Hemispheric asymmetry of endogenous neural oscillations in young children: implications for hearing speech in noise

Speech signals contain information in hierarchical time scales, ranging from short-duration (e.g., phonemes) to long-duration cues (e.g., syllables, prosody). A theoretical framework to understand how the brain processes this hierarchy suggests that hemispheric lateralization enables specialized tracking of acoustic cues at different time scales, with the left and right hemispheres sampling at short (25 ms; 40 Hz) and long (200 ms; 5 Hz) periods, respectively. In adults, both speech-evoked and endogenous cortical rhythms are asymmetrical: low-frequency rhythms predominate in right auditory cortex, and high-frequency rhythms in left auditory cortex. It is unknown, however, whether endogenous resting state oscillations are similarly lateralized in children. We investigated cortical oscillations in children (3–5 years; N = 65) at rest and tested our hypotheses that this temporal asymmetry is evident early in life and facilitates recognition of speech in noise. We found a systematic pattern of increasing leftward asymmetry for higher frequency oscillations; this pattern was more pronounced in children who better perceived words in noise. The observed connection between left-biased cortical oscillations in phoneme-relevant frequencies and speech-in-noise perception suggests hemispheric specialization of endogenous oscillatory activity may support speech processing in challenging listening environments, and that this infrastructure is present during early childhood

Signal Transmission in the Auditory System

Contains table of contents for Section 3, an introduction and reports on seven research projects.National Institutes of Health Grant P01-DC-00119National Institutes of Health Grant R01-DC-00194National Institutes of Health Grant R01 DC00238National Institutes of Health Grant R01-DC02258National Institutes of Health Grant T32-DC00038National Institutes of Health Grant P01-DC00361National Institutes of Health Grant 2RO1 DC00235National Institutes of Health Contract N01-DC2240

Thermal conductivity of refractory glass fibres

In the present study, the current international standards and corresponding apparatus for measuring the thermal conductivity of refractory glass fibre products have been reviewed. Refractory glass fibres are normally produced in the form of low-density needled mats. A major issue with thermal conductivity measurements of these materials is lack of reproducibility in the test results due to transformation of the test material during the test. Also needled mats are inherently inhomogeneous, and this poses additional problems. To be able to compare the various methods of thermal conductivity measurement, a refractory reference material was designed which is capable of withstanding maximum test temperatures (1673 K) with minimum transformation. The thermal conductivity of this reference material was then measured using various methods according to the different standards surveyed. In order to compare different materials, samples have been acquired from major refractory glass fibre manufacturers and the results have been compared against the newly introduced reference material. Materials manufactured by melt spinning, melt blowing and sol–gel have been studied, and results compared with literature values

Signal Transmission in the Auditory System

Contains table of contents for Section 3, an introduction and reports on six research projects.National Institutes of Health Grant RO1-DC-00194-11National Institutes of Health Grant PO1-DC00119 Sub-Project 1National Institutes of Health Grant F32-DC00073-3National Institutes of Health Contract P01-DC00119National Institutes of Health Grant R01 DC00238National Institutes of Health Grant P01-DC00119National Institutes of Health Grant T32-DC00038National Institutes of Health Contract P01-DC00361National Institutes of Health Grant R01-DC00235National Institutes of Health Contract NO1-DC2240

