Presence Of Gradient Research Articles

Effect of Induced Magnetic Field on MHD Flow Between Two Parallel Porous Plates at Constant Temperature Gradient in Presence of Inclined Magnetic Field

Effect of Induced Magnetic Field on MHD Flow Between Two Parallel Porous Plates at Constant Temperature Gradient in Presence of Inclined Magnetic Field

Resistivities across the vapor–liquid interface of a simple fluid: An assessment of methods

Heat and mass transfer across the interface between liquid and vapor is studied by means of molecular dynamics simulation. Two scenarios are considered to access the interface resistivities, specifying either the evaporation rate or the temperature gradient. Spatially resolved profiles of density, temperature, chemical potential, pressure tensor elements, and hydrodynamic velocity are sampled with large-scale molecular dynamics simulations to elucidate the structural and dynamic properties across the interface under non-equilibrium conditions. The employed interaction model is appropriate for simple fluids, like argon, while its thermodynamic properties in bulk phases are fully known. Most of the temperature range from the triple point to the critical point is investigated, varying the heat flux and the particle flux over one to two orders of magnitude. Different approaches are followed to determine the interface resistivities, and their results are compared to literature data and kinetic gas theory. It is found that the interface resistivities are a sole function of the interface temperature and are independent of the chemical potential gradient or the temperature gradient. This also holds for its thickness and surface tension up to the very large gradients that are typically imposed in molecular dynamics simulations. It stands to reason that this is also the case under the presence of gradients with a magnitude that is technically relevant and thus much smaller.

Controlled tumor heterogeneity in a co-culture system by 3D bio-printed tumor-on-chip model

Cancer treatment resistance is a caused by presence of various types of cells and heterogeneity within the tumor. Tumor cell–cell and cell-microenvironment interactions play a significant role in the tumor progression and invasion, which have important implications for diagnosis, and resistance to chemotherapy. In this study, we develop 3D bioprinted in vitro models of the breast cancer tumor microenvironment made of co-cultured cells distributed in a hydrogel matrix with controlled architecture to model tumor heterogeneity. We hypothesize that the tumor could be represented by a cancer cell-laden co-culture hydrogel construct, whereas its microenvironment can be modeled in a microfluidic chip capable of producing a chemical gradient. Breast cancer cells (MCF7 and MDA-MB-231) and non-tumorigenic mammary epithelial cells (MCF10A) were embedded in the alginate-gelatine hydrogels and printed using a multi-cartridge extrusion bioprinter. Our approach allows for precise control over position and arrangements of cells in a co-culture system, enabling the design of various tumor architectures. We created samples with two different types of cells at specific initial locations, where the density of each cell type was carefully controlled. The cells were either randomly mixed or positioned in sequential layers to create cellular heterogeneity. To study cell migration toward chemoattractant, we developed a chemical microenvironment in a chamber with a gradual chemical gradient. As a proof of concept, we studied different migration patterns of MDA-MB-231 cells toward the epithelial growth factor gradient in presence of MCF10A cells in different ratios using this device. Our approach involves the integration of 3D bioprinting and microfluidic devices to create diverse tumor architectures that are representative of those found in various patients. This provides an excellent tool for studying the behavior of cancer cells with high spatial and temporal resolution.

Regulation of NK cell chemotaxis by KCa3.1 channels

Abstract CD8+ T cells and NK cells are the primary line of defense against tumor cells. However, the tumor microenvironment impairs their anti-tumor capabilities. One of the key functions impaired is the ability of T and NK cells to infiltrate the tumor, essential to allow the direct contact with a target cell and its killing. Kv1.3 and KCa3.1 K +channels have a multitude of essential functions that have been established in CD8+ T cells: Kv1.3 regulates cytotoxicity and KCa3.1 chemotaxis. However, less is known about K +channels in NK cells. Herein, we performed electrophysiological and 3D chemotaxis experiments to study the activity and functional role of K +channels in human NK cells. NK cells were isolated from healthy donors (HD) and head and neck cancer (HNC) patients and activated with IL-2 and IL-15 for 24–48 hr. Activation led to an increase in Kv1.3 currents of 49.6% at 24 hr and 434.1% at 48 hr . KCa3.1 activity increased by 42.8% at 24 hr and 54.2% at 48 hr. Chemotaxis experiment showed that activated NK cells move randomly in the collagen matrix and migrated towards the chemokine gradient in presence of CXCL10. Chemotaxis, but not random migration, was inhibited by the selective KCa3.1 blocker TRAM-34 in NK cells from HD and HNC patients. Shk-Dap22, a Kv1.3 blocker, did not alter either chemotaxis or random migration. Overall, TRAM-34 reduced the distance achieved by NK cells in the chemokine gradient by 157% in HD (4 donors) and 89% in HNC NK cells (1 donor). These data highlight the critical role of KCa3.1 channels in NK cell migration and open the possibility of targeting KCa3.1 to facilitate tumor infiltration by NK cells.

