In total, 0.5 wt% CuZnAl memory particles with the diameters (2–6 μm) were added into Sn–58Bi solder in order to enhance the properties of solder joints in electronic packaging. The interface ...reaction and the growth kinetics of intermetallic compounds at Sn–58Bi/Cu interface and Sn–58Bi–0.5CuZnAl/Cu interface were studied systematically at 250 °C, 230 °C and 210 °C, the results indicate that the growth rate of intermetallic compounds (IMC) at both interfaces at 250 °C was higher than that at 230 °C, the addition of CuZnAl memory particles can reduce the diffusion coefficient of interfacial IMC, and however, at 210 °C the inhibition effect of CuZnAl particles was so small. Based on the transient liquid phase bonding, it is demonstrated that Cu/Sn–58Bi–0.5CuZnAl/Cu-bonded joints can achieve the chip stacking in 3D packaging with 10 μm thickness with obvious superiority.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
The size of C‐nanodots can be electrochemically tuned by changing the applied potential during their preparation. The higher the applied potential, the smaller the resulting C‐nanodots. Moreover, the ...surface oxidation degree of the C‐nanodots can also be electrochemically tuned. The red‐shift of emission independent of the size provides an insight into the luminescence mechanism of C‐nanodots.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
The heavy-tailed distributions of corrupted outliers and singular values of all channels in low-level vision have proven effective priors for many applications such as background modeling, ...photometric stereo and image alignment. And they can be well modeled by a hyper-Laplacian. However, the use of such distributions generally leads to challenging non-convex, non-smooth and non-Lipschitz problems, and makes existing algorithms very slow for large-scale applications. Together with the analytic solutions to <inline-formula><tex-math notation="LaTeX">\ell _{p}</tex-math> <inline-graphic xlink:href="shang-ieq1-2748590.gif"/> </inline-formula>-norm minimization with two specific values of <inline-formula><tex-math notation="LaTeX">p</tex-math> <inline-graphic xlink:href="shang-ieq2-2748590.gif"/> </inline-formula>, i.e., <inline-formula> <tex-math notation="LaTeX">p=1/2</tex-math> <inline-graphic xlink:href="shang-ieq3-2748590.gif"/> </inline-formula> and <inline-formula><tex-math notation="LaTeX">p=2/3</tex-math> <inline-graphic xlink:href="shang-ieq4-2748590.gif"/> </inline-formula>, we propose two novel bilinear factor matrix norm minimization models for robust principal component analysis. We first define the double nuclear norm and Frobenius/nuclear hybrid norm penalties, and then prove that they are in essence the Schatten-<inline-formula> <tex-math notation="LaTeX">1/2</tex-math> <inline-graphic xlink:href="shang-ieq5-2748590.gif"/> </inline-formula> and <inline-formula><tex-math notation="LaTeX">2/3</tex-math> <inline-graphic xlink:href="shang-ieq6-2748590.gif"/> </inline-formula> quasi-norms, respectively, which lead to much more tractable and scalable Lipschitz optimization problems. Our experimental analysis shows that both our methods yield more accurate solutions than original Schatten quasi-norm minimization, even when the number of observations is very limited. Finally, we apply our penalties to various low-level vision problems, e.g., text removal, moving object detection, image alignment and inpainting, and show that our methods usually outperform the state-of-the-art methods.
