Polarization of bilayer membranes in phase separation. A quasi-one-dimensional model

A theoretical quasi-one-dimensional model of nonlinear oscillations of lipid bilayer director at phase separation region is considered. An arising orientational wave of deformation of the lipid bilayer must lead to spontaneous electrical polarization of the bilayer in the transmembrane field. If the orientational wave of bilayer deformation is of a nonlinear pattern the lipid director oscillations can relate to briather solution of sine-Godon equation within the framework of our model. In terms of the theoretical model are frequencies and spontaneous electrical polarization are estimated. The conclusion about the effect of radiofrequency electromagnetic wave resonance interaction with the briather structures on the cell membrane lipid bilayer is drawn.     

Institute of Social Research

In November 1965 the first Scientific Research Institute for Complex Social Research in the country was organized at the A. A. Zhdanov Leningrad State University. It is made up of eight laboratories: Social-Economic Research (director, V. R. Polozov), Sociological Research (director, V. A. Yadov), Engineering Psychology (director, B. F. Lomov), Differential Psychology and Anthropology (director, acting member of the RSFSR Academy of Pedagogical Sciences B. G. Anan'yev), Social Psychology (director, Ye. S. Kuz'min), Legal Research (director, corresponding member of the USSR Academy of Sciences D. A. Kerimov), Programmed Instruction (director, A. F. Esaulov), Efficient Management in Work Collectives (director, L. L. Gremyako).     

Reviews

Book reviewed in this article: Larsson, P. & Weider , L. J. (eds.) 1995: Cladocera as model organisms in biology. Poncin, P., Berrebi, J., Philippart, C. & Ruwet , J.-Cl. eds, 1993: Biologie des Barbus européens, africains et asiatiques. Birkhead , T. 1993: Great Auk Islands. A field biologist in the Arctic. Expert-Center for Taxonomic Identification (ETI) (ed.) 1994: Birds of Europe. Packer , C. 1994: Into Africa Norton, B. G., Hutchins, M., Stevens, E. F., Maple, T. L. & Wuichet , J. (eds.) 1995: Ethics on the ark.     

Modelling Beauveria bassiana horizontal transmission

1 We modelled horizontal transmission of Beauveria bassiana in Colorado potato beetle (CPB) between larval cadavers and soil inhabiting prepupae. 2 The rate of disease transmission, based on the probability of a prepupa contacting sporulating cadavers on the soil surface, is a non‐linear function of cadaver density and also dependent upon temperature. 3 The spatial pattern of cadavers is needed to estimate prepupal contacts with cadavers. Observational field studies determined Johnson distributions to model the spatial pattern of cadavers and prepupae in the field. The model also implicitly incorporates within‐field larval spatial pattern into estimates of field‐level horizontal transmission. 4 Potential for horizontal transmission is higher in simulations using weather data from the warmer year of 1995, than in simulations of the cooler growing season of 1993. 5 Simulations of CPB populations under northern Maine climatic conditions recorded in 1993 and 1995 suggest that horizontal transmission can range from 3 to 24% depending upon the timing of primary infection of larvae in the field. 6 Two simulated sequential applications of B. bassiana targeted at peak first instars resulted in maximum horizontal infection in both years. 7 Sensitivity analysis suggests that horizontal transmission is most sensitive to changes in the proportion of cadavers that sporulate and least sensitive to changes in the time between larval death and the onset of cadaver sporulation. 8 Field validation of the model indicates good prediction of one measure of horizontal infection, the proportion of prepupae which eventually sporulated after being released in controlled field experiments.     

Director Field Model of the Primary Visual Cortex for Contour Detection

We aim to build the simplest possible model capable of detecting long, noisy contours in a cluttered visual scene. For this, we model the neural dynamics in the primate primary visual cortex in terms of a continuous director field that describes the average rate and the average orientational preference of active neurons at a particular point in the cortex. We then use a linear-nonlinear dynamical model with long range connectivity patterns to enforce long-range statistical context present in the analyzed images. The resulting model has substantially fewer degrees of freedom than traditional models, and yet it can distinguish large contiguous objects from the background clutter by suppressing the clutter and by filling-in occluded elements of object contours. This results in high-precision, high-recall detection of large objects in cluttered scenes. Parenthetically, our model has a direct correspondence with the Landau - de Gennes theory of nematic liquid crystal in two dimensions.     

