Infrared and THz studies of polar phonons and improper magnetodielectric effect in multiferroic BFO3 ceramics

BFO3 ceramics were investigated by means of infrared reflectivity and time domain THz transmission spectroscopy at temperatures 20 - 950 K, and the magnetodielectric effect was studied at 10 - 300 K, with the magnetic field up to 9 T. Below 175 K, the sum of polar phonon contributions into the permittivity corresponds to the value of measured permittivity below 1 MHz. At higher temperatures, a giant low-frequency permittivity was observed, obviously due to the enhanced conductivity and possible Maxwell-Wagner contribution. Above 200 K the observed magnetodielectric effect is caused essentially through the combination of magnetoresistance and the Maxwell-Wagner effect, as recently predicted by Catalan (Appl. Phys. Lett. 88, 102902 (2006)). Since the magnetodielectric effect does not occur due to a coupling of polarization and magnetization as expected in magnetoferroelectrics, we call it improper magnetodielectric effect. Below 175 K the magnetodielectric effect is by several orders of magnitude lower due to the decreased conductivity. Several phonons exhibit gradual softening with increasing temperature, which explains the previously observed high-frequency permittivity increase on heating. The observed non-complete phonon softening seems to be the consequence of the first-order nature of the ferroelectric transition.Comment: subm. to PRB. revised version according to referees' report

Working conditions and the professional oncological disease, working in Primorye territore

The estimation of working conditions of workers, the analysis of disease and the organisation of preliminary and periodic medical inspections, population prophylactic medical examinations is spent for the purpose of improvement of working conditions and preventive maintenance of professional oncological diseases, revealing of signs of diseases at early stages of development, preservation of health and increase in able-bodied age of the population of Primorye Territory.Оценка условий труда работников, анализ заболеваемости и организации предварительных и периодических медицинских осмотров, диспансеризации населения проводится с целью улучшения условий труда и профилактики профессиональных онкологических заболеваний, выявления признаков заболеваний на ранних стадиях развития, сохранения здоровья и увеличение трудоспособного возраста населения Приморского края

Functional MRI evidence for the decline of word retrieval and generation during normal aging

International audienceThis fMRI study aimed to explore the effect of normal aging on word retrieval and generation. The question addressed is whether lexical production decline is determined by a direct mechanism, which concerns the language operations or is rather indirectly induced by a decline of executive functions. Indeed, the main hypothesis was that normal aging does not induce loss of lexical knowledge, but there is only a general slowdown in retrieval mechanisms involved in lexical processing , due to possible decline of the executive functions. We used three tasks (verbal fluency, object naming , and semantic categorization). Two groups of participants were tested (Young, Y and Aged, A), without cognitive and psychiatric impairment and showing similar levels of vocabulary. Neuropsychological testing revealed that older participants had lower executive function scores, longer processing speeds, and tended to have lower verbal fluency scores. Additionally, older participants showed higher scores for verbal automa-tisms and overlearned information. In terms of behav-ioral data, older participants performed as accurate as younger adults, but they were significantly slower for the semantic categorization and were less fluent for verbal fluency task. Functional MRI analyses suggested that older adults did not simply activate fewer brain regions involved in word production, but they actually showed an atypical pattern of activation. Significant correlations between the BOLD (Blood Oxygen Level Dependent) signal of aging-related (A > Y) regions and cognitive scores suggested that this atypical pattern of the activation may reveal several compensatory mechanisms (a) to overcome the slowdown in retrieval, due to the decline of executive functions and processing speed and (b) to inhibit verbal automatic processes. The BOLD signal measured in some other aging-dependent regions did not correlate with the behavioral and neuro-psychological scores, and the overactivation of these uncorrelated regions would simply reveal dedifferentia-tion that occurs with aging. Altogether, our results suggest that normal aging is associated with a more difficult access to lexico-semantic operations and representations by a slowdown in executive functions, without any conceptual loss

Machine learning assisted DSC-MRI radiomics as a tool for glioma classification by grade and mutation status

