A solar energy collector apparatus and method, the apparatus including an open-top shell structure configured with either an enclosed or lattice configuration and having a Fresnel lens system covering the open top of the shell structure. A mirror system and solar energy absorber apparatus are placed inside the shell structure. The shell structure is mounted upon a hollow axle for rotation about its longitudinal axis. The shell structure is also mounted for vertical movement of one end of the longitudinal axis to adapt the shell structure for following north-south changes in the sun's seasonal position. The hollow axle supports the solar energy absorber apparatus nonrotatably inside the shell structure and in fluid communication with insulated heat transfer conduits that pass nonrotatably through the hollow axle. A photovoltaic apparatus may be included in the shell structure for converting at least a portion of the solar flux to electrical energy while the heat transfer conduits supply any necessary cooling to the photovoltaic apparatus. This combination of features provides higher solar efficiencies and higher temperatures in the heat transfer fluid. The method includes tracking the sun with the solar energy collector apparatus thereby maximizing the amount of solar energy collected while eliminating twisting and thereby coupling failures in the heat transfer conduits.

1. Field of the Invention
This invention relates to solar energy collector apparatus and, more particularly, to a solar energy collector apparatus and method whereby focusing and reflecting apparatus for the solar collector is rotatably movable about a generally stationary solar energy absorber apparatus to improve collector efficiencies and also eliminate expensive and failure-prone rotatable couplings in the fluid heat transfer conduits.
This application contains patentably distinct subject matter from copending applications, Ser. No. 970,761 and Ser. No. 970,673, both filed on even date herewith.
2. The Prior Art
Currently, the only inexhaustable source of energy available to mankind is solar energy. Solar energy or solar flux is customarily measured in langleys per minute, one langley being equivalent to one calorie of radiation energy per square centimeter. The intensity of the solar flux varies with geographical location, time of day, season, cloud cover, atmospheric dust, and the like, and this intensity varies between about zero and 1.5 calories per square centimeter per minute. Therefore, assuming a solar flux of one langley per minute, one square meter receives 10,000 calories per minute while a house roof, having 100 square meters, receives about 1,000,000 calories per minute. With an average of one langley per minute for 500 minutes per day (which is slightly more than 8 hours), the 100 square meter roof receives, in bright sunshine, about 500,000 kilocalories per day. This energy is the equivalent in thermal energy to burning about 14 gallons of gasoline. Therefore, solar energy represents a valuable, inexhaustable energy resource.
When an object such as a solar collector is exposed to solar radiation, its temperature rises until its heat losses become equal to its heat gains. The losses depend on the emission of radiation by the heated material, movement of the surrounding colder air, and thermal conductivity of the materials in contact with it. The gains depend upon the intensity of solar radiation and the absorptivity of solar radiation by its absorption surface. Customarily, solar energy is collected by two general techniques to produce higher temperatures: (1) by covering a receiving surface with a sunlight-transparent sheet of glass or plastic (flat plate collector), and (2) by focusing the solar radiation from a large area onto a receiver of small area (focusing collectors).
Flat plate collectors are usually stationary but should be repositioned every few days to follow the seasonal variations in the solar track. Flat plate collectors have the advantage of being generally cheaper to fabricate and also have the advantage in absorbing heat from diffuse solar radiation as well as the direct radiation by being able to operate on cloudly but bright days.
Focusing collectors can produce much higher temperatures although they can use direct radiation only and require turning throughout the day to follow the sun. Although focusing collectors are useful in obtaining higher temperatures from solar energy, (1) they usually cost more, (2) they need to be moved continuously to track the sun, and (3) they can use only direct solar radiation that is unscattered by clouds or haze. One common form of focusing collector is a parabolic mirror which has been used to obtain temperatures up to about 3500.degree. C. depending upon the optical perfection of the parabolic surface. Unfortunately, parabolic collectors are relatively expensive, require sophisticated mountings and the absorption surface is usually interposed between the sun and the parabolic reflector at a position adjacent the focal point of the parabolic curvature.
Another device for useful focusing solar energy in a focusing collector is the Fresnel lens. The Fresnel lens consists of nested grooves cut or otherwise formed in one face of a transparent material such as plastic. The sides of each successive groove is set in such a way that the light passing through each groove is refracted at a slightly different angle so as to converge on a common focal point or line. Such lenses have been pressed from rigid sheets of plastic material and are, therefore, relatively inexpensive while being effective to give a relatively sharp focus. A more detailed discussion on the use of a Fresnel lens in a solar concentrator can be found in "Large-Scale Fresnel Lens Solar Concentrator" Marshall Space Flight Center, Alabama; NASA Tech Briefs; Winter (1977) p. 461.
Since focusing collectors require tracking mechanism for tracking the sun, various types of tracking devices have been developed. Tracking of the sun in its east-west movement only is relatively simple since the sun moves at a rate of 15.degree. of arc every hour. This calculation is determined on the basis of the earth making one complete revolution of 360.degree. in a 24 hour period so that in one hour it moves 360.degree. divided by 24 or 15.degree.. However, the annual motion of the earth relative to the sun causes the sun to appear to move in declination by about 47.degree.. This wide range from summer solstice to winter solstice is a major problem any focusing collector system must face. Thus, any fully tracking collector that is focused continuously on the position of the sun in the sky requires motion in two coordinates. While the exact coordinates in which the motion is made are not deemed important, one set of coordinates may be rendered redundant by using an equatorial mounting where one axis of rotation is supported parallel to the axis of rotation of the earth. The sun then appears to have no significant daily motion in the transverse coordinate (declination). Meanwhile, any other set of axes of motion requires two motions to track the daily motion of the sun. However, in order to accommodate seasonal variations, it is necessary to include within the equitorial mounting a mechanism for matching daily changes in the seasonal position of the sun. Thus, an equatorial mounting presents the more feasible mounting system for a tracking or focusing solar collector.
Additional information regarding solar collectors can be found in APPLIED SOLAR ENERGY, Aden B. Meinel and Marjorie P. Meinel, Addison-Wesley Publishing Company, Reading, Mass. (1976) Library of Congress Catalog Card No. 75-40904, and DIRECT USE OF THE SUN'S ENERGY, Farrington Daniels, Ballantine Books, N.Y. (1977) Library of Congress Catalog Card No. 64-20913.
Utilization of collected solar energy very often occurs at a location other than the center of focus for a focusing collector. The exception to this statement are those focusing collectors which are used primarily as photovoltaic power towers, solar cookers, etc. The technique for transferring solar energy from its collection site to its utilization site generally involves some form of fluid heat transfer medium. The fluid heat transfer medium is conducted through conduits to and from the solar energy absorption site. The heat transfer medium is heated by the thermal energy produced by the absorbed solar energy and carries the thermal energy to the utilization site where the thermal energy is either utilized directly or stored for subsequent use. Unfortunately, the combination of movable solar collectors and fluid heat transfer conduits presents difficulties with regard to fabricating solar collectors which will accommodate flexure or otherwise movement of the fluid heat transfer conduits.
In view of the foregoing, it would be an advantage in the art to provide improvements in solar collector apparatus and the method for collecting solar energy. It would also be an advancement in the art to provide a solar collector apparatus for tracking the sun, the apparatus including mechanism for accommodating the movement of the solar collector while minimizing excessive flexure or twisting of the fluid heat transfer conduits. Such an invention is disclosed and claimed herein.

Focusing cover solar energy collector apparatus


A cooling apparatus includes a container filled with a quantity of coolant fluid initially cooled to a solid phase, a cooling loop disposed between a heat load and the container. A pump for circulating a quantity of the same type of coolant fluid in a liquid phase through the cooling loop, a pair of couplings for communicating the liquid phase coolant fluid into the container in a direct interface with the solid phase coolant fluid.

1. Technical Field of Field of Invention
The present invention relates generally to the field of heat transfer and, more specifically, to a direct-interface, fusible heat sink for non-venting, regenerable and self-contained thermal regulation.
2. Description of the Prior Art
Astronaut cooling during extravehicular activity (EVA) is a critical design issue in developing a portable life support system that meets the requirements of a space station mission. Some of the requirements are that the cooling device be easily regenerable and non-venting during operation.
During EVA, a crew member generates metabolic energy, while portable life support systems and equipment produce additional heat. Ninety percent of metabolic energy is in the form of waste heat that must be removed from the body during the EVA to allow crew comfort and performance. Once removed from the body, the heat may be either stored or rejected, or both.
On orbit, heat rejection occurs only by radiation or mass transfer. Heat storage may be accomplished by inducing a phase change in a substance or by causing an endothermic reaction to take place. Any self-contained system that attempts to control the thermal condition of an astronaut wearing a space suit will be limited by either capacity or rate of heat transfer. For example, a storage system will be limited by capacity, as will a mass transfer system. A radiation system will be limited by heat-transfer rate.
Thermal regulation of astronauts during EVA has been accomplished in the past by use of a sublimator or an umbilical coolant supply. These systems provide adequate capacity and rate and are compact and light weight. However, they have disadvantages in that they require venting and subsequent loss of water during operation. Also, the umbilicals are awkward and difficult to manage.
Future exploration missions will require an EVA system that can provide routine, possibly daily, operation that continues for months without support or resupply from surface-based resources or facilities. For these reasons, it is desirable for a thermal regulation system to be easily regenerable, non-venting, and extremely reliable. Some specific requirements are that the total capacity be about 11,680 Btu (3,420 W-hr) for an 8 hr EVA and that the device be able to cool at 2,000 Btu/hr (585.6 W) for 15 minutes any time during this 8 hr period. More specific requirements are listed below in Table 1:
TABLE 1 ______________________________________ Design and Performance Requirements ______________________________________ EVA duration 8 hr EVA environment LEO (any orientation) Environment load 0 Btu/hr (0 W) Metabolic heat load Minimum 400 Btu/hr (117 W) Average 1000 Btu/hr (293 W) Maximum 2000 Btu/hr (5686 W) PLSS heat load Average, 635 Btu/hr (186 W) Net Heat Load Minimum 635 Btu/hr (186 W) 8-hr average 1500 Btu/hr (439 W) 15-min max 2000 Btu/hr (586 W) Total heat capacity 11680 Btu (3420 W) Cooling garment temperatures Minimum 60.degree. F. (15.5.degree. C.) (5) Maximum 85.degree. F. (29.4.degree. C.) Heat-sink outlet temperature <40.degree. F. (4.4.degree. C.) (humidity control) Regeneration time Less than 16 hr EVA frequency 8 hr/day, 6 day/Wk Mission duration 6 mo Operational lifetime >1228 hr ______________________________________
While there has been a number of astronaut cooling devices that use fusible heat sinks, none has demonstrated a direct interface between the cooling liquid transport loop and the phase-change material. Moreover, all the previous designs have incorporated conventional heat exchangers.

