Effect Of Diffusion Time Research Articles

Numerical Investigation of the Effects of Diffusion Time on the Mechanisms of Transition from a Turbulent Jet Flame to Detonation in a H2-Air Mixture

The current study primarily aimed to simulate detonation initiation via turbulent jet flame acceleration in partial-premixed H2-air mixtures. Different vertical concentration gradients were generated by varying the duration of hydrogen injection (diffusion time) within an enclosed channel filled with air. H2-air mixtures with average hydrogen concentrations of 22.5% (lean mixture) and 30% (near stoichiometric mixture) were investigated at diffusion times of 3, 5, and 60 s. Numerical results show that the vertical concentration gradient significantly influences the early stage of flame acceleration (FA). In the stratified lean mixture, detonation began at all the diffusion times, and comparing the flame-speed graphs showed that a decrease in the diffusion time and an increase in the mixture inhomogeneity speeded up the flame propagation and the jet flame-to-detonation transition occurrence in the channel. In the stratified H2-air mixture with an average hydrogen concentration of 30%, the transition from a turbulent jet flame to detonation occurred in all the cases, and the mixture inhomogeneity weakened the FA and delayed the detonation initiation.

Diffusion-time dependent diffusion MRI: effect of diffusion-time on microstructural mapping and prediction of prognostic features in breast cancer.

This study aimed to evaluate the effect of achievable td on the accuracy of microstructural mapping based on simulation and patient experiments, and investigate the feasibility of td-dMRI in distinguishing prognostic factors in breast cancer patients. Simulation was performed using different td settings. Patients with breast cancer were enrolled prospectively between November 2020 and January 2021, who underwent oscillating and pulsed gradient encoded dMRI on a 3-T scanner using short-/long-td protocol with oscillating frequency up to 50/33Hz. Data were fitted with a two-compartment model to estimate cell diameter (d), intracellular fraction (fin), and diffusivities. Estimated microstructural markers were used to differentiate immunohistochemical receptor status and the presence of lymph node (LN), which were correlated with histopathological measurements. Simulation results showed that d fitted from the short-td protocol significantly reduced estimation error than those from long-td (2.07 ± 1.51% versus 3.05 ± 1.92%, p < 0.0001) while the estimation error of fin was robust to different protocols. Among a total of 37 breast cancer patients, the estimated d was significantly higher in HER2-positive and LN-positive (p < 0.05) groups compared to their negative counterparts only using the short-td protocol. Histopathological validation in a subset of 6 patients with whole slide images showed the estimated d was highly correlated with measurements from H&E staining (r = 0.84, p = 0.03) only using the short-td protocol. The results indicated the necessity of short-td for accurate microstructural mapping in breast cancer. The current td-dMRI with a total acquisition time of 4.5min showed its potential in the diagnosis of breast cancer. • Short td is important for accurate microstructural mapping in breast cancer using the td-dMRI technique, based on simulation and histological validation. • The 4.5-min td-dMRI protocol showed potential clinical value for breast cancer, given the difference in cell diameter between HER2/LN positive and negative groups.

Effect of diffusion time on the mechanism of deflagration to detonation transition in an inhomogeneous mixture of hydrogen-air

This study aimed to numerically investigate the effect of diffusion time between H2 injection and ignition on mechanisms behind deflagration to detonation transition (DDT) in an inhomogeneous H2/Air mixture. The combustion chamber is a closed, rectangular tube with seven obstructions and a blockage ratio of 30%. From the top wall of the air channel, hydrogen is injected with diffusion times of 3, 5, 7.5, and 10 s. As a result, the inhomogeneous mixtures with different concentrations gradients are formed in the vertical direction of flame propagation. The solution method is the finite-volume method with k−ωSST turbulence model and the Weller flame wrinkling combustion model. The current findings reveal that shortening the diffusion time between H2 injection and ignition, or increasing the mixture's inhomogeneity, causes DDT to occur faster for a lean inhomogeneous H2-Air mixture of 20%. The onset of detonation in a lean mixture is caused by shock waves focusing ahead of the flame front at the channel's top wall, where hydrogen concentration is higher. For a rich inhomogeneous H2/Air mixture of 35%, the concentration gradient weakens flame acceleration and delays the initiation of detonation. In the rich mixture, three different regimes of onset of detonation appear by changing diffusion time. In the first regime, a strong curved incident shock wave forms a Mach stem. Behind this Mach stem, chemical reactions are being activated. Finally, the flame front and the reaction region behind the Mach stem collide, causing DDT to happen. In the second regime, Mach stem does not form; however, DDT occurs in the direct vicinity of the flame where reflected shock waves from the obstacles collide flame front. In the third regime, neither the Mach stem nor the reflected shock waves play a significant role in detonation initiation.

