Presence Of Transport Research Articles

Geometric phaselike effects of driven transport in presence of reservoir squeezing.

In a bare bosonic site coupled to two reservoirs, we explore the statistics of boson exchange in the presence of two simultaneous processes: squeezing the two reservoirs and driving the two reservoirs. The squeezing parameters compete with the geometric phaselike effect or geometricity to alter the nature of the steady-state flux and noise. The even (odd) geometric cumulants and the total minimum entropy are found to be symmetric (antisymmetric) with respect to exchanging the left and right squeezing parameters. Upon increasing the strength of the squeezing parameters, loss of geometricity is observed. Under maximum squeezing, one can recover a standard steady-state fluctuation theorem even in the presence of phase-different driving protocol. A recently proposed modified geometric thermodynamic uncertainty principle is found to be robust.

Subdiffusive transport of runaway electrons in presence of small amplitude MHD perturbations in COMPASS

Radial transport of runaway electrons (REs) in tokamaks is affected by the presence of magnetic perturbations, either caused by internal magnetohydrodynamic instabilities or induced by external coils. The magnetic field configuration inside the plasma volume consists in general of intact magnetic surfaces alternated with magnetic islands and stochastic layers, which make the usual diffusive approach, based on the Rechester–Rosenbluth formula, inadequate to the study of transport. Here the fractional diffusion approach is employed to model RE transport in presence of intrinsic magnetic perturbations (magnetic islands) in the flat-top phase of RE-dedicated discharges on COMPASS tokamak. The character of RE transport is found to be subdiffusive. The degree of subdiffusion is evaluated by running simulations with the ORBIT code and a time-fractional diffusion equation is applied to calculate the time evolution of RE particle number. The results are compared with the observed RE losses, estimated from the time integrated neutron signal.

Investigation of Monte Carlo simulations of the electron transport in external magnetic fields using Fano cavity test

PurposeMonte Carlo simulations are crucial for calculating magnetic field correction factors kB for the dosimetry in external magnetic fields. As in Monte Carlo codes the charged particle transport is performed in straight condensed history (CH) steps, the curved trajectories of these particles in the presence of external magnetic fields can only be approximated. In this study, the charged particle transport in presence of a strong magnetic field B→ was investigated using the Fano cavity test. The test was performed in an ionization chamber and a diode detector, showing how the step size restrictions must be adjusted to perform a consistent charged particle transport within all geometrical regions. MethodsMonte Carlo simulations of the charged particle transport in a magnetic field of 1.5 T were performed using the EGSnrc code system including an additional EMF-macro for the transport of charged particle in electro-magnetic fields. Detailed models of an ionization chamber and a diode detector were placed in a water phantom and irradiated with a so called Fano source, which is a monoenergetic, isotropic electron source, where the number of emitted particles is proportional to the local density. ResultsThe results of the Fano cavity test strongly depend on the energy of charged particles and the density within the given geometry. By adjusting the maximal length of the charged particle steps, it was possible to calculate the deposited dose in the investigated regions with high accuracy (<0.1%). The Fano cavity test was performed in all regions of the detailed detector models. Using the default value for the step size in the external magnetic field, the maximal deviation between Monte Carlo based and analytical dose value in the sensitive volume of the ion chamber and diode detector was 8% and 0.1%, respectively. ConclusionsThe Fano cavity test is a crucial validation method for the modeled detectors and the transport algorithms when performing Monte Carlo simulations in a strong external magnetic field. Special care should be given, when calculating dose in volumes of low density. This study has shown that the Fano cavity test is a useful method to adapt particle transport parameters for a given simulation geometry.

Interplay of band geometry and topology in ideal Chern insulators in the presence of external electromagnetic fields

Ideal Chern insulating phases arise in two-dimensional systems with broken time-reversal symmetry. They are characterized by having nearly-flat bands, and a uniform quantum geometry -- which combines the Berry curvature and quantum metric -- and by being incompressible. In this work, we analyze the role of the quantum geometry in ideal Chern insulators aiming to describe transport in presence of external out-of-plane magnetic and electric fields. We firstly show that in the absence of external perturbations, novel Berry connections appear in ideal Chern insulating phases. Secondly, we provide a detailed analysis of the deformation of the quantum geometry once weak out-of-plane magnetic fields are switched on. The perturbed Berry curvature and quantum metric provide an effective quantum geometry, which is analyzed in the insulating regime and provides an application of our novel connections. The conditions under which the Girvin-MacDonald-Platzman algebra is realized in this situation are discussed. Furthermore, an investigation of electrical transport due to the new effective quantum geometry is presented once an electric field is added. Restricting to the case of two bands in the metallic regime the quantum metric appears as measurable quantum mechanical correction in the Hall response. Our findings can be applied, for instance, to rhombohedral trilayer graphene at low energies.