Developing ultra-high strength in rare-earth-free Mg alloys using conventional extrusion process is a great challenge. What is even more difficult is to achieve such a goal at a lower processing ...cost. In this work, we report a novel low-alloyed Mg-2Sn-2Ca alloy (in wt. %) that exhibits tunable ultra-high tensile yield strength (360–440 MPa) depending on extrusion parameters. More importantly, there is little drop in mechanical properties of this alloy even when it is extruded at a speed several times higher than those used in the reported high strength Mg alloys. Examination of as-extruded microstructures of this Ca-containing Mg alloy reveals that the ultra-high strength is mainly associated with the presence of surprisingly submicron matrix grains (down to ∼0.32 μm). The results suggest that the Ca addition promotes accumulations of the pyramidal dislocations, which eventually transform into the low angular grain boundaries (LAGBs). The high number density of LAGBs separate the α-Mg matrix via either discontinuous dynamic recrystallization (DDRX) mechanism in the early stage or the continuous dynamic recrystallization (CDRX) mechanism in the later stage of extrusion, which effectively enhances the nucleation rates of the DRXed grains. More importantly, large amount of Ca segregation along LAGBs, accompanied with dynamically precipitated Mg2Ca nano-phases, are detected in the present non-severely deformed samples. It is the combination of solute segregations and numerous Mg2Ca nano-precipitates that contributes to the formation of the ultra-fine grains via pinning mechanism. The ultrafine grains size, Ca enrichment in most LAGBs, and residual Mg2Ca nano-precipitates would in turn contribute significantly to the enhancement of the yield strength of the as-extruded Mg-2Sn-2Ca (wt.%) alloy. The low content of alloying elements and the fast one-step extrusion process render the present alloys low-cost and thus have great potential in large-scale industry applications.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Low-temperature oxidation of CO, perhaps the most extensively studied reaction in the history of heterogeneous catalysis, is becoming increasingly important in the context of cleaning air and ...lowering automotive emissions. Hopcalite catalysts (mixtures of manganese and copper oxides) were originally developed for purifying air in submarines, but they are not especially active at ambient temperatures and are also deactivated by the presence of moisture. Noble metal catalysts, on the other hand, are water tolerant but usually require temperatures above 100 °C for efficient operation. Gold exhibits high activity at low temperatures and superior stability under moisture, but only when deposited in nanoparticulate form on base transition-metal oxides. The development of active and stable catalysts without noble metals for low-temperature CO oxidation under an ambient atmosphere remains a significant challenge. Here we report that tricobalt tetraoxide nanorods not only catalyse CO oxidation at temperatures as low as -77 °C but also remain stable in a moist stream of normal feed gas. High-resolution transmission electron microscopy demonstrates that the Co3O4 nanorods predominantly expose their {110} planes, favouring the presence of active Co3+ species at the surface. Kinetic analyses reveal that the turnover frequency associated with individual Co3+ sites on the nanorods is similar to that of the conventional nanoparticles of this material, indicating that the significantly higher reaction rate that we have obtained with a nanorod morphology is probably due to the surface richness of active Co3+ sites. These results show the importance of morphology control in the preparation of base transition-metal oxides as highly efficient oxidation catalysts.
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DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Here, a facile, low-cost, and high-efficiency method to construct a vertically aligned hexagonal boron nitride nanosheet (hBNN) thermal conduction channel structure is proposed to improve the thermal ...conductivity. First, exfoliated negatively charged BNNs and positively charged FeCo nanocubes self-assemble to form complex nanomaterials by strong electrostatic interactions. Then, the BNNs can orient with FeCo nanocubes in magnetic field, and the {001} facets of BNNs adsorb on the {100} facets of FeCo nanocubes. The large scale range and high-density FeCo/hBN-aligned structures are observed by scanning electron microscopy, which can act as thermal dissipation channels by conveying more phonons through a preponderant thermally conductive direction. The thermal conductivity of the composite films with 30 wt % FeCo and 50 wt % BN filler is 2.25 W m–1 K–1, 7 times higher than that of the films only containing 50 wt % randomly distributed hBN filler (0.325 W m–1 K–1) and 20 times higher than pure polydimethylsiloxane films (0.114 W m–1 K–1). The thermal management capability of the composite films is evaluated as a thermal conducting substrate of a light-emitting diode chip and the infrared thermal technology. Apart from the surprising thermal conductivity, FeCo–BNNs composite films also exhibit superb flexibility.
