An adaptive weaver architecture radio with spectrum sensing capabilities to relax RF component requirements

This paper presents an architecture that utilizes spectrum sensing with a Weaver architecture receiver to ease the requirements on the RF front-end components. With the ability to sense the environment, large interferers that overwhelm small desired signals can be avoided. The learning and adapting capabilities are enabled by means of a flexible receiver architecture employing variable local oscillators (LOs) at RF and intermediate frequency (IF). Avoiding large interferers can reduce image rejection ratio (IRR) requirements for a given performance and results in a greater tolerance to the Q of filters and receiver mismatches. The design approach is applied to an IEEE 802.11a receiver and the results show that for a given performance level, the proposed design requires an IRR that is 40 dB less than that required for conventional Weaver receivers     

Deterministic analysis of sigma–delta modulation for linear and non-linear signal reconstruction

Deterministic analysis is becoming increasingly popular to study the theoretical mechanisms of ΣΔ modulation, as opposed to the classical noise-shaping approach. This paper gives an overview of its application to the specific problem of signal reconstruction. Once an input signal has been processed through a ΣΔ modulator of given specifications, the fundamental question is to know what deterministic information can be retrieved about this signal from the ΣΔ output. The paper summarizes all results obtained in this research under a unified presentation framework. © 1997 by John Wiley & Sons, Ltd.     

Uncertainty assessment of streamflow projection under the impact of climate change in the Lower Mekong Basin: a case study of the Srepok River Basin,Vietnam

Uncertainty assessment of future projection of streamflow is of the essence for an effective formulation of water resources management and planning adaptive to climate change. The aim of this study is to investigate the uncertainty in streamflow projection under the climate change impact in the Srepok River Basin. Uncertainty associated with emission scenarios (RCP2.6, RCP4.5 and RCP8.5), General Circulation Models (GCMs) (CanESM2, CNMR‐CM5 and HadGEM2‐AO), statistical downscaling methods (delta change method, quantile mapping and SDSM), and hydrological models (ANN, HEC‐HMS and SWAT) is examined. The results showed the largest uncertainty source of the streamflow projection is the GCM simulations, followed by the statistical downscaling methods, hydrological models and emission scenarios. In addition, the use of hydrological models has a considerable impact on uncertainty in the simulations of dry seasonal streamflow. Generally, the present study highlighted the importance of using multi‐GCMs in the studies on hydrological impact of climate change.     

Dedifferentiation of Human Cardiac Myofibroblasts Is Independent of Activation of COX-2/PGE2 Pathway

The differentiation of cardiac fibroblasts to myofibroblasts is considered to be a critical step in activation and progression of cardiac fibrosis in heart disease. TGF-β is one of the key cytokines that promotes transition of fibroblasts to myofibroblasts. Dedifferentiation of formed myofibroblasts or reversal of formed myofibroblasts to fibroblasts remains incompletely understood. Prostaglandin E₂ (PGE₂) has been shown to dedifferentiate human lung myofibroblasts. The role of activation of the COX-2/PGE₂ pathway in dedifferentiation of cardiac myofibroblasts remains unknown. Here, we show that phorbol 12-myristate 13-acetate (PMA) but not PGE₂ induces dedifferentiation of de novo adult human cardiac myofibroblasts stimulated by TGF-β1 from human cardiac fibroblasts as evidenced by reduced expression of α-smooth muscle actin (α-SMA). PMA remarkably increased endogenous levels of PGE₂ in human cardiac myofibroblasts. Pretreatment of myofibroblasts with NS-398, a selective COX-2 inhibitor, and PF-04418948, a selective PGE₂ receptor type 2 (EP2) antagonist, had no effect on expression of α-SMA nor abolished the dedifferentiation induced by PMA. Our results indicated that endogenous and exogenous PGE₂ has no effects on dedifferentiation of cardiac myofibroblasts. PMA-induced dedifferentiation of cardiac myofibroblast is independent of activation of COX-2 and PGE₂ pathway. The mechanism in PMA-induced reversal of cardiac myofibroblasts needs to be explored further.     

Hierarchical modeling and analysis of embedded systems

This paper describes the modeling language CHARON for modular design of interacting hybrid systems. The language allows specification of architectural as well as behavioral hierarchy and discrete as well as continuous activities. The modular structure of the language is not merely syntactic, but is exploited by analysis tools and is supported by a formal semantics with an accompanying compositional theory of refinement. We illustrate the benefits of CHARON in the design of embedded control software using examples from automated highways concerning vehicle coordination.     