Novel and versatile PEI modified ZIF-8 hollow nanotubes to construct CO2 facilitated transport pathway in MMMs

1D nanotube (HNT) based MMM presents high CO2 permeation due to its long and hollow structure. However, the improvement of selectivity is still challenging. In this study, small PEI molecules with abundant amino groups were introduced into the nanocages of ZIF-8 HNTs to construct facilitated CO2 transmission channel with low resistance. In the PEI@ZIF-8 HNTs, the –NH2 groups can facilitate CO2 transport in presence of H2O, resulting in an improvement in both CO2 permeability and selectivity. Second, the introduction of PEI into the nanocages of ZIF-8 can adjust the effective sieving size to enhance CO2 selectivity. Third, the hydrogen bond between PEI and Pebax can strengthen the interfacial compatibility, further improving CO2/N2 selectivity of the MMMs. Finally, the 1D hollow structure of PEI@ZIF-8 HNTs provides CO2 molecules with low-resistance and fast transport channel, enhancing the CO2 permeability. Consequently, both the high CO2 permeability and the high CO2/N2 selectivity are acquired by the versatile filler of PEI@ZIF-8 HNTs. PEI@ZIF-8 HNTs based MMM at filler loading of 7 wt% under dry mixed gas, presents CO2 permeability of 177 Barrer and CO2/N2 selectivity of 72, which are 40% and 10.8% higher than those of ZIF-8 HNTs based MMM, respectively. Moreover, the permeability of CO2 and the selectivity of CO2/N2 reach 306 Barrer and 79 respectively under the wet mixed gas, which is far beyond the Robeson upper bound in 2008 and exceeds the McKeown upper bound in 2019. The proposed PEI@ZIF-8 HNTs are believed to be promising filler for MMMs based CO2 capture.

Infrared and NMR Spectroscopic Fingerprints of the Asymmetric H7+ O3 Complex in Solution.

Infrared (IR) absorption in the 1000–3700 cm−1 range and 1H NMR spectroscopy reveal the existence of an asymmetric protonated water trimer, H7 +O3, in acetonitrile. The core H7 +O3 motif persists in larger protonated water clusters in acetonitrile up to at least 8 water molecules. Quantum mechanics/molecular mechanics (QM/MM) molecular dynamics (MD) simulations reveal irreversible proton transport promoted by propagating the asymmetric H7 +O3 structure in solution. The QM/MM calculations allow for the successful simulation of the measured IR absorption spectra of H7 +O3 in the OH stretch region, which reaffirms the assignment of the H7 +O3 spectra to a hybrid‐complex structure: a protonated water dimer strongly hydrogen‐bonded to a third water molecule with the proton exchanging between the two possible shared‐proton Zundel‐like centers. The H7 +O3 structure lends itself to promoting irreversible proton transport in presence of even one additional water molecule. We demonstrate how continuously evolving H7 +O3 structures may support proton transport within larger water solvates.

Transport across twist angle domains in moiré graphene

Many of the experiments in twisted bilayer graphene (TBG) differ from each other in terms of the details of their phase diagrams. Few controllable aspects aside, this discrepancy is largely believed to be arising from the presence of a varying degree of twist angle inhomogeneity across different samples. Real space maps indeed reveal TBG devices splitting into several large domains of different twist angles. Motivated by these observations, we study the quantum mechanical tunneling across a domain wall (DW) that separates two such regions. We show that the tunneling of the moir\'e particles can be understood by the formation of an effective step potential at the DW. The height of this step potential is simply a measure of the difference in twist angles. These computations lead us to identify the global transport signatures for detecting and quantifying the local twist angle variations. In particular, Using Landauer-B\"uttiker formalism we compute single-channel conductance ($dI/dV$) and Fano factor for shot noise (ratio of noise power and mean current). A zero-bias, sub-meV transport gap is observed in the conductance which scales with the height of the step potential. One of the key findings of our work is that transport in presence of twist angle inhomogeneity is "noisy", though sub-Poissonian. In particular, the differential Fano factor peaks near the van Hove energies corresponding to the domains in the sample. The location and the strength of the peak is simply a measure of the degree of twist angle inhomogeneity.

