DYNAMIC BEHAVIOR OF PERIODIC FEEDBACK CONTROL SYSTEMS

Periodic feedback is a control strategy implemented by fast zero-average oscillations in the parameters of the control law. It is well known that time invariant feedback control offers no means for zeros relocation. Periodic feedback allows zeros relocation in an asymptotic sense, resulting in improved closed loop characteristics, such as increased gain margins.     

Risk assessment and food-borne micro-organisms: the difficulties of biological diversity

Quantitative risk assessment to estimate the probability of adverse health consequences from microbial pathogens in foods has developed from techniques used to assess the risk associated with chemicals. The procedure is complicated by numerous variabilities and uncertainties. While many of the microbial hazards have been identified, dose-response data are limited and variable. Little information is available to characterize the potential for exposure. The accuracy of dose-response models used to calculate the probability of infection is highly dependent on the assumptions used. The risk assessment is complicated by the fact that microbial populations are not static in foods. Mathematical models can generate numerical estimates of risk which are used in risk management. An acceptable level of risk should be based on what is technically feasible and economically achievable.     

Contributions of sibling relations to the adaptation of youths with insulin-dependent diabetes mellitus.

Associations among sibling relations and the psychosocial and illness-specific adaptation of youths (N?=?66) with insulin-dependent diabetes mellitus (IDDM) were examined. The findings suggest that sibling relations, especially sibling conflict, contribute an independent source of variance above and beyond that contributed by demographic characteristics, sibling constellation variables, and important dimensions of family relations in predicting the youths' adaptation. High family-life stress and high sibling status/power contributed unique variance in predicting internalizing behaviors, and male gender and sibling conflict contributed independently to externalizing problems. Sibling conflict also contributed unique variance to the youths' general self-esteem, along with social class and family cohesion, and to their adjustment to IDDM. Data suggest that parent–child dyads and sibling dyads represent interrelated and independent subsystems within the family, and that both subsystems may influence the psychosocial functioning of youths with IDDM. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A multiple controller structure and design strategy with stability analysis

This paper proposes a multi-controller structure for a plant and develops associated stability results. The main theoretical result of the paper is a quite simple necessary and sufficient condition for the closed-loop stability of the scheme. The result also specializes as a multi-controller generalization of the single controller Youla-Kucera theory for the class of all stabilizing controllers for a plant, and to known results concerning simultaneous stabilization. The plants considered are recursively expressed in terms of a set of approximations of frequency-shaped plant-model errors. The controllers in successive loops can be designed based on increasing refinement in model approximation, perhaps via on-line identification.An advantage of the proposed multi-controller strategy is that a number of various controller design techniques can be employed to achieve performance objectives which are not conveniently achievable by any one technique. A design example is included with first an LQG design applied for stabilization of a crude nominal model, and then an H^∞ optimal design, and finally an H² optimal design. The latter two designs are aimed at enhancing H^∞/H² performances. There could even be a further adaptive loop for on-line performance enhancement.     

Improved burn scar assessment with use of a new scar-rating scale

The subjective assessment of scar appearance is a widely used method in the evaluation of burn outcomes and the efficacy of treatment methods. The purpose of this study is to design a numeric scar-rating scale with better interrater reliability than has previously been reported. The rating scale assesses scar surface, thickness, border height, and color differences between a scar and the adjacent normal skin. Eight raters were trained with use of a standardized set of photographs that provide examples of the scores to be assigned to each level of severity of each scar characteristic. The raters then rated 10 photographs of different scars, referring to the teaching set of pictures for comparison. The intraclass correlation (interrater reliability) was 0.94, 0.95, 0.90, and 0.85 for scar surface, border height, thickness, and color, respectively. This rating system has proved to be a useful tool for the evaluation of scar surface, thickness, border height, and color.     

The fetoplacental pressor effects of low-dose acetylsalicylic acid and angiotensin II in the ex vivo cotyledon model