Differentiation of high-grade and low-grade intra-axial brain tumors by time-dependent diffusion MRI

IntroductionOscillating gradient spin-echo (OGSE) sequences enable acquisitions with shorter diffusion times. There is growing interest in the effect of diffusion time on apparent diffusion coefficient (ADC) values in patients with cancer. However, little evidence exists regarding its usefulness for differentiating between high-grade and low-grade brain tumors. The purpose of this study is to investigate the utility of changes in the ADC value between short and long diffusion times in distinguishing low-grade and high-grade brain tumors. Material and methodsEleven patients with high-grade brain tumors and ten patients with low-grade brain tumors were scanned using a 3 T magnetic resonance imaging with diffusion-weighted imaging (DWI) using OGSE and PGSE (effective diffusion time [Δeff]: 6.5 ms and 35.2 ms) and b-values of 0 and 1000 s/mm2. Using a region of interest (ROI) analysis of the brain tumors, we measured the ADC for two Δeff (ADCΔeff) values and computed the subtraction ADC (ΔADC = ADC6.5 ms − ADC35.2 ms) and the relative ADC (ΔADC = (ADC6.5 ms − ADC35.2 ms) / ADC35.2 ms × 100). The maximum values for the subtraction ADC (ΔADCmax) and the relative ADC (rADCmax) on the ROI were compared between low-grade and high-grade tumors using the Wilcoxon rank-sum test. A P-value <.05 was considered significant. The ROIs were also placed in the normal white matter of patients with high- and low-grade brain tumors, and ΔADCmax values were determined. ResultsHigh-grade tumors had significantly higher ΔADCmax and rADCmax than low-grade tumors. The ΔADCmax values of the normal white matter were lower than the ΔADCmax of high- and low-grade brain tumors. ConclusionThe dependence of ADC values on diffusion time between 6.5 ms and 35.2 ms was stronger in high-grade tumors than in low-grade tumors, suggesting differences in internal tissue structure. This finding highlights the importance of reporting diffusion times in ADC evaluations and might contribute to the grading of brain tumors using DWI.

Time-dependent diffusion MRI to distinguish malignant from benign head and neck tumors.

There is growing interest in the effect of diffusion time on apparent diffusion coefficient (ADC) values in cancers; however, little evidence exists regarding its utility to differentiate malignant from benign head and neck tumors. To investigate the utility of ADC value changes in distinguishing between malignant and benign head and neck tumors using the different diffusion times obtained from oscillating gradient spin-echo (OGSE) and pulsed gradient spin-echo (PGSE) MRI sequences. Prospective. Thirty-one consecutive patients with suspected head and neck tumors and a phantom. 3T MRI with diffusion-weighted imaging (DWI) using OGSE (effective diffusion time: 4.3 msec) and PGSE (effective diffusion time: 82.6 msec) sequences and b-values of 0 and 700 s/mm2 . ADC values using OGSE (ADCOGSE ) and PGSE (ADCPGSE ) and relative ADC value changes between ADCOGSE and ADCPGSE . Wilcoxon test, Mann-Whitney test, and McNemar test. Relative ADC changes for each polyvinylpyrrolidone (PVP) and water in the phantom between OGSE and PGSE sequences were small (relative ADC change within 0.6%). Malignant tumors had significantly smaller ADCOGSE and ADCPGSE values than benign tumors (P < 0.001 and < 0.0001, respectively). Significantly larger relative ADC changes were observed in malignant compared with benign head and neck tumors (P < 0.0001). ADCPGSE values were significantly lower than ADCOGSE values in both malignant and benign head and neck tumors (0.97 vs. 1.28 × 10-3 mm2 /s: P < 0.0001 and 1.93 vs. 1.99 × 10-3 mm2 /s: P = 0.0056, respectively). Relative ADC change and ADCPGSE tended to have higher diagnostic performance than ADCOGSE , with area under the curve (AUC) values of 0.97, 0.96, and 0.89, respectively. ADC values obtained using the PGSE sequence were lower than those obtained with OGSE. This difference was larger for malignant than benign tumors, suggesting differences in tissue structure (diffusion hindrance) or cell permeability, revealed by changes in diffusion time. The results underline the potential importance of reporting diffusion time for interpretation of head and neck diffusion MRI. 1 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2019;50:88-95.

