A thermal conductivity model for nanofluids including effect of the temperature-dependent interfacial layer

The interfacial layer of nanoparticles has been recently shown to have an effect on the thermal conductivity of nanofluids. There is, however, still no thermal conductivity model that includes the effects of temperature and nanoparticle size variations on the thickness and consequently on the thermal conductivity of the interfacial layer. In the present work, the stationary model developed by Leong et al. (J Nanopart Res 8:245–254, 2006) is initially modified to include the thermal dispersion effect due to the Brownian motion of nanoparticles. This model is called the ‘Leong et al.’s dynamic model’. However, the Leong et al.’s dynamic model over-predicts the thermal conductivity of nanofluids in the case of the flowing fluid. This suggests that the enhancement in the thermal conductivity of the flowing nanofluids due to the increase in temperature does not come from the thermal dispersion effect. It is more likely that the enhancement in heat transfer of the flowing nanofluids comes from the temperature-dependent interfacial layer effect. Therefore, the Leong et al.’s stationary model is again modified to include the effect of temperature variation on the thermal conductivity of the interfacial layer for different sizes of nanoparticles. This present model is then evaluated and compared with the other thermal conductivity models for the turbulent convective heat transfer in nanofluids along a uniformly heated tube. The results show that the present model is more general than the other models in the sense that it can predict both the temperature and the volume fraction dependence of the thermal conductivity of nanofluids for both non-flowing and flowing fluids. Also, it is found to be more accurate than the other models due to the inclusion of the effect of the temperature-dependent interfacial layer. In conclusion, the present model can accurately predict the changes in thermal conductivity of nanofluids due to the changes in volume fraction and temperature for various nanoparticle sizes.     

The optimal path of piston motion for Otto cycle with linear phenomenological heat transfer law

An Otto cycle engine with internal and external irreversibilities of friction and heat leakage, in which the heat transfer between the working fluid and the environment obeys linear phenomenological heat transfer law [q ∝△(T -1)], is studied in this paper. The optimal piston motion trajectory for maximizing the work output per cycle is derived for the fixed total cycle time and fuel consumed per cycle. Optimal control theory is applied to determine the optimal piston trajectories for the cases of with and w...     

Aharonov-bohm effect on multiwall carbon nanotubes under conditions close to strong carrier localization

The Aharonov-Bohm effect on multiwall carbon nanotubes has been studied under conditions of resistance with decreasing temperature as an inverse power function, which precede strong carrier localization. A periodic contribution with a period of 18 T corresponding to the magnetic flux quantum ħc/e per nanotube cross section has been revealed in the longitudinal magnetoresistance. The result points to the possibility of the ballistic motion of the carriers over the sample perimeter under conditions close to their strong localization in the longitudinal direction.     

A theoretical model for the collective motion of proteins by means of principal component analysis

A coarse grained model in the frame work of principal component analysis is presented. We used a bath of harmonic oscillators approach, based on classical mechanics, to derive the generalized Langevin equations of motion for the collective coordinates. The dynamics of the protein collective coordinates derived from molecular dynamics simulations have been studied for the Bovine Pancreatic Trypsin Inhibitor. We analyzed the stability of the method by studying structural fluctuations of the C _a atoms obtained from a 20 ns molecular dynamics simulation. Subsequently, the dynamics of the collective coordinates of protein were characterized by calculating the dynamical friction coefficient and diffusion coefficients along with time-dependent correlation functions of collective coordinates. A dual diffusion behavior was observed with a fast relaxation time of short diffusion regime 0.2–0.4 ps and slow relaxation time of long diffusion about 1–2 ps. In addition, we observed a power law decay of dynamical friction coefficient with exponent for the first five collective coordinates varying from −0.746 to −0.938 for the real part and from −0.528 to −0.665 for its magnitude. It was found that only the first ten collective coordinates are responsible for configuration transitions occurring on time scale longer than 50 ps.     

Gauge theory of ferroelastic interaction in crystals with polyatomic lattice

The gauge theory of dislocations and disclinations in crystals with polyatomic lattice is generalized to ferroelastic interactions. In this work, based on the SO(3N)λT(3N) gauge group, an unbouned isotropic continuous medium comprising dislocations and disclinations is used to model an actual crystal, where N is the number of atoms per unit cell and λ is the sign of a semidirect product.     