The United States of America as represented by the Administrator of the National Aeronautics and Space Administration


A structural insulated panel for use in a mine safe room, which includes a carbon foam core having a high ratio of compressive strength to density, desirable fire retardant properties, and resistance to environmental stress. The carbon foam structural insulated panel also includes a first layer and a second layer bound to a first surface and second surface of the carbon foam core.

1. Technical Field
The present invention relates to high strength structural panels useful for mine safe rooms, that is, chambers within mines where miners can retreat in an emergency, and where food, supplies, stores of oxygen, etc. are maintained. More particularly, the present invention relates to the use of carbon foam in structural insulated panels which are highly resistant to heat, moisture, and other environmental stresses while maintaining an extremely high compressive strength, thus providing a safe haven for trapped miners.
2. Background Art
Mine safety is becoming an increasingly important topic, especially as explosions and other emergency events have taken the lives of miners. One suggested safety measure for miners in the event of an emergency is the provision of so-called mine safe rooms. Mine safe rooms are structures within mines to which miners can retreat in the event an emergency or other situation prevents the miners from escaping to the surface. Mine safe rooms are sealed off from toxic gases which may collect after a fire or explosion, usually contain communications means, and are stocked with supplies, such as food, water and oxygen, to provide a safe haven for miners while they await rescue.
Current mine safe room technology has the walls of the safe room constructed of steel or other metal. While steel can provide blast protection, shielding miners from explosions, steel can do little to protect the miners from the heat generated by an explosion or resulting fire. Indeed, in the event of fire, mine safe rooms formed of steel can exacerbate the situation, because of the thermal conductivity of steel. Thus, the present invention relates to the formation of mine safe rooms using structural insulated panels which comprise carbon foam. While structural insulated panels (referred to in the industry as SIPs) are known, forming SIPs with a carbon foam core is not.
In Hardcastle et al. (U.S. Pat. No. 4,425,396) an insulating panel is disclosed with a synthetic organic polymeric foam with protective weathering layers comprised of multiple thermoplastic sheets.
Cahill (U.S. Pat. No. 6,656,858) describes a lightweight laminate wall comprised of a low density layer of from about 0.5 to 3 pounds per cubic foot and a second, reinforcing layer of a polymeric fabric. These structures are lightweight, have a low moisture resistance and meet building code requirements regarding transverse wind loading.
Porter (U.S. Pat. No. 6,599,621) describes a SIP with high strength and resistance to fire and particularly to water and changes in humidity. The disclosed structures are comprised of an inner insulating core with a gypsum fiberboard on one face of the insulating core and an oriented strand board on the second face of the insulating core. Preferably, the insulating core is comprised of a plastic foam such as expanded polystyrene or urethane which is bonded to both the gypsum fiberboard and the oriented strand board.
Porter (U.S. Pat. No. 6,588,172) describes the incorporation of a laminated layer of plastic impregnated paper into a SIP to increase the panel's tensile strength while rendering it impervious to moisture. This layer is typically situated between the gypsum board and plastic foam core, adhered through a conventional bonding agent.
Parker (U.S. Pat. No. 4,628,650) describes a SIP with a foam core with a layer having an overhang projecting from the foam core edges. The overhang is situated to facilitate an effective seal between adjacent SIPs, providing better thermal insulation. Additionally, the core of the panels has channels through the structure for the placement of joists, studs or rafters.
Clear (U.S. Pat. No. 6,079,175) describes a SIP of cementitious material for building structures. A lightweight fill material such as bottom ash, cement and water is poured between spaces of two outermost ribs, which is claimed to provide insulation, strength and also rigidity to the panel and therefore the structure the panel comprises. This SIP has the advantage of being constructed in remote or more barren areas as it is fairly inexpensive to create.
Pease (U.S. Pat. No. 6,725,616) prepares an insulated concrete wall either cast or built with blocks which is attached to reinforced insulated strips. The patentee indicates that users will require less time and labor in making insulated using the patentee's method of fixing reinforced rigid foam to the surface of a concrete wall.
Pease (U.S. Pat. No. 6,892,507) describes a method and apparatus for making an SIP with a rigid foam sheet. The rigid foam sheets have multiple grooves in which reinforcing strips are situated. The strips and rigid foam are then covered and bonded with a reinforcing sheet, the sheet providing both structural support and moisture retention.
Unfortunately, SIPs produced by the prior art are not effective for the formation of mine safe rooms, as lacking high strength including high compressive strength values. Furthermore, and more importantly, most conventional SIPs are not effective against high heat or open flames, either combusting or experiencing significant charring. In addition, the prior art SIPs generally lack a high strength to density ratio, making such SIPs ill suited for applications where a lightweight, insulating, yet strong panel is necessary for a safe room within a mine.
What is desired, therefore, is structural panel which is of a low density and has desirable thermal insulating properties, where the panel has a high strength and high strength to density ratio, and relatively non-combustible, and therefore useful for the construction of mine safe rooms. Indeed, a combination of characteristics, including strength to density ratios and compressive strength higher than contemplated in the prior art, as well as fire retardancy higher than contemplated in the prior art, have been found to be necessary for mine safe room structural applications.

This patent is subject to a terminal disclaimer.


An exit bar employs a dual action latch retractor comprising a slotted link which connects manual and electrically actuated latch retraction means. The slot permits the latch to be retracted by a solenoid latch retractor regardless of the position of the push bar or other manual latch retraction means. A buffer spring transmits energy from the solenoid latch retractor to the push pad so that under normal circumstances actuation of the solenoid latch retractor retracts both the latch and push pad. However, if the push pad is jammed in the projected position, the buffer spring is compressed to permit relative movement between the solenoid latch retractor and the manual latch retraction mechanism. As soon as the force holding the push pad in an extended position is removed, the energy stored in the buffer spring is applied to the push pad through the mechanical linkage to retract the push pad.

1. Field of the Invention
This invention relates to the field of door security systems. More specifically, this invention relates to the use of a push or exit bar for securing a doorway.
2. Description of the Related Art
Exit bars, also known as push bars or panic bars, that allow egress through a doorway while limiting ingress are well-known components of door security and emergency systems. The conventional exit bar is mounted on the interior side of the door to be secured and is oriented generally horizontally across the face of the door. A housing or frame supports a push pad or bar for receiving a push force. The push force applied to the movable push pad operates a door latch through a linkage to permit opening of the door. Conventional exit bars typically employ a mechanical linkage between the movable push pad and the latch to actuate the latch mechanism for unlatching the door.
To avoid excessive wear to the exit bar components during periods of high traffic through a doorway, it is known to fix or xe2x80x9cdogxe2x80x9d the exit bar in an unlocked condition. Typically, the push pad is locked in its depressed or actuated position to avoid unnecessary wear to the associated linkage. It is also known to equip an exit bar with an electromagnetic latch retractor as described in U.S. Pat. No. 6,104,594, assigned to the assignee of the present invention. By integrating a building security system with exit bars including electromagnetic latch retractors, it is possible to effectuate the latching and unlatching of exit bars remotely and/or automatically.
U.S. Pat. No. 6,104,594 describes the use of an electric circuit to generate a high energy pulse through the electromagnet to generate a retraction force sufficient to retract the push pad and with it the mechanical linkage and latch to unlock the door. A possible deficiency of this approach is that, if the push pad is held or jammed in an extended position, the latch cannot be retracted by the electromagnet (even at high power). An alternative arrangement is to apply the electromagnetic retraction force only to the latch, without also retracting the push pad as described in U.S. patent application Ser. No. 09/414,202, filed Oct. 7, 1999 and also assigned to the assignee of the present invention. This permits latch retraction regardless of the position of the push pad. However, in high traffic situations, the push pad and its associated linkages are free to move as people push to open the door and are exposed to the resulting high rates of wear.
There is a need in the art for an exit bar equipped with remotely actuateable means for retracting the latch as well as the push pad which will reliably retract the latch even if the push pad is jammed in an extended position.
An object of the present invention is to provide a new and improved dual action latch retractor for retracting the push pad and latch of an exit bar that will reliably retract the latch regardless of the position of the push pad.
Another object of the present invention is to provide a new and improved dual action latch retractor for remotely retracting the push pad and latch of an exit bar.
These and other objects are achieved in an exit bar in which a slotted link is used to connect a solenoid latch retractor to the push pad and the associated manual latch retraction mechanism. The slot permits the latch to be retracted by the solenoid latch retractor regardless of the position of the push bar. A buffer spring transmits energy from the solenoid latch retractor to the push pad so that under normal circumstances actuation of the solenoid latch retractor retracts both the latch and push pad. However, if the push pad is jammed in the projected position, the buffer spring is compressed to permit relative movement between the solenoid latch retractor and the manual latch retraction mechanism. Compression of the buffer spring permits the latch to be retracted while the push pad remains in the extended position. As soon as the force holding the push pad in an extended position is removed, the energy stored in the buffer spring is applied to the push pad through the mechanical linkage to retract the push pad.


