Volume Relaxation Research Articles

Phase field model for cell spreading dynamics.

We suggest a 3D phase field model to describe 3D cell spreading on a flat substrate. The model is a simplified version of a minimal model that was developed in Winkler (Commun Phys 2:82, 2019). Our model couples the order parameter u with 3D polarization (orientation) vector field [Formula: see text] of the actin network. We derive a closed integro-differential equation governing the 3D cell spreading dynamics on a flat substrate, which includes the normal velocity of the membrane, curvature, volume relaxation rate, a function determined by the molecular effects of the subcell level, and the adhesion effect. This equation is easily solved numerically. The results are in agreement with the early fast phase observed experimentally in Dobereiner (Phys Rev Lett 93:108105, 2004). Also we find agreement with the universal power law (Cuvelier in Curr Biol 17:694-699, 2007) which suggest that cell adhesion or contact area versus time behave as [Formula: see text] in the early stage of cell spreading dynamics, and slow down at the next stages.

Scale-Invariant Feature Transform (SIFT) Algorithm-Based Detection of Cardiac Insufficiency in Sepsis Patients with Echocardiography

This research aimed to explore the application of cardiac ultrasound imaging (CUI) in the examination and diagnosis of sepsis patients with cardiac insufficiency under a speckle tracking algorithm (STA). Scale-invariant feature transform (SIFT) algorithm was introduced to process images of CUI through STA under feature points of cardiac ultrasonic images. 90 patients with sepsis who were admitted to the hospital were selected and randomly divided into a sound cardiac function group (n = 62) (group A) and a cardiac insufficient group (n = 28) (group B) under whether they had cardiac insufficiency, and 20 healthy people were selected as a control group. Sepsis patients were examined on the seventh day after diagnosis including laboratory-related indicators, echocardiography, and echocardiographic data. The results showed that there were differences in cardiac ultrasound, cardiac marker, and laboratory examinations of subjects in the three groups ( P < 0.05). Creatine kinase isoenzyme-MB (CK-MB), glycogen phosphorylase isoenzyme BB (GPBB), and heart-type fatty acid-binding protein (H-FABP) of subjects in the three groups showed statistically marked differences ( P < 0.05). The other results indicated tricuspid late diastolic blood flow velocity (A′) value was greater than stroke volume (SV) and isovolumetric relaxation time (IVRT) value, followed by left ventricular ejection fraction (EF) and cardiac output per minute output (CO), and EF and CO values were over peak velocity of right ventricular free wall tricuspid valve systolic movement (SM) and left ventricular fractional shortening (FS) value, and left ventricular end-diastolic volume (EDV) value came next. The analysis of CUI based on STA could help doctors to judge sepsis patients with cardiac function. In addition, sepsis patients with sound cardiac function and sepsis patients with cardiac insufficiency could be distinguished by CUI, which had certain guiding significance for clinical diagnosis.

Anatomic and metabolic alterations in the rodent frontal cortex caused by clinically relevant fractionated whole-brain irradiation

Radiation-induced brain injury (RII) is a harmful side-effect occurring after conventional radiation therapy (usually fractionated whole-brain irradiation/fWBI) of patients with cerebral tumors and metastases. An important role in the quality of patients' lives plays cognitive, executive, and emotional functions, regulation on which are involved in frontal cortices pathways. This study assessed the morphologic and metabolic alterations in the rodent frontal cortex caused by fWBI with the total dose of 32 Gy in 4 fractions performed by linear accelerator Clinac iX. Nine male Wistar rats underwent radiation procedures, whereas the other nine rats were investigated as a sham-irradiated group. All eighteen animals were examined using magnetic resonance (MR) in three intervals - before, on 2nd, and 70th day after sham/irradiation. After ten weeks of surviving, all rats underwent histopathological analysis determined by image analysis of immunofluorescent stained sections in the frontal cortex. MR examination was performed on 7T MR scanner Bruker BioSpec 70/20 and consisted of MR-volumetry, T2 relaxometry, and single-voxel proton-1 MR spectroscopy localized in the frontal cortex. Both tissue volume and T2 relaxation time of the frontal cortex were significantly lower in animals after 2 and 70 days of exposure than in controls; however, there were no differences between irradiated groups. Similarly, in animals' frontal cortex after fWBI, increased levels of myoinositol and glutamate/glutamine ratios were observed. Ratios of N-acetyl-aspartate, choline, and peaks of lactate and lipids did not change between groups. The histopathological analysis of the frontal cortex showed increased signs of neurodegeneration and a slight increase in astrocytes and microglia in exposed animals. Early (2 days, 10 weeks) after clinically relevant fWBI were in the frontal cortices of exposed rodents confirmed morphologic and metabolic changes indicating neurodegenerative changes, initializing cerebral atrophy, and evident signs of endothelial disruption and dysregulated neurotransmission that may cause a wide range of functional as well as cognitive deficits.