Multiple Instantons Representing Higher-Order Chern–Pontryagin Classes

It has been shown in the work of Chakrabarti, Sherry and Tchrakian that the chiral SO _±(4 p) Yang–Mills theory in the Euclidean 4 p (p≥ 2) dimensions allows an axially symmetric self-dual system of equations similar to Witten's instanton equations in the classical 4-dimensional SU(2)∼SO _±(4) theory and the solutions represent a new class of instantons. However the rigorous existence of these higher-dimensional instanton solutions has remained open except for the solution of unit charge representing a single instanton. In this paper we establish an existence and uniqueness theorem for multi-instantons of arbitrary charges in the case p≥ 2. These solutions are the first known instantons, with the Chern–Pontryagin index greater than one, of the Yang–Mills model in higher dimensions. Our approach is a study of a nonlinear variational equation defined on the Poincaré half plane. Received: 20 May 1996 / Accepted: 30 April 1997     

Thermodynamic and kinetic considerations of nucleation and stabilization of acoustic cavitation bubbles in water

Qualitative explanation for a homogeneous nucleation of acoustic cavitation bubbles in the incompressible liquid water with simple phenomenological approach has been provided via the concept of the desorbtion of the dissolved gas and the vaporization of local liquid molecules. The liquid medium has been viewed as an ensemble of lattice structures. Validity of the lattice structure approach against the Brownian motion of molecules in the liquid state has been discussed. Criterion based on probability for nucleus formation has been defined for the vaporization of local liquid molecules. Energy need for the enthalpy of vaporization has been considered as an energy criterion for the formation of a vaporous nucleus. Sound energy, thermal energy of the liquid bulk (Joule-Thomson effect) and free energy of activation, which is associated with water molecules in the liquid state (Brownian motion) as per the modified Eyring's kinetic theory of liquid are considered as possible sources for the enthalpy of vaporization of water molecules forming a single unit lattice. The classical nucleation theory has then been considered for expressing further growth of the vaporous nucleus against the surface energy barrier. Effect of liquid property (temperature), and effect of an acoustic parameter (frequency) on an acoustic cavitation threshold pressure have been discussed. Kinetics of nucleation has been considered.     

Simulation of Topological Field Theories¶by Quantum Computers

Quantum computers will work by evolving a high tensor power of a small (e.g. two) dimensional Hilbert space by local gates, which can be implemented by applying a local Hamiltonian H for a time t. In contrast to this quantum engineering, the most abstract reaches of theoretical physics has spawned “topological models” having a finite dimensional internal state space with no natural tensor product structure and in which the evolution of the state is discrete, H≡ 0. These are called topological quantum field theories (TQFTs). These exotic physical systems are proved to be efficiently simulated on a quantum computer. The conclusion is two-fold: 1. TQFTs cannot be used to define a model of computation stronger than the usual quantum model “BQP”. 2. TQFTs provide a radically different way of looking at quantum computation. The rich mathematical structure of TQFTs might suggest a new quantum algorithm. Received: 4 May 2001 / Accepted: 16 January 2002     

A spherically symmetric gravitational collapse-field with radiation

An interior spherically symmetric solution of Einstein’s field equations corresponding to perfect fluid plus a flowing radiation-field is presented. The physical 3-spacet=constant of our solution is spheroidal. Vaidya’s pure radiation field is taken as the exterior solution. The inward motion of the collapsing boundary surface follows from the equations of fit. An approximation procedure is used to get a generalization of the standard Oppenheimer-Snyder model of collapse with outflow of radiation. One such explicit solution has been given correct to second power of eccentricity of the spheroidal 3-space.     

Thermoelectric power of cerium at high pressures

The electronic phase transition in cerium occurring near 7 kbar pressure at room temperature which is attributed to the 4f–5d electron promotion has been studied using thermoelectric power as a tool. The important results that have emerged out of this work are: (a) the relatively large variation in the absolute thermoelectric power ofγ-cerium (normal fcc phase) with pressure prior to the phase transition (in contrast to the rather small resistivity change with pressure in this region); (b) a sharp decrease in the thermoelectric power accompanying the iso-structuralγ-α phase transition; and (c) the continuous decrease in the thermoelectric power ofα-cerium (collapsed fcc phase) with pressure, ultimately changing sign at higher pressures. An explanation based on the “virtual bound state” model is proposed to account for these results.     

