A stochastic model for eye movements during fixation on a stationary target

A stochastic model describing small eye movements occurring during steady fixation on a stationary target is presented. Based on eye movement data for steady gaze, the model has a hierarchical structure; the principal level represents the random motion of the image point within a local area of fixation while the higher level mimics the jump processes involved in transitions from one local area to another. Target image motion within a local area is described by a Langevinlike stochastic differential equation taking into consideration, the microsaccadic jumps pictured as being due to point processes and the high frequency muscle tremor, represented as a white noise. The transform of the probability density function for local area motion is obtained, leading to explicit expressions for their means and moments. Evaluation of these moments based on the model are comparable with experimental results. A physiologically based criterion for the occurrence of local area changes is assumed and the renewal density of these transitions is obtained. These transitions are brought about by the occurrence of large saccades. Hence, our analysis leads us to derive expressions for the mean and moments of the occurrence of large saccades in a given time T. These predictions may be checked against experimental results.This investigation was supported by National Institutes of Health under Grants Numbers GM 16197-03, GM 16437, and RR-0712-04, by the National Science Foundation under Grant Number GK-1834X, and by the National Aeronautics and Space Administration under Grant Number NGL-05-018-022.R.Vasudevan and J.D. Smith are with the Department of Electrical Engineering, University of Southern California, Los Angeles, California. —R.Vasudevan is on leave of absence from the Institute of Mathematical Sciences, Madras, India.A.V. Phatak is now with Systems Control, Inc. in Palo Alto, California.     

Genetic and biochemical studies on the suppression of and a recovery from the tumorous state in higher plants

Summary Four neoplastic diseases of plants: crown gall, which is caused by Ti plasmid DNA; Black's wound tumor disease by an RNA virus; the Kostoff genetic tumors by chromosomal imbalance; and habituation, which results from a spontaneous activation of select biosynthetic systems, have been analyzed and compared. It has been found that both the development of a capacity for autonomous growth and the nature of the heritable cellular change that underlies tumorigenesis are similar in the four instances. All develop a capacity for autonomous growth as a result of the persistent activation of select biosynthetic systems, the products of which are concerned with cell growth and division. That the persistent activation of these biosynthetic systems does not involve heritable changes of an irreversible type is indicated by the finding that a reversal of the neoplastic state occurred in three of the test systems. Since the tumor cells in these instances were found to remain totipotent the results suggest that whether the normal or tumor phenotype is expressed is determined by how the genetic information is regulated in a cell. Regulation appears to be accomplished in part through positive feedback control mechanisms. Foreign genetic information could act either in a regulatory manner to persistently activate normal biosynthetic systems or it could code for one or more essential but normally limiting substance(s) and thus replace a substance(s) that in the case of the Kostoff tumors or habituation is specified by host cell genes, or it could do both. In either case, the foreign genetic information can be regulated in much the same manner as are the host cell genes to give rise to either the normal or tumor phenotype. Presented in the symposium on Gene Transfer, Differentiation and Neoplasia in Plant and Animal Cells at the 30th Annual Meeting of the Tissue Culture Association, Seattle, Washington, June 10–14, 1979. This symposium was supported in part by Grant CA 26748 from the National Cancer Institute, DHEW, and Grant RD-67 from the American Cancer Society. Certain of the investigations described above were supported in part by Grant Number CA-13808, awarded by the National Cancer Institute, U.S. Department of Health, Education, and Welfare, in which the author is the coprincipal investigator.     

Avoidance response of Midge Larvae (Chironomus Tentans) to sediments containing heavy metals

Avoidance reactions of chironomid larvae to contaminated sediment taken from a heavy metal impacted lake were studied. Heavy metal levels in the test sediment ranged from background of 0.6 parts per million (ppm) cadmium, 77 ppm zinc and 17 ppm chromium to a maximum of 1,029 ppm cadmium, 17,262 ppm zinc and 2,106 ppm chromium. A linear relationship was established between cadmium and zinc levels in the sediment and avoidance by chironomids.An approximate threshold avoidance of metals in the sediment was determined to be between 213–422 ppm cadmium, 4385–8330 ppm zinc and 799–1513 ppm chromium.Supported by NIH Training Grant Number 5T01-ES00071 from National Institute of Environmental Health Sciences and in part by an NSF (RANN) Grant Number GI-35106.Purdue University Agricultural Experiment Station, Jour. No. 6474.     

