An acoustic wave identification transponder device, having a substrate, an electroacoustic transducer generating an acoustic wave in said substrate and a set of encoding elements disposed in a path of the acoustic wave for modifying the acoustic wave, having at least two reflective elements disposed in the acoustic path of the acoustic wave such that an acoustic path length of the acoustic wave on the substrate is longer than twice a largest linear dimension of the substrate. The device preferably includes an angled elongated conductor formed on said substrate, having angle magnitudes whose sum exceeds .pi. radians, said angled elongated conductor defining at least a portion of the acoustic path.

A known acoustic radio frequency transponder system produces individualized responses to an interrogation signal. The code space for these devices may be, for example, 2.sup.12 codes, or more, allowing a large number of separate transponders to be produced without code reuse. These devices provide a piezoelectric substrate on which an aluminum pattern is formed, for example by a typical microphotolithography process, with a minimum feature size of, for example, one micron. As discussed more fully below, the metallized pattern defines a set of antenna pickups, electroacoustic transducers, acoustic paths, and elements which interact with the acoustic wave to produce an encoding of an acoustic wave which is converted to an electromagnetic wave and retransmitted.
The transponder devices thus include an acoustic wave device, generally operating with surface acoustic waves, in which an identification code is provided as a characteristic time-domain reflection, attenuation, phase delay, and/or transducer interaction pattern in a retransmitted signal, in a system which generally requires that the signal emitted from an exciting antenna be non-stationary with respect to a signal received from the tag. This ensures that the reflected signal pattern is distinguished from the emitted signal. In such a device, received RF energy, possibly with harmonic conversion, is emitted onto a piezoelectric substrate as an acoustic wave with an interdigital electrode system, from whence it travels through the substrate, interacting with reflector elements in the path of the wave. A portion of the acoustic wave is ultimately received by the same or a separate interdigital electrode system and retransmitted. These devices typically do not require a semiconductor memory. The propagation velocity of an acoustic wave in a surface acoustic wave device is slow as compared to the free space propagation velocity of a radio wave. Thus, assuming that the time for transmission between the radio frequency interrogation system is short as compared to the acoustic delay, the interrogation frequency typically changes by an amount sufficient such that a return signal having a minimum delay may be distinguished from the simultaneously transmitted interrogation signal, and in a manner that the interrogation frequency does not return to the same frequency during a period longer than the maximum acoustic delay period. Generally, such systems are interrogated with a pulse transmitter or chirp frequency system.
Systems for interrogating a passive transponder employing acoustic wave devices, carrying amplitude and/or phase-encoded information are disclosed in, for example, U.S. Pat. Nos. 4,059,831; 4,484,160; 4,604,623; 4,605,929; 4,620,191; 4,623,890; 4,625,207; 4,625,208; 4,703,327; 4,724,443; 4,725,841; 4,734,698; 4,737,789; 4,737,790; 4,951,057; 5,095,240; and 5,182,570, expressly incorporated herein by reference.
Because the encoded information normally includes an identification code which is unique or quasi-unique to each transponder, and because the transponders of this type are relatively light weight and small and may be easily attached to other objects to be identified, the transponders are sometimes referred to as "labels" or "tags". The entire system, including the interrogator/receiver apparatus and one or more transponders, which may be active or passive, is therefore often referred to as a "passive interrogator label system" or "PILS". Other types of passive interrogator label systems are disclosed, for example, in the U.S. Pat. Nos. 3,273,146; 3,706,094; 3,755,803; and 4,058,217, incorporated herein by reference.
When an acoustic wave pulse is reconverted into an electrical signal, it is supplied to an antenna on the transponder and transmitted as RF electromagnetic energy. This energy is received at a receiver and decoder, typically at the same location as the interrogating transmitter, and the information contained in this response to an interrogation signal is decoded. The tag typically has but a single antenna, used for both receiving the interrogation pulse and emitting an information bearing signal, but known systems employ multiple antennas.
In systems of this general type, the information code associated with and which identifies the passive transponder is built into the transponder at the time that a layer of metallization is finally defined on the substrate of piezoelectric material. This metallization thus defines the antenna coupling, launch transducers, acoustic pathways and information code elements, e.g., reflectors. Thus, the information code in this case is non-volatile and permanent. Since the transponder typically remains static over time, the encoded information may be retrieved by a single interrogation cycle. The information is present in the return signal as a set of characteristic perturbations of the interrogation signal, such as delay pattern and attenuation. In the case of a tag having launch transducers and a variable pattern of reflective elements, the number of possible codes is N.times.2.sup.M where N is the number of acoustic waves launched by the transducers and M is the number of reflective element positions for each transducer. Thus, with four launch transducers each emitting two acoustic waves, and a potential set of eight variable reflective elements in each acoustic path, the number of differently coded transducers is 2048. Therefore, for a large number of potential codes, it is necessary to provide a large number of launch transducers and/or a large number of reflective elements. However, efficiency is lost with increasing complexity, and a large number of distinct acoustic waves reduces the signal strength of the signal encoding the information in each.
The transponder tag thus includes a multiplicity of "signal conditioning elements", i.e., delay elements, reflectors, and/or amplitude modulators, are coupled to receive the first signal from a transponder antenna. Each signal conditioning element provides an intermediate signal having a known delay and a known amplitude modification to the first signal. Even where the signal is split into multiple portions, it is advantageous to reradiate the multiple portions of the signal through a single antenna. Therefore, a single "signal combining element" coupled to all of the signal conditioning elements and/or signal portions is provided for combining the intermediate signals to produce the second signal. This second signal is coupled out to the same or a separate antenna for transmission as a reply signal. As described above, the signal delay elements and/or the signal combining element impart a known, unique informational code to the second signal.
In the acoustic wave tags described above, the interrogator transmits a first signal that successively assumes a plurality of frequency values within a prescribed frequency range. This frequency range or band may, for example, be about 905-925 MHz, referred to herein as the 915 MHz band. Traditionally, the 915 MHz band has been available for unlicensed use, however, other or conflicting uses of this band may make other bands more attractive in the future.
Preferably, the passive acoustic wave transponder tag includes at least one element having predetermined characteristics, which assists in synchronizing the receiver and allows for temperature compensation of the system. As the temperature rises, the piezoelectric substrate may expand and contract, altering the characteristic delays and other parameters of the tag. Variations in the transponder response due to changes in temperature thus result, in part, from the thermal expansion of the substrate material. Although propagation distances are small, an increase in temperature of only 20.degree. C. can produce an increase in propagation time by the period of one entire cycle at a transponder frequency of about 915 MHz. The acoustic wave is often a surface acoustic wave, although bulk acoustic wave devices may also be constructed.
The transponder is constructed such that i.sup.th delay time t.sub.i =T.sub.0 +K.DELTA.T+.DELTA.V.sub.i, where K is a proportionality constant, .DELTA.T is the nominal, known difference in delay time between the intermediate signals of two particular successive ones of the signal delay elements in the group, and .DELTA.V.sub.i, is a modification factor due to inter-transponder variations, such as manufacturing variations. By measuring the quantities .DELTA.T and .DELTA.V.sub.i, it is possible to determine the expected delay time t.sub.i -T.sub.0 for each and every signal delay element from the known quantities K, .DELTA.T and .DELTA.V.sub.i. The manufacturing variations .DELTA.V.sub.i are comprised of a "mask" variation .DELTA.M.sub.i due to possible imperfections in the photolithographic mask; an "offset" variation .DELTA.O.sub.i which arises from the manufacturing process used to deposit the metal layer on the piezoelectric substrate; and a random variation .DELTA.R.sub.i which is completely unpredictable but usually neglectably small. Specific techniques are available for determining and compensating both the mask variations .DELTA.M.sub.i and the offset variations .DELTA.O.sub.i.
This surface acoustic wave transponder system provides a number of advantages, including high signal-to-noise performance, and the fact that the output of the signal mixer--namely, the signal which contains the difference frequencies of the first (interrogating) signal and the second (reply) signal--may be transmitted over inexpensive, shielded, twisted-pair wires because these frequencies are, for example, typically in the audio range. Furthermore, since the audio signal is not greatly attenuated or dispersed when transmitted over relatively long distances, the signal-processor may be located at a remote location from the signal mixer, or provided as a central processing site for multiple interrogator antennae.
Passive transponder encoding schemes include control over interrogation signal transfer function H(s) and delay functions f(z). These functions therefore typically generate a return signal in the same band as the interrogation signal. Since the return signal is mixed with the interrogation signal, the difference between the two will generally define the information signal, along with possible interference and noise. By controlling the rate of change of the interrogation signal frequency with respect to a maximum round trip propagation delay, including internal delay, as well as possible Doppler shift, the maximum bandwidth of the demodulated signal may be controlled.
