Structure in the Disk of epsilon Aurigae: Analysis of the ARCES and TripleSpec data obtained during the 2010 eclipse

Context: Worldwide interest in the recent eclipse of epsilon Aurigae resulted in the generation of several extensive data sets, including those related to high resolution spectroscopic monitoring. This lead to the discovery, among other things, of the existence of a mass transfer stream, seen notably during third contact. Aims: We explored spectroscopic facets of the mass transfer stream during third contact, using high resolution spectra obtained with the ARCES and TripleSpec instruments at Apache Point Observatory. Methods: One hundred and sixteen epochs of data between 2009 and 2012 were obtained, and equivalent widths and line velocities measured, selected according to reports of these being high versus low eccentricity disk lines. These datasets also enable greater detail to be measured of the mid-eclipse enhancement of the He I 10830A line, and the discovery of the P Cygni shape of the Pa beta line at third contact. Analysis: We found evidence of higher speed material, associated with the mass transfer stream, persisting between third and fourth eclipse contacts. We visualize the disk and stream interaction using SHAPE software, and use CLOUDY software to estimate that the source of the enhanced He I 10830A absorption arises from a region with log n = 10 (/cm3) and temperature of 20,000 K consistent with a mid B type central star. Results and Next Steps: Van Rensbergen binary star evolutionary models are somewhat consistent with the current binary parameters for the case of a 9 plus 8 solar mass initial binary, evolving into a 2.3 and 14.11 solar mass end product after 35 Myr. Prior to the next eclipse, it is possible to make predictions which suggest that continued monitoring will help resolve standing questions about this binary

Semiclassical description of resonant tunneling

We derive a semiclassical formula for the tunneling current of electrons trapped in a potential well which can tunnel into and across a wide quantum well. The calculations idealize an experimental situation where a strong magnetic field tilted with respect to an electric field is used. The resulting semiclassical expression is written as the sum over special periodic orbits which hit both walls of the quantum well and are perpendicular to the first wall.Comment: LaTeX, 8 page

Nuclear data for fusion: Validation of typical pre-processing methods for radiation transport calculations

AbstractNuclear data form the basis of the radiation transport codes used to design and simulate the behaviour of nuclear facilities, such as the ITER and DEMO fusion reactors. Typically these data and codes are biased towards fission and high-energy physics applications yet are still applied to fusion problems. With increasing interest in fusion applications, the lack of fusion specific codes and relevant data libraries is becoming increasingly apparent. Industry standard radiation transport codes require pre-processing of the evaluated data libraries prior to use in simulation. Historically these methods focus on speed of simulation at the cost of accurate data representation. For legacy applications this has not been a major concern, but current fusion needs differ significantly. Pre-processing reconstructs the differential and double differential interaction cross sections with a coarse binned structure, or more recently as a tabulated cumulative distribution function. This work looks at the validity of applying these processing methods to data used in fusion specific calculations in comparison to fission. The relative effects of applying this pre-processing mechanism, to both fission and fusion relevant reaction channels are demonstrated, and as such the poor representation of these distributions for the fusion energy regime. For the natC(n,el) reaction at 2.0MeV, the binned differential cross section deviates from the original data by 0.6% on average. For the 56Fe(n,el) reaction at 14.1MeV, the deviation increases to 11.0%. We show how this discrepancy propagates through to varying levels of simulation complexity. Simulations were run with Turnip-MC and the ENDF-B/VII.1 library in an effort to define a new systematic error for this range of applications. Alternative representations of differential and double differential distributions are explored in addition to their impact on computational efficiency and relevant simulation results

Confined magnetic guiding orbit states

We show how snake-orbit states which run along a magnetic edge can be confined electrically. We consider a two-dimensional electron gas (2DEG) confined into a quantum wire, subjected to a strong perpendicular and steplike magnetic field $B/-B$. Close to this magnetic step new, spatially confined bound states arise as a result of the lateral confinement and the magnetic field step. The number of states, with energy below the first Landau level, increases as $B$ becomes stronger or as the wire width becomes larger. These bound states can be understood as an interference between two counter-propagating one-dimensional snake-orbit states.Comment: 4 pages, 4 figure

