5,609 research outputs found
The V<sub>H</sub> gene repertoire of splenic B cells and somatic hypermutation in systemic lupus erythematosus
In systemic lupus erythematosus (SLE) it has been hypothesized that self-reactive B cells arise from virgin B cells that express low-affinity, nonpathogenic germline V genes that are cross-reactive for self and microbial antigens, which convert to high-affinity autoantibodies via somatic hypermutation. The aim of the present study was to determine whether the V<sub>H</sub> family repertoire and pattern of somatic hypermutation in germinal centre (GC) B cells deviates from normal in SLE. Rearranged immunoglobulin V<sub>H</sub> genes were cloned and sequenced from GCs of a SLE patient's spleen. From these data the GC V gene repertoire and the pattern of somatic mutation during the proliferation of B-cell clones were determined. The results highlighted a bias in V<sub>H</sub>5 gene family usage, previously unreported in SLE, and under-representation of the V<sub>H</sub>1 family, which is expressed in 20–30% of IgM+ B cells of healthy adults and confirmed a defect in negative selection. This is the first study of the splenic GC response in human SLE
A Data-Driven Approximation of the Koopman Operator: Extending Dynamic Mode Decomposition
The Koopman operator is a linear but infinite dimensional operator that
governs the evolution of scalar observables defined on the state space of an
autonomous dynamical system, and is a powerful tool for the analysis and
decomposition of nonlinear dynamical systems. In this manuscript, we present a
data driven method for approximating the leading eigenvalues, eigenfunctions,
and modes of the Koopman operator. The method requires a data set of snapshot
pairs and a dictionary of scalar observables, but does not require explicit
governing equations or interaction with a "black box" integrator. We will show
that this approach is, in effect, an extension of Dynamic Mode Decomposition
(DMD), which has been used to approximate the Koopman eigenvalues and modes.
Furthermore, if the data provided to the method are generated by a Markov
process instead of a deterministic dynamical system, the algorithm approximates
the eigenfunctions of the Kolmogorov backward equation, which could be
considered as the "stochastic Koopman operator" [1]. Finally, four illustrative
examples are presented: two that highlight the quantitative performance of the
method when presented with either deterministic or stochastic data, and two
that show potential applications of the Koopman eigenfunctions
Lessons and Prospects from the pMSSM after LHC Run I: Neutralino LSP
We study SUSY signatures at the 7, 8 and 14 TeV LHC employing the
19-parameter, R-Parity conserving p(henomenological)MSSM, in the scenario with
a neutralino LSP. Our results were obtained via a fast Monte Carlo simulation
of the ATLAS SUSY analysis suite. The flexibility of this framework allows us
to study a wide variety of SUSY phenomena simultaneously and to probe for weak
spots in existing SUSY search analyses. We determine the ranges of the
sparticle masses that are either disfavored or allowed after the searches with
the 7 and 8 TeV data sets are combined. We find that natural SUSY models with
light squarks and gluinos remain viable. We extrapolate to 14 TeV with both 300
fb and 3 ab of integrated luminosity and determine the expected
sensitivity of the jets + MET and stop searches to the pMSSM parameter space.
We find that the high-luminosity LHC will be powerful in probing SUSY with
neutralino LSPs and can provide a more definitive statement on the existence of
natural Supersymmetry.Comment: 41 pages, 27 figures. arXiv admin note: substantial text overlap with
arXiv:1307.844
Density Matrix Renormalization for Model Reduction in Nonlinear Dynamics
We present a novel approach for model reduction of nonlinear dynamical
systems based on proper orthogonal decomposition (POD). Our method, derived
from Density Matrix Renormalization Group (DMRG), provides a significant
reduction in computational effort for the calculation of the reduced system,
compared to a POD. The efficiency of the algorithm is tested on the one
dimensional Burgers equations and a one dimensional equation of the Fisher type
as nonlinear model systems.Comment: 12 pages, 12 figure
Surface drilling technologies for Mars
Rock drilling and coring conceptual designs for the surface activities associated with a manned Mars mission are proposed. Straightforward extensions of equipment and procedures used on Earth are envisioned for the sample coring and shallow high explosive shot holes needed for tunneling and seismic surveying. A novel rocket exhaust jet piercing method is proposed for very rapid drilling of shot holes required for explosive excavation of emergency radiation shelters. Summaries of estimated equipment masses and power requirements are provided, and the indicated rotary coring rigs are scaled from terrestrial equipment and use compressed CO2 from the Martian atmosphere for core bit cooling and cuttings removal. A mass of 120 kg and power of 3 kW(e) are estimated for a 10 m depth capability. A 100 m depth capacity core rig requires about 1150 kg and 32 km(e). The rocket exhaust jet equipment devised for shallow (3m) explosive emplacement shot holes requires no surface power beyond an electrical ignition system, and might have a 15 kg mass
More Energy, More Searches, but the pMSSM Lives On
We further examine the capability of the 7 and 8 TeV LHC to explore the
parameter space of the p(henomenological)MSSM with neutralino LSPs. Here we
present an updated study employing all of the relevant ATLAS SUSY analyses, as
well as all relevant LHC non-MET searches, whose data were publically available
as of mid-September 2012. We find that roughly 1/3 of our pMSSM model points
are excluded at present with an important role being played by both the heavy
flavor and multi-lepton searches, as well as those for heavy stable charged
particles. Nonetheless, we find that light gluinos, 1st/2nd generation squarks,
and stop/sbottoms (\lsim 400-700 GeV), as well as models with 1% fine-tuning or
better, are still viable in the pMSSM. In addition, we see that increased
luminosity at 8 TeV is unlikely to significantly improve the reach of the
"vanilla" searches. The impact of these null searches on the SUSY sparticle
spectrum is discussed in detail and the implications of these results for
models with low fine-tuning, a future lepton collider and dark matter searches
are examined.Comment: 33 pages, 9 figure
Linear models for control of cavity flow oscillations
Models for understanding and controlling oscillations in the flow past a rectangular cavity are developed. These models may be used to guide control designs, to understand performance limits of feedback, and to interpret experimental results. Traditionally, cavity oscillations are assumed to be self-sustained: no external disturbances are necessary to maintain the oscillations, and amplitudes are limited by nonlinearities. We present experimental data which suggests that in some regimes, the oscillations may not be self-sustained, but lightly damped: oscillations are sustained by external forcing, such as boundary-layer turbulence. In these regimes, linear models suffice to describe the behaviour, and the final amplitude of oscillations depends on the characteristics of the external disturbances. These linear models are particularly appropriate for describing cavities in which feedback has been used for noise suppression, as the oscillations are small and nonlinearities are less likely to be important. It is shown that increasing the gain too much in such feedback control experiments can lead to a peak-splitting phenomenon, which is explained by the linear models. Fundamental performance limits indicate that peak splitting is likely to occur for narrow-bandwidth actuators and controllers
pMSSM Benchmark Models for Snowmass 2013
We present several benchmark points in the phenomenological Minimal
Supersymmetric Standard Model (pMSSM). We select these models as experimentally
well-motivated examples of the MSSM which predict the observed Higgs mass and
dark matter relic density while evading the current LHC searches. We also use
benchmarks to generate spokes in parameter space by scaling the mass parameters
in a manner which keeps the Higgs mass and relic density approximately
constant.Comment: 10 pages, 6 figure
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