1,827 research outputs found
Magnetoresistance from Fermi Surface Topology
Extremely large non-saturating magnetoresistance has recently been reported
for a large number of both topologically trivial and non-trivial materials.
Different mechanisms have been proposed to explain the observed
magnetotransport properties, yet without arriving to definitive conclusions or
portraying a global picture. In this work, we investigate the transverse
magnetoresistance of materials by combining the Fermi surfaces calculated from
first principles with the Boltzmann transport theory approach relying on the
semiclassical model and the relaxation time approximation. We first consider a
series of simple model Fermi surfaces to provide a didactic introduction into
the charge-carrier compensation and open-orbit mechanisms leading to
non-saturating magnetoresistance. We then address in detail magnetotransport in
three representative materials: (i) copper, a prototypical nearly free-electron
metal characterized by the open Fermi surface that results in an intricate
angular magnetoresistance, (ii) bismuth, a topologically trivial semimetal in
which very large magnetoresistance is known to result from charge-carrier
compensation, and (iii) tungsten diphosphide WP2, a recently discovered type-II
Weyl semimetal that holds the record of magnetoresistance in compounds. In all
three cases our calculations show excellent agreement with both the field
dependence of magnetoresistance and its anisotropy measured at low
temperatures. Furthermore, the calculations allow for a full interpretation of
the observed features in terms of the Fermi surface topology. These results
will help addressing a number of outstanding questions, such as the role of the
topological phase in the pronounced large non-saturating magnetoresistance
observed in topological materials.Comment: 13 pages, 9 figure
Concerted suppressive effects of carisbamate, an anti-epileptic alkyl-carbamate drug, on voltage-gated Na+ and hyperpolarization-activated cation currents
Carisbamate (CRS, RWJ-333369) is a new anti-seizure medication. It remains unclear whether and how CRS can perturb the magnitude and/or gating kinetics of membrane ionic currents, despite a few reports demonstrating its ability to suppress voltage-gated Na+ currents. In this study, we observed a set of whole-cell current recordings and found that CRS effectively suppressed the voltage-gated Na+ (INa) and hyperpolarization-activated cation currents (Ih) intrinsically in electrically excitable cells (GH3 cells). The effective IC50 values of CRS for the differential suppression of transient (INa(T)) and late INa (INa(L)) were 56.4 and 11.4 μM, respectively. However, CRS strongly decreased the strength (i.e., Δarea) of the nonlinear window component of INa (INa(W)), which was activated by a short ascending ramp voltage (Vramp); the subsequent addition of deltamethrin (DLT, 10 μM) counteracted the ability of CRS (100 μM, continuous exposure) to suppress INa(W). CRS strikingly decreased the decay time constant of INa(T) evoked during pulse train stimulation; however, the addition of telmisartan (10 μM) effectively attenuated the CRS (30 μM, continuous exposure)-mediated decrease in the decay time constant of the current. During continued exposure to deltamethrin (10 μM), known to be a pyrethroid insecticide, the addition of CRS resulted in differential suppression of the amplitudes of INa(T) and INa(L). The amplitude of Ih activated by a 2-s membrane hyperpolarization was diminished by CRS in a concentration-dependent manner, with an IC50 value of 38 μM. For Ih, CRS altered the steady-state I–V relationship and attenuated the strength of voltage-dependent hysteresis (Hys(V)) activated by an inverted isosceles-triangular Vramp. Moreover, the addition of oxaliplatin effectively reversed the CRS-mediated suppression of Hys(V). The predicted docking interaction between CRS and with a model of the hyperpolarization-activated cyclic nucleotide-gated (HCN) channel or between CRS and the hNaV1.7 channel reflects the ability of CRS to bind to amino acid residues in HCN or hNaV1.7 channel via hydrogen bonds and hydrophobic interactions. These findings reveal the propensity of CRS to modify INa(T) and INa(L) differentially and to effectively suppress the magnitude of Ih. INa and Ih are thus potential targets of the actions of CRS in terms of modulating cellular excitability
Mucosal Macrophage Polarization Role in the Immune Modulation
Immunotherapy has advantages including few side effects and low probability of abuse by patients. Recently, functional materials with immunomodulatory functions, which act through reduction of free radicals, have been developed for cancer and anti-inflammatory therapy. However, the therapeutic application of natural functional materials involves a complex mechanism along with various organic factors. These substances, including polysaccharides and triterpenoids, have immunomodulatory effects. However, to our knowledge, the mechanism underlying the action of such substances in the physiological immunity of animals remains unclear. Immune cells, particularly macrophages, are crucial in the modulation of immune response. Macrophages polarise into two types, namely, M1 and M2, from the M0 form, based on the physiological microenvironment factors. M1 macrophages have functions in pathogen elimination through phagocytosis, oxidative damage, and complement system activation. M2 macrophages are involved in tissue recovery and tumour tissues containing ample M2 macrophages that release growth factors, which promote angiogenesis. In this study, we focus on the immunomodulation of the macrophage to further understand the effects of the physiological microenvironment factors on macrophage polarisation
Polarisation of Macrophage and Immunotherapy in the Wound Healing
