Exciton relaxation in KBr and CaF₂ at low temperature: molecular dynamics study

We report here recent study of molecular dynamics simulation of exciton relaxation in several ionic crystals at low temperature. Both the lowest energy spin triplet and some of the low lying hole excited states are allowed to relax in view of studying the radiation defect formation channels. The previously used semi-classical program has been modified to implement the solution of Newton’s equations with 0.48 fs time step. The relaxation of an exciton localized on a single site (as Br⁰ + e, or F⁰ + e, respectively) is studied at 10 K in KBr and in CaF₂. In KBr the triplet self-trapped exciton leads to separated Frenkel pair in about 1–2 ps, followed by slow oscillation of the hole center along the (110) axis. The defect pair created is separated by about 10 Å (third nearest neighbor). In CaF₂, the relaxation reaches the geometry of the nearest Frenkel pair, with the hole center oriented along a (111) axis in about 0.3 ps at 10 K. However, at 80 K the system can undergo further relaxation into a slightly more distant defect pairs. When the hole is excited to higher levels, the molecule bond of the hole center undergoes violent oscillations. In KBr, the hole center is found to form in the second nearest neighbor position within about 0.5 ps. The species formed are, however, different from the well known primary radiation defects. Similar process is also observed in CaF₂

INTERACTIONS OF HUMAN ORAL CELLS WITH ORAL BACTERIAL

poster abstractIntroduction: Streptococcus mutans is the main etiological cause of den-tal caries, and it has been shown that individuals who smoke have increased dental caries. S. mutans is known to bind to or interact with MG63 osteo-blasts. However, very little is known about the effects of tobacco directly on these bacteria on their ability to affect human pulp MG63 osteoblasts. We are hypothesizing that tobacco upregulates the expression of pro-inflammatory cytokines and MMPs to increase the pathogenic potential of S. mutans. The objective of this research project is to investigate the effects that nicotine, cigarette smoke condensate (CSC), and dissolvable smokeless tobacco (DST)-extract treated bacterial cells have on humanMG63 osteo-blasts, in respect to their release of pro-inflammatory and anti-inflammatory cytokines, as well as MMP expression. In addition, the effects of the S. mutans cells will be examined for the ability to affect MG63 osteoblast growth. The long-term goal is to develop treatment modalities to reduce the effects of smoking on dental caries. Materials and Methods: S. mutans UA159 was incubated in Tryptic Soy Broth (TSB), with the following concentrations: 2 mg/mL nicotine, 0.125 mg/mL CSC, 100 uL/3 mL DST-extract, and a 0 mg/mL control group. The cultures were grown in the presence of the tobacco products for 8 h at 37oC in 5% CO2, and centrifuged to isolate cells and supernatants. The cells were washed and heat-killed for 1 h at 60oC. Human MG63 osteoblasts were iso-lated from extracted teeth, and cell passages 3-8 will be used. The tobacco-treated S. mutans cells and supernatants will be incubated with the osteo-blasts in culture plates for 72 h and cytokine expression evaluated by re-verse transcriptase polymerase chain reaction. Results: The protein concentration of each tobacco-treated sample was found. The undiluted concentrations of the nicotine- and CSC-treated cells were slightly lower and the DST-treated cells was slightly higher than the control cells. The undiluted nicotine (p<0.05) and DST-treated supernatants were higher than the control, while the CSC supernatant protein concentra-tion was lower. From our previous studies, it was found that nicotine in-creases bacteriocin production of S. mutans, so we might hypothesize that nicotine induces bacteriocin secretion, thus increasing dental caries

Single-filament Composite MgB2/SUS Ribbons by Powder-In-Tube Process

We report the successful fabrication of single-filament composite MgB2/SUS ribbons, as an ultra-robust conductor type, employing the powder-in-tube (PIT) process, by swaging and cold rolling only. The remarkable transport critical current (Ic) of the non-sintered MgB2/SUS ribbon has observed, as an unexpected result. Transport critical currents Ic ~ 316 A at T = 4.2 K and Ic ~ 82 A at T = 20 K were observed at self-field, for the non-sintered composite MgB2/SUS ribbon. In addition, the persistent current density Jp values, that were estimated by Bean formula, were more than ~ 7 &#61620; 105 A/cm2 at T = 5 K, and ~ 1.2 &#61620; 105 A/cm2 at T = 30 K, for the sintered composite MgB2/SUS ribbon, at H = 0 G.Comment: 10 pages, 4 figure

