A new etchant was studied out for preferential etching the (112) face of AgGa0.8In0.2Se2 crystal at room temperature and a new etching technique was presented. AgGa0.8In0.2Se2 crystal was grown by improved Bridgman method and directively cut out the wafer of (112) face from the crystal. Then,the wafer was grinded,mechanically polished,and etched in the etching solution of HNO3(65%-68%)∶HCl(35%-38%)=1∶2.5 (volume ratio) for 5 min at room temperature with ultrasonic vibration. The etching pits were clearly observed under the metalloscope. The shape of the etch pits of the (112) face appeared approximately to equilateral triangle. The formation cause of etch pits and the shape on the (112) face were theoretically analyzed.
This paper considers the problem of mutual information maximization in a two-hop relay network with simultaneous wireless information and power transfer (SWIPT), where the relay nodes use the power splitting (PS) scheme to harvest the energy for information forwarding. Unlike previous research, this paper focuses on a more practical scenario, where the inputs to the network are assumed to be finite-alphabet signals. Although each node in the network is assumed to have single antenna, we show that the relay network can be regarded as an effective multiple-input multiple-output (MIMO) system. Our goal is to perform the joint optimization on the precoder at source and PS ratio at relays to maximize the mutual information. Although the formulated problem is nondeterministic polynomial-time (NP)-hard, we theoretically analyze the optimal PS ratio; then, by using the structure of optimization problem, a near optimal precoder design based on semidefinite relaxation (SDR) is proposed; further, to reduce the complexity of algorithm, another precoder design based on search technique, which exploiting the structure of precoder, is developed only with a slight performance degradation. Simulation results verify the efficacy of proposed precoder designs.
It has been widely recognized that placing cloud data centers near clean energy sources or in cooler environments may reduce the operational cost and carbon footprint. But when the scale of the system, in terms of the overall computing power and territorial coverage, is large, such benefits may be offset by the additional cost of moving data around and the complexity of efficiently utilizing the network and computational resources. In this paper, we discuss the benefits and challenges of a vastly distributed cloud computing infrastructure, in the particular context of the east-west synergized cloud computing project in China, i.e., the Dong Shu Xi Suan Project (DSXS). We discuss the state of art research that are relevant to this topic, and explore the potential technological advances such a project may bring.
In this paper, the problem of mutual information maximization in a two-hop multiple-input multiple-output (MIMO) relay network with simultaneous wireless information and power transfer (SWIPT) is investigated, where the relay node, without constant power supply, harvests the energy for information forwarding. The goal is to maximize the mutual information by using the joint design of source and relay precoders, which is formulated as an optimization problem under the constraints of transmit power and harvested energy. Two scenarios with practical energy harvesting schemes employed at the relay, i.e., power splitting (PS) and time switching (TS) schemes, are considered. Although the formulated optimization problems in the two scenarios are both nondeterministic polynomial-time (NP)-hard, by exploiting the structure of the optimization problems and analyzing the characteristics of precoders, we develop near optimal joint source and relay precoding algorithms for them. Additionally, we analyze the feasible regions of PS and TS ratios, respectively, and propose a backtracking line search based method to find near optimal PS and TS ratios. The main contributions of this paper are as follows: 1) Unlike existing works based on the assumption of ideal Gaussian signals, this paper supposes the inputs to the network are finite-alphabet signals, which is a more practical scenario. 2) The high complexity of mutual information with finite-alphabet signals leads to an intractable optimization problem; however, an efficient solving framework based on semidefinite relaxation (SDR) and Karush-Kuhn-Tucker (KKT) theorem is proposed. Finally, simulation results verify the efficacy of the proposed joint precoding designs.