Transponders which include an identification based on elements which alter a response of a SAW device are susceptible to interference which reduces the signal-to-noise ratio of the reply signal that is transmitted by the transponder antenna back to the interrogator. Interference may be caused by reflections from various metallized elements disposed on the surface of the SAW device in the acoustic wave travel paths. The amplitudes of such reflections are directly proportional to the change in velocity, .DELTA.V, of a surface acoustic wave as it passes from a metallization-free surface area on the SAW device to a metallized surface area and vice versa. Such surface acoustic wave reflections are reconverted into electrical signals by the transducers in their paths of travel, resulting in spurious electrical signals that appear as noise in the transmitted reply signal.
A known surface acoustic wave passive interrogator label system, as described, for example, in U.S. Pat. Nos. 4,734698; 4,737,790; 4,703,327; and 4,951,057, and shown in FIG. 1, includes an interrogator comprising a voltage controlled oscillator 10 which produces a first signal S1 at a radio frequency determined by a control voltage V supplied by a control unit 12. This signal S1 is amplified by a power amplifier 14 and applied to an antenna 16 for transmission to a transponder 20.
The signal S1 is received at the antenna 18 of the transponder 20 and passed to a signal transforming element 22. This signal transformer converts the first (interrogation) signal S1 into a second (reply) signal S2, encoded with an information pattern. The information pattern is encoded as a series of elements having characteristic delay periods T.sub.0 and .DELTA.T.sub.1, .DELTA.T.sub.2, . . . .DELTA.T.sub.N. Two common types of systems exist. In a first, the delay periods correspond to physical delays in the propagation of the acoustic signal. After passing each successive delay, a portion of the signal I.sub.0, I.sub.1, I.sub.2 . . . I.sub.N is tapped off and supplied to a summing element. The resulting signal S2, which is the sum of the intermediate signals I.sub.0. . . I.sub.N, is fed back to a transponder tag antenna, which may be the same or different than the antenna which received the interrogation signal, for transmission to the interrogator/receiver antenna. In a second system, the delay periods correspond to the positions of reflective elements, which reflect portions of the acoustic wave back to the launch transducer, where they are converted back to an electrical signal and emitted by the transponder tag antenna.
The signal S2 is passed either to the same antenna 18 or to a different antenna 24 for transmission back to the interrogator/receiver apparatus. This second signal S2 carries encoded information which, at a minimum, identifies the particular transponder 20.
The signal S2 is picked up by a receiving antenna 26. Both this second signal S2 and the first signal S1 (or respective signals derived from these two signals) are applied to a mixer (four quadrant multiplier) 30 to produce a third signal S3 containing frequencies which include both the sums and the differences of the frequencies contained in the signals S1 and S2. The signal S3 is passed to a signal processor 32 which determines the amplitude a, and the respective phase .phi..sub.i of each frequency component .phi..sub.i among a set of frequency components (.phi..sub.0,.phi..sub.1,.phi..sub.2 . . . ) in the signal S3. Each phase .phi..sub.1 is determined with respect to the phase .phi..sub.0 =0 of the lowest frequency component .phi..sub.0. The signal S3 may be intermittently supplied to the mixer by means of a switch.
The information determined by the signal processor 32 is passed to a computer system comprising, among other elements, a random access memory (RAM) 34 and a microprocessor 36. This computer system analyzes the frequency, amplitude and phase information and makes decisions based upon this information. For example, the computer system may determine the identification number of the interrogated transponder 20. This I.D number and/or other decoded information is made available at an output 38.
The transponder serves as a signal transforming element 22, which comprises N+1 signal conditioning elements 40 and a signal combining element 42. The signal conditioning elements 40 are selectively provided to impart a different response code for different transponders, and which may involve separate intermediate signals I.sub.0,I.sub.1 . . . I.sub.N within the transponder. Each signal conditioning element 40 comprises a known delay T.sub.i and a known amplitude modification A.sub.i (either attenuation or amplification). The respective delay T.sub.i and amplitude modification A.sub.i may be functions of the frequency of the received signal S1, or they may provide a constant delay and constant amplitude modification, respectively, independent of frequency. The time delay and amplitude modification may also have differing dependency on frequency. The order of the delay and amplitude modification elements may be reversed; that is, the amplitude modification elements A.sub.i may precede the delay elements T.sub.i. Amplitude modification A.sub.i can also occur within the path T.sub.i.
The signals are combined in combining element 42 which combines these intermediate signals (e.g., by addition, multiplication or the like) to form the reply signal S2 and the combined signal emitted by the antenna 18.
In one embodiment, as shown in FIG. 2, the voltage controlled oscillator 10 is controlled to produce a sinusoidal RF signal with a frequency that is swept in 128 equal discrete steps from 905 MHz to 925 MHz. Each frequency step is maintained for a period of 125 microseconds so that the entire frequency sweep is carried out in 16 milliseconds. Thereafter, the frequency is dropped back to 905 MHz in a relaxation period of 0.67 milliseconds. The stepwise frequency sweep 46 shown in FIG. 3B thus approximates the linear sweep 44 shown in FIG. 3A.
Assuming that the stepwise frequency sweep 44 approximates an average, linear frequency sweep or "chirp" 47, FIG. 3B illustrates how the transponder 20, with its known, discrete time delays T.sub.0,T.sub.1 . . . T.sub.N produces the second (reply) signal 52 with distinct differences in frequency from the first (interrogation) signal 51. Assuming a round-trip, radiation transmission time of t.sub.0, the total round-trip times between the moment of transmission of the first signal and the moments of reply of the second signal will be to t.sub.0 +T.sub.0,t.sub.0 +T.sub.1, . . . t.sub.0 +T.sub.N, for the delays T.sub.ON, T . . . , T.sub.1 respectively. Considering only the transponder delay T.sub.N, at the time t.sub.R when the second (reply) signal is received at the antenna 26, the frequency 48 of this second signal will be .DELTA.f.sub.N less than the instantaneous frequency 47 of the first signal S1 transmitted by the antenna 16. Thus, if the first and second signals are mixed or "homodyned", this frequency difference .DELTA.f.sub.N will appear in the third signal as a beat frequency. Understandably, other beat frequencies will also result from the other delayed frequency spectra 49 resulting from the time delays T.sub.0, T.sub.1 . . . T.sub.N-1. Thus, in the case of a "chirp" waveform, the difference between the emitted and received waveform will generally be constant. In mathematical terms, we assume that the phase of a transmitted interrogation signal is .phi.=2.pi.f.tau., where .tau. is the round-trip transmission time delay. For a ramped frequency df/dt or f, we have: 2.pi.f.tau.=d.phi./dt=.omega.. .omega., the beat frequency, is thus determined by .tau. for a given ramped frequency or chirp f. In this case, the signal S3 may be analyzed by determining a frequency content of the S3 signal, for example by applying it to sixteen bandpass filters, each tuned to a different frequency, f.sub.0,f.sub.1 . . . f.sub.E, f.sub.F. The signal processor determines the amplitude and phase of the signals that pass through these respective filters. These amplitudes and phases contain the code or "signature" of the particular signal transformer 22 of the interrogated transponder 20. This signature may be analyzed and decoded in known manner.
In one embodiment of a passive transponder, shown in FIGS. 6 and 7, the internal circuit operates to convert the received signal S1 into an acoustic wave and then to reconvert the acoustic energy back into an electrical signal S2 for transmission via a dipole antenna 70, connected to, and arranged adjacent a SAW device made of a substrate 72. More particularly, the signal transforming element of the transponder includes a substrate 72 of piezoelectric material such as a lithium niobate (LiNbO.sub.3) crystal, which has a free surface acoustic wave propagation velocity of about 3488 meters/second. On the surface of this substrate is deposited a layer of metal, such as aluminum, forming a pattern which includes transducers and delay/reflective elements.
One transducer embodiment includes a pattern consisting of two bus bars 74 and 76 connected to the dipole antenna 70, a "launch" transducer 78 and a plurality of "tap" transducers 80. The bars 74 and 76 thus define a path of travel 82 for a surface acoustic wave which is generated by the launch transducer and propagates substantially linearly, reaching the tap transducers each in turn. The tap transducers convert the surface acoustic wave back into electrical energy which is collected and therefore summed by the bus bars 74 and 76. This electrical energy then activates the dipole antenna 70 and is converted into electromagnetic radiation for transmission as the signal S2.
The tap transducers 80 are provided at equally spaced intervals along the surface acoustic wave path 82, as shown in FIG. 6, and an informational code associated with the transponder is imparted by providing a selected number of "delay pads" 84 between the tap transducers. These delay pads, which are shown in detail in FIG. 7, are preferably made of the same material as, and deposited with, the bus bars 74, 76 and the transducers 78, 80. Each delay pad has a width sufficient to delay the propagation of the surface acoustic wave from one tap transducer 80 to the next by one quarter cycle or 90.degree. with respect to an undelayed wave at the frequency of operation (in the 915 MHz band). By providing locations for three delay pads between successive tap transducers, the phase f of the surface acoustic wave received by a tap transducer may be controlled to provide four phase possibilities, zero pads=0.degree.; one pad=90.degree.; two pads=180.degree.; and three pads=270.degree..
The phase information .phi..sub.0 (the phase of the signal picked up by the first tap transducer in line), and .phi..sub.1,.phi..sub.2 . . . .phi..sub.N (the phases of the signals picked up by the successive tap transducers) is supplied to the combiner (summer) which, for example, comprises the bus bars 74 and 76. This phase information, which is transmitted as the signal S2 by the antenna 70, contains the informational code of the transponder.