Disclosed is a method and apparatus for attaching shaped charge units into a well perforating gun. The shaped charge unit has an ear shaped extension having a cavity for receiving a wire in the perforating assembly. A second extension is positioned on the perforating charge unit having a threaded hole for containing a screw which may be advanced into tight engagement with the wire in the cavity of the first extension. This arrangement allows perforating units to be quickly added or taken out of a perforating gun assembly by adjustment of the screws through the threaded assemblies of the perforating charges.

The invention disclosed herein is related to shaped charge perforators for use in oil wells, and is more particularly related to attachment means for attaching charges to the wires of a bi-wire type body for oil well perforators.
In the perforation of an oil well, it is desirable to assemble perforating units into guns having a plurality of units in a desired spacing and orientation. These perforating guns are assembled at one central point and taken to the site of an oil well in a standard configuration having a set orientation and density of charges per unit length. Many times after arriving at the site of an oil well, it is necessary to strip off some of the perforating units to change the density or orientation as may be dictated by the needs of the particular well or the preference of the owner or operator of the well.
In the prior art perforating guns are assembled with the unit strung together by sliding the perforating units onto either wires or strips with spacers between the units to achieve the desired spacing. Various means have been used to attach the perforating units to either strips or wires of the perforating gun. In this type design, if it is desirable to remove perforating units or change the density of the perforating units per unit length, it is necessary to strip off the charges and intermediate spacers one at a time and rethread the units and spacers in the desired configuration or density. In the hostile environment many times present at an oil well site, this is very difficult and time consuming.
Also known in the prior art, are perforating guns having bent wires for accepting perforating units at periodic bends in the wires. The bends are usually dimensioned such that they bend around the body of the perforating unit and are held in place by various attachment means. In such an assembly the charges may only be inserted where a bend is present in the wires and thus changing the density of the perforating units can only be accomplished by either placing or removing perforating units from the bent sections of the wire.
In the present invention a simple method and apparatus is disclosed for quickly attaching perforating units to a bi-wire carrier wherein each of the wires of the carrier is placed in ear shaped extensions of the perforating units, and a screw is tightened from another extension for trapping the wire in the ear shaped extension between an appropriate cavity in the case and the screw. This apparatus thus results in perforating units which may be quickly attached or removed from between two wires by simply loosening or tightening screws to engage the perforating units at the desired location on the wire carrier. To increase the density of the perforating units it is only necessary to loosen the screws and move the perforating units to a closer spacing and insert any additional perforating units which may be desired.
To remove units from a perforating carrier and decrease their density it is only necessary to remove the undesired units and loosen the screws of the other units and move the units to the desired spacing. The perforating units are then reattached at the desired location by simply tightening the screws.

Apparatus for perforating a well and its method of assembly


A method and apparatus employed in an X-ray apparatus for compensating for attenuation caused by a subject to perform an improved X-ray exposure. A table is created comprising entries accessible via power and attenuation values. Each of the entries includes a first value T representing a time for radiation in the system to reach a base ion count, and a second value C representing an offset ion count from the base ion count. A first set of entries in the table are referenced using a first power setting, and a first base ion count is determined based upon the first power setting, and a maximum radiation exposure is determined for the first power setting and a subject's mass. Then, an X-ray emitter is activated until a current ion count from a radiation sampling means has exceeded the base ion count or total radiation emitted has exceeded the maximum radiation allowed for the given mass of a subject. If the current radiation has exceeded the maximum radiation, then the X-ray emitter is deactivated and the process terminates. If the current ion count from the radiation sampling means has exceeded the base ion count, then it is determined whether the base ion count has been offset. If so, then the X-ray emitter is deactivated and the process terminates. If the base ion count has not been offset, then a matching entry is determined from the first set of entries which has the first value T less than or equal to the current exposure. Then, the second value C of the matching entry is added to the base ion count, and the process is repeated until the above conditions are matched.

1. Field of the Invention
The present invention relates to x-ray devices. Specifically, the present invention relates to an apparatus for providing automatic film exposure control to control the optical density in x-ray film radiographs to compensate for attenuation caused by a subject under examination.
2. Background of Related Art
It is a desired capability for modern x-ray systems to provide some sort of attenuation compensation. Such systems should have a capability to compensate for attenuation caused by different subjects to optimize the exposure for those particular subjects. For example, large-mass objects may require large amounts of x-ray radiation in order to perform an x-ray exposure which have sufficient optical density for the quality desired. Smaller massed objects, in contrast, may not require as much x-ray radiation in order to create the same optical density in the resulting image. Attenuation compensation is a desired capability in x-ray systems since overexposure or underexposure of an x-ray image essentially ruins the image for any useful diagnostic purpose. Additional exposures may thus have to be performed, exposing the subject to more radiation than would otherwise have been required.
Some prior art systems have utilized a technique for attenuation compensation which allows the operator to select, using a selector dial or a series of pushbuttons, a particular attenuation level. In other words, the exposure may be optimized for a large attenuator (e.g., a full-grown adult) or a small attenuator (e.g., a child). Operators of such prior an x-ray apparatus thus make subjective judgments on the attenuation based upon their estimation of the patient thickness. It is hoped that the operator accurately selects the proper attenuation to optimize the optical density of the exposure. These systems suffer from the disadvantage that the operator is forced to make a subjective judgment about the amount of attenuation caused by the subject. These devices also suffer from a cluttered control panel of the x-ray apparatus providing for a less user-friendly design. It is thus desired to control the variance and optical density of exposures within very specific parameters to optimize picture quality. Attenuation compensation is also increasingly a requirement in specifications for modern x-ray systems. Consistency of optical density is desired and may be optimized by the use of an exposure control system which regulates the amount of radiation reaching the film, as passed through an attenuator (e.g., a subject under examination). Such a system would provide many advantages over the prior an apparatus for attenuation control in an x-ray imaging system.


In a large vehicle, such as a bus, a fuel-fired coolant heating system. The heating system uses a heating unit to add heat energy to the coolant, which is then circulated to heat exchangers throughout the vehicle. Safety features in the system include an impact switch which immediately stops the flow of fuel to the heating unit in the event of an accident. Another feature which contributes to safe operation of the system is the presence of a deaeration tank in the coolant flow path. The tank allows for the removal of air so that air locks can be prevented and is fitted with a pressure relief valve should overheating occur. Finally, service and inspection of the system is facilitated by attaching components of the system to a slide panel, which can be pulled out of the side of the bus. By making the components of the system easily accessible, problems are generally avoided and safety is, therefore, improved. The heating unit for use with the present invention is one which is available from Espar Products, Inc., of Mississauga, Ontario, Canada, and is known as a D 12 W diesel-fired coolant heater having a capacity fo 41,000 BTU per hour. Safety features built into the Espar heater include a flame sensor and an overheat cutout switch. The impact switch, deaerator tank and slide panel of the present invention are added safety features which make diesel-fired heaters usable in critical applications such as school buses.

The present invention relates to coolant heating systems such as those which are used in large vehicles. In particular, the present invention relates to fuel burning coolant heaters of the type which are used on school buses.
Diesel-fired coolant heaters are designed to provide supplemental heat to the coolant used in water cooled engines and their related heating systems.
Auxiliary heaters are used to pre-heat coolant in cold weather situations, and are used to supplement and maintain heat energy in coolant systems of large vehicles. It is convenient to have diesel-fired coolant heaters which are capable of operating on the same diesel fuel as the engine of the vehicle. Such coolant heaters draw from the same main fuel tank as does the vehicle engine.
Since diesel fuel is highly flammable, safety is a major factor in the design of coolant heating systems. This is particularly true in the case of school buses, which are used to transport children. One of the ways in which the safety of a system can be enhanced is to make it easily accessible. By providing a system which can be easily serviced, problems which would otherwise result in accidents can be avoided.
Another possible hazard associated with diesel-fired coolant heaters is the possibility that the fuel supply line may be severed in an accident. If the fuel line is severed, and the fuel pump continues to operate, significant amounts of fuel can be spilled, resulting in a significant fire hazard.
Yet another problem associated with coolant heating systems is the presence of air in the coolant lines. The presence of air pockets may result in malfunctioning of the pumps which are used to cause coolant flow. If the pumps stall, overheating can result.
Therefore, it is an object of the present invention to provide a coolant heating system which reduces the possibility of accidents.
Another object of the present invention is to provide a coolant heating system which is easily serviced and inspected.
Still another object of the present invention is to provide a coolant heating system in which spillage of fuel is prevented in the event of an accident.
Yet another object of the present invention is to provide a coolant heating system in which air bubbles are removed from the coolant.
These and other objects and advantages of the invention are obtained with a coolant heating system in which an impact switch is used to stop the operation of a fuel pump upon a predetermined level of impact. The impact switch, which is more sensitive to lateral impact than vertical impact, is designed to stop the operation of the fuel pump when the switch is impacted.
The system includes a deaeration tank through which coolant is circulated. The deaeration tank allows air bubbles to rise to the top of the tank, while coolant is pumped from the bottom. The coolant heating system of the present invention is comprised of a heating unit which is mounted on a panel which slides in and out from a position from beneath a floor of a bus. The sliding panel allows for easy access to the components of the heating system, so that they can be easily serviced and inspected.
The objects and advantages of the invention will be better understood by reading the following specification in conjunction with the accompanying drawings.