Синтез направленного излучателя в диапазоне 0.9…5.8 ГГц

Introduction. In this work, we consider the problem of a radiator synthesis with the 50-Ohm port at the input in the frequency range of 0.9…5.8 GHz. At present, this frequency range is the most relevant for the electromagnetic environment analysis due to information exchange with the on-board equipment of unmanned aerial vehicles is most often realized in this frequency range.Objective. The main objective of this work is the synthesis of a radiator for an ultra-wideband antenna array in the frequency range of 0.9…5.8 GHz.Materials and methods. In this work, the method of full-wave electromagnetic simulation is used for the broadband radiator synthesis. The characteristics of the radiator are optimized by simulation and confirmed by experimental investigations of the radiator model. The antenna radiation pattern measurements are carried out in the anechoic chamber and standing wave ratio (SWR) is calculated by using the network analyzer.Results. A non-analytical method of the model parametric optimization considering the SWR<2 criterion and using the latest tools of the full-wave electromagnetic simulation is proposed. The examples of the designed optimized model with the final values of all parameters are reported. The calculated distributions of the electric field over the antenna, calculated radiation patterns at several frequency points, and calculated SWR of the model are presented. The radiator model is made taking into account simulation and optimization results. The measured main cross-sections of the radiation pattern and SWR of the model are shown. Conclusion. In the present work, the broadband radiator model in the frequency range of 0.9…5.8 GHz is designed. The machining and brief comparative analysis of the calculated and measured antenna characteristics is carried out and demonstrated a good agreement. The advantages of the proposed method and designed radiator model are described. The results of this work are relevant in the tasks of observation, direction finding and signals reception from unmanned aerial vehicles. Key words: ultra-wideband antenna, Vivaldi antenna, microwave range, full-wave electromagnetic simulation><2 criterion and using the latest tools of the full-wave electromagnetic simulation is proposed. The examples of the designed optimized model with the final values of all parameters are reported. The calculated distributions of the electric field over the antenna, calculated radiation patterns at several frequency points, and calculated SWR of the model are presented. The radiator model is made taking into account simulation and optimization results. The measured main cross-sections of the radiation pattern and SWR of the model are shown.Conclusion. In the present work, the broadband radiator model in the frequency range of 0.9…5.8 GHz is designed. The machining and brief comparative analysis of the calculated and measured antenna characteristics is carried out and demonstrated a good agreement. The advantages of the proposed method and designed radiator model are described. The results of this work are relevant in the tasks of observation, direction finding and signals reception from unmanned aerial vehicles.Введение. Рассмотрена проблема синтеза направленного излучателя с 50-омным портом на входе, в частотном диапазоне 0.9…5.8 ГГц. Данный диапазон на сегодняшний день является наиболее актуальным для анализа электромагнитной обстановки, так как в этой полосе частот наиболее часто реализуется обмен информацией с бортовой аппаратурой беспилотных летательных аппаратов. Цель работы. Синтез направленного широкополосного излучателя в частотном диапазоне 0.9…5.8 ГГц.Материалы и методы. Для синтеза широкополосного излучателя используется метод конечных элементов при электродинамическом моделировании в программном средстве HFSS. Характеристики излучателя, оптимизированные на электродинамической модели, подтверждаются с помощью натурных экспериментов на макете излучателя. Измерения диаграммы направленности, проводимые в безэховой камере, и коэффициента стоячей волны (КСВ) осуществляются с помощью анализатора цепей. Результаты. Предложен неаналитический метод параметрической оптимизации модели по критерию КСВ < 2 удобный для применения в средствах электродинамического моделирования (HFSS, CST, FEKO и др.). Приведены эскизы разработанной оптимизированной модели с указанием итоговых значений всех геометрических параметров излучателя. Представлены снимки расчетного распределения электрического поля на полотне антенны, расчетные диаграммы направленности на крайних частотных точках рабочего диапазона (0.9 ГГц…5.8 ГГц), расчетный КСВ модели. Полученные результаты дают представление об основных характеристиках синтезируемой антенны. По результатам моделирования и параметрической оптимизации геометрии излучателя изготовлен макет антенны. Приведены измеренные главные сечения диаграммы направленности и КСВ макета.Заключение. В результате представленного исследования разработана модель широкополосного излучателя в диапазоне 0.9…5.8 ГГц, проведено макетирование и краткий сравнительный анализ расчетных и измеренных характеристик антенны, демонстрирующий хорошее совпадение расчетных и измеренных диаграмм направленности и зависимостей КСВ от рабочей частоты. Описаны преимущества предложенного метода и самой модели излучателя. Результаты работы актуальны в задачах наблюдения, пеленгации и приема сигналов от беспилотных летательных аппаратов

Differentiation of acute and four-week old myocardial infarct with Gd(ABE-DTTA)-enhanced CMR