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IJS, KILJ, NUK, PNG, UL, UM
In a cellular wireless system, users located at cell edges often suffer significant out-of-cell interference. Assuming each base station is equipped with multiple antennas, we can model this scenario ...as a multiple-input single-output (MISO) interference channel. In this paper we consider a coordinated beamforming approach whereby multiple base stations jointly optimize their downlink beamforming vectors in order to simultaneously improve the data rates of a given group of cell edge users. Assuming perfect channel knowledge, we formulate this problem as the maximization of a system utility (which balances user fairness and average user rates), subject to individual power constraints at each base station. We show that, for the single-carrier case and when the number of antennas at each base station is at least two, the optimal coordinated beamforming problem is NP-hard for both the harmonic mean utility and the proportional fairness utility. For general utilities, we propose a cyclic coordinate descent algorithm, which enables each transmitter to update its beamformer locally with limited information exchange and establish its global convergence to a stationary point. We illustrate its effectiveness in computer simulations by using the space matched beamformer as the benchmark.
An important preliminary procedure in multi-sensor data fusion is sensor registration , and the key step in this procedure is to estimate sensor biases from their noisy measurements. There are ...generally two difficulties in this bias estimation problem: one is the unknown target states which serve as the nuisance variables in the estimation problem, and the other is the highly nonlinear coordinate transformation between the local and global coordinate systems of the sensors. In this article, we focus on the 3-dimensional asynchronous multi-sensor scenario and propose a weighted nonlinear least squares (NLS) formulation by assuming that there is a target moving with a nearly constant velocity. We propose two possible choices of the weighting matrix in the NLS formulation, which correspond to classical and weighted NLS estimation, respectively. To address the intrinsic nonlinearity, we propose a block coordinate descent (BCD) algorithm for solving the formulated problem, which alternately updates different kinds of bias estimates. Specifically, the proposed BCD algorithm involves solving linear LS problems and nonconvex quadratically constrained quadratic program (QCQP) problems with special structures. Instead of adopting the semidefinite relaxation technique, we develop a much more computationally efficient algorithm based on the alternating direction method of multipliers (ADMM) to solve the nonconvex QCQP subproblems. The convergence of the ADMM to the global solution of the QCQP subproblems is established under mild conditions. The effectiveness and efficiency of the proposed BCD algorithm are demonstrated via numerical simulations.
Probing signal waveforms play a central role in the signal processing performance of a multiple-input multiple-output (MIMO) radar. In practice, for a given desired beam pattern, we need to design a ...probing signal waveform whose beam pattern closely matches the desired one and whose autocorrelation and cross-correlation sidelobes are kept low. The latter properties are important to mitigate undesirable interference caused by multiple targets or scatterers. In this correspondence, we present an efficient optimization method to design a constant modulus probing signal which can synthesize a desired beam pattern while maximally suppressing both the autocorrelation and cross-correlation sidelobes at/between given spacial angles. We formulate this problem as an unconstrained minimization of a fourth order trigonometric polynomial and propose an efficient quasi-Newton iterative algorithm to solve it. Besides, we provide an analysis of the local minima of the fourth-order trigonometric polynomial and prove that any local minima is a 1/2-approximation of its global optimal solution. Numerical examples show that the proposed approach compares favorably with the existing approach.
To support multiple on-demand services over fixed communication networks, network operators must allow flexible customization and fast provision of their network resources. One effective approach to ...this end is network virtualization, whereby each service is mapped to a virtual subnetwork providing dedicated on-demand support to network users. In practice, each service consists of a prespecified sequence of functions, called a service function chain (SFC), while each service function in a SFC can only be provided by some given network nodes. Thus, to support a given service, we must select network function nodes according to the SFC and determine the routing strategy through the function nodes in a specified order. A crucial network slicing problem that needs to be addressed is how to optimally localize the service functions in a physical network as specified by the SFCs, subject to link and node capacity constraints. In this paper, we formulate the network slicing problem as a mixed binary linear program and establish its strong NP-hardness. Furthermore, we propose efficient penalty successive upper bound minimization (PSUM) and PSUM-R(ounding) algorithms, and two heuristic algorithms to solve the problem. Simulation results are shown to demonstrate the effectiveness of the proposed algorithms.
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