Disclosed is a battery cover locking device of a small electronic apparatus using a battery such as a radio paging receiver and a remote control box, wherein a battery cover comprises a locker having a hinge engaged with a guide box groove of a main housing, and said battery cover is slid and rotated in said main housing by operating said locker so as to be opened and closed for opening and closing a battery inserting hole formed on a side of said main housing.

The present invention relates to a locking device for preventing an unintentional opening of a cover of a battery inserting hole in a small electronic apparatus using a battery, such as a radio paging receiver and a remote control box.
Since a battery cover of a small electronic apparatus such as a radio paging receiver may be opened unintentionally by a hand touching, such a small electronic apparatus is usually provided with a locking device that makes it possible to open the battery cover only by applying an intentional force.
Referring to FIGS. 1A and 1B, a conventional locking device is described in detail as follows.
A cover groove 41 is formed on a bottom side of a main case 40, and one side of the cover groove comprises a battery inserting hole 42. A support plate 44 is formed on a side of the battery inserting hole 42 and has a guide groove 45 in its center portion. A guide rib 46 is formed on a side wall of the battery inserting hole 42. A cover 50 is shorter than the cover groove 41 by a given length and has a groove 51 extended to a horizontal direction on both sides. An opening is formed on a side of the cover 50 receiving a locker 60 having a hinge 61 on its side, of which hinge 61 is assembled with the cover 50. The locker 60 has a projection on both sides of its bottom side and a projection to be engaged with a fore end 45A of the guide groove 45.
At the time of closing the cover 50, a fore end 60B of the locker 60 is laid on a projection 53 of the cover wall because a rear end 60A of the locker 60 is contacted with the support plate 44. By pushing the cover 50 to the battery inserting hole 42, the cover 50 covers the inserting hole 42. Because the guide rib 46 is engaged with the groove 51 of the cover 50 and a projection 55 of fore end of the cover is engaged with a groove 48 of the main housing 40, the cover is not derailed. By pressing the fore end 60B of the locker 60 to a direction of the arrow in FIG. 1B, the locker 60 is rotated so as to contact its projection rib 65 with a wall 45A of the support plate 44 and prevent the cover 50 from being pushed backward. And the fore end of the locker 60 is not moved over a projection 53 without applying an external force. Finally the cover is locked completely.
When the cover 50 is opened for replacing a battery, the locker 60 is rotated counterclockwise, about the hinge 61, and the projection ridge 65 is slid over the support plate 44 by pressing the rear end 60A of the locker 60 downward. By sliding the cover 50 backward, the guide rib 46 of the side wall is disengaged with the groove 51 and the projection 55 is disengaged with the groove 48 of the main housing 40. Thereafter, the cover 50 is removed freely.
In such a conventional device, there occurs a case that the cover is apt to be lost frequently because the cover is removed completely for replacing a battery. Also, because it is very difficult to assemble the locker 60 with the cover 50, it results in an inefficiency of assembling. In addition, a seesaw motion of the locker 60 at the hinge 61 results in damaging the projection 53 for stopping the locker.


Temperature sensors for integrated circuits that use back-gate bias for low power operation. A temperature sensor can comprise a voltage-gate-source generator having sensing transistors; an Ibias generator; a back-gate bias generator; and a temperature read-out circuit. In a calibration mode, the temperature sensor determines a back-gate bias voltage and a resistor trimming code to be used during functional operation.

Temperature sensors are an integral part to many integrated circuits ("ICs"). Such sensors have applications ranging from optimizing computation speed in microprocessors to compensating for temperature dependency in high precision complex circuits.
For high precision temperature sensors and reference generations, typically, bipolar junction transistor ("BJT") devices are used to implement such temperature sensors because of their superior characteristics over other types of transistors. However, BJT-based diodes have larger voltage-base-to-emitter ("VBE") requirements and need more supply voltage head room. Hence, BJT-based temperature sensors can't be operated directly at low power voltage supply levels (e.g., at around 1V or sub-1V). Furthermore, in deep-submicron process technologies, parasitic variations can be significant in BJT-based temperature sensors. BJT-based temperature sensors can also have large process spread and may need additional mask layers for better control.
Operationally for BJT-based temperature sensors, a substantially similar amount of current is pumped into two BJT devices of different sizes to develop voltage differences Vb1 and Vb2, respectively, across each of the BJT devices. As widely known, voltage drop across a BJT device for a given current can be proportional to temperature. The two voltage drops across the two different BJT devices can then be used to solve for an unknown temperature value.
For the foregoing reasons, there is a need for new methods and apparatuses for temperature sensors for ICs that can accurately sense a wide range of temperatures and can also be operated at low power.

Temperature sensing for integrated circuits


A filter arrangement an AC voltage superposed on a DC voltage present across first (KO) and second (HO) poles of a DC voltage source. The arrangement includes between these first (KO) and second (HO) poles, a series coupling of a capacitance (C1) and an impedance (R5), and an amplifier arrangement (N1,C2,R2,C3,R3, C4,R4,D1,D2) that has an inverting input terminal which is coupled to the first pole (KO) and an output terminal which is coupled a the junction node of the capacitance (C1) and the impedance (R5).

1. Field of the Invention
The present invention relates to a filter arrangement for suppressing an AC voltage superposed on a DC voltage provided across first and second poles of a voltage source.
2. Description of the Prior Art
Such a filter arrangement is already known in the art, e.g. from the published European patent application EP 0363602A1. Therein, the voltage source includes a primary DC voltage source connected to the first and second poles via a series regulator regulating the DC voltage across these poles. This series regulator includes the series connection of a regulating transistor and a resistance between the primary DC voltage source and the first pole, and the regulating transistor is controlled so as to provide a predetermined voltage across the first and second poles. The filter arrangement includes a first capacitance which acts as a capacitive sensor for picking up from the second pole the AC voltage or noise voltage superposed on the DC voltage. This picked up AC voltage is then amplified by an operational amplifier providing a compensating voltage which is applied to the junction point between the regulating transistor and the resistance via a second capacitance preventing a DC voltage at the latter junction point from reaching the output of the operational amplifier. Thus, an active filter arrangement is obtained whose efficiency is determined by the values of the components used, i.e. mainly by the gain of the operational amplifier and the value of the resistance. Indeed, these values must be so chosen that the above compensating voltage is exactly opposite in phase and equal in amplitude to the AC voltage initially present at the junction point. This means that the filter arrangement is sensitive to variations of the values of these components.
To be noted that the operation of the above filter arrangement may also be appreciated from the fact that it is based on the insight that the operational amplifier injects at the above junction point an AC current which is equal in amplitude and opposite in phase to the AC current corresponding to the AC voltage superposed on the DC voltage present across the first and second poles. It may then also be appreciated that the amplitude of the AC current to be suppressed should be smaller than the DC current corresponding to the DC voltage in order to be able to effectively suppress it. When the DC voltage is applied to a so-called travelling wave tube (TWT) operating with a current which is typically equal to 0.1 milliampere (mA) to 1 mA whereas the AC current to be suppressed may well be equal to 1 mA to 2 mA, this AC current may thus not be effectively suppressed. Accordingly, in order to be able to be effectively suppressed the amplitude of the AC voltage to be suppressed should be relatively small.
An object of the present invention is to provide a filter arrangement of the above known type but which is less sensitive to variations of the values of its constituent components, and which puts no constraints on the amplitude of the AC voltage to be suppressed.

Filter arrangement for suppressing an AC voltage superposed on a DC voltage present across poles of a DC voltage source


Coexistence and migration of legacy and VXLAN networks may be provided. A first anchor leaf switch and a second anchor leaf switch may detect that they can reach each other over a Virtual Extensible Local Area Network (VXLAN) overlay layer 2 network. In response to detecting that they can reach each other over the VXLAN, the second anchor leaf switch may block VLANs mapped to the VXLAN's VXLAN Network Identifier (VNI) on the second anchor leaf switch's ports connecting to spine routers. In addition, the first anchor leaf switch and the second anchor leaf switch may detect that they can reach each other over a physical layer 2 network. In response to detecting that they can reach each other over a physical layer 2 network, the second anchor leaf switch may block Virtual Extensible Local Area Network (VXLAN) segments at the second anchor leaf switch.

Virtual Extensible LAN (VXLAN) is a network virtualization technology that attempts to ameliorate the scalability problems associated with large cloud computing deployments. It uses a VLAN-like encapsulation technique to encapsulate MAC-based OSI layer 2 Ethernet frames within layer 4 UDP packets, using 4789 as the default IANA-assigned destination UDP port number. VXLAN is an evolution of efforts to standardize on an overlay encapsulation protocol. It increases scalability up to 16 million logical networks and allows for layer 2 adjacency across IP networks. Multicast or unicast with HER (Head-End Replication) is used to flood BUM (broadcast, unknown destination address, multicast) traffic.