<p>Abstract</p> <p>Background</p> <p>Standard extracellular cardiovascular magnetic resonance (CMR) contrast agents (CA) do not provide differentiation between acute and older myocardial infarcts (MI). The purpose of this study was to develop a method for differentiation between acute and older myocardial infarct using myocardial late-enhancement (LE) CMR by a new, low molecular weight contrast agent.</p> <p>Dogs (n = 6) were studied in a closed-chest, reperfused, double myocardial infarct model. Myocardial infarcts were generated by occluding the Left Anterior Descending (LAD) coronary artery with an angioplasty balloon for 180 min, and four weeks later occluding the Left Circumflex (LCx) coronary artery for 180 min. LE images were obtained on day 3 and day 4 after second myocardial infarct, using Gd(DTPA) (standard extracellular contrast agent) and Gd(ABE-DTTA) (new, low molecular weight contrast agent), respectively. Triphenyltetrazolium chloride (TTC) histomorphometry validated existence and location of infarcts. Hematoxylin-eosin and Masson's trichrome staining provided histologic evaluation of infarcts.</p> <p>Results</p> <p>Gd(ABE-DTTA) or Gd(DTPA) highlighted the acute infarct, whereas the four-week old infarct was visualized by Gd(DTPA), but not by Gd(ABE-DTTA). With Gd(ABE-DTTA), the mean ± SD signal intensity enhancement (SIE) was 366 ± 166% and 24 ± 59% in the acute infarct and the four-week old infarct, respectively (P < 0.05). The latter did not differ significantly from signal intensity in healthy myocardium (P = NS). Gd(DTPA) produced signal intensity enhancements which were similar in acute (431 ± 124%) and four-week old infarcts (400 ± 124%, P = NS), and not statistically different from the Gd(ABE-DTTA)-induced SIE in acute infarct. The existence and localization of both infarcts were confirmed by triphenyltetrazolium chloride (TTC). Histologic evaluation demonstrated coagulation necrosis, inflammation, and multiple foci of calcification in the four day old infarct, while the late subacute infarct showed granulation tissue and early collagen deposition.</p> <p>Conclusions</p> <p>Late enhancement CMR with separate administrations of standard extracellular contrast agent, Gd(DTPA), and the new low molecular weight contrast agent, Gd(ABE-DTTA), differentiates between acute and late subacute infarct in a reperfused, double infarct, canine model.</p

Hippocampal and cortical mechanisms at retrieval explain variability in episodic remembering in older adults

Age-related episodic memory decline is characterized by striking heterogeneity across individuals. Hippocampal pattern completion is a fundamental process supporting episodic memory. Yet, the degree to which this mechanism is impaired with age, and contributes to variability in episodic memory, remains unclear. We combine univariate and multivariate analyses of fMRI data from a large cohort of cognitively normal older adults (N=100) to measure hippocampal activity and cortical reinstatement during retrieval of trial-unique associations. Trial-wise analyses revealed that (a) hippocampal activity scaled with reinstatement strength, (b) cortical reinstatement partially mediated the relationship between hippocampal activity and associative retrieval, (c) older age weakened cortical reinstatement and its relationship to memory behaviour. Moreover, individual differences in the strength of hippocampal activity and cortical reinstatement explained unique variance in performance across multiple assays of episodic memory. These results indicate that fMRI indices of hippocampal pattern completion explain within-and across-individual memory variability in older adults

In Vivo Serial MR Imaging of Magnetically Labeled Endothelial Progenitor Cells Homing to the Endothelium Injured Artery in Mice

Background: Emerging evidence of histopathological analyses suggests that endothelial progenitor cells (EPCs) play an important role in vascular diseases. Neointimal hyperplasia can be reduced by intravenous transfusion of EPCs after vascular injury in mice. Therefore, it would be advantageous to develop an in vivo technique that can explore the temporal and spatial migration of EPCs homing to the damaged endothelium noninvasively. Methodology/Principal Findings: The left carotid common artery (LCCA) was injured by removal of endothelium with a flexible wire in Kunming mice. EPCs were collected by in vitro culture of spleen-derived mouse mononuclear cells (MNCs). EPCs labeling was carried out in vitro using Fe2O3-poly-L-lysine (Fe2O3-PLL). In vivo serial MR imaging was performed to follow-up the injured artery at different time points after intravenous transfusion of EPCs. Vessel wall areas of injured artery were computed on T2WI. Larger MR signal voids of vessel wall on T2WI was revealed in all 6 mice of the labeled EPC transfusion group 15 days after LCCA injury, and it was found only in 1 mouse in the unlabeled EPC transfusion group (p = 0.015). Quantitative analyses of vessel wall areas on T2WI showed that the vessel wall areas of labeled EPC transfusion group were less than those of unlabeled EPC transfusion group and control group fifteen days after artery injury (p,0.05). Histopathological analyses confirmed accumulation and distribution of transfused EPCs at the injury site of LCCA. Conclusions/Significance: These data indicate that MR imaging might be used as an in vivo method for the tracking of EPC