As shown in FIG. 7, the three delay pads 84 between two tap transducers 80 are each of such a width L as to each provide a phase delay of 90.degree. in the propagation of an acoustic wave from one tap transducer to the next as compared to the phase in the absence of such a delay pad. This width L is dependent upon the material of both the substrate and the delay pad itself as well as upon the thickness of the delay pad and the wavelength of the surface acoustic wave.
The transducers are typically fabricated by an initial metallization of the substrate with a generic encoding, i.e., a set of reflectors or delay elements which may be further modified by removal of metal to yield the customized transponders. Thus, in the case of delay pads, three pads are provided between each set of transducers or taps, some of which may be later removed. Where the code space is large, the substrates may be partially encoded, for example with higher order code elements, so that only the lower order code elements need by modified in a second operation.
While a system of the type described above operates satisfactorily when the number of tap transducers does not exceed eight, the signal to noise ratio in the transponder reply signal is reduced as the number of tap transducers increases. This is because the tap transducers additionally act as launch transducers as well as partial reflectors of the surface acoustic wave so that an increase in the number of tap transducers results in a corresponding increase in spurious signals in the transponder replies. This limitation on the number of tap transducers places a limitation on the length of the informational code imparted in the transponder replies.
Spurious signals as well as insertion losses may be reduced in a passive transponder so that the informational code may be increased in size to any desired length, by providing one or more surface acoustic wave reflectors on the piezoelectric substrate in the path of travel of the surface acoustic wave, to reflect the acoustic waves back toward a transducer for reconversion into an electric signal.
A transducer 86 may thus be employed in conjunction with reflectors 88 and 90 in a unique configuration which replaces the aforementioned arrangement having a launch transducer 78 and tap transducers 80. In particular, the transducer 86 is constructed to convert electrical energy received at the terminals 92 and 94 into surface acoustic wave energy which propagates outward in opposite directions indicated by the arrows 96 and 98. The launch transducer is constructed in a well known manner with an inter-digital electrode assembly formed of individual electrode fingers arranged between and connected to the two bus bars 100 and 102. In the illustrated pattern, half the fingers are connected to the bus bar 100 and the other half are connected to the bus bar 102. Each electrode is connected to one or the other bus bar and extends toward a free end in the direction of the other bus bar. The distance between the centers of successive fingers is equal to 3.lambda./4 where .lambda. is the center wavelength of the surface acoustic wave. Furthermore, as may be seen, the length of the active region between the ends of the electrodes connected to the bus bar 100 and the ends of the electrodes connected to the bus bar 102 is K.lambda., where K is a proportionality constant.
Surface acoustic waves may encounter frequency selective filtering structures, partial reflectors, fill reflectors, phase delay pads or electroacoustic transducing elements as they travel across the substrate, which is typically lithium niobate (LiNbO.sub.3) which has a surface acoustic wave propagation velocity of 3488 m/sec and is piezoelectric. The system may have a single acoustic path or sets of acoustic paths which are, for example, parallel, as shown in FIG. 8A.
A wavefront produced by reflections from the leading and trailing edges of transducer fingers will be formed by the superposition of a first wave reflected from the first leading edge and successive waves reflected from successive edges and having differences in phase, with respect to the first wave, of -.lambda./4,.lambda./2,-3.lambda./4,.lambda., etc. As may be seen, the wave components having a phase -.lambda./4,.lambda./2 and -3.lambda./4 effect a cancellation, or at least an attenuation of the wave component reflected from the leading edge. The interdigital fingers of the transducers may therefore be advantageously split to reduce reflections, Conventional interdigital finger transducers which are constructed to operate at a fundamental, resonant frequency of 915 MHz, have a finger width (.lambda./4) of approximately 1 micron; a size which approaches the resolution limit of certain photolithographic fabrication techniques (the selective removal of metallization by (1) exposure of photoresist through a mask and (2) subsequent etching of the metallized surface to selectively remove the metal between and outside the transducer fingers). If the fingers are split, the width of each finger (.lambda./8) for a fundamental frequency of 915 MHz would be approximately 0.5 micron. The size would require sophisticated photolithographic fabrication techniques. In order to increase the feature sizes, the transducers in the transponder are constructed with a resonant frequency f.sub.0 of 305 MHz. In this case, the width of each finger is three times larger than transducer fingers designed to operate at 915 MHz, so that the width (.lambda./8) of the split fingers is approximately 1.5 microns. This is well within the capability of typical photolithographic fabrication techniques. Although such transducers are constructed with a resonant frequency of 305 MHz, they are nevertheless driven at the interrogation frequency of approximately 915 MHz; i.e., a frequency 3f.sub.0 which is the third harmonic of 305 MHz. The energy converted by a transducer, when driven in its third harmonic 3f.sub.0 (915 MHz), is about 1/3 of the energy that would be converted if the transducer were driven at its fundamental frequency f.sub.0 (305 MHz). Accordingly, it is necessary to construct the transducers to be as efficient as possible within the constraints imposed by the system. As is well known, it is possible to increase the percentage of energy converted, from electrical energy to SAW energy and vice versa, by increasing the number of fingers in a transducer. In particular, the converted signal amplitude is increased by about 2% for each pair of transducer fingers (either conventional fingers or split fingers) so that, for 20 finger pairs for example, the amplitude of the converted signal will be about 40% of the original signal amplitude. Such an amplitude percentage would be equivalent to an energy conversion of about 16%. In other words, the energy converted will be about 8 db down from the supplied energy.
The edge portions of the delay pads, as well as the lateral edges of the bus bars and (i.e., the edges transverse to the SAW paths of travel) are advantageously provided with two levels of serrations, which substantially reduce SAW reflections from these edges. The serrations include, for example, two superimposed "square waves" having the same pulse height but different pulse periods. For example, the pulse height for both square waves is .lambda./4, and the pulse period is .lambda./3 for one square wave and 6.lambda. for the other, where .lambda. is the SAW wavelength at 915 MHz. The first level of serrations serves to reduce reflections, while the second level serves to break up the average reflection plane.
The addition of finger pairs to the transducers therefore advantageously increases the energy coupling between electrical energy and SAW energy. However, as explained above in connection with FIGS. 1 and 3, the system according to the invention operates to excite the transducers over a range of frequencies between 905 MHz and 925 MHz. This requires the transducers to operate over a 20-25 MHz bandwidth: a requirement which imposes a constraint upon the number of transducer finger pairs because the bandwidth of a transducer is inversely proportional to its physical width. This relationship arises from the fact that the bandwidth is proportional to 1/.tau., where .tau. is the SAW propagation time from one side of the transducer to the other (the delay time across the transducer).
The transducer may be divided into several separate sections: a central section, two flanking sections and two outer sections. The central section includes interdigital transducer fingers which are alternately connected to two outer bus bars and to a central electrical conductor. This central section comprises a sufficient number of finger pairs to convert a substantial percentage of electrical energy into SAW energy and vice versa. By way of example and not limitation, there may be 12 finger pairs so that the converted amplitude is approximately 24% of the incoming signal amplitude. Flanking the central section, on both sides, are sections containing "dummy" fingers; that is, fingers which are connected to one electrode only and therefore serve neither as transducers nor reflectors. The purpose of these fingers is to increase the width of the transducer so that the outer sections will be spaced a prescribed distance, or SAW delay time, from the central section. For example, there may be 7 dummy fingers (or, more particularly, split fingers) in each of the sections. Finally, each of the outer sections of the transducer contains a single transducer finger pair which is used to shape the bandwidth of the transducer, e.g., maintain an effective bandwidth of about 25 MHz.
The transducer system preferably has an electrical impedance at the design frequency which matches the impedance of the antenna coupling, to maximize the power transfer between the antenna system and transducer. This matching is accomplished by forming series connections of transducer structures, which present as capacitive loads, to reduce impedance, as necessary, and providing heavy metal traces for the bus bars to reduce Ohmic losses. The bus bars are, for example, made approximately twice as thick as the other metallized elements on the substrate.
In practice, the metallization is deposited on the substrate surface using a two-layer photolithographic process. Two separate reticles are used in forming the photolithographic image: one reticle for the transducers, reflectors and phase pads as well as the alignment marks on the substrate, and a separate reticle for the bus bars. The process thus comprises the steps of depositing a 300 Angstrom layer of chromium and then 1000 Angstrom layer of aluminum on the substrate, followed by UV-exposure solubleizing resin spin coating, masking and etching of the bus bars, followed by deposition of 1000 Angstroms of aluminum and another UV activated resin spin coating, masking and etching to form the transducers, reflectors and phase pads as well as the alignment marks on the substrate, doubling the thickness of the bus bar structures.
Each two successive fingers of a transducer may be shorted at one or more locations between the bus bars. The shorts between successive fingers reduce energy loss due to Ohmic resistance of the fingers and render the reflector less susceptible to fabrication errors.
These various techniques and systems, described above, may advantageously be employed or combined with aspects of the present invention in known manner to achieve desired results.