Reduced-system analysis of the effects of serotonin on a molluscan burster neuron

The mathematical model described in Bertram (1993) is used to carry out a detailed examination of the manner in which the neurotransmitter serotonin modifies the voltage waveform generated endogenously by burster neuron R₁₅ of Aplysia. This analysis makes use of a reduced system of equations, taking advantage of the slow rate of change of a pair of system variables relative to the others. Such analysis also yields information concerning the sensitivity of the neuron to brief synaptic perturbations. Received: 24 March 1993/Accepted in revised form: 9 June 1993     

Bioelectrorheological model of the cell. 5. Electrodestruction of cellular membrane in alternating electric field.

Recently proposed analysis of the extensil stress developed in a cellular membrane subjected to an alternating electric field (Pawłowski, P., and M. Fikus, 1993. Bioelectrorheological model of the cell. 4. Analysis of the extensil deformation of the membrane in an alternating field. Biophys. J. 65:535-540) was applied in calculations of extensil stress threshold values, sigma eo[d], producing experimentally observed electrodestruction of cells within the frequency range of 7 x 10(1) - 3 x 10(5) Hz. It was shown that the susceptibility (s[d] = 1/sigma eo[d]), of the membrane to this process varies with field frequency and depends on the type of cells. Electrodestruction is facilitated in the 10(5)-Hz field. A rheological hypothesis explaining the experimentally observed dependence of membrane stability on electric field frequency was proposed and successfully tested for two other phenomena: electroporation and electrofusion.     

A theoretical model of phase transitions in the human brain

An experiment using a multisensor SQUID (superconducting quantum interference device) array was performed by Kelso and colleagues (1992) which combined information from three different sources: perception, motor response, and brain signals. When an acoustic stimulus frequency is changed systematically, a spontaneous transition in coordination occurs at a critical frequency in both motor behavior and brain signals. Qualitatively analogous transitions are known for physical and biological systems such as changes in the coordination of human hand movements (Kelso 1981, 1984). In this paper we develop a theoretical model based on methods from the interdisciplinary field of synergetics (Haken 1983, 1987) and nonlinear oscillator theory that reproduces the main experimental features very well and suggests a formulation of a fundamental biophysical coupling. Received: 8 September 1993     

基于信息平台的公立医院科主任绩效考核实证研究

???? 目的 探讨实施科主任绩效考核对提高科主任绩效和医院绩效的效果。方法 采用近3年科主任绩效考核平均分变化趋势,判断科主任绩效考核整体效果;利用与上海市市级综合性医院绩效数据均值横向比较的方法,评估医院绩效提升的效果。结果 科主任绩效考核平均分持续提高,医院绩效优于上海市市级综合性医院绩效均值。结论 通过科主任绩效考核实践,发挥考核的导向作用,深化信息平台建设,落实医院各项管理措施,科主任绩效和医院绩效得到明显提升。

     

Women's health. The childbearing years and after.

Health and development planners have tended to see women primarily in context of their reproductive role. As a result, solutions to women''s health needs have been restricted to expanding and improving maternal and child health systems. There has recently been a major shift in direction, largely because of the influence of the world conference on population and development held in Cairo in 1994. Dr Guiseppe Benagiano, director of the special programme of research, development and research training in human reproduction based at the WHO, says, "We need to remind ourselves constantly that reproductive health is not simply a biomedical issue but one with serious implications for our general health and by extension, for all our efforts in human social and economic development." The 1993 world development report on health identified the lack of a clear strategy for engaging women in health care and suggested that child health services, prenatal care, treatment of sexually transmitted diseases, and family planning services should be provided jointly at convenient times. In an example of this, the Chilean Institute of Reproductive Medicine now offers integrated family planning services at the same time as child health services, and Thailand is experimenting with mobile health clinics to reach women in their homes. As the proportion of elderly women increases, old age is increasingly being seen as a female issue. With the impact of urbanisation and industrialisation, more of these women are living isolated lives, often suffering from chronic debilitating diseases. In his opening statement to the global commission on women''s health in April 1995 which focused on health conditions of women in old age, Dr Hiroshi Nakajima, the WHO''s director general, said: "Our goal should not be solely to extend lives in the physical sense, but to ensure that the added years are worth living."     