Immune cells are involved in virtually every aspect of the wound repair process, from the initial stages where they participate in haemostasis and work to prevent infection to later stages where they drive scar formation. Immunotherapy is being developed offers some advantageous immunomodulation factors that are known in the field of alternative medicine, such as mushroom beta-glucan, anti-microbial peptides and triterpenoid; these factors represent a novel therapeutic approach for anti-inflammation to promote the wound healing
Giant vortex and Skyrmion in a rotating two-species Bose-Einstein condensate
Numerical simulations are performed for a rotating two-species Bose
condensate confined by a harmonic potential. The particle numbers of each
species are unequal. When the rotational speed exceeds a critical value, the
majority species reside in the center of the potential while the minority
species is pushed out to the outskirts, forming a giant vortex hole to contain
the majority species. A novel annular Skyrmion forms at the interface of the
two species.Comment: 5 pages, 5 figure
Magnetothermoelectric DC conductivities from holography models with hyperscaling factor in Lifshitz spacetime
We investigate an Einstein-Maxwell-Dilaton-Axion holographic model and obtain
two branches of a charged black hole solution with a dynamic exponent and a
hyperscaling violation factor when a magnetic field presents. The
magnetothermoelectric DC conductivities are then calculated in terms of horizon
data by means of holographic principle. We find that linear temperature
dependence resistivity and quadratic temperature dependence inverse Hall angle
can be achieved in our model. The well-known anomalous temperature scaling of
the Nernst signal and the Seebeck coefficient of cuprate strange metals are
also discussed.Comment: 1+23 pages, 4 figures, references adde
Simulation of Two-Fluid Flows by the Least-Squares Finite Element Method Using a Continuum Surface Tension Model
In this paper a numerical procedure for simulating two-fluid flows is presented. This procedure is based on the Volume of Fluid (VOF) method proposed by Hirt and Nichols and the continuum surface force (CSF) model developed by Brackbill, et al. In the VOF method fluids of different properties are identified through the use of a continuous field variable (color function). The color function assigns a unique constant (color) to each fluid. The interfaces between different fluids are distinct due to sharp gradients of the color function. The evolution of the interfaces is captured by solving the convective equation of the color function. The CSF model is used as a means to treat surface tension effect at the interfaces. Here a modified version of the CSF model, proposed by Jacqmin, is used to calculate the tension force. In the modified version, the force term is obtained by calculating the divergence of a stress tensor defined by the gradient of the color function. In its analytical form, this stress formulation is equivalent to the original CSF model. Numerically, however, the use of the stress formulation has some advantages over the original CSF model, as it bypasses the difficulty in approximating the curvatures of the interfaces. The least-squares finite element method (LSFEM) is used to discretize the governing equation systems. The LSFEM has proven to be effective in solving incompressible Navier-Stokes equations and pure convection equations, making it an ideal candidate for the present applications. The LSFEM handles all the equations in a unified manner without any additional special treatment such as upwinding or artificial dissipation. Various bench mark tests have been carried out for both two dimensional planar and axisymmetric flows, including a dam breaking, oscillating and stationary bubbles and a conical liquid sheet in a pressure swirl atomizer
Evidence for Effective Multiple K+-Current Inhibitions by Tolvaptan, a Non-peptide Antagonist of Vasopressin V2 Receptor
Tolvaptan (TLV), an oral non-peptide antagonist of vasopressin V2 receptor, has been increasingly used for managements in patients with hyponatremia and/or syndrome of inappropriate antidiuretic hormone secretion. However, none of the studies have thus far been investigated with regard to its possible perturbations on membrane ion currents in endocrine or neuroendocrine cells. In our electrophysiological study, the whole-cell current recordings showed that the presence of TLV effectively and differentially suppressed the amplitude of delayed rectifier K+ (IK(DR)) and M-type K+ current (IK(M)) in pituitary GH3 cells with an IC50 value of 6.42 and 1.91 μM, respectively. This compound was also capable of shifting the steady-state activation curve of IK(M) to less depolarized potential without any appreciable change in the gating charge of this current. TLV at a concentration greater than 10 μM also suppressed the amplitude of erg-mediated K+ current or the activity of large-conductance Ca2+-activated K+ channels; however, this compound failed to alter the amplitude of hyperpolarization-activated cation current in GH3 cells. In vasopressin-preincubated GH3 cells, TLV-mediated suppression of IK(M) remained little altered. Under current-clamp condition, we also observed that addition of TLV increased the firing of spontaneous action potentials in GH3 cells and further addition of flupirtine could reverse TLV-mediated elevation of the firing. In Madin-Darby canine kidney (MDCK) cells, the K+ current elicited by long ramp pulse was also effectively subject to inhibition by this compound. Findings from the present study were thus stated as saying that the suppression by TLV of multiple type K+ currents could be direct and independent of its antagonism of vasopressin V2 receptors. Our study also reveals an important aspect that should be considered when assessing aquaretic effect of TLV or its structurally similar compounds
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