This paper investigates the secure transmission problem in a cache-aided relaying network, where we assume that the source sends data to the destination via multiple cache-aided relays and the communication from the relays to the destination is wiretapped by an eavesdropper. Unlike the ideal assumption of Gaussian input signals, this paper considers practical finite-alphabet inputs, such as phase shift keying (PSK) and quadrature amplitude modulation (QAM). Our objective is to maximize the achievable secrecy rate by optimizing the beamforming vectors and power control at the source and relays as well as caching coefficient under constraints of transmit power, quality of service, and network congestion. For the formulated nonconvex multi-variable problem, we use the M/G/1 queueing theory to analyze the network congestion performance and reveal that the congestion decreases with increasing caching coefficient and increasing source-to-relay link rate but increases with increasing relay-to-destination link rate. Then, it is shown that the formulated problem can be solved by dividing it into two optimization subproblems. Subsequently, an auxiliary-variable based alternating optimization (AVAO) framework is developed, where the beamforming at each relay is designed by introducing the Moreau-Yosida regularization (MYR) technique and rank-one decomposition procedure (RDP) and the corresponding power control is derived by applying the optimality condition. Also, the complexity and convergence of the proposed framework are analyzed. Simulation results verify the efficacy of the proposed framework. Specifically, the algorithm based on finite-alphabet inputs proposed in this paper exhibits superior performance compared with the algorithm based on Gaussian inputs. Moreover, the secrecy rate increases with the congestion probability tolerance, the caching coefficient threshold, and the number of relays.
The Fe2+:ZnSe crystal is an important material for 3–5 μm mid-infrared lasers. In this work, we have grown different doping concentrations of Fe2+:ZnSe and Fe2+, Cr2+:ZnSe by the chemical vapor transport method. The doped crystals have the same structure. The lattice constant increases slightly with a higher Fe2+ concentration, while the doped Cr2+ has a great influence on the lattice constant. Besides, with a higher Fe2+ concentration, the TO mode has no change and the LO mode presents a small blue shift. The doped ZnSe crystals all have a wide absorption peak in the range of 2.3–4.5 μm, and these absorption peaks widen with the increase of the Fe2+ doping concentration. Besides, in the range of 5–20 μm, the crystals have good transparency. The concentrations of 3, 2, and 1% Fe2+ samples are calculated to be 4.15 × 1019, 3.27 × 1019, and 3.02 × 1019 cm–3, respectively, and the Fe2+ concentration of the Fe2+, Cr2+:ZnSe sample is 3.71 × 1019 cm–3. The band gap decreases from 2.52 to 2.27 eV with a higher Fe2+ doping concentration. Therefore, we can modulate the absorption bandwidth and band gap by doping the ion concentration, which is more suitable for developing mid-infrared gain medium applications.
LiGaTe2 is a promising nonlinear optical crystal with a large figure of merit (d362/n3), but it is difficult to grow the LiGaTe2 single crystal due to its extreme instability. In this work, we used Ag to replace Li and successfully grew a Li0.5Ag0.5GaTe2 crystal by the modified Bridgman method for the first time. We found it has thermal stability below 200 °C in an atmospheric environment, and the thermal expansion coefficient is positive. This is different from LiGaTe2 and AgGaTe2 which have a negative thermal expansion coefficient along the c-axis. When the temperature exceeds 200 °C, Li0.5Ag0.5GaTe2 is easily decomposed and oxidized. Under closed vacuum conditions, the melting and solidifying points of Li0.5Ag0.5GaTe2 are measured to be 719 and 694 °C. XPS spectra show that the binding energies of Li, Ga, and Te are higher than LiGaTe2, and the surface is easily oxidized. The A1 vibration modes are found at 117.72 and 135.44 cm–1 by the Raman spectrum which is related to the Te and Ga–Te bond in [GaTe4]5– tetrahedra. Li0.5Ag0.5GaTe2 has a wide transmittance range from 0.94 to 20 μm, and there was two-photon absorption near 16 μm. The phonon spectrum and PDOS were simulated by the DFT calculation to study the phonon vibration modes in the lattice, which shows that the density of the Raman vibration is higher than those of AgGaTe2 and LiGaTe2. The SHG test results showed that the SHG response intensity of Li0.5Ag0.5GaTe2 is 1.5 times that of AgGaS2, which shows its excellent nonlinear optical properties for mid-IR applications.
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