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We present a theory for plasmonic crystal instability in a semiconductor field-effect transistor with a dual grating gate, designed with strong asymmetry in the crystal elementary cell. Under the action of a dc current bias, we demonstrate that Bloch plasma waves in the resulting plasmonic crystal, formed in this transistor, develop the Dyakonov-Shur instability across the entire Brillouin zone. By calculating the energy spectrum of the plasmonic crystal and its instability increments, we analyze the dependence of the latter on the electron drift velocity and the extent of the structural asymmetry. Our results point to the possibility of exciting radiating steady-state plasma oscillations at room temperature, in transistors with asymmetric gate arrays that should be readily implementable via standard nanofabrication techniques. Long-range coherence of the unstable plasma oscillations, generated in the elementary cells of the crystal, should dramatically increase the radiated THz electromagnetic power, making this approach a promising pathway to the generation of THz signals., Comment: 17 pages, 3 figures

Radio Astronomy is undergoing a renaissance, as the next-generation of instruments provides a massive leap forward in collecting area and therefore raw sensitivity. However, to achieve this theoretical level of sensitivity in the science data products we need to address the much more pernicious systematic effects, which are the true limitation. These become all the more significant when we consider that much of the time used by survey instruments, such as the SKA, will be dedicated to deep surveys. CHILES is a deep HI survey of the COSMOS field, with 1,000 hours of VLA time. We present our approach for creating the image cubes from the first Epoch, with discussions of the methods and quantification of the data quality from 946 to 1420MHz -- a redshift range of 0.5 to 0. We layout the problems we had to solve and describe how we tackled them. These are of importance as CHILES is the first deep wideband multi-epoch HI survey and it has relevance for ongoing and future surveys. We focus on the accumulated systematic errors in the imaging, as the goal is to deliver a high-fidelity image that is only limited by the random thermal errors. To understand and correct these systematic effects we ideally manage them in the domain in which they arise, and that is predominately the visibility domain. CHILES is a perfect test bed for many of the issues we can expect for deep imaging with the SKA or ngVLA and we discuss the lessons we have learned., Comment: Accepted in AJ

In this study, the electrostatically induced quantum confinement structure, quantum point contact, has been realized in p-type trilayer tungsten diselenide-based van der Waals heterostructure with modified van der Waals contact method with degenerately doped transition metal dichalcogenide crystals. Clear quantized conductance and pinch-off state through the one-dimensional confinement were observed by dual-gating of split gate electrodes and top gate. Conductance plateaus were observed at step of 0.5 $\times$ 2e$^{2}$/h at zero and high magnetic field in addition to quarter plateaus at a finite bias voltage condition indicating the signature of spin-polarized quantum point contact realization., Comment: Paper:25 pages and 4 figures, SI: 13 pages and 10 figures, accepted for publication in Nano Letters

Deep networks are currently the state-of-the-art for sensory perception in autonomous driving and robotics. However, deep models often generate overconfident predictions precluding proper probabilistic interpretation which we argue is due to the nature of the SoftMax layer. To reduce the overconfidence without compromising the classification performance, we introduce a CNN probabilistic approach based on distributions calculated in the network's Logit layer. The approach enables Bayesian inference by means of ML and MAP layers. Experiments with calibrated and the proposed prediction layers are carried out on object classification using data from the KITTI database. Results are reported for camera ($RGB$) and LiDAR (range-view) modalities, where the new approach shows promising performance compared to SoftMax., Comment: Accepted at the Workshop on Perception for Autonomous Driving (PAD), European Conference on Computer Vision (ECCV) 2020

Mesoscopic conductance fluctuations are a ubiquitous signature of phase-coherent transport in small conductors, exhibiting universal character independent of system details. In this work, however, we demonstrate a pronounced breakdown of this universality, due to the interplay of local and remote phenomena in transport. Our experiments are performed in a graphene-based interaction-detection geometry, in which an artificial magnetic texture is induced in the graphene layer by covering a portion of it with a micromagnet. When probing conduction at some distance from this region, the strong influence of remote factors is manifested through the appearance of giant conductance fluctuations, with amplitude much larger than $e^2/h$. This violation of one of the fundamental tenets of mesoscopic physics dramatically demonstrates how local considerations can be overwhelmed by remote signatures in phase-coherent conductors

