江汉平原渍害田生态特征的研究

本文根据大量统计资料建立了江汉平原渍害田生态模式,分析了江汉平原地下水位埋深变化和田间渗漏量大小对农田生态系统的综合效应,采用渍害田与非渍害田对照的方式,给出了渍害灾变后的农田生态特征,并根据大量观测资料的分析结果,提出了识别渍害田的判据。     

Stereopsis and the random element in the organization of the striate cortex.

Receptive field position and orientation disparities are both properties of binocularly discharged striate neurons. Receptive field position desparities have been used as a key element in the neural theory for binocular depth discrimination. Since most striate cells in the cat are binocular, these position disparities require that cells immediately adjacent to one another in the cortex should show a random scatter in their monocular receptive field positions. Superimposed on the progressive topographical representation of the visual field on the striate cortex there is experimental evidence for a localized monocular receptive field position scatter. The suggestion is examined that the binocular position disparities are built up out of the two monocular position scatters. An examination of receptive field orientation disparities and their relation to the random variation in the monocular preferred orientations of immediately adjacent striate neurons also leads to the conclusion that binocular orientation disparities are a consequence of the two monocular scatters. As for receptive field position, the local scatter in preferred orientation is superimposed on a progressive representation of orientation over larger areas of the cortex. The representation in the striate cortex of visual field position and of stimulus orientation is examined in relation to the correlation between the disparities in receptive field position and preferred orientation. The role of orientation disparities in binocular vision is reviewed.     

不同干扰条件下枸杞园节肢动物群落结构与动态

2008年通过对宁夏银川地区不同干扰条件下枸杞园节肢动物群落的系统调查,共采集节肢动物151628头,鉴定出4纲27目76科167种,其中天敌亚群落61种,化防园23种,有机园30种,自生园61种,天敌总量的比例分别为10.87%、18.78%、70.34%。通过群落结构分析,自生园丰富度、个体数均明显高于化防园和有机园,有机园均匀度、多样性较高,而化防园丰富度、个体数指数都较低,而优势集中度高。通过主分量分析表明潜叶类害虫与刺吸类害虫是不同人工干扰条件下的主要害虫,刺吸类害虫成为发展有机枸杞的重要障碍,食花果类害虫具有较大的危害潜力;寄生类天敌、病原类天敌为自生园优势天敌,捕食类天敌是有机园、化防园的优势天敌,但化防园天敌作用较为微弱。自生园天敌亚群落与害虫亚群落第一对典型变量为V1=0.048x1-0.2533x2+0.5951x3+0.5207x4,W1=0.9021y1+0.0354y2+0.0223y3+0.1847y4-0.0591y5,相关系数为0.8635,化防园、有机园天敌亚群落与害虫亚群落第一对典型变量的相关系数分别为0.6826、0.7332。通过害虫-天敌亚群落的种群消长动态表明,天敌亚群落作为整体对害虫发挥着调控作用,自生园7-9月份寄生性天敌对刺吸式害虫的跟随作用很强,有机园较弱,化防园则不明显。     

Distinctive features of collisionless gradient drift instabilities in a high-β plasma in a highly nonuniform magnetic field

A set of Vlasov-Maxwell equations for collisionless electromagnetic drift instabilities of high-β plasma configurations with a nonuniform magnetic fields is solved. The effect of the transverse static magnetic field variation and magnetic field line curvature, as well as the plasma temperature and density gradients, is considered. It is shown that, in a nonuniform magnetic field, the behavior of the instabilities differs substantially from that in a uniform field. Electromagnetic modes propagating strictly transverse to the lines of the static magnetic field are analyzed in detail, and unstable solutions are obtained for both extraordinary and ordinary waves. Numerical results show that, in the latter case, instability occurs when the magnetic field decreases toward the periphery and the plasma temperature and density gradients are oppositely directed.     

Electromagnetic induced kinetic effects on charged substrates in localized enzyme systems.

