Color adaptation of spatial frequency detectors in the human visual system

Observers exposed alternately to a vertical grating of one spatial frequency in red light and a vertical grating of different spatial frequency in green light subsequently report frequency-specific color aftereffects when shown gratings in white light. Aftereffects occur, however, only when inspection gratings differ in spatial frequency by one octave or more and the frequency of at least one grating is above 3 cycles per degree. This spatial selectivity of the aftereffect is considered in terms of a neural adaptation model incorporating evidence on the tuning of spatial frequency detectors in the human visual system.     

Early receptor potential: photoreversible charge displacement in rhodopsin

When the eye is illuminated by an intense flash, the visual pigment rhodopsin begins to pass rapidly through a series of intermediate states, eventually becoming bleached. If a second flash is delivered during the lifetimes of these intermediates the rhodopsin can be photoregenerated. A fast electrical response of the visual receptors, the early receptor potential, is elicited by the first flash. A similar response is elicited by the second flash, but the polarity of this response is reversed. Moreover, this response can be separated into three components, each arising from the action of light on a different intermediate. It is likely that all these fast responses, including the early receptor potential, arise from charge displacements in the visual-pigment molecule.     

土壤电动修复中电极切换对土壤微生物群落的影响

通过细菌计数和Biolog方法,研究了在3.0 V·cm-1的电压梯度下,不同电场切换周期(24 h、5 h、10min和1 min)对土壤微生物群落的影响.结果表明,电压梯度为3.0 V·cm-1的电场作用能够促进土壤微生物的活性,但会轻微地降低土壤微生物功能多样性,电场切换不能改变这种电场对微生物群落的影响;长时间的电场处理下,电极反应对微生物数量和功能多样性损害严重,切换电场电极能有效消除电极效应,电场电极切换周期≤5 h时,可保护电极附近土壤微生物多样性,当切换周期≤10min时,不仅可保护土壤微生物多样性,而且可以保护微生物数量.研究结果说明了电场电极切换能有效降低电极反应对微生物群落的影响,揭示了电场电极切换对土壤微生物群落影响的规律,为电场电极切换方法在污染土壤电动强化生物修复技术中的深化和应用提供理论依据.     

植物花粉萌发与极性生长中的钙信号

概述了国内外对植物花粉萌发、花粉管生长的生理过程、植物体内的相关Ca2 离子通道和Ca2 泵的分类、信号转导、花粉极性生长的现象、Ca2 离子可能参于花粉萌发和极性生长的模式系统和机理。     

普通群体的遗传机制Ⅲ.两对等位基因的遗传

在普通群体中建立了两对等位基因遗传的数学模型,讨论了基因型频率在世代间的动态变化、遗传趋势、群体平衡及其性质,以及随机交配率、基因频率与基因型频率的关系。结果表明,在普通群体两对等位基因的遗传中,非平衡群体的数学模型(4)可以转换为随机交配群体的数学模型和非平衡自交群体的数学模型;平衡群体的数学模型(7)可以转换为随机交配群体的数学模型和平衡自交群体的数学模型。在群体平衡时,当两对等位基因频率均相等时,杂合子频率达到极大值。杂合子频率随r增大而增加,当r=1时达到最大值;当r=0时达到最小值。     

杜仲根段器官分化极性的研究

以杜仲根段为试材,种根竖直正插时两端根和芽的分化极性较强,上端形成芽,下段形成根。ＡＢＴ生根粉和６—ＢＡ分别可强化极性的表现。倒插时,形态学下段器官分化极性不显。     

Polarization of the C. elegans embryo by RhoGAP-mediated exclusion of PAR-6 from cell contacts

Early embryos of some metazoans polarize radially to facilitate critical patterning events such as gastrulation and asymmetric cell division; however, little is known about how radial polarity is established. Early embryos of Caenorhabditis elegans polarize radially when cell contacts restrict the polarity protein PAR-6 to contact-free cell surfaces, where PAR-6 regulates gastrulation movements. We have identified a Rho guanosine triphosphatase activating protein (RhoGAP), PAC-1, which mediates C. elegans radial polarity and gastrulation by excluding PAR-6 from contacted cell surfaces. We show that PAC-1 is recruited to cell contacts, and we suggest that PAC-1 controls radial polarity by restricting active CDC-42 to contact-free surfaces, where CDC-42 binds and recruits PAR-6. Thus, PAC-1 provides a dynamic molecular link between cell contacts and PAR proteins that polarizes embryos radially.     

