44,946 research outputs found
A 20 kiloHertz space station power system
The space station represents the next major U.S. commitment in space. The efficient delivery of power to multiple user loads is key to that success. In 1969, NASA Lewis Research Center began a series of studies with component and circuit developments that led to the high frequency, bi-directional, four quadrant resonant driven converter. Additional studies and subsequent developments into the early 1980's have shown how the high frequency ac power system could provide overall advantages to many aerospace power systems. Because of its wide versatility, it also has outstanding advantages for the Space Station Program and its wide range of users. High frequency ac power provides higher efficiency, lower cost, and improved safety. The 20 kHz power system has exceptional flexibility, is inherently user friendly, and is compatible with all types of energy sources - photovoltaic, solar dynamic, rotating machines or nuclear. Lewis has recently completed development under contract a 25 kW, 20 kHz ac power distribution system testbed. The testbed demonstrates flexibility, versatility, and transparency to user technology as well as high efficiency, low mass, and reduced volume
Performance characteristics of the 12 GHz, 200 watt transmitter experiment package for CTS
The experiment package consists of a 200 W output stage tube (OST) powered by a power processing system (PPS). Descriptions of both the PPS and OST are given. The PPS provides the necessary voltages with a measured dc/dc conversion efficiency of 89 percent. The OST, a traveling wave tube with multiple collectors, has a saturated rf output power of 224 W and operates at an overall efficiency exceeding 40 percent over an 85 MHz bandwidth at 12 GHz. OST performance given includes frequency response, saturation characteristics, group delay, AM to PM conversion, inter-modulation distortion, and two channel gain suppression. Single and dual channel FM video performance is presented. It was determined that for 12 MHz peak to peak frequency deviation on each channel, dual channel FM television signals can be transmitted through the TEP at 60 W, each channel, with 40 MHz channel spacing (center to center)
FID-Net: A Versatile Deep Neural Network Architecture for NMR Spectral Reconstruction and Virtual Decoupling
In recent years, the transformative potential of deep neural networks (DNNs) for analysing and interpreting NMR data has clearly been recognised. However, most applications of DNNs in NMR to date either struggle to outperform existing methodologies or are limited in scope to a narrow range of data that closely resemble the data that the network was trained on. These limitations have prevented a widescale uptake of DNNs in NMR. Addressing this, we introduce FID-Net, a deep neural network architecture inspired by WaveNet, for performing analyses on time domain NMR data. We first demonstrate the effectiveness of this architecture in reconstructing non-uniformly sampled (NUS) biomolecular NMR spectra. It is shown that a single network is able to reconstruct a diverse range of 2D NUS spectra that have been obtained with arbitrary sampling schedules, with a range of sweep widths, and a variety of other acquisition parameters. The performance of the trained FID-Net in this case exceeds or matches existing methods currently used for the reconstruction of NUS NMR spectra. Secondly, we present a network based on the FID-Net architecture that can efficiently virtually decouple 13Cα-13Cβ couplings in HNCA protein NMR spectra in a single shot analysis, while at the same time leaving glycine residues unmodulated. The ability for these DNNs to work effectively in a wide range of scenarios, without retraining, paves the way for their widespread usage in analysing NMR data
Detailed design specification for the Yield Estimation Subsystem Data Management System (YESDAMS)
There are no author-identified significant results in this report
Self-diffusion in a monatomic glassforming liquid embedded in the hyperbolic plane
We study by Molecular Dynamics simulation the slowing down of particle motion
in a two-dimensional monatomic model: a Lennard-Jones liquid on the hyperbolic
plane. The negative curvature of the embedding space frustrates the long-range
extension of the local hexagonal order. As a result, the liquid avoids
crystallization and forms a glass. We show that, as temperature decreases, the
single particle motion displays the canonical features seen in real
glassforming liquids: the emergence of a "plateau" at intermediate times in the
mean square displacement and a decoupling between the local relaxation time and
the (hyperbolic) diffusion constant.Comment: Article for the "11th International Workshop on Complex Systems
Peripherality of breakup reactions
The sensitivity of elastic breakup to the interior of the projectile wave
function is analyzed. Breakup calculations of loosely bound nuclei (8B and
11Be) are performed with two different descriptions of the projectile. The
descriptions differ strongly in the interior of the wave function, but exhibit
identical asymptotic properties, namely the same asymptotic normalization
coefficient, and phase shifts. Breakup calculations are performed at
intermediate energies (40-70 MeV/nucleon) on lead and carbon targets as well as
at low energy (26 MeV) on a nickel target. No dependence on the projectile
description is observed. This result confirms that breakup reactions are
