Shape Instabilities in the Dynamics of a Two-component Fluid Membrane

We study the shape dynamics of a two-component fluid membrane, using a dynamical triangulation monte carlo simulation and a Langevin description. Phase separation induces morphology changes depending on the lateral mobility of the lipids. When the mobility is large, the familiar labyrinthine spinodal pattern is linearly unstable to undulation fluctuations and breaks up into buds, which move towards each other and merge. For low mobilities, the membrane responds elastically at short times, preferring to buckle locally, resulting in a crinkled surface.Comment: 4 pages, revtex, 3 eps figure

A Novel Monte Carlo Approach to the Dynamics of Fluids --- Single Particle Diffusion, Correlation Functions and Phase Ordering of Binary Fluids

We propose a new Monte Carlo scheme to study the late-time dynamics of a 2-dim hard sphere fluid, modeled by a tethered network of hard spheres. Fluidity is simulated by breaking and reattaching the flexible tethers. We study the diffusion of a tagged particle, and show that the velocity autocorrelation function has a long-time $t^{-1}$ tail. We investigate the dynamics of phase separation of a binary fluid at late times, and show that the domain size $R(t)$ grows as $t^{1/2}$ for high viscosity fluids with a crossover to $t^{2/3}$ for low viscosity fluids. Our scheme can accomodate particles interacting with a pair potential $V(r)$,and modified to study dynamics of fluids in three dimensions.Comment: Latex, 4 pages, 4 figure

Active elastic dimers: self-propulsion and current reversal on a featureless track

We present a Brownian inchworm model of a self-propelled elastic dimer in the absence of an external potential. Nonequilibrium noise together with a stretch-dependent damping form the propulsion mechanism. Our model connects three key nonequilibrium features -- position-velocity correlations, a nonzero mean internal force, and a drift velocity. Our analytical results, including striking current reversals, compare very well with numerical simulations. The model unifies the propulsion mechanisms of DNA helicases, polar rods on a vibrated surface, crawling keratocytes and Myosin VI. We suggest experimental realizations and tests of the model.Comment: 4 page

Some Physiological Aspects Of The Soybean - Phytophthora Megasperma F Sp Glycinea Interaction, With Special Reference To The Phytoalexin, Glyceollin

The interaction of soybean cultivars (Glycine max) with Phytophthora megasperma f.sp. glycinea (Pmg) races is governed by single host genes (Rps) and is consistent with the gene-for-gene hypothesis. Using the near isogenic cultivars Harosoy ({dollar}rps\sb1{dollar}, susceptible to race 1) and Harosoy 63 ({dollar}Rps\sb1{dollar}, resistant) and Pmg race 1 it was demonstrated that the {dollar}Rps\sb1{dollar} gene is expressed in hypocotyls and roots of light and dark grown seedlings, in green cotyledons and leaves but not in immature leaves. Leaves of cv. Harosoy became resistant with age. The phytoalexins, glyceollin isomers I, II and III, accumulated rapidly in resistant responses. Proportions of the glyceollin isomers varied with the organ, exposure to light, interaction type and incubation period. The three isomers, also differed in their toxicities to Pmg. Glyceollin I was almost twice as inhibitory as glyceollin II and III to mycelial growth in vitro. An isolate of Pmg race 1 (Isolate 1.1) was obtained that was twice as tolerant to glyceollin I and III as race 1. Evidence was obtained for variability in morphology, growth, tolerance to glyceollin I and aggressiveness of single-zoospore progeny of race 1 and Isolate 1.1, that may be accounted for by cytoplasmic factors.;From pulse and pulse-chase experiments using L- (U{dollar}\sp{lcub}14{rcub}{dollar}C) -phenylalanine as precursor it is concluded that accumulation of higher levels of glyceollin I in resistant than in susceptible responses is due to differences in rates of biosynthesis. Rapid metabolism, which was not constitutive, was demonstrated in all interactions and controls. This is consistent with differences in phenylalanine ammonia-lyase (PAL) activity demonstrated in resistant and susceptible responses. PAL activity also was correlated with changes in glyceollin production and susceptibility at elevated temperatures. Differential effects of temperature on growth and glyceollin I sensitivity of Pmg races were demonstrated also. In some race-cultivar combinations reaction types may be related to the effect of temperature on production and sensitivity to glyceollin I.;A model is presented that attempts to accommodate the physiological data obtained in this study with the requirements of the gene-for-gene relationship of host-pathogen interactions

Immunolocalization of fibroblast growth factor-2 (FGF-2) in the developing root of the murine tooth

A dissertation submitted to the Faculty of Health Sciences, University of the Witwatersrand, in fulfilment of the requirements for the Degree of Master of Science (Medicine)Classical epithelio-mesenchymal interactions are said to result in root development. These interactions may be regulated by a number of growth factors. Fibroblast growth factors (FGF’s), members of a highly conserved family of polypeptides, the heparin binding growth factors (HBGF’s) are known to play a crucial role during the development of certain vertebrate organs, including the tooth. Previously, FGF-2, 3, 4, and 8 have been shown to play a role in crown development. The aim of this study was therefore to elucidate the spatial and temporal expression of FGF-2 in the developing root. Parasagittal sections of the maxillary and mandibular arches of six age groups of post-natal mice (days 9, 10, 12, 16, 20 and 24) were cut and the developing roots of the incisor and molar teeth identified. Immunocytochemistry utilizing anti-FGF-2 was performed on sections of teeth from all stages using the strept-avidin biotin technique. Appropriate positive, negative and absorption controls were performed to ensure the specificity of the antibody. FGF-2 was immunolocalized in the cytoplasm and nuclei of the odontoblasts, fibroblasts of the periodontal ligament and pulp chamber, as well as in the osteoblasts surrounding developing bone at all the stages examined. Intense staining for FGF-2 was observed in differentiating odontoblasts at the apical end and the furcation zone of the developing root. FGF-2 localization was also observed in the cytoplasm of the ameloblasts on days 9, 10 and 12 and in cementoblasts on day 16, 20 and 24. The spatio-temporal expression pattern of FGF-2 in the developing mouse tooth root suggests that FGF-2 with other signaling molecules previously reported such as bone morphogenetic proteins-2, 3 and 7 (BMP-2, 3 and 7) participate in the signaling network during the tooth root development.IT201

