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At least 163 records · Page 9

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NASA NTRS1992

Conceptual design of a fleet of autonomous regolith throwing devices for radiation shielding of lunar habitats

This report presents refinements in two areas of the initial design presented in the report entitled 'Conceptual Design of a Fleet of Autonomous Regolith Throwing Devices for Radiation Shielding of Lunar Habitats'. The first section presents an evaluation of the critical areas of the design and presents alternative solutions for these areas. The areas for design refinement are the traction required by the device and the stability of the device when throwing regolith. Several alternative methods are presented to solve these problems. First, the issue of required traction is covered. Next, the design is refined to provide a more stable device. The issue of stability is addressed both by presenting solutions for the configuration chosen for the computer simulation and by presenting two more device configurations. The next section presents the selected solutions. To prevent inadequate traction, the depth of dig-per-pass is reduced. A method combining a dynamic counterweight and an outrigger is chosen to provide a stable device.

Armstrong, Karem↗

NASA NTRS1995

Non-parabolic hydrodynamic formulations for the simulation of inhomogeneous semiconductor devices

Hydrodynamic models are becoming prevalent design tools for small scale devices and other devices in which high energy effects can dominate transport. Most current hydrodynamic models use a parabolic band approximation to obtain fairly simple conservation equations. Interest in accounting for band structure effects in hydrodynamic device simulation has begun to grow since parabolic models can not fully describe the transport in state of the art devices due to the distribution populating non-parabolic states within the band. This paper presents two different non-parabolic formulations of the hydrodynamic model suitable for the simulation of inhomogeneous semiconductor devices. The first formulation uses the Kane dispersion relationship (hk)(exp 2)/2m = W(1 + alpha(W)). The second formulation makes use of a power law ((hk)(exp 2)/2m = xW(sup y)) for the dispersion relation. Hydrodynamic models which use the first formulation rely on the binomial expansion to obtain moment equations with closed form coefficients. This limits the energy range over which the model is valid. The power law formulation readily produces closed form coefficients similar to those obtained using the parabolic band approximation. However, the fitting parameters (x,y) are only valid over a limited energy range. The physical significance of the band non-parabolicity is discussed as well as the advantages/disadvantages and approximations of the two non-parabolic models. A companion paper describes device simulations based on the three dispersion relationships: parabolic, Kane dispersion, and power low dispersion.

Smith, Arlynn W.↗

NASA NTRS1999

Modeling of SiC Lateral Resonant Devices Over a Broad Temperature Range

Finite-element analysis (FEA) modal results of 3C-SiC lateral resonant devices anchored to a Si substrate are presented as resonant frequency versus temperature. The suspended elements are etched from a 2 micron, 3C-SiC film grown at 1600 K on a 500 micron-thick, Si substrate. The analysis includes, temperature-dependent properties, shape change due to volume expansion with temperature, and thermal stress caused by differential thermal expansion of different materials. Two designs are considered: type I has anchor locations close to the geometric centroid and a small shuttle; type 11 has a large shuttle with anchors far from the centroid, The resonant frequency decreases approximately 3.5% over a 1000 K temperature increase for the type-I device, and behaves according to theory. The resonant frequency of the type-11 device decreases by 2% over the first 400 K, then rises slightly over the remaining 600 K. This device deviates from theory because of the high thermal stress induced in the beams. The thermal stress is caused by the differential thermal expansion of the suspended element relative to the substrate. The results show that the device geometry must be properly chosen if the resonant frequency of that device will be used to calculate the temperature coefficient of Young's modulus. These results apply only to resonators of one material on a substrate of a different material.

DeAnna, Russell G.↗

NASA NTRS1996

Non-Parabolic Hydrodynamic Formulations for the Simulation of Inhomogeneous Semiconductor Devices

Hydrodynamic models are becoming prevalent design tools for small scale devices and other devices in which high energy effects can dominate transport. Most current hydrodynamic models use a parabolic band approximation to obtain fairly simple conservation equations. Interest in accounting for band structure effects in hydrodynamic device simulation has begun to grow since parabolic models cannot fully describe the transport in state of the art devices due to the distribution populating non-parabolic states within the band. This paper presents two different non-parabolic formulations or the hydrodynamic model suitable for the simulation of inhomogeneous semiconductor devices. The first formulation uses the Kane dispersion relationship ((hk)(exp 2)/2m = W(1 + alphaW). The second formulation makes use of a power law ((hk)(exp 2)/2m = xW(exp y)) for the dispersion relation. Hydrodynamic models which use the first formulation rely on the binomial expansion to obtain moment equations with closed form coefficients. This limits the energy range over which the model is valid. The power law formulation readily produces closed form coefficients similar to those obtained using the parabolic band approximation. However, the fitting parameters (x,y) are only valid over a limited energy range. The physical significance of the band non-parabolicity is discussed as well as the advantages/disadvantages and approximations of the two non-parabolic models. A companion paper describes device simulations based on the three dispersion relationships; parabolic, Kane dispersion and power law dispersion.