Background: Combining MRI techniques with machine learning methodology is rapidly gaining attention as a promising method for staging of brain gliomas. This study assesses the diagnostic value of such a framework applied to dynamic susceptibility contrast (DSC)-MRI in classifying treatment-naïve gliomas from a multi-center patients into WHO grades II-IV and across their isocitrate dehydrogenase (IDH) mutation status. Methods: Three hundred thirty-three patients from 6 tertiary centres, diagnosed histologically and molecularly with primary gliomas (IDH-mutant = 151 or IDH-wildtype = 182) were retrospectively identified. Raw DSC-MRI data was post-processed for normalised leakage-corrected relative cerebral blood volume (rCBV) maps. Shape, intensity distribution (histogram) and rotational invariant Haralick texture features over the tumour mask were extracted. Differences in extracted features across glioma grades and mutation status were tested using the Wilcoxon two-sample test. A random-forest algorithm was employed (2-fold cross-validation, 250 repeats) to predict grades or mutation status using the extracted features. Results: Shape, distribution and texture features showed significant differences across mutation status. WHO grade II-III differentiation was mostly driven by shape features while texture and intensity feature were more relevant for the III-IV separation. Increased number of features became significant when differentiating grades further apart from one another. Gliomas were correctly stratified by mutation status in 71% and by grade in 53% of the cases (87% of the gliomas grades predicted with distance less than 1). Conclusions: Despite large heterogeneity in the multi-center dataset, machine learning assisted DSC-MRI radiomics hold potential to address the inherent variability and presents a promising approach for non-invasive glioma molecular subtyping and grading

NUCLEAR QUADRUPOLE AND ELECTROACOUSTIC ECHOES IN FERROELECTRIC SbSI

Des échos de quadrupoles nucléaires et électroacoustiques dans les ferroélectriques ont été étudiés. Les constantes de couplage quadrupolaire et les paramètres d'asymétrie des ions antimoine et iode sont comparés aux valeurs préalablement calculées d'après le modèle des ions ponctuels polarisables. Les temps de relaxation spin-spin et spin-réseau pour la transition 3/2 → 1/2 du noyau Sb121 sont mesurés à différentes températures. Les maxima de fréquence de relaxation sont observés à la température de Curie. Ces maxima sont probablement liés à la décroissance des fréquences du mode optique mou. En plus de l'écho NQR, on trouve un nouveau type d'écho à deux impulsions dans les cristaux SbSI. Cet écho se produit à toute fréquence dans l'intervalle examiné (de 5 à 70 Mc/s). Ce n'est pas un écho de spin. Il disparaît dans la phase paraélectrique. Son amplitude décroît de plusieurs ordres de grandeur si l'échantillon est placé dans un liquide, et augmente s'il est préalablement polarisé par un champ électrique. L'amplitude d'écho a été étudiée en fonction de la longueur de l'impulsion, de l'intervalle entre impulsions, de la température et de l'amplitude des impulsions. A partir des résultats on peut conclure que l'apparition d'écho dépend des vibrations piézoélectriques de l'échantillon. Cet écho peut être désigné comme l'écho électroacoustique.Nuclear quadrupole and electroacoustic echoes in ferroelectric crystal SbSJ have been investigated. The quadrupole coupling constants and asymmetry parameters of the antimony and iodine ions are compared with previously calculated data obtained on the assumption of the point polarizable ion model. The spin-spin and spin-lattice relaxation times for the 3/2 → 1/2 transition of the Sb121 nuclei were measured at different temperatures. The maxima of relaxation rates are observed at the Curie temperature. These maxima are probably connected with the decrease of the soft optical mode frequencies. In addition to the NQR echo a new type of a two-pulse echo is found in SbSJ crystals. This echo occurs at any frequency in the frequency interval examined (from 5 to 70 Mc/s). It is not a spin echo. It disappears in a paraelectric phase. Its amplitude decreases by some order of magnitude if the sample is placed into some liquid, and increases, if the sample is previously polarized by electric field. The dependences of the echo amplitude on the pulse length, the interval between pulses, temperature, pulse amplitudes have been investigated. The results obtained give the possibility to conclude that the echo occurrence depends on piezoelectric vibrations of the sample. This echo may be named as the electroacoustic one