SWISS-MODEL: An automated protein homology-modeling server

SWISS-MODEL (http://swissmodel.expasy.org) is a server for automated comparative modeling of three-dimensional (3D) protein structures. It pioneered the field of automated modeling starting in 1993 and is the most widely-used free web-based automated modeling facility today. In 2002 the server computed 120 000 user requests for 3D protein models. SWISS-MODEL provides several levels of user interaction through its World Wide Web interface: in the 'first approach mode' only an amino acid sequence of a protein is submitted to build a 3D model. Template selection, alignment and model building are done completely automated by the server. In the 'alignment mode', the modeling process is based on a user-defined target-template alignment. Complex modeling tasks can be handled with the 'project mode' using DeepView (Swiss-PdbViewer), an integrated sequence-to-structure workbench. All models are sent back via email with a detailed modeling report. WhatCheck analyses and ANOLEA evaluations are provided optionally. The reliability of SWISS-MODEL is continuously evaluated in the EVA-CM project. The SWISS-MODEL server is under constant development to improve the successful implementation of expert knowledge into an easy-to-use server.     

Use of a spreadsheet program to calculate the electric field/current density distributions induced in irregularly shaped,inhomogeneous biological structures by low-frequency magnetic fields

A commercially available spreadsheet program is used on a microcomputer to calculate the electric field/current density distributions induced in irregularly shaped, inhomogeneous objects by low-frequency magnetic fields. A finite-difference method is applied to an impedance grid that represents the object being modeled. This approach is validated by comparison with 1) the analytical results of an eccentric cylinder model and 2) measurements made on a square dish containing a saline solution and square, insulating inclusions. Application of the method is also made to a culture dish with a layer of sediment exposed to a horizontal magnetic field. © 1993 Wiley-Liss, Inc.     

Optimal Regulation of Gas Exchange: Evidence from Field Data

Since the work of Cowan in 1977 it has been assumed that plantsregulate their stomata in a way that maximizes photosynthesisat a constant average rate of transpiration. The approach wasfurther developed by Hari et al. (1986) by introducing additionalassumptions which enabled the mathematical solution of the optimizationproblem using the Lagrangian method. The solution is testedfor Scots pine seedlings against field data. The results supportthe optimization hypothesis.Copyright 1993, 1999 Academic Press Pinus sylvestris (L.), stomatal conductance, photosynthesis, transpiration, optimization, field measurements, mathematical model, Lagrangian method     

Simulations of the alpha motoneuron pool electromyogram reflex at different preactivation levels in man

The alpha motoneuron pool and the surface electromyogram (EMG) of the human soleus muscle are modelled, respectively, by an alpha motoneuron pool model generating the firing patterns in the motor units of e muscle and by a muscle model using these discharge patterns to simulate the surface EMG. In the alpha motoneuron pool model, we use a population of motoneurons in which cellular properties like cell size and membrane conductance are distributed according to experimentally observed data. By calculating the contribution from each motor unit, the muscle model predicts the EMG. Wave forms of the motor unit action potentials in the surface EMG are obtained from experimental data. Using the model, we are able to give a quantitative prediction of the motoneuron pool activity and the reflex EMG output at different preactivation levels. The simulated data are consistent with experimentally obtained results in healthy humans. During static isometric muscle preactivations, the simulations show that the reflex strength is highly dependent on the intrinsic threshold properties of the alpha motoneuron pool. Received: 27 April 1993/Accepted in revised form: 8 September 1993     

NMR of bicelles: orientation and mosaic spread of the liquid-crystal director under sample rotation

Model-membrane systems composed of liquid-crystalline bicellar phases can be uniaxially oriented with respect to a magnetic field, thereby facilitating structural and dynamics studies of membrane-associated proteins. Here we quantitatively characterize a method that allows the manipulation of the direction of this uniaxial orientation. Bicelles formed from DMPC/DHPC are examined by ³¹P NMR under variable-angle sample-spinning (VAS) conditions, confirming that the orientation of the liquid-crystalline director can be influenced by sample spinning. The director is perpendicular to the rotation axis when (the angle between the sample-spinning axis and the magnetic field direction) is smaller than the magic angle, and is parallel to the rotation axis when is larger than the magic angle. The new ³¹P NMR VAS data presented are considerably more sensitive to the orientation of the bicelle than earlier ²H studies and the analysis of the sideband pattern allows the determination of the orientation of the liquid-crystal director and its variation over the sample, i.e., the mosaic spread. Under VAS, the mosaic spread is small if deviates significantly from the magic angle but becomes very large at the magic angle.     

