Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “BUFFER”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1995

Growth and micro structural studies on Yittria Stabilized Zirconia (YSZ) and Strontium Titanate (STO) buffer layers

Microstructure of Yittria Stabilized Zirconia (YSZ) and Strontium Titanate (STO) of radio frequency magnetron sputtered buffer layers was studied at various sputtering conditions on Si (100), Sapphire and LaAlO3 (100) substrates. The effect of substrate temperatures up to 800 C and sputtering gas pressures in the range of 50 mTorr. of growth conditions was studied. The buffer layers of YSZ and STO showed a strong tendency for columnar growth was observed above 15 mTorr sputtering gas pressure and at high substrate temperatures. Post annealing of these films in oxygen atmosphere reduced the oxygen deficiency and strain generated during growth of the films. Strong c-axis oriented superconducting YBa2Cu3O7-x (YBCO) thin films were obtained on these buffer layers using pulsed laser ablation technique. YBCO films deposited on multilayers of YSZ and STO were shown to have better superconducting properties.

Srinivas, S.↗
NASA NTRS1995

Compiler-assisted multiple instruction rollback recovery using a read buffer

Multiple instruction rollback (MIR) is a technique that has been implemented in mainframe computers to provide rapid recovery from transient processor failures. Hardware-based MIR designs eliminate rollback data hazards by providing data redundancy implemented in hardware. Compiler-based MIR designs have also been developed which remove rollback data hazards directly with data-flow transformations. This paper describes compiler-assisted techniques to achieve multiple instruction rollback recovery. We observe that some data hazards resulting from instruction rollback can be resolved efficiently by providing an operand read buffer while others are resolved more efficiently with compiler transformations. The compiler-assisted scheme presented consists of hardware that is less complex than shadow files, history files, history buffers, or delayed write buffers, while experimental evaluation indicates performance improvement over compiler-based schemes.

Alewine, Neal J.↗
NASA NTRS2006

An Advanced Helium Buffer Seal for the SSME, ATD Oxygen Pump

The present configuration of Helium Buffer Seal on the ATD oxygen pump consists of a pair of opposed carbon rings are forced axially against their containment housings. Leakage occurs through the clearance between the rings and the shaft. The total helium leakage through both sides is approximately 239 SCFM. A reduction in leakage to 50 SCFM will result in less helium storage and consequently permit a substantial increase in payload. Under Phase 1 NASA SBIR, a solid T-Ring seal was analyzed and designed that could satisfy the criteria of reducing leakage to 50 SCFM or less. The design makes maximum use of available length and employs a mid length row of hydrostatic orifaces that feed buffer helium directly into a 2 to 3 mil clearance region. The flow splits into opposite paths to buffer oxygen gas on one side and hydrogen gas on the turbine side. The seal employs opposed hydrostatic tapered land secondary seals that provide friction free support of the primary seal and allows the primary seal to follow rotor excursion and maintain concentric operating clearance . The predicted performance of the T-seal is excellent with operation at a safe film thickness of 2 to 2.5 mils and leakage less than 50 SCFM.

Shapiro, Wilbur↗
NASA NTRSDate not supplied

Confidence-Based Buffer for Strategic Deconfliction with Probabilistic Operational Intent

This paper presents a methodology to expand the 95% confidence level of the elliptical geometry given by Unmanned Aircraft System (UAS) operators planning to fly Beyond Visual Line of Sight (BVLOS) to any confidence level before being fed to the strategic deconfliction (SD) module, effectively increasing the separation buffer between Operational Intents (OIs). To assess the performance of this approach, it is integrated within an adaptation of the Rolling Horizon with K-Position Search volume-based strategic deconfliction approach, previously developed at NASA Ames, preventing the 4D overlapping of OIs shaped by ellipses instead of traditional blocks. Safety and efficiency metrics are evaluated through the deconfliction of four simulated package delivery route network structures across the San Francisco Metropolitan Area with increasing numbers of crossing waypoints (network complexity). Safety assessment entails the in-house creation of a metric to quantify collision occurrences per flight hour based on the frequency at which the probabilistic operational volume segments are sampled, whereas efficiency is measured using ground delay. Results indicate that the largest buffer growth occurs when increasing the confidence level beyond 99.9% and demonstrate the negative impact of network complexity on both metrics, regardless of the OI geometry. Further, the ellipse-based SD adaptation more accurately estimates temporal separation at crossings, allowing deconflicted vehicles to be closer together. It is concluded that the proposed methodology enables the desired confidence level to serve as an effective controller of buffer size.

