explosives and drugs contain the same elements as most other items usually found in luggage. These elements include hydrogen (H), carbon (C), nitrogen (N) and oxygen (O). Explosives do contain characteristic ratios of these elements. However, in order to identify these ratios, a tomographic system would have to search an entire suitcase over small volume increments with an uncertainty of only a few percent. These tasks present enormous problems under current technology. Two problems, multiple scattering and measuring radiation over an x-y plane, were discussed above. In addition, the tomographic system would have to gather, reduce, and analyze data for millions of neutron interactions per second. The entire scan must be completed in seconds. The system must distinguish neutrons from gamma rays. New methods of data reduction and analysis would have to be developed for such a system to function with the speed and accuracy required for an airport system.
In summary, there are no tomographic systems which use a white neutron probe. There are numerous problems, unsolved under current technology, which prevent the operation of a workable system. These problems include multiple scattering of neutrons, detecting fast neutrons over a two-dimensional plane, calculating energies of the neutrons, and collecting, reducing and analyzing the data, all under circumstances when millions of neutrons will be incident on the sample and detector each second. The entire analysis of each sample must be completed in seconds. Such a system does not exist and cannot be built under current technology.

High energy x-y neutron detector and radiographic/tomographic device