Neurodegenerative and functional signatures of the cerebellar cortex in m.3243A > G patients.

Mutations of the mitochondrial DNA are an important cause of inherited diseases that can severely affect the tissue’s homeostasis and integrity. The m.3243A > G mutation is the most commonly observed across mitochondrial disorders and is linked to multisystemic complications, including cognitive deficits. In line with in vitro experiments demonstrating the m.3243A > G’s negative impact on neuronal energy production and integrity, m.3243A > G patients show cerebral grey matter tissue changes. However, its impact on the most neuron dense, and therefore energy-consuming brain structure—the cerebellum—remains elusive. In this work, we used high-resolution structural and functional data acquired using 7 T MRI to characterize the neurodegenerative and functional signatures of the cerebellar cortex in m.3243A > G patients. Our results reveal altered tissue integrity within distinct clusters across the cerebellar cortex, apparent by their significantly reduced volume and longitudinal relaxation rate compared with healthy controls, indicating macroscopic atrophy and microstructural pathology. Spatial characterization reveals that these changes occur especially in regions related to the frontoparietal brain network that is involved in information processing and selective attention. In addition, based on resting-state functional MRI data, these clusters exhibit reduced functional connectivity to frontal and parietal cortical regions, especially in patients characterized by (i) a severe disease phenotype and (ii) reduced information-processing speed and attention control. Combined with our previous work, these results provide insight into the neuropathological changes and a solid base to guide longitudinal studies aimed to track disease progression.

Logarithmic Relaxation of the Specific Volume and Optical Properties of GeS2 Densified Glass

Logarithmic Relaxation of the Specific Volume and Optical Properties of GeS2 Densified Glass

Radiation induced segregation near dislocations and symmetric tilt grain boundaries in Fe-Cr alloys: A phase-field study

A phase-field model dedicated to dislocation climb under irradiation has been coupled to point defects and chemical species transport equations. It allows to predict radiation induced segregation in Fe-Cr alloys around dislocations in the isolated or stacking configuration like in symmetric tilt grain boundaries. This work is challenging for several reasons: (i) radiation induced segregation in Fe-Cr is difficult to simulate since Cr depletion or enrichment can occur, depending on the Cr nominal composition and temperature, (ii) dislocations are biased sinks due to their elastic fields which can not be ignored in this case and (iii) other surrounding microstructural defects can interact with dislocations and impact point defect and solute transport. To overcome (iii), a mean-field approach is adopted, in which the influence of the surrounding sinks is taken into account through the introduction of an overall and uniform sink strength in the point defect diffusion equations. Despite the numerous parameters of the model, unknown experimental information and approximations made to make the simulations tractable, the numerical results are in good agreement with the experimental ones. Moreover, the model allows to identify the main physical parameters to correctly quantify radiation induced segregation in the case of dislocations. Among them, the point defect relaxation volumes are of first importance in comparison with the solute relaxation volume or the nature of the slip system.

Post-irradiation microstructural examination of EUROFER-ODS steel irradiated at 300°C and 400°C

The effect of neutron irradiation on the microstructure of EUROFER-ODS alloy reinforced with an addition of 0.5% Y 2 O 3 was analyzed by transmission electron microscopy . The irradiation of up to 16.2 dpa damage dose at 300°C and 400°C was performed in Petten High Flux Reactor. This study focuses on the imaging, identification, and quantitative analysis of interstitial loops and voids located on ODS particles. The nano-sized loops and point defects with b½〈111〉 Burgers vectors are preferentially located near structural defects such as the line dislocations or impurities in the material irradiated at 300°C. Homogeneously distributed loops having Burgers vectors of b½〈111〉 and b〈100〉 types were found in the material irradiated at 400°C. The obtained quantitative data on radiation-induced defects such as size, number density and relaxation volume were compared with EUROFER97 irradiated at the same conditions. It was found that the occurrence of radiation induced defects depends on the local number density and the size distribution of the ODS particles and not only on the irradiation damage and temperature.

