Спектральные и электрические свойства светодиодных гетероструктур с активной областью на основе InAs

The results of the study of optical and structural properties of epitaxial InAs layers grown on an n-InAs substrate, and spectral and electrical properties of light-emitting diode (LED) heterostructures with an InAs active layer and various design and chemical composition of barrier layers are presented; the properties of heterostructures were studied in the temperature range 4.2−300 K. A significant influence of the degree of substrate doping and the properties of heterointerfaces on the form of emission spectra and power characteristics of heterostructures is shown. The mechanisms of the carrier transport are studied, and the prevalence of the diffusion component of the current at temperatures above 200 K and the presence of the tunneling component at lower temperatures are shown.

Age and gender dependence of liver diffusion parameters and the evidence of intravoxel incoherent motion modelling of perfusion component is constrained by diffusion component

ObjectivesTo establish reference values for middle aged subjects and investigate age and gender dependence of liver diffusion MRI parameters.MethodsThe IVIM type of liver diffusion scan was based on a single-shot spin-echo type echo-planar sequence using a 1.5-T magnet with 16 b-values. DDVD (diffusion-derived vessel density) was the signal difference between b=0 and b=2 s/mm2 images after removing visible vessels. IVIM analysis was performed with full-fitting and segmented-fitting, and with threshold b-value of 60 or 200 s/mm2, and fitting started from b=2 s/mm2. 32 men (age range: 25-71 years) and 26 men (age: 22-69 years) had DDVD and IVIM analysis respectively, while 36 women (age: 20-71 years) had DDVD and IVIM analysis.ResultsDDVD had an age-related reduction noted for women. IVIM results of full fitting had good agreement with segmented fitting with threshold b of 60 s/mm2 results, but less so with results of threshold b of 200 s/mm2. As age increases, female subjects’ Dslow measure had significant reduction, and PF and Dfast measure had significant increase. For the age group of 40-55 years, DDVD, Dslow, PF, and Dfast were 12.27±3.90, 1.072±0.067 (10−3mm2/s), 0.141±0.025, 61.0±14.0 (10−3mm2/s), and 13.4±3.6, 1.069±0.074 mm2/s, 0.119±0.014, 57.1±13.2 mm2/s, for men and women, respectively.ConclusionDDVD measure suggest that aging may be associated with reduction in liver perfusion. Lower Dslow measurement can lead to artificial higher PF and Dfast measurement, providing the evidence of IVIM modeling of perfusion component is constrained by diffusion component.

Characterization of the Diffusion Signal of Breast Tissues using Multi-exponential Models

BackgroundDiffusion-weighted magnetic resonance imaging (DW-MRI) has demonstrated potential as an exogenous contrast-free diagnostic tool for breast cancer screening. Advanced non-Gaussian models of the DW-MRI signal provide insight into the tissue microstructure. Restriction spectrum imaging (RSI) is a mathematical framework that improves tumor conspicuity by decomposing the DW-MRI signal into separate diffusion components. The number of diffusion components and corresponding apparent diffusion coefficients (ADCs) optimal for RSI are organ-specific and determined empirically. The outputs of RSI are the signal contributions of each separable diffusion component.PurposeTo understand the diffusion-weighted MRI signal of cancerous and healthy breast tissues in the context of RSI.Study TypeProspective.Populations74 women, from two sites, with pathology-proven breast cancer.Field Strength/Sequence3.0TAssessmentThe DW-MRI signal was described using a linear combination of a variable number of exponential components. The ADC for each component was estimated across all voxels from control and cancer regions of interest (ROIs), patients and sites. Once ADCs were determined, the signal contributions of each diffusion component were estimated using these fixed ADC values. Conventional ADC (mono-exponential) values were also estimated.Statistical TestsThe relative fitting residual and relative Bayesian information criterion (BIC) were assessed. The signal contributions of each diffusion component were compared using analysis of variance (ANOVA) and post-hoc tests.ResultsEstimated ADCs for the bi-exponential model were D1,2 = 2.0 × 10−5 and D2,2 = 2.2 × 10−3 mm2/s, and D1,3=0, D2,3 = 1.4 × 10−3 and D3,3=10.2 × 10−3 mm2/s for tri-exponential model, which in practice is reduced to a bi-exponential model with an offset, or a three-component model. The relative fitting residuals of conventional ADC, bi-exponential and three-component models in control ROIs were 2.1%, 1.62%, and 1.03%, and 3.3%, 1.0%, and 0.3% for cancer ROIs. BIC was smaller for the three-component model, indicating an improved fitting of breast DW-MRI data compared to the bi-exponential model.ConclusionBreast DW-MRI signal was best described using a tri-exponential model. The signal contributions of the slower component in bi- or tri-exponential models were larger in tumor lesions. These data may be used as differential features between healthy and malignant breast tissues.

Ammonia mobility in chabazite: insight into the diffusion component of the NH3-SCR process

To assess the effect of counterion presence on NH3 mobility in commercial automotive emission control zeolite catalysts, NH3 mobility in NH3-SCR catalyst Cu-CHA was compared with H-CHA using quasielastic neutron scattering and molecular dynamics simulations.

A two-pool model to describe the IVIM cerebral perfusion

IntraVoxel Incoherent Motion (IVIM) is a magnetic resonance imaging (MRI) technique capable of measuring perfusion-related parameters. In this manuscript, we show that the mono-exponential model commonly used to process IVIM data might be challenged, especially at short diffusion times. Eleven rat datasets were acquired at 7T using a diffusion-weighted pulsed gradient spin echo sequence with b-values ranging from 7 to 2500 s/mm2 at three diffusion times. The IVIM signals, obtained by removing the diffusion component from the raw MR signal, were fitted to the standard mono-exponential model, a bi-exponential model and the Kennan model. The Akaike information criterion used to find the best model to fit the data demonstrates that, at short diffusion times, the bi-exponential IVIM model is most appropriate. The results obtained by comparing the experimental data to a dictionary of numerical simulations of the IVIM signal in microvascular networks support the hypothesis that such a bi-exponential behavior can be explained by considering the contribution of two vascular pools: capillaries and somewhat larger vessels.