Model of a fluid at small and large length scales and the hydrophobic effect

We present a statistical field theory to describe large length scale effects induced by solutes in a cold and otherwise placid liquid. The theory divides space into a cubic grid of cells. The side length of each cell is of the order of the bulk correlation length of the bulk liquid. Large length scale states of the cells are specified with an Ising variable. Finer length scale effects are described with a Gaussian field, with mean and variance affected by both the large length scale field and by the constraints imposed by solutes. In the absence of solutes and corresponding constraints, integration over the Gaussian field yields an effective lattice gas Hamiltonian for the large length scale field. In the presence of solutes, the integration adds additional terms to this Hamiltonian. We identify these terms analytically. They can provoke large length scale effects, such as the formation of interfaces and depletion layers. We apply our theory to compute the reversible work to form a bubble in liquid water, as a function of the bubble radius. Comparison with molecular simulation results for the same function indicates that the theory is reasonably accurate. Importantly, simulating the large length scale field involves binary arithmetic only. It thus provides a computationally convenient scheme to incorporate explicit solvent dynamics and structure in simulation studies of large molecular assemblies

Relativistic graphene ratchet on semidisk Galton board

Using extensive Monte Carlo simulations we study numerically and analytically a photogalvanic effect, or ratchet, of directed electron transport induced by a microwave radiation on a semidisk Galton board of antidots in graphene. A comparison between usual two-dimensional electron gas (2DEG) and electrons in graphene shows that ratchet currents are comparable at very low temperatures. However, a large mean free path in graphene should allow to have a strong ratchet transport at room temperatures. Also in graphene the ratchet transport emerges even for unpolarized radiation. These properties open promising possibilities for room temperature graphene based sensitive photogalvanic detectors of microwave and terahertz radiation.Comment: 4 pages, 4 figures. Research done at Quantware http://www.quantware.ups-tlse.fr/. More detailed analysis is give

Effect of protease on growth performance and carcass characteristics of growing-finishing pigs

No Abstrac

Streamer Wave Events Observed in Solar Cycle 23

In this paper we conduct a data survey searching for well-defined streamer wave events observed by the Large Angle and Spectrometric Coronagraph (LASCO) on-board the Solar and Heliospheric Observatory (SOHO) throughout Solar Cycle 23. As a result, 8 candidate events are found and presented here. We compare different events and find that in most of them the driving CMEs ejecta are characterized by a high speed and a wide angular span, and the CME-streamer interactions occur generally along the flank of the streamer structure at an altitude no higher than the bottom of the field of view of LASCO C2. In addition, all front-side CMEs have accompanying flares. These common observational features shed light on the excitation conditions of streamer wave events. We also conduct a further analysis on one specific streamer wave event on 5 June 2003. The heliocentric distances of 4 wave troughs/crests at various exposure times are determined; they are then used to deduce the wave properties like period, wavelength, and phase speeds. It is found that both the period and wavelength increase gradually with the wave propagation along the streamer plasma sheet, and the phase speed of the preceding wave is generally faster than that of the trailing ones. The associated coronal seismological study yields the radial profiles of the Alfv\'en speed and magnetic field strength in the region surrounding the streamer plasma sheet. Both quantities show a general declining trend with time. This is interpreted as an observational manifestation of the recovering process of the CME-disturbed corona. It is also found that the Alfv\'enic critical point is at about 10 R$_\odot$ where the flow speed, which equals the Alfv\'en speed, is $\sim$ 200 km s$^{-1}$

Effects of dimensionality and anisotropy on the Holstein polaron

We apply weak-coupling perturbation theory and strong-coupling perturbation theory to the Holstein molecular crystal model in order to elucidate the effects of anisotropy on polaron properties in D dimensions. The ground state energy is considered as a primary criterion through which to study the effects of anisotropy on the self-trapping transition, the self-trapping line associated with this transition, and the adiabatic critical point. The effects of dimensionality and anisotropy on electron-phonon correlations and polaronic mass enhancement are studied, with particular attention given to the polaron radius and the characteristics of quasi-1D and quasi-2D structures. Perturbative results are confirmed by selected comparisons with variational calculations and quantum Monte Carlo data

The CDF dijet excess from intrinsic quarks

The CDF collaboration reported an excess in the production of two jets in association with a $W$. We discuss constraints on possible new particle state interpretations of this excess. The fact of no statistically significant deviation from the SM expectation for {$Z$+dijet} events in CDF data disfavors the new particle explanation. We show that the nucleon intrinsic strange quarks provide an important contribution to the $W$ boson production in association with a single top quark production. Such {$W$+t} single top quark production can contribute to the CDF {$W$+dijet} excess, thus the nucleon intrinsic quarks can provide a possible explanation to the CDF excess in {$W$+dijet} but not in {$Z$+dijet} events.Comment: 4 latex pages, 1 figure. Version for journal publicatio