Coexistence and migration of legacy ethernet and overlay networks


A cover for a computer monitor is provided which permits storage of office materials in side flaps attached to the cover and which provides a support platforms for holding documents being examined by the user the invention also provides a shield piece which can quickly be placed over the monitor screen to block viewing of the matter being displayed on the monitor.

The present invention relates to accessories for computers. In particular the present invention provides a cover for a computer cathode ray tube (CRT) or other display monitor which is adapted to provide storage flaps and pockets and to support documents and materials which are being examined by the user while working at the computer.
Typically, computer cathode ray tubes (CRTs or monitors) are relatively large objects to have on a desk top. A 14-inch monitor by screen size is approximately 14 inches wide by 15 inches deep and 16 inches high. A 17-inch monitor is 17 inches wide by 17 inches deep and 17 inches high. These two typically-sized monitors, therefore, consume a great deal of desk-top space and are not particularly mobile. As a result, monitors tend to remain in the location in which they are placed. Thus, when a monitor is in the middle of a desk top having conveniently available drawers, the desk top cannot be used for other purposes. This often results in the monitor being placed on a convenient side table or adjacent to other work area where convenient drawer space and storage space is not present. Thus, it would be of great utility to have available an amount of convenient storage space adjacent to a monitor which is not dependent upon the available table top area for location of the storage space.
A further drawback of the computer monitor or CRT, is that the work on the CRT is available for any passerby to view. While a user can remove the particular work from being displayed on the computer screen, they nevertheless, will have to look at whatever "computer desktop" or computer screen saver image that is installed on the computer. Therefore, a useful alternative to being limited to such screen-saver images or minimizing the program and use, would be a means of quickly covering the viewing screen of the CRT or computer monitor to present either an image of interest to the viewer, or to eliminate the viewing of a dark, blank screen when the computer is turned off.
Yet another drawback with the current computer CRT or monitor is a user must accept the design and coloration and esthetic effect of the computer monitor case that is sold by the manufacture. In view of the immense amount of cubic volume of any desk or work area which a computer monitor consumes, it represents a substantial component of the office or work space decor. Therefore, it would be advantageous for a user to be able to select or redesign the exterior appearance of the monitor to a design selected by the user.
These limitations and drawbacks of the current computer CRT or computer monitor are overcome and corrected by the present invention which permits a user to quickly cover the viewing screen of the CRT when interrupted during work or to simply cover the blank screen when the computer is turned off. In addition, the present invention permits the user to select an appropriate and interesting appearance for the computer CRT or monitor casing which is appropriate to the particular decor and yet pleasant for the user to experience. In addition, the present invention provides the user with convenient and accessible storage areas adjacent to the computer monitor, as well as a means for displaying current materials upon which the user is working so that they are at a convenient location during the input procedure by the user.
These advantages and additional features will be apparent and appreciated by those skilled in the art when the following description of the invention is read in conjunction with the drawings attached hereto which particularly describe a preferred embodiment of the invention.


Two embodiments of off the road motorcycles embodying low pressure balloon tires. In each embodiment, an improved final drive arrangement is provided that includes a ring gear that is disposed substantially inwardly of the outer periphery of the rear wheel to provide a relatively compact final drive housing to facilitate leaning of the motorcycle. In one embodiment, the ring gear is driven by a pinion gear that is directly affixed to one end of a drive shaft and which is driven at its other end from the engine by means of a chain drive. In the other embodiment, the ring gear is driven by a pair of transfer spur gears from a drive shaft that is articulated and which is driven directly from the engine output shaft.

This invention relates to an offset drive for a balloon tired motorcycle and more particularly to an improved compact drive arrangement for a driven wheel.
Recently, it has been proposed to equip motorcycles with large, low pressure balloon tires to adapt them for off the road use. Such balloon tires are normally inflated to a pressure in the range of 0.1 to 0.2 kg/cm.sup.2 and particularly adapt the vehicle to off the road use over a wide variety of terrains. Although such vehicles have this advantage, the use of the large, low pressure balloon tire on the driven wheel presents a number of problems in connection with transferring the drive to the rear wheel. Among these problems are the spatial requirements of the final drive for the rear wheel. With final drives of the types heretofore proposed, the final drive extends outwardly a substantial lateral distance beside the rear wheel and also has a relatively large diameter. This can substantially restrict the amount of leaning which the rider may utilize when handling the vehicle. This is an obvious disadvantage.
It is, therefore, a principal object of this invention to provide an improved compact drive for the wheel of a vehicle.
It is a further object of this invention to provide a final drive for a balloon tired wheel in which the final drive does not extend laterally a significant distance outwardly from the wheel and in which the diameter of the final drive is substantially reduced.

Offset drive for balloon tired motorcycle


According to one embodiment, a document detecting apparatus includes a light-emitting element, a photoelectric conversion element, a light-emission controller and a detection processor. The light-emitting element projects light onto a detection position of a document. The light-emitting element is not used for reading an image of the document. The photoelectric conversion element converts light projected onto the detection position into an electric signal and outputs the electric signal. The light-emission controller changes the light quantity of the light emitted by the light-emitting element during a predetermined interval. The detection processor detects the presence or absence of the document at the detection position of the document based on whether a value of the output electric signal during the predetermined interval changes in correspondence to the change of the light quantity caused by the light-emission controller.

For example, a scanner provided in a multi function peripherals includes a document detecting apparatus to detect the presence or absence of a document and the size of the document. The document detecting apparatus detect the presence or absence of the document based on a signal of a reflection-type or transmission-type sensor. For example, the reflection-type or transmission-type sensor projects light for detecting the presence or absence of a document onto a detection position, and detects the presence or absence of the document based on an output value obtained by converting the light received from the detection position. However, when the sensor receives stray light other than the light projected to detect the presence or absence of the document, erroneous detection on the presence or absence of the document can occur. A document detecting apparatus is desired which discriminates the stray light and can detect the presence or absence of a document at high accuracy.

Document detecting apparatus, image forming apparatus and document detecting method


A portable outdoor activity shelter including a flexible cover and a frame. The frame including a plurality of sidewall poles convertible between a first configuration and a second configuration, when in the first configuration, the frame and flexible cover together moveable between a collapsed position and a deployed position. When in the deployed position, the frame to support the flexible cover to form a roof, opposed first and second sidewalls, and opposed front and rear walls, wherein at least one sidewall pole is moveable from a first position to a second position to convert the frame from the first configuration to the second configuration to provide access to a door in a corresponding one of the opposed first and second opposed sidewalls.

Portable outdoor activity shelters, such as hunting and ice fishing shelters, have become increasingly popular. Such shelters generally include a base to which a frame and flexible outer covering is attached, where the frame and covering can be extended from a collapsed or stowed position to a deployed position to form an enclosure.

Portable outdoor activity shelter with convertible frame


An analog video signal supply circuit includes a processing circuit that supplies first and second digital video signals. First and second digital-to-analog converters convert digital signals to analog signals. A control circuit controls operation in a first configuration where the first digital video signal is applied to an input of the first digital-to-analog converter and the second digital video signal to an input of the second digital-to-analog converter. The control circuit further controls operation in a second configuration where the first digital video signal is simultaneously applied to the inputs of the first and second digital-to-analog converters.

A video decoder is conventionally placed upstream of a display device such as a television set, a video projector, a computer screen, etc. The decoder receives a compressed digital video flow, for example, from the Internet (ADSL, cable, etc.), from a digital optical disk (DVD, Blu-ray, etc.), from a hard disk, from a digital radio receiver, or from any storage or digital transmission support, and converts this flow into a video signal adapted to the downstream display device. To ensure a compatibility with various display devices, a video decoder generally has a plurality of output interfaces capable of supplying the decoded video flow in different formats. In recent installations, the link between the decoder and the display device most often is a digital link, for example, an HDMI link or a DVI link. However, to ensure the compatibility with older installations and/or with certain specific applications, video decoders are almost systematically equipped, in addition to one or a plurality of digital outputs, with one or a plurality of analog video outputs, for example, an output at the CVBS format (composite video) and/or an output at the YPbPr format. Circuits for supplying the decoded video signals in analog form are here more particularly considered.


An adjustable platen is provided. The adjustable platen includes a platen body having a top region and a bottom region. The platen body is oriented under a linear polishing pad of a CMP system. An air bearing is integrated with the platen body at the top region, and the air bearing is configured to apply an air pressure to an underside of the linear polishing pad. A set of bearings are connected to the bottom region of the platen body to enable controlled vertical movement of the top region of the platen body closer or further from the underside of the linear polishing pad depending on the applied air pressure. The applied air pressure is configured to exert a controllable force to the underside of the linear polishing pad. The force is controlled to meet a desired process parameters, while the carrier simply moves the wafer into position over the linear polishing pad.

