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91.
Hosein Morshedi Mosayeb Naseri Mohammad Reza Hantehzadeh Seyed Mohammad Elahi 《Journal of Electronic Materials》2018,47(4):2290-2297
In this paper, using a first principles calculation, a two-dimensional structure of silicon-antimony named penta-Sb\(_{2}\)Si is predicted. The structural, kinetic, and thermal stabilities of the predicted monolayer are confirmed by the cohesive energy calculation, phonon dispersion analysis, and first principles molecular dynamic simulation, respectively. The electronic properties investigation shows that the pentagonal Sb\(_{2}\)Si monolayer is a semiconductor with an indirect band gap of about 1.53 eV (2.1 eV) from GGA-PBE (PBE0 hybrid functional) calculations which can be effectively engineered by employing external biaxial compressive and tensile strain. Furthermore, the optical characteristics calculation indicates that the predicted monolayer has considerable optical absorption and reflectivity in the ultraviolet region. The results suggest that a Sb\(_{2}\)Si monolayer has very good potential applications in new nano-optoelectronic devices. 相似文献
92.
There has been much interest to emulate the behavior of Output Queued switches. The early result of such attempts was reported by Prabhakar and McKeown using the CIOQ switches with speedup factor of 4. Subsequently, Stoica and Zhang and independently Chuang et al. showed that a speedup of 2 in conjunction with their scheduling schemes would be sufficient for CIOQ switches to emulate Output Queued switches.Additionally, Chuang et al. showed that in “Average Sense” a speedup of 2?1/N is necessary and sufficient for CIOQ to emulate Output Queued switch behavior.Our paper reports that in the “Strict Sense” a speedup of 2 is both necessary and sufficient. We show this requirement using examples for 2x2 and 3x3 switches. Then, with a constructed traffic pattern, it is proved that in the “Strict Sense” a speedup of 2 is necessary to emulate the behavior of an Output Queued switch for any switch size N.Combining this result with the previous scheduling schemes, we conclude that in the “Strict Sense”, a speedup of 2 is the necessary and sufficient condition to emulate the behavior of an Output Queued switch, using a CIOQ switch.Additionally, easing the assumptions and allowing the packet segmentation, it is shown that the speedup requirement to emulate the behavior of an Output Queued switch can be reduced to values even smaller than 2?1/N. For this case a lower bound of 3/2 and an upper bound of 2 is proved. 相似文献
93.
Shidrokh Goudarzi Wan Haslina Hassan Mohammad Hossein Anisi Seyed Ahmad Soleymani 《Wireless Personal Communications》2017,92(2):399-436
The hybrid algorithm for real-time vertical handover using different objective functions has been presented to find the optimal network to connect with a good quality of service in accordance with the user’s preferences. Markov processes are widely used in performance modelling of wireless and mobile communication systems. We address the problem of optimal wireless network selection during vertical handover, based on the received information, by embedding the decision problem in a Markov decision process (MDP) with genetic algorithm (GA), we use GA to find a set of optimal decisions that ensures the best trade-off between QoS based on their priority level. Then, we emerge improved genetic algorithm (IGA) with simulated annealing (SA) as leading methods for search and optimization problems in heterogeneous wireless networks. We formulate the vertical handoff decision problem as a MDP, with the objectives of maximizing the expected total reward and minimizing average number of handoffs. A reward function is constructed to assess the QoS during each connection, and the AHP method are applied in an iterative way, by which we can work out a stationary deterministic handoff decision policy. As it is, the characteristics of the current mobile devices recommend using fast and efficient algorithms to provide solutions near to real-time. These constraints have moved us to develop intelligent algorithm that avoid the slow and massive computations. This paper compares the formulation and results of five recent optimization algorithms: artificial bee colony, GA, differential evolution, particle swarm optimization and hybrid of (GA–SA). Simulation results indicated that choosing the SA rules would minimize the cost function, and also that, the IGA–SA algorithm could decrease the number of unnecessary handovers, and thereby prevent the ‘Ping-Pong’ effect. 相似文献
94.
