Isotropic heating of galaxy cluster cores via rapidly reorienting active galactic nucleus jets

Active galactic nucleus (AGN) jets carry more than sufficient energy to stave off catastrophic cooling of the intracluster medium (ICM) in the cores of cool-core clusters. However, in order to prevent catastrophic cooling, the ICM must be heated in a near-isotropic fashion and narrow bipolar jets with P-jet = 10(44-45) erg s(-1), typical of radio AGNs at cluster centers, are inefficient in heating the gas in the transverse direction to the jets. We argue that due to existent conditions in cluster cores, the supermassive black holes (SMBHs) will, in addition to accreting gas via radiatively inefficient flows, experience short stochastic episodes of enhanced accretion via thin disks. In general, the orientation of these accretion disks will be misaligned with the spin axis of the black holes (BHs) and the ensuing torques will cause the BH's spin axis (and therefore the jet axis) to slew and rapidly change direction. This model not only explains recent observations showing successive generations of jet-lobes-bubbles in individual cool-core clusters that are offset from each other in the angular direction with respect to the cluster center, but also shows that AGN jets can heat the cluster core nearly isotropically on the gas cooling timescale. Our model does require that the SMBHs at the centers of cool-core clusters be spinning relatively slowly. Torques from individual misaligned disks are ineffective at tilting rapidly spinning BHs by more than a few degrees. Additionally, since SMBHs that host thin accretion disks will manifest as quasars, we predict that roughly 1-2 rich clusters within z < 0.5 should have quasars at their centers.

Yb:YAG/YAG复合陶瓷薄片连续和调Q输出特性

采用面泵浦的CAMIL结构，我们研究了970 nm泵浦的Yb:YAG/YAG复合陶瓷薄片激光器，获得了连续和调Q的激光输出。在连续运转情况下，获得了最高1.05 W的激光输出，中心波长为1031 nm，后腔输出镜透射率为2％。我们同时获得了声光调Q的脉冲输出，重复频率从1 kHz到30 kHz，脉宽分别从166 ns到700 ns。

Surface wave techniques for the study of engineering structures and materials

A wire drive pulse echo method of measuring the spectrum of solid bodies described. Using an 's' plane representation, a general analysis of the transient response of such solids has been carried out. This was used for the study of the stepped amplitude transient of high order modes of disks and for the case where there are two adjacent resonant frequencies. The techniques developed have been applied to the measurenent of the elasticities of refractory materials at high temperatures. In the experimental study of the high order in-plane resonances of thin disks it was found that the energy travelled at the edge of the disk and this initiated the work on one dimensional Rayleigh waves.Their properties were established for the straight edge condition by following an analysis similar to that of the two dimensional case. Experiments were then carried out on the velocity dispersion of various circuits including the disk and a hole in a large plate - the negative curvature condition.Theoretical analysis established the phase and group velocities for these cases and experimental tests on aluminium and glass gave good agreement with theory. At high frequencies all velocities approach that of the one dimensional Rayleigh waves. When applied to crack detection it was observed that a signal burst travelling round a disk showed an anomalous amplitude effect. In certain cases the signal which travelled the greater distance had the greater amplitude.An experiment was designed to investigate the phenanenon and it was established that the energy travelled in two nodes with different velocities.It was found by analysis that as well as the Rayleigh surface wave on the edge, a seoond node travelling at about the shear velocity was excited and the calculated results gave reasonable agreement with the experiments.

Can the viscosity in astrophysical black hole accretion disks be close to its string theory bound?

String theory and gauge/gravity duality suggest the lower bound of shear viscosity (eta) to entropy density (s) for any matter to be mu h/4 pi k(B), when h and k(B) are reduced Planck and Boltzmann constants respectively and mu <= 1. Motivated by this, we explore eta/s in black hole accretion flows, in order to understand if such exotic flows could be a natural site for the lowest eta/s. Accretion flow plays an important role in black hole physics in identifying the existence of the underlying black hole. This is a rotating shear flow with insignificant molecular viscosity, which could however have a significant turbulent viscosity, generating transport, heat and hence entropy in the flow. However, in presence of strong magnetic field, magnetic stresses can help in transporting matter independent of viscosity, via celebrated Blandford-Payne mechanism. In such cases, energy and then entropy produces via Ohmic dissipation. In,addition, certain optically thin, hot, accretion flows, of temperature greater than or similar to 10(9) K, may be favourable for nuclear burning which could generate/absorb huge energy, much higher than that in a star. We find that eta/s in accretion flows appears to be close to the lower bound suggested by theory, if they are embedded by strong magnetic field or producing nuclear energy, when the source of energy is not viscous effects. A lower bound on eta/s also leads to an upper bound on the Reynolds number of the flow.

Laser-induced changes on the complex refractive indices of phase-change thin film

The refractive indices of crystalline phase-change films are usually obtained by thermal-induced crystallization. However, this is not accurate, because the crystallization of phase-change film in rewritable optical disks is laser induced. In this study, we use the initializer to crystallize the phase-change films. The dependence of the refractive index n and the extinction coefficient k of the phase-change films on the initialization conditions are studied. Remarkable changes of the refractive indices (especially k) are found when the initialization laser power density is 6.63 mW/mum(2) and the initialization velocity is 4.0 m/s. At the same time, the structure changes of the phase-change films are also studied. This dependence is explained by the structure change of the films. These results are significant in improving the accuracy of optical design and the thermal simulation of phase-change optical disks, as well as in the study of phase-change optical disks at shorter wavelengths. (C) 2003 Society of Photo-Optical Instrumentation Engineers.