CMR-derived myocardial strain analysis differentiates ischemic and dilated cardiomyopathy\u2014a propensity score-matched study

Left ventricular (LV) longitudinal, circumferential, and radial motion can be measured using feature tracking of cardiac magnetic resonance (CMR) images. The aim of our study was to detect differences in LV mechanics between patients with dilated cardiomyopathy (DCM) and ischemic cardiomyopathy (ICM) who were matched using a propensity score-based model. Between April 2017 and October 2019, 1224 patients were included in our CMR registry, among them 141 with ICM and 77 with DCM. Propensity score matching was used to pair patients based on their indexed end-diastolic volume (EDVi), ejection fraction (EF), and septal T1 relaxation time (psmatch2 module L Feature tracking provided six parameters for global longitudinal, circumferential, and radial strain with corresponding strain rates in each group. Strain parameters were compared between matched pairs of ICM and DCM patients using paired t tests. Propensity score matching yielded 72 patients in each group (DCM mean age 58.6 ± 11.6 years, 15 females; ICM mean age 62.6 ± 13.2 years, 11 females, p = 0.084 and 0.44 respectively; LV-EF 32.2 ± 13.5% vs. 33.8 ± 12.1%, p = 0.356; EDVi 127.2 ± 30.7 ml/m2 vs. 121.1 ± 41.8 ml/m2, p = 0.251; native T1 values 1165 ± 58 ms vs. 1167 ± 70 ms, p = 0.862). There was no difference in global longitudinal strain between DCM and ICM patients (− 10.9 ± 5.5% vs. − 11.2 ± 4.7%, p = 0.72), whereas in DCM patients there was a significant reduction in global circumferential strain (− 10.0 ± 4.5% vs. − 12.2 ± 4.7%, p = 0.002) and radial strain (17.1 ± 8.51 vs. 21.2 ± 9.7%, p = 0.039). Our data suggest that ICM and DCM patients have inherently different myocardial mechanics, even if phenotypes are similar. Our data show that GCS is significantly more impaired in DCM patients. This feature may help in more thoroughly characterizing cardiomyopathy patients.

Hippocampal acidity and volume are differentially associated with spatial navigation in older adults

The hippocampus is negatively affected by aging and is critical for spatial navigation. While there is evidence that wayfinding navigation tasks are especially sensitive to preclinical hippocampal deterioration, these studies have primarily used volumetric hippocampal imaging without considering microstructural properties or anatomical variation within the hippocampus. T1ρ is an MRI measure sensitive to regional pH, with longer relaxation rates reflecting acidosis as a marker of metabolic dysfunction and neuropathological burden. For the first time, we investigate how measures of wayfinding including landmark location learning and delayed memory in cognitively normal older adults (N = 84) relate to both hippocampal volume and T1ρ in the anterior and posterior hippocampus. Regression analyses revealed hippocampal volume was bilaterally related to learning, while right lateralized T1ρ was related to delayed landmark location memory and bilateral T1ρ was related to the delayed use of a cognitive map. Overall, results suggest hippocampal volume and T1ρ relaxation rate tap into distinct mechanisms involved in preclinical cognitive decline as assessed by wayfinding navigation, and laterality influenced these relationships more than the anterior-posterior longitudinal axis of the hippocampus.

The Effect of Intraventricular Hemorrhage on Brain Development in Premature Infants: A Synthetic MRI Study.