peripheral in the sense that they probe only the external part of the wave
function. These measurements are thus not directly sensitive to the total
normalization of the wave function, i.e. spectroscopic factor.Comment: Reviewed version accepted for publication in Phys. Rev. C; 1 new
section (Sec. III E), 2 new figures (Figs. 3 and 5
Sources of magnetic fields in recurrent interplanetary streams
The sources of magnetic fields in recurrent streams were examined. Most fields and plasmas at 1 AU were related to coronal holes, and the magnetic field lines were open in those holes. Some of the magnetic fields and plasmas were related to open field line regions on the sun which were not associated with known coronal holes, indicating that open field lines are more basic than coronal holes as sources of the solar wind. Magnetic field intensities in five equatorial coronal holes ranged from 2G to 18G. Average measured photospheric magnetic fields along the footprints of the corresponding unipolar fields on circular equatorial arcs at 2.5 solar radii had a similar range and average, but in two cases the intensities were approximately three times higher than the projected intensities. The coronal footprints of the sector boundaries on the source surface at 2.5 solar radii, meandered between -45 deg and +45 deg latitude, and their inclination ranged from near zero to near ninety degrees
Electroneutrality and Phase Behavior of Colloidal Suspensions
Several statistical mechanical theories predict that colloidal suspensions of
highly charged macroions and monovalent microions can exhibit unusual
thermodynamic phase behavior when strongly deionized. Density-functional,
extended Debye-H\"uckel, and response theories, within mean-field and
linearization approximations, predict a spinodal phase instability of charged
colloids below a critical salt concentration. Poisson-Boltzmann cell model
studies of suspensions in Donnan equilibrium with a salt reservoir demonstrate
that effective interactions and osmotic pressures predicted by such theories
can be sensitive to the choice of reference system, e.g., whether the microion
density profiles are expanded about the average potential of the suspension or
about the reservoir potential. By unifying Poisson-Boltzmann and response
theories within a common perturbative framework, it is shown here that the
choice of reference system is dictated by the constraint of global
electroneutrality. On this basis, bulk suspensions are best modeled by
density-dependent effective interactions derived from a closed reference system
in which the counterions are confined to the same volume as the macroions.
Linearized theories then predict bulk phase separation of deionized suspensions
only when expanded about a physically consistent (closed) reference system.
Lower-dimensional systems (e.g., monolayers, small clusters), depending on the
strength of macroion-counterion correlations, may be governed instead by
density-independent effective interactions tied to an open reference system
with counterions dispersed throughout the reservoir, possibly explaining
observed structural crossover in colloidal monolayers and anomalous
metastability of colloidal crystallites.Comment: 12 pages, 5 figures. Discussion clarified, references adde
Density functional theory of vortex lattice melting in layered superconductors: a mean-field--substrate approach
We study the melting of the pancake vortex lattice in a layered
superconductor in the limit of vanishing Josephson coupling. Our approach
combines the methodology of a recently proposed mean-field substrate model for
such systems with the classical density functional theory of freezing. We
derive a free-energy functional in terms of a scalar order-parameter profile
and use it to derive a simple formula describing the temperature dependence of
the melting field. Our theoretical predictions are in good agreement with
simulation data. The theoretical framework proposed is thermodynamically
consistent and thus capable of describing the negative magnetization jump
obtained in experiments. Such consistency is demonstrated by showing the
equivalence of our expression for the density discontinuity at the transition
with the corresponding Clausius-Clapeyron relation.Comment: 11 pages, 4 figure
Virtual Homonuclear Decoupling in Direct Detection NMR Experiments using Deep Neural Networks
Nuclear magnetic resonance (NMR) experiments are frequently complicated by the presence of homonuclear scalar couplings. For the growing body of biomolecular 13C-detected methods, one-bond 13C-13C couplings significantly reduce sensitivity and resolution. The solution to this problem has typically been to record in-phase and anti-phase (IPAP) or spin state selective excitation (S3E) spectra and take linear combinations to yield singlet resolved resonances. This however, results in a doubling of the effective phase cycle and requires additional delays and pulses to create the necessary magnetisation. Here, we propose an alternative method of virtual decoupling using deep neural networks. This methodology requires only the in-phase spectra, halving the experimental time and, by decoupling signals, gives a significant boost in resolution while concomitantly doubling sensitivity relative to the in-phase spectrum. We successfully apply this methodology to virtually decouple in-phase CON (13CO-15N) protein NMR spectra and 13C-13C correlation spectra of protein side chains
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