41,214 research outputs found
Diffusion of multiple species with excluded-volume effects
Stochastic models of diffusion with excluded-volume effects are used to model
many biological and physical systems at a discrete level. The average
properties of the population may be described by a continuum model based on
partial differential equations. In this paper we consider multiple interacting
subpopulations/species and study how the inter-species competition emerges at
the population level. Each individual is described as a finite-size hard core
interacting particle undergoing Brownian motion. The link between the discrete
stochastic equations of motion and the continuum model is considered
systematically using the method of matched asymptotic expansions. The system
for two species leads to a nonlinear cross-diffusion system for each
subpopulation, which captures the enhancement of the effective diffusion rate
due to excluded-volume interactions between particles of the same species, and
the diminishment due to particles of the other species. This model can explain
two alternative notions of the diffusion coefficient that are often confounded,
namely collective diffusion and self-diffusion. Simulations of the discrete
system show good agreement with the analytic results
Layout design for final focus systems and applications for the LHC interaction region upgrade
The design of a final focus system should aim in finding the best compromise between beam size and the maximum quadrupole gradient allowed by a given magnet technology. This article shows a method and a parametric layout that can be used as a design tool and allows relating the final focus limitations with the limits coming from magnet technologies. An application for the case of the LHC IR upgrade is shown
Phase 1 Optics: Merits and Challenges
Low gradient optics have been proposed for an upgrade of the LHC interaction region. Using lower gradient, larger aperture and longer NbTi quadrupoles with respect to the nominal layout, it is possible to achieve = 25 cm with additional aperture margins and better dynamic aperture. The main drawbacks are an increase of the number of the long range interactions and limitations in the downstream matching section. Four layouts and optics, which span the parameter space and modularity for NbTi technology, are proposed and studied extensively in order identify and quantify the merits and challenges
LHC IR upgrade: dipole first with chromaticity and dynamic aperture issues
A dipole first layout for the LHC interaction region upgrade, while offering a potential reduction of the limitations due the long range beam-beam collisions, charged debris with respect to the quadrupole first layout, presents an enhancement of the chromatic and geometric aberration due large values in the triplet. These two effects are studied in the following for the dipole first option presented in [1]
Apoptotic signaling through CD95 (Fas/Apo-1) activates an acidic sphingomyelinase.
Intracellular pathways leading from membrane receptor engagement to apoptotic cell death are still poorly characterized. We investigated the intracellular signaling generated after cross-linking of CD95 (Fas/Apo-1 antigen), a broadly expressed cell surface receptor whose engagement results in triggering of cellular apoptotic programs. DX2, a new functional anti-CD95 monoclonal antibody was produced by immunizing mice with human CD95-transfected L cells. Crosslinking of CD95 with DX2 resulted in the activation of a sphingomyelinase (SMase) in promyelocytic U937 cells, as well as in other human tumor cell lines and in CD95-transfected murine cells, as demonstrated by induction of in vivo sphingomyelin (SM) hydrolysis and generation of ceramide. Direct in vitro measurement of enzymatic activity within CD95-stimulated U937 cell extracts, using labeled SM vesicles as substrates, showed strong SMase activity, which required pH 5.0 for optimal substrate hydrolysis. Finally, all CD95-sensitive cell lines tested could be induced to undergo apoptosis after exposure to cell-permeant C2-ceramide. These data indicate that CD95 cross-linking induces SM breakdown and ceramide production through an acidic SMase, thus providing the first information regarding early signal generation from CD95, and may be relevant in defining the biochemical nature of intracellular messengers leading to apoptotic cell death
Effect of calcium sulfate source on the hydration of calcium sulfoaluminate eco-cement
The availability of cements, including eco-cements, with tailored mechanical properties is very important
for special applications in the building industry. Here we report a full study of the hydration of calcium
