Numerical simulation of liquid sloshing in LNG tanks using a compressible two-fluid flow model

In this investigation the Reynolds-Averaged Navier-Stokes (RANS) equations are modified to account for variable density and viscosity of the two-fluids flow (i.e. water-air), assuming both fluids compressible. By introducing a preconditioner, the governing equations in terms of primitive variables are solved for both fluids in a unified manner. The non-conservative implicit Split Coefficient Matrix Method (SCMM) is modified to approximate convective flux vectors in the dual time formulation. The free surface waves inside the tank, due to sloshing, are implicitly captured by using a level set approach. The method is illustrated through applications to rectangular and chamfered tanks subject to sway or roll motions at different filling levels and excitation conditions (i.e. amplitude and frequency of oscillation). Comparisons are made between calculated and experimental pressures, where available

Quantum radiation by electrons in lasers and the Unruh effect

In addition to the Larmor radiation known from classical electrodynamics, electrons in a laser field may emit pairs of entangled photons -- which is a pure quantum effect. We investigate this quantum effect and discuss why it is suppressed in comparison with the classical Larmor radiation (which is just Thomson backscattering of the laser photons). Further, we provide an intuitive explanation of this process (in a simplified setting) in terms of the Unruh effect.Comment: 4 pages, 3 figure

New Insights into Uniformly Accelerated Detector in a Quantum Field

We obtained an exact solution for a uniformly accelerated Unruh-DeWitt detector interacting with a massless scalar field in (3+1) dimensions which enables us to study the entire evolution of the total system, from the initial transient to late-time steady state. We find that the Unruh effect as derived from time-dependent perturbation theory is valid only in the transient stage and is totally invalid for cases with proper acceleration smaller than the damping constant. We also found that, unlike in (1+1)D results, the (3+1)D uniformly accelerated Unruh-DeWitt detector in a steady state does emit a positive radiated power of quantum nature at late-times, but it is not connected to the thermal radiance experienced by the detector in the Unruh effect proper.Comment: 6 pages, invited talk given by SYL at the conference of International Association for Relativistic Dynamics (IARD), June 2006, Storrs, Connecticut, US

Resolution Tests of CsI(Tl) Scintillators Read Out by Pin Diodes

This research was sponsored by the National Science Foundation Grant NSF PHY 87-1440

Observer dependence for the phonon content of the sound field living on the effective curved space-time background of a Bose-Einstein condensate

We demonstrate that the ambiguity of the particle content for quantum fields in a generally curved space-time can be experimentally investigated in an ultracold gas of atoms forming a Bose-Einstein condensate. We explicitly evaluate the response of a suitable condensed matter detector, an ``Atomic Quantum Dot,'' which can be tuned to measure time intervals associated to different effective acoustic space-times. It is found that the detector response related to laboratory, ``adiabatic,'' and de Sitter time intervals is finite in time and nonstationary, vanishing, and thermal, respectively.Comment: 9 pages, 2 figures; references updated, as published in Physical Review

A comparison of the flow fields generated for spark and controlled auto-ignition

Valve timing strategies aimed at producing internal exhaust gas re-circulation in a conventional spark ignition, SI, engine have recently demonstrated the ability to initiate controlled auto-ignition, CAI. Essentially the exhaust valves close early, to trap a quantity of hot exhaust gases in-cylinder, and the fresh air-fuel charge is induced late into the cylinder and then mixing takes place. As a logical first step to understanding the fluid mechanics, the effects of the standard and modified valve timings on the in-cylinder flow fields under motored conditions were investigated. Laser Doppler anemometry has been applied to an optical engine that replicates the engine geometry and different valve cam timings. The cycle averaged time history mean and RMS velocity profiles for the axial and radial velocity components in three axial planes were measured throughout the inlet and compression stroke. The turbulent mixing for the two cases are described in terms of the flow field maps of the velocity vectors, vorticity and turbulence kinetic energy and the integrated tumble ratio as a function of crankangle

Homogeneous Charge Compression Ignition combustion and fuel composition

Homogeneous charge compression ignition, HCCI, combustion has potentials to deliver high efficiency and negligible cycle-to-cycle variations, while keeps NOx and particulate emissions at very low levels in comparison with conventional SI and CI combustion concepts. Since HCCI combustion is an auto ignited combustion, fuel structure has direct impact on its auto-ignition performance. In this research, by mixing iso-octane and n-heptane, the auto-ignition nature of fuels with different research octane number, RON, were simulated and analysed using a single-zone engine combustion model with detailed chemical kinetics and convective heat transfer loss. The effects of internally recirculated engine exhaust gas, IEGR, as a potential control strategy was also calculated

Diffusive Charge Transport in Graphene on SiO2

We review our recent work on the physical mechanisms limiting the mobility of graphene on SiO2. We have used intentional addition of charged scattering impurities and systematic variation of the dielectric environment to differentiate the effects of charged impurities and short-range scatterers. The results show that charged impurities indeed lead to a conductivity linear in density in graphene, with a scattering magnitude that agrees quantitatively with theoretical estimates [1]; increased dielectric screening reduces scattering from charged impurities, but increases scattering from short-range scatterers [2]. We evaluate the effects of the corrugations (ripples) of graphene on SiO2 on transport by measuring the height-height correlation function. The results show that the corrugations cannot mimic long-range (charged impurity) scattering effects, and have too small an amplitude-to-wavelength ratio to significantly affect the observed mobility via short-range scattering [3, 4]. Temperature-dependent measurements show that longitudinal acoustic phonons in graphene produce a resistivity linear in temperature and independent of carrier density [5]; at higher temperatures, polar optical phonons of the SiO2 substrate give rise to an activated, carrier density-dependent resistivity [5]. Together the results paint a complete picture of charge carrier transport in graphene on SiO2 in the diffusive regime.Comment: 28 pages, 7 figures, submitted to Graphene Week proceeding

The influence of cluster emission and the symmetry energy on neutron-proton spectral double ratios

Emissions of free neutrons and protons from the central collisions of 124Sn+124Sn and 112Sn+112Sn reactions are simulated using the Improved Quantum Molecular Dynamics model with two different density dependence of the symmetry energy in the nuclear equation of state. The constructed double ratios of the neutron to proton ratios of the two reaction systems are found to be sensitive to the symmetry terms in the EOS. The effect of cluster formation is examined and found to affect the double ratios mainly in the low energy region. In order to extract better information on symmetry energy with transport models, it is therefore important to have accurate data in the high energy region which also is affected minimally by sequential decays.Comment: 11 pages, 4 figure

Soft and hard wall in a stochastic reaction diffusion equation

We consider a stochastically perturbed reaction diffusion equation in a bounded interval, with boundary conditions imposing the two stable phases at the endpoints. We investigate the asymptotic behavior of the front separating the two stable phases, as the intensity of the noise vanishes and the size of the interval diverges. In particular, we prove that, in a suitable scaling limit, the front evolves according to a one-dimensional diffusion process with a non-linear drift accounting for a "soft" repulsion from the boundary. We finally show how a "hard" repulsion can be obtained by an extra diffusive scaling.Comment: 33 page