Determination and analysis of the optical constants of thin films of nickel(II) and copper(II) hydrazone complexes by spectroscopic ellipsometry

Thin films of four nickel(II) and copper(II) hydrazone complexes, which will hopefully be used as recording layers for the next-generation of high-density recordable disks, were prepared by using the spin-coating method. Absorption spectra of the thin films on K9 optical glass substrates in the 300-700 nm wavelength region were measured. Optical constants (complex refractive indices N) and thickness d of the thin films prepared on single-crystal silicon substrates in the 275-675 nm wavelength region were investigated on a rotating analyzer-polarizer scanning ellipsometer by fitting the measured ellipsometric angles (Psi(lambda) and Delta(lambda)) with a 3-layer model (Si/dye film/air). The dielectric functions epsilon and absorption coefficients alpha as a function of the wavelength were then calculated. Additionally, a design to achieve high reflectivity and optimum dye film thickness with an appropriate reflective layer was performed with the Film Wizard software using a multilayered model (PC substrate/reflective layer/dye film/air) at 405 nm wavelength.

Growth and shape control of disks by bending and extension

Differential growth of thin elastic bodies furnishes a surprisingly simple explanation of the complex and intriguing shapes of many biological systems, such as plant leaves and organs. Similarly, inelastic strains induced by thermal effects or active materials in layered plates are extensively used to control the curvature of thin engineering structures. Such behaviour inspires us to distinguish and to compare two possible modes of differential growth not normally compared to each other, in order to reveal the full range of out-of-plane shapes of an initially flat disk. The first growth mode, frequently employed by engineers, is characterised by direct bending strains through the thickness, and the second mode, mainly apparent in biological systems, is driven by extensional strains of the middle surface. When each mode is considered separately, it is shown that buckling is common to both modes, leading to bistable shapes: growth from bending strains results in a double-curvature limit at buckling, followed by almost developable deformation in which the Gaussian curvature at buckling is conserved; during extensional growth, out-of-plane distortions occur only when the buckling condition is reached, and the Gaussian curvature continues to increase. When both growth modes are present, it is shown that, generally, larger displacements are obtained under in-plane growth when the disk is relatively thick and growth strains are small, and vice versa. It is also shown that shapes can be mono-, bi-, tri- or neutrally stable, depending on the growth strain levels and the material properties: furthermore, it is shown that certain combinations of growth modes result in a free, or natural, response in which the doubly curved shape of disk exactly matches the imposed strains. Such diverse behaviour, in general, may help to realise more effective actuation schemes for engineering structures. © 2012 Elsevier Ltd. All rights reserved.

Speciation of lead in seawater and river water by using Saccharomyces cerevisiae immobilized in agarose gel as a binding agent in the diffusive gradients in thin films technique

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Use of Saccharomyces cerevisiae immobilized in agarose gel as a binding agent for diffusive gradients in thin films

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Effect of diamond-like carbon thin film coated acrylic resin on candida albicans biofilm formation

Purpose: The purpose of this study was to evaluate the effect of diamond-like carbon thin films doped and undoped with silver nanoparticles coating poly(methyl methacrylate) (PMMA) on Candida albicans biofilm formation. The control of biofilm formation is important to prevent oral diseases in denture users. Materials and Methods: Forty-five PMMA disks were obtained, finished, cleaned in an ultrasonic bath, and divided into three groups: Gc, no surface coating (control group); Gdlc, coated with diamond-like carbon film; and Gag, coated with diamond-like carbon film doped with silver nanoparticles. The films were deposited using a reactive magnetron sputtering system (physical vapor deposition process). The specimens were characterized by optical profilometry, atomic force microscopy, and Rutherford backscattering spectroscopy analyses that determined differences in chemical composition and morphological structure. Following sterilization of the specimens by γ-ray irradiation, C. albicans (ATCC 18804) biofilms were formed by immersion in 2 ml of Sabouraud dextrose broth inoculated with a standardized fungal suspension. After 24 hours, the number of colony forming units (cfu) per specimen was counted. Data concerning biofilm formation were analyzed using ANOVA and the Tukey test (p < 0.05). Results: C. albicans biofilm formation was significantly influenced by the films (p < 0.00001), reducing the number of cfu, while not affecting the roughness parameters (p > 0.05). The Tukey test showed no significant difference between Gdlc and Gag. Films deposited were extremely thin (∼50 nm). The silver particles presented a diameter between 60 and 120 nm and regular distribution throughout the film surface (to Gag). Conclusion: Diamond-like carbon films, doped or undoped with silver nanoparticles, coating the base of PMMA-based dentures could be an alternative procedure for preventing candidosis in denture users. © 2013 by the American College of Prosthodontists.

Investigation of RuO2/Ta2O5 thin film evolution by thermogravimetry combined with mass spectrometry

The thermal evolution process of RuO2–Ta2O5/Ti coatings with varying noble metal content has been investigated under in situ conditions by thermogravimetry combined with mass spectrometry. The gel-like films prepared from alcoholic solutions of the precursor salts (RuCl3·3H2O, TaCl5) onto titanium metal support were heated in an atmosphere containing 20% O2 and 80% Ar up to 600 °C. The evolution of the mixed oxide coatings was followed by the mass spectrometric ion intensity curves. The cracking of retained solvent and the combustion of organic surface species formed were also followed by the mass spectrometric curves. The formation of carbonyl- and carboxylate-type surface species connected to the noble metal was identified by Fourier transform infrared emission spectroscopy. These secondary processes–catalyzed by the noble metal–may play an important role in the development of surface morphology and electrochemical properties. The evolution of the two oxide phases does not take place independently, and the effect of the noble metal as a combustion catalyst was proved.