Relative growth and nutrient accumulation rates for tobacco

Summary Tobacco plants (Nicotiana tabacum L.) were grown from transplanting until floral expression in the phytotron units of Southeastern Plant Environment Laboratories to evaluate the relationship between relative growth rate (RGR) and relative accumulation rates (RAR) of N, P, K, Ca, and Mg. RAR is calculated to be analogous to RGR. Plants were grown in both controlled-environment rooms with artificial light and air-conditioned greenhouses with natural light at three temperature conditions and three application rates of N-P-K. RGR and RAR were calculated only for the period of grand growth which occurred within the interval from 7 to 32 days after transplanting. In general, neither RGR nor RAR were affected by temperature or nutrient level. However, both temperature and nutrient level affected dry matter accumulation of the plants apparently by an influence on the rapidity with which plants adjusted to their new environment during the initial 7-day interval after transplanting. RAR for P and K were coequal with RGR of the whole plant; thus, the concentrations of P and K within the plant tended to remain constant during growth. RAR for N, Ca, and Mg were less than RGR for the whole plant; thus, internal concentrations of these nutrients declined during growth. RAR of N, Ca, and Mg for the whole plant were equivalent to RGR of the roots. As a rationale for the association of RGR of roots and RAR of N, it is proposed that the soluble carbohydrate pool in the roots concurrently influences both N absorption, as NO₃ ^-, and growth of new roots of immature plants. Research reported in this paper was supported in part by National Science Foundation (RANN) Grants GI-39229 and GI-39230. Operation of the Phytotron Units of Southeastern Plant Environmental Laboratories at Duke and North Carolina State Universities was supported by National Science Foundation Grants GB-28950-1A and GI-28951. Approved as Paper Number 4773 of the Journal Series of the North Carolina Agricultural Experiment Station, Raleigh, NC. Research reported in this paper was supported in part by National Science Foundation (RANN) Grants GI-39229 and GI-39230. Operation of the Phytotron Units of Southeastern Plant Environmental Laboratories at Duke and North Carolina State Universities was supported by National Science Foundation Grants GB-28950-1A and GI-28951. Approved as Paper Number 4773 of the Journal Series of the North Carolina Agricultural Experiment Station, Raleigh, NC.     

Modeling of biological tree structures

Biological tree-like structures, such as mammalian tracheobronchial airways, are complicated branching systems. One problem in modeling such systems is the reassignment of the number of segments at a given generation in the model being constructed. A hypothesis is proposed which has successfully been used in modeling mammalian lung airways. Research supported by the National Institute of Environmental Health Sciences through U.S. Department of Energy Contract Number EY-76-C-04-1013.     

The evolution of the protein synthesis system

An evolutionary picture of the early protein synthesis was presented in relation to the problem of the origin and the evolution of life. A model of an autocatalytic system was studied in this connection. The system in this model included a template nucleotide and two activated amino acid polymerases with or without a nucleotide polymerase. Variables defining the system were: (1) Catalytic activity of the polymerases, (2) Number of amino acid residues at the activity site of the polymerases, (3) Number of amino acid residues at the selectivity site of the polymerases, (4) Number of the polymerases, (5) Accuracy of polymerization and activity of the polymerases, (6) Number of evolutionary improvements, and (7) The probability of an occurrence of beneficial mutations. The population changes of the systems were obtained by computer calculations. The simulation results indicated that even a very small enzymic activity and specificity of the polymerases could eventually lead the system to the most accurate protein synthesis, as far as transitions to systems with higher accuracy were allowed. The model study would encourage further quantiative investigations on catalytic activities of synthetic peptides, and on interactions between nucleotides and amino acids, and constructions of autocatalytic systems from a chemical evolutionary point of view.This is a part of a dissertation of HM to be presented to the Graduate School of the University of Maryland in partial fulfilment of the requirements for the Ph.D.     

