Anomalies in the antiferromagnetic phase of metamagnets

Motivated by recent experiments on the metamagnet FeBr2, anomalies of the magnetization and the specific heat in the antiferromagnetic phase of related spin models are studied systematically using Monte Carlo simulations. In particular, the dependence of the anomalous behavior on competing intralayer interactions, the spin value and the Ising-like anisotropy of the Hamiltonian is investigated. Results are compared to experimental findings on FeBr2.Comment: 19 pages, 15 figures, submitted to Phys. Rev.

Mitochondrial Translation Products before and after Integration into the Mitochondrial Membrane in Neurospora crassa

# 1. Nascent translation products on mitochondrial ribosomes were selectively labeled in vivo in the presence of cycloheximide with radioactive leucine. They were isolated together with the ribosomes. # 2. The labeled polypeptides show a high tendency to aggregate and can only be kept in solution in the presence of detergents such as dodecylsulfate. Also, mitochondrial ribosomes carrying nascent peptide chains easily form aggregates. # 3. The polypeptides adhering to mitochondrial monomeric ribosomes differ from those adhering to polymeric ribosomes. Gel electrophoresis in the presence if dodecylsulfate shows for the peptidyl transfer RNA products at the monomer, an apparent molecular weight of 27000. After removing the transfer RNA, an apparent molecular weight of less than 10000 is registered. The peptides adhering to mitochondrial polymeric ribosomes display a broad range of apparent molecular weights. In contrast, translation products associated with cytoplasmic monomeric and polymeric ribosomes all show quite disperse molecular weights. # 4. Using gel-chromatographic analysis no difference in the elution characteristics between translation products associated with mitochondrial monomeric and polymeric ribosomes was found. In both cases apparent molecular weights of about 11000 were obtained. # 5. A kinetic study of the appearance of mitochondrial translation products in the mitochondrial membrane was carried out. A conversion process of products with lower apparent molecular weights to those with higher apparent molecular weights is observed. This suggests that mitochondrial ribosomes form polypeptides which are modified during or after integration into the membrane. # 6. The hypothesis is discussed that mitochondria possess their own system of transcription and translation, because the hydrophobic nature of the translation products makes it necessary that they are formed inside the inner mitochondrial membrane, into which they are integrated

Guaranteed characterization of exact non-asymptotic confidence regions

accepté à AutomaticaIn parameter estimation, it is often desirable to supplement the estimates with an assessment of their quality. A new family of methods proposed by Campi et al. for this purpose is particularly attractive, as it makes it possible to obtain exact, non-asymptotic con dence regions under mild assumptions on the noise distribution. A bottleneck of this approach, however, is the numerical characterization of these con dence regions. So far, it has been carried out by gridding, which provides no guarantee as to its results and is only applicable to low dimensional spaces. This paper shows how interval analysis can contribute to removing this bottleneck

Guaranteed characterization of exact confidence regions for FIR models under mild assumptions on the noise via interval analysis

International audienceSPS is one of the two methods proposed recently by Campi et al. to obtain exact, non-asymptotic confidence regions for parameter estimates under mild assumptions on the noise distribution. It does not require the measurement noise to be Gaussian (or to have any other known distribution for that matter). The numerical characterization of the resulting confidence regions is far from trivial, however, and has only be carried out so far on very low-dimensional problems via methods that could not guarantee their results and could not be extended to large-scale problems because of their intrinsic complexity. The aim of the present paper is to show how interval analysis can contribute to a guaranteed characterization of exact confidence regions in large-scale problems. The application considered is the estimation of the parameters of finite-impulse response (FIR) models. The structure of the problem makes it possible to define a very efficient specific contractor, allowing the treatement of models with a large number of parameters, as is the rule for FIR models, and thus escaping the curse of dimensionality that often plagues interval methods

Guaranteed characterization of exact non-asymptotic confidence regions as defined by LSCR and SPS

International audienceIn parameter estimation, it is often desirable to supplement the estimates with an assessment of their quality. A new family of methods proposed by Campi et al. for this purpose is particularly attractive, as it makes it possible to obtain exact, non-asymptotic confidence regions under mild assumptions on the noise distribution. A bottleneck of this approach, however, is the numerical characterization of these confidence regions. So far, it has been carried out by gridding, which provides no guarantee as to its results and is only applicable to low dimensional spaces. This paper shows how interval analysis can contribute to removing this bottleneck