Objectives: Synthetic MRI can obtain multiple parameters in one scan, including T1 and T2 relaxation time, proton density (PD), brain volume, etc. This study aimed to investigate the parameter values T1 and T2 relaxation time, PD, and volume characteristics of intraventricular hemorrhage (IVH) newborn brain, and the ability of synthetic MRI parameters T1 and T2 relaxation time and PD to diagnose IVH.Materials and methods: The study included 50 premature babies scanned with conventional and synthetic MRI. Premature infants were allocated to the case group (n = 15) and NON IVH (n = 35). The T1, T2, PD values, and brain volume were obtained by synthetic MRI. Then we assessed the impact of IVH on these parameters.Results: In the posterior limbs of the internal capsule (PLIC), genu of the corpus callosum (GCC), central white matter (CWM), frontal white matter (FWM), and cerebellum (each p < 0.05), the T1 and T2 relaxation times of the IVH group were significantly prolonged. There were significant differences also in PD. The brain volume in many parts were also significantly reduced, which was best illustrated in gray matter (GM), cerebrospinal fluid and intracranial volume, and brain parenchymal fraction (BPF) (each p < 0.001, t = −5.232 to 4.596). The differential diagnosis ability of these quantitative values was found to be excellent in PLIC, CWM, and cerebellum (AUC 0.700–0.837, p < 0.05).Conclusion: The quantitative parameters of synthetic MRI show well the brain tissue characteristic values and brain volume changes of IVH premature infants. T1 and T2 relaxation times and PD contribute to the diagnosis and evaluation of IVH.

Volume and T2 relaxation time measurements of quadriceps femoris and hamstring muscles are reliable and reproducible

Background/aimVolume and T2 relaxation time measurements of the skeletal muscle provide quantitative information. We aimed to evaluate the interobserver reliability and the intraobserver reproducibility of measurements of volumes and T2 relaxation times of the quadriceps femoris and the hamstring muscles.Materials and methodsA cross-sectional reliability study was conducted on ten recreational athletes. The images of the quadriceps and the hamstring muscles of both limbs were obtained using a 3.0 Tesla magnetic resonance imaging (MRI) scanner. Two sports medicine specialists measured muscle volumes from a total of 2560 images and T2 relaxation times from a total of 40 images, and repeated this once more. The intraobserver and interobserver compliance were assessed by the intraclass correlation coefficient (ICC) and Cronbach’s alpha (α).ResultsVolume and T2 relaxation time of quadriceps femoris and hamstring muscle measurements with MRI had good to excellent reliability (Muscle volume; intraobserver ICCs: between 0.97 and 0.99, α: between 0.98 and 0.99 and interobserver ICCs: between 0.96 and 0.99, α: 0.99. T2 relaxation time; intraobserver ICCs: between 0.74 and 0.96, α: between 0.85 and 0.98 and interobserver ICCs: between 0.75 and 0.90, α: between 0.85 and 0.95).ConclusionVolume and T2 relaxation time measurements of the quadriceps femoris and the hamstring muscles are reliable and reproducible.

Two-dimensional thermo-mechanical fractional responses to biological tissue with rheological properties

PurposeThe system of equations for fractional thermo-viscoelasticity is used to investigate two-dimensional bioheat transfer and heat-induced mechanical response in human skin tissue with rheological properties.Design/methodology/approachLaplace and Fourier’s transformations are used. The resulting formulation is applied to human skin tissue subjected to regional hyperthermia therapy for cancer treatment. The inversion process for Fourier and Laplace transforms is carried out using a numerical method based on Fourier series expansions.FindingsComparisons are made with the results anticipated through the coupled and generalized theories. The influences of volume materials properties and fractional order parameters for all the regarded fields are examined. The results indicate that volume relaxation parameters, as well as fractional order parameters, play a major role in all considered distributions.Originality/valueBio-thermo-mechanics includes bioheat transfer, biomechanics, burn injury and physiology. In clinical applications, knowledge of bio-thermo-mechanics in living tissues is very important. One can infer from the numerical results that, with a finite distance, the thermo-mechanical waves spread to skin tissue, removing the unrealistic predictions of the Pennes’ model.

Structural origin of thermal shrinkage in soda-lime silicate glass below the glass transition temperature: A theoretical investigation by microsecond timescale molecular dynamics simulations.

