Numerical Study of Wave Propagation in Uniaxially Anisotropic Lorentzian Backward Wave Slabs

The propagation and refraction of a cylindrical wave created by a line current through a slab of backward wave medium, also called left-handed medium, is numerically studied with FDTD. The slab is assumed to be uniaxially anisotropic. Several sets of constitutive parameters are considered and comparisons with theoretical results are made. Electric field distributions are studied inside and behind the slab. It is found that the shape of the wavefronts and the regions of real and complex wave vectors are in agreement with theoretical results.Comment: 6 pages, figure

Tunneling of Cooper pairs across voltage biased asymmetric single-Cooper-pair transistors

We analyze tunneling of Cooper pairs across voltage biased asymmetric single-Cooper-pair transistors. Also tunneling of Cooper pairs across two capacitively coupled Cooper-pair boxes is considered, when the capacitive coupling and Cooper pair tunneling are provided by a small Josephson junction between the islands. The theoretical analysis is done at subgap voltages, where the current-voltage characteristics depend strongly on the macroscopic eigenstates of the island(s) and their coupling to the dissipative environment. As the environment we use an impedance which satisfies Re[Z]<<R_Q and a few LC-oscillators in series with Z. The numerically calculated I-V curves are compared with experiments where the quantum states of mesoscopic SQUIDs are probed with inelastic Cooper pair tunneling. The main features of the observed I-V data are reproduced. Especially, we find traces of band structure in the higher excited states of the Cooper-pair boxes as well as traces of multiphoton processes between two Cooper-pair boxes in the regime of large Josephson coupling.Comment: 9 pages, 9 figures, Revtex

Investigation of foamed metals for application on space capsules annual report, 29 jun. 1963 - 15 aug. 1964

Foamed metal development for space capsules - brazing, variable density beam, thermal testing, mechanical tests, and machinin

A modified SST k-? turbulence model to predict the steady and unsteady sheet cavitation on 2D and 3D hydrofoils

The paper presents a study of using a modified SST (Shear-Stress Transport) k-? model with a multi-phase mixture flow RANS solver to predict the steady and unsteady cavitating flows around 2D and 3D hydrofoils. Based on Reboud et al [6] s idea of modifying turbulent viscosity for a RNG k-­ model, a modification is applied to a SST k-? model in the present work. The cavitation is modeled by Schnerr-Sauer s cavitation model [16]. First, results of 2D NACA0015 foil at two cavitation numbers, ? =1.6 (stable sheet cavitation) and ?=1.0 (unsteady with shedding) are compared for different grids and with available experiment data. Then, the problem of the standard SST model in predicting unsteady cavitation is discussed. Finally the results for a 3D twisted hydrofoil are compared with the experiment by Foeth and Terwisga [3]. It is found that with the modified SST k-? model the RANS solver is able to predict the essential features like development of re-entrant jets, the pinch-off, the shedding of vortex and cloud cavities for the 2D NACA0015 foil at ? =1.0. For the case at ? =1.6, the model predicts a high frequency fluctuating sheet cavity with minor shedding at its closure. Compared with the standard SST model, the global quantities like lift, drag, and shedding frequency predicted by the modified model are closer to the experimental data, although considerable discrepancy with the experiment data is noted for the unsteady case at ? =1.0. In addition, a special type of secondary cavities, developed downstream an upstream-moving collapse cavity and termed as vortex group cavitation by Bark et al [1], appears to be observable in the simulation at this condition. The existence of this type of cavity has been reconfirmed in a recent experiment in the SSPA s cavitation tunnel.http://deepblue.lib.umich.edu/bitstream/2027.42/84288/1/CAV2009-final107.pd

Efficient Constant-Round Multi-party Computation Combining BMR and SPDZ

© 2019, International Association for Cryptologic Research. Recently, there has been huge progress in the field of concretely efficient secure computation, even while providing security in the presence of malicious adversaries. This is especially the case in the two-party setting, where constant-round protocols exist that remain fast even over slow networks. However, in the multi-party setting, all concretely efficient fully secure protocols, such as SPDZ, require many rounds of communication. In this paper, we present a constant-round multi-party secure computation protocol that is fully secure in the presence of malicious adversaries and for any number of corrupted parties. Our construction is based on the constant-round protocol of Beaver et al. (the BMR protocol) and is the first version of that protocol that is concretely efficient for the dishonest majority case. Our protocol includes an online phase that is extremely fast and mainly consists of each party locally evaluating a garbled circuit. For the offline phase, we present both a generic construction (using any underlying MPC protocol) and a highly efficient instantiation based on the SPDZ protocol. Our estimates show the protocol to be considerably more efficient than previous fully secure multi-party protocols.status: publishe

A Flexible Privacy-preserving Framework for Singular Value Decomposition under Internet of Things Environment

The singular value decomposition (SVD) is a widely used matrix factorization tool which underlies plenty of useful applications, e.g. recommendation system, abnormal detection and data compression. Under the environment of emerging Internet of Things (IoT), there would be an increasing demand for data analysis to better human's lives and create new economic growth points. Moreover, due to the large scope of IoT, most of the data analysis work should be done in the network edge, i.e. handled by fog computing. However, the devices which provide fog computing may not be trustable while the data privacy is often the significant concern of the IoT application users. Thus, when performing SVD for data analysis purpose, the privacy of user data should be preserved. Based on the above reasons, in this paper, we propose a privacy-preserving fog computing framework for SVD computation. The security and performance analysis shows the practicability of the proposed framework. Furthermore, since different applications may utilize the result of SVD operation in different ways, three applications with different objectives are introduced to show how the framework could flexibly achieve the purposes of different applications, which indicates the flexibility of the design.Comment: 24 pages, 4 figure

On homogenization of electromagnetic crystals formed by uniaxial resonant scatterers

Dispersion properties of electromagnetic crystals formed by small uniaxial resonant scatterers (magnetic or electric) are studied using the local field approach. The goal of the study is to determine the conditions under which the homogenization of such crystals can be made. Therefore the consideration is limited by the frequency region where the wavelength in the host medium is larger than the lattice periods. It is demonstrated that together with known restriction for the homogenization related with the large values of the material parameters there is an additional restriction related with their small absolute values. From the other hand, the homogenization becomes allowed in both cases of large and small material parameters for special directions of propagation. Two unusual effects inherent to the crystals under consideration are revealed: flat isofrequency contour which allows subwavelength imaging using canalization regime and birefringence of extraordinary modes which can be used for beam splitting.Comment: 16 pages, 12 figures, submitted to PR

Observation of shot-noise-induced asymmetry in the Coulomb blockaded Josephson junction

We have investigated the influence of shot noise on the IV-curves of a single mesoscopic Josephson junction. We observe a linear enhancement of zero-bias conductance of the Josephson junction with increasing shot noise power. Moreover, the IV-curves become increasingly asymmetric. Our analysis on the asymmetry shows that the Coulomb blockade of Cooper pairs is strongly influenced by the non-Gaussian character of the shot noise.Comment: 4 pages, 5 figures, RevTE

Inverse proximity effect in superconductors near ferromagnetic material

We study the electronic density of states in a mesoscopic superconductor near a transparent interface with a ferromagnetic metal. In our tunnel spectroscopy experiment, a substantial density of states is observed at sub-gap energies close to a ferromagnet. We compare our data with detailed calculations based on the Usadel equation, where the effect of the ferromagnet is treated as an effective boundary condition. We achieve an excellent agreement with theory when non-ideal quality of the interface is taken into account.Comment: revised, 7 pages, 3 figure