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In this research, using Geant4 Monte Carlo simulation tool, we have investigated the shielding properties of aluminum oxide, magnesium fluoride, aluminum fluoride, titanium dioxide, magnesium diboride, magnesium silicide, calcium disilicate, and Fluental in the energy range of 0.015 to 10 MeV. In this review, we have calculated and analyzed the linear attenuation coefficient (LAC) and mass attenuation coefficients (MAC), half-value layer (HVL), tenth value layer (TVL), mean free path (MFP), and effective atomic number, effective electron density, equivalent atomic number and buildup factor. In the continuation of the work, we have compared the calculated results of mass attenuation coefficient by Geant4 Monte Carlo simulation tool with the experimental results of others and with the simulation data by XMuDat code, and they have a very low relative error and are in good agreement with each other. Finally, the results obtained for the selected materials are shown in appropriate figures. [ABSTRACT FROM AUTHOR]

We investigate the gas flows near to solid surfaces in terms of the local spatial variation in the molecular mean free path (MFP). Molecular dynamics (MD) is the appropriate scientific tool for obtaining molecularly-accurate dynamic information in micro and nano-scale gas flows, and has been used to evaluate the molecular mean free path of gases. In the calibration procedure, the viscosity of a gas in the homogeneous case can be recovered in our MD simulations and reach good agreement with the theoretical prediction and data from NIST. In surface-bounded gas flows, if the collisions between gas molecules and walls are counted, a spatially-varying mean free path is presented, and for the first time we have observed that the distribution of the free paths deviates from the exponential one and spikes appear in their distributions at larger Kn, i.e. in the transition flow regime. Based on elementary kinetic theory, the effective viscosity of the gas derived from the mean free path has been incorporated into the framework of the continuum-fluid dynamics equations, and micro-Couette flows are performed to demonstrate this potential application. [ABSTRACT FROM AUTHOR]

Abstract: The role of interlayer rotation on the electrical transport of few layer graphene (FLG) is rarely considered. In this paper, the impact of twisting angle on physical and electrical properties of synthetic single crystal bilayer and few layer graphene deposited on thermal SiO2 substrate is systematically studied. Bernal AB‐stacked graphene layers show low carrier mobility due to strong interlayer coupling and substrate scattering. A dramatic increase in carrier mobility and conductivity is observed when the graphene layers are twisted. A field effect mobility up to 15000 cm2 V−1 s−1 and 460 nm mean free path is measured on a twisted three‐layer graphene at room temperature is among the highest for graphene transferred to SiO2. In average, twisted graphene shows a fivefold improvement compared to AB stacked graphene in terms of mobility and conductivity, regardless of twist angles. [ABSTRACT FROM AUTHOR]

In this work, we have evaluated the γ-ray shielding parameters such as mass attenuation coefficient (μ/ρ), effective atomic number (Z eff ), half value layer (HVL), mean free path (MFP) and exposure buildup factors (EBF) for heavy metal fluoride (PbF 2 ) based tellurite-rich glasses. In addition, neutron total macroscopic cross sections (∑ R ) for these glasses were also calculated. The maximum value for µ/ρ, Z eff and ∑ R was found for heavy metal (Bi 2 O 3 ) oxide introduced glass. The results of the selected glasses have been compared, in terms of MFP with different glass systems. The shielding effectiveness of the selected glasses is found comparable or better than of common ones, which indicates that these glasses with suitable oxides could be developed for gamma ray shielding applications. [ABSTRACT FROM AUTHOR]

In this work, we evaluate the material properties of graphene and assess the potential application of graphene to replace copper wires in Back-End-Of-Line (BEOL) interconnects. Based on circuit and system-level simulations, high restrictions are imposed to graphene with respect to contact resistance and mean free path. Experimentally we evaluate single and multi-layer graphene wires and we measure carrier mean free paths (MFPs) above ~ 110 nm. However, contact engineering will be the key issue for integration of graphene as interconnect. [ABSTRACT FROM AUTHOR]

In this paper, an improved physics-based virtual-source (VS) model to describe transport in quasi-ballistic transistors is discussed. The model is based on the Landauer scattering theory, and incorporates the effects of: 1) degeneracy on thermal velocity and mean free path of carriers in the channel; 2) drain-bias dependence of gate capacitance and VS charge, including the effects of band nonparabolicity; and 3) nonlinear resistance of the extrinsic device region on gm -degradation at high drain currents in the channel. The improved charge model captures the phenomenon of reduction in VS charge under nonequilibrium transport conditions in a quasi-ballistic transistor. [ABSTRACT FROM AUTHOR]

The thermal conductivity of a material or device is dependent on its characteristic dimension. When the characteristic dimension is commensurate to the mean free paths of thermal energy carriers, the thermal conductivity decreases. The precise relationship between characteristic size and thermal conductivity, which depends on the distribution of energy carrier mean free paths in the material, is not straightforward to determine experimentally. The utility of this relationship has led many researchers to study the mean free path dependent contributions of thermal energy carriers to the thermal conductivity of materials, known as the thermal conductivity accumulation function. This review highlights a number of recent experimental results and techniques used to study the thermal conductivity accumulation function, including transient thermal grating, time domain thermoreflectance, and broadband frequency domain thermoreflectance. In these techniques, nondiffusive thermal transport is induced (i.e., thermal gradients occur over length scales comparable to energy carrier mean free paths) and an effective thermal conductivity of the material is determined. We conclude with our outlook on future directions for the field focused on improved interpretations of the experiments and new materials with unique mean free path distributions. [ABSTRACT FROM AUTHOR]

We have developed a robust analytical methodology for modeling the anisotropic transport distribution function, which can be then used to describe various transport properties of anisotropic systems, including the electrical conductivity, carrier mobility, Seebeck coefficient, and thermal conductivity. Our methodology has considered the general cases for 3-, 2-, and 1-dimensional systems with parabolic, non-parabolic, and linear dispersion relations. Calculations are made using both the relaxation time approximation and the mean free path approximation. We have found that the Onsager relation can be violated under certain conditions. Furthermore, the methodology developed in the present work is compared with the traditionally used numerical methodology. [ABSTRACT FROM AUTHOR]

String theory methods led to the hypothesis that the ratio of a shear viscosity coefficient to the volume density of entropy of any physical system has a lower bound. Systems with strong coupling have a small viscosity as compared to weakly coupled plasmas in which the viscosity is proportional to the mean free path. Here, we have estimated the fully ionized strongly coupled plasma viscosity based on the dynamic experimental data on electrical conductivity and have shown that the ratio of viscosity to entropy of the strongly coupled plasma is very close to that of the lower bound predicted by the string theory. [ABSTRACT FROM AUTHOR]