Model study on extraction of fermentable sugars and nonstructural carbohydrate from sweet sorghum using diffusion process

Sweet sorghum stores a high concentration of soluble sugars in its stalk and produces grain in the panicle. This grain represents a significant amount of starch. The ethanol industry currently uses sugarcane processing methods for sweet sorghum; however, sweet sorghum differs from sugarcane in that sweet sorghum produces significant quantities of grain which is predominantly starch. The objective of this research was to increase ethanol production from sweet sorghum by fully utilizing all fermentable sugars which include starch in the grain and nonstructural carbohydrates in the stalk. The diffusion process was utilized to extract fermentable sugars and nonstructural carbohydrates from chopped sweet sorghum biomass and grains. Response surface methodology (RSM) was applied in order to optimize diffusion conditions and to explore effects of diffusion time, diffusion temperature, ratio of sweet sorghum grain to total biomass on starch-to-sugar efficiency, and total sugar recovery from sweet sorghum. RSM results showed that starch conversion efficiency and sugar recovery efficiency of 96% and 98.5%, respectively, were achieved at an optimized time of 114.9min, temperature of 95°C, and 22% grain loading.

Fabrication, characterization and tensile property of a novel Ti2Ni/TiNi micro-laminated composite

A novel Ti2Ni/TiNi laminated composite has been fabricated by diffusion bonding using Ti foils and Ni foils under the protection of argon gas at 900°C. The effect of diffusion time on the microstructure of the composite was investigated. The results indicate that with the increase of diffusion time, Ti and Ni foils were gradually consumed while forming different intermetallics (Ti2Ni, TiNi, Ni3Ti). When the diffusion time reached 36h, the final composite consisting of alternative layers of Ti2Ni and TiNi was fabricated. XRD results reveal that TiNi layer in Ti2Ni/TiNi laminated composite has a complex monoclinic B19′-type crystal structure and DSC results show that As, Af, Ms, Mf and transition hysteresis temperature of the composite are 83.3°C,106.7°C,71.8°C,51.2°C and 35.7°C, respectively. The tensile experiment reveals that the Ti2Ni/TiNi laminated composite exhibits a high ultimate tensile strength of 790MPa and a high elongation of 9.3% which overcomes the brittleness of Ti2Ni. The formation of transverse cracks in brittle Ti2Ni layers getting arrested at ductile TiNi layers, the deflection and the connection of consequently produced cracks caused the delamination and final fracture of the whole composite.

Ex vivo cardiac DTI: on the effects of diffusion time and b-value

Background For in-vivo an ex-vivo studies of myocardial structure, generally a spin echo (SE) or stimulated echo (STE) based sequence is used. Diffusion weighting is reported with a large range of diffusion times (50 and 1000 ms). Furthermore, in-vivo studies generally use low b-values (300 s/mm) whereas ex-vivo experiments allow for much higher b-values. For interpretation of in-vivo cardiac DTI a understanding of the effects of sequence parameters on the derived diffusion parameters is needed. In this study, we therefore studied the impact of diffusion time and b-value on these parameters.