Microscopic dynamical features in the relaxation of glass structures are one of the most important unsolved problems in condensed matter physics. Although the structural relaxation processes in the vicinity of glass transition temperature are phenomenologically expressed by the Kohlrausch-Williams-Watts function and the relaxation time can be successfully interpreted by Adam-Gibbs theory and/or Narayanaswamy's model, the atomic rearrangement, which is the origin of the volume change, and its driving force have not been elucidated. Using the microsecond time-scale molecular dynamics simulations, this study provides insights to quantitatively determine the origin of the thermal shrinkage below Tg in a soda-lime silicate glass. We found that during annealing below Tg, Na ions penetrate into the six-membered silicate rings, which remedies the acute O-O-O angles of the energetically unstable rings. The ring structure change makes the space to possess the cation inside the rings, but the ring volume is eventually reduced, which results in thermal shrinkage of the soda-lime silica glass. In conclusion, the dynamical structural relaxation due to the cation displacement evokes the overall volume relaxation at low temperature in the glassy material.

Daily cumulative load and body mass index alter knee cartilage response to running in women.

It is unknown whether a greater accumulation of knee load over a typical day is related to how cartilage responds to an acute bout of loading. This information may clarify the role of habitual activity on cartilage function. Is there a relationship between change in tibial and femoral cartilage thickness, volume, and T2 relaxation time following running with daily cumulative knee load in women? Secondarily, is there a relationship between cartilage change following running and the statistical interaction of body mass index (BMI) and daily steps? Participants (n = 15) completed gait analyses and wore an accelerometer over a week. Daily cumulative knee load was the statistical interaction between tibial compressive joint reaction force (JRF) impulse with the average number of daily steps measured using accelerometry. Magnetic resonance imaging scans were acquired before and immediately after 15-min of treadmill running. Changes in tibial and femoral cartilage thickness, volume, and T2 relaxation time were calculated. Multiple linear regressions tested the associations of cartilage change outcomes with: baseline (thickness, volume, T2), JRF impulse, steps, and the interaction JRF impulse*steps. Secondarily, BMI was substituted for JRF impulse. Tibial volume change was explained by baseline volume, JRF impulse, steps, and JRF impulse*steps (R2 = 0.50, p = 0.013). Additionally, tibial volume change was explained by baseline volume, BMI, steps, and BMI*steps (R2 = 0.43, p = 0.002). Those who were more physically active with lower JRF impulse (or lower BMI) showed less change in tibial cartilage after a running exposure. This may suggest cartilage conditioning.

Improvement the plasticity of Fe-based bulk metallic glass via low temperature annealing

Generally, annealing below the glass transition temperature causes embrittlement of the bulk metallic glasses (BMGs). Here we found the plasticity of Fe75Mo5P13C7 BMG can be improved by annealing at low temperature. The improvement of plasticity is attributed to bits of nano-crystallization during the annealing and the free volume which has not been annihilated. The correlation of plasticity with micro-structure, relaxation and free volume characteristic varies in Fe75Mo5P13C7 BMG with its annealed state under different temperatures. It is demonstrated that the ratio of relaxation enthalpy decreases rapidly with the annealed temperature, and the ratio of crystallization increases slowly with the annealed temperature. The plasticity will be largest when the ratio of nanocrystals is equivalent to the free volume.

Theory of structural relaxation in glass from the thermodynamics of irreversible processes

This work proposes a fundamental thermodynamic description of structural relaxation in glasses by establishing a link between the Prony series solution to volume relaxation derived from the principles of irreversible thermodynamics and asymmetric Lévy stable distribution of relaxation rates. Additionally, it is shown that the bulk viscosity of glass, and not the shear viscosity, is the transport coefficient governing structural relaxation. We also report the distribution of relaxation times and energy barrier heights underpinning stretched exponential relaxation. It is proposed that this framework may be used for qualitative and quantitative descriptions of the relaxation kinetics in glass.

