12,980 research outputs found
Spin glass behavior in an interacting gamma-Fe2O3 nanoparticle system
In this paper we investigate the superspin glass behavior of a concentrated
assembly of interacting maghemite nanoparticles and compare it to that of
canonical atomic spin glass systems. ac versus temperature and frequency
measurements show evidence of a superspin glass transition taking place at low
temperature. In order to fully characterize the superspin glass phase, the
aging behavior of both the thermo-remanent magnetization (TRM) and ac
susceptibility has been investigated. It is shown that the scaling laws obeyed
by superspin glasses and atomic spin glasses are essentially the same, after
subtraction of a superparamagnetic contribution from the superspin glass
response functions. Finally, we discuss a possible origin of this
superparamagnetic contribution in terms of dilute spin glass models
Interferon beta in multiple sclerosis: experience in a British specialist multiple sclerosis centre
Background: The efficacy of interferon beta (IFN beta) is well established in relapsing-remitting multiple sclerosis (MS). However, the use of this drug in clinical practice is complex, especially because it is only partially effective, its long term efficacy and side effects are unknown, its efficacy may be abrogated by the development of neutralising antibodies, compliance is variable, and its cost effectiveness is controversial.
Objectives and Methods: Analysis of a prospectively followed up series of 101 MS patients treated with IFN beta was undertaken to: (1) monitor the outcome of IFN beta treatment in clinical practice; (2) compare the immunogenicity of the three commercial IFN beta preparations available; (3) assess the proportion of patients fulfilling the current guidelines of the Association of British Neurologists for stopping IFN beta therapy.
Results: During a median treatment period of 26 months (range 2–85), the relapse rate decreased by 41%. Although the reduction in the relapse rate was similar for all three commercial products, none of the Avonex treated patients were relapse free, compared with 19% of the Betaferon treated and 27% of the Rebif treated patients (p=0.02). Neutralising antibodies were not detected in Avonex treated patients (0 of 18), compared with 12 of 32 (38%) Betaferon treated and 10 of 23 (44%) Rebif treated patients (p=0.02). Forty of 101 (40%) patients satisfied the current (2001) Association of British Neurologists criteria for stopping IFN beta treatment at some stage during their treatment.
Conclusion: IFN beta is effective in reducing the relapse rate in patients with relapsing-remitting MS in routine clinical practice. However, after a median treatment duration of 26 months, 40% of initially relapsing-remitting MS patients seem to have ongoing disease activity, presenting as disabling relapses or insidious progression
A unified view of some representations of imprecise probabilities
International audienceSeveral methods for the practical representation of imprecise probabilities exist such as Ferson's p-boxes, possibility distributions, Neumaier's clouds, and random sets . In this paper some relationships existing between the four kinds of representations are discussed. A cloud as well as a p-box can be modelled as a pair of possibility distributions. We show that a generalized form of p-box is a special kind of belief function and also a special kind of cloud
Risk and Business Goal Based Security Requirement and Countermeasure Prioritization
Companies are under pressure to be in control of their assets but at the same time they must operate as efficiently as possible. This means that they aim to implement “good-enough security” but need to be able to justify their security investment plans. Currently companies achieve this by means of checklist-based security assessments, but these methods are a way to achieve consensus without being able to provide justifications of countermeasures in terms of business goals. But such justifications are needed to operate securely and effectively in networked businesses. In this paper, we first compare a Risk-Based Requirements Prioritization method (RiskREP) with some requirements engineering and risk assessment methods based on their requirements elicitation and prioritization properties. RiskREP extends misuse case-based requirements engineering methods with IT architecture-based risk assessment and countermeasure definition and prioritization. Then, we present how RiskREP prioritizes countermeasures by linking business goals to countermeasure specification. Prioritizing countermeasures based on business goals is especially important to provide the stakeholders with structured arguments for choosing a set of countermeasures to implement. We illustrate RiskREP and how it prioritizes the countermeasures it elicits by an application to an action case
Orientational instabilities in nematics with weak anchoring under combined action of steady flow and external fields
We study the homogeneous and the spatially periodic instabilities in a
nematic liquid crystal layer subjected to steady plane {\em Couette} or {\em
Poiseuille} flow. The initial director orientation is perpendicular to the flow
plane. Weak anchoring at the confining plates and the influence of the external
{\em electric} and/or {\em magnetic} field are taken into account. Approximate
expressions for the critical shear rate are presented and compared with
semi-analytical solutions in case of Couette flow and numerical solutions of
the full set of nematodynamic equations for Poiseuille flow. In particular the
dependence of the type of instability and the threshold on the azimuthal and
the polar anchoring strength and external fields is analysed.Comment: 12 pages, 6 figure
Damping rate of plasmons and photons in a degenerate nonrelativistic plasma
A calculation is presented of the plasmon and photon damping rates in a dense
nonrelativistic plasma at zero temperature, following the resummation program
of Braaten-Pisarski. At small soft momentum , the damping is dominated by scattering processes corresponding to double longitudinal Landau
damping. The dampings are proportional to , where
is the Fermi velocity.Comment: 9 pages, 2 figure
AMBER on the VLTI: data processing and calibration issues
We present here the current performances of the AMBER / VLTI instrument for
standard use and compare these with the offered modes of the instrument. We
show that the instrument is able to reach its specified precision only for
medium and high spectral resolution modes, differential observables and bright
objects. For absolute observables, the current achievable accuracy is strongly
limited by the vibrations of the Unit Telescopes, and also by the observing
procedure which does not take into account the night-long transfer function
monitoring. For low-resolution mode, the current limitation is more in the data
reduction side, since several effects negligible at medium spectral resolution
are not taken into account in the current pipeline. Finally, for faint objects
(SNR around 1 per spectral channel), electromagnetic interferences in the VLTI
interferometric laboratory with the detector electronics prevents currently to
get unbiased measurements. Ideas are under study to correct in the data
processing side this effect, but a hardware fix should be investigated
seriously since it limits seriously the effective limiting magnitude of the
instrument.Comment: 10 page
Algebraic characterization of the Wess-Zumino consistency conditions in gauge theories
A new way of solving the descent equations corresponding to the Wess-Zumino
consistency conditions is presented. The method relies on the introduction of
an operator which allows to decompose the exterior space-time
derivative as a commutator. The case of the Yang-Mills theories is
treated in detail.Comment: 16 pages, UGVA-DPT 1992/08-781 to appear in Comm. Math. Phy
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