Nonlinear transport and oscillating magnetoresistance in double quantum wells

We study the evolution of low-temperature magnetoresistance in double quantum wells in the region below 1 Tesla as the applied current density increases. A flip of the magneto-intersubband oscillation peaks, which occurs as a result of the current-induced inversion of the quantum component of resistivity, is observed. We also see splitting of these peaks as another manifestation of nonlinear behavior, specific for the two-subband electron systems. The experimental results are quantitatively explained by the theory based on the kinetic equation for the isotropic non-equilibrium part of electron distribution function. The inelastic scattering time is determined from the dependence of the inversion magnetic field on the current.Comment: 20 pages, 10 figure

Experimental violation of a spin-1 Bell inequality using maximally-entangled four-photon states

We demonstrate the first experimental violation of a spin-1 Bell inequality. The spin-1 inequality is a calculation based on the Clauser, Horne, Shimony and Holt formalism. For entangled spin-1 particles the maximum quantum mechanical prediction is 2.552 as opposed to a maximum of 2, predicted using local hidden variables. We obtained an experimental value of 2.27 $\pm 0.02$ using the four-photon state generated by pulsed, type-II, stimulated parametric down-conversion. This is a violation of the spin-1 Bell inequality by more than 13 standard deviations.Comment: 5 pages, 3 figures, Revtex4. Problem with figures resolve

Experimental Polarization State Tomography using Optimal Polarimeters

We report on the experimental implementation of a polarimeter based on a scheme known to be optimal for obtaining the polarization vector of ensembles of spin-1/2 quantum systems, and the alignment procedure for this polarimeter is discussed. We also show how to use this polarimeter to estimate the polarization state for identically prepared ensembles of single photons and photon pairs and extend the method to obtain the density matrix for generic multi-photon states. State reconstruction and performance of the polarimeter is illustrated by actual measurements on identically prepared ensembles of single photons and polarization entangled photon pairs

Comparison between disordered quantum spin 1/2 chains

We study the magnetic properties of two types of one dimensional XX spin 1/2 chains. The first type has only nearest neighbor interactions which can be either antiferromagnetic or ferromagnetic and the second type which has both nearest neighbor and next nearest neighbor interactions, but only antiferromagnetic in character. We study these systems in the presence of low transverse magnetic fields both analytically and numerically. Comparison of results show a close relation between the two systems, which is in agreement with results previously found in Heisenberg chains by means of a numerical real space renormalization group procedure.Comment: 7 page

Riodinid butterfly fauna (Lepidoptera) of the Cosñipata Region, Peru: Annotated checklist, community structure, and contrast with Lycaenidae

A team of experienced lepidopterists sampled the butterfly fauna of Peru’s Cosñipata Region from 400 to 4,000 m elevation for more than a decade (7,440 field person-hours) and supplemented this sam­ple with data from museum specimens and the scientific literature. An annotated checklist of Cosñipata Riodinidae (Lepidoptera: Papilionoidea) documents 398 species, which represents 29% of the world Rio­dinidae fauna. For each, it lists sample abundance, adult behavior, elevation, and temporal distribution. In the fieldwork sample, 75 species (20.9%) were sampled once and 39 (9.8%) were not encountered (collected or imaged by others). A riodinid species of median abundance was sampled an average of once every 826 field person-hours. Sampled sex ratios were 81.2% male, but were not statistically higher in species in which male perching behavior was observed. We document examples of conspicuous geographic variation in the time of male perching behavior. Species richness is greatest at low elevation and at the transition between the dry and wet seasons. There is little evidence that the community is composed of species restricted to narrow elevational bands or restricted in the adult stage to a single season. Compared with Lycaenidae, Riodinidae are significantly more restricted to lowland habitats and were sampled 2.5 times as frequently with a mean number of individuals per species more than twice as great as that of Lycaenidae

A remarkable new butterfly species from western Amazonia (Lepidoptera, Nymphalidae, Satyrinae)

A distinctive new species of butterfly in the subtribe Euptychiina (Nymphalidae: Satyrinae), which is widespread throughout the upper Amazon in Colombia, Ecuador and Peru, is here described. The species is provisionally placed in the genus Magneuptychia Forster, 1964, although this is likely to change as the higher level taxonomy of Euptychiina is resolved and the genus is reviewed in detail.Authorisation has been given for this article to be loaded into the NHM repository (email A. Quevedo, Executive Director of ProAves, 17.1.2017). The attached file is the published version

Measurement of miniband parameters of a doped superlattice by photoluminescence in high magnetic fields

We have studied a 50/50\AA superlattice of GaAs/Al$_{0.21}$Ga$_{0.79}$As composition, modulation-doped with Si, to produce $n=1.4\times 10^{12}$ cm$^{-2}$ electrons per superlattice period. The modulation-doping was tailored to avoid the formation of Tamm states, and photoluminescence due to interband transitions from extended superlattice states was detected. By studying the effects of a quantizing magnetic field on the superlattice photoluminescence, the miniband energy width, the reduced effective mass of the electron-hole pair, and the band gap renormalization could be deduced.Comment: minor typing errors (minus sign in eq. (5)

Resonance oscillations of magnetoresistance in double quantum wells

We present experimental and theoretical studies of the magnetoresistance oscillations induced by resonance transitions of electrons between tunnel-coupled states in double quantum wells. The suppression of these oscillations with increasing temperature is irrelevant to the thermal broadening of the Fermi distribution and reflects the temperature dependence of the quantum lifetime of electrons. The gate control of the period and amplitude of the oscillations is demonstrated.Comment: 5 pages 4 figures, to be published in the Physical Review

Underground mine scheduling under uncertainty

17 USC 105 interim-entered record; under review.The article of record as published may be found at http://dx.doi.org/10.1016/j.ejor.2021.01.011Underground mine schedules seek to determine start dates for activities related to the extraction of ore, often with an objective of maximizing net present value; constraints enforce geotechnical precedence between activities, and restrict resource consumption on a per-time-period basis, e.g., development footage and extracted tons. Strategic schedules address these start dates at a coarse level, whereas tactical schedules must account for the day-to-day variability of underground mine operations, such as unanticipated equipment breakdowns and ground conditions, both of which might slow production. At the time of this writing, the underground mine scheduling literature is dominated by a deterministic treatment of the problem, usually modeled as a Resource Constrained Project Scheduling Problem (RCPSP), which precludes mine operators from reacting to unforeseen circumstances. Therefore, we propose a stochastic integer programming framework that: (i) characterizes uncertainty in duration and economic value for each underground mining activity; (ii) formulates a new stochastic variant of the RCPSP; (iii) suggests an optimization-based heuristic; and, (iv) produces implementable, tactical schedules in a practical amount of time and provides corresponding managerial insights.National Institute of Occupational Safety and HealthNational Agency for Research and Development (ANID