ITG mode driven vortices in spatially inhomogeneous magnetoplasma with generalized (r, q) distribution

In this paper, we have investigated the ion temperature gradient (ITG) driven electrostatic drift waves in the presence of non-thermal electrons that follow the generalized (r, q) distribution. In the linear regime, we have derived the linear dispersion relation of the coupled drift-ion acoustic wave. In the nonlinear regime, stationary solutions of the nonlinear equations have been obtained in the presence of gradients in equilibrium density, temperature and magnetic field. It has been found that the tail parameter q and the flatness parameter r strongly affect the profiles of linear and non-linear propagation characteristics of ITG driven electrostatic drift ion acoustic waves. It has been found that the flat-topped distribution augments the growth rate of the ITG driven electrostatic modes under consideration which is undesirable from the confinement stand point. It has also been shown that the double spectral indices r and q affect the structure of the nonlinear vortex structures. The comparison of the spatial scales over which vortices are formed for different distributions has also been presented.

Tertiary pyroelectric effect in TGS group crystals

In this paper, the study of the dynamic pyroelectric effect under different powers of modulated heat flux in deuterated triglycine sulfate (DTGS) near the Curie point is presented. It was found that pyroelectric coefficient was essentially dependent on the power of the modulated radiation, especially in the phase transition region. It is shown that a tertiary pyroelectric effect makes an additional contribution to the pyroelectric response observed in TGS group crystals near phase transition region. The tertiary pyroelectric effect is caused by a nonuniform distribution of piezoelectric coefficients in the samples as a result of temperature gradient presence.

Global turbulence features across marginality and non-local pedestal-core interactions

Spatially non-local aspects of turbulent transport in tokamak plasmas are examined with global gyrokinetic simulations using the ORB5 code. Inspired by very accurate measurements in the TCV tokamak in L-mode, we initialise plasma profiles with constant logarithmic gradients in the core and constant linear gradients in the ‘pedestal’ (). The main finding is that transport in the core is strongly affected by the presence of pedestal gradients. This non-local pedestal-core coupling appears to be correlated with the appearance of repetitive avalanches that propagate across both pedestal and core regions. Below a certain threshold value in pedestal gradient, no well-defined frequency is found for avalanches. Above this threshold, a well-defined frequency shows up, which roughly matches that of the local geodesic acoustic mode (GAM) frequency near the plasma edge and is thus well below the local GAM frequency in the core: this behaviour is very similar to the global coherent mode structure observed in TCV. Above this threshold in pedestal gradient, the core transport increases sharply: there is therefore a non-locality in marginality. The probability density functions (PDFs) of density, temperature, temperature gradient and potential are found to have nearly Gaussian distributions, whereas the heat flux can have, in the presence of avalanches, a more or less strongly positively skewed PDF, which could be fitted by a log-normal distribution. The skewness of the heat flux is found to be radially and non-locally dependent: its value in the plasma core critically depends on the presence of gradients in the pedestal. The relation flux versus gradient is examined in detail. The local instantaneous flux versus gradient relation shows a hysteresis behaviour during an avalanche but no clear correlation, unlike the flux and zonal flow (ZF) shearing rate, which are anti-correlated: flux is higher when shearing rate is lower. This leads to corrugated time-averaged radial profiles of transport, heat and temperature gradient, with heat diffusivity having local maxima where the ZF shearing rate goes to zero and temperature gradient has local minima. Finally, we show how the flux versus gradient relation can be analysed locally for series of simulations with different averaged gradients.

Intrinsic strain-induced segregation in multiply twinned Cu-Pt icosahedra.

