Inter-Particle Distribution Functions for One-Species Diffusion-Limited Annihilation, A+A->0

Diffusion-limited annihilation, $A+A\to 0$, and coalescence, $A+A\to A$, may both be exactly analyzed in one dimension. While the concentrations of $A$ particles in the two processes bear a simple relation, the inter-particle distribution functions (IPDF) exhibit remarkable differences. However, the IPDF is known exactly only for the coalescence process. We obtain the IPDF for the annihilation process, based on the Glauber spin approach and assuming that the IPDF's of nearest-particle pairs are statistically independent. This assumption is supported by computer simulations. Our analysis sheds further light on the relationship between the annihilation and the coalescence models.Comment: 15 pages, plain TeX, 3 figures - available upon request (snail mail

Correlation of the Sulphur River Formation

The geologic relations here exhibited and the radiocarbon dates obtained suggest a correlation of the Sulphur River Formation with the Prairie Formation, of the Red River terrace sequence, and with the Holloway Prairie Formation of the Gulf Coastal Plain. Radiocarbon dates of 8,000 and 12,000 B.P. have been measured on materials presumably taken from the latter (Bray and Nelson, 1956; Stevens et al., 1956)

Exponentially growing solutions in homogeneous Rayleigh-Benard convection

It is shown that homogeneous Rayleigh-Benard flow, i.e., Rayleigh-Benard turbulence with periodic boundary conditions in all directions and a volume forcing of the temperature field by a mean gradient, has a family of exact, exponentially growing, separable solutions of the full non-linear system of equations. These solutions are clearly manifest in numerical simulations above a computable critical value of the Rayleigh number. In our numerical simulations they are subject to secondary numerical noise and resolution dependent instabilities that limit their growth to produce statistically steady turbulent transport.Comment: 4 pages, 3 figures, to be published in Phys. Rev. E - rapid communication

FARM COSTS AND EXPORTS

International Relations/Trade,

Predicting the Relative Sensitivity of Sturgeons to Aryl Hydrocarbon Receptor Agonists

Along with overexploitation and habitat loss, pollution is one cause for decreases in populations of fishes. One class of pollutants of particular global environmental concern to fishes are dioxin-like compounds (DLCs). DLCs elicit their toxicity through activation of the aryl hydrocarbon receptor (AHR). Despite this common mechanism of all DLCs, dramatic differences in sensitivity exist among fishes. Sturgeons (Acipenseridae) are an ancient family of fishes in which most species are endangered. It is hypothesized that pollutants, including DLCs, might be contributing to the observed declines in populations because sturgeons have a unique life-style that makes them susceptible to exposure to bioaccumulative chemicals. However, determining sensitivities of sturgeons to DLCs through traditional in vivo toxicity testing is not feasible for practical and ethical reasons. Therefore, the aim of this research was to develop a mechanism-based biological model capable of predicting the relative sensitivity of sturgeons to DLCs. This mechanism-based biological model was developed through investigations into the AHR and AHR-mediated molecular and biochemical responses of white sturgeon (Acipenser transmontanus) relative to teleost fishes and another species of sturgeon. White sturgeon responded to activation of the AHR in a manner that is consistent with responses of teleost fishes (induction of cytochrome P450 1A). Two AHRs with similar levels of expression were identified in white sturgeon, an AHR1 that resembles AHR1s of tetrapods and an AHR2 that resembles AHR2s of other fishes. Both AHR1 and AHR2 of white sturgeon were activated by exposure to five selected DLCs in vitro with effect concentrations less than any other AHR tested to date. These findings were suggestive that white sturgeon might be among the most sensitive species of fish to exposure to DLCs. These findings raised the question as to whether other members of the Acipenseridae are similarly sensitive to exposure to DLCs. Therefore, AHR1 and AHR2 were identified in a second species of sturgeon, the lake sturgeon (Acipenser fulvescens). AHR1 of lake sturgeon had the same in vitro sensitivity to activation by the five selected DLCs as AHR1 of white sturgeon, while AHR2 of lake sturgeon was 10-fold less sensitive to activation by the five selected DLCs relative to AHR2 of white sturgeon. AHR2 has been demonstrated to drive adverse effects of DLCs in other fishes, while AHR1 has no known role in mediating toxicities in fishes. Therefore, it was hypothesized that white sturgeon are 10-fold more sensitive to DLCs relative to lake sturgeon in vivo. However, there were uncertainties in whether differences in activation of the AHR are representative of differences at higher levels of biological organization. Therefore, whole transcriptome and whole proteome responses were investigated following exposure to equipotent concentrations of three agonists of the AHR. Equal activation of the AHR of white sturgeon resulted in similar global responses and magnitude of responses across levels of biological organization. This supports the hypothesis that activation of the AHR is predictive of apical level adverse effects of regulatory relevance, such as mortality of embryos. In order to test this hypothesis, AHR1s and AHR2s from seven species of fish of known sensitivity were investigated and the relationship between in vitro and in vivo sensitivities were characterized for the model DLC, 2,3,7,8-TCDD. All AHR1s and AHR2s were activated in vitro by 2,3,7,8-TCDD. There was no significant linear relationship between in vitro sensitivity of AHR1 and in vivo sensitivity among the seven species. However, there was a highly significant linear relationship between in vitro sensitivity of the AHR2 and in vivo sensitivity. The equation of this relationship enables the prediction of the in vivo sensitivity of any species of fish based on in vitro sensitivity of the AHR2. This predictive model could be essential in guiding more objective risk assessments of DLCs to fishes, including endangered species such as sturgeons