OBJECTIVE: Our purpose was to investigate perfusion pressure changes ex vivo induced by angiotensin II on fetoplacental vasculature pretreated with low-dose acetylsalicylic acid. STUDY DESIGN: Two cotyledons from each of 12 placentas were perfused. The intervillous space of one cotyledon was infused with acetylsalicylic acid (5 x 10(-5) mol/L) similar to the serum concentration of women receiving daily low-dose aspirin therapy (60 to 81 mg). The control cotyledon was infused with an equivalent amount of normal saline solution. Two doses of angiotensin II, 1 x 10(-11.5) and 1 x 10(-10) moles, were injected as boluses into the chorionic arteries of each cotyledon. A 3 x 10(-7) mole dose of angiotensin II was also injected into the intervillous space. Statistical analysis was performed with analysis of variance, and results are expressed as mean pressure change in millimeters of mercury +/- SEM. RESULTS: Perfusion pressure response did not vary between cotyledons pretreated with acetylsalicylic acid and control cotyledons when 3 x 10(-7) moles of angiotensin II was injected into the intervillous space (8.0 +/- 1.9 mm Hg vs 9.8 +/- 1.6 mm Hg, p = 0.59). There were no differences between cotyledons in pressure response to 1 x 10(-11.5) moles of angiotensin II injected into the fetal circuit (5.9 +/- 0.8 mm Hg vs 6.7 +/- 0.9 mm Hg, p = 0.51). However, in the cotyledons pretreated with acetylsalicylic acid there was a decrease in the pressor response to 1 x 10(-10) moles of angiotensin II (14.1 +/- 1.4 mm Hg vs 21.5 +/- 3.3 mm Hg, p = 0.05). CONCLUSIONS: Low-dose aspirin infused into the intervillous space decreases vasoconstriction elicited by angiotensin II in the fetoplacental compartment. This suggests that maternal low-dose aspirin therapy has effects in the fetoplacental circulation in addition to its effects in the maternal circulation.     

Missing information in selection: An application of the Einhorn-Hogarth ambiguity model.

This article argues that the devaluation of options with missing information, found in previous research, is a specific example of ambiguity avoidance in choice. H. J. Einhorn and R. M. Hogarth's (see record 1986-13621-001) ambiguity model was used to make predictions concerning responses to missing information in an employee-selection context. A within-subjects design was used to test the hypothesis that decision makers would avoid options with missing information when they were anticipating gain, but they would prefer such options when they were anticipating loss. Degree of ambiguity was expected to interact with this effect. The results supported the hypothesized effect of decision-maker perspective on choice. However, although there was a significant interaction between decision-maker perspective and degree of ambiguity, it was not of the nature that was predicted by the Einhorn-Hogarth model. Generalized pessimism was negatively correlated with preferences for missing-information options. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sparse LCMV beamformer design for suppression of ground clutter inairborne radar

Cancellation of the ground clutter received at an airborne phased array radar is an inherently two dimensional problem. Clutter returns are Doppler shifted due to platform motion forcing the use of processors that can resolve targets in both velocity (Doppler) and azimuth. Fully adaptive processors that operate in both dimensions require prohibitively large computation so that reduced adaptive dimension, or partially adaptive processors must be considered. In conventional partially adaptive linearly constrained minimum variance (LCMV) beamformer design the approach taken has been to represent the interference subspace with some reduced set of vectors, typically the eigenvectors associated with the largest eigenvalues of the interference covariance matrix. This technique does yield good performance but will not give the optimum performance for a given partially adaptive dimension. In this paper, an off-line method for selecting the “best” degrees of freedom to be retained in a partially adaptive design is presented. The sequential algorithm described selects those degrees of freedom that best minimize the beamformer output mean square error. This approach leads to a sparse structure for the transformation matrix, which when implemented in a generalized sidelobe canceller (GSC) structure results in a reduction in the computational load. This approach also allows a reduction in the required adaptive dimension as compared to the eigenvector based approach. Illustrative examples demonstrate the effectiveness of this method     

纳米银粉在电子工业中的最新发展

一、引言 银粉和碎银薄片广泛应用于电子工业.白银在其中的作用是作为导电的粘结剂:触摸开关膜片(MTS)、低温陶瓷(LTCC)、等离子显示器面板等.高集成电子器件的需求推动了银粉制造业生产出更小的颗粒和特定的颗粒分布.过去5年出现的各种技术革新满足不断增长的需求.各种各样的专利应运而生,技术手段从生物方法到雾化沉积法,但任何一种方法都存在优缺点.现在纳米银粉的成本和收益仍处于评估过程中.正如Nanodyanamics的Alan Rae所说,纳米技术只能在性价比合适的情况下才能实现应用,很多新技术对于工业化生产而言还是"奢侈品",科研与实践总有一段距离需要跨越.消费领域中有个例子是:VCR,DVD,DVD-R;在工业生产中离散的嵌入电容.每个例子都不同,但是都存在着一个市场采纳新技术的交叉点.