Systematic study of heavy cluster emission from {210-226}^Ra isotopes

The half lives for various clusters lying in the cold reaction valleys of {210-226}^Ra isotopes are computed using our Coulomb and proximity potential model (CPPM). The computed half lives of 4^He and 14^C clusters from {210-226}^Ra isotopes are in good agreement with experimental data. Half lives are also computed using the Universal formula for cluster decay (UNIV) of Poenaru et al., and are found to be in agreement with CPPM values. Our study reveals the role of doubly magic 208^Pb daughter in cluster decay process. Geiger - Nuttall plots for all clusters up to 62^Fe are studied and are found to be linear with different slopes and intercepts. {12,14}^C emission from 220^Ra; 14^C emission from {222,224}^Ra; 14^C and 20^O emission from 226^Ra are found to be most favourable for measurement and this observation will serve as a guide to the future experiments.Comment: 22 pages, 6 figures; Nuclear Physics A (2012

A Secure and Fair Resource Sharing Model for Community Clouds

Cloud computing has gained a lot of importance and has been one of the most discussed segment of today\u27s IT industry. As enterprises explore the idea of using clouds, concerns have emerged related to cloud security and standardization. This thesis explores whether the Community Cloud Deployment Model can provide solutions to some of the concerns associated with cloud computing. A secure framework based on trust negotiations for resource sharing within the community is developed as a means to provide standardization and security while building trust during resource sharing within the community. Additionally, a model for fair sharing of resources is developed which makes the resource availability and usage transparent to the community so that members can make informed decisions about their own resource requirements based on the resource usage and availability within the community. Furthermore, the fair-share model discusses methods that can be employed to address situations when the demand for a resource is higher than the resource availability in the resource pool. Various methods that include reduction in the requested amount of resource, early release of the resources and taxing members have been studied, Based on comparisons of these methods along with the advantages and disadvantages of each model outlined, a hybrid method that only taxes members for unused resources is developed. All these methods have been studied through simulations

Cluster formation probability in the trans-tin and trans-lead nuclei

Within our fission model, the Coulomb and proximity potential model (CPPM) cluster formation probabilities are calculated for different clusters ranging from carbon to silicon for the parents in the trans-tin and trans- lead regions. It is found that in trans-tin region the 12^C, 16^O, 20^Ne and 24^Mg clusters have maximum cluster formation probability and lowest half lives as compared to other clusters. In trans-lead region the 14^C, 18, 20^O, 23^F, 24,26^Ne, 28,30^Mg and 34^Si clusters have the maximum cluster formation probability and minimum half life, which show that alpha like clusters are most probable for emission from trans-tin region while non-alpha clusters are probable from trans-lead region. These results stress the role of neutron proton symmetry and asymmetry of daughter nuclei in these two cases.Comment: 20 pages, 6 figure

Anomalous transport and phonon renormalization in a chain with transverse and longitudinal vibrations

We study thermal transport in a chain of coupled atoms, which can vibrate in longitudinal as well as transverse directions. The particles interact through anharmonic potentials upto cubic order. The problem is treated quantum mechanically. We first calculate the phonon frequencies self-consistently taking into account the anharmonic interactions. We show that for all the modes, frequencies must have linear dispersion with wave-vector $q$ for small $q$ irrespective of their bare dispersions. We then calculate the phonon relaxation rates $\Gamma_i(q)$, where $i$ is the polarization index of the mode, in a self-consistent approximation based on second order perturbation diagrams. We find that the relaxation rate for the longitudinal phonon, $\Gamma_x(q) \propto q^{3/2}$, while that for the transverse phonon $\Gamma_y(q) \propto q^2$. The consequence of these results on the thermal conductivity $\kappa(N)$ of a chain of $N$ particles is that $\kappa(N) \propto N^{1/2}$

Sexual selection mechanisms in a simultaneously hermaphroditic flatworm

Male and female animals often display striking differences in shape, behaviour, or reproductive strategies. For the most part, this was attributed to evolution under sexual selection where males and females are thought to be under different selection regimes. Although initially described to occur mainly through contests between males for mates and mate choice by females, sexual selection is now widely accepted to occur after copulations through sperm competition and/or cryptic female choice. However, studying these post-copulatory processes proved to be challenging because they occur internally and are often difficult to observe and measure. Therefore, advancements in understanding post-copulatory sexual selection greatly depend on the development of techniques that facilitate the observation of internal processes. Moreover, measuring the reproductive success of individuals under competitive conditions hinges on techniques that allow easy identification of the parentage of offspring. During my PhD project, I used the simultaneously hermaphroditic flatworm Macrostomum lignano to study aspects of pre- and postcopulatory sexual selection. The establishment of a transgenic line of worms expressing a green fluorescent protein (GFP) in all cells provides a unique opportunity to differentiate and track sperm under competitive scenarios within the female reproductive tract in vivo. Additionally, a suite of transgenic lines (NL lines), each expressing fluorescent proteins localized to specific tissues of the body or nuclei of cells, provide distinct inheritable markers that enable efficient identification of parentage in offspring from mating crosses. I tested and validated the reliability of the NL lines, mating crosses between lines, and other GFP techniques, which I could then effectively use to study central aspects of sexual selection in M. lignano. The NL lines were instrumental in my experiment designed to measure the strength of sexual selection in the male and female sex functions in M. lignano. The difference in the strength of sexual selection between the sexes, i.e., stronger sexual selection in males than in females, has been attributed to the difference in costs of producing male and female gametes (i.e., anisogamy). Therefore, theoretical considerations of simultaneous hermaphrodites that also exhibit anisogamy predict stronger sexual selection in the male compared to the female sex function. M. lignano exhibits a reciprocal mating system (i.e., worms donate and receive sperm simultaneously), where the copulations in the male and female sex functions are strictly linked. My measurements of standardised selection metrics in M. lignano revealed substantial scope for sexual selection in both male and female sex functions with no significant difference between the same. My findings thus suggest that although anisogamy may lead to a difference in the reproductive interests of the male and female sex functions, the actual strength of sexual selection may be influenced by other factors, such as the mating system. Previous studies in M. lignano have shown that sexual selection predominantly occurs in post-copulatory episodes. My investigation into the role of sperm size in a post-copulatory episode of selection revealed a non-linear association with a competitive advantage for intermediate sperm size. I speculate that the observed selection for intermediate size may arise due to the trade-off between sperm size and the number of sperm produced. That is, an increase in sperm size may be associated with fewer sperm produced and transferred to the partner, leading to fewer sperm represented in sperm competition. Therefore, the selective forces for more competitive larger sperm and that for numerous but smaller sperm may reach a balance at an intermediate optimum. In conclusion, I took advantage of several features and powerful techniques established in M. lignano to obtain novel insights into the operation of sexual selection. My PhD works further signify the importance of sexual selection as an evolutionary agent in simultaneous hermaphrodites

Continuous Functional Calculus for Quaternionic Bounded Normal Operators

In this article we give an approach to define continuous functional calculus for bounded quaternionic normal operators defined on a right quaternionic Hilbert space.Comment: Submitted to a journal. There was a gap in the previous version. We have corrected it and stated all the results for bounded cas