Gluon Field Strength Correlation Functions within a Constrained Instanton Model

We suggest a constrained instanton (CI) solution in the physical QCD vacuum which is described by large-scale vacuum field fluctuations. This solution decays exponentially at large distances. It is stable only if the interaction of the instanton with the background vacuum field is small and additional constraints are introduced. The CI solution is explicitly constructed in the ansatz form, and the two-point vacuum correlator of gluon field strengths is calculated in the framework of the effective instanton vacuum model. At small distances the results are qualitatively similar to the single instanton (SI) case, in particular, the form factor $D_{1}$ is small, which is in agreement with the lattice calculations.Comment: 25 pages (RevTex), 7 ps figures; some references added, one figure replace

Advances in modeling gas adsorption in porous materials for the characterization applications

The dissertation studies methods for mesoporous materials characterization using adsorption at various levels of scale and complexity. It starts with the topic introduction, necessary notations and definitions, recognized standards, and a literature review. Synthesis of novel materials requires tailoring of the characterization methods and their thorough testing. The second chapter presents a nitrogen adsorption characterization study for silica colloidal crystals (synthetic opals). These materials have cage-like pores in the range of tens of nanometers. The adsorption model can be described within a macroscopic approach, based on the Derjaguin-Broekhoff-de Boer (DBdB) theory of capillary condensation. A kernel of theoretical isotherms is built and applied to the solution of the adsorption integral equation to derive the pore-size distribution from experimental data. The technique is validated with a surface modification of the samples so that it changes the interaction but not the pore size. The second chapter deals with the characterization of three-dimensional ordered mesoporous (3DOm) carbons. Similar to opals, these materials have cage-like mesopores, however, these pores are connected with large windows. These windows affect the adsorption process and calculated pore-size distributions. The grand canonical Monte Carlo simulations with derived solid-fluid potentials, which take into account the 3DOm carbons geometry, confirm the critical role of interconnections, their size, and number, for correct interpretation of adsorption data for the PSD calculations. The fourth chapter discusses a method for the pore size estimation that can serve as an alternative to the adsorption isotherms analysis. It is based on measurements of elastic properties of liquid that can be useful for the pore size estimation. A Vycor glass sample, a disordered mesoporous material with channel-like pores having a characteristic size of ca. 6-8 nm, is considered. The changes in longitudinal and shear moduli from the experimental data and molecular simulations are predicted with a near-quantitative agreement. Then, it follows by their relation of the moduli to the pore size, which is promising for characterization. The last fifth chapter considers a promising Monte Carlo method, the Kinetic Monte Carlo (kMC) algorithm. This method is efficient for the vapor-liquid equilibrium prediction in dense regions. This chapter shows a benchmark with conventional Metropolis et al algorithms as well as a parallelization scheme of the kMC algorithm

How much laser power can propagate through fusion plasma?

Propagation of intense laser beams is crucial for inertial confinement fusion, which requires precise beam control to achieve the compression and heating necessary to ignite the fusion reaction. The National Ignition Facility (NIF), where fusion will be attempted, is now under construction. Control of intense beam propagation may be ruined by laser beam self-focusing. We have identified the maximum laser beam power that can propagate through fusion plasma without significant self-focusing and have found excellent agreement with recent experimental data, and suggest a way to increase that maximum by appropriate choice of plasma composition with implication for NIF designs. Our theory also leads to the prediction of anti-correlation between beam spray and backscatter and suggests the indirect control of backscatter through manipulation of plasma ionization state or acoustic damping.Comment: 15 pages, 4 figures, submitted to Plasma Physics and Controlled Fusio

Multilevel Analysis of Oscillation Motions in Active Regions of the Sun

We present a new method that combines the results of an oscillation study made in optical and radio observations. The optical spectral measurements in photospheric and chromospheric lines of the line-of-sight velocity were carried out at the Sayan Solar Observatory. The radio maps of the Sun were obtained with the Nobeyama Radioheliograph at 1.76 cm. Radio sources associated with the sunspots were analyzed to study the oscillation processes in the chromosphere-corona transition region in the layer with magnetic field B=2000 G. A high level of instability of the oscillations in the optical and radio data was found. We used a wavelet analysis for the spectra. The best similarities of the spectra of oscillations obtained by the two methods were detected in the three-minute oscillations inside the sunspot umbra for the dates when the active regions were situated near the center of the solar disk. A comparison of the wavelet spectra for optical and radio observations showed a time delay of about 50 seconds of the radio results with respect to optical ones. This implies a MHD wave traveling upward inside the umbral magnetic tube of the sunspot. Besides three-minute and five-minute ones, oscillations with longer periods (8 and 15 minutes) were detected in optical and radio records.Comment: 17 pages, 9 figures, accepted to Solar Physics (18 Jan 2011). The final publication is available at http://www.springerlink.co