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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.

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At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

Direct detection optical intersatellite link at 220 Mbps using AlGaAs laser diode and silicon APD with 4-ary PPM signaling

A newly developed 220 Mbps free-space 4-ary pulse position modulation (PPM) direct detection optical communication system is described. High speed GaAs integrated circuits were used to construct the PPM encoder and receiver electronic circuits. Both PPM slot and word timing recovery were provided in the PPM receiver. The optical transmitter consisted of an AlGaAs laser diode (Mitsubishi ML5702A, lambda=821nm) and a high speed driver unit. The photodetector consisted of a silicon avalanche photodiode (APD) (RCA30902S) preceded by an optical interference filter (delta lambda=10nm). Preliminary tests showed that the self-synchronized PPM receiver could achieve a receiver bit error rate of less than 10(exp -6) at 25 nW average received optical signal power or 360 photons per transmitted information bit. The relatively poor receiver sensitivity was believed to be caused by the insufficient electronic bandwidth of the APD preamplifier and the poor linearity of the preamplifier high frequency response.

Sun, Xiaoli↗
DOE OSTI2017

A new APDS approach - alarm processing based on alarm prioritization - 201

We take for granted that the advances in technology bring improvements to the conditions in which humans perform activities associated to them. Is that the case for digital alarm systems in nuclear power plants? The answer is not that simple. A review of the related literature, shows that still, the single most significant problem with alarm systems, is the large number of alarm messages presented to the operator at once. This is an issue that affects analog I and C control rooms with conventional annunciators and gets aggravated in digital I and C based control rooms. Digital alarm systems present the alarms in the form of lists in computer screens. This kind of presentation forces the operator to scroll or navigate pages to review the active alarms. Also, the alarm lists do not allow the operator to apply the pattern recognition practices acquired during training when using with fixed position alarm systems. An Alarm Processing and Diagnostic System (APDS) facilitates the alarm monitoring task by applying alarm reduction techniques based on alarm priorities. It allows the operators to focus on the most important alarms during plant upsets. A new generation of APDS should be based in an improved alarm analysis methodology. To develop such methodology, Tecnatom reviewed applicable standards and our own alarm analysis experiences. This paper documents the process and conclusions of the methodology development. (authors)

42 ENGINEERING↗
DOE OSTI2017

The Role of Structural and Compositional Heterogeneities in the Insulator-to-Metal Transition in Hole-Doped APd 3 O 4 (A = Ca, Sr)

The cubic semiconducting compounds APd 3 O 4 (A = Ca, Sr) can be hole-doped by Na substitution on the A site and driven toward more conducting states. This process has been followed here by a number of experimental techniques to understand the evolution of electronic properties. While an insulator-to-metal transition is observed in Ca 1–x Na x Pd 3 O 4 for x ≥ 0.15, bulk metallic behavior is not observed for Sr 1–x Na x Pd 3 O 4 up to x = 0.20. Given the very similar crystal and (calculated) electronic structures of the two materials, the distinct behavior is a matter of interest. We present evidence of local disorder in the A = Sr materials through the analysis of the neutron pair distribution function, which is potentially at the heart of the distinct behavior. Solid-state 23 Na nuclear magnetic resonance studies additionally suggest a percolative insulator-to-metal transition mechanism, wherein presumably small regions with a signal resembling metallic NaPd 3 O 4 form almost immediately upon Na substitution, and this signal grows monotonically with substitution. Here, some signatures of increased local disorder and a propensity for Na clustering are seen in the A = Sr compounds.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1992

Performance measurement results for a 220 Mbps QPPM optical communication receiver with an EG/G Slik APD

The performance of a 220 Mbps quaternary pulse position modulation (QPPM) optical communication receiver with a 'Slik' silicon avalanche photodiode (APD) and a wideband transimpedance preamplifier in a small hybrid circuit module was measured. The receiver performance had been poor due to the lack of a wideband and low noise transimpedance preamplifier. With the new APB preamplifier module, the receiver achieved a bit error rate (BER) of 10 exp -6 at an average received input optical signal power of 4.2 nW, which corresponds to an average of 80 received (incident) signal photons per information bit.

Davidson, Frederic M.↗
NASA NTRS1995

Dosimetry on STS-42 with the RME APD

Beginning with the STS-42 mission, this laboratory began participating in instrument comparison studies in which space radiation was measured contiguously by passive and active methods. The active instrument was the RME-3 microdosimeter. This instrument measures four-channel LET spectra and employs a tissue-equivalent proportional counter. It is sensitive to the full LET range of ionizing radiation present. Our area passive dosimeter, the RME APD, contained arrays of plastic nuclear track detectors (PNTD's) and thermoluminescent detectors (TLD's). The PNTD's measure LET spectra, while the TLD's measure total absorbed dose. The object of this experiment is to compare the active and passive measurements on the basis of LET spectra, total absorbed dose, and dose equivalent. The STS-42 mission was launched on January 22, 1992, with a flight duration of 8.052 days. The orbit had an inclination of 57 deg and an altitude of 302 km. The shuttle in this orbit is expected to encounter radiation levels dominated by galactic cosmic rays (GCR's) with a lesser contribution from trapped protons in the lower region of the South Atlantic Anomaly (SAA).

Source record↗
NASA NTRS1994

Design Issues of GaAs and AlGaAs Delta-Doped p-i-n Quantum-Well APD's

We examine the basic design issues in the optimization of GaAs delta-doped and AlGAs delta-doped quantum-well avalanche photodiode (APD) structures using a theoretical analysis based on an ensemble Monte Carlo simulation. The devices are variations of the p-i-n doped quantum-well structure previously described in the literature. They have the same low-noise, high-gain and high-bandwidth features as the p-i-n doped quantum-well device. However, the use of delta doping provides far greater control or the doping concentrations within each stage possibly enhancing the extent to which the device can be depleted. As a result, it is expected that the proposed devices will operate at higher gain levels (at very low noise) than devices previously developed.

Wang, Yang↗
DOE OSTI2016

Two-dimensional APDs and SPADs and related methods

Avalanche photodiodes (APDs) and single photon avalanche detectors (SPADs) are provided with a lateral multiplication region that provides improved amplification through increased impact ionization.

36 MATERIALS SCIENCE↗
NASA NTRS2000

Capacity of PPM on APD-Detected Optical Channels

This report defines the fundamental parameters affecting the capacity of a soft-decision optical channel, and relates them to corresponding parameters for the well-understood AWGN channel.

AWGN PPM APD-Detected Optical Channels↗
DOE OSTI2013

PHENIX Muon Piston Calorimeter (MPC) APD and Prototype MPC Extension (MPC-EX) Tests

This is a technical scope of work (TSW) between the Fermi National Accelerator Laboratory (Fermilab) and the experimenters of Muon Piston Calorimeter Extension (MPC-EX) Collaboration who have committed to participate in beam tests to be carried out during the 2013- 2014 Fermilab Test Beam Facility program.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

Photon-counting Properties of SAPHIRA APD Arrays

We measure the ability of the Leonardo Selex Advanced Photodiode HgCdTe Infrared Array (SAPHIRA) avalanche photodiode array to perform photon counting. The current SAPHIRA arrays achieve >90% single-photon efficiency (independent of quantum efficiency expected to be also >90%) and a time resolution of 125 μs with a dark current of 21e {sup −} s{sup −1} pix{sup −1}. Our characterization of several iterations of the SAPHIRA detector over the past 3 years of its development have also revealed a broader pulse height distribution than was originally expected.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