Smith, A. W.↗

NASA NTRS2001

Computational Hemodynamics Involving Artificial Devices

This paper reports the progress being made towards developing complete blood flow simulation capability in human, especially, in the presence of artificial devices such as valves and ventricular assist devices. Devices modeling poses unique challenges different from computing the blood flow in natural hearts and arteries. There are many elements needed such as flow solvers, geometry modeling including flexible walls, moving boundary procedures and physiological characterization of blood. As a first step, computational technology developed for aerospace applications was extended in the recent past to the analysis and development of mechanical devices. The blood flow in these devices is practically incompressible and Newtonian, and thus various incompressible Navier-Stokes solution procedures can be selected depending on the choice of formulations, variables and numerical schemes. Two primitive variable formulations used are discussed as well as the overset grid approach to handle complex moving geometry. This procedure has been applied to several artificial devices. Among these, recent progress made in developing DeBakey axial flow blood pump will be presented from computational point of view. Computational and clinical issues will be discussed in detail as well as additional work needed.

Kwak, Dochan↗

NASA NTRS2001

Assembly For Moving a Robotic Device Along Selected Axes

An assembly for moving a robotic device along selected axes includes a programmable logic controller (PLC) for controlling movement of the device along selected axes to effect movement of the device to a selected disposition. The PLC includes a plurality of single axis motion control modules, and a central processing unit (CPU) in communication with the motion control modules. A human-machine interface is provided for operator selection of configurations of device movements and is in communication with the CPU. A motor drive is in communication with each of the motion control modules and is operable to effect movement of the device along the selected axes to obtain movement of the device to the selected disposition.

Brentley Craig Nowlin↗

NASA NTRS2003

Portable Wireless LAN Device and Two-way Radio Threat Assessment for Aircraft Navigation Radios

Measurement processes, data and analysis are provided to address the concern for Wireless Local Area Network devices and two-way radios to cause electromagnetic interference to aircraft navigation radio systems. A radiated emission measurement process is developed and spurious radiated emissions from various devices are characterized using reverberation chambers. Spurious radiated emissions in aircraft radio frequency bands from several wireless network devices are compared with baseline emissions from standard computer laptops and personal digital assistants. In addition, spurious radiated emission data in aircraft radio frequency bands from seven pairs of two-way radios are provided, A description of the measurement process, device modes of operation and the measurement results are reported. Aircraft interference path loss measurements were conducted on four Boeing 747 and Boeing 737 aircraft for several aircraft radio systems. The measurement approach is described and the path loss results are compared with existing data from reference documents, standards, and NASA partnerships. In-band on-channel interference thresholds are compiled from an existing reference document. Using these data, a risk assessment is provided for interference from wireless network devices and two-way radios to aircraft systems, including Localizer, Glideslope, Very High Frequency Omnidirectional Range, Microwave Landing System and Global Positioning System. The report compares the interference risks associated with emissions from wireless network devices and two-way radios against standard laptops and personal digital assistants. Existing receiver interference threshold references are identified as to require more data for better interference risk assessments.

Nguyen, Truong X.↗

NASA NTRS2003

Silicon Carbide Diodes Performance Characterization and Comparison With Silicon Devices

Commercially available silicon carbide (SiC) Schottky diodes from different manufacturers were electrically tested and characterized at room temperature. Performed electrical tests include steady state forward and reverse I-V curves, as well as switching transient tests performed with the diodes operating in a hard switch dc-to-dc buck converter. The same tests were performed in current state of the art silicon (Si) and gallium arsenide (GaAs) Schottky and pn junction devices for evaluation and comparison purposes. The SiC devices tested have a voltage rating of 200, 300, and 600 V. The comparison parameters are forward voltage drop at rated current, reverse current at rated voltage and peak reverse recovery currents in the dc to dc converter. Test results show that steady state characteristics of the tested SiC devices are not superior to the best available Si Schottky and ultra fast pn junction devices. Transient tests reveal that the tested SiC Schottky devices exhibit superior transient behavior. This is more evident at the 300 and 600 V rating where SiC Schottky devices showed drastically lower reverse recovery currents than Si ultra fast pn diodes of similar rating.