Benthic macroinvertebrates along the Czech part of the Labe and lower section of the Vltava rivers from 1996–2005, with a particular focus on rare and alien species

In the Czech part of the Labe River and the lower part of the Vltava River, we examined if the benthic macroinvertebrate composition changed from 1996 to 2005 due to expected improvements in water quality resulting from socioeconomic changes in the Czech Republic since the 1990s. Special attention was given to rare and alien species. The four biological metrics used (Number of taxa, BMWP, Number of sensitive taxa, and Number of EPT taxa) demonstrated that there was indeed an improvement in water quality as well as a slight improvement of the Labe microhabitats during the investigated period. An increasing Number of taxa over time was observed at most sites. Two main concurrent ecological processes are recently in progress in the Labe: a recovery of native species and an expansion of alien species, some of which are considered invasive. The caddisfly Setodes punctatus and the beetle Pomatinus substriatus, considered as regionally extinct in the Czech Republic until 2005, were rediscovered during our investigations. Findings of the crustacean Hemimysis anomala (invasive) and the chironomids Stenochironomus sp. and Lipiniella sp. were the first records of these taxa in the Czech Republic.     

Enhanced rate of ethanol production from D-xylose using recycled or immobilized cells ofPachysolen tannophilus

Summary Enhanced rates of ethanol production byPachysolen tannophilus from D-xylose were obtained by performing the fermentation with recycled cells in suspension culture or immobilized in a Ca-alginate gel. Fermentation under these conditions did not require aeration. Increasing temperature from 30 to 37°C enhanced the amount of ethanol produced in 24 hours from the recycled or the immobilized cells.Issued as National Research Council of Canada Publication Number 19475.     

Ecology of Infectious Disease: Forging an Alliance

The Ecology of Infectious Diseases (EID) program is a joint National Science Foundation–National Institutes of Health initiative to produce predictive understanding of disease dynamics, with a focus on diseases with an environmental component. The interdisciplinary research projects funded by this program take advantage of the wide range of theoretical and methodological advances developed over the past 30 years. The challenge for disease ecology is to unravel these systems, discover how complex they truly are, and to determine if they can be predicted and controlled using targeted environmental, public health, or medical interventions. Between 1999 and 2005, a total of 42 research awards were made under the EID program. EID projects have had affects on policy in two areas: adoption of novel interventions on a local scale and use of models by government agencies for the purpose of allocating public health resources. The past 6 years have been an exciting time for the field of disease ecology; we expect the coming years to be even more exciting and productive. As US federal government employees writing an article as part of our official duties, copyright of all publications is retained by the US government. The views expressed here by Samuel M. Scheiner and Joshua P. Rosenthal are those of the authors and do not represent official views or policies of the National Science Foundation, the National Institutes of Health, or the United States Government.     

A model of the peripheral auditory system

Summary Recent electrophysiological data obtained from auditory nerve fibers of cats have made possible the formulation of a model of the peripheral auditory system that relates the all-or-none activity of these fibers to acoustic stimulation. The components of the model are intended to represent the major functional components of the peripheral system. These components are: (i) a linear mechanical system intended to represent the outer, middle, and mechanical parts of the inner ear; (ii) a transducer intended to represent the action of the sensory cells; and (iii) a model neuron whose properties are intended to represent the nerve excitation process. A general-purpose digital computer has been used to determine the response of the model to a variety of acoustic stimuli. These results have been compared with data obtained from auditory nerve fibers.This work was supported in part by the Joint Services Electronics Program (Contract DA 36-039-AMC-03200(E); and in part by the National Science Foundation (Grant GP-2495), the National Institutes of Health (Grant MH-04737-05), the National Aeronautics and Space Administration (Grant NsG-496); and by Research Grant NB-01344, National Institute of Neurological Diseases and Blindness of the National Institutes of Health, Public Health Service.     

野双峰驼各分布区的生存环境差异及评价

世界上野双峰驼(Camelus bactrianus ferus)目前仅分布于中国新疆境内及中蒙边境,即：中国新疆的塔克拉玛干沙漠、阿尔金山北麓、戛顺戈壁、中蒙边境及蒙古国西部的外阿尔泰戈壁。总数共计730～880头。目前已为极度濒危物种。本文对野驼在不同分布区由于生境及人类活动影响所造成的差异加以对比研究并进行评价,为野骆驼保护提供依据。     