Investigation of tetracosane thermal transport in presence of graphene and carbon nanotube fillers––A molecular dynamics study

Abstract This paper examines the thermal properties of pure tetracosane paraffin, tetracosane-graphene, and tetracosane-carbon nanotube mixed phase change materials (PCM). The most important properties studied were thermal capacity in constant volume (Cv), mean square displacement of atoms (MSD), radial distribution function (RDF), density, phonon density of states (PDOS) and thermal conductivity (k) under different temperatures. The results show that graphene and carbon nanotube increase the thermal conductivity of the tetracosane at different temperatures, but decrease the molecular movement and its thermal capacity (except after about 360 K), and it can be said that this slightly decreases the paraffin melting temperature. It was demonstrated that carbon nanotube is more efficient than graphene to increase the thermal conductivity of the proposed PCM.

Separation/Competitive Transport of Heavy Metal Ions across the Bulk Liquid Membranes with N,N',N''-Tris(4-methylphenyl)phosphoric Triamide As Carrier

The competitive bulk liquid membrane transport of seven metal ion by N,N',N''-tris(4-methylphen-yl)phosphoric triamide carrier was studied using a flame atomic absorption spectrometry. Dichloromethane (DCM), chloroform (CHCl3), nitrobenzene (NB) and 1,2-dichloroethane (1,2-DCE) solvents have been used as bulk liquid membranes (BLM). The carrier has been shown the maximum transport rate for Cu2+ cation in all of the BLM systems (except of 1,2-DCE) in comparison to the other cations containing Co2+, Cd2+, Ag+, Pb2+, Ni2+, Cu2+, and Zn2+. The obtained results show that the selectivity and efficiency of transport in presence of this ligand change with the type of organic solvents. Various factors that affect the transport efficiency of this heavy metal cations have been optimized in order to obtain maximum transport. The complexation process between phosphoric triamide and Cu2+cation have also been examined by conductomery method. The stoichiometry of the complex and the formation constant of phosphoric triamid-Cu2+ complex have been determined.

Preparation and characterization of novel solid electrolytes based on [EMIM] BF4 and lithium nitrate confined silica gels

Novel ionic liquid ([EMIM]BF4) and lithium nitrate confined silica gel composites have been prepared via hydrolytic sol-gel process and found to exhibit electrical conductivity up to 10−4 Ω−1cm−1 in the temperature range 150–300 °C. The composites are thermally stable at this temperature range and measurements are repeatable. Powder X-ray diffraction patterns suggest that the composites are amorphous in nature. FE-SEM (EDS elemental mapping) and DSC measurements further confirm IL confinement in the matrix. Electrical conductivity (150–300 °C) has been studied as a function of IL and Li+ ion content. The samples with no IL content are essentially electronic in nature. Addition of IL in small amounts (1 mol%) enhances the total conductivity at least by an order of magnitude. Further addition of salt (LiNO3) enhances ionic transport by orders of magnitude. The electronic conductivity and ionic mobility along with OCV measurements on cells of type Li/composite/LiCoO2 suggests facilitation of Li+ ion transport in presence of IL in small amount. However, further increasing the content of IL in the composition while keeping the salt ion concentration same, does not improve conductivity, rather reduces it. This complex behavior may be due to possibility of Li+ ions forming complex with IL anion and further investigations are required in this regard. Preliminary findings suggest that these materials have good potential for their applications in all-solid-state supercapacitors.

