59,624 research outputs found
NTF: Soldering Technology Development for Cryogenics
The advent of the National Transonic Facility (NTF) brought about a new application for an old joining method, soldering. Soldering for use at cryogenic temperatures requires that solders remain ductile and free from tin-pest (grey tin), have toughness to withstand aerodynamic loads associated with flight research, and maintain their surface finishes. Solders are used to attach 347 Stainless-Steel tubing in surface grooves of models. The solder must fill up the gap and metallurgically bound to the tubing and model. Cryogenic temperatures require that only specific materials for models can be used, including: Vasco Max 200 CVM, lescalloy A-286 Vac Arc, pH 13-8 Mo. Solders identified for testing at this time are: 50% Sn - 49.5% Pb - 0.5% Sb, 95% Sn - 5% Sb, 50% In 50% Pb, and 37.5% Sn - 37.5% Pb - 25% In. With these materials and solders, it is necessary to determine their solderability. After solderability is determined, tube/groove specimens are fabricated and stressed under cryogenic temperatures. Compatible solders are then used for acutual models
A Physical Axiomatic Approach to Schrodinger's Equation
The Schrodinger equation for non-relativistic quantum systems is derived from
some classical physics axioms within an ensemble hamiltonian framework. Such an
approach enables one to understand the structure of the equation, in particular
its linearity, in intuitive terms. Furthermore it allows for a physically
motivated and systematic investigation of potential generalisations which are
briefly discussed.Comment: Extended version. 14 page
Large time scale variation in hydrogen emission from Jupiter and Saturn
The IUE and Voyager spacecraft observations of Jupiter and Saturn were combined to obtain a consistent measurement of temporal variation of the equatorial subsolar hydrogen emission. The outer planets appear to have rather independent behavior over time scales of the order of 10 yr, particularly in emission from the H Ly alpha line. The time interval from 1978 to the present shows variation of mean equatorial H Ly alpha brightness of 2 at Jupiter and 5 at Saturn. The relative magnitudes of the variations is sufficiently different to suggest that response to input from the Sun is at least nonlinear. The brightness of H2 band emission appears to be relatively more stable than H Ly alpha. There is evidence in IUE observations of a moderate increase in H2 band brightness with increasing time at Jupiter, in opposition to the variation in H Ly alpha
Anisotropic intrinsic anomalous Hall effect in ordered 3dPt alloys
By performing first principles calculations we investigate the intrinsic
anomalous Hall conductivity (AHC) and its anisotropy in ordered L1o FePt, CoPt
and NiPt ferromagnets, and their intermediate alloys. We demonstrate that the
AHC in this family of compounds depends strongly on the direction of the
magnetization in the crystal. We predict that such pronounced orientational
dependence in combination with the general decreasing trend of the AHC when
going from FePt to NiPt leads to a sign change of the AHC upon rotating the
magnetization direction in the crystal of CoPt alloy. We also suggest that for
a range of concentration x in Co(x)Ni(1-x)Pt alloy it is possible to achieve a
complete quenching of the anomalous Hall current for a certain direction of the
magnetization in the crystal. By analyzing the spin-resolved AHC in 3dPt alloys
we endeavor to relate the overall trend of the AHC in these compounds to the
changes in their densities of d-states around the Fermi energy upon varying the
atomic number. Moreover, we show the generality of the phenomenon of
anisotropic anomalous Hall effect by demonstrating its occurrence within the
three-band tight-binding model.Comment: 10 page
Suppression of intrinsic neutron background in the Multi-Grid detector
One of the key requirements for neutron scattering instruments is the
Signal-to-Background ratio (SBR). This is as well a design driving requirement
for many instruments at the European Spallation Source (ESS), which aspires to
be the brightest neutron source of the world. The SBR can be effectively
improved with background reduction. The Multi-Grid, a large-area thermal
neutron detector with a solid boron carbide converter, is a novel solution for
chopper spectrometers. This detector will be installed for the three
prospective chopper spectrometers at the ESS. As the Multi-Grid detector is a
large area detector with a complex structure, its intrinsic background and its
suppression via advanced shielding design should be investigated in its
complexity, as it cannot be naively calculated. The intrinsic scattered neutron
background and its effect on the SBR is determined via a detailed Monte Carlo
simulation for the Multi-Grid detector module, designed for the CSPEC
instrument at the ESS. The impact of the detector vessel and the neutron
entrance window on scattering is determined, revealing the importance of an
optimised internal detector shielding. The background-reducing capacity of
common shielding geometries, like side-shielding and end-shielding is
determined by using perfect absorber as shielding material, and common
shielding materials, like BC and Cd are also tested. On the basis of the
comparison of the effectiveness of the different shielding topologies and
materials, recommendations are given for a combined shielding of the Multi-Grid
detector module, optimised for increased SBR.Comment: 26 pages, 18 figures, revise
Quantum fluctuations of a vortex in an optical lattice
Using a variational ansatz for the wave function of the Bose-Einstein
condensate, we develop a quantum theory of vortices and quadrupole modes in a
one-dimensional optical lattice. We study the coupling between the quadrupole
modes and Kelvin modes, which turns out to be formally analogous to the theory
of parametric processes in quantum optics. This leads to the possibility of
squeezing vortices. We solve the quantum multimode problem for the Kelvin modes
and quadrupole modes numerically and find properties that cannot be explained
with a simple linear-response theory.Comment: final version, minor change
Coherent states for compact Lie groups and their large-N limits
The first two parts of this article surveys results related to the
heat-kernel coherent states for a compact Lie group K. I begin by reviewing the
definition of the coherent states, their resolution of the identity, and the
associated Segal-Bargmann transform. I then describe related results including
connections to geometric quantization and (1+1)-dimensional Yang--Mills theory,
the associated coherent states on spheres, and applications to quantum gravity.
The third part of this article summarizes recent work of mine with Driver and
Kemp on the large-N limit of the Segal--Bargmann transform for the unitary
group U(N). A key result is the identification of the leading-order large-N
behavior of the Laplacian on "trace polynomials."Comment: Submitted to the proceeding of the CIRM conference, "Coherent states
and their applications: A contemporary panorama.
Depletion isolation effect in Vertical MOSFETS during transition from partial to fully depleted operation
A simulation study is made of floating-body effects (FBEs) in vertical MOSFETs due to depletion isolation as the pillar thickness is reduced from 200 to 10 nm. For pillar thicknesses between 200–60 nm, the output characteristics with and without impact ionization are identical at a low drain bias and then diverge at a high drain bias. The critical drain bias Vdc for which the increased drain–current is observed is found to decrease with a reduction in pillar thickness. This is explained by the onset of FBEs at progressively lower values of the drain bias due to the merging of the drain depletion regions at the bottom of the pillar (depletion isolation). For pillar thicknesses between 60–10 nm, the output characteristics show the opposite behavior, namely, the critical drain bias increases with a reduction in pillar thickness. This is explained by a reduction in the severity of the FBEs due to the drain debiasing effect caused by the elevated body potential. Both depletion isolation and gate–gate coupling contribute to the drain–current for pillar thicknesses between 100–40 nm
Ultra wide band near-field 3-D radar cross section (RCS) holography
RCS impulse holography is a new concept for obtaining near-field, three-dimensional RCS measurements and low-observable diagnostic image reconstructions. The high-resolution images (holographic reconstruction) maps the target’s scattering areas and identifies the “hot spots” at each frequency (i.e., in the pulse bandwidth) which dominate the far-field return to the radar. The combination of these two salient features (i.e., predictive and diagnostic) provides an extremely attractive, economic near-field measurement technique that can be utilized by the military
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