Non-Riemannian vortex geometry of rotational viscous fluids and breaking of the acoustic Lorentz invariance

Acoustic torsion recently introduced in the literature (Garcia de Andrade,PRD(2004),7,64004) is extended to rotational incompressible viscous fluids represented by the generalised Navier-Stokes equation. The fluid background is compared with the Riemann-Cartan massless scalar wave equation, allowing for the generalization of Unruh acoustic metric in the form of acoustic torsion, expressed in terms of viscosity, velocity and vorticity of the fluid. In this work the background vorticity is nonvanishing but the perturbation of the flow is also rotational which avoids the problem of contamination of the irrotational perturbation by the background vorticity. The acoustic Lorentz invariance is shown to be broken due to the presence of acoustic torsion in strong analogy with the Riemann-Cartan gravitational case presented recently by Kostelecky (PRD 69,2004,105009). An example of analog gravity describing acoustic metric is given based on the teleparallel loop where the acoustic torsion is given by the Lense-Thirring rotation and the acoustic line element corresponds to the Lense-Thirring metric

Primordial magnetic fields constrained by CMB anisotropies and dynamo cosmology

Magneto-curvature stresses could deform magnetic field lines and this would give rise to back reaction and restoring magnetic stresses [Tsagas, PRL (2001)]. Barrow et al [PRD (2008)] have shown in Friedman universe the expansion to be slow down in spatial section of negative Riemann curvatures. From Chicone et al [CMP (1997)] paper, proved that fast dynamos in compact 2D manifold implies negatively constant Riemannian curvature, here one applies the Barrow-Tsagas ideas to cosmic dynamos. Fast dynamo covariant stretching of Riemann slices of cosmic Lobachevsky plane is given. Inclusion of advection term on dynamo equations [Clarkson et al, MNRAS (2005)] is considered. In absence of advection a fast dynamo is also obtained. Viscous and restoring forces on stretching particles decrease, as magnetic rates increase. From COBE data ($\frac{{\delta}B}{B}\approx{10^{-5}}$), one computes stretching $\frac{{\delta}V^{y}}{V^{y}}=1.5\frac{{\delta}B}{B}\approx{1.5{\times}10^{-5}}$. Zeldovich et al has computed the maximum magnetic growth rate as ${\gamma}_{max}\approx{8.0{\times}10^{-1}t^{-1}}$. From COBE data one computes a lower growth rate for the magnetic field as ${\gamma}_{COBE}\approx{6.0{\times}10^{-6}t^{-1}}$, well-within Zeldovich et al estimate. Instead of the Harrison value $B\approx{t^{{4/3}}}$ one obtains the lower primordial field $B\approx{10^{-6}t}$ which yields the $B\approx{10^{-6}G}$ at the $1s$ Big Bang time.Comment: Dept of theoretical physics-UERJ-Brasi

Lattice perturbation theory for gluonic and fermionic actions

We calculate the two loop Landau mean links and the one loop renormalisation of the anisotropy for Wilson and improved SU(3) gauge actions, using twisted boundary conditions as a gauge invariant infrared regulator. We show these accurately describe simulated results, and outline a method for generating Feynman rules for general lattice field theories, in a form suitable for efficient numerical calculation of perturbative loop diagrams.Comment: 6 pages of LaTeX. Two posters at Lattice2002(improve) combine

One-Dimensional Control System for a Linear Motor of a Two-Dimensional Nanopositioning Stage Using Commercial Control Hardware

A two-dimensional (2D) nanopositioning platform stage (NanoPla) is in development at the University of Zaragoza. To provide a long travel range, the actuators of the NanoPla are four Halbach linear motors. These motors present many advantages in precision engineering, and they are custom made for this application. In this work, a one-dimensional (1D) control strategy for positioning a Halbach linear motor has been developed, implemented, and experimentally validated. The chosen control hardware is a commercial Digital Motor Control (DMC) Kit from Texas Instruments that has been designed to control the torque or the rotational speed of rotative motors. Using a commercial control hardware facilitates the applicability of the developed control system. Nevertheless, it constrains the design, which needs to be adapted to the hardware and optimized. Firstly, a dynamic characterization of the linear motor has been performed. By leveraging the dynamic properties of the motor, a sensorless controller is proposed. Then, a closed-loop control strategy is developed. Finally, this control strategy is implemented in the control hardware. It was verified that the control system achieves the working requirements of the NanoPla. It is able to work in a range of 50 mm and perform a minimum incremental motion of 1 mu m

