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Results for “Phase shift”

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 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
NASA NTRS2003

Multiple bit differential detection of offset quadrature phase-shift-keying

Analogous to multiple symbol differential detectionof quadrature phase-shift-keying (QPSK), a multiple bit differential detection scheme is described for offset QPSK that also exhibits continuous improvement in performance with increasing observation interval. Being derived from maximum-likelihood (ML) considerations, the proposed scheme is purported to be the most power efficient scheme for such a modulation and detection method. Extension of the results to shaped offset QPSK is also possible.

Digital communications offset quadriphase modulati↗
NASA NTRS1995

Acute exposure to 2G phase shifts the rat circadian timing system

The circadian timing system (CTS) provides internal and external temporal coordination of an animal's physiology and behavior. In mammals, the generation and coordination of these circadian rhythms is controlled by a neural pacemaker, the suprachiasmatic nucleus (SCN), located within the hypothalamus. The pacemaker is synchronized to the 24 hour day by time cures (zeitgebers) such as the light/dark cycle. When an animal is exposed to an environment without time cues, the circadian rhythms maintain internal temporal coordination, but exhibit a 'free-running' condition in which the period length is determined by the internal pacemaker. Maintenance of internal and external temporal coordination are critical for normal physiological and psychological function in human and non-human primates. Exposure to altered gravitational environments has been shown to affect the amplitude, mean, and timing of circadian rhythms in species ranging from unicellular organisms to man. However, it has not been determined whether altered gravitational fields have a direct effect on the neural pacemaker, or affect peripheral parameters. In previous studies, the ability of a stimulus to phase shift circadian rhythms was used to determine whether a stimulus has a direct effect on the neural pacemaker. The present experiment was performed in order to determine whether acute exposure to a hyperdynamic field could phase shift circadian rhythms.

Hoban-Higgins, T. M.↗
DOE OSTI2023

High dimensional binary classification under label shift: phase transition and regularization

Label Shift has been widely believed to be harmful to the generalization performance of machine learning models. Researchers have proposed many approaches to mitigate the impact of the label shift, e.g., balancing the training data. However, these methods often consider the underparametrized regime, where the sample size is much larger than the data dimension. The research under the overparametrized regime is very limited. Here, to bridge this gap, we propose a new asymptotic analysis of the Fisher Linear Discriminant classifier for binary classification with label shift. Specifically, we prove that there exists a phase transition phenomenon: Under certain overparametrized regime, the classifier trained using imbalanced data outperforms the counterpart with reduced balanced data. Moreover, we investigate the impact of regularization to the label shift: The aforementioned phase transition vanishes as the regularization becomes strong.

binary classification↗
NASA NTRS2000

Application of ANFIS to Phase Estimation for Multiple Phase Shift Keying

The paper discusses a novel use of Adaptive Neuro-Fuzzy Inference Systems (ANFIS) for estimating phase in Multiple Phase Shift Keying (M-PSK) modulation. A brief overview of communications phase estimation is provided. The modeling of both general open-loop, and closed-loop phase estimation schemes for M-PSK symbols with unknown structure are discussed. Preliminary performance results from simulation of the above schemes are presented.

Drake, Jeffrey T.↗
NASA NTRS1977

High-energy heavy-ion scattering and the optical phase shift function

Within the framework of the Glauber approximation, an exact expression for the optical phase shift function is derived which takes into account the center-of-mass correlation function. We calculate total and differential cross sections using the first-order term for the shift function and compare them with the usual (first-order) optical limit results and, for the lighter nuclei, with the exact Glauber results. The nucleus-nucleus elastic scattering amplitude does not exhibit the large-q divergence which characterizes the usual optical limit. The obtained results improve the calculated total and differential cross sections dramatically for light nuclei, and significantly for medium and heavy nuclei.

Franco, V.↗
NASA NTRS2008

Measurement and Calibration of PSD with Phase-shifting Interferometers

We discuss the instrumental aspects affecting the measurement accuracy when determining PSD with phase shifting interferometers. These include the source coherence, optical train effects, and detector effects. The use of a carefully constructed calibration standard will also be discussed. We will end with a recommended measurement and data handling procedure.

Lehan, J. P.↗
NASA NTRS1980

Voltage-controlled attenuator with low phase shift

Five megahertz RF (radiofrequency) signal attenuator utilizing RF quadrature hybrid, and optically viable-resistance load controlled by lamp circuit exhibits little phase shift. Circuit is designed to help distribute standard RF signal of controlled amplitude, and phase throughout complex of facilities could be useful in application to precision test equipment and communication electronics.

Lutes, G. F., Jr.↗
DOE OSTI2022

Compact instantaneous phase-shifting Sagnac interferometer for nanoscale tilt measurement

There is a large inter disciplinary need for high precision angular sensors in state-of-the-art technologies. This particularly applies to optical metrology in the field of Extreme Ultraviolet (EUV) or X-ray where the optics are commonly characterized in terms of slope errors at a nanoradian scale level. Here, in this paper, we present the in-lab development of an angular sensor based on a single reflection compact Sagnac interferometer using instantaneous phase shifting. Our automated prototype and first results show less than 15 nrad RMS repeatability, at least 200 nrad sensitivity and 280 nrad reproducibility over 100 μrad angular range.

36 MATERIALS SCIENCE↗
NASA NTRS1992

The effect of temperature on attenuation-correction schemes in rain using polarization propagation differential phase shift

The study elucidates and quantifies differences in the response of the rate of change of polarization propagation differential phase shift Phi, the rate of attenuation for a horizontally/vertically polarized wave A(H,V), and the rate of polarization differential attenuation A(H-V) to temperature. It is shown that if the effects of temperature when estimating A(H) and A(H-V) from Phi are neglected, the average fractional standard error increases only slightly at 9 GHz but significantly at 5 and 3 GHz. Errors at 5 and 3 GHz are about two to three times those at 9 GHz. The performance of Phi-based schemes of attenuation correction at these lower frequencies is much more significantly degraded by temperature uncertainty than at 9 GHz. It is concluded that it is best to use Phi to correct for attenuation at the least-attenuating frequencies.

Jameson, A. R.↗
DOE OSTI2022

Triple Phase-Shift Optimization of SiC-based Dual-Active Bridge DC/AC Converter

This paper presents a loss-optimized Triple Phase-Shift (TPS) switching strategy for Dual-Active Bridge (DAB) based converters. The proposed strategy considers minimizing total converter loss with respect to minimizing device rms cur-rents, enabling Zero-Voltage Switching (ZVS) turn-on of devices and accurate control of device turn-off current. A model for switching currents is presented, followed by a loss model and optimization strategy. A 1.3kV/100kW prototype based on SiC MOSFETs was used in this work and experimental results up to 10kW show the proposed TPS strategy to be more efficient for operation.

Vetrivelan, Adithyan↗