Surface acoustic wave transponder configuration


An acrylic monomer which is an amino sugar alcohol whose primary or secondary amino group has been derivatized by an acryloyl or a methacryloyl function. The amino group can be linked to any carbon of five or six-carbon sugar alcohols. The acrylic monomer has the formula: ##STR1## where R.sub.1 is H, CH.sub.2 OH or (CHOH).sub.m CH.sub.2 OH, m being 1 or 2;. R.sub.2 is monohydroxyalkyl, polyhydroxyalkyl or hydrocarbon radical; PA0 R.sub.3 is H or CH.sub.3 ; and PA0 n is an integer of 1-4. The acrylic monomer can be polymerized by a free radical polymerization, either alone or with other compounds and materials having polymerizable double bonds. The so formed polymers are linear or branched (cross-linked). The cross-linked polymers are usually in the form of gels. The gels can be polymerized in different forms and shapes, i.e., beads, thin sheets, rods, blocks, etc. and are useful as separation media, e.g., the transparent gels are useful as an anticonvective matrix in electrophoresis, whereas the opaque gels prepared in a bead form are useful in chromatography.

There are two important techniques for separation of biomolecules. Chromatography is generally used for a preparative purification of biological molecules, whereas electrophoresis is the most powerful technique for analysis of the molecules in crude samples and at various stages of a purification procedure.
Each of these two techniques uses separation media of unique properties. Nevertheless, media for both or either chromatography and electrophoresis can be prepared from the same starting material. Until now, only two acrylic monomers have been successfully used to prepare gels for electrophoresis and chromatography. These two monomers are acrylamide and N-acryloyl-tris(hydroxymethyl)-aminomethane (NAT). One of the inventors of the present invention is one of the persons who have introduced the NAT-monomer to prepare poly-NAT gels for electrophoresis (Kozulic, M., Kozulic, B., and Mosbach, K. (1987), R. Anal. Biochem. 21 26 23 2, 2, 506-512 (reference 1); Kozulic, B., Mosbach, K., and Pietrzak., M. (1988), Anal. Biochem. 21 27 20 2, 2, 478-484 (reference 2); and International Patent Application No. PCTEP88/00515) (Reference 3).
The poly-NAT gels possess several advantages over the polyacrylamide gels. In addition to their pronounced hydrophilicity, their most important advantage is the higher porosity of these gels. Since a gel even more hydrophilic and porous than a poly-NAT gel would be beneficial in many applications, a search was made for a monomer which could be polymerized to produce such a gel.
A NAT solution has a molar concentration lower than a polyacrylamide solution of the same weight percentage, because the molecular weight of NAT is about 2.5 fold higher than the molecular weight of acrylamide. The poly-NAT gels have been found to be approximately 3 times more porous than the corresponding polyacrylamide gels, which is in good agreement with the 2.5 fold lower molarity. Thus, one can assume that the lower molar concentration of NAT solutions results, after polymerization, in fewer polymer chains per unit volume, leading to gels of increased porosity. If this assumption is correct, then even more porous gels will be formed from monomers of even higher molecular weight. However, the lack of mechanical strength may be a drawback of gels produced from monomers of very high molecular weight. The optimal properties are expected to be inherent to the monomers of medium size, due to a balanced ratio between the size of the polymer backbone and the size of the side chains present in every repeating unit.
In addition to the size of a monomer, other factors can influence the porosity of a gel. If interactions exist between monomer molecules, or between a monomer and a growing polymer, or between the two growing polymer chains, then as a result of these interactions the polymer chains will not be randomly distributed. They are likely to form some kind of bundles and thus create large pores. It is generally accepted that the high porosity of agarose gels comes from an association of polymer chains during the gelation process. The resulting bundles of polymer chains are presumably held together by hydrogen bonds. Other types of stabilizing forces, such as hydrophobic interaction or ionic bonds, are not compatible with the media that are to be used for electrophoresis or chromatography.
From the above considerations, it appeared that monomers composed of sugar alcohols might form gels with desirable properties. They are hydrophilic, they are of medium size and they have 4-5 hydroxyl groups which could form hydrogen bonds. As shown in the present invention, many such compounds can be conveniently and controllably synthesized. In addition, such synthesized compounds easily polymerize and form gels useful for electrophoresis and chromatography. Two monomers of the general type described herein, N-acryloyl-1-amino-1-deoxy-D-glucitol and N-methacryloyl-1-amino-1-deoxy-D-glucitol, have been synthesized previously (Whistler, R. L., Panzer, H. P., and Roberts, H. J. (1961), J. Org. Chem. Vol. 26 p. 1583-1588), but they were not used to prepare crosslinked gels for electrophoresis or chromatography.

Hydrophilic and amphiphatic monomers, their polymers and gels and hydrophobic electrophoresis


A cable organizer for fiber optic cables includes a support structure, and a groove plate mounted to the support structure. The groove plate has an access groove for managing fiber optic cables on the groove plate. Fiber optic trays are pivotally mounted to the groove plate, and each fiber optic tray is configured to manage an optical fiber from the fiber optic cables. The access groove is at an angle relative to the fiber optic trays to provide a side access to the fiber optic cables.

Fiber optic cables are often managed by a cable organizer housed inside a telecommunications closure. The cable organizer typically includes a plurality of pivotally mounted trays mounted on a groove plate. The groove plate can manage a fiber optic cable so that an optical fiber from the cable can be guided to a tray. The tray can include various cable and fiber guides, guide walls, and retaining tabs for guiding incoming and outgoing cables and fibers to and from the telecommunications closure.
The spaces between the groove plate and the pivotally mounted trays are often tight and narrow which can make it difficult to guide the fiber optic cables onto the trays. Therefore, improvements in cable organizers are needed.


At least one exemplary embodiment is directed to a projection optical system that projects an image of a pattern of a first object onto a second object includes a first image forming optical system, a second image forming optical system, and a light-shielding member. The first image forming optical system forms an intermediate image of the pattern, and includes a concave mirror and a reflecting mirror. The concave mirror has a reflecting surface opposing the second object. The reflecting mirror directs light from the first object to the concave mirror. The second image forming optical system forms an image of the intermediate image onto the second object, and includes a lens. The light-shielding member is disposed between the concave mirror and the lens.

1. Field of the Invention
The present invention generally relates to a projection optical system that projects a pattern on a reticle (mask) onto a substrate. More particularly, though not exclusively, the present invention relates to a catadioptric projection optical system including a lens and a reflecting mirror.
2. Description of the Related Art
Hitherto, a projection exposure apparatus that projects a circuit pattern on a reticle onto a wafer, serving as a substrate, by a projection optical system, and that transfers the circuit pattern onto the wafer has been used. In recent years, the required resolution of the projection optical system is becoming increasingly higher. To achieve the required high resolution of the projection optical system, it is necessary to either reduce the wavelength of exposure light or to increase a numerical aperture NA of the projection optical system.
At present, an ArF laser having a wavelength of 193 nm is used as exposure light. However, since only quartz and fluorite are available as glass materials that efficiently transmit light having a wavelength of 193 nm, it is very difficult to correct chromatic aberration. In addition, increasing the diameter of the glass material due to an increase in NA is a significant factor that increases the cost of the apparatus. In particular, in a projection optical system of an immersion exposure apparatus in which liquid is filled between the projection optical system and the wafer, NA is greater than 1. Therefore, an increase in the diameter of the glass material is a serious problem.
Accordingly, to overcome, for example, the problems regarding the difficulty in correcting chromatic aberration and an increase in the diameter of the glass material, various proposals involving the use of a catadioptric projection optical system, including a reflecting mirror, as a projection optical system have been made (refer to Japanese Patent Laid-Open No. 2001-228401 and the pamphlet of International Publication No. 2005/069055).
The catadioptric projection optical systems discussed in Japanese Patent Laid-Open No. 2001-228401 and the pamphlet of International Publication No. 2005/069055 have common features.
The catadioptric projection optical systems will hereunder be described with reference to FIG. 1. FIG. 1 is a schematic view of the catadioptric projection optical system discussed in Japanese Patent Laid-Open No. 2001-228401. In the projection optical system, a pattern of a first object 101 (reticle), disposed in an object plane, is focused onto a second object 102 (wafer), disposed in an image plane.
Here, a common feature is that the projection optical systems discussed in Japanese Patent Laid-Open No. 2001-228401 and the pamphlet of International Publication No. 2005/069055 each include a first image forming optical system and a second image forming optical system G1 (this common feature will hereunder be referred to as "feature A"). The first image forming optical system includes a reflecting mirror M1 and a concave mirror M2 and forms an intermediate image 180 which is an actual image. The second image forming optical system G1 forms an image of the intermediate image 180. Accordingly, the catadioptric projection optical systems discussed in Japanese Patent Laid-Open No. 2001-228401 and the pamphlet of International Publication No. 2005/069055 have the feature A. In addition, in each of these projection optical systems, an area of a reflecting surface of the reflecting mirror M1 where exposure light is reflected does not include an optical axis 103 of the projection optical system. Further, in each of these projection optical systems, a central portion of a pupil at the projection optical system is not shielded from light (or a pupil plane of the projection optical system is free of a void area).
In each of the catadioptric projection optical systems having the feature A, light from the first object can be reflected by an optical element (such as a lens), making up the image forming optical system G1, other than the reflecting mirror. In this case, light reflected by the optical element may be reflected again by the concave mirror M2 (whose reflecting surface opposes the first object 101) and converged, thereby producing a flare on the second object 102 near the optical axis 103. (The flare will hereunder be referred to as "flare (A).") FIG. 2A shows a distribution of light that is projected onto the image plane when a slit illumination area in the object plane of the catadioptric projection optical system shown in FIG. 24 in Japanese Patent Laid-Open No. 2001-228401 is illuminated with light. In FIG. 2A, reference numeral 301A denotes an image in an illumination area, and reference numeral 302A denotes the flare (A). Referring to FIG. 2A, the flare (A) 302A is produced near the optical axis 103 so as to be separated from the image 301A in the illumination area. Similarly, FIG. 2B shows a distribution of light that is projected onto the image plane when a slit illumination area in the object plane of the catadioptric projection optical system shown in FIG. 30 in the pamphlet of International Publication No. 2005/069055 is illuminated with light. Referring to FIG. 2B, a flare (A) 302B is produced near the optical axis 103 so as to be separated from an image 301B in an illumination area. The flare (A) does not occur only in these projection optical systems. It also occurs in many other catadioptric projection optical systems having the feature (A).


An integral multilayer analytical element for the determination of ammonia or an ammonia-producing substance comprising a light-transmissive liquid-impermeable support, an indicator layer containing an indicator which produces a detectable change by gaseous ammonia, a liquid permeation barrier layer, a reagent layer containing an alkaline buffer and optionally a reagent capable of reacting with a substance to produce ammonia and a spreading layer laminated in this order, which is improved by that the indicator layer contains a polyvinyl alkyl ether, and/or which is improved by that the surface of said support facing toward the indicator layer is undercoated with a polyvinyl alkyl ether, a hydroxyalkyl cellulose, an alkyl cellulose, polystyrene, a polyalkyl methacrylate, polyviriylidene chloride, polyvinyl alcohol or polyvinyl pyrrolidone, substantially not containing ammonia and ammonium ion. By using the above analytical element, ammonia or an ammonia-producing substance can be analyzed at a high coloring optical density and a high accuracy. The measuring accuracy is further improved by lowering the background optical density.

