Probing SUSY effects in KS0→μ+μ−K_S^0\rightarrow\mu^+\mu^-

We explore supersymmetric contributions to the decay $K_S^0\rightarrow\mu^+\mu^-$, in light of current experimental data. The Standard Model (SM) predicts $\mathcal{B}(K_S^0\rightarrow\mu^+\mu^-)\approx5\times 10^{-12}$. We find that contributions arising from flavour violating Higgs penguins can enhance the branching fraction up to $\approx 35\times 10^{-12}$ within different scenarios of the Minimal Supersymmetric Standard Model (MSSM), as well as suppress it down to $\approx 0.78\times 10^{-12}$. Regions with fine-tuned parameters can bring the branching fraction up to the current experimental upper bound, $8\times 10^{-10}$. The mass degeneracy of the heavy Higgs bosons in MSSM induces correlations between $\mathcal{B}(K_S^0\rightarrow\mu^+\mu^-)$ and $\mathcal{B}(K_L^0\rightarrow\mu^+\mu^-)$. Predictions for the $CP$ asymmetry in $K^0\rightarrow\mu^+\mu^-$ decays in the context of MSSM are also given, and can be up to eight times bigger than in the SM.Comment: 36 pages, 31 fig

First Principles Simulations of Boron Diffusion in Graphite

Boron strongly modifies electronic and diffusion properties of graphite. We report the first ab initio study of boron interaction with the point defects in graphite, which includes structures, thermodynamics, and diffusion. A number of possible diffusion mechanisms of boron in graphite are suggested. We conclude that boron diffuses in graphite by a kick-out mechanism. This mechanism explains the common activation energy, but large magnitude difference, for the rate of boron diffusion parallel and perpendicular to the basal plane. © 2007 The American Physical Society

Effect of microstructure on the thermal conductivity of disordered carbon

Computational methods are used to control the degree of structural order in a variety of carbonmaterials containing primarily sp2 bonding. Room-temperature thermal conductivities arecomputed using non-equilibrium molecular dynamics. Our results reproduce experimental data foramorphous and glassy carbons and confirm previously proposed structural models for vitreouscarbons. An atomistic model is developed for highly oriented thin films seen experimentally, with amaximum computed thermal conductivity of 35 W m1 K1. This value is much higher than thatof the amorphous and glassy structures, demonstrating that the microstructure influences thethermal conductivity more strongly than the density

Cryptanalysis of a group key establishment protocol

In this paper, we analyze the security of a group key establishment scheme proposed by López-Ramos et al. This proposal aims at allowing a group of users to agree on a common key. We present several attacks against the security of the proposed protocol. In particular, an active attack is presented, and it is also proved that the protocol does not provide forward secrecy

A comparative study of density functional and density functional tight binding calculations of defects in graphene

The density functional tight binding approach (DFTB) is well adapted for the study of point and line defects in graphene based systems. After briefly reviewing the use of DFTB in this area, we present a comparative study of defect structures, energies and dynamics between DFTB results obtained using the dftb+ code, and density functional results using the localised Gaussian orbital code, AIMPRO. DFTB accurately reproduces structures and energies for a range of point defect structures such as vacancies and Stone-Wales defects in graphene, as well as various unfunctionalised and hydroxylated graphene sheet edges. Migration barriers for the vacancy and Stone-Wales defect formation barriers are accurately reproduced using a nudged elastic band approach. Finally we explore the potential for dynamic defect simulations using DFTB, taking as an example electron irradiation damage in graphene

Graphene edge structures: Folding, scrolling, tubing, rippling and twisting

Conventional three-dimensional crystal lattices are terminated by surfaces, which can demonstrate complex rebonding and rehybridisation, localised strain and dislocation formation. Two dimensional crystal lattices, of which graphene is the archetype, are terminated by lines. The additional available dimension at such interfaces opens up a range of new topological interface possibilities. We show that graphene sheet edges can adopt a range of topological distortions depending on their nature. Rehybridisation, local bond reordering, chemical functionalisation with bulky, charged, or multi-functional groups can lead to edge buckling to relieve strain, folding, rolling and even tube formation. We discuss the topological possibilities at a 2D graphene edge, and under what circumstances we expect different edge topologies to occur. Density functional calculations are used to explore in more depth different graphene edge types.Comment: Additional figure in published versio

Mastitis Management: A Training Handbook for Extension Workers

Mastitis is a complex multifactorial disease affecting many farmers in low-income countries. Early detection of mastitis and good management practices are necessary to tackle the disease in the short and long term. Even though dairy farmers are aware of the disease, cultural practices, poor knowledge, lack of money and therefore supplies, manure management and other factors make it difficult to prevent and control mastitis. This handbook is a tool to help local extension officers facilitate farmer workshops on the causes and prevention of mastitis. If farmers identify the causes of mastitis for themselves and they identify ways of preventing mastitis then they are more likely to implement the changes on a long-term basis. The aim of the farmer workshop is to give the relevant information to dairy farmers and their advisors, but also to bring about change in practices, which will reduce mastitis

Nomenclature of sp2 carbon nanoforms

Carbon’s versatile bonding has resulted in the discovery of a bewildering variety of nanoforms which urgently need a systematic and standard nomenclature [1]. Besides fullerenes, nanotubes and graphene, research teams around the globe now produce a plethora of carbon-based nanoforms such as ‘bamboo’ tubes, ‘herringbone’ and ‘bell’ structures. Each discovery duly gains a new, sometimes whimsical, name, often with its discoverer unaware that the same nanoform has already been reported several times but with different names (for example the nanoform in Fig. 1h is in different publications referred to as ‘bamboo’ [2], ‘herringbone-bamboo’ [3], ‘stacked-cups’ [4] and ‘stacked-cones’ [5]). In addition, a single name is often used to refer to completely different carbon nanoforms (for example, the ‘bamboo’ structure in [2] is notably different from ‘bamboo’ in [6]). The result is a confusing overabundance of names which makes literature searches and an objective comparison of results extremely difficult, if not impossible

Molecular dynamics simulations of the transformation of carbon peapods into double-walled carbon nanotubes

The transformation of carbon peapods (encapsulated fullerenes in nanotubes) into doublewalled nanotubes was studied using molecular dynamics simulation. The simulations reproduce the two main trends known experimentally: the production of low-defect nanotubes and the templating effect of the outer tube. The process involves a low-temperature polymerization of the fullerenes followed by higher temperature self-assembly into a tube. Modelling of this second stage is made possible by the use of the Environment-Dependent Interaction Potential, a large number of atoms and long-time annealing. Analysis shows that the outer tube acts as a container for the self-assembly process, analogous to previous simulations and experiments in which free surfaces, either external or internal, template the formation of highly ordered sp2 phases