The Demographic Modeling Of Household Cycles: Analytical And Microsimulation Approaches

This dissertation first identifies the household cycle as the core concept in formal household demography, and presents a simple model of the determinants of the size distribution and the average size of the household. In this model, the proximate processes which govern the end points of the household cycle are fission, fusion, and fission-fusion of households and the joint mortality of household members. The growth of the household during its cycle is, on the other hand, influenced by events occurring to individual household members given that the household is viable. Analytical models then can be developed for the study of the household using the concept of the household cycle as the unit of analysis.;From the perspective of the household cycle, then, Ryder\u27s model of the average size of the household cycle is first formalized, and then extended to two cases: the extended family household with and without a foster mother. Expressions of average household size are determined in terms of various demographic parameters such as the gross level of fertility, parental survival, and the net reproduction rate. Illustrative results are provided for three hypothetical societies described in the classical theory of demographic transition.;In addition, a microsimulation model of Canadian household cycles is developed in order to examine the sensitivity of average household size to different demographic parameters associated with the formation, growth, and extinction of households. An interesting and counterintuitive finding of this research is that the overall influence of mortality would depend on the net outcome of the two contradictory effects at the two levels of analysis--the household and the individual. Fertility increase necessarily leads to an increase in the average size of the household, keeping other factors constant. Nuclear family household formation, the last component in the simulation model, on the other hand, checks the growth of households and lowers the average size of the household.;It is finally suggested that more varieties of household organization could be modeled using the analytical approaches developed in this Dissertation One could also use the microsimulation model to study the demographic component of the size distribution of households

DISSECTING THE BIOSYNTHESES OF GILVOCARCINS AND RAVIDOMYCINS

Gilvocarcin V (GV) and ravidomycin (RMV) exhibit excellent antitumor activities in the presence of near-UV light at low concentration maintaining a low in vivo cytotoxicity. Although, the exact molecular mechanism for in vivo actions of these antibiotics has yet to be determined, a [2+2] cycloaddition reaction of the vinyl side chain with DNA thymidine residues in addition to the inhibition of topoisomerase II and DNAhistone H3 cross-linking are reported for the GV’s mechanism of action. Such activities have made these molecules interesting candidates for the biosynthetic investigation to generate analogues with improved activity/solubility. Previous biosynthetic studies have suggested that the GV biosynthetic pathway involves a number of synchronously occurring transformations leading to the oxidative C-C bond cleavage and other intriguing biosynthetic reactions, such as the vinyl side chain formation, methylations, Cglycosylation and dehydrogenation. Although gene inactivation results identified many candidate genes whose corresponding enzymes are involved in these biochemical transformations, their exact functional roles and the identity of their natural substrates remained elusive. To provide more insights into these complex biochemical tranfrormations, three specific aims were set up. Specific aim 1 was to clone and characterize the RMV biosynthetic gene cluster. Through the comparison of GV cluster with the RMV cluster, the genes encoding the biosynthesis of sugar and tetracyclic aromatic moieties were identified. RavGT, the sole glycosyltransferase of the RMV cluster has demonstrated to have unprecedented sugar donor substrate flexibility, transferring an amino-pyranose sugar as well as a neutral furanose sugar. Specific aim 2 was to characterize all of the TDP-D-ravidosamine biosynthetic enzymes. The aim also included to a one-pot enzymatic synthetic protocol for the routine production of TDP-D-ravidosamine. Specific aim 3 focussed on a total enzymatic synthesis of defucogilvocarcin M (defucoGM), the polyketide-derived core of GV and RMV. This aim clearly identified the minimal enzymes required to biosynthesize the complex architecture of defucoGM from the simple building blocks acetate and malonate. In addition, the GV-pathway enzyme GilR was fully characterized. Through in vitro studies, GilR was shown to catalyze the dehydrogenation of hemiacetal moiety of the penultimate intermediate pregilvocarcin V to the lactone moiety of GV at the last step

Farm-economics of genetically improved carp strains in major Asian countries and carp seed price policy model

The study has conducted the micro level analysis of hatchery operators, fishseed-rearing farmers and carp farmers with respect to their socio-economic characteristics, infrastructural development, husbandry practices and economics returns, based on the survey and on-farm trial data collected by the research partners in six Asian countries, viz. Bangladesh, China, India, Indonesia, Thailand and Vietnam. The genetically-improved carp strain is economically viable and socially acceptable. The attractive profits to hatchery operators and nursery and carp farmers have created conducive environment for the dissemination of improved carp strain. Price policy models for improved strains have been developed. The premium price for fingerlings and broodstock with improved strain has been assessed. The high price of genetically-improved nuclear seed and broodstock would build self-supportive research and extension systems in the country. A business plan for Jayanti rohu has been worked out, as an example for replacement of rohu by Jayanti rohu.Livestock Production/Industries,