1. Field of the Invention
This invention relates generally to chemical mechanical planarization (CMP) systems, and more particularly, to systems having force applying air platens.
2. Description of the Related Art
In the fabrication of semiconductor devices, there is a need to perform Chemical Mechanical Planarization (CMP) operations, including polishing, buffing and wafer cleaning. Typically, integrated circuit devices are in the form of multi-level structures. At the substrate level, transistor devices having diffusion regions are formed. In subsequent levels, interconnect metallization lines are patterned and electrically connected to the transistor devices to define the desired functional device. As is well known, patterned conductive layers are insulated from other conductive layers by dielectric materials, such as silicon dioxide. As more metallization levels and associated dielectric layers are formed, the need to planarize the dielectric material increases. Without planarization, fabrication of additional metallization layers becomes substantially more difficult due to the higher variations in the surface topography. In other applications, metallization line patterns are formed in the dielectric material, and then metal CMP operations are performed to remove excess metallization.
In the prior art, CMP systems typically implement belt, orbital, or brush stations in which belts, pads, or brushes are used to scrub, buff, and polish one or both sides of a wafer. Slurry is used to facilitate and enhance the CMP operation. Slurry is most usually introduced onto a moving preparation surface, e.g., belt, pad, brush, and the like, and distributed over the preparation surface as well as the surface of the semiconductor wafer being buffed, polished, or otherwise prepared by the CMP process. The distribution is generally accomplished by a combination of the movement of the preparation surface, the movement of the semiconductor wafer and the friction created between the semiconductor wafer and the preparation surface.
FIG. 1 illustrates an exemplary prior art CMP system 10. The CMP system 10 in FIG. 1 is a belt-type system, so designated because the preparation surface is an endless belt-type polishing pad 18 mounted on two drums 24 which drive the pad in a rotational motion as indicated by belt rotation directional arrows 26. A wafer 12 is mounted on a carrier 14. The carrier 14 is rotated in direction 16, which can be either clockwise or counterclockwise. The rotating wafer 12 is then applied against the polishing pad 18 with a force F to accomplish a CMP process. Some CMP processes require significant force F to be applied and monitored. A platen 22 is provided to stabilize the polishing pad 18 and to provide a support onto which to apply the wafer 12. The platen 22 is designed with an air bearing 23, which is designed to supply a constant flow of air during movement of the polishing pad 18. The constant flow of air therefore provides a consistent cushion over which the polishing pad 18 can traverse. To facilitate polishing, slurry 28 composed of an aqueous solution such as NH4OH or DI containing dispersed abrasive particles is introduced upstream of the wafer 12.
Typically, a load cell (LC) is integrated as part of the carrier 14 to enable monitoring of the pressure being applied to the wafer during processing. In practice, the carrier 14 is lowered onto the polishing pad 18 while the wafer is rotated in the direction 16. In addition to being lowered, the load cell (LC) is designed to provide pressure data to monitoring electronics. If more or less pressure is needed for a particular process, the spindle is instructed to make the pressure adjustment. Accordingly, not only is the spindle designed to move up and down, rotate at a particular rate, but also continuously adjust the force on the wafer (in the form of pressure) as transmitted by the carrier 14 to achieve the appropriate CMP parameters.
Because the carrier 14 is designed to place a force onto a moving polishing pad 18, frictional forces will build at the spindle so as to generate mechanical hysteresis. These frictional forces are known to reduce an actuator""s (which is designed to apply a force to the carrier 14) ability to maintain a constant force during small amplitude variations in carrier 14 vertical position during polishing. The challenge of maintaining a constant force during precision polishing operations therefore complicates the design of the carrier 14 and its accompanying electronics and controls. In some cases, even very expensive an complex controls are unable to ensure a uniform application of force since the carrier, which is measuring the forces, is continuously under frictional stress from the moving polishing pad 18.
In view of the foregoing, a need exists for a chemical mechanical planarization system that can provide a stable and accurate force to a substrate being planarized.
Broadly speaking, the present invention fills these needs by providing a chemical mechanical planarization system that has an adjustable platen. The adjustable platen is designed to apply a force to an underside of the polishing pad during operation, while the carrier is simply lowered into position over the polishing pad to achieve the appropriate planarization result. It should be appreciated that the present invention can be implemented in numerous ways, including as a process, an apparatus, a system, a device, or a method. Several inventive embodiments of the present invention are described below.
In one embodiment, a chemical mechanical planarization (CMP) system having a polishing pad, a wafer carrier, and an adjustable platen is disclosed. The adjustable platen includes a platen body and an air bearing that is integrated in the platen body for applying air pressure to an underside of the polishing pad. A set of bearings are connected to the platen body to enable movement of the platen body closer and further from the underside of the polishing pad. A load cell is connected to the platen body, and the load cell is configured to output a load signal that is indicative of a force being applied to the underside of the polishing pad. An air supply for applying air flow to the air bearing is also provided. The air flow is adjustable in response to changes in the force being applied to the underside of the polishing pad.
In another embodiment, an adjustable platen is disclosed. The adjustable platen includes a platen body having a top region and a bottom region. The platen body is oriented under a linear polishing pad. An air bearing is integrated with the platen body at the top region, and the air bearing is configured to apply an air pressure to an underside of the linear polishing pad. A set of bearings are connected to the bottom region of the platen body to enable controlled movement of the top region of the platen body closer or further from the underside of the linear polishing pad depending on the applied air pressure. The applied air pressure is configured to exert a controllable force to the underside of the linear polishing pad.
In yet another embodiment, another platen is disclosed. The platen includes a platen body having a top region and a bottom region. The platen body is positioned under a linear polishing pad of a chemical mechanical polishing (CMP) system, and the CMP system is designed to receive a wafer to be polished on a top surface of the linear polishing pad when positioned for processing by a spindle and carrier of the CMP system. An air bearing is coupled with the platen body at the top region, and the air bearing is configured to deliver an air flow to an underside of the linear polishing pad. A set of linear bearings are coupled to the bottom region of the platen body to enable controlled vertical movement of the platen body closer and further from the underside of the linear polishing pad. The vertical movement of the platen body is determined by the air flow, and the air flow is variable so as to set a desired force to the underside of the linear polishing pad.
In still another embodiment, a platen design is disclosed. The platen includes a platen body having a top region and a bottom region. The platen body is positioned under a linear polishing pad of a chemical mechanical polishing (CMP) system, and the CMP system is designed to receive a wafer to be polished on a top surface of the linear polishing pad when positioned for processing by a spindle and carrier of the CMP system. An air bearing is coupled with the platen body at the top region, and the air bearing is configured to deliver a fixed air flow to an underside of the linear polishing pad. A load cell for determining a force being applied to the underside of the linear polishing pad by the fixed air flow is integrated with the platen body. An actuator provided to vertically adjust the platen body closer and further from the underside of the linear polishing pad.
The advantages of the present invention are numerous. Most notably, by having the platen apply controlled forces from under the polishing pad, the spindle controlling the wafer carrier can be greatly simplified, and can eliminate the need for a splined spindle and complicated monitoring and compensating electronics. As is well known, the splines spindle is a mechanical device that allows for rotational motion about it""s long axis while allowing for translation about the same axis. Furthermore, the bearing(s) used to guide the platen are not affected by frictional forces, which eliminates the hystersis problems caused by side forces. Additionally, placing the load cell behind the platen as described in one of the possible system configurations would greatly reduce the complexity and cost of the load cell as well as dramatically increase reliability. Other aspects and advantages of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.

Adjustable force applying air platen and spindle system, and methods for using the same


This invention pertains to helicopter airborne load systems and composite aircraft configurations. The composite aircraft configurations are designed to allow a fixed wing aircraft to take off and land either vertically or in a short ground run when assisted by a rotary winged aircraft such as a helicopter, and includes a maneuverable probe system used to attach two aircraft to form a composite aircraft configuration, the fixed wing aircraft embodying the use of a receptacle or attachment device cooperative with the maneuverable probe to effect the uniting of the aircraft. The helicopter systems airborne includes the use of the probe to cooperate with special external pods capable of carrying loads, fuel and instrumented devices.

The concept of a rotary wing-fixed wing composite aircraft system and method of flight was recognized as early as 1958 by Bennett, as set forth in U.S. Pat. No. 2,843,337 which was issued July 15, 1958, and was assigned to Hiller Helicopters. The Bennett patent disclosed a rotary wing aircraft attached above the longitudinal center of gravity of a fixed wing aircraft with the attachment points being close to the main structure of the fixed wing aircraft and with attachment fittings on the rotary wing aircraft housed in leg fairings of a skid type under carriage. The attachment disclosed effected a rigid connection directly between strong points on the upper and lower aircrafts, with an arrangement in which the attachment point on the fixed wing aircraft could be retracted when released for independent flight. In a disclosure by E. F. Andrews, as set forth in U.S. Pat. No. 2,797,881 of July 2, 1957, another rotary wing-fixed wing composite aircraft system was described. In both of these disclosures the attachment means on the rotary wing aircraft was neither extendible nor maneuverable and was rigidly attached to the rotary wing aircraft structure. In addition the engine thrust of the fixed wing aircraft could not be directed or utilized to help lift or assist in the fixed wing aircraft take-off or landing.
Other kinds of composite aircraft such as fixed wing-fixed wing and dirigible-fixed wing systems have also been previously disclosed.
There preceded Bennett the concept of launching and retrieving a small fixed wing aircraft from the bomb bay of a large fixed wing aircraft, as disclosed by Barkey in U.S. Pat. No. 2,653,777, which was issued Sept. 29, 1953. This patent was directed to the mechanism for achieving that result.
Prior to the Bennett and Barkey disclosures, Richardson disclosed, in U.S. Pat. No. 1,869,506 which issued Aug. 2, 1932, an arrangement for catching a powered airplane while in flight from another aircraft, and more particularly disclosed apparatus to permit an operator from within a dirigible to catch and temporarily suspend an aircraft from the underside of the dirigible. The disclosure of the preferred method derived by Richardson was directed to manual control over the securing or mooring means, since the pilots of the respective components were not considered in position to visually superintend the catching operation.