We present neutral hydrogen (HI) and ionized hydrogen (H${\alpha}$) observations of ten galaxies out to a redshift of 0.1. The HI observations are from the first epoch (178 hours) of the COSMOS HI Large Extragalactic Survey (CHILES). Our sample is HI biased and consists of ten late-type galaxies with HI masses that range from $1.8\times10^{7}$ M$_{\odot}$ to $1.1\times10^{10}$ M$_{\odot}$. We find that although the majority of galaxies show irregularities in the morphology and kinematics, they generally follow the scaling relations found in larger samples. We find that the HI and H${\alpha}$ velocities reach the flat part of the rotation curve. We identify the large-scale structure in the nearby CHILES volume using DisPerSE with the spectroscopic catalog from SDSS. We explore the gaseous properties of the galaxies as a function of location in the cosmic web. We also compare the angular momentum vector (spin) of the galaxies to the orientation of the nearest cosmic web filament. Our results show that galaxy spins tend to be aligned with cosmic web filaments and show a hint of a transition mass associated with the spin angle alignment., Comment: 24 pages, 25 figures, 6 tables, accepted for publication in MNRAS

The differential conductance of graphene is shown to exhibit a zero-bias anomaly at low temperatures, arising from a suppression of the quantum corrections due to weak localization and electron interactions. A simple rescaling of these data, free of any adjustable parameters, shows that this anomaly exhibits a universal, temperature- ($T$) independent form. According to this, the differential conductance is approximately constant at small voltages ($V

Investigations of the origin and evolution of the Milky Way disk have long relied on chemical and kinematic identification of its components to reconstruct our Galactic past. Difficulties in determining precise stellar ages have restricted most studies to small samples, normally confined to the solar neighbourhood. Here we break this impasse with the help of asteroseismic inference and perform a chronology of the evolution of the disk throughout the age of the Galaxy. We chemically dissect the Milky Way disk population using a sample of red giant stars spanning out to 2~kpc in the solar annulus observed by the {\it Kepler} satellite, with the added dimension of asteroseismic ages. Our results reveal a clear difference in age between the low- and high-$\alpha$ populations, which also show distinct velocity dispersions in the $V$ and $W$ components. We find no tight correlation between age and metallicity nor [$\alpha$/Fe] for the high-$\alpha$ disk stars. Our results indicate that this component formed over a period of more than 2~Gyr with a wide range of [M/H] and [$\alpha$/Fe] independent of time. Our findings show that the kinematic properties of young $\alpha$-rich stars are consistent with the rest of the high-$\alpha$ population and different from the low-$\alpha$ stars of similar age, rendering support to their origin being old stars that went through a mass transfer or stellar merger event, making them appear younger, instead of migration of truly young stars formed close to the Galactic bar., Comment: 15 pages, 16 figures, MNRAS accepted

APOGEE-2 is a high-resolution, near-infrared spectroscopic survey observing roughly 300,000 stars across the entire sky. It is the successor to APOGEE and is part of the Sloan Digital Sky Survey IV (SDSS-IV). APOGEE-2 is expanding upon APOGEE's goals of addressing critical questions of stellar astrophysics, stellar populations, and Galactic chemodynamical evolution using (1) an enhanced set of target types and (2) a second spectrograph at Las Campanas Observatory in Chile. APOGEE-2 is targeting red giant branch (RGB) and red clump (RC) stars, RR Lyrae, low-mass dwarf stars, young stellar objects, and numerous other Milky Way and Local Group sources across the entire sky from both hemispheres. In this paper, we describe the APOGEE-2 observational design, target selection catalogs and algorithms, and the targeting-related documentation included in the SDSS data releases., Comment: 19 pages, 6 figures. Accepted to AJ

