On the capacity of the multiple-hop relay channel with linear relaying

The relay nodes with linear relaying transmit linear combination of their past received signals. The capacity of the multiple-hop Gaussian relay channel with linear relaying is derived, assuming that each node in the channel only communicates with its nearest neighbor nodes. The capacity is formulated as an optimization problem over the relaying matrices and the covariance matrix of the signals transmitted from the source. It is proved that the solution to this optimization problem is equivalent to a “single-letter” optimization problem when some certain conditions are satisfied. We also show that the solution to the “single-letter” optimization problem has the same form as the expression of the rate achieved by time-sharing amplify-and-forward (TSAF). In order to solve this equivalent problem, we give an iterative algorithm. Simulation results show that the achievable rate with TSAF is close to the capacity, if channel gain of one certain hop is smaller than that of all the other hops relatively.     

Bubble dynamics and interactions with a pair of micro pillars in tandem

This study investigates flow patterns and bubble dynamics of two-phase flow around two 100 μm diameter circular pillars in tandem, which were entrenched inside a horizontal micro channel. Bubble velocity, trajectory, size, and void fraction were measured using a high speed camera and analyzed using a particle tracking velocimetry method. A range of gas and liquid superficial velocities were tested, resulting in different bubbly flow patterns, which were consistent with previous studies. These flow patterns were altered as they interacted with the pillars. Depending on the relative transverse location of bubbles to the pillars, and through bubble–bubble interaction, the flow sometimes returned to its original state. It was also determined that the pillars altered both the bubble trajectory and void fraction, especially in the pillars region.     

砂砾岩油藏渗透系数研究

为了掌握砂砾岩油藏渗流规律,基于砂砾岩中砾和砂含量及其排列方式不同,开展了理论和实验研究。把砂砾岩孔隙度和渗透率设为砾、砂含量的函数,再基于Kozeny-Carman方程建立渗透率与孔隙度和颗粒粒径的函数关系。研究表明,砂砾岩组成及颗粒排列方式是控制砂砾岩渗透系数的主要因素,砂砾岩渗透率与孔隙度为一种线性关系。水驱油实验进一步表明,束缚水饱和度依赖于砂、砾含量,含水上升快,揭示了砂砾岩油藏特有的渗流特点。     

Economic application in a finite capacity multi-channel queue with second optional channel

We consider a finite capacity M/M/R queue with second optional channel. The interarrival times of arriving customers follow an exponential distribution. The service times of the first essential channel and the second optional channel are assumed to follow an exponential distribution. As soon as the first essential service of a customer is completed, a customer may leave the system with probability (1 − θ) or may opt for the second optional service with probability θ (0 ? θ ? 1). Using the matrix-geometric method, we obtain the steady-state probability distributions and various system performance measures. A cost model is established to determine the optimal solutions at the minimum cost. Finally, numerical results are provided to illustrate how the direct search method and the tabu search can be applied to obtain the optimal solutions. Sensitivity analysis is also investigated.     

Quality improvement vs. advertising support: Which strategy works better for a manufacturer?

We consider a marketing channel with a single manufacturer and a single retailer, where both advertising and quality improvement contribute to the build-up of goodwill. In a non-coop scenario, the retailer controls the advertising efforts while the manufacturer controls the quality improvements and wholesale price. Although improving quality positively contributes to goodwill, it also increases the production cost, thereby reducing the manufacturer’s profit. In a coop scenario, the manufacturer supports the retailer’s advertising while decreasing his investments in quality. We investigate the conditions under which a coop program is beneficial when such a trade-off occurs. Our results demonstrate that only when advertising significantly contributes to goodwill the manufacturer has an incentive to cooperate and a coop program turns out to be Pareto-improving. Conversely, the retailer is always better off with a coop program. Moreover, the channel is operational- and marketing-driven when quality effectiveness is high independent of advertising effectiveness or when both quality and advertising effectiveness are large. In all other cases, the channel is marketing-driven.     

Allowable propagation of short pulse laser beam in a plasma channel and electromagnetic solitary waves

Nonparaxial and nonlinear propagation of a short intense laser beam in a parabolic plasma channel is analyzed by means of the variational method and nonlinear dynamics. The beam propagation properties are classified by five kinds of behaviors. In particularly, the electromagnetic solitary wave for finite pulse laser is found beside the other four propagation cases including beam periodically oscillating with defocussing and focusing amplitude, constant spot size, beam catastrophic focusing. It is also found that the laser pulse can be allowed to propagate in the plasma channel only when a certain relation for laser parameters and plasma channel parameters is satisfied. For the solitary wave, it may provide an effective way to obtain ultra-short laser pulse.     

LDC-CNTFET: A carbon nanotube field effect transistor with linear doping profile channel

In this paper, a novel carbon nanotube field effect transistor with linear doping profile channel (LDC-CNTFET) is presented. The channel impurity concentration of the proposed structure is at maximum level at source side and linearly decreases toward zero at drain side. The simulation results show that the leakage current, on-off current ratio, subthreshold swing, drain induced barrier lowering, and voltage gain of the proposed structure improve in comparison with conventional CNTFET. Also, due to spreading the impurity throughout the channel region, the proposed structure has superior performance compared with a single halo CNTFET structure with equal saturation current. Design considerations show that the proposed structure enhances the device performance all over a wide range of channel lengths.     

Nanoscale SiGe-on-insulator (SGOI) MOSFET with graded doping channel for improving leakage current and hot-carrier degradation

A novel graded doping profile, for the first time is introduced for reliability improvement and leakage current reduction. The proposed structure is called graded doping channel SiGe-on-insulator (GDC-SGOI). The key idea in this work is to modify the electric field and band energy with novel doping distribution in the channel for improving leakage current and hot electron. Using two-dimensional two-carrier simulation we demonstrate that the GDC-SGOI shows lower electron temperature near the drain region in the channel in comparison with the conventional SGOI (C-SGOI) with uniform doping. On the other hand, short channel effects (SCEs) such as drain induced barrier lowering (DIBL) and threshold voltage roll-off improvement leads to leakage current reduction. DIBL decrement and less dependence of the threshold voltage and DIBL on channel length variation in the GDC-SGOI structure show SCEs suppression. Furthermore the on-off current ratio (I_on/I_off) in the GDC-SGOI is higher than that achieved from the C-SGOI. Therefore, the results show that the GDC-SGOI structure especially in low power and device reliability has excellent performance in comparison with the C-SGOI.