This invention relates to an integral multilayer analytical element for the determination of ammonia or an ammonia-producing substance in a liquid sample. More particularly, this invention relates to an integral multilayer analytical element suitable for the determination of ammonia or an ammonia-producing substance such as creatinine or urea contained in a biological body fluid such as blood, urine or lymph.
The quantitative analysis of ammonia, creatinine, urea or the like is very important for the diagnosis of various diseases such as nephropathy, the inspection for the medical treatment course of the disease, and the inspection of renal functions.
A representative analytical method for an ammonia-producing substance comprises a process for producing ammonia from the ammonia-producing substance and a process for determining the produced ammonia. The analytical method of utilizing the conversion to ammonia has been widely utilized in the so-called wet analysis or the solution method. Recently, in the dry analysis using a dry analytical device represented by integral multilayer analytical elements, the analytical method of utilizing the conversion to ammonia has been applied or proposed.
As the process for producing ammonia from an ammonia-producing substance, a common method is of producing ammonia by the action of an enzyme. For example, creatinine in a biological body fluid is determined by utilizing creatinine deiminase (EC 184.108.40.206) which hydrolzes specifically creatinine in the body fluid to ammonia and N-methylhydantion. Urea nitrogen (BUN) in a biological body fluid is determined by utilizing urease which hydrolyzes urea to ammonia and carbon dioxide. In the above methods, since the ammonia-producing substance, which is an analyte, is a substrate of an enzyme, the substance is called also ammonia-producing substrate. Analytical methods of the ammonia-producing substance are described in various references, such as "Analytical Chemistry", 46, 246 (1974), "Climica Clinica Acta", 18, 409 (1967), "Rinsho Kagaku Bunseki III Gan-Chisso Seibun (Clinical Chemical Analysis III Nitrogen-Containing Components) 2nd Edition", Tokyo Kagaku Dojin, Tokyo, 13-14, 67-87 (1979) and "Rinsho Kensa (Journal of Medical Technology)" 5(6), 387-391 (1961).
Integral analytical elements usable for the analysis of ammonia or an ammonia-producing substrate are the integral multilayer analytical element described in Japanese Patent KOKOKU No. 58(1983)-19062 (U.S. Pat. No. Reissue No. 30,267), the integral multilayer analytical elements for the analysis of ammonia or an ammonia-producing substrate disclosed in U.S. Pat. No. 4,548,906 (Japanese Patent KOKAI No. 58(1983)-77661) and Japanese Patent KOKAI No. 58(1983)-77660 and the like. The fundamental construction of the above analytical elements is composed of a light-transmissive, liquid-impermeable support, an ammonia indicator layer containing an indicator which produces a detectable change by contacting ammonia, a liquid permeation barrier layer which is permeable to gaseous ammonia and substantially impermeable to liquid, a reaction layer containing a reagent which reacts with an ammonia-producing substrate to produce ammonia and a porous spreading layer laminated in this order. The integral multilayer analytical element disclosed in EP 0 204 334 A has a trapping function of the ammonia contained in a body fluid (endogeneous ammonia) in the analytical element itself, and the analytical element can remove the influence of the endogeneous ammonia. This analytical element is provided with an endogeneous ammonia-trapping layer which conducts an ammonia-trapping reaction above the layer generating ammonia through an ammonia-producing reaction in contact therewith. The integral multilayer analytical element disclosed in EP 0 287 112 A is provided with a layer having a diffusion-preventing ability which does not perform trapping of ammonia and ammonia-producing reaction between the endogeneous ammonia-trapping layer and the ammonia-producing reaction reagent layer.
Heretofore, a copolymer latex of polyvinyl acetate-acrylate ester was used as the binder of the indicator layer. However, the analytical element using the above copolymer latex is insufficient in sensitivity, and the accuracy (CV=variation coefficient) is inferior. Since the coating solution is latex, it is inferior in the liquid stability because of the occurrence of precipitation. Moreover, since a pH variation of the latex solution occurs, this analytical element is unsuitable for the system using a pH indiator.

Integral multilayer analytical element for determination of ammonia or ammonia-producing substance


A tubular mount system for a rocker arm which includes a rigid clamp at the base of the engine head is disclosed. Included is a pedestal mount/adjuster with external threads engageable with internal threads of a trunnion assembly cooperatively associated with a rocker arm whereby the rocker arm can be raised or lowered by turning the pedestal mount/adjuster, rotatably received by a rocker stud. This eliminates the need for an adjuster stud and nut on the rocker arm and a pillow block to hold the device together.

1. Field of the Invention
The present invention generally relates to a rocker arm assembly. More particularly, the present invention relates to a rocker arm assembly for enabling engine technicians to more quickly and efficiently make valve lash adjustment.
2. Description of the Prior Art
A normal maintenance item for most engines is valve adjustment. Also known as setting "valve clearance" or "valve lash," this adjustment is an important maintenance item to insure lengthy, proper, and efficient operation of a four stroke engine. The valves in a four stroke engine open and close to allow intake air to flow into and exhaust gases to flow out of the engine. Often times a rocker/follower rides on the cam lobe (with the crankshaft and timing belt/chain turning the cams) and the rocker/follower thus actuates the valves. The cam has a "lump" for lift and a "base circle" for the duration of the engine rotation where the valve is closed. In order to insure that the valves close completely the "valve clearance" or "valve lash" is set so that there is a known clearance between the valves and the rocker arm.
The valve adjustment is important for two reasons. One, if the valves do not close properly, the engine can lose a substantial amount of power since the intake mixture will be "squeezed out" during the compression cycle (hence less mixture burned, less energy resulting from combustion). This might also result in burned valves as the exhaust valves depend partly on contact with the valve seat (head) for cooling. Second, if the valves do not open all the way, the engine will receive poor flow through the head (less mixture) and again lose power.
As the engine ages and more miles are put on it, the valve clearance can change. Repeated thermal cycling of the mechanism as well as mechanical wear will alter the adjustment slightly, resulting (typically) in increased clearance. This increase in clearance is usually characterized by an increased "ticking" at idle. Depending on the motor and the methodology, one may set this adjustment by measuring the clearance between the valve and rocker or the rocker and the cam. It will thus be understood that valve lash adjustment is required with respect to engine rocker arm systems.
Conventional stud mount rocker arm systems are economical to produce but due to the point of claiming, are too flexible and weak. Shaft mount rocker systems provide a rigid mount but with the added expense of necessary pillow blocks. More importantly, the shaft mount system adds reciprocating weight to the end of the rocker arm, reciprocating weight being the enemy of valve train lash.
U.S. Pat. No. 5,645,025 ('025 Patent), which issued to Caya et al., discloses an Internal Combustion Engine. The '025 Patent teaches an internal combustion engine comprising a cast cylinder head having as-cast alignment ribs that align a squared-off fulcrum in a rocker assembly. The rocker arm also has two substantially flat surfaces that engage the planar sides of the fulcrum to minimize lateral movement of the rocker arm. The fulcrum is received between the cast alignment ribs. The ribs are biased from a major axis to insure proper fulcrum alignment during assembly without the use of a jig. More particularly, the '025 Patent teaches a rocker arm having a rocker body that rotates around a trunnion. The trunnion slips over a rocker stud. A nut screws onto the rocker stud to hold the rocker assembly in adjustment. This structural assembly is deficient since the clamping point or bending moment is on the bottom side of the nut, which is a distance away from the head casting.
It will thus be seen from an inspection of the foregoing as well as other teachings commonly known in the art that the prior art does not teach an adjustable rocker arm assembly whereby the rocker stud serves as a fixed mount axis about which an adjustment tower may rotate for adjusting the rocker arm assembly and thus providing valve lash adjustment. The prior art thus perceives a need for an adjustable rocker arm assembly whereby the rocker stud functions as a fixed mount axis about which an adjustment tower may rotate for adjusting the rocker arm assembly, thus providing improved valve lash adjustment

Adjustable rocker arm assembly for easing valve lash adjustment


The present invention discloses novel hybrid proteins that have both plasminogen activator and anti-thrombotic properties, including clot specific action, that renders these as highly advantageous for the treatment of circulatory disorders involving fibrin clot formation due to underlying tissue damage in the blood vessels leading to myocardial infarction, strokes etc. Also disclosed are new proteins, and methods of obtaining the same, that help to dissolve blood clots by activating plasminogen in a plasmin or thrombin dependent manner and also inhibit both the activity and generation of thrombin through the intrinsic pathway of blood coagulation.