We present an atomistic simulation study on the compositional arrangements throughout Cu-Pt icosahedra, with a specific focus on the effects of inherent strain on general segregation trends. The coexistence of radial and site-selective segregation patterns is found in bimetallic nanoparticles for a broad range of sizes and compositions, consistent with prior analytical and atomistic models. Through a thorough comparison between the composition patterns and strain-related patterns, it is suggested that the presence of gradient and site-selective segregation is natural to largely relieve the inherent strain by preferential segregation of big atoms at tensile sites and vice versa, as previously hypothesized in the literature. Analogous to the case of single crystal particles, Cu-rich surface and damped oscillations can also be found in the outer shells of icosahedra, which are dominated by the lowering of both the surface energy and the chemical energy. The thermodynamic stability of segregated icosahedra is similar to segregated cuboctahedra but higher than disordered bulk alloys, validating prior thinking that element segregation driven by strain relief can extend the stability range of multiply-twinned nanoparticles. Our work sheds new light on understanding strain-induced segregation in multiply-twinned nanosystems that have elements with large lattice mismatch and strong alloying ability.

Pumping of electrolytes by electrical forces induced on the diffusion layer: A weakly nonlinear analysis

Pumping of electrolytes in microchannels can be achieved with the use of microelectrodes subjected to AC potentials. Experiments have shown an influence of Faradaic currents in the pumping performance, and theoretical studies for asymmetric electrolytes suggest that induced charges in the diffusion layer play an important role. In this work we consider the case of a diffusion layer induced by an array of electrodes subjected to a traveling wave potential and we include Faradaic currents. Previous theoretical studies considered the case of very small applied voltages, which allowed for two major simplifications: (i) Butler-Volmer (B-V) equation was linearized, and (ii) the presence of gradients in ion concentration was neglected. We extend previous results and used the full nonlinear B-V equation. A comparison with the linear limit shows that the flow rate in both cases coincides for voltages around and below ≈0.25 V. For voltages larger than this, the nonlinear equations show that gradients in ion concentration appear and have an important influence, therefore, the predictions deviate from the linear model. We show that the electrical force in the diffusion layer can induce pumping either in the same or the opposite direction of the applied traveling-wave potential and it could be responsible for the reversal of the flow as observed in experiments.

Solidification of fluid saturated in open-cell metallic foams with graded morphologies

Solidification of distilled water saturated in open-cell metallic foams with graded morphologies was investigated experimentally. Open-cell foams having different morphological properties including porosity, pore density (PPI) and materials for the porous matrix were cut into pieces and stacked up, forming a whole porous layer with gradient morphological features. Systematic measurements of temporal solidification front and full solidification time for distilled water saturated in the morphology gradient foams were carried out. Meanwhile, numerical simulations of solidification in fluid-saturated metallic foams with uniform morphological properties were performed. It was found that the presence of gradient in foam properties affect significantly the solidification rate and full solidification time. The results showed that compared to the single-layered foam with fixed morphology, the stacked foams with properly designed morphology gradient would reduce more effectively the full solidification time, due to the enhanced heat transfer.

Role of stress Echo on the Prognosis of Hypertrophic Cardiomyopathy

mtsAc ABSTRACT Background: Patients with hypertrophic cardiomyopathy (HCM) frequently present with confusing and misleading symptoms. In these instances stress tests may help to stratify the risk of future events. Objective: The purpose of this study was to assess the prognostic usefulness of the different variables obtained with exercise stress echo (ESE) in patients with HCM. Methods: A retrospective and observational study was performed in 110 patients evaluated with ESE. Patients were divided into 3 groups according to their left ventricular outflow tract obstruction level (LVOTO): 1) persistent LVOTO (peak instantaneous gradient at rest obtained by continuous Doppler ≥ 30 mmHg), 2) latent LVOTO (gradient ≥ 50 mmHg with exercise); and no LVOTO. Median follow-up was 2.7 years. The primary endpoint was the composite of death, sudden death, sustained ventricular tachycardia or hospitalization for heart failure. Results: Persistent LVOTO was present in 19.1% of cases, latent LVOTO in 31.8% and no LVOTO in 49.1%. Ventricular function, wall thicknesses and diameters were similar for the three groups. Poor prognostic variables were significantly higher for persistent LVOTO. The latent LVOTO group developed more symptoms, electrocardiographic changes and mitral regurgitation after exercise than the group without LVOTO, although it was not associated with a higher number of events. Variables that were associated with increased rate of events during follow-up were the presence of gradient ≥ 30 mmHg at rest (p=0.07), electrocardiographic changes during the test (p=0.020) and the inverse relationship of METs (p=0.07). Conclusions: Patients with HCM who achieved a high exercise capacity, expressed as METs ≥ 7, showed excellent mid- to long-term outcomes. LVOTO at rest and electrocardiographic changes during maximal stress exercise were associated with an increased number of events during follow-up.