In the updated APOGEE-Kepler catalog, we have asteroseismic and spectroscopic data for over 3000 first ascent red giants. Given the size and accuracy of this sample, these data offer an unprecedented test of the accuracy of stellar models on the post-main-sequence. When we compare these data to theoretical predictions, we find a metallicity dependent temperature offset with a slope of around 100 K per dex in metallicity. We find that this effect is present in all model grids tested and that theoretical uncertainties in the models, correlated spectroscopic errors, and shifts in the asteroseismic mass scale are insufficient to explain this effect. Stellar models can be brought into agreement with the data if a metallicity dependent convective mixing length is used, with $ \Delta\alpha_{\rm ML, YREC} \sim 0.2$ per dex in metallicity, a trend inconsistent with the predictions of three dimensional stellar convection simulations. If this effect is not taken into account, isochrone ages for red giants from the Gaia data will be off by as much as a factor of 2 even at modest deviations from solar metallicity ([Fe/H]=$-$0.5)., Comment: 13 pages, 10 figures. Accepted for publication in the Astrophysical Journal. For a brief video discussing key results from this paper see https://www.youtube.com/watch?v=cV_0AhPAIRo . The data and models used in this paper are available at http://www.astronomy.ohio-state.edu/~tayar/MixingLength.htm

In this theoretical study, we explore the manner in which the quantum correction due to weak localization is suppressed in weakly-disordered graphene, when it is subjected to the application of a non-zero voltage. Using a nonequilibrium Green function approach, we address the scattering generated by the disorder up to the level of the maximally crossed diagrams, hereby capturing the interference among different, impurity-defined, Feynman paths. Our calculations of the charge current, and of the resulting differential conductance, reveal the logarithmic divergence typical of weak localization in linear transport. The main finding of our work is that the applied voltage suppresses the weak localization contribution in graphene, by introducing a dephasing time that decreases inversely with increasing voltage., Comment: Content contained in the theory section of arXiv:1802.09922

A critical aspect of quantum mechanics is the nonlocal nature of the wavefunction, a characteristic that may yield unexpected coupling of nominally-isolated systems. The capacity to detect this coupling can be vital in many situations, especially those in which its strength is weak. In this work we address this problem in the context of mesoscopic physics, by implementing an electron-wave realization of a Fano interferometer using pairs of coupled quantum point contacts (QPCs). Within this scheme, the discrete level required for a Fano resonance is provided by pinching off one of the QPCs, thereby inducing the formation of a quasi-bound state at the center of its self-consistent potential barrier. Using this system, we demonstrate a form of \textit{nonequilibrium} Fano resonance (NEFR), in which nonlinear electrical biasing of the interferometer gives rise to pronounced distortions of its Fano resonance. Our experimental results are captured well by a quantitative theoretical model, which considers a system in which a standard two-path Fano interferometer is coupled to an additional, \textit{intruder}, continuum. According to this theory, the observed distortions in the Fano resonance arise \textit{only} in the presence of coupling to the intruder, indicating that the NEFR provides a sensitive means to infer the presence of weak coupling between mesoscopic systems., Comment: 13 pages, 6 figures, published version

We present the stellar kinematics across the Galactic bulge and into the disk at positive longitudes from the SDSS-III APOGEE spectroscopic survey of the Milky Way. APOGEE includes extensive coverage of the stellar populations of the bulge along the mid-plane and near-plane regions. From these data, we have produced kinematic maps of 10,000 stars across longitudes 0 deg < l < 65 deg, and primarily across latitudes of |b| < 5 deg in the bulge region. The APOGEE data reveal that the bulge is cylindrically rotating across all latitudes and is kinematically hottest at the very centre of the bulge, with the smallest gradients in both kinematic and chemical space inside the inner-most region (l,|b|) < (5,5) deg. The results from APOGEE show good agreement with data from other surveys at higher latitudes and a remarkable similarity to the rotation and dispersion maps of barred galaxies viewed edge on. The thin bar that is reported to be present in the inner disk within a narrow latitude range of |b| < 2 deg appears to have a corresponding signature in [Fe/H] and [alpha/Fe]. Stars with [Fe/H] > -0.5 have dispersion and rotation profiles that are similar to that of N-body models of boxy/peanut bulges. There is a smooth kinematic transition from the thin bar and boxy bulge (l,|b|) < (15,12) deg out into the disk for stars with [Fe/H] > -1.0, and the chemodynamics across (l,b) suggests the stars in the inner Galaxy with [Fe/H] > -1.0 have an origin in the disk., Comment: Accepted by ApJ 15 December 2015

