18,346 research outputs found
Investigation of performance limits in axial groove heat pipes
The entrainment-shear performance limit which occurs in axial groove heat pipes was investigated and explained. In the existing heat pipe literature the entrainment heat flux limit is defined as the condition where the Weber number is greater than or equal to one. In this analysis, the critical value for the entrainment Weber number is found to be 2 pi less than or equal to 3 pi. Perhaps more important to the heat pipe designer than the entrainment performance limit is the prediction of the performance degradation due to vapor-liquid shearing stress which is also described. Preliminary qualitative experiments were conducted to observe the shear. stress wave formation phenomena. The equations presented may be used to predict and minimize the vapor-liquid shear stress performance effects that occur in axial groove and puddle flow artery heat pipes
Calculation of Cu/Ta interface electron transmission and effect on conductivity in nanoscale interconnect technology
Resistivity augmentation in nanoscale metal interconnects is a performance
limiting factor in integrated circuits. Here we present calculations of
electron scattering and transmission at the interface between Cu interconnects
and their barrier layers, in this case Ta. We also present a semiclassical
model to predict the technological impact of this scattering and find that a
barrier layer can significantly decrease conductivity, consistent with
previously published measurements.Comment: To appear in Appl. Phys. Lett., Nov. 2009. Replaced with version
accepted for publication, clarifies discussion of semiclassical model.
Conclusions unchange
Rectification in Y-junctions of Luttinger liquid wires
We investigate rectification of a low-frequency ac bias in Y-junctions of
one-channel Luttinger liquid wires with repulsive electron interaction.
Rectification emerges due to three scatterers in the wires. We find that it is
possible to achieve a higher rectification current in a Y-junction than in a
single wire with an asymmetric scatterer at the same interaction strength and
voltage bias. The rectification effect is the strongest in the absence of the
time-reversal symmetry. In that case, the maximal rectification current can be
comparable with the total current even for low voltages, weak
scatterers and modest interaction strength. In a certain range of low voltages,
the rectification current can grow as the voltage decreases. This leads to a
bump in the - curve.Comment: 14 pages, 4 figures; The latest versio
Fermi surfaces in general co-dimension and a new controlled non-trivial fixed point
Traditionally Fermi surfaces for problems in spatial dimensions have
dimensionality , i.e., codimension along which energy varies.
Situations with arise when the gapless fermionic excitations live at
isolated nodal points or lines. For weak short range interactions are
irrelevant at the non-interacting fixed point. Increasing interaction strength
can lead to phase transitions out of this Fermi liquid. We illustrate this by
studying the transition to superconductivity in a controlled
expansion near . The resulting non-trivial fixed point is shown to
describe a scale invariant theory that lives in effective space-time dimension
. Remarkably, the results can be reproduced by the more familiar
Hertz-Millis action for the bosonic superconducting order parameter even though
it lives in different space-time dimensions.Comment: 4 page
A Lunar Penetrator to Determine Solar-wind-implanted Resources at Depth in the Lunar Regolith
Several volatiles implanted into the lunar regolith by the solar wind are potentially important lunar resources. He-3 might be mined as a fuel for lunar nuclear fusion reactors. Even if the mining of He-3 turns out not to be feasible, several other elements commonly implanted by the solar wind (H,C, and N) could be important for life support and for propellant or fuel production for lunar bases. A simple penetrator-borne instrument package to measure the abundance of H at depth is proposed. Since solar-wind-implanted volatiles tend to correlate with one another, this can be used to estimate global inventories and to design extraction strategies for all of these species
Constructive Field Theory and Applications: Perspectives and Open Problems
In this paper we review many interesting open problems in mathematical
physics which may be attacked with the help of tools from constructive field
theory. They could give work for future mathematical physicists trained with
the constructive methods well within the 21st century
The Fourth Positive System of Carbon Monoxide in the Hubble Space Telescope Spectra of Comets
The rich structure of the Fourth Positive System (A-X) of carbon monoxide
accounts for many of the spectral features seen in long slit HST-STIS
observations of comets 153P/Ikeya-Zhang, C/2001 Q4 (NEAT), and C/2000 WM1
(LINEAR), as well as in the HST-GHRS spectrum of comet C/1996 B2 Hyakutake. A
detailed CO fluorescence model is developed to derive the CO abundances in
these comets by simultaneously fitting all of the observed A-X bands. The model
includes the latest values for the oscillator strengths and state parameters,
and accounts for optical depth effects due to line overlap and self-absorption.
The model fits yield radial profiles of CO column density that are consistent
with a predominantly native source for all the comets observed by STIS. The
derived CO abundances relative to water in these comets span a wide range, from
0.44% for C/2000 WM1 (LINEAR), 7.2% for 153P/Ikeya-Zhang, 8.8% for C/2001 Q4
(NEAT) to 20.9% for C/1996 B2 (Hyakutake). The subtraction of the CO spectral
features using this model leads to the first identification of a molecular
hydrogen line pumped by solar HI Lyman-beta longward of 1200A in the spectrum
of comet 153P/Ikeya-Zhang. (Abridged)Comment: 12 pages, 11 figures, ApJ accepte
No quasi-long-range order in strongly disordered vortex glasses: a rigorous proof
The paper contains a rigorous proof of the absence of quasi-long-range order
in the random-field O(N) model for strong disorder in the space of an arbitrary
dimensionality. This result implies that quasi-long-range order inherent to the
Bragg glass phase of the vortex system in disordered superconductors is absent
as the disorder or external magnetic field is strong.Comment: 3 pages, Revte
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