sulfoaluminate eco-cements with different sulfate sources (gypsum, bassanite and anhydrite) and two
water/cement ratios (0.50 and 0.65). These parameters have been chosen because they are known to
strongly modify the mechanical properties of the resulting mortars and concretes. The applied multitechnique
characterization includes: phase assemblage by Rietveld method, evolved heat, conductivity,
rheology, compressive strength and expansion/retraction measurements. The dissolution rate of the sulfate
sources is key to control the hydration reactions. Bassanite dissolves very fast and hence the initial
setting time of the pastes and mortars is too short (20 min) to produce homogeneous samples. Anhydrite
dissolves slowly so, at 1 hydration-day, the amount of ettringite formed (20 wt%) is lower than that in
gypsum pastes (26 wt%) (w/c = 0.50), producing mortars with lower compressive strengths. After 3
hydration-days, anhydrite pastes showed slightly larger ettringite contents and hence, mortars with
slightly higher compressive strengths. Ettringite content is the chief parameter to explain the strength
development in these eco-cements.Universidad de Málaga. Campus de Excelencia Interncaional Andalucía Tech
Structure, Atomistic Simulations, and Phase Transition of Stoichiometric Yeelimite
ABSTRACT: Yeelimite, Ca4[Al6O12]SO4, is outstanding as an aluminate
sodalite, being the framework of these type of materials flexible and dependent
on ion sizes and anion ordering/disordering. On the other hand, yeelimite is also
important from an applied perspective as it is the most important phase in
calcium sulfoaluminate cements. However, its crystal structure is not well
studied. Here, we characterize the room temperature crystal structure of
stoichiometric yeelimite through joint Rietveld refinement using neutron and Xray
powder diffraction data coupled with chemical soft-constraints. Our structural
study shows that yeelimite has a lower symmetry than that of the previously
reported tetragonal system, which we establish to likely be the acentric
orthorhombic space group Pcc2, with a √2a × √2a × a superstructure based on
the cubic sodalite structure. Final unit cell values were a = 13.0356(7) Å, b =
13.0350(7) Å, and c = 9.1677(2) Å. We determine several structures using
density functional theory calculations, with the lowest energy structure being Pcc2 in agreement with our experimental result.
Yeelimite undergoes a reversible phase transition to a higher-symmetry phase which has been characterized to occur at 470 °C by
thermodiffractometry. The higher-symmetry phase is likely cubic or pseudocubic possessing an incommensurate superstructure,
as suggested by our theoretical calculations which show a phase transition from an orthorhombic to a tetragonal structure. Our
theoretical study also predicts a pressure-induced phase transition to a cubic structure of space group I43m. Finally, we show that
our reported crystal structure of yeelimite enables better mineralogical phase analysis of commercial calcium sulfoaluminate
cements, as shown by RF values for this phase, 6.9% and 4.8% for the previously published orthorhombic structure and for the
one reported in this study, respectively.Universidad de Málaga. Campus de Excelencia Internacional. Andalucía Tech
Higgs look-alikes at the LHC
The discovery of a Higgs particle is possible in a variety of search channels
at the LHC. However the true identity of any putative Higgs boson will at first
remain ambiguous, until one has experimentally excluded other possible
assignments of quantum numbers and couplings. We quantify to what degree one
can discriminate a Standard Model Higgs boson from "look-alikes" at, or close
to, the moment of discovery at the LHC. We focus on the fully-reconstructible
"golden" decay mode to a pair of Z bosons and a four-lepton final state,
simulating sPlot-weighted samples of signal and background events. Considering
both on-shell and off-shell Z's, we show how to utilize the full decay
information from the events, including the distributions and correlations of
the five relevant angular variables. We demonstrate how the finite phase space
acceptance of any LHC detector sculpts the decay distributions, a feature
neglected in previous studies. We use likelihood ratios to discriminate a
Standard Model Higgs from look-alikes with other spins or nonstandard parity,
CP, or form factors. For a benchmark resonance mass of 200 GeV/c^2, we achieve
a median expected discrimination significance of 3 sigma with as few as 19
events, and even better discrimination for the off-shell decays of a 145
GeV/c^2 resonance.Comment: 39 pages, 55 figures, typos fixed, figures added, and minor
clarification
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