Gradient-echo 3D imaging of Rb polarization in fiber-coupled atomic magnetometer

The analogy between atomic and nuclear spins is exploited to implement 3D imaging of polarization inside the cell of an atomic magnetometer. The resolution of 0.8mm×1.2mm×1.4mm has been demonstrated with the gradient-echo imaging method. The imaging can be used in many applications. One such an application is the evaluation of active volume of an atomic magnetometer for sensitivity analysis and optimization. It has been found that imaging resolution is limited due to de-phasing from spin-exchange collisions and diffusion in the presence of gradients, and for a given magnetometer operational parameters, the imaging sequence has been optimized. Diffusion decay of the signal in the presence of gradients has been modeled numerically and analytically, and the analytical results, which agreed with numerical simulations, have been used to fit the spin-echo gradient measurements to extract the diffusion coefficient. The diffusion coefficient was found in agreement with previous measurements.

The Relativistic Three-Dimensional Evolution of SN 1987A

The high velocities observed in supernovae require a relativistic treatment for the equation of motion in the presence of gradients in the density of the interstellar medium. The adopted theory is that of the thin layer approximation. The chosen medium is auto-gravitating with respect to an equatorial plane. The differential equation which governs the relativistic conservation of momentum is solved in numerically and by recursion. The asymmetric field of relativistic velocities as well the time dilation are plotted at the age of 1 yr for SN 1987A.

Taxonomic revision of the genusNeoheligmonellaDurette-Desset, 1971 (Nematoda, Heligmonellidae) parasitic in Muridae mainly from the Ethiopian Region

The genus Neoheligmonella Durette-Desset, 1971 (Nippostrongylinae) is revised and split into three genera, one of them with two subgenera. The new genera can be discriminated mainly by characters of the synlophe which had been not considered previously at the supraspecific level. These characters include the presence of a careen, the size of the right ridge relative to the left ridge, and the presence of gradients in the ridge size. The genus Neoheligmonella sensu stricto is proposed to include species with a careen, and it is divided into two subgenera: Neoheligmonella (Neoheligmonella) characterized by a right ridge measuring more than 45% of the ventral ridge of the careen, and Neoheligmonella (Duplantierus) n. subgen. with a right ridge measuring less than 45% of the ventral ridge of the careen. Dioufnema n. gen. includes one species with neither a careen nor hypertrophied ridges and having a bursa of type 1-3-1. Taranchonema n. gen. includes species without a careen, with the left ridge and the right ridge hypertrophied, and without a dorsal gradient in ridge size. A dichotomous key to the new genera and subgenera is provided. Five species of unknown synlophe, originally placed in the former genus Neoheligmonella and validated by other characters, are considered as Nippostrongylinae incertae sedis.

Gradients and Modulation of K+ Channels Optimize Temporal Accuracy in Networks of Auditory Neurons

Accurate timing of action potentials is required for neurons in auditory brainstem nuclei to encode the frequency and phase of incoming sound stimuli. Many such neurons express “high threshold” Kv3-family channels that are required for firing at high rates (>∼200 Hz). Kv3 channels are expressed in gradients along the medial-lateral tonotopic axis of the nuclei. Numerical simulations of auditory brainstem neurons were used to calculate the input-output relations of ensembles of 1–50 neurons, stimulated at rates between 100–1500 Hz. Individual neurons with different levels of potassium currents differ in their ability to follow specific rates of stimulation but all perform poorly when the stimulus rate is greater than the maximal firing rate of the neurons. The temporal accuracy of the combined synaptic output of an ensemble is, however, enhanced by the presence of gradients in Kv3 channel levels over that measured when neurons express uniform levels of channels. Surprisingly, at high rates of stimulation, temporal accuracy is also enhanced by the occurrence of random spontaneous activity, such as is normally observed in the absence of sound stimulation. For any pattern of stimulation, however, greatest accuracy is observed when, in the presence of spontaneous activity, the levels of potassium conductance in all of the neurons is adjusted to that found in the subset of neurons that respond better than their neighbors. This optimization of response by adjusting the K+ conductance occurs for stimulus patterns containing either single and or multiple frequencies in the phase-locking range. The findings suggest that gradients of channel expression are required for normal auditory processing and that changes in levels of potassium currents across the nuclei, by mechanisms such as protein phosphorylation and rapid changes in channel synthesis, adapt the nuclei to the ongoing auditory environment.