轴肩圆角拉弯时应力集中系数的最新研究结果

过去出版物中弹性应力集中系数在受弯状态低估了21％，受拉状态低估了40％．对轴肩圆角应力集中系数所列的图表是根据对其它类似几何形状的分析结果提供的近似值。经过对含各种尺寸的轴肩圆角模型进行拉弯状态下详细的有限元分析，在三方面得出有用结论：直修正弹性应力集中系数；2修正冯·密歇斯等效应力集中系数；3圆角处最大应力位置。最新结果以人们熟悉的图形形式表示．而由曲线回归出的经验公式适用于设计中的数字计算。     

Prevalence, risk factors, O serogroups, and virulence profiles of Shiga toxin-producing bacteria from cattle production environments

Shiga toxin (Stx)-producing bacteria are important human pathogens that have been linked with cattle and associated food products. We recovered Stx-producing bacteria from 27.5% of cattle, 6.8% of water, and 2.3% of wildlife samples from a cattle production area during an 11-month period. Positive samples were found during every month and on 98% of sampling days. We recovered isolates from all cattle operations sampled, and prevalence within operations ranged from approximately 5 to 33%. Cattle prevalence was associated with the presence of Stx-producing bacteria in water and the production group and environment of cattle, with an interaction between production group and environment. Odds of recovering isolates from cattle were highest for groups of adult cows and their unweaned calves in pasture environments. Overall, 49 O serogroups were identified from 527 isolates. Seventy of the isolates contained virulence genes that encoded intimin and enterohemorrhagic Escherichia coli hemolysin. These were serogroups O111, O157, O109, O103, O145, O172, O84, O26, O108, O117, O126, O159, O5, O69, O74, O98, and O-rough. Our results suggest that the prevalence of Stx-producing bacteria can be relatively high in cattle, and associated factors may not be entirely similar to those reported for serotype O157:H7. Although Stx-producing bacteria were frequently detected, the strains may not be equally pathogenic for humans given the wide variety of serogroups and virulence genes. However, focusing on O157:H7 in food safety and surveillance programs may allow other Stx-producing bacteria, which appear to be widespread in cattle, to go undetected.     

Isolation and identification of three ecdysteroid conjugates with a C-20 hydroxy group in eggs of Locusta migratoria

Three ecdysteroids conjugates with a hydroxy group at C-20 were isolated from developing eggs of locusta migratoria and identified as 22-phosphate conjugates of 2-deoxy-20-hydroxy-ecdysone, 20-hydroxyecdysone and 20-hydroxyecdysone acetate.     

Processing of polyurethane/polyester interpenetrating polymer networks by reaction injection molding. Part III: Flow reorientation through multiple impingement

This is the third of a three-part paper investigating the feasibility of processing polyurethane/polyester Interpenetrating Polymer Networks (IPN) by Reaction Injection Molding (RIM).

1 Part of this paper was presented at the Third International Conference on Reactive Processing. Bischenberg Congress Center, Alsace, France, September 4– (1984)

Two basic issues are addressed concerning the improvement of the mixing scale in impingement mixing, namely, the influence of multiple impingement on the microscale and the number of flow dividing elements needed to achieve a certain degree of mixing. It was found that the incorporation of cascading stages does improve mixing further. The extent of improvement depends on the secondary stream Reynolds number and the local impingement pressure. A transition zone generally demarcates the beginning of marginal improvement on the number of elements used. Since the cascading configuration operates in a manner analogous to “motionless mixers,” there is a practical limit to the number of stages that can be used. At a primary impingement pressure of 18,000 psi, for instance, an overall improvement of 53 percent is recorded for a flow through a total of 80 stages. A noticeable 23 percent is noted within the first ten stages while the next 70 stages enhance mixing by only 30 percent. Thermal and dynamic mechanical analysis revealed some degree of interpenetration between the two networks.     

论创新型教师的人格特征

兴国的教育、必有兴教的良师;良师之本,重在人格。师资队伍建设应立足于塑造具有高度的自主性、强烈的情感、坚强的意志和刚毅的性格等人格特征,促使现代教师向着人格的最高境界升华。