Randomness in flow turbulence around a bridge pier in a sand mined channel

Mining activities have the potential to cause excess scour and affect the streambed stability around bridge piers present in the vicinity. Randomness characteristics of turbulence around the pier in a mining infested channel can be helpful in better understanding of this phenomenon. In this study, the effect of a mining pit on the randomness in turbulent flow around the pier has been explored on the basis of Kolmogorov complexity (KC) measure and its derivative, i.e. KC spectrum. Conventionally, turbulent stresses are supposed to govern the sediment transport characteristics, hence the Reynolds shear stresses (RSS) and bursting events are also analyzed. Results of two cases have been comparatively studied; for the first case, only an oblong pier is embedded in the channel while in the second case, a rectangular mining pit is excavated upstream of the pier. Quadrant analysis of the Reynolds shear stress revealed that strong ejection events in the upstream side and inward interaction events in the downstream side of the pier cause excess momentum transport in presence of a mining pit. Streamwise and vertical turbulence intensities also increase by 20% and 33% respectively in the down-flow zone in front of the pier. KC value of turbulence around the pier, especially in the down-flow zone and separation zone is found to be 10% and 12% higher due to pit excavation. Comparing the KC spectra for both cases suggests that dredging of a pit in the channel increases the degree of randomness of higher velocity scales around the bridge pier. These alterations in turbulent stresses and randomness characteristics can be helpful in explaining the streambed scour and undermining of bridge piers due to mining activities.

Investigation of cross-diffusion effects on Casson fluid flow in existence of variable fluid properties

A numerical investigation has been carried out for coupled partial differential equations which describe varying fluid properties on unsteady, free convective chemically reacting fluid flow on a moving vertical cone and flat plate. The computations for flow, heat, and mass transport in presence of thermal radiation, viscous dissipation, Soret and Dufour effects are carried out using Crank-Nicolson scheme. The influence of active parameters on transport properties of the fluid is displayed in form of graphs and tables. The results elucidate that the consideration of variable fluid properties has a significant influence on the flow, heat and mass transfer characteristics. Strengthening the Casson fluid parameter tends to decelerate the fluid velocity and escalate the local skin friction.

Electrochemical Capacitance and Transit Time in Quantum Hall Conductors

In a two dimensional electron gas, low energy transport in presence of a magnetic field occurs in chiral 1D channels located on the edge of the sample. In the AC description of quantum transport, the emittance determines the amplitude of the imaginary part of the admittance, whose sign and physical meaning are determined by the sample topology: a Hall bar is inductive while a Corbino ring is capacitive. In this article, the perfect capacitive character of Corbino samples in the quantum Hall effect regime is shown. A vanishing conductance and an electrochemical capacitance which depends on the density of states of 1D channels are measured. Our samples have no gate, neither on the side nor on the top, and the inner capacitances are measured. The transit time of electrons across the device is obtained and the drift velocity of carriers is deduced.

Non-equilibrium quantum transport in presence of a defect: the non-interacting case

We study quantum transport after an inhomogeneous quantum quench in a free fermion lattice system in the presence of a localised defect. Using a new rigorous analytical approach for the calculation of large time and distance asymptotics of physical observables, we derive the exact profiles of particle density and current. Our analysis shows that the predictions of a semiclassical approach that has been extensively applied in similar problems match exactly with the correct asymptotics, except for possible finite distance corrections close to the defect. We generalise our formulas to an arbitrary non-interacting particle-conserving defect, expressing them in terms of its scattering properties.

Remarkable role of [formula omitted] on transportation of [formula omitted] hybrid nanoparticles influenced by thermal deposition and internal heat generation

The present work focuses on examining nanofluidic transport in presence of temperature dependent viscosity. In order to conduct a comparative investigation Silicon dioxide and Molybdenum disulfide nanoparticles are considered to be suspended in propylene glycol. Furthermore, heat transfer has been inspected for nano and hybrid nanofluids influenced by internal heat source/sink, thermal radiation, and heat dissipation. Additionally, the Cartesian coordinate system opts for mathematical formulation of governing equations. Moreover, similarity analysis is employed to obtain the system of highly nonlinear coupled equations which is solved numerically by means of shooting technique. The key findings include that nanofluid and hybrid nanofluid floe decelerates for increasing values of the viscosity parameter and magnetic parameter while a contrary trend was observed for the rising values of Grashof number. Volumetric fraction ϕ1 and ϕ2 contributed in decelerating fluid flow for plate-shaped particles of nanofluid as well as of hybrid nanofluid. Temperature distribution up surged for rising values of Biot number, Eckert number, viscosity parameter, magnetic parameter, heat generation parameter and lessened for rising values of radiation parameter, Grashof number. This trend was noted for SiO2 and MoS2−SiO2 nanofluids. Moreover, magnetic field, viscous dissipation and heat generation contributed in rising Nusselt number while opposite behavior was observed in presence of thermal radiation and convective boundaries. Furthermore, the maximum Nusselt number was attained for needle shape nanoparticles of MoS2−SiO2 and the minimum value was noted for plate-shaped SiO2 nanoparticles. Nanoparticle volumetric fractions play role in rising skin fraction of SiO2 nanofluid while it decreased in case of hybrid nanofluid. Moreover, minimum skin fraction was noted for needle-shaped nanoparticles of hybrid nanofluid and the maximum value was recorded for plate-shaped nanoparticles of SiO2 .