Helicopter airborne load systems and composite aircraft configurations


A method for the continuous culturing of microbes in a plug-flow reactor which comprises the steps of:. A. supplying medium to microbes immobilized on a porous inorganic support at a rate sufficient to maintain such microbes substantially in a logarithmic growth state PA1 B. removing microbe-containing effluent from the immobilized microbes at a rate equal to the medium supply rate, wherein the microbes are selected from the group consisting of bacteria, yeasts, and fungus-like organisms; such reactor is operated continuously in a substantially plug-flow mode; the immobilized microbes are substantially covered by said medium; and such porous inorganic support has a controlled porosity such that at least 70% of the pores, on a pore size distribution basis, have a pore diameter,. and. a. in the case of bacteria, at least as large as the smallest major dimension of the microbes but less than about five times the largest major dimension of the microbes; PA2 b. in the case of yeasts, at least as large as the smallest dimension of the microbes but less than about four times the largest dimension of the microbes; and PA2 c. in the case of fungus-like organisms, at least as large as the smallest major dimension of the microbes but less than about sixteen times the largest major dimension of the microbes.

The continuous culturing of microbes (i.e., microorganisms) is, in principle, well known for the production of large quantities of microbes, both as a research tool and for the preparation or isolation of microbial products. Thus, such continuous culturing is useful for general research purposes, such as the isolation of such cellular components as enzymes, cell walls, cytochromes, and the like; as a source of microorganisms for industrial biochemical processes, such as the production of fermented beverages, antibiotics, alcohol, organic carboxylic acids, cheeses, and the like; for the production of single-cell protein as an animal feed supplement; and for the production of bacterial vaccines, to name but a few examples.
In the past, the continuous culturing of microbes most often has utilized either the chemostat or the turbidostat. See, e.g., J. R. Norris and D. W. Ribbons, Editors, "Methods in Microbiology", Vol. 2, Academic Press Inc. (London) Ltd., London, 1970, pp. 259-276 and 349-376.
In the chemostat, a culture of fixed volume is contained in a suitably-constructed vessel to which medium is pumped at a constant rate. Typically, constant culture volume is achieved by employing a vessel which has a constant level overflow device. The medium is compounded to contain an excess of all substances essential for maximum microbial growth, except for one which is present in a growth-limiting amount. As a consequence, the culture can grow only at a rate which is directly proportional to the medium flow rate.
The turbidostat is a continuous-culture apparatus in which a photoelectric monitor detects deviations from some pre-selected culture turbidity (i.e., constant microbial population density) and passes a signal calling for a compensatory increase or decrease in dilution rate to a pump or valve controlling the flow of growth medium. Apart from the photoelectric control system and some simple optical requirements with respect to the culture vessel, all of the components of a turbidostat have functions similar to those of a chemostat.
In practice, both the chemostat and the turbidostat are designed to utilize microbial specific growth rates of less than about one-half the maximum specific growth rate. Furthermore, both devices are subject to wash-out which occurs when the rate of dilution (i.e., medium flow rate) is increased beyond the culture growth rate. Because there is a significant lag in the adjustment of growth rate to dilution, such lag and the problems associated with wash-out must be taken into account in continuous culture systems. See, e.g., R. I. Mateless et al., Nature, 208, 263 (1965).

Method for continuous culturing of microbes


The invention provides materials and methods for modeling human blood vessels. Including panels of anatomically accurate vascular phantoms, such as carotid artery phantoms, comprising a range of stenotic conditions and other geometric variations; methods of making anatomically accurate vascular phantoms using stereolithography with an input data set representation of a natural vascular lumenal surface to construct an anatomically accurate vascular phantom comprising a physical representation of the surface; and methods of using the subject phantoms and panels of phantoms, such as methods of measuring a parameter of fluid flow through a panel of anatomically accurate vascular phantoms comprising a range of stenotic conditions.

Flow studies with models of vascular geometries are useful for analyzing hemodynamics in complex geometries and for development and validations of imaging methodologies. One of the more widely used imaging techniques is angiography, an invasive technique requiring that a catheter be manipulated into the carotid artery and a radio-opaque dye injected. Angiography actually causes stroke in a small group of patients. Non-invasive techniques, such as ultrasound and magnetic resonance angiography (MRA) may also be used to determine the degree of vascular stenosis. However, the results obtained with these modalities may vary widely between laboratories because of differences in both hardware and technical expertise. The result is that vascular laboratories find themselves increasingly in a situation where they have no independent validation method. Several alternative models have been proposed for the calibration of ultrasound equipment, such as restricted surgical tubing (Anthropomorphic Vascular Phantoms, Shelley Medical Imaging Technologies, Ontario, Canada), moving strings (Doppler QA Phantom System, Nuclear Associates, Carle Place, N.Y.) or vibrating plates (Doppler Sensitivity Phantom, Nuclear Associates); however, these modalities do not test the ability of the equipment to measure velocities in flow regimes comparable to those found in vivo. Accordingly, the present invention provides a series of anatomically accurate, clinically relevant stenosis phantoms, which can be transported between centers, allowing assessment of the accuracy of a given laboratory and providing a dramatic effect on the reproducibility of vascular imaging techniques.
Relevant Literature
Imbesi et al. (1998) Am J Neuroradiol 19, 761-766 describe a lost-wax procedure for making a replica of an ulcerated atherosclerotic human carotid bulb.

The Regents of the University of California


Methods for preparing a green sheet and a glass ceramic substrate are herein disclosed.. The object of these methods is to make green sheets and glass ceramic substrates practically acceptable, the green sheets and the glass ceramic substrates having a low dielectric constant and low scattering in properties, and the method comprises the steps of preparing a mixture of hollow silica microspheres, borosilicate glass powder and ceramic powder as a principal ingredient, adding a plasticizer, a binder and a solvent to the mixture, kneading the mixture and forming it into a green sheet, wherein the shell-thickness of the hollow silica microspheres is controlled so that the specific gravity of the hollow silica microspheres is approximately equal to that of the solvent and wherein an inorganic substance containing aluminum as a constituent element such as alumina, mullite or aluminum nitride is used as the ceramic powder for forming the green sheet; or the method further comprises the step of calcining the resulting green sheet.

1. Field of the Invention
The present invention relates to a method for preparing a green sheet and a method for preparing, from the green sheet obtained according to the foregoing method, a glass ceramic substrate which has a low dielectric constant and which only shows a slight scatter (i.e. variation) in properties from substrate to substrate.
2. Description of the Related Art
Frequencies of signals used are becoming increasingly higher for the purpose of more quickly processing large quantity of information and furthermore, optical signal communication has been adopted as a means for transmitting such high frequency information signals.
In this respect, a multilayered circuit board on which an electronic circuit for processing such high speed or high frequency, is to be formed, must fulfill the requirements such that the delay time .tau. of an electric signal should be as small as possible and that the cross talk between wirings should be very low. In order to obtain substrates which these requirements, the dielectric constant .epsilon. of materials for the substrate must be reduced, as will be seen from the following relation (1): EQU .tau.=.epsilon..sup.1/2 /c (1)
Wherein .epsilon. is the dielectric constant of the material or substrate and c represents the velocity of light.
To substantially reduce the transmission loss, conductive lines, to be formed in a pattern on the substrate, must be formed from a metal having low specific resistance.
Incidentally, it is a matter of course that variations in the electric properties, such as dielectric constant and insulation resistance as well as mechanical properties such as surface roughness and the shrinkage factor, should be very low, from substrate to substrate.
The inventors of this invention have already proposed, as a means for solving these problems, that glass ceramics be used as materials for substrates and that electronic circuits should be formed from copper (Cu).
More specifically, the green sheets mainly comprising alumina (Al.sub.2 O.sub.3 ; .epsilon.=10) should be calcined at a temperature of not less than 1300.degree. C., while the burning temperature for glass ceramic green sheets mainly comprising a mixture of alumina powder and borosilicate glass powder can be reduced down to not more than 1000.degree. C. (see Japanese Unexamined Patent Publication No. 57-995). This permits the formation of a wiring pattern with Cu (having a melting point of 1084.degree. C.).
However, the dielectric constant of such a glass ceramic substrate ranges from 4 to 6 and correspondingly, the reduction of the delay time of signals is not yet sufficient.
Under such circumstances, the inventors of this invention have also proposed the use of hollow silica microspheres to reduce the dielectric constant of substrates (Japanese Patent Application No. 2-252500).
In other words, among the inorganic dielectrics, silica (SiO.sub.2) has the lowest dielectric constant .epsilon. of the order of 3.8. Further, silica powder can be made hollow to thus form a composite dielectric with air. As a result, the dielectric constant can further be reduced as seen from the following relation (2): EQU .epsilon..sub.0 =(.epsilon..sub.1 .multidot..epsilon..sub.2)/(.epsilon..sub.1 v.sub.2 +.epsilon..sub.2 v.sub.1) (2)
Wherein .epsilon..sub.0 is the dielectric constant of the composite dielectric; v.sub.1 is the ratio of the volume occupied by the dielectric having a dielectric constant of .epsilon..sub.1 to the whole volume of the composite dielectric; and v.sub.2 is the ratio of the volume occupied by the dielectric (air) having a dielectric constant of .epsilon..sub.2 to the whole volume of the composite dielectric.
The hollow silica microspheres can be prepared by making use of the phenomenon that in the heat-decomposition of organic silicon-containing compounds such as methoxy silicate [Si(OCH.sub.3).sub.4 ] or ethoxy silicate [Si(OC.sub.2 H.sub.5).sub.4 ], the constituent thereof is separated and forms bubbles. Among the hollow silica microspheres thus prepared, those having a particle size of not less than 100 .mu.m have presently been used as fillers for concrete or additives for light weight molded bodies of resins.
The inventors have also proposed a glass ceramic substrate whose dielectric constant is reduced by the use of hollow silica microspheres having a particle size of not more than 20 .mu.m and preferably 1-10 .mu.m in place of a ceramic which constitutes a glass ceramic substrate (Japanese Unexamined Patent Publication No. 59-111345).
However, in practical applications of such a substrate, the following problems arise:
It was found that when a green sheet was formed in the conventional manner, calcined to give a substrate and the dielectric constant thereof was determined, the dielectric constant varied from substrate to substrate although green sheets prepared from the same slurry were used. Moreover, it was also found that when the green sheets were prepared by the doctor blade method, the dielectric constant of the substrate obtained from the front portion of the slurry was greater than that of the substrate obtained from the middle and end portions of the slurry (see, FIG. 1, FIG. 3 and FIG. 4).
Furthermore, it was likewise found that the green sheet caused crystallization during the burning process, the surface of the resulting substrate was extremely uneven, the thermal expansion coefficient thereof was abnormally increased and thus the resulting substrate was unfavorable for fitting it with an Si semiconductor chip.
Moreover, the inventors have also proposed, as a means for forming a glass ceramic substrate having a low dielectric constant, a method for preparing a glass ceramic substrate which comprises the steps of providing hollow silica microspheres, forming a green sheet from a mixed powder mainly comprising the hollow silica microspheres and borosilicate glass powder and then calcining the green sheet (Japanese Patent Application No. 2-252500).
However, this method suffers from a variety of problems which remains to be solved. For instance, the dielectric constant of the substrates thus prepared greatly varies from substrate to substrate (see FIG. 4) and the silica causes crystallization during the burning process of a green sheet containing the same.
In the preparation of multilayered ceramic substrates, a sheet called "green sheet" comprising a ceramic and a resin is first prepared. However, the hollow silica microspheres, added to a solvent used for the preparation, float on the surface of the resulting slurry (FIG. 1) and finally causes separation, because the specific gravity thereof is smaller than that of the solvent and this correspondingly leads to the formation of non-uniform green sheets (FIG. 3). Moreover, the preparation of a multilayered substrate by the green sheet method suffers from another problem in that a part of the hollow silica microspheres are destroyed because of the pressure of a press applied during lamination. Further, when hollow silica microspheres are incorporated into a resin for the purpose of reducing the weight or dielectric constant thereof, they preferentially distribute in the upper portion of the resin matrix before the solidification thereof because of the difference in the specific gravity between the hollow silica microspheres and the resin and hence it is likewise difficult to uniformly distribute the hollow silica microspheres in this case. For this reason, the shrinkage factor of the portion rich in the hollow silica microspheres after heating is high, while that of the portion deficient in the hollow silica microspheres is low. This becomes a cause of deformation, warps or peeling in case of films, upon heating.


