13,335 research outputs found
The photovoltaic properties of an Al In As/InP heterojunctions grown by LPE method
Work is presented on heterojunction solar cells which were studied under the NASA/Arizona State University intern program. The heterojunction solar cells were fabricated by the liquid phase epitaxy method. The basic conversion efficiency was measured at 5 percent. It was determined that a thicker epilayer is needed, and that the density of recombination center should be reduced to give a smaller saturation current and hence a larger open-circuit voltage
A Large Deviation Rate and Central Limit Theorem for Horton Ratios
Although originating in hydrology, the classical Horton analysis is based on a geometric progression that is widely used in the empirical analysis of branching patterns found in biology, atmospheric science, plant pathology, etc., and more recently in tree register allocation in computer science. The main results of this paper are a large deviation rate and a central limit theorem for Horton bifurcation ratios in a standard network model. The methods are largely self-contained. In particular, derivations of some previously known results of the theory are indicated along the way
Pooling, Separating, and Cream-Skimming In Relative-Performance Contracts
Existing research on tournament-style contests suggests that mechanisms to sort contestants by ability level are unnecessary in the case of linear relative-performance contracts. This paper suggests that this result stems from uniform treatment of workers' marginal returns from effort, marginal disutilities of effort, and reservation wages. Here, we investigate relative-performance contracts with a model that allows these three factors to vary by growers' unobservable ability. Given this framework, we find that it is possible for processors to improve expected profits and total expected welfare by replacing a single contract offering meant to pool all growers with an offering of two contracts meant to separate growers by ability. Under some circumstances, a "cream-skimming" contract offering designed to attract only workers above a minimum ability level can also improve expected profits.Production Economics,
Domain wall formation in late-time phase transitions
We examine domain wall formulation in late time phase transitions. We find that in the invisible axion domain wall phenomenon, thermal effects alone are insufficient to drive different parts of the disconnected vacuum manifold. This suggests that domain walls do not form unless either there is some supplemental (but perhaps not unreasonable) dynamics to localize the scalar field responsible for the phase transition to the low temperature maximum (to an extraordinary precision) before the onset of the phase transition, or there is some non-thermal mechanism to produce large fluctuations in the scalar field. The fact that domain wall production is not a robust prediction of late time transitions may suggest future directions in model building
Symmetric Gapped Interfaces of SPT and SET States: Systematic Constructions
Symmetry protected topological (SPT) states have boundary 't Hooft anomalies
that obstruct an effective boundary theory realized in its own dimension with
UV completion and an on-site -symmetry. In this work, yet we show that a
certain anomalous non-on-site symmetry along the boundary becomes on-site
when viewed as an extended symmetry, via a suitable group extension . Namely, a non-perturbative global (gauge/gravitational)
anomaly in becomes anomaly-free in . This guides us to construct exactly
soluble lattice path integral and Hamiltonian of symmetric gapped boundaries,
always existent for any SPT state in any spacetime dimension of any
finite symmetry group, including on-site unitary and anti-unitary time-reversal
symmetries. The resulting symmetric gapped boundary can be described either by
an -symmetry extended boundary of bulk , or more naturally by a
topological emergent -gauge theory with a global symmetry on a 3+1D bulk
or above. The excitations on such a symmetric topologically ordered boundary
can carry fractional quantum numbers of the symmetry , described by
representations of . (Apply our approach to a 1+1D boundary of 2+1D bulk, we
find that a deconfined gauge boundary indeed has spontaneous symmetry breaking
with long-range order. The deconfined symmetry-breaking phase crosses over
smoothly to a confined phase without a phase transition.) In contrast to known
gapped interfaces obtained via symmetry breaking (either global symmetry
breaking or Anderson-Higgs mechanism for gauge theory), our approach is based
on symmetry extension. More generally, applying our approach to SPT,
topologically ordered gauge theories and symmetry enriched topologically
ordered (SET) states, leads to generic boundaries/interfaces constructed with a
mixture of symmetry breaking, symmetry extension, and dynamical gauging.Comment: 144 pages, 29 figures, 22 tables. v3: Refinement/Refs added.
Un/Trimmed version on arXiv/PR
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