Longitudinal Electrical Conductivity Research Articles

Effective description of hot QCD medium in strong magnetic field and longitudinal conductivity

Hot QCD medium effects have been studied in the effective quasi-particle description of quark-gluon plasma. This model encodes the collective excitation of gluons and quarks/anti-quarks in the thermal medium in terms of effective quarks and gluons having non-trivial energy dispersion relation. The present investigation involves the extension of the effective quasi-particle model in strong magnetic field limit. Realizing, hot QCD medium in the strong magnetic field as an effective grand canonical system in terms of the modified quark, anti-quark and gluonic degrees of freedom, the thermodynamics has been studied. Further, the Debye mass in hot QCD medium has to be sensitive to the magnetic field, and subsequently the same has been observed for the effective hot QCD coupling. As an implication, electrical conductivity (longitudinal) has been studied within an effective kinetic theory description of hot QCD in the presence of the strong magnetic field. The hot QCD equation of state (EoS), dependence entering through the effective coupling and quasi-parton distribution function, found to have a significant impact on the longitudinal electrical conductivity in strong magnetic field background.

Longitudinal conductivity in strong magnetic field in perturbative QCD: Complete leading order

We compute the longitudinal electrical conductivity in the presence of strong background magnetic field in complete leading order of perturbative QCD, based on the assumed hierarchy of scales $\alpha_s eB\ll (m_q^2,T^2)\ll eB$. We formulate an effective kinetic theory of lowest Landau level quarks with the leading order QCD collision term arising from 1-to-2 processes that become possible due to 1+1 dimensional Landau level kinematics. In small $m_q/T\ll 1$ regime, the longitudinal conductivity behaves as $\sigma_{zz}\sim e^2(eB)T/(\alpha_s m_q^2\log(m_q/T))$, where the quark mass dependence can be understood from the chiral anomaly with the axial charge relaxation provided by a finite quark mass $m_q$. We also present parametric estimates for the longitudinal and transverse "color conductivities" in the presence of strong magnetic field, by computing dominant damping rates for quarks and gluons that are responsible for color charge transportation. We observe that the longitudinal color conductivity is enhanced by strong magnetic field, which implies that the sphaleron transition rate in perturbative QCD is suppressed by strong magnetic field due to the enhanced Lenz's law in color field dynamics.

Effect of carbon nanotubes on the thermoelectric properties of CFRP laminate for aircraft applications

The present paper focuses on the thermoelectric behavior of carbon nanotube-charged carbon fiber-reinforced polymer composite materials for aircraft applications. Two types of samples: Type A with carbon nanotube and Type B without carbon nanotube), and with two different stacking sequences (unidirectional—[0]8, cross orthogonal—[0/90]4) were manufactured for the thermoelectric experiments, DC electrical current was injected through the specimens, and the temperature of the specimens was monitored simultaneously in order to deduce the effect of carbon nanotube on the electrical conductivity change of the specimen. During the test, transient and steady temperature fields were measured on the sample surfaces by infrared thermography, and real-time voltage measurements monitor the sample electrical resistance. The results show that the presence of carbon nanotube produces increasing values of longitudinal electric conductivity σ L of about 10%. At 9 A, the maximum temperature value is around 95℃ for unidirectional and 145℃ for cross orthogonal samples. The presence of carbon nanotube tends to decrease the entire range of maximum temperatures, about 7% on average for the unidirectional and about 4% on average for cross orthogonal samples.

Thermoelectric properties of Weyl and Dirac semimetals

We study the electronic contribution to the thermal conductivity and the thermopower of Weyl and Dirac semimetals using a semiclassical Boltzmann approach. We investigate the effect of various relaxation processes including disorder and interactions on the thermoelectric properties, and also consider doping away from the Weyl or Dirac point. We find that the thermal conductivity and thermopower have an interesting dependence on the chemical potential that is characteristic of the linear electronic dispersion, and that the electron-electron interactions modify the Lorenz number. For the interacting system, we also use the Kubo formalism to obtain the transport coefficients. We find exact agreement between the Kubo and Boltzmann approaches at high temperatures. We also consider the effect of electric and magnetic fields on the thermal conductivity in various orientations with respect to the temperature gradient. Notably, when the temperature gradient and magnetic field are parallel, we find a large contribution to the longitudinal thermal conductivity that is quadratic in the magnetic field strength, similar to the magnetic field dependence of the longitudinal electrical conductivity due to the presence of the chiral anomaly when no thermal gradient is present.