Superconductivity-induced transfer of in-plane spectral weight in Bi2Sr2CaCu2O8+delta

Optical data are reported on a spectral weight transfer over a broad frequency range of Bi2Sr2CaCu2O8+delta, when this material became superconducting. Using spectroscopic ellipsometry, we observed the removal of a small amount of spectral weight in a broad frequency band from 10(4) cm(-1) to at least 2 x 10(4) cm(-1), due to the onset of superconductivity. We observed a blue shift of the ab-plane plasma frequency when the material became superconducting, indicating that the spectral weight was transferred to the infrared range. Our observations are in agreement with models in which superconductivity is accompanied by an increased charge carrier spectral weight. The measured spectral weight transfer is large enough to account for the condensation energy in these compounds.     

Geomagnetic Reversals during the Phanerozoic

An antalysis of worldwide paleomagnetic measurements suggests a periodicity of 350 x 10(6) years in the polarity of the geomagnetic field. During the Mesozoic it is predominantly normal, whereas during the Upper Paleozoic it is predominantly reversed. Although geomagnetic reversals occur at different rates throughout the Phanerozoic, there appeaars to be no clear correlation between biological evolutionary rates and reversal frequency.     

单船海上视觉搜寻水上人员的搜寻方式效率比较

分析了单船海上扩展方形和扇形视觉搜寻水上人员两种方式,通过建立衡量单船海上视觉搜寻水上人员两种高效搜寻方式的数学模型并结合《国际航空和海上搜寻救助手册》对其进行定量分析,得出在搜寻半径为2～5 n mile的较小搜寻区域内,扩展方形视觉搜寻方式的效率高于扇形视觉搜寻方式的结论,为海上视觉搜寻决策者进行科学决策提供依据。     

Cell polarity: quantitative modeling as a tool in cell biology

Among a number of innovative approaches that have modernized cell biology, modeling has a prominent yet unusual place. One popular view is that we progress linearly, from conceptual to ever more detailed models. We review recent discoveries of cell polarity mechanisms, in which modeling played an important role, to demonstrate that the experiment-theory feedback loop requires diverse models characterized by varying levels of biological detail and mathematical complexity. We argue that a quantitative model is a tool that has to fit an experimental study, and the model's value should be judged not by how complex and detailed it is, but by what could be learned from it.     

普通群体的遗传机制Ⅱ.复等位基因的遗传

在普通群体中,建立了3个及3个以上复等位基因的基因频率、基因型频率和随机交配率的关系及其数学模型,讨论了复等位基因及其频率,以及由复等位基因所构成的各种基因型频率在世代中的动态规律、遗传趋势、群体平衡及其性质。结果表明,在普通群体遗传中,非平衡群体的数学模型(4)可以转换为随机交配群体的数学模型和非平衡自交群体的数学模型;平衡群体的数学模型(7)可以转换为随机交配群体的数学模型和平衡自交群体的数学模型。在普通群体遗传平衡时,当3个复等位基因频率相等且随机交配率等于3/5时,群体各种基因型频率相等。     

溶液极性对H2O2酶活力的影响研究

研究了醇类和丙酮、二甲亚砜等水溶液极性对H2O2酶活力的影响。结果表明,H2O2酶的活力随着溶液极性的降低按线性规律下降,在丙醇、氯乙醇水溶液中,H2O2酶具有稳定的中间态,当二者浓度极低时,H2O2酶可被激活,活力最大可提高20%和26%,溶液极性对H2O2酶活力的影响可逆,有机溶剂使H2O2酶的吸收光谱峰值从270nm移到280nm。     

