Absence of Embedded Mass Shells: Cerenkov Radiation and Quantum Friction

We show that, in a model where a non-relativistic particle is coupled to a quantized relativistic scalar Bose field, the embedded mass shell of the particle dissolves in the continuum when the interaction is turned on, provided the coupling constant is sufficiently small. More precisely, under the assumption that the fiber eigenvectors corresponding to the putative mass shell are differentiable as functions of the total momentum of the system, we show that a mass shell could exist only at a strictly positive distance from the unperturbed embedded mass shell near the boundary of the energy-momentum spectrum.Comment: Revised version: a remark added at the end of Section

Quantum Brownian Motion in a Simple Model System

We consider a quantum particle coupled (with strength λ) to a spatial array of independent non-interacting reservoirs in thermal states (heat baths). Under the assumption that the reservoir correlations decay exponentially in time, we prove that the motion of the particle is diffusive at large times for small, but finite λ. Our proof relies on an expansion around the kinetic scaling limit ( $${\lambda \searrow 0}$$ , while time and space scale as λ−2) in which the particle satisfies a Boltzmann equation. We also show an equipartition theorem: the distribution of the kinetic energy of the particle tends to a Maxwell-Boltzmann distribution, up to a correction of O(λ2

Analysis of Wind Vertical Profiles of Thunderstorm Events in the Mediterranean

This paper was reviewed and accepted by the APCWE-IX Programme Committee for Presentation at the 9th Asia-Pacific Conference on Wind Engineering, University of Auckland, Auckland, New Zealand, held from 3-7 December 2017

Transport of Aflatoxin M1 in Human Intestinal Caco-2/TC7 Cells

Aflatoxin M1 (AFM1) is a hydroxylated metabolite of aflatoxin B1 (AFB1). After it is formed, it is secreted in the milk of mammals. Despite the potential risk of human exposure to AFM1, data reported in literature on the metabolism, toxicity, and bioavailability of this molecule are limited and out of date. The aim of the present research was to study the absorption profile of AFM1 and possible damage to tight junctions (TJ) of the intestinal Caco-2/TC7 clone grown on microporous filter supports. These inserts allowed for the separation of the apical and basolateral compartments which correspond to the in vivo lumen and the interstitial space/vascular systems of intestinal mucosa respectively. In this study, the Caco-2/TC7 cells were treated with different AFM1 concentrations (10–10,000 ng/kg) for short (40 min) and long periods of time (48 h). The AFM1 influx/efflux transport and effects on TJ were evaluated by measuring trans-epithelial electrical resistance and observing TJ protein (Zonula occludens-1 and occludin) localization. The results showed that: (i) when introduced to the apical and basolateral compartments, AFM1 was poorly absorbed by the Caco-2/TC7 cells but its transport across the cell monolayer occurred very quickly (Papp value of 105.10 ± 7.98 cm/s × 10−6). (ii) The integrity of TJ was not permanently compromised after exposure to the mycotoxin. Viability impairment or barrier damage did not occur either. The present results contribute to the evaluation of human risk exposure to AFM1, although the AFM1 transport mechanism need to be clarified

Measurements of jaw movements and TMJ pain intensity in patients treated with GaAlAs laser

The aim of this study was to evaluate the effectiveness of low-level laser therapy (LLLT) on the improvement of the mandibular movements and painful symptoms in individuals with temporomandibular disorders (TMD). Forty patients were randomly divided into two groups (n=20): Group 1 received the effective dose (GaAlAs laser ? 830 nm, 40 mW, 5J/cm2) and Group 2 received the placebo application (0 J/cm2), in continuous mode on the affected condyle lateral pole: superior, anterior, posterior, and posterior-inferior, twice a week during 4 weeks. Four evaluations were performed: E1 (before laser application), E2 (right after the last application), E3 (one week after the last application) and E4 (30 days after the last application). The Kruskal-Wallis test showed significant more improvements (p<0.01) in painful symptoms in the treated group than in the placebo group. A significant improvement in the range of mandibular movements was observed when the results were compared between the groups at E4. Laser application can be a supportive therapy in the treatment of TMD, since it resulted in the immediate decrease of painful symptoms and increased range of mandibular movements in the treated group. The same results were not observed in the placebo group.O objetivo deste estudo foi avaliar a eficácia da terapia com laser de baixa intensidade na melhora dos movimentos mandibulares e dos sintomas dolorosos em pacientes com disfunção temporomandibular (DTM). Quarenta pacientes foram aleatoriamente divididos em dois grupos (n=20): Grupo 1 recebeu a dose efetiva (laser de AsGaAl 830 nm, 40 mW, 5 J/cm2) e Grupo 2 recebeu a aplicação placebo (0 J/cm2), no modo contínuo no pólo lateral do côndilo afetado: superior, anterior, e posterior-posterior e inferior, 2 vezes por semana, por 2 meses. Quatro avaliações foram feitas: A1 (antes da aplicação), A2 (imediatamente após a última aplicação), A3 (uma semana após a última aplicação) e A4 (um mes após a última aplicação). O teste estatístico de Kruskal-Wallis mostrou melhoras significativas (p<0,01) nos sintomas dolorosos no grupo 1, diferentemente do grupo 2. Uma melhora significativa na extensão dos movimentos mandibulares foi observada quando os resultados foram comparados entre os dois grupos na A4. A aplicação do laser é uma terapia de suporte no tratamento da DTM, uma vez que resultou em imediata redução dos sintomas dolorosos e aumento na extensão dos movimentos mandibulares no grupo experimental. Os mesmos resultados não foram observados no grupo placebo

