Performance Analysis of Communication System with Nonlinear Power Amplifier

A communication system with nonlinear Power Amplifier (PA) is considered. The PA nonlinearity forces the designer of communication system to choose proper Back-Off, which influences three major parameters of the communication system: (i) power efficiency, (ii) Adjacent Channel Power Ratio (ACPR), and (iii) bit rate expressed by Mutual Information (MI). Having these three parameters, we propose to evaluate the performance of a communication system with nonlinear PA using the fact that ACPR is dictated by the regulator/communication standard. In what follows we propose to find power efficiency and MI as a function of ACPR. To illustrate the usefulness of the proposed method, the Solid State Power Amplifier (SSPA), and two linearized versions of SSPA are considered. The first version is a perfectly linearized PA using pre-distortion resulting with Soft Envelope Limiter (SEL), and the second is the Feed-Forward (FF) architecture based on SSPA. For each of the PAs ACPR, power efficiency and MI are found. While the analysis of SSPA and SEL is mainly based on the existing literature, the analysis of FF may be considered as a new contribution. From the results of the analysis it is concluded that linearization improves the overall performance of communication system. It is also shown that the pre-distortion method (SEL) shows better performance than FF.     

Determination of band offsets in heterostructured colloidal nanorods using scanning tunneling spectroscopy

The ability to tailor the properties of semiconductor nanocrystals through creating core/shell heterostructures is the cornerstone for their diverse application in nanotechnology. The band-offsets between the heterostructure components are determining parameters for their optoelectronic properties, dictating for example the degree of charge-carrier separation and localization. So far, however, no method was reported for direct measurement of these factors in colloidal nanocrystals and only indirect information could be derived from optical measurements. Here we demonstrate that scanning tunneling spectroscopy along with theoretical modeling can be used to determine band-offsets in such nanostructures. Applying this approach to CdSe/CdS quantum-dot/nanorod core/shell nanocrystals portrays its type I band structure where both the hole and electron ground state are localized in the CdSe core, in contrast to previous reports which predicted electron delocalization. The generality of the approach is further demonstrated in ZnSe/CdS nanocrystals where their type II band alignment, leading to electron-hole separation, is manifested.     

Dynamic non-Bayesian decision making in multi-agent systems

We consider a group of several non-Bayesian agents that can fully coordinate their activities and share their past experience in order to obtain a joint goal in face of uncertainty. The reward obtained by each agent is a function of the environment state but not of the action taken by other agents in the group. The environment state (controlled by Nature) may change arbitrarily, and the reward function is initially unknown. Two basic feedback structures are considered. In one of them — the perfect monitoring case — the agents are able to observe the previous environment state as part of their feedback, while in the other — the imperfect monitoring case — all that is available to the agents are the rewards obtained. Both of these settings refer to partially observable processes, where the current environment state is unknown. Our study refers to the competitive ratio criterion. It is shown that, for the imperfect monitoring case, there exists an efficient stochastic policy that ensures that the competitive ratio is obtained for all agents at almost all stages with an arbitrarily high probability, where efficiency is measured in terms of rate of convergence. It is also shown that if the agents are restricted only to deterministic policies then such a policy does not exist, even in the perfect monitoring case. This revised version was published online in June 2006 with corrections to the Cover Date.     