Smed-betacatenin-1 is required for anteroposterior blastema polarity in planarian regeneration

Planarian flatworms can regenerate heads at anterior-facing wounds and tails at posterior-facing wounds throughout the body. How this regeneration polarity is specified has been a classic problem for more than a century. We identified a planarian gene, Smed-betacatenin-1, that controls regeneration polarity. Posterior-facing blastemas regenerate a head instead of a tail in Smed-betacatenin-1(RNAi) animals. Smed-betacatenin-1 is required after wounding and at any posterior-facing wound for polarity. Additionally, intact Smed-betacatenin-1(RNAi) animals display anteriorization during tissue turnover. Five Wnt genes and a secreted Frizzled-related Wnt antagonist-like gene are expressed in domains along the anteroposterior axis that reset to new positions during regeneration, which suggests that Wnts control polarity through Smed-betacatenin-1. Our data suggest that beta-catenin specifies the posterior character of the anteroposterior axis throughout the Bilateria and specifies regeneration polarity in planarians.     

Abnormal polarity of thunderclouds grown from negatively charged air

Experiments were carried out in New Mexico to determine whether the electrification processes that lead to the formation of lightning in clouds are influenced by the polarity of the charges in the air from which the clouds grow. The normal, positive space charge in the sub-cloud air was reversed by negative charge released from an electrified wire, suspended across a 2-kilometer-wide canyon. On more than four occasions when the clouds over the wire grew and became electrified, they were of abnormal polarity with dominant positive charges instead of the usual negative charges in the lower part of the cloud. The formation of these abnormally electrified clouds suggests both that the electrification process in thunderclouds can be initiated and that its polarity may be determined by the small charges that are present in the atmosphere.     

Regulated pole-to-pole oscillations of a bacterial gliding motility protein

Little is known about directed motility of bacteria that move by type IV pilus-mediated (twitching) motility. Here, we found that during periodic cell reversals of Myxoccocus xanthus, type IV pili were disassembled at one pole and reassembled at the other pole. Accompanying these reversals, FrzS, a protein required for directed motility, moved in an oscillatory pattern between the cell poles. The frequency of the oscillations was controlled by the Frz chemosensory system, which is essential for directed motility. Pole-to-pole migration of FrzS appeared to involve movement along a filament running the length of the cell. FrzS dynamics may thus regulate cell polarity during directed motility.     

基于CIS战略的新时期图书馆形象塑造

概述了CIS以及借鉴CIS的必要性与可行性;从理念识别、行为识别和视觉识别三个要素对重塑图书馆形象进行探讨,认为重塑图书馆形象应建立创新服务模式、加强队伍建设、提高馆员素质、优化馆藏资源、采取多种形式宣传图书馆,并提出了借鉴CIS应注意的一些问题。     

Vision guides the adjustment of auditory localization in young barn owls

Barn owls raised with one ear plugged make systematic errors in auditory localization when the earplug is removed. Young owls correct their localization errors within a few weeks. However, such animals did not correct their auditory localization errors when deprived of vision. Moreover, when prisms were mounted in front of their eyes, they adjusted their auditory localization to match the visual error induced by the prisms, as long as the visual and auditory errors were within the same quadrant of directions. The results demonstrate that, during development, the visual system provides the spatial reference for fine-tuning auditory localization.     

Endothelial cell membranes: polarity of particles as seen by freeze-fracturing

Freeze-fracturing shows particles within membranes. In plasma membranes of most cells the particles are more strongly bound to the inner half. In unfixed endothelial cells, this polarity is reversed. Glutaraldehyde fixation results in conventional polarity. The reverse polarity may be related to a mechanism for preferential fusion of pinocytotic vesicles with the plasma membrane.