Large thermoelectric power and figure of merit in a ferromagnetic-quantum dot-superconducting device

We investigate the thermoelectric properties of a quantum dot coupled to ferromagnetic and superconducting electrodes. The combination of spin polarized tunneling at the ferromagnetic-quantum dot interface and the application of an external magnetic field that Zeeman splits the dot energy level leads to large values of the thermopower (Seebeck coefficient). Importantly, the thermopower can be tuned with an external gate voltage connected to the dot. We compute the figure of merit that measures the efficiency of thermoelectric conversion and find that it attains high values. We discuss the different contributions from Andreev reflection processes and quasiparticle tunneling into and out of the superconducting contact. Furthermore, we obtain dramatic variations of both the magnetothermopower and the spin Seebeck effect, which suggest that in our device spin currents can be controlled with temperature gradients only.Comment: 9 pages, 6 figure

Thermoelectric effects in quantum Hall systems beyond linear response

We consider a quantum Hall system with an antidot acting as an energy dependent scatterer. In the purely charge case, we find deviations from the Wiedemann-Franz law that take place in the nonlinear regime of transport. We also discuss Peltier effects beyond linear response and describe both effects using magnetic-field asymmetric transport coefficients. For the spin case such as that arising along the helical edge states of a two-dimensional topological insulator, we investigate the generation of spin currents as a result of applied voltage and temperature differences in samples attached to ferromagnetic leads. We find that in the parallel configuration the spin current can be tuned with the leads' polarization even in the linear regime of transport. In contrast, for antiparallel magnetizations the spin currents has a strict nonlinear dependence on the applied fields.Comment: 17 pages, 8 figure

Cross thermoelectric coupling in normal-superconductor quantum dots

We discuss the nonlinear current of an interacting quantum dot coupled to normal and superconducting reservoirs with applied voltage and temperature differences. Due to the particle-hole symmetry introduced by the superconducting lead, the pure (subgap) thermoelectric response vanishes. However, we show that the Andreev bound states shift as the thermal gradient increases. As a consequence, the $I$--$V$ characteristic can be tuned with a temperature bias if the system is simultaneously voltage biased. This is a cross effect that occurs beyond linear response only. Furthermore, we emphasize the role of quasiparticle tunneling processes in the generation of high thermopower sensitivities.Comment: 6 pages, 5 figure

Effects of Degeneration and Load History on Nucleus Pulposus Behavior

The nucleus pulposus (NP) plays a critical role in resisting loads placed on the spine, and therefore, the intervertebral disc. The function of the NP is to generate a hydrostatic pressure to evenly disperse the load within the disc. This ability hinges on the hydration of the disc, which is affected by age, health and even prior load history. This dissertation aims to elucidate key points about how the disc functions and reacts, both mechanically and biologically, to different sets of axial loading. We demonstrate our ability to create a degenerate disc model using trans-annular puncture in caudal rat discs and verify using viscoelastic analysis and histologic examination. Using a custom miniature fiber-optic pressure sensor, we determined the loss of pressurization in a degenerate versus a healthy disc. This compromised ability to generate an intradiscal pressure is essential, and indicates that a degenerate disc inadequately distributes the load and may lead to pain, injury and lack of function. We then investigated the influence of load history on the NP. Using a preload placed on a disc beforehand, we change the hydrated state of the disc before the exertion load is applied. The viscoelastic creep response was analyzed and showed changes due to the addition of the preload. We also directly observed this change by using the miniature pressure sensors to measure intradiscal pressure during the loading regime. To further track changes caused by the introduction of a preload, we examined the gene expression of several associated extracellular matrix proteins after loading. The results demonstrate changing gene expression contrary to the expected outcome, given the understood pressurized cellular environment. We speculate that instead of a hydrostatic pressure driven response, the tonic environment dictated genetic upregulation. Using collaborative efforts, we assessed the ability to use Pneumatic Artificial Muscles as the actuating element in a long term loading device for caudal rat discs. In conclusion, we gathered new reactions from the NP given a variety of changed states, both diseased and loaded. Our new findings will help complete the picture to fully understand how the disc functions, specifically the response of the N