strategic deconfliction↗
NASA NTRSDate not supplied

Confidence-Based Buffer for Strategic Deconfliction with Probabilistic Operational Intent

This paper presents a methodology to expand the 95% confidence level of the elliptical geometry given by Unmanned Aircraft System (UAS) operators planning to fly Beyond Visual Line of Sight (BVLOS) to any confidence level before being fed to the strategic deconfliction (SD) module, effectively increasing the separation buffer between Operational Intents (OIs). To assess the performance of this approach, it is integrated within an adaptation of the Rolling Horizon with K-Position Search volume-based strategic deconfliction approach, previously developed at NASA Ames, preventing the 4D overlapping of OIs shaped by ellipses instead of traditional blocks. Safety and efficiency metrics are evaluated through the deconfliction of four simulated package delivery route network structures across the San Francisco Metropolitan Area with increasing numbers of crossing waypoints (network complexity). Safety assessment entails the in-house creation of a metric to quantify collision occurrences per flight hour based on the frequency at which the probabilistic operational volume segments are sampled, whereas efficiency is measured using ground delay. Results indicate that the largest buffer growth occurs when increasing the confidence level beyond 99.9% and demonstrate the negative impact of network complexity on both metrics, regardless of the OI geometry. Further, the ellipse-based SD adaptation more accurately estimates temporal separation at crossings, allowing deconflicted vehicles to be closer together. It is concluded that the proposed methodology enables the desired confidence level to serve as an effective controller of buffer size.

safety↗
NASA NTRS1998

Buffer Management Simulation in ATM Networks

This paper presents a simulation of a new dynamic buffer allocation management scheme in ATM networks. To achieve this objective, an algorithm that detects congestion and updates the dynamic buffer allocation scheme was developed for the OPNET simulation package via the creation of a new ATM module.

simulations Asynchronous Transfer Mode ATM Switch ↗
NASA NTRS1967

Field effect transistors improve buffer amplifier

Unity gain buffer amplifier with a Field Effect Transistor /FET/ differential input stage responds much faster than bipolar transistors when operated at low current levels. The circuit uses a dual FET in a unity gain buffer amplifier having extremely high input impedance, low bias current requirements, and wide bandwidth.

Source record↗
NASA NTRS1969

Improved pH buffering agent for sodium hypochlorite

Sodium citrate/citric acid was found to be an effective buffer for pH control when used with sodium hypochlorite. The mixture does not corrode aluminum. The buffer appears to form a type of conversion coating that may provide corrosion-resistant properties to aluminum in other applications.

Nash, J. R.↗
NASA NTRS1972

Light and buffer-gas frequency shifts in the Rb-85 maser frequency standard.

The effect of buffer gas and pumping light on the output frequency of the Rb-85 maser is discussed. In contrast to a primary standard, these frequency shifts can be used to advantage when it is necessary to operate the maser at a frequency which differs from the ground-state hyperfine frequency by a few kilohertz. Using appropriate mixtures of buffer gas and carefully shaped lamp spectral profiles, it is also possible to operate the maser exactly at the ground-state hyperfine frequency. It is pointed out that the short-term phase stability of the maser is not impaired by these shifts.

Stern, W. A.↗
NASA NTRS1971

Compatibility of buffered uranium carbides with tungsten.

Results of compatibility tests between tungsten and hyperstoichiometric uranium carbide alloys run at 1800 C for 1000 and 2500 hours. These tests compared tungsten-buffered uranium carbide with tungsten-buffered uranium-zirconium carbide. The zirconium carbide addition appeared to widen the homogeneity range of the uranium carbide, making additional carbon available for reaction. Reaction layers could be formed by either of two diffusion paths, one producing UWC2, while the second resulted in the formation of W2C. UWC2 acts as a diffusion barrier for carbon and slows the growth of the reaction layer with time, while carbon diffusion is relatively rapid in W2C, allowing equilibrium to be reached in less than 2500 hours at a temperature of 1800 C.