Social learning: Public information in insects

Although it has received less coverage than in vertebrates, the study of insect social learning has a rich history with spectacular examples of how individuals extract knowledge from other animals. Several new studies on crickets and social bees have now shown how insects can adjust their behaviour adaptively by making use of cues generated inadvertently by other individuals

Decay of quantised vorticity by sound emission

It is thought that in a quantum fluid sound generation is the ultimate sink of turbulent kinetic energy in the absence of any other dissipation mechanism near absolute zero. We show that a suitably trapped Bose-Einstein condensate provides a model system to study the sound emitted by accelerating vortices in a controlled way.Comment: 6 pages, 3 figure

Onset voltage shift due to non-zero Landau ground state level in coherent magnetotransport

Coherent electron transport in double-barrier heterostructures with parallel electric and magnetic fields is analyzed theoretically and with the aid of a quantum simulator accounting for 3-dimensional transport effects. The onset-voltage shift induced by the magnetic field in resonant tunneling diodes, which was previously attributed to the cyclotron frequency $w_c$ inside the well is found to arise from an upward shift of the non-zero ground (lowest) Landau state energy in the entire quantum region where coherent transport takes place. The spatial dependence of the cyclotron frequency is accounted for and verified to have a negligible impact on resonant tunneling for the device and magnetic field strength considered. A correction term for the onset-voltage shift arising from the magnetic field dependence of the chemical potential is also derived. The Landau ground state with its nonvanishing finite harmonic oscillator energy $\hbar w_c /2$ is verified however to be the principal contributor to the onset voltage shift at low temperatures.Comment: 13 pages, and 3 figures. Accepted for publication in Phys. Rev.

Conspecific and Heterospecific Information Use in Bumblebees

Heterospecific social learning has been understudied in comparison to interactions between members of the same species. However, the learning mechanisms behind such information use can allow animals to be flexible in the cues that are used. This raises the question of whether conspecific cues are inherently more influential than cues provided by heterospecifics, or whether animals can simply use any cue that predicts fitness enhancing conditions, including those provided by heterospecifics. To determine how freely social information travels across species boundaries, we trained bumblebees (Bombus terrestris) to learn to use cues provided by conspecifics and heterospecific honey bees (Apis mellifera) to locate valuable floral resources. We found that heterospecific demonstrators did not differ from conspecifics in the extent to which they guided observers' choices, whereas various types of inorganic visual cues were consistently less effective than conspecifics. This was also true in a transfer test where bees were confronted with a novel flower type. However, in the transfer test, conspecifics were slightly more effective than heterospecific demonstrators. We then repeated the experiment with entirely naïve bees that had never foraged alongside conspecifics before. In this case, heterospecific demonstrators were equally efficient as conspecifics both in the initial learning task and the transfer test. Our findings demonstrate that social learning is not a unique process limited to conspecifics and that through associative learning, interspecifically sourced information can be just as valuable as that provided by conspecific individuals. Furthermore the results of this study highlight potential implications for understanding competition within natural pollinator communities

Magnetic Quantum Dot: A Magnetic Transmission Barrier and Resonator

We study the ballistic edge-channel transport in quantum wires with a magnetic quantum dot, which is formed by two different magnetic fields B^* and B_0 inside and outside the dot, respectively. We find that the electron states located near the dot and the scattering of edge channels by the dot strongly depend on whether B^* is parallel or antiparallel to B_0. For parallel fields, two-terminal conductance as a function of channel energy is quantized except for resonances, while, for antiparallel fields, it is not quantized and all channels can be completely reflected in some energy ranges. All these features are attributed to the characteristic magnetic confinements caused by nonuniform fields.Comment: 4 pages, 4 figures, to be published in Physical Review Letter