Effect of diffusion time on liver DWI: An experimental study of normal and fibrotic livers

To investigate whether diffusion time (Δ) affects the diffusion measurements in liver and their sensitivity in detecting fibrosis. Liver fibrosis was induced in Sprague-Dawley rats (n = 12) by carbon tetrachloride (CCl(4)) injections. Diffusion-weighted MRI was performed longitudinally during 8-week CCl(4) administration at 7 Tesla (T) using single-shot stimulated-echo EPI with five b-values (0 to 1000 s/mm(2)) and three Δs. Apparent diffusion coefficient (ADC) and true diffusion coefficient (D(true)) were calculated by using all five b-values and large b-values, respectively. ADC and D(true) decreased with Δ for both normal and fibrotic liver at each time point. ADC and D(true) also generally decreased with the time after CCl(4) insult. The reductions in D(true) between 2-week and 4-week CCl(4) insult were larger than the ADC reductions at all Δs. At each time point, D(true) measured with long Δ (200 ms) detected the largest changes among the 3 Δs examined. Histology revealed gradual collagen deposition and presence of intracellular fat vacuoles after CCl(4) insult. Our results demonstrated the Δ dependent diffusion measurements, indicating restricted diffusion in both normal and fibrotic liver. D(true) measured with long Δ acted as a more sensitive index of the pathological alterations in liver microstructure during fibrogenesis.

The influence of lung airways branching structure and diffusion time on measurements and models of short-range 3He gas MR diffusion

Hyperpolarized 3He diffusion experiments have been shown to be sensitive to changes in acinar structure due to emphysematous lung disease. Extracting quantitative information about lung microstructure from the diffusion signal is complicated due its dependence on a number of factors including diffusion time and the complex branching acinar geometry. A theoretical model (cylinder model) has been proposed as a means of estimating acinar airway dimensions from measured diffusivities. This model assumes that the effects of acinar branching geometry and finite airway length upon 3He diffusion behaviour are negligible. In this work, we use finite element simulations of diffusion in a model of branching alveolar ducts to investigate in detail the effects of acinar branching structure and finite airway length on short-range 3He diffusion measurements. The results show that branching effects have a significant influence upon 3He diffusivity, even at short diffusion times. The expressions of the cylinder model theory do not account for significant dependences upon diffusion time, branching geometry and airway length, as a consequence of the oversimplified geometrical model used. The effect of diffusion time on 3He ADC was also investigated through experiments with healthy human volunteers. The results demonstrate that the cylinder model can produce inaccurate estimates of the airway dimensions as a consequence of incompletely accounting for the diffusion-time dependence in the model equations and confirmed the predicted limitations of the cylinder model for reliable lung morphometry measurements. The results and models presented in this work may help in the development of a more realistic theoretical framework for ‘in vivo lung morphometry’ using 3He diffusion MR.

Diffusion Tensor Metric Measurements as a Function of Diffusion Time in the Rat Central Nervous System

MRI and Monte Carlo simulated data of pulsed gradient spin echo experiments were used to study the effects of diffusion time, gradient strength and b-value on diffusion tensor (DT) metrics using real and simulated fixed rat spines. Radial (λ⊥) in grey matter and simulation data, axial (λ||) in both grey and white matter in fixed rat spinal cords and mean diffusivity in all tissues showed a significant decrease with diffusion time at b = 1 μm2/ms. All diffusivities significantly decreased with b-value at g = 116 mT/m and at Δeff = 23 ms. The fractional anisotropy (FA) significantly increased with diffusion time at b = 1 μm2/ms in the simulation data and grey matter. FA significantly increased in white matter and simulation data and significantly decreased in grey matter with b-value at g = 116 mT/m and at Δeff = 23 ms. These data suggest that DTI metrics are highly dependent on pulse sequence parameters.

Effects of diffusion time on short‐range hyperpolarized 3He diffusivity measurements in emphysema

To characterize the effect of diffusion time on short-range hyperpolarized (3)He magnetic resonance imaging (MRI) diffusion measurements across a wide range of emphysema severity. (3)He diffusion MRI was performed on 19 lungs or lobes resected from 18 subjects with varying degrees of emphysema using three diffusion times (1.6 msec, 5 msec, and 10 msec) at constant b value. Emphysema severity was quantified as the mean apparent diffusion coefficient (ADC) and as the percentage of pixels with ADC higher than multiple thresholds from 0.30-0.55 cm(2)/sec (ADC index). Quantitative histology (mean linear intercept) was obtained in 10 of the lung specimens from 10 of the subjects. The mean ADCs with diffusion times of 1.6, 5.0, and 10.0 msec were 0.46, 0.40, and 0.37 cm(2)/sec, respectively (P < 0.0001, analysis of variance [ANOVA]). There was no relationship between the ADC magnitude and the effect of diffusion time on ADC values. The mean linear intercept correlated with ADC (r = 0.91-0.94, P < 0.001) and ADC index (r = 0.78-0.92, P < 0.01) at all diffusion times. Decreases in ADC with longer diffusion time were unrelated to emphysema severity. The strong correlations between the ADC at all diffusion times tested and quantitative histology demonstrate that ADC is a robust measure of emphysema.