A speed-change control system for an automatic transmission includes a vehicle speed sensor, an engine load sensor, speed change program memory circuits, a comparator for comparing signals from the sensors with signals from the memory circuit, and a speed change control circuit for producing a signal for changing the transmission into a determined speed position in response to an output from the comparator.. According to the invention the control system comprises a differentiation unit for differentiating the signal from the vehicle speed sensor to produce a signal corresponding to an actual acceleration, a programmed acceleration memory circuit for storing programmed accelerations obtained corresponding to the signals from the engine load sensor at every speed positions to produce signals corresponding to the programmed accelerations, and means for changing the speed change programs in response to differences between the signals corresponding to the actual acceleration and to the programmed acceleration, thereby automatically selecting a speed change program suitable for a grade of a road and a loaded condition without a troublesome hand operation of a switch for selecting a speed change program by a driver.

1. Field of the Invention
The present invention relates to a speed-change control system for an automatic transmission including a vehicle speed sensor for electrically detecting vehicle speeds, an engine load sensor for detecting engine loads and an electronic circuit to which are supplied outputs from the sensors and comparing these outputs with predetermined relations between these outputs to produce signals for instructing speed changes.
2. Description of the Prior Art
An automatic transmission of this kind as shown in FIG. 1 has been suggested, wherein a vehicle speed sensor 1 detects revolutions of an output shaft of the transmission to produce actual vehicle speed signals which are proportional to actual vehicle travelling speeds.
An engine load sensor 2 detects loads of an engine to generate signals corresponding to the loads. In effect, the sensor 2 may be a conventional throttle opening sensor for generating signals proportional to opened degrees of a throttle of the engine or a conventional negative pressure sensor for generating signals proportional to negative pressures in an intake duct of the engine, which may be selected as the case may be. In the following explanation with respect to the prior art and embodiments of the invention, the throttle opening sensor is used as the engine load sensor.
Speed change program memory circuits 3 and 4 are supplied with the engine load signals from the engine load sensor 2 and produce reference change speed signals representing vehicle speeds which are suitable for the engine loads by means of a predetermined engine load-speed change reference program. The speed change program memory circuits 3 and 4 store the engine load-speed change reference programs as shown in FIG. 2, respectively.
With the program shown in FIG. 2 illustrating an example of an automatic transmission having three speed positions, the graph includes 2 to 1 down-shift program 21, 1 to 2 up-shift program 22, 3 to 2 down-shift program 23 and 2 to 3 up-shift program 24.
As shown in FIG. 2, for example as to 2 to 1 down-shift program 21 and 1 to 2 up-shift program 22, reference change speeds V.sub.D and V.sub.U are determined for the same throttle opening .theta..sub.1, respectively. The reference up-shift change speed V.sub.U is set on the side higher than the reference down-shift change speed V.sub.D. The difference between the reference speeds V.sub.U and V.sub.D serves as a hysteresis to obtain a stable speed change. The same holds true in case of the 3 to 2 down-shift program 23 and the 2 to 3 up-shift program 24.
The speed change memory circuits 3 and 4 are supplied with program select signals later described to select associated programs in first, second and third speed ranges as shown in FIGS. 3a-3c among the stored speed change programs. FIGS. 3a-3c illustrate the selected programs when the transmission is in first, second and third speed positions, respectively. When the transmission is in the second speed position in FIG. 3b, the 2 to 1 down-shift program 21 and the 2 to 3 up-shift program 24 are alternately selected by a control of time division by means of clock pulses from a pulse generator 10. (These operations will be explained later).
The speed change program memory circuits 3 and 4 store respective different programs. The memory circuit 3 stores a speed change program which produces lower reference change speed signals for the same throttle opening suitable for travelling on a flat road and the memory circuit 4 stored a speed change program which produces higher reference change speed signals for the same throttle opening suitable for an uphill road.
A multiplexer 5 selects any one of reference change speed signals received from the speed change program memory circuits 3 and 4 by means of an inclined angle sensor 6 or a program change-over switch 7 later described, which selected reference change speed signal is then supplied to a comparator 8.
The inclined angle sensor 6 produces signals proportional to inclined angles of roads in a travelling direction of the vehicle. If the signal exceeds a determined value, the reference change speed signal from the speed change program memory circuit 4 is supplied through the multiplexer 5 to the comparator 8. The program change-over switch 7 is manually operated by a driver to generate a signal which is applied to the multiplexer 5 for selecting the speed change program memory circuit 3 or 4.
The comparator 8 compares the signal proportional to an actual vehicle speed from the vehicle speed sensor 1 and the reference change speed signal received through the multiplexer 5 to produce a high level signal H when the actual vehicle speed signal is greater than the reference change speed signal and to produce a low level signal L when the actual vehicle speed signal is smaller.
A speed change control circuit 9 receives the output signals H and L of the comparator 8 to control an energization and deenergization of a plurality of solenoid valves for controlling operations of a clutch and a brake which serve to change over connected relations of a sun gear, a carrier and a ring gear of a planetary gear unit to determined speed positions of the transmission. Furthermore, the speed change control circuit 9 supplies the program select signals to the speed change program memory circuits 3 and 4 to select the relevant speed change program as above described referring to FIGS. 3a-3c.
When the transmission is in the second speed position, the speed change control circuit 9 alternately produces program select signals for selecting the 2 to 1 down-shift speed change program 21 and the 2 to 3 up-shift speed change program 24. The transmission is kept in the second speed position, if the output of the comparator 8 is the H signal when the program select signal for selecting the speed change program 21 is produced and if the output of the comparator 8 is the L signal when the program select signal for selecting the speed change program 24 is produced. If the output of the comparator 8 does not correspond to the above program select signals, the speed change control circuit 9 operates to change the solenoid to be energized for changing the transmission into the first or third speed position, with the result that the speed change control circuit 9 produces the program select signal for selecting the speed change program 22 or 23 as shown in FIGS. 3a or 3c.
With this arrangement of the prior art, the speed change program corresponding to a speed position is selected by the program select signal and the signal from the throttle opening sensor 2 corresponding to an engine load determines a reference change speed with which an actual vehicle speed sensed in the vehicle speed sensor 1 is compared to select the up-shift or down-shift for a suitable speed change.
With this arrangement, however, a driver must select the program memory circuit 3 or 4 in consideration to a grade of a road by a manual operation of the program change-over switch 7 which is troublesome. On the other hand, the inclined angle sensor 6 does not detect the change in weight of load on the vehicle. If the speed change program memory circuit 4 is set to store a speed change program the most suitable for a heavy load on an uphill road, the speed change program memory circuit 4 is selected even when the vehicle is under a slightly loaded condition, so that the up-shift of the transmission is not readily effected.

Speed-change control system for an automatic transmission