Dynamic Chains of Spiral Magnetic Domains

In this paper we present the results of investigation of spiral dynamic domains of a highly anisotropic iron garnet film with a perpendicular anisotropy in magnetic field with a constant dimensional gradient. The experiment showed how the presence of gradient of constant field affects the main parameters of spiral dynamic domains – geometrical form, life time, amount of orbits.

Bare bones pattern formation: a core regulatory network in varying geometries reproduces major features of vertebrate limb development and evolution.

BackgroundMajor unresolved questions regarding vertebrate limb development concern how the numbers of skeletal elements along the proximodistal (P-D) and anteroposterior (A-P) axes are determined and how the shape of a growing limb affects skeletal element formation. There is currently no generally accepted model for these patterning processes, but recent work on cartilage development (chondrogenesis) indicates that precartilage tissue self-organizes into nodular patterns by cell-molecular circuitry with local auto-activating and lateral inhibitory (LALI) properties. This process is played out in the developing limb in the context of a gradient of fibroblast growth factor (FGF) emanating from the apical ectodermal ridge (AER).ResultsWe have simulated the behavior of the core chondrogenic mechanism of the developing limb in the presence of an FGF gradient using a novel computational environment that permits simulation of LALI systems in domains of varying shape and size. The model predicts the normal proximodistal pattern of skeletogenesis as well as distal truncations resulting from AER removal. Modifications of the model's parameters corresponding to plausible effects of Hox proteins and formins, and of the reshaping of the model limb, bud yielded simulated phenotypes resembling mutational and experimental variants of the limb. Hypothetical developmental scenarios reproduce skeletal morphologies with features of fossil limbs.ConclusionsThe limb chondrogenic regulatory system operating in the presence of a gradient has an inherent, robust propensity to form limb-like skeletal structures. The bare bones framework can accommodate ancillary gene regulatory networks controlling limb bud shaping and establishment of Hox expression domains. This mechanism accounts for major features of the normal limb pattern and, under variant geometries and different parameter values, those of experimentally manipulated, genetically aberrant and evolutionary early forms, with no requirement for an independent system of positional information.

Comment on “Signatures of Surface States in Bismuth at High Magnetic Fields”

Nernst effect is the transverse electric field due to a longitudinal thermal gradient in presence of magnetic field. Its magnitude was recently studied up to 33 T in a bismuth single crystal with a magnetic field oriented along the trigonal axis . In addition to quantum oscillations of the Nernst response, a rich structure with several additional peaks was also detected when the magnetic field exceeded the quantum limit, which is of the order of 10 T in this configuration. The origin of these high-field Nernst anomalies is a subject of ongoing research. Very recently, Seradjeh, Wu, and Phillips have suggested that a surface state can give rise to these anomalies. This proposal does not resist a critical examination.

Nernst effect and dimensionality in the quantum limit

Nernst effect, the transverse voltage generated by a longitudinal thermal gradient in presence of magnetic field has recently emerged as a very sensitive, yet poorly understood, probe of electron organization in solids. Here we report on an experiment on graphite, a macroscopic stack of graphene layers, which establishes a fundamental link between dimensionality of an electronic system and its Nernst response. In sharp contrast with single-layer graphene, the Nernst signal sharply peaks whenever a Landau level meets the Fermi level. This points to the degrees of freedom provided by finite interlayer coupling as a source of enhanced thermoelectric response in the vicinity of the quantum limit. Since Landau quantization slices a three-dimensional Fermi surface, each intersection of a Landau level with the Fermi level modifies the Fermi surface topology. According to our results, the most prominent signature of such a topological phase transition emerges in the transverse thermoelectric response.

On the thermodynamics of higher-order gradient plasticity for size-effects at the micron and submicron length scales

A physically motivated and thermodynamically consistent formulation of higher-order gradient plasticity theory is presented. This proposed model is a two non-local parameter framework that takes into consideration: (1) the presence of plastic strain gradients, which is motivated by the evolution of dislocation density tensor that results from non-vanishing net Burgers vector and, hence, incorporating additional kinematic hardening and (2) the presence of gradients in the equivalent (effective) plastic strain (history variable), which is motivated by the accumulation of geometrically necessary dislocations and, hence, incorporating additional isotropic hardening. It is demonstrated that the non-local yield condition, flow rule and non-classical microscopic boundary conditions can be derived directly from the principle of virtual power. It is also shown that the local Clausius-Duhem inequality does not hold for gradient-dependent material and, therefore, a non-local form should be adopted. Applications of the proposed theory for size effects in metallic thin films are presented.