Spatial characterization of T1 and T2 relaxation times and the water apparent diffusion coefficient in rabbit Achilles tendon subjected to tensile loading

Tendons exhibit viscoelastic mechanical behavior under tensile loading. The elasticity arises from the collagen chains that form fibrils, while the viscous response arises from the interaction of the water with the solid matrix. Therefore, an understanding of the behavior of water in response to the application of a load is crucial to the understanding of the origin of the viscous response. Three-dimensional MRI mapping of rabbit Achilles tendons was performed at 2.0 T to characterize the response of T(1) and T(2) relaxation times and the apparent diffusion coefficient (ADC) of water to tensile loading. The ADC was measured in directions both parallel (ADC( parallel)) and perpendicular (ADC( perpendicular)) to the long axis of the tendon. At a short diffusion time (5.8 ms) MR parameter maps showed the existence of two regions, here termed "core" and "rim", that exhibited statistically significant differences in T(1), T(2), and ADC( perpendicular) under the baseline loading condition. MR parameter maps were also generated at a second loading condition of approximately 1 MPa. At a diffusion time of 5.8 ms, there was a statistically significant increase in the rim region for both ADC( perpendicular) (57.5%) and ADC( parallel) (20.5%) upon tensile loading. The changes in core ADC(( perpendicular), ( parallel)), as well as the relaxation parameters in both core and rim regions, were not statistically significant. The effect of diffusion time on the ADC(( perpendicular), ( parallel)) values was investigated by creating maps at three additional diffusion times (50.0, 125.0, 250.0 ms) using a diffusion-weighted, stimulated-echo (DW-STE) pulse sequence. At longer diffusion times, ADC(( perpendicular), ( parallel)) values increased rather than approaching a constant value. This observation was attributed to T(1) spin-editing during the DW-STE pulse sequence, which resulted in the loss of short-T(1) components (with correspondingly lower ADCs) at longer diffusion times (corroborating the results from earlier spectroscopic work). The T(1) spin-editing effect was observed both in the core and in the rim regions of the tendon and hence was not solely due to the redistribution of water from the core to the rim upon loading. A measure reflective of the regional change in proton density was noted to be consistent with tensile-load-induced water transport from the central to the peripheral tendon region.

Analysis of titanium diffused planar optical waveguides in lithium niobate

Characteristics of titanium indiffused waveguides in lithium niobate have been investigated. The effects of diffusion time, temperature, and ambient atmosphere on mode structure, surface refractive index, and profile, waveguide depth, surface morphology, and composition are described. Similarities and discrepancies between these and any previously published results are discussed and mechanisms for new features proposed. The necessity for fabrication in an oxygen atmosphere at elevated temperatures is demonstrated, and directions for further investigation indicated.

Determination of nanogram amounts of fluorine in breast milk by ashing-diffusion method and the fluoride electrode

A method for the determination of nanogram amounts of fluorine in breast milk is described. Two fluorine fractions were separated: diffusable fluorine liberated by perchloric acid at 60° C and bound fluorine detectable only after ashing. The diffusable fluorine was separated with a new type of diffusion cell — a cell that was found suitable for the analysis of other biological materials as well. The effects of diffusion time, diffusion acid concentration and sample chloride content on the recovery of added fluoride were investigated. Three reference materials (Bowen's Kale, Orchard Leaves and Milk Powder) were also analysed. Fluorine losses and contamination during ashing of breast milk with and without fixatives were studied: of the examined fixatives only magnesium succinate gave reproducible results and quantitative recovery of added fluoride. Breast milk samples collected from four mothers at different stages of the lactating period were analysed for total fluorine content. Fluorine concentrations ranged between 2.2 and 11.3 ng/ml. No tendency of the content to vary as a function of lactating time was found.