Theory of magnetic oscillations in Weyl semimetals

Weyl semimetals are a new class of Dirac material that posses bulk energy nodes in three dimensions. In this paper, we study a Weyl semimetal subject to an applied magnetic field. We derive expressions for the density of states, electronic specific heat, and the quantum oscillations of the magnetization, DC conductivity, and thermal conductivity. We find phase shifts in the quantum oscillations that distinguish the Weyl semimetal from conventional three dimensional Schr\"odinger Fermions.Comment: 11 pages, 5 figure

SCRAM: Software configuration and management for the LHC Computing Grid project

Recently SCRAM (Software Configuration And Management) has been adopted by the applications area of the LHC computing grid project as baseline configuration management and build support infrastructure tool. SCRAM is a software engineering tool, that supports the configuration management and management processes for software development. It resolves the issues of configuration definition, assembly break-down, build, project organization, run-time environment, installation, distribution, deployment, and source code distribution. It was designed with a focus on supporting a distributed, multi-project development work-model. We will describe the underlying technology, and the solutions SCRAM offers to the above software engineering processes, while taking a users view of the system under configuration management.Comment: Computing in High Energy and Nuclear Physics, La Jolla, California, March 24-28, 2003 1 tar fil

Impact of Electron-Phonon Coupling on Near-Field Optical Spectra

The finite momentum transfer ($\boldsymbol{q}$) longitudinal optical response $\sigma^L(\boldsymbol{q},\omega)$ of graphene has a peak at an energy $\omega=\hbar v_F q$. This corresponds directly to a quasiparticle peak in the spectral density at momentum relative to the Fermi momentum $k_F -q$. Inclusion of coupling to a phonon mode at $\omega_E$ results, for $\omega<|\omega_E|$, in a constant electron-phonon renormalization of the bare bands by a mass enhancement factor $(1+\lambda)$ and this is followed by a phonon kink at $\omega_E$ where additional broadening begins. Here we study the corresponding changes in the optical quasiparticle peaks which we find to continue to directly track the renormalized quasiparticle energies until $q$ is large enough that the optical transitions begin to sample the phonon kink region of the dispersion curves where linearity in momentum is lost in the renormalized Dirac Fermion dispersion curves and the correspondence to a single quasiparticle energy is lost. Nevertheless there remains in $\sigma^L(\boldsymbol{q},\omega)$ features analogous to the phonon kinks of the dispersion curves which are observable through variation of $q$ and $\omega$.Comment: 6 pages, 5 figure

Museums as experimental test-beds: Lessons from a university museum

Resistance to change is an accusation that has anecdotally been thrown at museum curators, but in my experience, today’s museum professionals have extraordinary capacity to be innovators and experimenters. Here I will describe why and how museums might want to establish formal strategies to develop themselves as places where innovative ideas and practices can be tested as part of their everyday operations. I will set out why museums might want to establish a publicly visible experimental philosophy, focusing on lessons learned from the activities of the Grant Museum of Zoology, UCL. The benefits of innovation include advocacy, raised profile, and an enhanced visitor experience. I will discuss various models to embed experimental practice. These can operate at different scales, ranging from small visitor studies and pilots to large-scale interventions potentially engaging every museum visitor, but all contributing to an atmosphere where experimentation is encouraged and ingrained. In this atmosphere, it is crucial that there is understanding and planning that allows for failure – some experiments do not work, and that is totally fine

The impact of global communication latency at extreme scales on Krylov methods

Krylov Subspace Methods (KSMs) are popular numerical tools for solving large linear systems of equations. We consider their role in solving sparse systems on future massively parallel distributed memory machines, by estimating future performance of their constituent operations. To this end we construct a model that is simple, but which takes topology and network acceleration into account as they are important considerations. We show that, as the number of nodes of a parallel machine increases to very large numbers, the increasing latency cost of reductions may well become a problematic bottleneck for traditional formulations of these methods. Finally, we discuss how pipelined KSMs can be used to tackle the potential problem, and appropriate pipeline depths

Re-evaluation of the first synthetic estrogen, 1-keto-1,2,3,4-tetrahydrophenanthrene, and bisphenol A, using both the ovariectomised rat model used in 1933 and additional assays

1-Keto-1,2,3,4-tetrahydrophenanthrene (THP-1) was reported by Cook et al in 1933 as the first synthetic estrogen. Estrogenic activity was assessed by the induction of vaginal cornification in ovariectomised rats. The corresponding 4-isomer (THP-4) was shown to be inactive. Both chemicals have been re-synthesised and assessed for hormonal activity. Each chemical bound weakly and to the same extent to isolated estrogen receptors, but only at high concentrations. However, they each lacked estrogenic or anti-estrogenic activity when evaluated in vitro using a yeast hER assay, and both failed to induce vaginal cornification or uterotrophic effects in ovariectomised rats. THP-1, and to a lesser extent THP-4, were shown to possess weak androgenic and anti-androgenic activity in vitro when evaluated using an hAR yeast assay. Estrogenic activity for bisphenol A (BPA) was subsequently demonstrated by Dodds and Lawson (1936) using the same ovariectomised rat protocol, and this activity has been confirmed and supplemented by positive uterotrophic effects for BPA in the same bioassays. The present results illustrate the complexity of deriving conclusions regarding the hormonal activities of chemicals. First, some activities observed in isolated hormonal receptor binding assays may not be expressed in functional hormonal assays. This indicates the need for functional hormonal assays in any screening programme. Second, that activities observed for a chemical in one hormonal assay may not be reflected in related hormonal assays. This indicates the need to define assay protocols with some precision when incorporating them into screening batteries. Finally, that some literature reports of hormonal activity for chemicals may not be capable of independent confirmation under apparently identical conditions of test. This illustrates the need to use lists of hormonally active chemicals with car