Molecular dynamic study for concentration-dependent volume relaxation of vacancy

In this paper, large-scale molecular dynamic (MD) simulation is performed to investigate the concentration-dependent vacancy volume relaxation in Al, Cu, and Au, respectively. The vacancy volume relaxation factor is calculated and correlated to the microstructure change based on MD results. It is found that the vacancy volume relaxation factor is nearly a constant at low to mid-vacancy concentration level, i.e., from 10−6 to 10−3 of the lattice concentrations. However, the volume of vacancies will completely collapse at the high vacancy concentration, and the coalescence of vacancies will form massive dislocations. The simulation results are in good agreement with the existing data from both experiments and simulations in the literature. A uniform empirical equation is developed to obtain the vacancy volume relaxation factor as a function of vacancy concentration. Furthermore, the hydrostatic stress is also calculated based on MD simulations. This paper also discusses the relationship between the vacancy volume relaxation and the diffusion-induced strain, such as in the application of electromigration. For a constrained condition, the hydrostatic stresses obtained from MD-based vacancy volume relaxation and a commonly used stress-vacancy equation are compared. An insight on the critical vacancy concentration at which electromigration failure would occur is discussed in detail.

A time-shift correction for extraction of viscoelastic parameters from ramp-hold AFM experiments

The stress relaxation and creep measurements are commonly implemented in AFM indentation experiments to analyze the viscoelastic properties of a sample in the time domain. The assumption of an instantaneous step load is often applied which can lead to erroneous estimation of viscoelastic parameters from the experimental data. A viscoelastic solution for the ramp-hold indentation profile might be used but requires higher computational costs. Here, we employed simulations for the ramp-hold indentations for the power-law rheology (PLR) and standard linear solid models. The error coming from the instantaneous load assumption was analyzed and a simple empirical correction for the finite ramp time was employed as a time shift of the hold region. The correction was tested in experiments on cells, in which the data from stress relaxation, creep, and force volume experiments were compared. The correction showed good applicability for the extraction of the PLR viscoelastic parameters.

Myeloarchitectonic Asymmetries of Language Regions in the Human Brain.

One prominent theory in neuroscience and psychology assumes that cortical regions for language are left hemisphere lateralized in the human brain. In the current study, we used a novel technique, quantitative magnetic resonance imaging (qMRI), to examine interhemispheric asymmetries in language regions in terms of macromolecular tissue volume (MTV) and quantitative longitudinal relaxation time (T1) maps in the living human brain. These two measures are known to reflect cortical myeloarchitecture from the microstructural perspective. One hundred and fifteen adults (55 male, 60 female) were examined for their myeloarchitectonic asymmetries of language regions. We found that the cortical myeloarchitecture of inferior frontal areas including the pars opercularis, pars triangularis, and pars orbitalis is left lateralized, while that of the middle temporal gyrus, Heschl’s gyrus, and planum temporale is right lateralized. Moreover, the leftward lateralization of myelination structure is significantly correlated with language skills measured by phonemic and speech tone awareness. This study reveals for the first time a mixed pattern of myeloarchitectonic asymmetries, which calls for a general theory to accommodate the full complexity of principles underlying human hemispheric specialization.

Elastic dipole tensors and relaxation volumes of point defects in concentrated random magnetic Fe-Cr alloys

Point defects in body-centred cubic Fe, Cr and concentrated random magnetic Fe-Cr are investigated using density functional theory and theory of elasticity. The volume of a substitutional Cr atom in ferromagnetic bcc Fe is approximately 18% larger than the volume of a host Fe atom, whereas the volume of a substitutional Fe atom in antiferromagnetic bcc Cr is 5% smaller than the volume of a host Cr atom. In an alloy, elastic dipole P and relaxation volume Ω tensors of vacancies and self-interstitial atom (SIA) defects exhibit large fluctuations, with vacancies having negative and SIA large positive relaxation volumes. Dipole tensors of vacancies are nearly isotropic across the entire alloy composition range, with diagonal elements Pii decreasing as a function of Cr content. Fe-Fe and Fe-Cr SIA dumbbells are more anisotropic than Cr-Cr dumbbells. We find that fluctuations of elastic dipole tensors of SIA defects are primarily associated with the variable crystallographic orientations of the dumbbells. Statistical properties of tensors P and Ω are analysed using their principal invariants, suggesting that point defects differ significantly in alloys containing below and above 10% at. Cr. The von Mises stresses caused by dumbbells are notably larger than those caused by vacancies. The relaxation volume of a vacancy depends sensitively on whether it occupies a Fe or a Cr lattice site. A correlation between elastic relaxation volumes and magnetic moments of defects found in this study suggests that magnetism is a significant factor influencing elastic fields of defects in Fe-Cr alloys.