呼吸代谢参与粉红单端孢侵染厚皮甜瓜果实不同阶段的防御反应

目的：探讨三羧酸（tricarboxylic acid cycle,TCA）循环和磷酸戊糖途径（pentose phosphate pathway,PPP）在病原真菌侵染果实中的作用。方法：用粉红单端孢（Trichothecium roseum）接种‘玉金香’厚皮甜瓜果实,观察（22±2）℃、相对湿度55%～60%条件下病斑直径的变化,测定接种果实病健交界处组织TCA循环和PPP关键酶活力以及中间产物含量的变化,分析不同侵染阶段TCA循环和PPP发挥的作用。结果：果实病斑直径在接种后24 h内无明显变化,48 h时明显增大,72 h时显著高于对照组（P＜0.05）。与对照组相比,接种粉红单端孢显著降低了早期果实的异柠檬酸脱氢酶活力（P＜0.05）,而显著提高了苹果酸脱氢酶（malate dehydrogenase,MDH）活力（P＜0.05）,24 h时MDH活力是对照组的2.14 倍;显著提高了早期果实烟酰胺腺嘌呤二核苷酸（nicotinamide adenine dinucleotide,NAD）和还原型烟酰胺腺嘌呤二核苷酸含量（P＜0.05）,24 h时分别高出对照组50.37%和50.31%;激活了果实的NAD激酶,显著提高了后期葡萄糖-6-磷酸脱氢酶和6-磷酸葡萄糖酸脱氢酶的活力（P＜0.05）,48 h时分别是对照组的1.83 倍和2.51 倍;显著促进了后期果实烟酰胺腺嘌呤二核苷酸磷酸和葡萄糖-6-磷酸的合成（P＜0.05）;显著降低了早期和中期果实核糖-5-磷酸异构酶活力和核酮糖-5-磷酸含量（P＜0.05）。结论：粉红单端孢侵染厚皮甜瓜早期诱导了果实组织TCA循环,后期促进了PPP,说明TCA循环参与了更多果实早期的抗病防御,而PPP在后期寄主防御反应中发挥更大的作用。     

Seasickness as a self-fulfilling prophecy: Raising self-efficacy to boost performance at sea.

Applying the self-fulfilling prophecy (SFP) approach to combating seasickness, the authors experimentally augmented the self-efficacy of naval cadets by telling them that they were unlikely to experience seasickness and that, if they did, it was unlikely to affect their performance at sea. Naval cadets (N?=?25) in the Israel Defense Forces were randomly assigned to experimental and control conditions. At the end of a 5-day training cruise, experimental cadets reported less seasickness and were rated as better performers by naive training officers than were the control cadets. There was a nonsignificant tendency for the experimental effects to be stronger among cadets of lower initial self-efficacy, suggestive of behavioral plasticity. Reducing seasickness by verbally enhancing self-efficacy is discussed as an application of "verbal placebo." These findings extend the generalizability of the SFP-at-work model and suggest new arenas for its practical application. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Correlation Between the Total Morphology of an Epoxy System and Some of its Properties

Due to the ever growing use of epoxy resins for structural applications, more information is required about their structure-properties relationship. Much work was done on this subject by us and by others, but many questions still remain unanswered. Some problems which require more detailed studies are the influence of factors like compositional changes in the resin (ratio of prepolymer-curing agent), postcuring and cooling of the polymerized resin from temperatures above T_g to room temperature, on physical properties of the product.     

一种在矢量基础上进行图形识别的通用方法

本文描述了一种在矢量基础上进行图形识别的通用方法．该方法包括２个步骤：第１步,寻找组成该图形的第１个关键图素;第２步,根据该图形的构造模式,从第１个关键图素出发,不断在其周围区域寻找组成该图形的其它图素．本文还提出了一种新的平面空间数据结构——位置索引．这种数据结构把平面图上的图形及图素用它们的平面位置索引组织起来,从而提高了按区域位置查找的效率．本文还介绍了该方法的２个应用实例：虚线识别和剖面线识别.     

Mode I interlaminar fracture toughness of Nylon 66 nanofibrilmat interleaved carbon/epoxy laminates

Carbon/epoxy laminates interleaved with laboratory scale electrospun Nylon 66 nanofibrilmat and spunbonded nonwoven mats were investigated. The effect of the nanoscale fibers on the fracture toughness of the composite under pure Mode I loading was evaluated. It was shown that the nanofibrilmat is responsible for a major interlaminar fracture toughness improvement, as high as 255–322%, compared to a noninterleaved carbon/epoxy reference laminate. We further studied the improvement mechanism of the electrospun nanofibrilmat compared to a commercial spunbonded nonwoven Nylon 66 mat. A combination of two interlayer fracture mechanisms responsible for the toughness improvement is suggested: the first is related to the high energy dissipated by bridged thermoplastic nanofibers and the second is attributed to the generation of a plastic zone near the crack tip. The interlaminar fracture mechanisms of both electrospun nanofibrilmat and the nonwoven mat interleaving was analyzed and discussed. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers