We formulate a robust mathematical model for two predators having an overlapping dietary niche breadth. We use the BeddingtonaDeAngelis functional and numerical responses which are relevant in ...addressing the principle of competitive exclusion as species interact. The stabilizing effect of additional food in relation to the relative diffusivity D, and wave number k, has been investigated. Stability, dissipativity, permanance, persistence and periodicity of the model have been studied using the routine and limit cycle perturbation methods. Besides revealing irregular periodic travelling wave behaviour due to predator interference, numerical results also show oscillatory temporal dynamics resulting from additional food supplements combined with high predation rates.
A recently proposed method based on Levitation and Blow torch effects, is employed here to see if it can separate a mixture of neopentane and n‐hexane. The results show that the mixture can be ...separated with a hot zone temperature of just 40 K above the ambient temperature, 300 K. The two components are found to accumulate at the two extreme ends of the zeolite column. The computed separation factor is in the range of 1015–1020 (as compared to 104 for existing separation methods). The energy expense for the separation is significantly smaller than for existing separation methods by several orders of magnitude. Transport (D11), self (Ds), and distinct diffusivities (Dd) of the mixture were computed. The contribution of distinct diffusivity to the transport diffusivity is 70% as compared to 10%–30% seen in other separation methods and is larger by 2.3 times as compared to the self‐diffusivity.
Snapshots of the separation process is shown at various times. Molecules are distributed uniformly throughout the simulation cell to begin with. As simulation proceeds, one of the components diffuses towards the left, while the other diffuses towards to right leading to separation. The resulting separation factor is 1016 as compared to 104 for existing methods of separation. The main contribution to separation is from the distinct diffusivity. The energy required is smaller by several orders of magnitude.
Mechanistic understanding of diffusion and sorption of radionuclides and metals in clay-based engineered barriers is essential to develop models and define parameters for transport calculations for ...the safety analysis of disposal systems. Here we studied diffusion of uranyl (UO22+) species in the clay interparticle pore or macropores of bentonite clay by means of molecular dynamics simulation (MDS) for pore sizes ranging from 8.37 to 33.5 nm. The conceptual model of the clay pore system considered diffusion as a combination of pore diffusion (Dp) and surface diffusion DS (i.e. diffusion of adsorbed cations within the electrical double layer of the clay surfaces), from which the apparent diffusion Da was calculated as the weighted sum of Dp and DS, using a weighing factor f calculated as the ratio of adsorbed to total UO22+ in the system. Diffusivities at equilibrium for the largest pore size of 33.5 nm were: Da=7.37×10−10 m2 s−1, Dp=1.14×10−9 m2 s−1, and Ds=1.97×10−13 m2 s−1. The Ds was several orders of magnitude smaller than Dp. This was evident from the much smaller gradient of the mean-square displacement vs time lag curve for the adsorbed species than that of the species in the pore space. We found a remarkable consistency between our theoretical derivation and independent MDS evidence. For the slit-shaped interparticle pore, the retardation factor Rf was found to be the reciprocal of the unabsorbed fraction (Rf=1/1−f) and the capacity factor α was a ratio of the porosity to the unadsorbed fraction (α=ε1−f) or the ratio of the diffusant density in the bulk sample to the corresponding density in the pore solution. MD simulations of diffusion and sorption processes can be applied to other transport related problems at continuum scale, pore scale and molecular scale, such as for improved modelling of global elemental cycles, CO2 geosequestration, or the performance of desalination membranes.
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•Conceptual model of bentonite clay considered a combination of pore and surface diffusion.•MDS simulations of apparent diffusion of uranyl consistency with theoretical derivation.•Molecular-scale values of apparent (Da), pore (Dp), and surface (DS) diffusivity derived from MDS.•MDS surface diffusivity for UO22+ is of a similar magnitude as experimentally derived values.
Depression is among the most debilitating diseases worldwide. Long-term exposure to stressors plays a major role in development of human depression. Chronic mild stress (CMS) seems to be a valid ...animal model for depression. Diffusion tensor imaging (DTI) is capable of inferring microstructural abnormalities of the white matter and has shown to serve as non-invasive marker of specific pathology. We developed a CMS rat model of depression and validated with behavioral experiments. We measured the diffusion indices (mean diffusivity (MD), fractional anisotropy (FA), axial ( lambda ) and radial ( lambda ) diffusivity) to investigate the changes in CMS rat brain during depression onset. Diffusion indices have shown to be useful to discriminate myelin damage from axon loss. DTI was performed in both control and CMS rats (n =10, in each group) and maps of FA, MD, lambda and lambda diffusivity values were generated using in-house built software. The diffusion indices were calculated by region of interest (ROI) analysis in different brain regions like the frontal cortex, hippocampus, hypothalamus, cingulum, thalamus, caudate putamen, corpus callosum, cerebral peduncle and sensory motor cortex. The results showed signs of demyelination, reflected by increased MD, decreased FA and increased lambda . The results also suggest a possible role of edema or inflammation concerning the brain morphology in CMS rats. The overall finding using DTI suggests there might be a major role of loss of myelin sheath, which leads to disrupted connectivity between the limbic area and the prefrontal cortex during the onset of depression. Our findings indicate that interpretation of these indices may provide crucial information about the type and severity of mood disorders.
•MUSE-DTI acquired a better image quality compared to traditional DTI.•MUSE-DTI parameters of the spinal cord at MCL in CSM patients were significantly grade-dependent and all correlated with ...clinical JOA scores.•The ADC2 values can reflect the secondary damage of distal spinal cord.
The most frequent type of spinal cord injury is cervical spondylotic myelopathy (CSM). Conventional structural magnetic resonance imaging (MRI) is the gold diagnosis standard for CSM. Diffusion tensor imaging (DTI) could reflect microstructural changes in the spinal cord by tracing water molecular diffusion in early stages of CSM. However, due to the complex local anatomical structure and small field of view of the spinal cord, the imaging effect of traditional DTI imaging on the spinal cord is limited. MUSE (MUltiplexed Sensitivity-Encoding) -DTI is a novel diffusion-weighted imaging (DWI) sequence that achieves higher signal intensity through multiple excitation acquisition. MUSE sequence may improve the quality of spinal cord DTI imaging.
Prospective study.
This study aimed to investigate the clinical diagnosis value of a novel protocol of MUSE-DTI in patients with cervical spondylotic myelopathy (CSM).
From August 2021 to March 2022, a total of 60 subjects (22–71 years) were enrolled, including 51 CSM patients (22 males, 29 females) and 9 healthy subjects (4 males and 5 females). Each subject underwent a MUSE-DTI examination and a clinical Japanese Orthopedic Association (JOA) scale.
We measured values of FA (Fractional Anisotropy), MD (Mean Diffusivity), AD (Axial Diffusivity), and RD (Radial Diffusivity), and collected the clinical JOA scores of each subject before the MR examination.
A 3.0T MR scanner (Signa Architect, GE Healthcare) performed the MUSE-DTI sequence on each subject. The cervical canal stenosis of subjects was classified from grade 0 to grade Ⅲ according to the method of an MRI grading system. FA, MD, AD, and RD maps were generated by postprocessing MUSE-DTI data on the GE workstation. Regions of interest (ROIs) were manually drawn at the C2 vertebral body level and C2/3-C6/7 intervertebral disc levels by covering the whole spinal cord. The clinical severity of myelopathy of subjects was assessed by the clinical Japanese Orthopedic Association scale (JOA).
MUSE-DTI can acquire a high-resolution diffusion image compared to traditional DTI. The FAMCL values showed a decreasing trend from grade 0 to grade Ⅲ, while the MDMCL, ADMCL, and RDMCL values showed an overall increasing trend. Significant differences in MDMCL, ADMCL, and RDMCL values were found between adjacent groups among grades Ⅰ-Ⅲ (p<.05). The ADC2 values in CSM patients (grade I–Ⅲ) were significantly lower than in healthy individuals (grade 0) (p=.019). The clinical JOA score has a significant correlation with FAMCL (p=.035), MDMCL (p<.001), ADMCL (p<.001), and RDMCL (p<.001) values.
MUSE-DTI displayed a better image quality compared to traditional DTI. MUSE-DTI parameters displayed a grade-dependent trend. All the MUSE-DTI parameters at MCL were correlated with the clinical JOA scores. The ADC2 values can reflect the secondary damage of distal spinal cord. Therefore, MUSE-DTI could be a reliable biomarker for clinical auxiliary diagnosis of spinal cord injury severity in cervical spondylotic myelopathy.
•Laminar burning velocity was studied in a wide range of experimental conditions.•The empirical correlation between LBV and effective parameters was studied.•Empirical equations with good predictive ...ability was proposed.•The variation of flame temperature and diffusivity with hydrogen ratio were studied.•Reactions R(3) and R(4) generate key radicals to accelerates the reaction.