Photoinduced quantum spin and valley Hall effects, and orbital magnetization in monolayerMoS2

We theoretically demonstrate that 100\% valley-polarized transport in monolayers of MoS$_{2}$ and other group-VI dichalcogenides can be obtained using off-resonant circularly polarized light. By tuning the intensity of the off-resonant light the intrinsic band gap in one valley is reduced, while it is enhanced in the other valley, enabling single valley quantum transport. As a consequence, we predict (i) enhancement of the longitudinal electrical conductivity, accompanied by an increase in the spin-polarization of the flowing electrons, (ii) enhancement of the intrinsic spin Hall effect, together with a reduction of the intrinsic valley Hall effect, and (iii) enhancement of the orbital magnetic moment and orbital magnetization. These mechanisms provide appealing opportunities to the design of nanoelectronics based on dichalcogenides.

Longitudinal electric conductivity in a quantum plasma with a variable collision frequency in the framework of the Mermin approach

In the framework of the Mermin approach, we obtain formulas for the longitudinal electric conductivity in a quantum collisional plasma with a collision frequency depending on the momentum. We use a kinetic equation in the momentum space in the relaxation approximation. We show that as the Planck constant tends to zero, the derived formula transforms into the corresponding formula for a classical plasma. We also show that as the frequency of collisions between plasma particles tends to zero (the plasma transforms into a collisionless plasma), the derived formula transforms into the well-known Klimontovich-Silin formula for the collisionless plasma. We show that if the collision frequency is constant, then the derived formula for the permittivity transforms into the well-known Mermin formula.

Inhomogeneous longitudinal electric field-induced anomalous Hall conductivity in a ferromagnetic two-dimensional electron gas

We consider a five-dimensional Minimal Supersymmetric Standard Model compactified on a S1/Z2 orbifold, and study the evolution of neutrino masses, mixing angles and phases for different values of tan beta and different radii of compactification. We consider the usual four dimensional Minimal Supersymmetric Standard Model limit plus two extra-dimensional scenarios: where all matter superfields can propagate in the bulk, and where they are constrained to the brane. We discuss in both cases the evolution of the mass spectrum, the implications for the mixing angles and the phases. We find that a large variation for the Dirac phase is possible, which makes models predicting maximal leptonic CP violation especially appealing.

Influence of topological transitions in a quantizing magnetic field and anisotropy of current carrier scattering by acoustic phonons on the longitudinal electrical conductivity of layered crystals with open fermi surfaces

It is demonstrated that the dependence of Fermi’s energy on the magnetic field causes a set of the Shubnikov – de Haas (SDH) oscillation frequencies to change, and their relative contribution to the total longitudinal conductivity of layered crystals depends on whether the scattering of current carriers is isotropic or anisotropic. Owing to the topological transition in a strong magnetic field, Fermi’s surface (FS) is transformed from open into closed one and is compressed in the magnetic field direction. Therefore, in an ultraquantum limit, disregarding the Dingle factor, the longitudinal electrical conductivity of the layered crystal tends to zero as a reciprocal square of the magnetic field for the isotropic scattering and as a reciprocal cube of the magnetic field for the anisotropic scattering. All calculations are performed in the approximation of relaxation time considered to be constant versus the quantum numbers for the isotropic scattering and proportional to the longitudinal velocity of current carriers for the anisotropic scattering.

Electrical conductivity of double-walled carbon nanotubes in the framework of the Hubbard model

The electrical conductivity of double-walled carbon nanotubes of the “armchair” type with the ABAB packing of layers is investigated theoretically. The temperature dependences of the longitudinal electrical conductivity σ(T) for a number of double-walled carbon nanotubes, such as the (3, 3)@(8, 8), (5, 5)@(10, 10), (8, 8)@(13, 13), (10, 10)@(15, 15), and (15, 15)@(20, 20) nanotubes, are obtained in the framework of the Hubbard model with the use of the Green’s function method. It is revealed that the dependences of the electrical conductivity for single-walled and double-walled carbon nanotubes exhibit different behavior in the temperature range from 30 to 60 K. In particular, the dependence of the electrical conductivity for the double-walled carbon nanotubes flattens out in this temperature range.