An analytical expression for the rate efficiency factor of planar localized enzyme systems is derived. The derivation takes into account the isothermal kinetic effect under the externally imposed perturbation of combined electrostatic and high frequency time-varying fields. The contribution of each individual field to the enzyme reaction is examined through the basic mechanism in which charged substrates interact with the specific perturbing field. The interaction mechanisms for the electrostatic and for the time-varying fields are found to be different. This difference regulates the different manners in which enzymatic reaction rates are altered. Enzymatic reactions under electrostatic perturbation can be retarded or enhanced depending on the field polarization. At sufficiently high field intensities the reaction rate may approach zero or approach a maximum value equal to the turnover number of the enzyme. Time-varying field perturbations, on the other hand, always enhance the enzymatic reactions if bunching effects are negligible. At sufficiently high field intensities, the reaction may approach a value equal to that of the free enzyme system. Several typical numerical examples on pure eletrostatic field perturbations, pure time-varying field perturbations, and combined field perturbations are also presented.     

上下视野空间选择性注意的ERP研究

该文主要研究上、下视野空间选择性注意早期所诱发的ＥＲＰ反应,探讨注意上、下视野视觉信息处理的特征与差别。１０名被试的主要实验果为：１）对上、下视野的选择注意产生类似于注意左、右视野时Ｐ１、Ｎ１,Ｐ２的相对增强;２）偶极子定位显示,上、下视野刺激的早期注意反应（Ｐ１）以交叉方式投射到枕区,即下视野刺激的注意反应偏向枕区的背侧,而上视野刺激的注意反应偏向枕区的腹侧;３）上下视野的早期注意反应（Ｐ１）具     

Magnetohydrodynamics of a weakly ionized plasma: Ambipolar magnetic diffusion and shock front structure

Kinetic equations with the BGK collision integral are used to derive MHD equations for a weakly ionized plasma that are applicable over a broad range of magnetic field strengths. In strong magnetic fields, a substantial contribution to the transverse diffusion of the magnetic field comes from the ambipolar magnetic diffusion, which is associated with the motion of both the charged component and the magnetic field against the background of the neutral plasma component. The problems of the magnetic field diffusion in a weakly ionized plasma and the shock wave structure are solved.     

The bioelectric field of the catfish Ictalurus nebulosus.

The variability of the bioelectric field of the electrosensitive catfish, Ictalurus nebulosus, was investigated by recording the potential variation occurring when the fish passed a stationary electrode, and by recording the field of a stationary fish by a 15-electrode array. A good first order approximation of the recorded field of a 20 cm long fish is a dipole dc source with the source and sink about 7 cm apart, carrying a current of about 1 microA in water with a specific resistivity of 3.3 kohm cm. At 5 cm distance from the dipole axis such a source generates an electric potential swing in the order of 50 microV in free space, head negative, tail positive. Superimposed on the basic component are respiration related fluctuations, and fluctuations related to the activity of the alimentary canal, gills, and skin. Novel stimuli, or stressors like investigators approaching the aquarium, evoke sudden increases in field strength. which last about 15 min. Demineralization of the aquarium water causes changes in field strength and reversal of field polarity. The administration of food causes field variations in the vicinity of the anal opening. The bioelectric field shows diurnal fluctuations of 100 microV. The peak is at about 04:00, the dip at 14:00. The fluctuations of the bioelectric field are sufficiently strong and specilic to serve as electrical stimuli to other electrosensitive catfish. It is suggested that the field changes allow a simple form of electrocommunication. i.e. inform conspecifics about some physiological properties of the field source. The cellular mechanisms underlying the fluctuations of the bioelectric field are homeostatic processes mediated by ion pumps and ion channels.     

Effect of the transmembrane electric field on the photochemical and quenching properties of photosystem II in vivo.

The intermediate phase of fluorescence relaxation (lms-ls) (Joliot, P., Joliot, A., Bouges, B, and Barbieri, G. (1971) Photochem. Photobiol. 14, 287-305), following a single saturating flash, is shown to be controlled by a slow phase of the reoxidation of Q- by a secondary acceptor and, in vivo, by the transmembrane electric field. The kinetics of reoxidation of Q- are slowed by lowering the pH. This slowing effect is interpreted in terms of the reversible formation at low pH of QH which is not oxidizable by the secondary acceptor. The electric field transforms Photosystem II centers into a non-quenching photochemically inactive state that cannot be attributed to an accumulation of Q-. Centers are unequally sensitive to the field. A critical field strength can be defined for each center above which that center is blocked and below which the center is photochemically active. The transformation from the active to inactive state occurs over a narrow range of field strength. Sensitive centers are blocked by the field in less than 1 ms and become active again in less than 10 ms as the field strength falls. Two hypotheses are proposed for the mechanism of blockage of centers by the field: (1) a field induced conformational change in the centers, (2) the formation or suppression of a dipole critical to the function of a center. The activity of the ATP synthetase, determining the rate of relaxation of the field, was controlled by a light-dark treatment or by a chemical method using p-benzoquinone.     

