10,656 research outputs found
Magnetic structure of Cd-doped CeCoIn5
The heavy fermion superconductor CeCoIn5 is believed to be close to a
magnetic instability, but no static magnetic order has been found. Cadmium
doping on the In-site shifts the balance between superconductivity and
antiferromagnetism to the latter with an extended concentration range where
both types of order coexist at low temperatures. We investigated the magnetic
structure of nominally 10% Cd-doped CeCoIn5, being antiferromagnetically
ordered below T_N=3 K and superconducting below T_c=1.3 K, by elastic neutron
scattering. Magnetic intensity was observed only at the ordering wave vector
Q_AF = (1/2,1/2,1/2) commensurate with the crystal lattice. Upon entering the
superconducting state the magnetic intensity seems to change only little. The
commensurate magnetic ordering in CeCo(In1-xCdx)5 is in contrast to the
incommensurate antiferromagnetic ordering observed in the closely related
compound CeRhIn5. Our results give new insights in the interplay between
superconductivity and magnetism in the family of CeTIn5 (T=Co, Rh, and Ir)
based compounds.Comment: 4 pages, 4 figure
Neural Modeling and Control of Diesel Engine with Pollution Constraints
The paper describes a neural approach for modelling and control of a
turbocharged Diesel engine. A neural model, whose structure is mainly based on
some physical equations describing the engine behaviour, is built for the
rotation speed and the exhaust gas opacity. The model is composed of three
interconnected neural submodels, each of them constituting a nonlinear
multi-input single-output error model. The structural identification and the
parameter estimation from data gathered on a real engine are described. The
neural direct model is then used to determine a neural controller of the
engine, in a specialized training scheme minimising a multivariable criterion.
Simulations show the effect of the pollution constraint weighting on a
trajectory tracking of the engine speed. Neural networks, which are flexible
and parsimonious nonlinear black-box models, with universal approximation
capabilities, can accurately describe or control complex nonlinear systems,
with little a priori theoretical knowledge. The presented work extends optimal
neuro-control to the multivariable case and shows the flexibility of neural
optimisers. Considering the preliminary results, it appears that neural
networks can be used as embedded models for engine control, to satisfy the more
and more restricting pollutant emission legislation. Particularly, they are
able to model nonlinear dynamics and outperform during transients the control
schemes based on static mappings.Comment: 15 page
Role of Light Vector Mesons in the Heavy Particle Chiral Lagrangian
We give the general framework for adding "light" vector particles to the
heavy hadron effective chiral Lagrangian. This has strong motivations both from
the phenomenological and aesthetic standpoints. An application to the already
observed D \rightarrow \overbar{K^*} weak transition amplitude is discussed.Comment: 19 pages, LaTeX documen
Charge carrier localization induced by excess Fe in the Fe1+y(Te,Se) superconductor system
We have investigated the effect of Fe nonstoichiometry on properties of the
Fe1+y(Te, Se) superconductor system by means of resistivity, Hall coefficient,
magnetic susceptibility, and specific heat measurements. We find that the
excess Fe at interstitial sites of the (Te, Se) layers not only suppresses
superconductivity, but also results in a weakly localized electronic state. We
argue that these effects originate from the magnetic coupling between the
excess Fe and the adjacent Fe square planar sheets, which favors a short-range
magnetic order.Comment: 15 pages, 6 figures accepted for publication in PR
Modeling the regulatory network of histone acetylation in Saccharomyces cerevisiae
Acetylation of histones plays an important role in regulating transcription. Histone acetylation is mediated partly by the recruitment of specific histone acetyltransferases (HATs) and deacetylases (HDACs) to genomic loci by transcription factors, resulting in modulation of gene expression. Although several specific interactions between transcription factors and HATs and HDACs have been elaborated in Saccharomyces cerevisiae, the full regulatory network remains uncharacterized. We have utilized a linear regression of optimized sigmoidal functions to correlate transcription factor binding patterns to the acetylation profiles of 11 lysines in the four core histones measured at all S. cerevisiae promoters. The resulting associations are combined with large-scale protein–protein interaction data sets to generate a comprehensive model that relates recruitment of specific HDACs and HATs to transcription factors and their target genes and the resulting effects on individual lysines. This model provides a broad and detailed view of the regulatory network, describing which transcription factors are most significant in regulating acetylation of specific lysines at defined promoters. We validate the model, both computationally and experimentally, to demonstrate that it yields accurate predictions of these regulatory mechanisms
Implicit and explicit solvent models for the simulation of a single polymer chain in solution: Lattice Boltzmann vs Brownian dynamics
We present a comparative study of two computer simulation methods to obtain
static and dynamic properties of dilute polymer solutions. The first approach
is a recently established hybrid algorithm based upon dissipative coupling
between Molecular Dynamics and lattice Boltzmann (LB), while the second is
standard Brownian Dynamics (BD) with fluctuating hydrodynamic interactions.
Applying these methods to the same physical system (a single polymer chain in a
good solvent in thermal equilibrium) allows us to draw a detailed and
quantitative comparison in terms of both accuracy and efficiency. It is found
that the static conformations of the LB model are distorted when the box length
L is too small compared to the chain size. Furthermore, some dynamic properties
of the LB model are subject to an finite size effect, while the BD
model directly reproduces the asymptotic behavior. Apart from
these finite size effects, it is also found that in order to obtain the correct
dynamic properties for the LB simulations, it is crucial to properly thermalize
all the kinetic modes. Only in this case, the results are in excellent
agreement with each other, as expected. Moreover, Brownian Dynamics is found to
be much more efficient than lattice Boltzmann as long as the degree of
polymerization is not excessively large.Comment: 11 figures, submitted to J. Chem. Phy
Infusion of donor leukocytes to induce tolerance in organ allograft recipients
To further enhance chimerism, 229 primary allograft recipients have received perioperative intravenous infusion of a single dose of 3 to 6 x 108 unmodified donor bone marrow (BM) cells/kg body weight. In addition, 42 patients have been accrued in a concurrent protocol involving multiple (up to three) sequential perioperative infusions of 2 x 108 BM cells/kg/day from day 0-2 posttransplantation (PTx). Organ recipients (n = 133) for whom BM was not available were monitored as controls. The infusion of BM was safe and except for 50 (18%), all study patients have optimal graft function. Of the control patients, allografts in 30 (23%) have been lost during the course of follow-up. The cumulative risk of acute cellular rejection (ACR) was statistically lower in the study patients compared with that of controls. It is interesting that, 62% of BM-augmented heart recipients were free of ACR (Grade ≥ 3A) in the first 6 months PTx compared to controls. The incidence of obliterative bronchiolitis was also statistically lower in study lung recipients (3.8%) compared with the contemporaneously acquired controls (31%). The levels of donor cell chimerism were at least a log higher in the peripheral blood of majority of the study patients compared with that of controls. The incidence of donor-specific hyporeactivity, as determined by one-way mixed leukocyte reaction, was also higher in those BM-augmented liver, kidney, and lung recipients that could be evaluated compared to controls
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