2,608 research outputs found
Impact of built-in fields and contact configuration on the characteristics of ultra-thin GaAs solar cells
We discuss the effects of built-in fields and contact configuration on the
photovoltaic characteristics of ultrathin GaAs solar cells. The investigation
is based on advanced quantum-kinetic simulations reaching beyond the standard
semi-classical bulk picture concerning the consideration of charge carrier
states and dynamics in complex potential profiles. The thickness dependence of
dark and photocurrent in the ultra-scaled regime is related to the
corresponding variation of both, the built-in electric fields and associated
modification of the density of states, and the optical intensity in the films.
Losses in open-circuit voltage and short-circuit current due to leakage of
electronically and optically injected carriers at minority carrier contacts are
investigated for different contact configurations including electron and hole
blocking barrier layers. The microscopic picture of leakage currents is
connected to the effect of finite surface recombination velocities in the
semi-classical description, and the impact of these non-classical contact
regions on carrier generation and extraction is analyzed.Comment: 5 pages, 8 figure
From Loop Groups to 2-Groups
We describe an interesting relation between Lie 2-algebras, the Kac-Moody
central extensions of loop groups, and the group String(n). A Lie 2-algebra is
a categorified version of a Lie algebra where the Jacobi identity holds up to a
natural isomorphism called the "Jacobiator". Similarly, a Lie 2-group is a
categorified version of a Lie group. If G is a simply-connected compact simple
Lie group, there is a 1-parameter family of Lie 2-algebras g_k each having
Lie(G) as its Lie algebra of objects, but with a Jacobiator built from the
canonical 3-form on G. There appears to be no Lie 2-group having g_k as its Lie
2-algebra, except when k = 0. Here, however, we construct for integral k an
infinite-dimensional Lie 2-group whose Lie 2-algebra is equivalent to g_k. The
objects of this 2-group are based paths in G, while the automorphisms of any
object form the level-k Kac-Moody central extension of the loop group of G.
This 2-group is closely related to the kth power of the canonical gerbe over G.
Its nerve gives a topological group that is an extension of G by K(Z,2). When k
= +-1, this topological group can also be obtained by killing the third
homotopy group of G. Thus, when G = Spin(n), it is none other than String(n).Comment: 40 page
Twisted Mass Finite Volume Effects
We calculate finite volume effects on the pion masses and decay constant in
twisted mass lattice QCD (tmLQCD) at finite lattice spacing. We show that the
lighter neutral pion in tmLQCD gives rise to finite volume effects that are
exponentially enhanced when compared to those arising from the heavier charged
pions. We demonstrate that the recent two flavour twisted mass lattice data can
be better fitted when twisted mass effects in finite volume corrections are
taken into account.Comment: 17 pages, revte
Effect of spin-orbit coupling on zero-conductance resonances in asymmetrically coupled one-dimensional rings
The influence of Rashba spin-orbit coupling on zero conductance resonances
appearing in one dimensional ring asymmetrically coupled to two leads is
investigated. For this purpose, the transmission function of the corresponding
one-electron scattering problem is derived analytically and analyzed in the
complex energy plane with focus on the zero-pole structure characteristic of
transmission (anti)resonances. The lifting of real conductance zeros due to
spin-orbit coupling in the asymmetric Aharonov-Casher (AC) ring is related to
the breaking of spin reversal symmetry in analogy to the time-reversal symmetry
breaking in the asymmetric Aharonov-Bohm (AB) ring.Comment: 10 pages, 11 figure
Freezing of parallel hard cubes with rounded edges
The freezing transition in a classical three-dimensional system of parallel
hard cubes with rounded edges is studied by computer simulation and
fundamental-measure density functional theory. By switching the rounding
parameter s from zero to one, one can smoothly interpolate between cubes with
sharp edges and hard spheres. The equilibrium phase diagram of rounded parallel
hard cubes is computed as a function of their volume fraction and the rounding
parameter s. The second order freezing transition known for oriented cubes at s
= 0 is found to be persistent up to s = 0.65. The fluid freezes into a
simple-cubic crystal which exhibits a large vacancy concentration. Upon a
further increase of s, the continuous freezing is replaced by a first-order
transition into either a sheared simple cubic lattice or a deformed
face-centered cubic lattice with two possible unit cells: body-centered
orthorhombic or base-centered monoclinic. In principle, a system of parallel
cubes could be realized in experiments on colloids using advanced synthesis
techniques and a combination of external fields.Comment: Submitted to JC
Long-Term Technology Assessment: Mortality, Hospitalization, and Work Loss Due to Peptic Ulcer and Gastritis/Duodenitis in the Federal Republic of Germany