This Report explores recent advances in our understanding of the physics of open quantum systems (OQSs) which consist of some localized region that is coupled to an external environment. Examples of such systems may be found in numerous areas of physics including mesoscopic physics that provides the main focus of this review. We provide a detailed discussion of the behavior of OQSs in terms of the projection-operator formalism, according to which the system under study is considered to be comprised of a localized region ($Q$), embedded into a well-defined environment ($P$) of scattering wavefunctions (with $Q+P=1$). The $Q$ subspace must be treated using the concepts of non-Hermitian physics, and of particular interest here is: the capacity of the environment to mediate a coupling between the different states of $Q$; the role played by the presence of exceptional points (EPs) in the spectra of OQSs; the influence of EPs on the rigidity of the wavefunction phases, and; the ability of EPs to initiate a dynamical phase transition (DPT). DPTs occur when the quantum dynamics of the open system causes transitions between non-analytically connected states, as a function of some external control parameter. In addition to discussing experiments on mesoscopic quantum point contacts, we also review manifestations of DPTs in mesoscopic devices and other systems. Other possible manifestations of this phenomenon are presented. From these discussions a generic picture of OQSs emerges in which the environmentally-mediated coupling between different quantum states plays a critical role in governing the system behavior., Comment: Title changed; 1 reference added; published Rep. Progr. Phys. 78 (2015) 114001 (37pp); here: Abstract (full length), Introduction (including 1 figure), Conclusions, References

A large reverberation mapping study of the Seyfert 1 galaxy NGC 7469 has yielded emission-line lags for Hbeta 4861 and He II 4686 and a central black hole mass measurement of about 10 million solar masses, consistent with previous measurements. A very low level of variability during the monitoring campaign precluded meeting our original goal of recovering velocity-delay maps from the data, but with the new Hbeta measurement, NGC 7469 is no longer an outlier in the relationship between the size of the Hbeta-emitting broad-line region and the AGN luminosity. It was necessary to detrend the continuum and Hbeta and He II 4686 line light curves and those from archival UV data for different time-series analysis methods to yield consistent results., Comment: 9 Pages, 7 figures, 6 tables. Accepted for publication in The Astrophysical Journal

Through a combination of experiment and theory we establish the possibility of achieving strong tuning of Fano resonances (FRs), by allowing their usual two-path geometry to interfere with an additional, 'intruder', continuum. As the coupling strength to this intruder is varied, we predict strong modulations of the resonance line shape that, in principle at least, may exceed the amplitude of the original FR itself. For a proof-of-concept demonstration of this phenomenon, we construct a nanoscale interferometer from nonlocally coupled quantum point contacts and utilize the unique features of their density of states to realize the intruder. External control of the intruder coupling is enabled by means of an applied magnetic field, in the presence of which we demonstrate the predicted distortions of the FR. This general scheme for resonant control should be broadly applicable to a variety of wave-based systems, opening up the possibility of new applications in areas such as chemical and biological sensing and secure communications., Comment: 19 pages, 4 figures

We have performed magnetotransport measurements on a multi-layer graphene flake. At the crossing magnetic field Bc, an approximately temperature-independent point in the measured longitudinal resistivity, which is ascribed to the direct insulator-quantum Hall (I-QH) transition, is observed. By analyzing the amplitudes of the magnetoresistivity oscillations, we are able to measure the quantum mobility of our device. It is found that at the direct I-QH transition, the product of the quantum mobility and is about 0.37 which is considerably smaller than 1. In contrast, at Bc, the longitudinal resistivity is close to the Hall resistivity, i.e., the product of the classical mobility and the crossing field is about 1. Therefore our results suggest that different mobilities need to be introduced for the direct I-QH transition observed in multi-layered graphene. Combined with existing experimental results obtained in various material systems, our data obtained on graphene suggest that the direct I-QH transition is a universal effect in 2D., Comment: 4 figures