Reptation and diffusive modes of motion of linear macromolecules

It is shown that the model of underlying stochastic motion of a macromolecule leads to two modes of motion: reptative and isotropically diffusive. There is a length of a macromolecule M* ≈ 10M _e , where M _e is “the macro-molecule length between adjacent entanglements,” above which macromolecules of a melt can be regarded as obstacles to motion of each other, and the macromolecules reptate. The transition to the reptation mode of motion is determined by both topological restrictions and local anisotropy of motion. The investigation confirm that the reptation motion determines the M ⁻² molecular-weight dependence of the self-diffusion coefficient of macromolecules in melts. The text was submitted by the author in English.     

Physical device models: A potential tool in investigating conductivity in ionic and mixed conductors

Extensive work has been done in the last three decades on modelling classical semiconductor devices through physical device models. The majority of these models is based on the simultaneous solution of Poisson's equation, current and continuity equations for electrons and holes using iterative techniques. The vast work done on classical semiconductor devices has been extended to include the study of the motion of charged species upon the application of external fields in insulators, ionic materials, mixed conductors or proton conductors. In this paper the methods used are discussed together with their potential in leading to an understanding of the mechanisms governing charge transport in materials exhibiting more complex conductivity than classical semiconductors. Paper presented at the 5th Euroconference on Solid State Ionics, Benalmádena, Spain, Sept. 13–20, 1998.     

Investigation of material removal mechanism of silicon wafer in the chemical mechanical polishing process using molecular dynamics simulation method

Chemical mechanical polishing (CMP) technology, being the mainstream technique of acquiring global planarization and nanometer level surface, has already become an attractive research item. In the case of CMP process, the indentation depth lies in the range of nanometer or sub-nanometer, huge hydrostatic pressure induced in the local deformation area which makes the material removal and surface generation process different from traditional manufacturing process. In order to investigate the physical essence of CMP technique, the authors carry out molecular dynamics (MD) analysis of chemical mechanical polishing of a silicon wafer. The simulation result shows that huge hydrostatic pressure is induced in the local area and leads to the silicon atom transform from the classical diamond structure (α silicon) to metal structure (β silicon). This important factor results in the ductile fracture of silicon and then in the acquisition of a super-smooth surface.     

钕玻璃放大器氙灯泵浦的优化设计

建立了氙灯辐射光谱，求银感容（ＬＣ）供电网络电路和研究泵浦动力学过程中粒子数反转的模拟计算程序，并根据国内外的实验和计算结果进行了校核。氙灯单位侧面积上的输入功率光电流密度能更好描述氙灯的工作特性，计算结果还表明，当单位侧面积上的输入功率增加时氙灯的光谱效率下降，在似稳态条件下当输入功经不变时，不同直径的氙灯在泵浦区区域内的辐射光谱和光谱效率几乎不变，电流密度条件下当输入功率不变时，不同直径的氙灯     

Octupolar excitation of ion motion in a penning trap

The excitation of the motion of ions in a Penning trap at twice their cyclotron frequency, 2ν _c , by means of an azimuthal octupolar RF field has been studied with the LEBIT facility at the NSCL. The possibility of such an RF octupolar excitation has been verified. Compared to ion excitation at ν _c by means of quadrupolar fields an increased resolving power is observed in the cyclotron resonance curves, which may have important implications for Penning trap mass measurements. Numerical simulations have been used to characterize important properties of this type of excitation in detail and to predict the behavior of the ion motion under realistic conditions. Good agreement with the experimental results is observed.      