Quasi-Freestanding Multilayer Graphene Films on the Carbon Face of SiC

The electronic band structure of as-grown and doped graphene grown on the carbon face of SiC is studied by high-resolution angle-resolved photoemission spectroscopy, where we observe both rotations between adjacent layers and AB-stacking. The band structure of quasi-freestanding AB- bilayers is directly compared with bilayer graphene grown on the Si-face of SiC to study the impact of the substrate on the electronic properties of epitaxial graphene. Our results show that the C-face films are nearly freestanding from an electronic point of view, due to the rotations between graphene layers.Comment: http://link.aps.org/doi/10.1103/PhysRevB.81.24141

Improved Combinatorial Group Testing Algorithms for Real-World Problem Sizes

We study practically efficient methods for performing combinatorial group testing. We present efficient non-adaptive and two-stage combinatorial group testing algorithms, which identify the at most d items out of a given set of n items that are defective, using fewer tests for all practical set sizes. For example, our two-stage algorithm matches the information theoretic lower bound for the number of tests in a combinatorial group testing regimen.Comment: 18 pages; an abbreviated version of this paper is to appear at the 9th Worksh. Algorithms and Data Structure

Exact non-linear equations for cosmological perturbations

We present a complete set of exact and fully non-linear equations describing all three types of cosmological perturbations -- scalar, vector and tensor perturbations. We derive the equations in a thoroughly gauge-ready manner, so that any spatial and temporal gauge conditions can be employed. The equations are completely general without any physical restriction except that we assume a flat homogeneous and isotropic universe as a background. We also comment briefly on the application of our formulation to the non-expanding Minkowski background.Comment: (v1) 10 pages, 1 table; (v2) important update to employ any spatial gauge condition; (v3) more discussions, to appear in Journal of Cosmology and Astroparticle Physic

Cheese Flavor Development in Ultrafiltered Whole Milk Concentrates

The development of cheese flavor in ultrafiltered whole milk retentates was investigated. Acidified (pH 5.7) pasteurized whole milk was concentrated to 21% fat, 17% protein and 41% total solids, and then divided into six lots. Each lot was subdivided into three groups of two samples each. Each group was inoculated with one of three lactic cultures -- Streptococcus lactis C6 , commercial mixed concentrated Marschall\u27s MD294S or CCI299S. One sample in each group was treated with rennet and the other sample left rennet free. All samples were incubated at 30 C until the pH reached 5.2-5.1. Each of the fermented retentates was further divided into 12 samples. Six of them were incubated at 22 C and the other six at 30 C. After two weeks incubation, the samples were evaluated for flavor quality, body quality and flavor intensity. A similar analysis was conducted after two weeks for a total incubation period of four weeks. The effects of culture, rennet and incubation temperature on product quality were determined. Rennet and temperature were the only factors with significant impact on flavor intensity or body and flavor quality. No significant effects were attributed to the lactic cultures, although bitterness was more frequently found in retentates fermented with culture C6. Samples containing rennet and ripened at 30 C developed the highest levels of soluble nitrogen (23-25% of total nitrogen) but had the poorest flavor intensity, flavor quality and body quality. Samples without rennet and ripened at 22 Chad the lowest levels of soluble nitrogen (13-18% of total nitrogen), and the most satisfactory organoleptic scores

Full Resolution Image Compression with Recurrent Neural Networks

This paper presents a set of full-resolution lossy image compression methods based on neural networks. Each of the architectures we describe can provide variable compression rates during deployment without requiring retraining of the network: each network need only be trained once. All of our architectures consist of a recurrent neural network (RNN)-based encoder and decoder, a binarizer, and a neural network for entropy coding. We compare RNN types (LSTM, associative LSTM) and introduce a new hybrid of GRU and ResNet. We also study "one-shot" versus additive reconstruction architectures and introduce a new scaled-additive framework. We compare to previous work, showing improvements of 4.3%-8.8% AUC (area under the rate-distortion curve), depending on the perceptual metric used. As far as we know, this is the first neural network architecture that is able to outperform JPEG at image compression across most bitrates on the rate-distortion curve on the Kodak dataset images, with and without the aid of entropy coding.Comment: Updated with content for CVPR and removed supplemental material to an external link for size limitation