Direction-of-Arrival Estimation Based on Sparse Recovery with Second-Order Statistics

Traditional direction-of-arrival (DOA) estimation techniques perform Nyquist-rate sampling of the received signals and as a result they require high storage. To reduce sampling ratio, we introduce level-crossing (LC) sampling which captures samples whenever the signal crosses predetermined reference levels, and the LC-based analog-to-digital converter (LC ADC) has been shown to efficiently sample certain classes of signals. In this paper, we focus on the DOA estimation problem by using second-order statistics based on the LC samplings recording on one sensor, along with the synchronous samplings of the another sensors, a sparse angle space scenario can be found by solving an $ell_1$ minimization problem, giving the number of sources and their DOA's. The experimental results show that our proposed method, when compared with some existing norm-based constrained optimization compressive sensing (CS) algorithms, as well as subspace method, improves the DOA estimation performance, while using less samples when compared with Nyquist-rate sampling and reducing sensor activity especially for long time silence signal

Strain distributions in lattice-mismatched semiconductor core-shell nanowires

The authors study the elastic deformation field in lattice-mismatched core-shell nanowires with single and multiple shells. The authors consider infinite wires with a hexagonal cross section under the assumption of translational symmetry. The strain distributions are found by minimizing the elastic energy per unit cell using the finite element method. The authors find that the trace of the strain is discontinuous with a simple, almost piecewise variation between core and shell, whereas the individual components of the strain can exhibit complex variations.Comment: 4 pages, 3 figure

Robust Feature-Preserving Mesh Denoising Based on Consistent Sub-Neighborhoods

published_or_final_versio

Schottky barrier and contact resistance of InSb nanowire field effect transistors

Understanding of the electrical contact properties of semiconductor nanowire (NW) field effect transistors (FETs) plays a crucial role in employing semiconducting NWs as building blocks for future nanoelectronic devices and in the study of fundamental physics problems. Here, we report on a study of the contact properties of Ti/Au, a widely used contact metal combination, to individual InSb NWs via both two-probe and four-probe transport measurements. We show that a Schottky barrier of height $\Phi_{\rm{SB}}\sim20\ \rm{meV}$ is present at the metal-InSb NW interfaces and its effective height is gate tunable. The contact resistance ($R_{\rm{c}}$) in the InSb NWFETs is also analyzed by magnetotransport measurements at low temperatures. It is found that $R_{\rm{c}}$ at on-state exhibits a pronounced magnetic field dependent feature, namely it is increased strongly with increasing magnetic field after an onset field $B_{\rm{c}}$. A qualitative picture that takes into account magnetic depopulation of subbands in the NWs is provided to explain the observation. Our results provide a solid experimental evidence for the presence of a Schottky barrier at Ti/Au-InSb NW interfaces and can be used as a basis for design and fabrication of novel InSb NW based nanoelectronic devices and quantum devices.Comment: 12 pages, 4 figure

Integrated health monitoring for a steel beam : an experimental study

Civil infrastructures begin to deteriorate once they are built and used. Detecting damages in a structure to maintain its safety is a topic that has received considerable attention in the literature in recent years. Many methods are developed, including global vibration-based methods and local GW-based methods. The global vibration-based method uses changes in modal properties to detect damage. The advantage of this approach is that the vibration properties are straightforward to be measured. The disadvantage of this method is that it might not be sensitive to small damage. On the other hand, local method, such as the guided waves (GW) based method is sensitive to small damage, but its sensing range is small. In this paper, an integrated structural health monitoring test scheme is developed to detect damage in a steel beam. Different saw cuts of various depths are made to simulate crack damage. Vibration tests and guided wave tests are conducted after each cut. The vibration method is used to detect the overall condition change of the beam, whereas the GW method is used to locate and quantify the damage. Experimental results show that the integrated method is efficient to detect and quantify local crack damage in steel structures and its influence on the global structure conditions

Quantum Information Approach to Bose-Einstein Condensate in a Tilted Double-Well System

We study the ground state properties of bosons in a tilted double-well system. We use fidelity susceptibility to identify the possible ground state transitions under different tilt values. For a very small tilt (for example $10^{-10}$), two transitions are found. For a moderate tilt (for example $10^{-3}$), only one transition is found. For a large tilt (for example $10^{-1}$), no transition is found. We explain this by analyzing the spectrum of the ground state. The quantum discord and total correlation of the ground state under different tilts are also calculated to indicate those transitions. In the transition region, both quantities have peaks decaying exponentially with particle number $N$. This means for a finite-size system the transition region cannot be explained by the mean-field theory, but in the large-$N$ limit it can be.Comment: 5 pages, 5 figures, slightly different from the published versio

Boundary effects to the entanglement entropy and two-site entanglement of the spin-1 valence-bond solid

We investigate the von Neumann entropy of a block of subsystem for the valence-bond solid (VBS) state with general open boundary conditions. We show that the effect of the boundary on the von Neumann entropy decays exponentially fast in the distance between the subsystem considered and the boundary sites. Further, we show that as the size of the subsystem increases, its von Neumann entropy exponentially approaches the summation of the von Neumann entropies of the two ends, the exponent being related to the size. In contrast to critical systems, where boundary effects to the von Neumann entropy decay slowly, the boundary effects in a VBS, a non-critical system, decay very quickly. We also study the entanglement between two spins. Curiously, while the boundary operators decrease the von Neumann entropy of L spins, they increase the entanglement between two spins.Comment: 4 pages, 2 figures. Physical Review B (in press