Molecular identification of two novel Munc-18 isoforms expressed in non- neuronal tissues

Munc-18, also known as n-Sec1 or rbSec1, is a syntaxin-binding protein thought to play a role in regulating synaptic vesicle exocytosis. Although a gene family of syntaxins has been identified, only a limited subset bind to Munc-18. This implicates the existence of other mammalian Munc-18 homologues that may be involved in a range of vesicle transport reactions. The purpose of the present study was to identify other members of the Munc-18 family by cDNA cloning. Three distinct Munc-18 isoforms, Munc-18a, previously identified in neuronal tissue, and two novel isoforms, Munc-18b and Munc-18c, were isolated from a 3T3-L1 adipocyte cDNA library by screening with a rat brain Munc-18 DNA probe. Munc-18a is identical to Munc-18 and by Northern analysis is expressed predominantly in brain and to a lesser extent in testis and 3T3-L1 cells. Munc-18b is 62% identical to Munc-18 at the amino acid level and is expressed in testis, intestine, kidney, rat adipose tissue, and 3T3-L1 cells. Munc-18c is 51% identical to Munc-18 and is ubiquitously expressed. It is likely, based on these findings, that unique Munc-18/syntaxin interactions may play an important role in generating a combinatorial mechanism for the regulation of vesicle transport in mammalian cells

The curious case of the camelthorn: competition, coexistence and nest-site limitation in a multispecies mutualism

Myrmecophyte plants house ants in domatia in exchange for protection from herbivores. Ant-myrmecophyte mutualisms exhibit two general patterns due to competition between ants for plant occupancy: i) domatia nest-sites are a limiting resource and ii) each individual plant hosts one ant species at a time. However, individual camelthorn trees (Vachellia erioloba) typically host two to four ant species simultaneously, often coexisting in adjacent domatia on the same branch. Such fine-grain spatial coexistence brings into question the conventional wisdom on ant-myrmecophyte mutualisms. Camelthorn ants appear not to be nest-site limited, despite low abundance of suitable domatia, and have random distributions of nest-sites within and across trees. These patterns suggest a lack of competition between ants for domatia and contrast strongly with other ant-myrmecophyte systems. Comparison of this unusual case with others suggests that spatial scale is crucial to coexistence or competitive exclusion involving multiple ant species. Furthermore, coexistence may be facilitated when co-occurring ant species diverge strongly on at least one niche axis. Our conclusions provide recommendations for future ant-myrmecophyte research, particularly in utilising multispecies systems to further our understanding of mutualism biology

Periodic Travelling Waves in Dimer Granular Chains

We study bifurcations of periodic travelling waves in granular dimer chains from the anti-continuum limit, when the mass ratio between the light and heavy beads is zero. We show that every limiting periodic wave is uniquely continued with respect to the mass ratio parameter and the periodic waves with the wavelength larger than a certain critical value are spectrally stable. Numerical computations are developed to study how this solution family is continued to the limit of equal mass ratio between the beads, where periodic travelling waves of granular monomer chains exist

Return-Volatility Relationship: Insights from Linear and Non-Linear Quantile Regression

The purpose of this paper is to examine the asymmetric relationship between price and implied volatility and the associated extreme quantile dependence using linear and non linear quantile regression approach. Our goal in this paper is to demonstrate that the relationship between the volatility and market return as quantified by Ordinary Least Square (OLS) regression is not uniform across the distribution of the volatility-price return pairs using quantile regressions. We examine the bivariate relationship of six volatility-return pairs, viz. CBOE-VIX and S&P-500, FTSE-100 Volatility and FTSE-100, NASDAQ-100 Volatility (VXN) and NASDAQ, DAX Volatility (VDAX) and DAX-30, CAC Volatility (VCAC) and CAC-40 and STOXX Volatility (VSTOXX) and STOXX. The assumption of a normal distribution in the return series is not appropriate when the distribution is skewed and hence OLS does not capture the complete picture of the relationship. Quantile regression on the other hand can be set up with various loss functions, both parametric and non-parametric (linear case) and can be evaluated with skewed marginal based copulas (for the non linear case). Which is helpful in evaluating the non-normal and non-linear nature of the relationship between price and volatility. In the empirical analysis we compare the results from linear quantile regression (LQR) and copula based non linear quantile regression known as copula quantile regression (CQR). The discussion of the properties of the volatility series and empirical findings in this paper have significance for portfolio optimization, hedging strategies, trading strategies and risk management in general

The wave equation on singular space-times

We prove local unique solvability of the wave equation for a large class of weakly singular, locally bounded space-time metrics in a suitable space of generalised functions.Comment: Latex, 19 pages, 1 figure. Discussion of class of metrics covered by our results and some examples added. Conclusion more detailed. Version to appear in Communications in Mathematical Physic

Abelian D-terms and the superpartner spectrum of anomaly-mediated supersymmetry breaking

We address the tachyonic slepton problem of anomaly mediated supersymmetry breaking using abelian D-terms. We demonstrate that the most general extra U(1) symmetry that does not disrupt gauge coupling unification has a large set of possible charges that solves the problem. It is shown that previous studies in this direction that added both an extra hypercharge D-term and another D-term induced by B-L symmetry (or similar) can be mapped into a single D-term of the general ancillary U(1)_a. The U(1)_a formalism enables identifying the sign of squark mass corrections which leads to an upper bound of the entire superpartner spectrum given knowledge of just one superpartner mass.Comment: 10 pages, 2 figures, [v2] reference added, [v3] Eq. (9) corrected, results unaffected, [v4] version to be published in Phys. Rev. D, expanded parameter space for figures to match tex

Kinetic and isotherm studies on adsorption of arsenic using silica based catalytic media

This study investigates the removal of arsenic (both As (III) and As (V)) from drinking water using a silica based catalytic media (DMI-65). In this study, BET, FTIR, XRD, SEM and XRF were used to characterize the adsorbent before and after contact with As (III) and As (V). Batch experiments were performed to evaluate the adsorption kinetics at different pH (5, 6, 7 and 8.5). The kinetic study showed that a contact time of 6 h was needed to reach equilibrium and the experimental data were best fitted to the pseudo second-order kinetic model for both As (III) and As (V). Several batch tests were conducted with different concentration of arsenic at different pH conditions (5, 6, 7 and 8.5). During the adsorption test, the maximum adsorption of As (III) occurred at pH 5, while As (V) adsorption reached its maximum at pH 8.5. The adsorption data showed a good fit to Langmuir isotherm models and the maximum adsorption capacity of the silica based catalytic media for As (III) and As (V) were estimated to be 0.318 mg/g and 0.237 mg/g respectively

Influence of dietary niacin on starter pig performance

Two experiments were conducted using 415 weanling pigs (175 in Exp. 1, 240 in Exp. 2) to determine the influence of dietary niacin inclusion on starter pig performance. Pigs were fed a control diet with no added niacin or the control diet with 25, 50, 75 or 100 g/ton of added niacin. From d 0 to 8, increasing dietary niacin increased ADG and ADFI up to 50 g/ton of added niacin. Overall, pigs fed increasing levels of niacin tended to have improved ADG. These results suggest feeding 50 g/ton of added dietary niacin to complex nursery pig diets to improve growth performance