From Bloch model to the rate equations II: the case of almost degenerate energy levels

Bloch equations give a quantum description of the coupling between an atom and a driving electric force. In this article, we address the asymptotics of these equations for high frequency electric fields, in a weakly coupled regime. We prove the convergence towards rate equations (i.e. linear Boltzmann equations, describing the transitions between energy levels of the atom). We give an explicit form for the transition rates. This has already been performed in [BFCD03] in the case when the energy levels are fixed, and for different classes of electric fields: quasi or almost periodic, KBM, or with continuous spectrum. Here, we extend the study to the case when energy levels are possibly almost degenerate. However, we need to restrict to quasiperiodic forcings. The techniques used stem from manipulations on the density matrix and the averaging theory for ordinary differential equations. Possibly perturbed small divisor estimates play a key role in the analysis. In the case of a finite number of energy levels, we also precisely analyze the initial time-layer in the rate aquation, as well as the long-time convergence towards equilibrium. We give hints and counterexamples in the infinite dimensional case

Reference based contrast functions in a semi-blind context

International audienceWe deal with blind signal extraction in the framework of a convolutive mixture of independent sources. Considering so-called reference signals, we generalize former identifiability conditions. Based on this result, we propose to incorporate some a priori information in the references. We show the validity of reference based contrast functions in two semi-blind situations. The results are confirmed by computer simulation

Генетический полиморфизм клонов и их семенного потомства в архивно-клоновой плантации плюсовых деревьев сосны обыкновенной

Изучена генетическая изменчивость по 12 аллозимным локусам (10 полиморфных) архивно-клоновой плантации 23 плюсовых деревьев Pinus sylvestris L. и их семенного потомства на юго-востоке Украины. Более половины клонов имели 4–8 гетерозиготных локусов, а их семенное потомство отличалось меньшим уровнем изменчивости, чем материнские растения. Семенное потомство получено от высокой доли ауткроссинга (tm = = 95 %). Для потомства клонов характерна повышенная доля нарушений сегрегации аллелей в мегагаметофитах и высокая встречаемость существенных отклонений в распределении генотипов зародышей семян от теоретически ожидаемого согласно закону Харди Вайнберга.Досліджено генетичну мінливість за 12 алозимними локусами (10 поліморфних) архівно-клонової плантації 23 плюсових дерев Pinus sylvestris L. та їх насіннєвого потомства на південному сході України. Понад половина клонів мали 4–8 гетерозиготних локусів, а їх насіннєве потомство відрізнялося нижчим рівнем мінливості, ніж материнські рослини. Насіннєве потомство отримано від високої частки ауткросинга (tm = 95 %). Для потомства клонів характерна підвищена частка порушень сегрегації алелів у мегагаметофітах і висока частота відхилень розподілу генотипів зародків насіння від очікуваного згідно з законом Харді-Вайнберга.Genetic variation at 12 allozyme loci (10 of them being polymorphic ones) has been studied in the archive-clone plantation of 23 Pinus sylvestris plus-trees and their seed progeny in the south-east of Ukraine. More than a half of clones had 4–8 heterozygous loci, whereas their seed progeny was marked by a lower variation than maternal trees. Seed progeny was obtained at a high outcrossing rate (tm= 95 %). The clone progeny was characterized by a high percentage of abnormal allele segregation in megagametophytes. There was also a high frequency of significant deviation in distribution of seed embryo genotypes from the theoretically expected one according to the Hardy-Weinberg law

Semiautomatic mammographic parenchymal patterns classification using multiple statistical features.

RATIONALE AND OBJECTIVES: Our project was to investigate a complete methodology for the semiautomatic assessment of digital mammograms according to their density, an indicator known to be correlated to breast cancer risk. The BI-RADS four-grade density scale is usually employed by radiologists for reporting breast density, but it allows for a certain degree of subjective input, and an objective qualification of density has therefore often been reported hard to assess. The goal of this study was to design an objective technique for determining breast BI-RADS density. MATERIALS AND METHODS: The proposed semiautomatic method makes use of complementary pattern recognition techniques to describe manually selected regions of interest (ROIs) in the breast with 36 statistical features. Three different classifiers based on a linear discriminant analysis or Bayesian theories were designed and tested on a database consisting of 1408 ROIs from 88 patients, using a leave-one-ROI-out technique. Classifications in optimal feature subspaces with lower dimensionality and reduction to a two-class problem were studied as well. RESULTS: Comparison with a reference established by the classifications of three radiologists shows excellent performance of the classifiers, even though extremely dense breasts continue to remain more difficult to classify accurately. For the two best classifiers, the exact agreement percentages are 76% and above, and weighted kappa values are 0.78 and 0.83. Furthermore, classification in lower dimensional spaces and two-class problems give excellent results. CONCLUSION: The proposed semiautomatic classifiers method provides an objective and reproducible method for characterizing breast density, especially for the two-class case. It represents a simple and valuable tool that could be used in screening programs, training, education, or for optimizing image processing in diagnostic tasks

Derivation of an observer model adapted to irregular signals based on convolution channels.

Anthropomorphic model observers are mathe- matical algorithms which are applied to images with the ultimate goal of predicting human signal detection and classification accuracy across varieties of backgrounds, image acquisitions and display conditions. A limitation of current channelized model observers is their inability to handle irregularly-shaped signals, which are common in clinical images, without a high number of directional channels. Here, we derive a new linear model observer based on convolution channels which we refer to as the "Filtered Channel observer" (FCO), as an extension of the channelized Hotelling observer (CHO) and the nonprewhitening with an eye filter (NPWE) observer. In analogy to the CHO, this linear model observer can take the form of a single template with an external noise term. To compare with human observers, we tested signals with irregular and asymmetrical shapes spanning the size of lesions down to those of microcalfications in 4-AFC breast tomosynthesis detection tasks, with three different contrasts for each case. Whereas humans uniformly outperformed conventional CHOs, the FCO observer outperformed humans for every signal with only one exception. Additive internal noise in the models allowed us to degrade model performance and match human performance. We could not match all the human performances with a model with a single internal noise component for all signal shape, size and contrast conditions. This suggests that either the internal noise might vary across signals or that the model cannot entirely capture the human detection strategy. However, the FCO model offers an efficient way to apprehend human observer performance for a non-symmetric signal

Colloidal brazil nut effect in sediments of binary charged suspensions

Equilibrium sedimentation density profiles of charged binary colloidal suspensions are calculated by computer simulations and density functional theory. For deionized samples, we predict a colloidal ``brazil nut'' effect: heavy colloidal particles sediment on top of the lighter ones provided that their mass per charge is smaller than that of the lighter ones. This effect is verifiable in settling experiments.Comment: 4 pages, 4 figure