Effects of warm water inflows on the dispersion of pollutants in small reservoirs

The effects of the warm water discharged by a nuclear power plant (NPP) into a small reservoir are studied. A case study is presented (José Cabrera NPP—Zorita Hidráulica Reservoir) with experimental data of the reservoir stratification and predicted data of the dispersion of radioactive pollutants from operative or accidental releases. The vertical and longitudinal temperature profiles, electrical conductivity and transparency of the reservoir water were measured for an annual cycle. The results indicate that the continuous warm water discharge from the NPP causes permanent and artificial reservoir stratification. The stratification is significant within 1500 m upstream and 1000 m downstream from the warm water outfall. The pollutant dispersion has been predicted by using a flow model based on N T perfect-mixing compartments in series with feedback. The model parameter, N T , is calculated from the longitudinal diffusion coefficient. The prediction of pollutant dispersion by means of this model shows that the stratification slows down the vertical mixing in the whole water body, and reduces the reservoir volume that is effective for the dilution and dispersion of pollutants. This means that, in the case of a radioactive pollutant release, the reservoir radioactivity level could increase significantly.

High-temperature quantum size oscillations of the conductivity in thin metal films

The longitudinal electrical conductivity of a thin conducting film in the presence of electron and hole groups of charge carriers is calculated by the Kubo method under conditions such that the carrier motion is spatially quantized. It is shown that in the case of elastic scattering on impurities there are quantum high-temperature oscillations of the conductivity which are relatively insensitive to the temperature smearing of the Fermi level.

Quantitative damage detection in CFRP composites: coupled mechanical and electrical models

Electrical resistance in carbon-fiber reinforced polymers has been shown experimentally to be a sensitive measure of internal damage. To quantify the dependence of electrical resistance on mechanical fiber damage at the micromechanical level, a numerical electrical resistor network model has been developed. The electrical model is coupled to the fiber damage through a numerical mechanical model, which here is a shear-lag model; the latter informs the electrical model of the locations of broken fibers and the stresses on unbroken sections of fiber. The electrical model accounts for both the longitudinal fiber electrical conductivity and the occasional fiber–fiber contacts that permit electrical coupling of touching fibers. An earlier analytic model based on the global load sharing (GLS) theory is tested against the numerical simulations. Good agreement is found for voltage leads that contact the ends of all fibers in the composite and when the “electrical ineffective length” in the GLS model is related to the density of fiber contacts f c in the numerical model by the relationship δ ce eff = L (1+f c L) where L is the sample gauge length. Voltage leads that contact only surface fibers lead to a resistance behavior that cannot be predicted by the analytic model; this demonstrates the spatial sensitivity of the electrical response to damage and the need for simulation models to correlate local electrical response to local damage. Sensitivity of the electrical response to the voltage lead geometry suggests that the coupled numerical model can be used to design electrode arrays to optimize spatial damage detection inside composite structures.

Anisotropic electrical conduction in gum arabica—a biopolymer

Gum arabica, a natural biopolymer, exhibits electrical properties like conducting polymers. Earlier investigations show its ion-conducting superionic nature rather than its proton conducting nature with room temperature d.c. conductivity 10e−07 S/cm. The present study shows more interesting electrical characters gum arabica, XRD study of its powdered sample shows an amorphous nature and that of caste and textured specimen show an increased RDF. The same indicates a possibility of crystallization, which is a difficult task for this solid gel-like substance. Specimen with preferred molecular orientation is prepared by casting thin layer of gum arabica on scratched (∼10 μm) metal electrode and glass substrate. The desired anisotropy thus produced is confirmed by XRD study. The morphology of ordinarily caste specimen and textured specimen were studied and compared by SEM study. The impedance spectroscopy carried over this specimen shows an electrical conductivity like that of crystalline conducting polymer. Transverse and longitudinal electrical conductivity with their frequency dispersion show marked difference. Its further investigation and applications are under progress.