Once the effects of short-term data analysis of new medical technology appear clear, additional or long-term analyses are infrequently performed on subsequent information. This often leads to incomplete understanding of the technology's full medical, social, and economic effects. Available data for the Federal Republic of Germany on mortality, hospitalization, and work loss due to gastric and duodenal ulcer and gastritis/duodenitis allowed long-term analysis of direct and indirect impacts on the population from 1975 through 1984. Mortality rates declined for all ages (Ï â€ 0.01) except for those age 75 and older, and nearly equally for all study diagnoses. Hospital discharge rates for all diagnoses rose slowly and steadily, while those for persons diagnosed with gastric ulcer, duodenal ulcer or gastritis/duodenitis declined sharply (Ï = 0.04). Declines of hospital discharges were greater for men than for women. The ongoing decline in rates of mortality and hospital discharges increased after 1977. Rates of work loss per 10,000 population-at-risk for study diagnoses were either stable or increasing until 1979, after which there was a marked decline (Ï = 0.03 for gastric ulcer, Ï = 0.02 for duodenal ulcer, Ï = 0.008 for gastritis/duodenitis). Work loss due to study diseases declined as a percentage of work loss for all diseases during the later study years. Only by examining many years' data could the accelerating declines be discerned, not only for mortality and hospitalizations, which have been examined before, but also for work loss, an infrequently analyzed effect of diseas
Dissipative Hydrodynamics and Heavy Ion Collisions
Recent discussions of RHIC data emphasized the exciting possibility that the
matter produced in nucleus-nucleus collisions shows properties of a
near-perfect fluid. Here, we aim at delineating the applicability of fluid
dynamics, which is needed to quantify the size of corresponding dissipative
effects. We start from the equations for dissipative fluid dynamics, which we
derive from kinetic theory up to second order (Israel-Stewart theory) in a
systematic gradient expansion. In model studies, we then establish that for too
early initialization of the hydrodynamic evolution (\tau_0 \lsim 1 fm/c) or
for too high transverse momentum (p_T \gsim 1 GeV) in the final state, the
expected dissipative corrections are too large for a fluid description to be
reliable. Moreover, viscosity-induced modifications of hadronic transverse
momentum spectra can be accommodated to a significant degree in an ideal fluid
description by modifications of the decoupling stage. We argue that these
conclusions, drawn from model studies, can also be expected to arise in
significantly more complex, realistic fluid dynamics simulations of heavy ion
collisions.Comment: 18 pages, 5 figures, uses revtex4; v2: references added, typos
correcte
Advanced magneto-optical microscopy: Imaging from picoseconds to centimeters - imaging spin waves and temperature distributions (invited)
© 2016 Author(s).Recent developments in the observation of magnetic domains and domain walls by wide-field optical microscopy based on the magneto-optical Kerr, Faraday, Voigt, and Gradient effect are reviewed. Emphasis is given to the existence of higher order magneto-optical effects for advanced magnetic imaging. Fundamental concepts and advances in methodology are discussed that allow for imaging of magnetic domains on various length and time scales. Time-resolved imaging of electric field induced domain wall rotation is shown. Visualization of magnetization dynamics down to picosecond temporal resolution for the imaging of spin-waves and magneto-optical multi-effect domain imaging techniques for obtaining vectorial information are demonstrated. Beyond conventional domain imaging, the use of a magneto-optical indicator technique for local temperature sensing is shown
On the Construction of Common Size, Value and Momentum Factors in International Stock Markets: A Guide with Applications
Demand is growing for a better understanding of how assets are priced in countries outside of the U.S. While financial data are available for many firms world-wide, it is important to have a reliable and replicable method of constructing high-quality systematic risk factors from these data. This paper first documents that appropriately screened data from Thomson Reuters Datastream and Thomson Reuters Worldscope can be used to replicate closely not only U.S. market returns and the corresponding momentum risk factor (as existing work has suggested), but also the widely-used U.S. size and value risk factors. We then build novel pan-European and country-specific momentum, size, and value risk factors. By comparing our pan-European market returns and risk factors with their counterparts in the U.S., we find that they are astonishingly highly correlated. The factors we compute are made available to other researchers.Risk factors; value, size, momentum, international equity markets, asset pricing anomalies
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