Thrombosis, the formation and development of a blood clot or thrombus within the vascular system, while a life saving process when it occurs during a hemorrhage, can be life threatening when it occurs at any other time. The thrombus can block a vessel and stop blood supply to an organ or other body part. If detached, the thrombus can become an embolus and occlude a vessel distant from the original site. Thrombotic disorders now constitute one of the major causes of mortality in both developing and developed countries world-wide. Although still the most preferred emergency ("SOS") medication against thrombotic circulatory disorders, the plasminogen activator protein drugs, such as streptokinase (SK), staphylokinase (SAK) and tissue plasminogen activator (tPA), are slowly losing their supremacy to emergency cardiac interventions such as stenting and bypass surgeries in the affluent countries because of bleeding risks associated with their use, and also the often-encountered problem of clot reformation at the same site of vascular injury due to thrombin activity and/or fresh generation of thrombin. Thus, there is an acute need to develop smarter and more effective thrombolytic drugs with additional features such as clot specificity and anti-thrombotic properties.
Blood clot formation is an end-result of a complex set of cascade reactions wherein several biochemical events cause the sealing, or repair, at the site of injury (Butenas and Mann 2002). On the basis of initiation of the blood coagulation cascade, pathways have been divided into extrinsic and intrinsic pathway, wherein the extrinsic pathway is initiated by the exposure of tissue factor (TF), whereas the intrinsic pathway is initiated by factor XII (Hageman factor), high molecular weight kininogen (HK), or prekallikrain. However, both cascade pathways ultimately join at the point of factor Xa generation, and subsequently follow common thrombin mediated fibrin generation (Cannon and Tracy 1995).
Thrombin generation is the central step of the blood coagulation process in vertebrates. During the thrombin generation process small amount of thrombin gets incorporated into the fibrin clot/network as it expands, and the catalytic site of this protease, being free in this absorbed thrombin, is able to amplify the clot growth (Liu, Nossel et al. 1979; Vali and Scheraga 1988). Thrombin interacts with diverse substrates and activates several clot promoting factors e.g. (a) it causes the activation of platelets by cleaving their cognate receptors (b) causes feed-back activation of factor V, VIII and XI (c) cause the activation of transglutminase, factor XIII and (d) converts fibrinogen into fibrin. Once the clot forms and stabilizes by inter-strand cross-linking, under the pathological conditions, it impedes the normal blood flow in vessels and leads to blockage of arteries and veins.
One of the most common, and preferred, medications against circulatory disorders emanating from pathological thrombus formation in animals/humans such as myocardial infarction, is the intravenous infusion of thrombolytic agents (Lijnen and Collen 1988; Collen and Lijnen 1990; Francis and Marder 1991). Available thrombolytics such as streptokinase (SK), urokinase (UK) and tissue type plasminogen activator (tPA) essentially operate through the same, plasmin-dependent mechanism (since these are plasminogen activators), where these cleave the scissile peptide between residues 561 and 562 of plasminogen and convert it into its proteolytically activated form, plasmin. Tissue type plasminogen activator and urokinase are proteases that specifically recognize the scissile peptide bond in human plasminogen (direct activators), whereas streptokinase and staphylokinase (which are protein 'co-factors' rather than proteases and thus 'indirect' activators; (see: (De Renzo, Boggiano et al. 1967; Buck, Hummel et al. 1968; McClintock and Bell 1971) first make tight 1:1 complexes with plasmin or plasminogen, and the resultant proteolytically active complex(es) cleave the scissile peptide bond of other, 'free' plasminogen molecules and exponentially generate plasmin (Reviewed by: (Wohl, Summaria et al. 1978; Castellino and Powell 1981; Wohl, Sinio et al. 1983; Davidson, Higgins et al. 1990). Of all the currently available clot-busters, that is, plasminogen activator protein drugs, streptokinase exhibits the highest thrombolytic power, although, being (like SAK) of bacterial origin, it has the limitation of engendering immune reactions in a small minority of patients. Nevertheless, it is widely used as an affordable thrombolytic because of its relatively low cost as compared to tPA and UK.
Successful thrombolytic therapy helps maintain normal blood flow and improves the survival in a significant number of patients (Verstraete 1990), but early re-occlusion or re-thrombosis, often at the same site, has continued to limit the successful application of thrombolytic drugs. Several studies demonstrate that early reocclusion occurs in up to 30% of patients after thrombolytic therapy (Ohman, Califf et al. 1990). The cause of rethrombosis or early reocclusion is explained by plasmin activity which increases the hyper coagulability of blood (Eisenberg, Miletich et al. 1988); it is proposed that plasmin activates contact factors (Ewald and Eisenberg 1995), factor V (Lee and Mann 1989) and likely also prothrombin (Seitz et al., 1993). Another suggested reason is the exposure of clot-bound thrombin subsequent to the latter's dissolution, which, in turn, generates more thrombin, with fibrin-bound thrombin being relatively resistant to anti-thrombin inhibitor/s (Hogg and Jackson 1989; Weitz, Hudoba et al. 1990); the 'released' thrombin again locally activates the procoagulant activity and starts to activate platelets (Kumar, Beguin et al. 1994; Puri, Kumar et al. 1995), thereby promoting a cycle of biochemical events leading to rethrombosis. Thus, inhibition of the thrombin at the site of injury both directly, and at the 'secondary' level of its procoagulant activity, should greatly thwart the above-described, unwanted chain of events. If such a property is integrated successfully in the same molecule as the thrombolytic drug, the advantages in terms of lives saved are obvious.
Plasminogen activators are a family of proteases which characteristically catalyse the enzymatic conversion of plasminogen to plasmin. TPA the enzymatic conversion of plasminogen to plasmin through the hydrolysis of a single Arginine-Valine bond.
Tissue plasminogen activator (also known as fibrinokinase, extrinsic plasminogen activator, t-PA or TPA) is a glycoprotein and has an approximate molecular weight (MW) of about 70,000 Daltons (68,000 Daltons). It is a serine protease which catalyses the enzymatic conversion of pro-enzyme plasminogen to active enzyme plasmin through the hydrolysis of a single Arginine-Valine bond. The catalytic site of t-PA is composed of amino acids His-322, Asp-371 and Ser-478. t-PA is a poor plasminogen activator in the absence of fibrin. The amino-terminal region is composed of several domains, which are homologous to other proteins. These distinct domains are involved in several functions of the enzyme, including binding to fibrin, fibrin-specific plasminogen activation, binding to endothelial cell receptors and rapid clearance in vivo. One such domain, comprising amino acid residues 50 to 87 (E domain) is homologous to Human Epidermal Growth Factor and seems to be involved in fibrin binding, fibrin affinity and in vivo clearance. The t-PA cDNA was cloned and subsequently expressed in Chinese hamster ovary (CHO) cells.
Tissue plasminogen activator (t-PA) is a component of the mammalian fibrinolytic system responsible for the specific activation of plasminogen associated with fibrin clots (i.e. it is capable of dissolving blood clots). Tissue plasminogen activator-mediated clot dissolution shows increased level of fibrinopeptide-A in plasma, which is a direct marker of clot-bound thrombin (Weitz, Leslie et al. 1998). A combination of tissue plasminogen activator and currently known anti-thrombin drugs such as heparin and hirudinis often used in medication but this anti-thrombin acts only on free thrombin, and the clot-bound thrombin is resistant towards heparin and other the inhibitors due to their low affinity. Besides, these drugs do not affect the indirect promoters of further thrombin generation (e.g. Factor V and Factor VIII). Hence, new chimeric proteins need to be designed which activate plasminogen along with inhibition of clot bound thrombin as well as the indirect promoters of thrombin, such as Factor V and Factor VIII.
Work on post-thrombolytic plasmin activity and consequent thrombin generation clearly suggests that there are potent factors which lead to the re-activation of the coagulation pathway even when the pathological clot has been cleared by a clot-buster drug. In addition, the generated thrombin is itself a potent coagulation pathway activator. It is remarkable that thrombin also performs an anti-coagulant function, which is an elegant example of the "self-limiting" control mechanisms of the hemostasis system such that there is no 'run away' coagulation throughout the vasculature. Free thrombin makes a 1:1 high-affinity, non-covalent complex with thrombomodulin, a cell surface protein (Kurosawa, Galvin et al. 1987). Once the thrombin-thrombomodulin complex is formed its substrate specificity is redirected from a pro-coagulant mode to an anti-coagulant one, whereby it activates the Protein C anticoagulant pathway. Thus, even though thrombin alone can activate protein C but once it complexes with thrombomodulin it accelerates protein C activation by nearly a 1000-fold (Esmon and Owen 1981; Owen and Esmon 1981)).
Mature thrombomodulin contains different domains responsible for different functions, namely thrombin inhibition and protein C activation which reside in the epidermal growth factor-like domains of this large protein. Epidermal growth factor-like (EGF) domains 5 and 6 are responsible mainly for thrombin affinity and EGF 4, 5 and 6 domains, activate protein C together (Kurosawa, Stearns et al. 1988; Stearns, Kurosawa et al. 1989). Thrombomodulin, or its isolated EGF domains 4, 5 and 6, are known to activate the protein C-centered anticoagulant pathway, and also directly inhibit thrombin's activity, but cannot dissolve the fibrin clots by themselves. For this, a thrombolytic agent is necessary. Both types of agents can, independently of each other, be used during cardiac thrombotic maladies, but the advantages of a single drug with both types of attributes (which has not been demonstrated so far) are obvious.
The term 'hemostasis' refers to the balance between anticoagulant and procoagulant activities in the blood/vascular system, wherein normally, the blood components, particularly platelets, do not interact abnormally with the blood vessels' inner lining. In case of injury or disease condition, platelets tend to adhere, and as a result, blood coagulation factors start to accumulate and get activated at the site of this injury, which, although a response to initiate repair at the site of injury, results in blood occlusion, thereby often precipitating thrombotic crises.
Blood coagulation and dissolution of a clot, inside blood vessels, are both necessary physiological processes for normal hemostasis. Clot formation and dissolution mechanisms inside the blood vessel are well known in the literature, and the role of different pro-coagulant proteins (clot promoting) and anti-coagulant proteins are now fairly also well-studied. Clot formation is the result of a complex set of reactions wherein thrombin plays a central role in initiation as well as coagulation cascade acceleration, with the end-result appearing in the form of a stable fibrin mesh.
Every modern thrombolytic/fibrinolytic therapy usually combines an anti-thrombotic medication as well (such as aspirin, heparin etc) which is required for the maintenance of normal equilibrium between the pro-coagulants and anti-coagulants during the clot lysis. During lysis, the transiently released thrombin initiates a self-generation loop to amplify clot growth; sometimes this results in a shift of the equilibrium towards the reformation of clot, or activation of the pro-coagulants/clot promoters.
Thrombolytics dissolve pathological clots by activating intrinsic plasminogen in the circulatory system. Among the available and therapeutically useful thrombolytics, streptokinase exhibits the highest thrombolytic potential but sometimes it leads to hemorrhage during the medication because of a lack of clot specificity. This problem is relatively less associated with other thrombolytics (tPA and SAK) because of their relatively increased fibrin clot specificity, but other shortcomings of these thrombolytics are lesser fibrinolytic potential and shorter in vivo half life. All the thrombolytics have essentially same mechanism of thrombolysis (plasminogen activation), but share a common problem, in that that after thrombolysis the generated thrombin often further amplifies thrombin generation by a feed-back mechanism controlled by blood coagulation factor Va and factor VIIIa. In the thrombolysis process, the clot-bound thrombin is also released into the circulation which is relatively resistant to in-built anti-thrombin and other externally provided thrombin inhibitory drugs. This clot-bound thrombin, present at the near vicinity of the 'original' injury also helps to generate even more thrombin in the vicinity of the clot/site of injury, particularly after incomplete removal of clot, which leads to the clinically grave, early re-occlusion problem.
Thombin generation during the lysis and activation of other intrinsic pro-coagulants is a normal part of the hemostasis equilibrium. Anti-thrombin agents like heparin, hirudin and chemically synthesized drugs can inhibit thrombin and prevent its subsequent transient effects, like suppression of hyper-responsive platelet formation process, inhibition of fibrinogen to fibrin conversion and other clot promoting activities which induces hyper-coagulibility in blood. Notably, however, all these direct inhibitors act on transiently generated thrombin, but not on those factors which actually speed up thrombin generation and play key roles in the procoagulant pathway. Thus, none of these drugs acts as efficaciously as desired on blood coagulation factors V and VIII, which play crucial role in thrombin generation and early re-occlusion.
The well-known cell surface molecule thrombomodulin, which makes 1:1 complexes with thrombin and directs its pro-coagulant function into a potent anti-coagulant, namely protein C activator. Both activated protein C and protein S degrade activated factor V and factor VIII (Esmon 1989).
Although all available thrombolytics do possess clot dissolving capability and their mechanism is well evident in literature, but during clot lysis, remnants of clot and plasmin lead to thrombin generation; at the same time, since these agents cannot inactivate the thrombin which makes a transient appearance during thelysis of the clot, the result is that reocclusion is a common problem subsequent to thrombolytic therapy. To date, no anti-thrombin drugs are available with a combination of thrombolytic and anti-thrombin properties, especially the pro-coagulant activity so as to inactivate the 'real culprit' which is chiefly responsible for re-thrombosis.