Absorption and Transmission Power Coefficients for Millimeter Waves in a Weakly Ionised Vegetation Fire

A vegetation fire plume is a weakly ionised gaseous medium. Electrons in the plume are mainly due to thermal ionisation of incumbent alkali impurities. The medium is highly collisional with free electron - neutral particle been the dominant particle interaction mechanism. Signal strength of an incident millimetre wave (MM-Wave) may be significantly attenuated in the plume depending on the extent of ionisation. A numerical experiment was set to investigate signal power loss of a MM-Wave incident on a simulated weakly ionised fire plume with flame maximum (seat) temperature ranging from 1000–1150 K. The simulated fire plume had alkali impurities (potassium) content of 1.0% per unit volume. MM-Wave frequency range investigated in the experiment is from 30–60 GHz. The simulation has application in the prediction of MM-Wave propagation in a crown forest fire and may also be applied in remote sensing studies of forest fire environments. Simulated attenuation per unit path length for the MM-Wave frequencies ranged from 0.06–24.00 dBm⁻¹. Phase change per unit path length was simulated to range from 2.97–306.17°m⁻¹ while transmission power coefficients ranged from maximum of 0.9996 for a fire plume at 1000 K to a minimum value of 0.8265 for a plume at a temperature of 1150 K over a plume depth of 1.20 m. Absorption power coefficient ranged from a minimum value of 0.0004 to maximum value of 0.1585 at a seat temperature of 1150 K over the plume depth.     

Classical and Non-relativistic Limits of a Lorentz-Invariant Bohmian Model for a System of Spinless Particles

A completely Lorentz-invariant Bohmian model has been proposed recently for the case of a system of non-interacting spinless particles, obeying Klein-Gordon equations. It is based on a multi-temporal formalism and on the idea of treating the squared norm of the wave function as a space-time probability density. The particle’s configurations evolve in space-time in terms of a parameter σ with dimensions of time. In this work this model is further analyzed and extended to the case of an interaction with an external electromagnetic field. The physical meaning of σ is explored. Two special situations are studied in depth: (1) the classical limit, where the Einsteinian Mechanics of Special Relativity is recovered and the parameter σ is shown to tend to the particle’s proper time; and (2) the non-relativistic limit, where it is obtained a model very similar to the usual non-relativistic Bohmian Mechanics but with the time of the frame of reference replaced by σ as the dynamical temporal parameter.     

Numerical investigation of air free convection in a room with heat source

Mathematical modelling of three-dimensional steady free convective incompressible viscous gas flows in the rooms with a heat source is carried out within the framework of the Navier — Stokes equations with the effective viscosity determined on the basis of the κ-ɛ turbulence model. The investigation is carried out for the case of model rooms and heat sources having the form of rectangular parallelepipeds with square bases. The influence of the heat source power and the sizes of the room base on local and averaged values of the air velocity and temperature in the rooms is analysed. The flow pattern in the room is shown to have a torus-like shape. It is found that the variation of sizes of the room base rather than the capacity variation of the heat source is of determining importance for the gas motion character in a closed volume.     

Curved polymer and polyelectrolyte brushes beyond the Daoud-Cotton model

We revise the classical Daoud-Cotton (DC) model to describe conformations of polymer and polyelectrolyte chains end-grafted to convex spherical and cylindrical surfaces. In the framework of the DC model, local stretching of chains in the brush does not depend on the degree of polymerization of grafted chains, and the polymer density profile follows a single-exponent power law. This model, however, does not correspond to a minimum in free energy of the curved brush. The nonlocal (NL) approximation exploited in the present paper implies the minimization of the overall free energy of the brush and predicts that the polymer density profile does not follow a single-exponent power law. In the limit of large surface curvature the NL approximation provides the same scaling laws for brush thickness and free energy as the local DC model. Numerical prefactors are however different. Extra extension of chains in the brush interior region leads to larger equilibrium brush thickness and lower free energy per chain. A significant difference between outcomes of the two models is found for brushes formed by ionic polymers, particularly for weakly dissociating (p H-sensitive) polyelectrolytes at low solution salinity.     

Positron lifetime as a function of grain size

Published data on positron annihilation lifetime in copper as a function of grain size have been analyzed to show that there is a linear relationship between the internal grain boundary surface area, per unit volume,S _v, and the positron lifetime, τ. The analysis indicates that grain boundaries are important in the trapping of positrons. It is suggested that the slope of the resulting straight line,dS _v/dτ, can be used to determine the annihilation rate of the grain boundaries.