Phillips, W. M.↗
NASA NTRS1974

Fracture of composite plates containing periodic buffer strips

Fracture of a composite plate which consists of perfectly bonded parallel load carrying laminates and buffer strips is considered. Fatigue cracks appear and spread in main laminates or in buffer strips or in both perpendicular to the interfaces. The external load is applied to the plate parallel to the strips and away from the crack region. The problem is solved for fully imbedded cracks and for broken laminates or strips. Corresponding stress intensity factors are calculated.

Erdogan, F.↗
NASA NTRS1976

A 128K-bit CCD buffer memory system

A prototype system was implemented to demonstrate that CCD's can be applied advantageously to the problem of low power digital storage and particularly to the problem of interfacing widely varying data rates. 8K-bit CCD shift register memories were used to construct a feasibility model 128K-bit buffer memory system. Peak power dissipation during a data transfer is less than 7 W., while idle power is approximately 5.4 W. The system features automatic data input synchronization with the recirculating CCD memory block start address. Descriptions are provided of both the buffer memory system and a custom tester that was used to exercise the memory. The testing procedures and testing results are discussed. Suggestions are provided for further development with regards to the utilization of advanced versions of CCD memory devices to both simplified and expanded memory system applications.

Siemens, K. H.↗
NASA NTRS1978

Preliminary investigation of crack arrest in composite laminates containing buffer strips

The mechanical properties of some hybrid buffer strip laminates and the crack arrest potential of laminates containing buffer strips were determined. The hybrid laminates consisted of graphite with either S-glass, E-glass, or Kevlar. Unnotched tensile coupons and center-cracked fracture coupons were tested. Elastic properties, complete stress/strain curves, and critical stress intensity values are given. The measured elastic properties compare well with those calculated by classical lamination theory for laminates with linear stress/strain behavior. The glass hybrids had more delamination and higher fracture toughness than the all-graphite or the Kevlar hybrid.

Goree, J. G.↗
NASA NTRS1981

Common data buffer

Time-shared interface speeds data processing in distributed computer network. Two-level high-speed scanning approach routes information to buffer, portion of which is reserved for series of "first-in, first-out" memory stacks. Buffer address structure and memory are protected from noise or failed components by error correcting code. System is applicable to any computer or processing language.

Byrne, F.↗
NASA NTRS1979

Test evaluation of shock buffering concept for hydrodynamic ram induced by yawing projectile impacting a simulated integral fuel tank

A concept for containing the shock inputs due to hydrodynamic ram caused by an impacting projectile within a fuel cell is discussed. This is to provide a buffering layer of foam, flexible, rigid or a combination thereof, which is sealed from the liquid. A program is described in which this buffering concept was tested. The effectiveness of a novel muzzle-mounted, 'tumble', test device is shown.

Zabel, P. H.↗
NASA NTRS1980

Collisional narrowing by polyatomic buffer gases in an optically pumped CH3F laser

The gain linewidth of an optically pumped CH3F molecular laser is observed with the addition of various polyatomic buffer gases. This is interpreted as collisional (Dicke) narrowing. The measurement is the first observation of collisional narrowing by polyatomic buffer gases. It is also the first observation of the effect in a laser oscillator. The effect was observed using a heterodyne mixing technique at the laser emission frequency of 604 GHz. Collision cross sections for SF6-CH3F and CS2-CH3F are obtained.

Lawandy, N. M.↗
NASA NTRS1980

Detection of individual atoms in helium buffer gas and observation of their real-time motion

Single atoms are detected and their motion measured for the first time to our knowledge by the fluorescence photon-burst method in the presence of large quantities of buffer gas. A single-clipped digital correlator records the photon burst in real time and displays the atom's transit time across the laser beam. A comparison is made of the special requirements for single-atom detection in vacuum and in a buffer gas. Finally, the probability distribution of the bursts from many atoms is measured. It further proves that the bursts observed on resonance are due to single atoms and not simply to noise fluctuations.

Pan, C. L.↗