Magneto-transport controlled by Landau polariton states

Hybrid excitations, called polaritons, emerge in systems with strong light-matter coupling. Usually, they dominate the linear and nonlinear optical properties with applications in quantum optics. Here, we show the crucial role of the electronic component of polaritons in the magneto-transport of a cavity-embedded 2D electron gas in the ultrastrong coupling regime. We show that the linear dc resistivity is significantly modified by the coupling to the cavity even without external irradiation. Our observations confirm recent predictions of vacuum-induced modification of the resistivity. Furthermore, photo-assisted transport in presence of a weak irradiation field at sub-THz frequencies highlights the different roles of localized and delocalized states.

On force consideration in coupled ISPH framework for sediment transport in presence of free-surface flow

A coupled divergence-free Incompressible Smoothed Particle Hydrodynamics (ISPH) framework for sediment transport is extended for application in generalized free-surface flow situations. The computation of interaction force pair between pure fluid and sediment modules makes the model flexible enough to be applicable for diverse scenarios with variable resolutions. Three scenarios are included to quantify the contribution of individual components in the force pair. First two scenarios with rapid free-surface variation highlight the effect of fluid pressure gradient on granular flow. The third scenario with minimal free-surface variation considers bed movement under a horizontal marine pipeline for a prolonged time period. The framework can simulate sediment transport for generalized problems with slowly/rapidly varying free-surface flow conditions.

Quantum Transport in Presence of Bound States – Noise Power

The impact of bound states in Landauer‐Büttiker scattering approach to non‐equilibrium quantum transport is investigated. We show that the noise power at frequency ν is sensitive to all bound states with energies ωb satisfying . We derive the exact expression of the bound state contribution and compare it to the one produced by the scattering states alone. The theoretical and experimental consequences of this result are discussed.

THERMAL RADIATION EFFECT ON MHD NATURAL CONVECTION BOUNDARY LAYER FLOW OVER A PLATE WITH SUCTION (INJECTION) AND VARIABLE VISCOSITY

The effect of thermal radiation on steady natural convection boundary layer flow over a plate with variable viscosity and magnetic field has been studied in this paper. The effect of suction and injection is also considered in the investigation. The system of partial differential equations governing the nonsimilar flow has been solved numerically using implicit finite difference scheme along with a quasilinearization technique. The thermal radiation has significant effect on heat transfer coefficient and thermal transport in presence of viscosity variation parameter and magnetic field in case of suction and injection.

Competition between ro–ro and lo–lo services in short sea shipping market: The case of Mediterranean countries

A relevant portion of the scientific literature focuses on the competition of short sea shipping (SSS) with land transport in presence of international programmes that provide financial support to SSS services (e.g. Motorway-of-the-Sea).The paper analyses the competition inside the maritime SSS market, comparing roll on–roll off (ro–ro) vs. lift on–lift off (lo–lo) services. The market has two structural pillars: (a) the analysed services connect Italy and a set of countries belonging to the south-eastern range of the Mediterranean basin, then without any financial support to the services; (b) there are no available land transport services for all the considered relationships.The two above pillars allow to quantify the reciprocal advantage of the two maritime services, by purifying the market from the bias generated by the presence of available land transport services and of any kind of financial support to SSS services.An aggregate discrete choice model, simulating the split between ro–ro and lo–lo services of freight flow exchanged by sea between countries facing the Mediterranean basin, has been specified and calibrated. The important element that emerges, in general terms, is the segmentation of the market in relation to the distances existing between each couple of countries.