Photometric properties of resolved and unresolved magnetic elements

We investigate the photometric signature of magnetic flux tubes in the solar photosphere. We developed two dimensional, static numerical models of isolated and clustered magnetic flux tubes. We investigated the emergent intensity profiles at different lines-of-sight for various spatial resolutions and opacity models. We found that both geometric and photometric properties of bright magnetic features are determined not only by the physical properties of the tube and its surroundings, but also by the particularities of the observations, including the line/continuum formation height, the spatial resolution and the image analyses techniques applied. We show that some observational results presented in the literature can be interpreted by considering bright magnetic features to be clusters of smaller elements, rather than a monolithic flux tube.Comment: 12 page

Observed flux density enhancement at submillimeter wavelengths during an X-class flare

We analyse the 30 October, 2004, X1.2/SF solar event that occurred in AR 10691 (N13 W18) at around 11:44 UT. Observations at 212 and 405 GHz of the Solar Submillimeter Telescope (SST), with high time resolution (5 ms), show an intense impulsive burst followed by a long-lasting thermal phase. EUV images from the Extreme Ultraviolet Imaging Telescope (SOHO/EIT) are used to identify the possible emitting sources. Data from the Radio Solar Telescope Network (RSTN) complement our spectral observations below 15 GHz. During the impulsive phase the turnover frequency is above 15.4 GHz. The long-lasting phase is analysed in terms of thermal emission and compared with GOES observations. From the ratio between the two GOES soft X-ray bands, we derive the temperature and emission measure, which is used to estimate the free-free submillimeter flux density. Good temporal agreement is found between the estimated and observed profiles, however the former is larger than the latter.Comment: 13 pages, 7 figure

Radio spectral study of the cluster of galaxies Abell 2255

Spectral index studies of halos, relics, and radio galaxies provide useful information on their origin and connection with merger processes. We present WSRT multi-wavelength observations of the galaxy cluster Abell 2255 at 25 cm, 85 cm, and 2 m. The spectral index images allowed us to study the integrated spectrum of halo and relic and to investigate the physical properties of the Beaver head-tail radio galaxy belonging to the cluster. In the radio halo, the spectral index is steeper at the center and flatter at the locations of the radio filaments, clearly detected at 25 cm. In the relics, the spectral index flattens, moving away from the cluster center. For the Beaver radio galaxy, the spectrum severely steepens from the head towards the end of the tail, because of the energy losses suffered by the relativistic particles. In the 2 m map, which is the first high-sensitivity image presented in the literature at such a long wavelength, a new Mpc-size emission region is detected between the known radio halo and the NW relic. Not detecting this feature in the more sensitive 85 cm observations implies that it must have a very steep spectrum (alpha <= -2.6). The observational properties of the radio halo suggest that either we are looking at a superposition of different structures (filaments in the foreground plus real halo in the background) seen in projection across the cluster center or that the halo is intrinsically peculiar. The newly detected extended region to the NW of the halo could be considered as an asymmetric extension of the halo itself. However, since radio halos are known in the literature as structures showing a regular morphology, the new feature could represent the first example of steep Mpc-size diffuse structures (MDS), detected around clusters at very low frequencies.Comment: 23 pages, 18 figures. A&A, in pres

Liquid aspersion efficiency quantification experiment: application in ladder-type distributors

O presente texto descreve um equipamento na escala-piloto e um método simples para comparar a eficiência de distribuidores de líquido. A técnica consiste basicamente em analisar a massa do líquido coletado em 21 tubos verticais de 52mm de diâmetro interno e 800 mm de comprimento dispostos em arranjo quadrático colocados abaixo do distribuidor. Uma manta acrílica que não dispersa o líquido com 50 mm de espessura foi fixada entre o distribuidor e o banco de tubos para evitar respingos. Como exemplo de aplicação foram realizados ensaios com nove distribuidores do tipo espinha de peixe de 4 tubos paralelos cada, para uma coluna com 400 mm de diâmetro. Variaram-se o número (n) de furos (95, 127 e 159 furos/m²), o diâmetro (d) dos furos (2, 3 e 4 mm) e as vazões (q) de (1,2; 1,4 e 1,6m³/h). A melhor eficiência de espalhamento pelo menor desvio-padrão foi obtida com n de 159, d de 2 e q de 1,4 indicando as limitações de regras práticas de projeto. A pressão (p), na entrada do distribuidor, para essa condição, foi de apenas 51000 Pa (0,51 kgf/cm²) e a velocidade média (v) em cada orifício foi de 6,3 m/s.This paper describes a device developed on the pilot scale and a simple approach to compare liquid distributor efficiencies. The technique consists basically of analyzing the mass of the liquid collected in 21 vertical pipes measuring 52 mm in internal diameter and 800 mm in length placed in a quadratic arrangement and positioned below the distributor. A 50 mm thick acrylic blanket that does not disperse liquids was placed between the distributor and the pipe bank to avoid splashes. Assays were carried out with ladder-type distributors equipped with 4 parallel pipes each for a column measuring 400 mm in diameter as an example of the application. The number (n) of orifices (95, 127, and 159 orifices/m²), orifice diameter (d) (2, 3, and 4 mm) and the flowrate (q) (1.2; 1.4; and 1.6 m3/h) were varied. The best spread efficiency, which presented the lowest standard deviation, was achieved with 159 orifices, 2 mm and 1.4 m³/h. The pressure (p) at the distributor's inlet for this condition was only 51000 Pa (0.51 kgf/cm²), while the average velocity (v) was 6.3 m/s in each orifice. These results show some limitations of the practical rules used in distributor designs