2,828 research outputs found
Reliable method for testing gross leaks in semiconductor component packages
Simple, reliable, inexpensive method for gross-leak testing has been devised, based upon the conventional fine-leak technique. The sensitivity ranges from the detection of very large leaks down to leaks of 10 to the minus seven cc helium per sec
Orifice gross leak tester Patent
Test chambers with orifice and helium mass spectrometer for detecting leak rate of encapsulated semiconductor device
Entanglement entropy in one-dimensional disordered interacting system: The role of localization
The properties of the entanglement entropy (EE) in one-dimensional disordered
interacting systems are studied. Anderson localization leaves a clear signature
on the average EE, as it saturates on length scale exceeding the localization
length. This is verified by numerically calculating the EE for an ensemble of
disordered realizations using density matrix renormalization group (DMRG). A
heuristic expression describing the dependence of the EE on the localization
length, which takes into account finite size effects, is proposed. This is used
to extract the localization length as function of the interaction strength. The
localization length dependence on the interaction fits nicely with the
expectations.Comment: 5 pages, 4 figures, accepted for publication in Physical Review
Letter
Anderson localisation in tight-binding models with flat bands
We consider the effect of weak disorder on eigenstates in a special class of
tight-binding models. Models in this class have short-range hopping on periodic
lattices; their defining feature is that the clean systems have some energy
bands that are dispersionless throughout the Brillouin zone. We show that
states derived from these flat bands are generically critical in the presence
of weak disorder, being neither Anderson localised nor spatially extended.
Further, we establish a mapping between this localisation problem and the one
of resonances in random impedance networks, which previous work has suggested
are also critical. Our conclusions are illustrated using numerical results for
a two-dimensional lattice, known as the square lattice with crossings or the
planar pyrochlore lattice.Comment: 5 pages, 3 figures, as published (this version includes minor
corrections
The Effects of U.S. Tax Policy on the Income Repatriation Patterns of U.S. Multinational Corporations
U.S. corporations owe taxes to the U.S. Treasury on income earned both inside and outside American borders. This paper examines the incentives created by the U.S. tax system for the legal avoidance of taxes on foreign source income. Using data from 1986 corporate tax returns, we investigate the extent to which U.S. corporations structure and coordinate remittances of income from their foreign subsidiaries to reduce their U.S. and foreign tax liabilities. In contrast to previous work in this area, our estimates of the tax consequences of income remittances from foreign subsidiaries to parent corporations explicitly take into account the ability to use foreign tax credits generated from one source of foreign income to offset the U.S. tax liability generated by other sources of foreign income, withholding tax rates on income remittances, variations in source country corporate income tax systems, and dynamic aspects of the U.S. tax system. Our findings indicate that U.S. multinationals are able to take advantage of the U.S. tax system to avoid paying much U.S. tax on their foreign source income.
Origin of ferromagnetism in (Zn,Co)O from magnetization and spin-dependent magnetoresistance
In order to elucidate the nature of ferromagnetic signatures observed in
(Zn,Co)O we have examined experimentally and theoretically magnetic properties
and spin-dependent quantum localization effects that control low-temperature
magnetoresistance. Our findings, together with a through structural
characterization, substantiate the model assigning spontaneous magnetization of
(Zn,Co)O to uncompensated spins at the surface of antiferromagnetic nanocrystal
of Co-rich wurtzite (Zn,Co)O. The model explains a large anisotropy observed in
both magnetization and magnetoresistance in terms of spin hamiltonian of Co
ions in the crystal field of the wurtzite lattice.Comment: 6 pages, 6 figure
Critical level statistics and anomalously localized states at the Anderson transition
We study the level-spacing distribution function at the Anderson
transition by paying attention to anomalously localized states (ALS) which
contribute to statistical properties at the critical point. It is found that
the distribution for level pairs of ALS coincides with that for pairs of
typical multifractal states. This implies that ALS do not affect the shape of
the critical level-spacing distribution function. We also show that the
insensitivity of to ALS is a consequence of multifractality in tail
structures of ALS.Comment: 8 pages, 5 figure
Chiral single-wall gold nanotubes
Based on first-principles calculations we show that gold atoms can form both
free-standing and tip-suspended chiral single-wall nanotubes composed of
helical atomic strands. Free-standing, infinite (5,5) tube is found to be
energetically the most favorable. While energetically less favorable, the
experimentally observed (5,3) tube stretching between two tips corresponds to a
local minimum in the string tension. Similarly, the (4,3) tube is predicted as
a favorable structure yet to be observed experimentally. Analysis of band
structure, charge density, and quantum ballistic conductance suggests that the
current on these wires is less chiral than expected, and there is no direct
correlation between the numbers of conduction channels and helical strands.Comment: Figures provided in eps forma
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