Protein fusion constructs possessing thrombolytic and anticoagulant properties


A process is for laser-welding resinous members, and includes the steps of overlapping a transparent resinous member on an absorptive resinous material, and irradiating the transparent resinous member with a laser beam, thereby welding an interface between the transparent resinous member and the absorptive resinous member as a strip shape, wherein the energy of the laser beam acting on a side of a major-curvature-radius curved part of the strip-shaped welded interface and the energy of the laser beam acting on a side of a minor-curvature-radius curved part thereof are averaged.

1. Field of the Invention
The present invention relates to a process for laser welding resinous members, an apparatus for the same, and a laser-welded resinous product. More specifically, it relates to a process for integrally bonding transparent resinous members exhibiting transmissivity to laser beams and absorptive resinous members exhibiting absorptivity to laser beams by laser welding, an apparatus for the same, and the resulting laser-welded resinous products.
2. Description of the Related Art
Recently, from the viewpoint of weight saving and cost reduction, it has been carried out extensively to resinify component parts of various fields, such as automobile component parts, thereby making them into resinous molded products. Moreover, from the perspective of producing resinous molded products with high productivity, it is often the case to employ the following measures. A resinous molded product is molded as a plurality of the component parts separately in advance. Then, the resulting independent component parts are bonded with each other.
Laser welding processes have been utilized conventionally in order to bond a resin with another resin. For example, Japanese Unexamined Patent Publication (KOKAI) No. 11-348,132 discloses a laser welding process. In the conventional laser welding process, a transparent resinous member exhibiting transmissivity to a laser beam is overlapped on an absorptive resinous member exhibiting to absorptivity to the laser beam. Thereafter, the transparent resinous member is irradiated with the laser beam. Thus, the transparent resinous member and absorptive resinous member are heated to melt at the surfaces, thereby bonding them integrally.
In the conventional laser welding process, the laser beam is absorbed at the interface of the absorptive resinous member when it transmits through the transparent resinous member and reaches the interface. The laser beam absorbed at the interface is accumulated as energy. As a result, the interface of the absorptive resinous member is heated to melt, and simultaneously the interface of the transparent resinous member is heated to melt by the heat transfer from the interface of the absorptive resinous member. When the interface of the transparent resinous member and the interface of the absorptive resinous member are applied to each other under the circumstance, it is possible to bond them integrally.
However, it is not necessarily possible to obtain a uniform welded state by the above-described conventional laser welding process in certain cases. Let us consider the case of welding a resinous product, a box-shaped container, by the conventional laser welding process with reference to FIG. 18. For instance, a box 4 has an opening molded from an absorptive resin, and is welded to a cover 3 composed of a transparent resin. The box 4 and cover 3 are welded by using a laser beam 1 along a weld line 2 to complete a welded product 5. When scanning the linear parts of the weld line 2 with the laser beam 1 to weld thereat, the laser energy per unit time is constant on the surface 4′ of the box 4 under the conditions that the laser power, the scanning speed and the thickness of the cover 3 are constant. Accordingly, it is possible to weld uniformly in the longitudinal direction and widthwise direction of the weld line 2 in welding at the interface between the cover 3 and the box 4. However, the laser beam 1 has a finite irradiation cross-sectional area. Consequently, it is not necessarily possible to weld uniformly at the curved parts 2′ of the weld line 2 (i.e., parts adjacent to the corners of the welded product 5) at which the scanning direction of the laser beam 1 is changed from one direction to another.
Moreover, FIG. 17 illustrates a relationship between a welding line 2 and a laser-beam spot 3 adjacent to a corner of the welding line 2 when a laser beam has an ellipse cross section and a spot diameter equal to the width of the weld line 2. Under the condition that the scanning speed of the laser beam is constant, the travel distance of the laser beam along the left-hand side tangent "A" of the laser-beam spot 3 forming the weld line 2 is equal to the travel distance of the right-side tangent "B" thereof at the linear parts of the weld line 2; but the travel distance of the laser beam along the major-curvature-radius curved part R2 (or along the outermost peripheral line "A") is longer than the travel distance of the laser beam along the minor-curvature-radius curved part R1 (or along the innermost peripheral line "B") at the curved part of the weld line 2. This implies that, when the energy of the laser beam irradiating per unit time is equalized at the locus 1 of the center of the laser spot 3 (shown with the alternate long and short dash line of the drawing), the energy is insufficient at the outermost peripheral line "A"; but it is excessive at the innermost peripheral line "B." Thus, the energy density has become higher at the minor-curvature-radius curved part R1 than at the major-curvature-radius curved part R2 in the curved part of the weld line 2. As a result, the curved part of the welding line 2 is inferior to the linear parts thereof in terms of the weld strength. Moreover, the weld might be insufficient at the major-curvature-radius curved part R2, and the constituent resin might be degraded at the minor-curvature-radius curved part R1 because of the excessive energy.

Process for laser welding resinous members, apparatus for the same and laser-welded resinous product


An image sensor has a pixel array, a readout portion configured to read out a signal from the pixel array, and a control portion which controls the readout portion. The readout portion includes a row selecting portion which selects a row in the pixel array, a column selecting portion which selects a column in the pixel array, and an output portion which outputs a signal from a pixel, of pixels on a row selected by the row selecting portion, which corresponds to a column selected by the column selecting portion. The pixel array includes blocks differing in distance from the output portion, and the control portion controls readout periods required by the readout portion to read out signals from the blocks so as to read out signals from blocks in longer readout periods as distances from the output portion increase.

1. Field of the Invention
The present invention relates to an image sensor, an imaging system, a sensor, and an operation method for the image sensor.
2. Description of the Related Art
In an image sensor, a row selecting circuit selects a row of a pixel array, and a plurality of pixels on the selected row output signals to a plurality of column signal lines. A column selecting circuit then outputs signals from the pixels on one row while sequentially selecting a plurality of column signal lines. The image sensor sequentially performs this operation for a plurality of rows while changing a row to be selected. In a conventional image sensor, a readout period for signals is constant regardless of any row selected from a plurality of rows of a pixel array.
However, in an image sensor including a pixel array and a horizontal output circuit which sequentially selects and outputs signals output from the pixel array to a plurality of column signal lines, a shortage of readout period can occur more with an increase in distance from the horizontal output circuit. Such a problem becomes more conspicuous in an image sensor with a large pixel array size of several tens of cm. Shortages of readout period corresponding to row positions can cause shading.

Image sensor, imaging system, sensor, and operation method for image sensor


A crankcase of an internal combustion engine with at least one main lubricant channel for supplying the internal combustion engine with lubricant and with at least one oil return flow channel (10) for return guidance of the excess lubricant into a reservoir container (11), wherein the oil return flow channel (10) exhibits a peg-shaped widening (12), which is formed by the attachment a bearing support of an oil channel core (18). An oil channel core as well as a process for producing a crankcase.

1. Field of the Invention
The invention concerns a crankcase, an oil channel core for producing a crankcase, and a process for producing a crankcase according to the main claim and the dependent claims.
It is known to produce crankcases for internal combustion engines as cast parts in a sand casting or pressure casting process. Conventionally, oil channels such as oil return channels of a crankcase housing are shaped by a core withdrawal process using shaped parts or oil channel cores. For smoothing the surface of the thus produced work pieces, refractory dressings are used on the sand molds, which are applied onto the oil channel cores in order to flatten or smooth the porous surface of the oil channel cores. Conventionally, for this finely ground, thermally-stable to high-temperature fire-stable materials are employed as base material. The coating layer insulates the substrate and protects it from thermal stress due to the molten metal.
2. Description of Related Art
In the German patent document DE 39 14 124 C2, oil channel cores are disclosed having for example a slat shape or peg-shape.
The problem therewith is that the oil return flow channels are elongate and have a narrow diameter relative to their longitudinal direction. If the oil channel core is supported, during a drying process following coating, for example during an oven treatment, on supports above and below the later produced cast part, the oil channel core bends, which can lead to a detrimental deformation of the oil return flow channel. Supporting or bearing the piece in the area between the above-mentioned support points is undesirable since the coating will become damaged at the bearing location, and during the later casting the casting material of the crankcase housing penetrates into the mold. It is a problem herein that this produces a defect that is difficult to purge.
In the utility models DE 29 812 739 U1 and DE 20 303 276 U1, specially shaped oil channel mold supports are proposed, in order to minimize the above-described problem. This type of support must however be produced separately, which necessary leads to an increase in the production costs.

Crankcase, oil channel mold core for producing a crankcase and process for producing a crankcase


A process of repulping paper a product comprising cellulose fibers, comprising forming an aqueous suspension of paper product to be repulped and an oxidizing agent comprising at least one persulfate salt, and maintaining the pH of the aqueous suspension in a range of from about 2.3 to about 6.5. The process is preferably conducted in the presence of preferred buffer systems. Compositions for conducting such processes are also provided.