Formation of quasi-two-dimensional dust structures in an external electric field

Conditions are considered under which quasi-two-dimensional extended structures are formed consisting of charged dust grains that are suspended in a gravitational field by an external electric field. Formulas are derived that describe the relationships between the parameters of the intergrain interaction potential, the number of dust grains, and the gradients of the linear electric field of the device. A criterion is proposed that determines the onset of a new dust layer in a quasi-two-dimensional dust system.     

The Influence of Electric Field and Confinement on Cell Motility

The ability of cells to sense and respond to endogenous electric fields is important in processes such as wound healing, development, and nerve regeneration. In cell culture, many epithelial and endothelial cell types respond to an electric field of magnitude similar to endogenous electric fields by moving preferentially either parallel or antiparallel to the field vector, a process known as galvanotaxis. Here we report on the influence of dc electric field and confinement on the motility of fibroblast cells using a chip-based platform. From analysis of cell paths we show that the influence of electric field on motility is much more complex than simply imposing a directional bias towards the cathode or anode. The cell velocity, directedness, as well as the parallel and perpendicular components of the segments along the cell path are dependent on the magnitude of the electric field. Forces in the directions perpendicular and parallel to the electric field are in competition with one another in a voltage-dependent manner, which ultimately govern the trajectories of the cells in the presence of an electric field. To further investigate the effects of cell reorientation in the presence of a field, cells are confined within microchannels to physically prohibit the alignment seen in 2D environment. Interestingly, we found that confinement results in an increase in cell velocity both in the absence and presence of an electric field compared to migration in 2D.     

Conditioned responding to magnetic fields by honeybees

Summary Individual honeybees were trained in two experiments to come for sucrose solution to a target set on a shelf before an open laboratory window. On some visits, the target was presented in the ambient geomagnetic field, and on other visits in a field modified in the vicinity of the target by passing a direct current through a coil under the shelf. The target contained 50% sucrose when it was in one of the two fields and 20% sucrose when it was in the other. Tested subsequently with a pair of targets, one in the ambient field, one in the modified field, and both containing tap water, the animals significantly preferred the target in the field in which they had been given the 50% sucrose during training. Four modified fields, produced with different coils and currents, were discriminated equally well from the ambient field, and performance was as good when the 50% sucrose was given in the ambient field as when it was given in the modified field. Data are provided also to illustrate the excellent discriminative performance attainable when two targets are presented on each training visit — one in a modified field, the other in the ambient field — and choice of one is rewarded with 50% sucrose while choice of the other is punished with mild electric shock. Our results show that foragers attend to magnetic stimuli at the feeding site and that discriminative training techniques are appropriate for the study of magnetoreception and its mechanism in honeybees.     

Effect of the external magnetic field on the MHD turbulence spectra

The turbulent properties of conducting fluids in an external constant magnetic field are known to change with increasing field strength. A study is made of the behavior of the second-order structural function of the velocity field in a homogeneous incompressible turbulent fluid in the presence of an external uniform magnetic field. It is shown that, depending on the magnetic field strength, there may be different governing parameters of the system in both the inertial and dissipative intervals of turbulence. This leads to new spectral scalings that are consistent with experimental ones.     

Effect of the transmembrane electric field on the photochemical and quenching properties of Photosystem II in vivo

The intermediate phase of fluorescence relaxation (lms-ls) (Joliot, P., Joliot, A., Bouges, B, and Barbieri, G. (1971) Photochem. Photobiol. 14, 287–305), following a single saturating flash, is shown to be controlled by a slow phase of the reoxidation of Q^? by a secondary acceptor and, in vivo, by the transmembrane electric field.The kinetics of reoxidation of Q^? are slowed by lowering the pH. This slowing effect is interpreted in terms of the reversible formation at low pH of QH which is not oxidizable by the secondary acceptor.The electric field transforms Photosystem II centers into a non-quenching photochemically inactive state that cannot be attributed to an accumulation of Q^?. Centers are unequally sensitive to the field. A critical field strength can be defined for each center above which that center is blocked and below which the center is photochemically active. The transformation from the active to inactive state occurs over a narrow range of field strength.Sensitive centers are blocked by the field in less than 1 ms and become active again in less than 10 ms as the field strength falls. Two hypotheses are proposed for the mechanism of blockage of centers by the field: (1) a field induced conformational change in the centers, (2) the formation or suppression of a dipole critical to the function of a center.The activity of the ATP synthetase, determining the rate of relaxation of the field, was controlled by a light-dark treatment or by a chemical method using $\text{p-}\text{benzoquinone}$.     