RNA interference screening reveals host CaMK4 as a regulator of cryptococcal uptake and pathogenesis

ABSTRACT Cryptococcus neoformans , the causative agent of cryptococcosis, is an opportunistic fungal pathogen that kills over 200,000 individuals annually. This yeast may grow freely in body fluids, but it also flourishes within host cells. Despite extensive research on cryptococcal pathogenesis, host genes involved in the initial engulfment of fungi and subsequent stages of infection are woefully understudied. To address this issue, we combined short interfering RNA silencing and a high-throughput imaging assay to identify host regulators that specifically influence cryptococcal uptake. Of 868 phosphatase and kinase genes assayed, we discovered 79 whose silencing significantly affected cryptococcal engulfment. For 25 of these, the effects were fungus specific, as opposed to general alterations in phagocytosis. Four members of this group significantly and specifically altered cryptococcal uptake; one of them encoded CaMK4, a calcium/calmodulin-dependent protein kinase. Pharmacological inhibition of CaMK4 recapitulated the observed defects in phagocytosis. Furthermore, mice deficient in CaMK4 showed increased survival compared to wild-type mice upon infection with C. neoformans . This increase in survival correlated with decreased expression of pattern recognition receptors on host phagocytes known to recognize C. neoformans . Altogether, we have identified a kinase that is involved in C. neoformans internalization by host cells and in host resistance to this deadly infection. </jats:p

Design of a large-scale virus capsid model for educational use

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2005.Includes bibliographical references (leaf 23).A foot-scale model of an icosahedral virus capsid, as opposed to a helical capsid shape, was modeled in preparation for manufacture for educational use. We chose to model the icosahedral virus capsid for manufacture because understanding the structure of this type of capsid is of biological importance, the icosahedral structure is well-established, and because the icosahedral structure and geometry is representative of many viruses, it is important to virology. A small icosahedral virus capsid consists of 60 identical proteins. Larger capsids are formed by adding quasi-equivalent proteins, with 60 copies of each unique protein. Our model calls for the creation of an injection mold for one unique protein. 60 parts should snap together with one another after manufacture to create an icosahedron. The protein was modeled using the SolidWorks computer aided drawing (CAD) software. The CAD model could then be converted to a file that enables us to mill a two part mold out of aluminum blocks. This aluminum mold will then be used to injection mold parts made out of polypropylene. The parting lines and sprue of the final parts will be cleaned up and then assembled to complete the model. This thesis details the specifics of the modeling of this protein, focusing on the design of the attachment method for capsid assembly from a single injection mold.by Heather A. Doering.S.B

Subdiffusion-limited reactions

We consider the coagulation dynamics A+A -> A and A+A A and the annihilation dynamics A+A -> 0 for particles moving subdiffusively in one dimension. This scenario combines the "anomalous kinetics" and "anomalous diffusion" problems, each of which leads to interesting dynamics separately and to even more interesting dynamics in combination. Our analysis is based on the fractional diffusion equation