Simulated bipolar cells in fovea of human retina

This static bipolar cell (BC) model of the human fovea is based on a number of reasonable assumptions. The human fovea is directly responsible for visual acuity and color vision. The fovea can be considered as having two parts; a central fovea with only red- and green-sensitive cones and a parafovea with blue-sensitive cones added to the other two. A cone mosaic can be precisely organized spatially into unit hexagons that specify inputs to horizontal cells (HC) and BCs. The retina up to and including BCs is piece-wise linear, i.e. at a given steady-state adapting light intensity BC outputs are linear functions of the physical image. BC centers receive inputs directly from weighted cones, while antagonistic surrounds receive inverted inputs from HCs. Appropriate optical and chromatic filtering due to the eye that are taken from human data are incorporated into the model. Chromatic aberrations are simulated by three separate point spread functions that also are taken from human data. Automatic gain control of cones is a function of intensity and wavelength of the steady adapting light.The major part of this work was done while the author was a Senior Research Associate of the National Research Council, USA     

Can Vaccination Save a Zika Virus Epidemic?

Zika virus (ZIKV) is a vector-borne disease that has rapidly spread during the year 2016 in more than 50 countries around the world. If a woman is infected during pregnancy, the virus can cause severe birth defects and brain damage in their babies. The virus can be transmitted through the bites of infected mosquitoes as well as through direct contact from human to human (e.g., sexual contact and blood transfusions). As an intervention for controlling the spread of the disease, we study a vaccination model for preventing Zika infections. Although there is no formal vaccine for ZIKV, The National Institute of Allergy and Infectious Diseases (part of the National Institutes of Health) has launched a vaccine trial at the beginning of August 2016 to control ZIKV transmission, patients who received the vaccine are expected to return within 44 weeks to determine if the vaccine is safe. Since it is important to understand ZIKV dynamics under vaccination, we formulate a vaccination model for ZIKV spread that includes mosquito as well as sexual transmission. We calculate the basic reproduction number of the model to analyze the impact of relatively, perfect and imperfect vaccination rates. We illustrate several numerical examples of the vaccination model proposed as well as the impact of the basic reproduction numbers of vector and sexual transmission and the effect of vaccination effort on ZIKV spread. Results show that high levels of sexual transmission create larger cases of infection associated with the peak of infected humans arising in a shorter period of time, even when a vaccine is available in the population. However, a high level of transmission of Zika from vectors to humans compared with sexual transmission represents that ZIKV will take longer to invade the population providing a window of opportunities to control its spread, for instance, through vaccination.     

白粉病菌诱导的小麦表达序列标签(EST)研究(英)

白粉病是我国小麦的主要病害之一。尝试用表达序列标签 (expressedsequencetags,EST)技术 ,研究了经白粉病菌诱导后的小麦基因表达。从构建的普通cDNA文库中随机挑取约 15 0 0个阳性克隆并进行测序 ,获不重复ESTs序列 387条。不重复序列均获GenBank的存储号。其中 4 9.4 %的序列与已知基因同源 ,196条序列功能未知 ,84条序列为新ESTs。将不重复序列制备成高密度点阵膜 ,用差示杂交法筛选到几个抗病相关序列。     

Hydrolysis of wheat starch and its effect on the falling number procedure: mathematical model

A population balance model was developed for wheat starch hydrolysis to simulate the performance parameters of a viscosity-based device, known as the Falling Number instrument. The instrument is widely used as an indirect means to gauge the level of preharvest sprout activity in cereal grains such as wheat and barley. The model consists of three competing kinetics: starch gelatinization, enzymatic hydrolysis, and enzyme thermal deactivation. Using established principles of starch rheology and fluid mechanics, the model simulates the velocity profiles of the falling stirrer, starch gel viscosity, and the Falling Number readings at various levels of alpha-amylase. Model predictions for the velocity of the stirrer at any time during the downward fall, as well as the prediction of the total time needed for the fall, defined as the Falling Number, were in fair agreement with experimental measurements. There was better agreement between the modeled viscosity and the final viscosity of the starch gel as measured by a precision rheometer than there was with the measured Falling Number.     