Optimal SMDP‐Based Connection Admission Control Mechanism in Cognitive Radio Sensor Networks 下载免费PDF全文
Traffic management is a highly beneficial mechanism for satisfying quality‐of‐service requirements and overcoming the resource scarcity problems in networks. This paper introduces an optimal connection admission control mechanism to decrease the packet loss ratio and end‐to‐end delay in cognitive radio sensor networks (CRSNs). This mechanism admits data flows based on the value of information sent by the sensor nodes, the network state, and the estimated required resources of the data flows. The number of required channels of each data flow is estimated using a proposed formula that is inspired by a graph coloring approach. The proposed admission control mechanism is formulated as a semi‐Markov decision process and a linear programming problem is derived to obtain the optimal admission control policy for obtaining the maximum reward. Simulation results demonstrate that the proposed mechanism outperforms a recently proposed admission control mechanism in CRSNs. 相似文献
95.
Seyed M. Hosseini Mahdi Teimouri Saralees Nadarajah 《Wireless Personal Communications》2012,65(2):319-334
Cognitive radios (CRs) have been recently proposed for the problem of spectrum scarcity. The principle of CRs?? operation is based on the opportunistic access to the frequency spectrum mainly dedicated to primary users (PUs). The statistical time pattern of PUs?? channel usage and arrival can affect the usability of specific frequency bands for CRs. In this note, the effect of the arrival rate and channel holding time of PUs on the available times for CRs is analyzed. To this end, first, based on Poissonian arrivals, the available time for CRs is calculated. Then, assuming a gamma distribution for the inter-arrival times and a uniform distribution of channel holding time of PU in these intervals, the probability density function and moments of the available time for CRs are derived. Next, the effect of PUs statistical parameters on the average number of packets and the average symbol rate that a CR can transmit is analyzed. Also, taking that CR needs at least T seconds, the average waiting time is calculated. 相似文献
96.
Delingette H Billet F Wong KC Sermesant M Rhode K Ginks M Rinaldi CA Razavi R Ayache N 《IEEE transactions on bio-medical engineering》2012,59(1):20-24
Personalization is a key aspect of biophysical models in order to impact clinical practice. In this paper, we propose a personalization method of electromechanical models of the heart from cine-MR images based on the adjoint method. After estimation of electrophysiological parameters, the cardiac motion is estimated based on a proactive electromechanical model. Then cardiac contractilities on two or three regions are estimated by minimizing the discrepancy between measured and simulation motion. Evaluation of the method on three patients with infarcted or dilated myocardium is provided. 相似文献
97.
This paper presents a software-based error detection scheme called enhanced committed instructions counting (ECIC) for embedded and real-time systems using commercial off-the-shelf (COTS) processors. The scheme uses the internal performance monitoring features of a processor, which provides the ability to count the number of committed instructions in a program. To evaluate the ECIC scheme, 6000 software induced faults are injected into a 32-bit Pentium® processor. The results show that the error detection coverage varies between 90.52% and 98.18%, for different workloads. 相似文献
98.
Shagufta Naureen Naeem Shahid Reza Sanatinia Srinivasan Anand 《Advanced functional materials》2013,23(13):1620-1627
In the fabrication of III–V semiconductor nanostructures for electronic and optoelectronic devices, techniques that are capable of removing material with monolayer precision are as important as material growth to achieve best device performances. A robust chemical treatment is demonstrated using sulfur (S)‐oleylamine (OA) solution, which etches layer by layer in an inverse epitaxial fashion and simultaneously passivates the surface. The application of this process to push the limits of top‐down nanofabrication is demonstrated by the realization of InP‐based high optical quality nanowire arrays, with aspect ratios more than 50, and nanostructures with new topologies. The findings are relevant for other III–V semiconductors and have potential applications in III–V device technologies. 相似文献
99.
Mohammad Reza Motazedi 《International Journal of Electronics》2013,100(2):328-342
In this work, two new techniques using Reed–Solomon (RS) codes over GF(257) and GF(65,537) are proposed for peak-to-average power ratio (PAPR) reduction in coded orthogonal frequency division multiplexing (OFDM) systems. The lengths of these codes are well-matched to the length of OFDM frames. Over these fields, the block lengths of codes are powers of two and we fully exploit the radix-2 fast Fourier transform algorithms. Multiplications and additions are simple modulus operations. These codes provide desirable randomness with a small perturbation in information symbols that is essential for generation of different statistically independent candidates. Our simulations show that the PAPR reduction ability of RS codes is the same as that of conventional selected mapping (SLM), but contrary to SLM, we can get error correction capability. Also for the second proposed technique, the transmission of side information is not needed. To the best of our knowledge, this is the first work using RS codes for PAPR reduction in single-input single-output systems. 相似文献
100.
Wireless Personal Communications - Network coding (NC) significantly increases communication opportunities and improves network performance. The focus of most research is on performance analysis... 相似文献