Lebron-Velilla, Ramon C.↗

NASA NTRS1954

An Investigation in the Ames 40- by 80-Foot Wind Tunnel of a YT-56A Turboprop Engine Incorporating a Decoupler and a Controlled-Feathering Device

An investigation of a decoupler and a controlled-feathering device incorporated with the YT-56A turboprop engine has been made to determine the effectiveness of these devices in reducing the high negative thrust (drag) which accompanies power failure of this type of engine. Power failures were simulated by fuel cut-off, both without either device free to operate, and with each device free to operate singly. The investigation was made through an airspeed range from 50 to 230 mph. It was found that with neither device free to operate, the drag levels realized after power failures at airspeeds above 170 mph would impose vertical tail loads higher than those allowable for the YC-130, the airplane for which the test power package was designed. These levels were reached in approximately one second. The maximum drag realized after power failure was not appreciably altered by the use of the decoupler although the decoupler did put a limit on the duration of the peak drag. The controlled-feathering device maintained a level of essentially zero drag after power failure. The use of the decoupler in the YT-56A engine complicates windmilling air-starting procedures and makes it necessary to place operating restrictions on the engine to assure safe flight at low-power conditions,

Rogallo, Vernon L.↗

NASA NTRS1946

Preliminary Tests of a Buffet Stall-Warning Device on a 1/5-Scale Model of the Republic XP-84 Airplane

During the first flight tests of the Republic XP-84 airplane it was discovered that there was a complete lack of stall warning. A short series of development tests of a suitable stall-warning device for the airplane was therefore made on a 1/5-scale model in the Langley 300 MPH 7- by 10-foot tunnel. Two similar stall-warning devices, each designed to produce early root stall which would provide a buffet warning, were tested. It appeared that either device would give a satisfactory buffet warning in the flap-up configuration, at the cost of an increase of 8 or 10 miles per hour in minimum speed. Although neither device seemed to give a true buffet warning in the flaps-down configuration, it appeared that either device would improve the flaps-down stalling characteristics by lessening the severity of the stall and by maintaining better control at the stall. The flaps-down minimum-speed increase caused by the devices was only 1 or 2 miles per hour.

Tucker, Warren A.↗

NASA NTRS2007

Determining Desirable Cursor Control Device Characteristics for NASA Exploration Missions

A test battery was developed for cursor control device evaluation: four tasks were taken from ISO 9241-9, and three from previous studies conducted at NASA. The tasks focused on basic movements such as pointing, clicking, and dragging. Four cursor control devices were evaluated with and without Extravehicular Activity (EVA) gloves to identify desirable cursor control device characteristics for NASA missions: 1) the Kensington Expert Mouse, 2) the Hulapoint mouse, 3) the Logitech Marble Mouse, and 4) the Honeywell trackball. Results showed that: 1) the test battery is an efficient tool for differentiating among input devices, 2) gloved operations were about 1 second slower and had at least 15% more errors; 3) devices used with gloves have to be larger, and should allow good hand positioning to counteract the lack of tactile feedback, 4) none of the devices, as designed, were ideal for operation with EVA gloves.

Sandor, Aniko↗

NASA NTRS2006

Comparison of Bystander Cardiopulmonary Resuscitation (BCPR) Performance in the Absence and Presence of Timing Devices for Coordinating Delivery of Ventilatory Breaths and Cardiac Compressions in a Model of Adult Cardiopulmonary Arrest

Astronaut crew medical officers (CMO) aboard the International Space Station (ISS) receive 40 hours of medical training during the 18 months preceding each mission. Part of this training ilncludes twoperson cardiopulmonary resuscitation (CPR) per training guidelines from the American Heart Association (AHA). Recent studies concluded that the use of metronomic tones improves the coordination of CPR by trained clinicians. Similar data for bystander or "trained lay people" (e.g. CMO) performance of CPR (BCPR) have been limited. The purpose of this study was to evailuate whether use of timing devices, such as audible metronomic tones, would improve BCPR perfomance by trained bystanders. Twenty pairs of bystanders trained in two-person BCPR performled BCPR for 4 minutes on a simulated cardiopulmonary arrest patient using three interventions: 1) BCPR with no timing devices, 2) BCPR plus metronomic tones for coordinating compression rate only, 3) BCPR with a timing device and metronome for coordinating ventilation and compression rates, respectively. Bystanders were evaluated on their ability to meet international and AHA CPR guidelines. Bystanders failed to provide the recommended number of breaths and number of compressions in the absence of a timing device and in the presence of audible metronomic tones for only coordinating compression rate. Bystanders using timing devices to coordinate both components of BCPR provided the reco number of breaths and were closer to providing the recommended number of compressions compared with the other interventions. Survey results indicated that bystanders preferred to use a metronome for delivery of compressions during BCPR. BCPR performance is improved by timing devices that coordinate both compressions and breaths.