Tearing instability of a force-free magnetic configuration in a collisionless plasma

The equilibrium and stability of a sheared force-free magnetic field in a collisionless plasma are investigated, and the main features of charged particle motion in such a field are analyzed. A steady solution is derived to the Vlasov-Maxwell equations for the charged particle distribution function that describes different equilibrium configurations. The tearing instability of the magnetic field configurations is studied both analytically and by particle-in-cell simulations.     

Pulsed field electrophoresis

Pulsed field electrophoresis, or PFE, provides good separation between large molecules that under constant field electrophoresis are hard to isolate. This is due to the weak dependence of the constant field mobility on the molecular weight for these large molecules. If a spectrum of relaxation times exists that describes the recovery of the mobility to its constant field value after a reversal of the field, then we show that molecules with differing molecular weights are separated into two groups. Those with short relaxation times are unaffected by the cycling of the field and those with long relaxation times exhibit reduced mobilities. If the molecules adopt conformations that decrease their mobility initially, after a field reversal we demonstrate that a minimum develops in the mobility as a junction of the relaxation time. Using the model we demonstrate that effects of varying the switching times as a function of time. We predict that exponential rather than linear dependencies of the switching times on time increase the range of molecular weights over which enhanced separation can occur.     

Field fluctuation in ionic solutions and its biological significance

The thermal fluctuation of the electric potential, the electric field and the charge density of various modes are theoretically analysed in a homogeneous solution of simple electrolytes. The mean square of the fluctuating potential difference between two points at a finite distance averaged in a finite time and the mean square of the fluctuating field at a point averaged in a finite time are calculated. The response of a macromolecule in the solution to such a time-space averaged potential or field is discussed. Numerical estimation shows that the fluctuating potential or field may be actually important in various biological systems. Connection of the present result with the macroscopic case is also shown.     

The response of European Daphnia magna Straus and Australian Daphnia carinata King to changes in geomagnetic field

This study investigates the effects of lifelong exposure to reversed geomagnetic and zero geomagnetic fields (the latter means absence of geomagnetic field) on the life history of Daphnia carinata King from Australia and Daphnia magna Straus from Europe. Considerable deviation in the geomagnetic field from the usual strength, leads to a decrease in daphnia size and life span. Reduced brood sizes and increased body length of neonates are observed in D. magna exposed to unusual magnetic background. The most apparent effects are induced by zero geomagnetic field in both species of Daphnia. A delay in the first reproduction in zero geomagnetic field is observed only in D. magna. No adaptive maternal effects to reversed geomagnetic field are found in a line of D. magna maintained in these magnetic conditions for eight generations. Integrally, the responses of D. magna to unusual geomagnetic conditions are more extensive than that in D. carinata. We suggest that the mechanism of the effects of geomagnetic field reversal on Daphnia may be related to differences in the pattern of distribution of the particles that have a magnetic moment, or to moving charged organic molecules owing to a change in combined outcome and orientation of the geomagnetic field and Earth's gravitational field. The possibility of modulation of self-oscillating processes with changes in geomagnetic field is also discussed.     

Harmonic Dissonance: Reflections on Dwelling in the Field

Focusing on the idea of dwelling in the field, this paper explores the moral grammar of living with others in field settings, including the texture of membership in one's own family and host families. Through a comparative analysis of two ethnographic research contexts – one on transnational Christian non-governmental organizations in the US and Zimbabwe in 1996 –97, and the other on orphans and philanthropy in India in 2004–05 – I interrogate what it means to inhabit the field. In the world of multi-sited ethnography all research sites are not created equal; both in terms of the kinds of data one can collect and the types of observations one can make. How ethnographers are situated in a web of affliations affects their experience in the field, what they observe, and their research practice. I propose renewed attention to how anthropologists live in the field, including how relationships are interpreted in the field by ethnographers and their informants.