A thermodynamic basis for charged particles transport in viscoelastic fluids

A calculation for the generalized longitudinal stress modulus and electric conductivity in an ionic-viscoelastic medium is presented. The system is described within the framework of extended irreversible thermodynamics in terms of the regular conserved variables and of an additional set of independent variables consisting of the stress tensor, its trace, and the electric flux. Using the standard procedure, we derive the time evolution equations for the additional variables. These equations are used to obtain general wave vector and frequency dependent expressions for measurable properties of the system. We obtain for the linear case results that have not been derived previously in the literature.

A simulation of cardiac action currents having curl.

A digital simulation of a two dimensional cardiac slice has been performed. It is stimulated at the center and an action potential propagates outward. An anisotropic bidomain model is used in which fast sodium physiology connects the intracellular and extracellular domains. For cases in which the inner asymmetry (expressed as longitudinal versus transverse electrical conductivity) is greater than the outer asymmetry, a current flow pattern is observed for which there is nonzero curl. Such a result explains recent observations of nonzero Bz magnetic field detected above a slab of tissue in the x-y plane. The current loop producing this field consists of outer domain current in the longitudinal direction flowing around in space to return at the AP location in the transverse direction in the outer domain and then completing the loop in the longitudinal direction by passing distally through the AP in the inner domain where resistance is extremely low.

The longitudinal electrical conductivity of metal matrix composites at cryogenic temperature in the presence of a longitudinal magnetic field

Utilisation des resultats de la partie I pour deduire deux expressions integrales pour la conductivite electrique, quand un champ magnetique B est ajoute a un faible champ electrique egalement parallele aux fibres

Physical properties of phenanthrene-TCNQ complex

The 1:1 charge-transfer complex of phenanthrene (PH) and TCNQ has been prepared and characterized. It is stable at 195°C under nitrogen atmosphere. Its charge-transfer band is found at 520 nm (2.38 eV) in the solid state. Longitudinal electrical conductivity is 2.37 × 10 −7 Scm −1 at 300 K with activation energy of 0.32 eV. The energy gap (0.64 eV) associated with this semiconductor is much smaller than the energy of the charge-transfer excitation. The diamagnetic susceptibility of this complex is found to be less than the sum of the constituent molecules indicates that PH-TCNQ is weakly paramagnetic.

Remarks on the use of Boltzmann's equation for electrical conduction calculations in metal matrix and in situ composites

The Boltzmann equation and its solutions are cental to the development of microscopic models describing the longitudinal and transverse electrical conductivity of metal matrix and in situ composites. Such solutions are needed to describe electron and phonon scattering and transport phenomena in the matrix due to the presence of a second filamentary phase, and to describe electrical conductivity at cryogenic and higher temperatures. In this paper, we derive solutions to the Boltzmann equation in the relaxation time approximation in cylindrical coordinates. It is shown that one solution for the electric field parallel to the fibre direction leads to an expression for composite conductivity at cryogenic and higher temperatures. We also present a solution for the case in which the electric field is normal to the fibre direction.

Nonlinear piezoresistance in p-type silicon

An investigation was made of the longitudinal and transverse piezoresistance and electrical conductivity of p-type silicon under conditions of uniaxial compression, x‖ [111], in the temperature range 77–300°K and hole concentration range 2.1015−5.1018 cm−3. The transverse component of the electrical conductivity tensor, ‖ [11¯2], was found to depend nonmonotonically on the degree of compression. Compression decreases π44 and increases the combination π11+ 2π12. The nonlinearity oi the longitudinal piezoresistance increases with increasing hole concentration and T = 77°K. The results are explained by the rearrangement of the valence band under the deformation and the formation near the top of this band of a section of the spectrum described in the approximation of “low” energies of Pikus-Bir theory.

Effects of ultrasonic waves on linear longitudinal conductivity in non-degenerate semiconductors

Effects of ultrasonic waves propagating at an angle theta relative to the direction of a DC magnetic field on the linear longitudinal electrical conductivity in non-degenerate semiconductors such as n-type InSb have been studied by using a quantum treatment which is valid at high frequencies and in strong magnetic fields. Numerical results show that the linear longitudinal conductivity depends strongly on the DC magnetic field, the sound frequency, the temperature, and the direction of the propagation of ultrasonic waves relative to that of the field.