Plant interspecies competition for sunlight: a mathematical model of canopy partitioning

We examine the influence of canopy partitioning on the outcome of competition between two plant species that interact only by mutually shading each other. This analysis is based on a Kolmogorov-type canopy partitioning model for plant species with clonal growth form and fixed vertical leaf profiles (Vance and Nevai in J. Theor. Biol., 2007, to appear). We show that canopy partitioning is necessary for the stable coexistence of the two competing plant species. We also use implicit methods to show that, under certain conditions, the species’ nullclines can intersect at most once. We use nullcline endpoint analysis to show that when the nullclines do intersect, and in such a way that they cross, then the resulting equilibrium point is always stable. We also construct surfaces that divide parameter space into regions within which the various outcomes of competition occur, and then study parameter dependence in the locations of these surfaces. The analysis presented here and in a companion paper (Nevai and Vance, The role of leaf height in plant competition for sunlight: analysis of a canopy partitioning model, in review) together shows that canopy partitioning is both necessary and, under appropriate parameter values, sufficient for the stable coexistence of two hypothetical plant species whose structure and growth are described by our model. A. L. Nevai was supported in part by the National Institutes of Health, National Research Service Award (T32-GM008185) from the National Institute of General Medical Sciences (NIGMS).     

Ultrastructure of the male nephridium and its role in spermatophore formation in spionid polychaetes (Annelida)

Summary The mature male nephridia ofPolydora ligni andP. websteri (Polychaeta: Spionidae) are segmental organs composed of a ciliated nephrostome connected to a nephridial canal that crosses the intersegmental septum, expands into a large modified part extending dorsally through the coelom and subsequently narrows into a canal terminating in a dorsal nephridiopore. The nephridial canal is ciliated throughout and is composed of several cell types. Cells in the expanded region of the nephridia of both species contain large urn-shaped depressions filled with long microvilli. InP. ligni, one section of a nephridium contains cells packed with electron-dense granules that are not observed inP. websteri.The spermatophores ofPolydora ligni are composed of a central sperm mass surrounded by a layer of randomly oriented tubules that form a capsule around the sperm and taper into a long thin tail. These tubules are identical in dimensions to the microvilli present in parts of a nephridium and apparently are derived from these microvilli. The spermatophore capsule ofP. websteri is composed of similar tubules also presumed to originate from nephridial microvilli.The microvilli in nephridia of both species are surrounded with a glycocalyx that may function as an adhesive to hold the spermatophore capsule together. This glycocalyx may also function as a species specific message when encountered by a receptive female.Contribution Number 179 from Harbor Branch Foundation, Inc.     

Changes in ribosomal patterns and a related membrane fraction during induction of cold hardiness in mimosa epicotyl tissues

Sucrose gradient profiles of polyribosomes from epicotyl tissuesof mimosa seedlings (Albizzia julibrissin Durazzini) were followedthroughout induction of cold hardiness. An unusual fractionappeared in the polyribosome region of sucrose gradients withadvancing stages of cold hardiness. Treatment of this unusualfraction and polyribosome fractions with RNase, Triton X-100and deoxycholate suggests that the unusual fraction consistedof chloroplast or mitochondrial membrane fragments. Free polyribosome patterns were retained throughout inductionof cold hardiness. However, the presence of polyribosomes duringadvancing stages of cold hardiness does not necessarily insureactive protein synthesis. ¹ This investigation was supported in part by National ScienceFoundation Grant GB 8692. ² Contribution from the Missouri Agricultural Experiment Station.Journal Series Number 6253. (Received November 30, 1971; )     

Development and characterization of highly polymorphic microsatellite loci for the Western Spadefoot toad, Pelobates cultripes

Nine highly polymorphic microsatellite markers were isolated and characterized for the Western Spadefoot, Pelobates cultripes. Remarkably, for this amphibian species high numbers of microsatellites were found as part of larger repeat containing regions, making primer design difficult. For nine loci, primers were designed successfully and genotyping of individuals was reliable and consistent. Number of alleles and heterozygosity for these loci ranged from 9 to 34 and from 0.72 to 0.94, respectively. The high levels of polymorphism revealed by our developed loci should provide insight into population genetic structure and levels of dispersal for this typical Mediterranean temporary pond-breeding amphibian.     

Stochastic compartmental modeling and parameter estimation with application to cancer treatment follow-up studies

In this paper we use marginal probabilities to derive expressions for the means, variances and covariances ofm-compartment systems. We also present an efficient algorithm for the estimation of the parameters of the system using time series data when measurements are available fromk of them compartments. An application of the analysis and parameter estimation procedure for a model representing the results of a cancer treatment follow-up study is given. Supported in part by NSF Grant Number DCR74-17282.