Carbon-free hydrogen and ammonia have their own drawbacks when used alone. The composite fuel system formed by the combination of hydrogen and ammonia can not only solve the current energy demand and environmental pollution problems, but also effectively overcome the shortcomings of pure fuel application. Laminar flames are the basis for the study of other flame forms. In this paper, the laminar combustion characteristics of hydrogen/ammonia/air mixture were studied in a constant volume combustor. The initial pressures range from 0.5 to 1.5 atm, the equivalence ratios range 0.5 to 1.5, and the hydrogen ratios range from 0 to 1.0. The laminar burning velocity increases monotonously with the increase of hydrogen ratio, while presents an inverted U-shaped relationship with the equivalence ratio. Compared with the hydrogen ratio and the equivalence ratio, the initial pressure has the weakest effect on the laminar burning velocity of hydrogen/ammonia/air mixture. The laminar burning velocity gradually decreases with the initial pressure. This paper also gives an empirical exponential fitting equation for the laminar burning velocity of hydrogen/ammonia/air mixtures, which can well predict the laminar burning velocity of the mixed gas under various equivalence ratios (0.8–1.2) and various hydrogen ratios (0–1.0) at atmospheric pressure. The influence of fuel composition on the laminar burning velocity should be the result of the combined effect of thermal diffusivity and mass diffusivity. The important fuel consumption pathways R3 and R4 generate more key radicals with increasing hydrogen ratio, thereby promoting the combustion process.
We collected MRI diffusion tensor imaging data from 80 younger (20–32 years) and 63 older (60–71 years) healthy adults. Tract-based spatial statistics (TBSS) analysis revealed that white matter ...integrity, as indicated by decreased fractional anisotropy (FA), was disrupted in numerous structures in older compared to younger adults. These regions displayed five distinct region-specific patterns of age-related differences in other diffusivity properties: (1) increases in both radial and mean diffusivity; (2) increases in radial diffusivity; (3) no differences in parameters other than FA; (4) a decrease in axial and an increase in radial diffusivity; and (5) a decrease in axial and mean diffusivity. These patterns suggest different biological underpinnings of age-related decline in FA, such as demyelination, Wallerian degeneration, gliosis, and severe fiber loss, and may represent stages in a cascade of age-related degeneration in white matter microstructure. This first simultaneous description of age-related differences in FA, mean, axial, and radial diffusivity requires histological and functional validation as well as analyses of intermediate age groups and longitudinal samples.
In March 2024 Construction and Building Materials published “Water distribution characteristics of capillary absorption in internally cured concrete with superabsorbent polymers”, which claims to ...present a water distribution model characterising the spatiotemporal moisture content evolution in internally cured concrete with superabsorbent polymers during capillary absorption. This discussion, considered a post-publication critique, establishes that the paper’s water distribution model conflicts with the paper’s capillary absorption tests. While the model is based on the premise of the square-root-of-time behaviour of capillary absorption, the tests do not demonstrate that square-root-of-time behaviour. This critique in addition questions the paper’s forthright application of the power-law diffusivity expression with exponent 4, given that its validity for the paper’s materials has not been verified. It is shown that different but equivalent diffusivity expressions lead to different moisture diffusivities at lower moisture contents.
•This post-publication review formulates concerns on a previously published paper.•The paper’s water distribution model and capillary absorption tests are in conflict.•The paper’s adoption of an unverified moisture diffusivity expression is doubtful.
The use of the diffusion tensor imaging (DTI) is rapidly growing in the neuroimaging field. Nevertheless, rigorously performed quantitative validation of DTI pathologic metrics remains very limited ...owing to the difficulty in co-registering quantitative histology findings with magnetic resonance imaging. The aim of this review is to summarize the existing state-of-the-art knowledge with respect to axial (λ
) and radial (λ
) diffusivity as DTI markers of axonal and myelin damage, respectively. First, we provide technical background for DTI and briefly discuss the specific organization of white matter in bundles of axonal fibers running in parallel; this is the natural target for imaging based on diffusion anisotropy. Second, we discuss the four seminal studies that paved the way for considering axial (λ
) and radial (λ
) diffusivity as potential
surrogate markers of axonal and myelin damage, respectively. Then, we present difficulties in interpreting axial (λ
) and radial (λ
) diffusivity in clinical conditions associated with inflammation, edema, and white matter fiber crossing. Finally, future directions are highlighted. In summary, DTI can reveal strategic information with respect to white matter tracts, disconnection mechanisms, and related symptoms. Axial (λ
) and radial (λ
) diffusivity seem to provide quite consistent information in healthy subjects, and in pathological conditions with limited edema and inflammatory changes. DTI remains one of the most promising non-invasive diagnostic tools in medicine.
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