Cooperative self-organization of afferent and lateral connections in cortical maps

A self-organizing neural network model called LISSOM for the synergetic development of afferent and lateral connections in cortical feature maps is presented. The weight adaptation process is purely activity-dependent, unsupervised, and local. The afferent input weights self-organize into a topological map of the input space. At the same time, the lateral interconnection weights adapt, and a unique lateral interaction profile develops for each neuron. Weak lateral connections die off, leaving a pattern of connections that represents the significant long-term correlations of activity on the feature map. LISSOM demonstrates how self-organization can bootstrap based on input information only, without global supervision or predetermined lateral interaction. The model gives rise to a nontopographically organized lateral connectivity similar to that observed in the mammalian neocortex as illustrated by a LISSOM model of ocular dominance column formation in the primary visual cortex. In addition, LISSOM can potentially account for the development of multiple maps of different modalities on the same undifferentiated cortical architecture. Received: 12 May 1993/Accepted in revised form: 22 September 1993     

Effect of degree of uniformity on predicted visual cortical response tuning curves

 The different cortical visual cells exhibit a large repertoire of responses to sinusoidal gratings, depending on their receptive field structure and the stimulation parameters. It has been shown previously that the tuning curves and histogram shapes of cell responses are affected by subunit distances. One receptive field model (Spitzer and Hochstein 1985b) incorporated subunit distance but assigned it as a constant parameter, for ease of calculation. Here we investigate different tuning curve properties of various primary cortical cell types during testing of 10 deg of nonuniform distances of the receptive fields’ subunits. The effect of nonuniformity was compared for average responses, tuning curve shapes, maximum peak responses, and bandwidths across four cell types of different sizes. The shapes and other properties of tuning curves are usually found to be retained also when the degree of uniformity is not very high for most of the cell types. In addition, the effect of uniformity is compared across these different response properties. The maximum peak responses of the tuning curve are found to display a lower coefficient of variation than the bandwidth, for all cell types, for most degrees of uniformity. Received: 15 June 1993/Accepted in revised form: 5 August 1994     

Dr. Haifan Lin. Interviewed by Han Lee and Rachel Rosenstein

Dr. Haifan Lin is professor of Cell Biology at Yale University, where he studies the mechanism of stem cell self-renewal in fruit flies, mice, and human cancer cells. Recently named director of the Yale Stem Cell Center, Dr. Lin has made seminal contributions to the stem cell field, most notably his demonstration of the stem cell niche theory using the fruit fly model, his discovery of the PIWI/AGO gene family that is essential for stem cell division in diverse organisms, and his recent finding of a group of small RNAs called PIWI-interacting, or piRNAs, which may play a crucial role in stem cell proliferation and germline development. Dr. Lin’s work on piRNAs was recognized by Science Magazine as a top scientific breakthrough of 2006. Recently, the Lin lab has begun exploring the role of these molecules in stem cell division and oncogenesis.     

Magnetically orientable phospholipid bilayers containing small amounts of a bile salt analogue, CHAPSO.

Buffered mixtures of the detergent 3-(cholamidopropyl)dimethylammonio-2-hydroxy-1-propanesulfonate (CHAPSO) and dimyristoylphosphatidylcholine (DMPC) orient in the presence of a strong magnetic field over a wide range of water contents (at least 65-85%) and CHAPSO:DMPC molar ratios (typically 1:10-1:3). 31P NMR studies show that the phospholipid in such mixtures is oriented with its director axis perpendicular to the magnetic field. 31P and 2H NMR results also suggest that the structure and dynamics of the DMPC molecules are similar to that of pure phospholipids existing in the liquid crystalline (L alpha) bilayer phase. The ability of 1:5 CHAPSO:DMPC samples to orient is highly tolerant of large changes in temperature, pH, and ionic strength, as well as to the addition of substantial amounts of charged amphiphiles or soluble protein. However, 2H NMR studies of deuterated beta-dodecyl melibiose (DD-MB) solubilized in the system indicate the head group conformation and/or dynamics of this glycolipid analogue is dependent upon the CHAPSO concentration. Despite the latter results, the orientational versatility of the system, together with the nondenaturing properties of CHAPSO, makes this system useful in spectroscopic studies of membrane-associated phenomena.     

Psychospiritual ecoscience: The Ju/'hoansi and cultural tourism

The relation between knowledge and the visual, on the one hand, and knowledge about peoples on the other, is a prime concern in visual anthropology. The impact of the visual on the everyday life of the Ju/'hoansi is my concern here. This paper is offered in two parts: this article and the one which follows.

The results of a field‐trip in July 1996 to Otjozondjupa (previously known as Bush‐manland) in Namibia are discussed in terms of the question: How do subjects make sense of the anthropological?¹ Our “subject community” was the Ju/'hoansi of Nyae Nyae. The “texts” we interrogated through Ju/'hoansi popular memory were those made of them by the documentary filmmaker John Marshall, a South African feature‐film director, Jamie Uys, and one by the Discovery Channel.