1. Field of the Invention
The present invention is related to processes and compositions for repulping wet strength paper and paper products such as paperboard and the like, and in particular to repulping such materials which exhibit increased wet strength by virtue of having added thereto a wet strength resin.
2. Description of Background Information
Paper and paperboard are ubiquitous in our society, where these products are employed in numerous applications. Paper is an ideal material, not only for its functionalities, but also for its ability to be recycled. Its inherent recyclability is an important factor in today's market.
Paper is recycled via a process called repulping, wherein the cellulose fibers that comprised the original sheet are separated. These fibers can be cleaned, treated, redispersed, and prepared into a pulp slurry essentially similar to that used to make the original sheet. The normal papermaking process is then followed to form a sheet made from recycled fibers. The process of repulping involves mixing, under shear, in water. Chemicals may be added to accelerate the process; and elevated temperatures are often used.
Paper is made to provide specific functional properties. Chemicals are often added to impart and/or enhance these properties. Amongst the more widely used additives are wet strength resins. These chemicals act to provide strength to wet paper and are used in, among other paper products, paper towel and packaging.
Repulping paper containing a wet strength resin is difficult because the resin (such as a polyamide-epichlorohydrin resin) is added during paper production to enhance the strength of the paper produced so that the paper does not fall apart when used under wet conditions. The wet strength resin binds the cellulose fibers together, impeding the repulping process of separating the cellulose fibers. Typically, paper treated with wet strength resins will retain at least 15% of the dry strength of the paper when wet. Paper without wet strength resin generally retains only 2-7% of its dry strength when wet.
Oxidation facilitates the breakdown of the wet strength resin to permit separation of the cellulose fibers. Hypochlorite, particularly sodium hypochlorite, is typically used by paper mills in the repulping of wet strength paper to oxidize the wet strength resin to facilitate fiber separation. Hypochlorite oxidizes the wet strength resins within a narrow, carefully maintained pH range and within a temperature range of from about 122.degree. F. (50.degree. C.) to 158.degree. F. (70.degree. C.).
Environmental issues have been raised concerning the use of hypochlorite for repulping. These concerns relate to the formation of organic halides which are adsorbed by the pulp, chloroform emission, and the problem of adding chlorinated hydrocarbons to the effluent stream. For these reasons, non-halogen containing compounds, such as persulfates have been used to oxidize wet strength resin during the repulping process.
Thus, more recently it has been found that persulfate salts can be used to degrade the wet strength resin, facilitating the repulping process. Any persulfate salt, typically sodium, can be used. This material can also be used with alkali metal, alkaline earth metal, or ammonium salts of carbonate, bicarbonate or sesquicarbonate to enhance repulping performance. Mixtures of persulfate and carbonate, bicarbonate or sesquicarbonate can be prepared which do not separate in storage containers, and which exhibit substantially increased handling safety over persulfate alone.
In general, however, systems employing persulfate salts are slower than hypochlorite or similar systems. Moreover, the introduction of additional heat, beyond that used with hypochlorite, is generally required for repulping suspensions employing such persulfate salts, in order to accelerate the degradation of the wet strength resins to a commercially-acceptable rate.
WO 94/20682 A1 discloses a composition containing a persulfate and a carbonate, bicarbonate or sesquicarbonate for use in oxidizing wet strength resin containing paper. The present invention accelerates the action of this material.
U.S. Pat. No. 3,427,217 discloses a process for repulping wet-strength broke containing wet-strength resin which comprises slurrying the broke in a dilute aqueous solution of an inorganic oxidizing agent. The oxidizing agent is selected from a group which includes persulfates.
WO 95/05504 A1 discloses a formulation for repulping and/or decoloring broke comprising 51-94 wt % persulfate; 4-43 wt % pH adjuster; 0.05-6 wt % soluble catalyst selected from one or more of a soluble salt of Cu, Fe, Ag and Ni; and 0-10 wt % of a saccharide which has no greater ability to reduce the catalyst than does D-mannitol. This document also relates to a method for repulping and/or decolorizing broke. Preferably the pH adjuster is a base selected from alkali metal, alkaline earth metal or ammonium salts of carbonate, bicarbonate or sesquicarbonate. The catalyst is a Cu salt. The saccharide is ascorbic acid, D-sorbitol and/or D-mannitol. It is stated that the composition permits separation of the fiber without destruction of the cellulose, yet permits alerting the chromophore to decolorize. The composition is said to effectively meet environmental requirements. The pH range of the solutions of Example 1 are relatively high, and the control of pH by the use of a buffer or other means is not disclosed.
THORP, et al., "Chlorine-Free Wet-Strength Paper Repulping and Decolorizing with Activated Persulfates", 1995 Papermakers Conference: Proceedings (TAPPI); 163-168 (Apr. 26, 1995; TAPPI Press) discloses a sodium persulfate mixture containing an activated persulfate catalyst used in laboratory trials carried out on wet-strength broke that investigated the use of activated persulfates for repulping and decolorizing papers treated with neutral/alkaline wet-strength resins. Reaction time, persulfate concentration, temperature, and pH were identified as the critical process parameters in optimizing repulping performance. Paper additives, lignin content, dye chemistry, and mechanical agitation were also found to affect persulfate performance. Page 165 discloses that wet strength broke is most effectively repulped by activated persulfates under alkaline conditions. This page also states that a pH range of 9-11 usually yields the best repulping results.
It is known that the ratio of persulfate to base can be adjusted to provide a neutral, acidic, or basic pH during the repulping process for the oxidation of the wet strength resin. Such pH regulation by adjustment of the persulfate to base ratio in the combined product avoids the need for an additional process step for pH adjustment and permits a single package chemical treatment for repulping. Repulping using persulfate is conducted under alkaline conditions, because conventional wisdom dictates that repulping using persulfates is optimal, for example faster, under alkaline conditions.
For Example, ESPY, et al., "Persulfates as Repulping Reagents for Neutral/alkaline Wet-strength Broke", Tappi J., Volume: 76 Number: 2, pages 139-42 (1993) CA: 119(10)98260h discloses alkali metal persulfates have been found to repulp neutral/alkaline wet strength broke. Persulfate salts defiber paper made with polyamide-epichlorohydrin resins, although slower than hypochlorite salts. Persulfate salts are said to be an acceptable substitute for hypochlorite because they do not generate organic chlorides in pulping effluents. Persulfate salts are especially effective in broke made with polyamide- or polyamine-epichlorohydrin wet-strength resins. Temperature and pH conditions are also described.
ESPY, et al., Proceedings of the TAPPI Papermakers Conference--1990, pg. 147-149, discloses that repulping is much faster under alkaline and neutral conditions than acidic conditions (pH 4). The pH of the suspension or system appears to vary considerably throughout the process and is not held or maintained substantially constant throughout the process. H. H. Espy and G. W. Geist, TAPPI Journal, pp. 139-142, Vol 76, Nov. 2, 1992, which is a related version of the foregoing, presents similar disclosure.
WO 95/06157 A1 discloses a process for repulping wet strength paper in which the initial breakdown is conducted at one pH; with substantial completion at a second, and high pH. The first pH value is no higher than 8, but is said to be typically about 8 (page 4, line 25), and preferably in the acidic range, and the pH adjusting agent for the first pH value is said to be typically an organic acid such as acetic acid, or an inorganic acid such as hydrochloric acid or sulfuric acid. The pH may be as low as 3 (Table 1, page 8) or 4 (Table 2, page 11, and Table 3, page 13). The pH is not controlled by a buffer solution, and the efficacy is undesirable.
U.S. Pat. No. 5,447,602 (which is a family member of WO 95/06157 A1 discussed above) discloses a process for repulping wet strength paper containing a wet strength resin. The process comprises (a) repulping the wet strength paper in a slurry containing an oxidizing agent and having a first pH to initiate breakdown of the paper to fibers; and (b) repulping the slurry at a second pH which is higher than the first pH until conversion of the wet strength paper is substantially complete. The process is said to be especially useful for repulping bleached paper and unbleached paper broke or corrugated containers.
EP 585 955 A1, a patent application of Hercules Incorporated, discloses the use of a non-chlorinating oxidizing agent and a water soluble buffering salt that is capable of maintaining pH between 7 and 12.
THIRKETTLE, "Broke Handling", Paper Review of the Year, Johnsen, Jorgensen & Wettre, Ltd., 1974 (pp. 126-136) discloses various aspects of handling "broke" (i.e., paper trimmings, scrap, and similar surplusage resulting from paper manufacture), including broke repulping. This document specifically teaches that repulping of broke treated with agents such as KYMENE 557 can be most efficiently accomplished under alkaline conditions at a pH of 10.5 and a temperature of 120.degree. F.
Each of the foregoing approaches suffers from disadvantages. For example, repulping using persulfates and similar agents is generally slower than repulping with hypochlorites, and so the use of persulfates also includes a sacrifice in speed, efficacy and efficiency.
Accordingly, the foregoing approaches have failed to provide processes and compositions which exhibit the desired degree of effectiveness, rapidity and simplicity, and there has been a continuing need for improvement.

Processes and compositions for repulping wet strength paper and paper products


A disposable single trap and holder for tacos and the like comprised of semi-rigid flat material to accommodate the ability of the holder to be efficiently packaged in a retail container. The holder has a flat circle shaped configuration with specific cuts and lines of weakness, whereas, when pressed outward from center, the holder will form first and second side walls extending from a generally horizontal base portion to accommodate and support a taco and the like in an upright position.

In providing a taco holder for inclusion in public restaurants and consumer use, among the considerations that must be addressed are the ease of assembly and use by the consumer: the efficiency for holding a taco in an upright position, to serve and the like without spillage or breakage during filling and possibly heating; the ability to hold a taco and the like for individaulized servings; and the ability of the holder to be efficiently packaged in a retail container.