Hurst, Victor, IV↗

NASA NTRS1991

Lift producing device exhibiting low drag and reduced ventilation potential and method for producing the same

A lift producing device is disclosed which is adapted to be connected to a vehicle to provide lift to the vehicle when the vehicle is moved relative to a first fluid medium having a first density and viscosity and being in contact with a second fluid medium adjacent the vehicle. The second fluid medium has a second fluid density which is different from the first fluid density. The lift producing device comprises opposed first and second major surfaces joined at a longitudinally extending leading edge and at a longitudinally extending trailing edge, with at least a portion of the longitudinally extending leading edge being spaced from the longitudinally extending trailing edge by a predetermined mean chord length. When the vehicle is moved relative to the first fluid medium at a velocity within a range of predetermined velocities, with each of the velocities having a direction inclined from a plane extending through the leading edge and the trailing edge within a predetermined angular range, a region of high pressure is generated in the first fluid medium adjacent the first major surface and a region of low pressure is generated in the first fluid medium adjacent the second major surface. The lift producing device has a cross-sectional shape which will generate a pressure distribution around the device when the vehicle is moved relative to the first fluid medium at a velocity within the range of predetermined velocities such that the first fluid medium exhibits attached laminar flow along the device for a portion of the predetermined mean chord length from the leading edge to the trailing edge and will neither form a laminar separation bubble adjacent the second major surface of the device, nor exhibit turbulent separation adjacent the second major surface for substantially all of the predetermined mean chord length from the leading edge to the trailing edge. The portion along which attached laminar flow is maintained is the longest portion which will still fulfill the flow separation requirements. A method for producing the foil is also disclosed.

Caldwell, Richard A.↗

NASA NTRS1996

Monolithic prestressed ceramic devices and method for making same

Monolithic, internally asymmetrically stress biased electrically active ceramic devices and a method for making same is disclosed. The first step in the method of the present invention is to fabricate a ceramic element having first and second opposing surfaces. Next, only the first surface is chemically reduced by heat treatment in a reducing atmosphere. This produces a concave shaped, internally asymmetrically stress biased ceramic element and an electrically conducting, chemically reduced layer on the first surface which serves as one of the electrodes of the device. Another electrode can be deposited on the second surface to complete the device. In another embodiment of the present invention two dome shaped ceramic devices can be placed together to form a completed clamshell structure or an accordion type structure. In a further embodiment, the clamshell or accordion type structures can be placed on top of one another. In another embodiment, a pair of dome shaped ceramic devices having opposing temperature characteristics can be placed on top of each other to produce an athermalized ceramic device.

Haertling, Gene H.↗

NASA NTRS2006

Tunable resonator-based devices for producing variable delays and narrow spectral linewidths

Devices with two or more coupled resonators to produce narrow spectral responses due to interference of signals that transmit through the resonators and techniques for operating such devices to achieve certain operating characteristics are described. The devices may be optical devices where optical resonators such as whispering gallery mode resonators may be used. In one implementation, at least one of the coupled optical resonators is a tunable resonator and is tuned to change its resonance frequency to tune the spectral response of the device. The described devices and techniques may be applied in optical filters, optical delays, optical waveform generators, and other applications.

Savchenkov, Anatoliy↗

NASA NTRS1989

Method of making a semiconductor device assembly

The invention is a semiconductor device assembly and method of making the same. A mounting plate has positioning means for positioning the plate relative to a header, a first mounting surface of the plate is attached to the header and a semiconductor device is attached to a second mounting surface of the mounting plate. The assembly is made by forming the mounting plate, positioning the mounting plate relative to the header by the positioning means, attaching the first mounting surface to the header and the semiconductor device to the second mounting surface. Another method of making the assembly is by defining and etching a mounting plate and attaching the first mounting surface to the header and the semiconductor device to the second mounting surface. This assembly and process provides an efficient means for mounting semiconductor devices and in particular electro-optic devices such as lasers.

Dholakia, Anil R.↗

NASA NTRS2007

Hand Held Device for Wireless Powering and Interrogation of Biomems Sensors and Actuators

A compact, hand-held device for wireless powering, interrogation and data retrieval from at least one implanted sensor. The hand-held device includes an antenna for powering an implanted sensor and for receiving data from the implanted sensor to the hand-held device for at least one of storage, display or analysis. The hand-held device establishes electromagnetic coupling with a low radiating radio frequency power inductor in the implanted sensor at a predefined separation and the antenna geometry allows for the antenna to power, interrogate and retrieve data from the implanted sensor without strapping the hand-held device to a human body housing the implanted sensor The hand-held device optionally allows for activation of the implanted sensor only during interrogation and data retrieval.

Miranda, Felix Antonio↗

NASA NTRS1989

Semiconductor device assembly and method of making same

Dholakia, Anil R.↗