计算机控制系统信号重构容错算法研究

信号重构是计算机系统与被控对象进行信息通信的重要环节,在简要分析Shannon重构、ZOH重构和一阶重构等信号重构方法局限性的基础上,提出了一组基于三点插值的重构算法和被控过程采样数据的一步容错预测算法,并将一步容错预测与三点插值算法相结合,建立了对于被控过程信号异常情况有良好容错能力的一步容错预测二阶重构算法。上述的一步容错预测二阶重构算法不仅结构简单、可用于在线控制,而且算法精度和可靠性明显高于普通的ZOH重构和一阶重构算法。     

Temporal difference models describe higher-order learning in humans

The ability to use environmental stimuli to predict impending harm is critical for survival. Such predictions should be available as early as they are reliable. In pavlovian conditioning, chains of successively earlier predictors are studied in terms of higher-order relationships, and have inspired computational theories such as temporal difference learning. However, there is at present no adequate neurobiological account of how this learning occurs. Here, in a functional magnetic resonance imaging (fMRI) study of higher-order aversive conditioning, we describe a key computational strategy that humans use to learn predictions about pain. We show that neural activity in the ventral striatum and the anterior insula displays a marked correspondence to the signals for sequential learning predicted by temporal difference models. This result reveals a flexible aversive learning process ideally suited to the changing and uncertain nature of real-world environments. Taken with existing data on reward learning, our results suggest a critical role for the ventral striatum in integrating complex appetitive and aversive predictions to coordinate behaviour.     

Mutations in the gene encoding the lamin B receptor produce an altered nuclear morphology in granulocytes (Pelger-Huët anomaly)

Pelger-Hu?t anomaly (PHA; OMIM *169400) is an autosomal dominant disorder characterized by abnormal nuclear shape and chromatin organization in blood granulocytes. Affected individuals show hypolobulated neutrophil nuclei with coarse chromatin. Presumed homozygous individuals have ovoid neutrophil nuclei, as well as varying degrees of developmental delay, epilepsy and skeletal abnormalities. Homozygous offspring in an extinct rabbit lineage showed severe chondrodystrophy, developmental anomalies and increased pre- and postnatal mortality. Here we show, by carrying out a genome-wide linkage scan, that PHA is linked to chromosome 1q41-43. We identified four splice-site, two frameshift and two nonsense mutations in LBR, encoding the lamin B receptor. The lamin B receptor (LBR), a member of the sterol reductase family, is evolutionarily conserved and integral to the inner nuclear membrane; it targets heterochromatin and lamins to the nuclear membrane. Lymphoblastoid cells from heterozygous individuals affected with PHA show reduced expression of the lamin B receptor, and cells homozygous with respect to PHA contain only trace amounts of it. We found that expression of the lamin B receptor affects neutrophil nuclear shape and chromatin distribution in a dose-dependent manner. Our findings have implications for understanding nuclear envelope-heterochromatin interactions, the pathogenesis of Pelger-like conditions in leukemia, infection and toxic drug reactions, and the evolution of neutrophil nuclear shape.     

Coherent emission of light by thermal sources

A thermal light-emitting source, such as a black body or the incandescent filament of a light bulb, is often presented as a typical example of an incoherent source and is in marked contrast to a laser. Whereas a laser is highly monochromatic and very directional, a thermal source has a broad spectrum and is usually quasi-isotropic. However, as is the case with many systems, different behaviour can be expected on a microscopic scale. It has been shown recently that the field emitted by a thermal source made of a polar material is enhanced by more than four orders of magnitude and is partially coherent at a distance of the order of 10 to 100nm. Here we demonstrate that by introducing a periodic microstructure into such a polar material (SiC) a thermal infrared source can be fabricated that is coherent over large distances (many wavelengths) and radiates in well defined directions. Narrow angular emission lobes similar to antenna lobes are observed and the emission spectra of the source depends on the observation angle--the so-called Wolf effect. The origin of the coherent emission lies in the diffraction of surface-phonon polaritons by the grating.     

The Par complex directs asymmetric cell division by phosphorylating the cytoskeletal protein Lgl

To generate different cell types, some cells can segregate protein determinants into one of their two daughter cells during mitosis. In Drosophila neuroblasts, the Par protein complex localizes apically and directs localization of the cell fate determinants Prospero and Numb and the adaptor proteins Miranda and Pon to the basal cell cortex, to ensure their segregation into the basal daughter cell. The Par protein complex has a conserved function in establishing cell polarity but how it directs proteins to the opposite side is unknown. We show here that a principal function of this complex is to phosphorylate the cytoskeletal protein Lethal (2) giant larvae (Lgl; also known as L(2)gl). Phosphorylation by Drosophila atypical protein kinase C (aPKC), a member of the Par protein complex, releases Lgl from its association with membranes and the actin cytoskeleton. Genetic and biochemical experiments show that Lgl phosphorylation prevents the localization of cell fate determinants to the apical cell cortex. Lgl promotes cortical localization of Miranda, and we propose that phosphorylation of Lgl by aPKC at the apical neuroblast cortex restricts Lgl activity and Miranda localization to the opposite, basal side of the cell.     

Wnt proteins are lipid-modified and can act as stem cell growth factors

Wnt signalling is involved in numerous events in animal development, including the proliferation of stem cells and the specification of the neural crest. Wnt proteins are potentially important reagents in expanding specific cell types, but in contrast to other developmental signalling molecules such as hedgehog proteins and the bone morphogenetic proteins, Wnt proteins have never been isolated in an active form. Although Wnt proteins are secreted from cells, secretion is usually inefficient and previous attempts to characterize Wnt proteins have been hampered by their high degree of insolubility. Here we have isolated active Wnt molecules, including the product of the mouse Wnt3a gene. By mass spectrometry, we found the proteins to be palmitoylated on a conserved cysteine. Enzymatic removal of the palmitate or site-directed and natural mutations of the modified cysteine result in loss of activity, and indicate that the lipid is important for signalling. The purified Wnt3a protein induces self-renewal of haematopoietic stem cells, signifying its potential use in tissue engineering.