The LHCb trigger and data acquisition system

The LHCb experiment is the most recently approved of the 4 experiments under construction at CERNs LHC accelerator. It is a special purpose experiment designed to precisely measure the CP violation parameters in the B-B system. Triggering poses special problems since the interesting events containing B-mesons are immersed in a large background of inelastic p-p reactions. We therefore decided to implement a 4 level triggering scheme. The LHCb Data Acquisition (DAQ) system will have to cope with an average trigger rate of ~40 kHz, after two levels of hardware triggers, and an average event size of ~100 kB. Thus an event-building network which can sustain an average bandwidth of 4 GB/s is required. A powerful software trigger farm will have to be installed to reduce the rate from the 40 kHz to ~100 Hz of events written to permanent storage. In this paper we outline the general architecture of the Trigger and DAQ system and the readout protocols we plan to implement. First results of simulations of the behavior of the event- building network implementations under the expected traffic patterns are presented. (8 refs)

Epistatic Interactions in the Arabinose Cis-Regulatory Element

Changes in gene expression are an important mode of evolution; however, the proximate mechanism of these changes is poorly understood. In particular, little is known about the effects of mutations within cis binding sites for transcription factors, or the nature of epistatic interactions between these mutations. Here, we tested the effects of single and double mutants in two cis binding sites involved in the transcriptional regulation of the Escherichia coli araBAD operon, a component of arabinose metabolism, using a synthetic system. This system decouples transcriptional control from any posttranslational effects on fitness, allowing a precise estimate of the effect of single and double mutations, and hence epistasis, on gene expression. We found that epistatic interactions between mutations in the araBAD cis-regulatory element are common, and that the predominant form of epistasis is negative. The magnitude of the interactions depended on whether the mutations are located in the same or in different operator sites. Importantly, these epistatic interactions were dependent on the presence of arabinose, a native inducer of the araBAD operon in vivo, with some interactions changing in sign (e.g., from negative to positive) in its presence. This study thus reveals that mutations in even relatively simple cis-regulatory elements interact in complex ways such that selection on the level of gene expression in one environment might perturb regulation in the other environment in an unpredictable and uncorrelated manner

On the convergence of a D.K.T. method valid for shells of arbitrary shape

In a recent paper by the same authors, we have thoroughly described how to extend to the case of general shells the well known D.K.T. methods (i.e. Discrete Kirchhoff Triangle) which are now classically used to solve plate problems. In this paper we have also detailed how to realize the implementation and we have reported some numerical results obtained over classical benchmarks. The aim of this paper is to prove the convergence ofa closely related method and to obtain corresponding error estimates

Finite strain Landau theory of high pressure phase transformations

The properties of materials near structural phase transitions are often successfully described in the framework of Landau theory. While the focus is usually on phase transitions, which are induced by temperature changes approaching a critical temperature T-c, here we will discuss structural phase transformations driven by high hydrostatic pressure, as they are of major importance for understanding processes in the interior of the earth. Since at very high pressures the deformations of a material are generally very large, one needs to apply a fully nonlinear description taking physical as well as geometrical nonlinearities (finite strains) into account. In particular it is necessary to retune conventional Landau theory to describe such phase transitions. In Troster et al (2002 Phys. Rev. Lett. 88 55503) we constructed a Landau-type free energy based on an order parameter part, an order parameter-(finite) strain coupling and a nonlinear elastic term. This model provides an excellent and efficient framework for the systematic study of phase transformations for a wide range of materials up to ultrahigh pressures

Magnetic superspace groups and symmetry constraints in incommensurate magnetic phases

Although superspace formalism has become the standard approach for the analysis of structurally modulated crystals, it has remained during the last thirty years almost unexplored as a practical tool to deal with magnetic incommensurate structures. This situation has recently changed with the development of new computer tools for magnetic phases based on this formalism. In this context we show here that, as in the case of nonmagnetic incommensurate systems, the concept of superspace symmetry provides a simple, efficient and systematic way to characterize the symmetry and rationalize the structural and physical properties of incommensurate magnetic materials. The method introduces significant advantages over the most commonly employed method of representation analysis for the description of the magnetic structure of a crystal. But, more importantly, in contrast with that method, it consistently yields and classifies all degrees of freedom of the system. The knowledge of the superspace group of an incommensurate magnetic material allows to predict its crystal tensor properties and to rationalize its phase diagram, previous to any appeal to microscopic models or mechanisms. This is especially relevant when the properties of incommensurate multiferroics are being studied. We present first a summary of the superspace method under a very practical viewpoint particularized to magnetic modulations. Its relation with the usual representation analysis is then analyzed in detail, with the derivation of important general rules for magnetic modulations with a single propagation vector. The power and efficiency of the formalism is illustrated with various selected examples, including some multiferroic materials

Diffusion tensor imaging in orthostatic tremor: a tract‐based spatial statistics study

[Abstract] Objective The pathogenesis of orthostatic tremor (OT) is unknown. We investigated OT‐related white matter changes and their correlations with scores from a neuropsychological testing battery. Methods Diffusion tensor imaging measures were compared between 14 OT patients and 14 age‐ and education‐matched healthy controls, using whole‐brain tract‐based spatial statistics analysis. Correlations between altered diffusion metrics and cognitive performance in OT group were assessed. Results In all cognitive domains (attention, executive function, visuospatial ability, verbal memory, visual memory, and language), OT patients’ cognitive performance was significantly worse than that of healthy controls. OT patients demonstrated altered diffusivity metrics not only in the posterior lobe of the cerebellum (left cerebellar lobule VI) and in its efferent cerebellar fibers (left superior cerebellar peduncle), but also in medial lemniscus bilaterally (pontine tegmentum), anterior limb of the internal capsule bilaterally, right posterior limb of the internal capsule, left anterior corona radiata, right insula, and the splenium of corpus callosum. No relationship was found between diffusion measures and disease duration in OT patients. Diffusion white matter changes, mainly those located in right anterior limb of the internal capsule, were correlated with poor performance on tests of executive function, visuospatial ability, verbal memory, and visual memory in OT patients. Interpretation White matter changes were preferentially located in the cerebellum, its efferent pathways, as well as in the pontine tegmentum and key components of the frontal–thalamic–cerebellar circuit. Further work needs to be done to understand the evolution of these white matter changes and their functional consequences.National Institutes of Health; R01 NS39422National Institutes of Health; R01 NS094607National Institutes of Health; R01 NS085136National Institutes of Health; R01 NS073872National Institutes of Health; R01 NS088257European Commission. Grant Number: ICT‐2011‐287739Ministerio de Ecnomía y Competitividad; RTC‐2015‐3967‐1Spanish Health Research Agency; FIS PI12/01602Spanish Health Research Agency; FIS PI16/00451Ministerio de Ecnomía y Competitividad; DPI‐2015‐68664‐C4‐1‐