Correlation between mechanical properties and dendrite array of the Sn-Zn alloy for lead-free solder

The development of lead-free solder has been an urgent and hard task for material due to health and environmental concerns over the lead content of conventional solders. The aim of the present work is to investigate the influence of microstructural dendritic array parameters of a Sn-4wt% and 12 wt% Zn lead-free solder alloys on its mechanical properties. A water-cooled (25 °C ±2°C) unidirectional solidification system was used in the experiments. The solidification set-up was designed in such way that the heat was extracted only through the water-cooled bottom, promoting vertical upward directional solidification. The experimental results permitted to establish correlations between thermal parameters and secondary dendrite arm spacings with ultimate tensile strength and elongation. It was concluded that the microstructural refinement has significantly improved the elongation (of about 10%). It was also found that, in a range of the cooling rate of about 0.5 and 10 ºC/s, the Sn-4 wt% Zn solder alloy has lower variation of the tensile strength (31 to 32 MPa) and elongation than the Sn-12 wt% Zn solder alloy (29 to 33 MPa).O desenvolvimento de solda sem chumbo tem sido uma tarefa árdua para cientistas de materiais pelas preocupações com a saúde e com o meio ambiente devido ao conteúdo de chumbo das soldas convencionais. O objetivo do presente trabalho é investigar a influência dos parâmetros da microestrutura dendrítica nas propriedades mecânicas das ligas sem chumbo: Sn-4 e 12%p Zn. Amostras das ligas em estudo foram obtidas por experimentos de solidificação conduzidos em um aparato que proporciona uma solidificação unidirecional vertical ascendente refrigerado à água (25 °C ±2°C), o qual garante a extração de calor apenas pela base do lingote em regime transitório de extração de calor. Os resultados experimentais permitiram estabelecer correlações entre parâmetros térmicos e espaçamentos dendríticos secundários com a resistência à tração e alongamento. Conclui-se dos resultados experimentais que o alongamento específico mostra-se significantemente melhorado (em torno de 10%) com o refino microestrutural para ambas as ligas. Encontrou-se também que em taxas de resfriamento na faixa entre 0,5 e 10 ºC/s, a liga Sn-4%p Zn é aquela que apresenta a menor variação entre limites de resistência à tração (31 a 32 MPa) e alongamento que a liga Sn-12%p Zn (29 a 33 MPa).767776Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

Quasi Free 238U (e,e'f)-Cross Section in Macroscopic-Microscopic Approach

We present the result of a theoretical study of inclusive quasi free electrofission of $^{238}$U. The off-shell $$cross sections for the quasi free reaction stage have been calculated within the Plane Wave Impulse Approximation (PWIA), using a Macroscopic -Microscopic description of the proton and neutron single particle momentum distributions. Electron wave function distortion corrections were included using the effective momentum approximation, and the Final State Interaction (FSI) effects were calculated using an optical potential. The fissility for the proton single hole excited states of the residual nucleus $^{237}$Pa was calculated both without and with contributions of the pre-equilibrium emission of the particles. The fissility for $^{237,238}U$ residual nuclei was calculated within the compound nucleus model. The $(e,e^{\prime}f)-$cross sections thus obtained were compared with available experimental data.Comment: 26 pages, 7 figure

Permeability, Roughness And Topography Of Enamel After Bleaching: Tracking Channels Of Penetration With Silver Nitrate

Aim: This study evaluated the surface roughness, topography and permeability of bovine enamel by profilometry and scanning electron microscopy (SEM) with and without silver nitrate solution, after exposure to different bleaching agents. Methods: Fifty-two enamel samples were randomly divided into four groups (n=13): CP16% -16% carbamide peroxide - Whiteness Perfect; HP6% - 6% hydrogen peroxide - White Class; HP35% - 35% hydrogen peroxide Whiteness HP Maxx; and Control - not bleached and kept in artificial saliva. For roughness analysis, average surface roughness (Ra) and flatness coefficient (Rku) parameters were used. The topography and permeability were examined by SEM. For permeability evaluation, the samples were immersed in a 50% silver nitrate solution and analyzed using a backscattered electron and secondary electron mode. Results: For the roughness (Ra) evaluation, Kruskal-Wallis and Wilcoxon Signed Ranks Test were used, showing an increase on the surface roughness in all bleached groups. The Rku parameter suggested changes on enamel integrity. The SEM micrographs indicated changes on enamel topography and different levels of silver nitrate penetration in the samples of the bleached groups. In the overall analysis, the bleaching agents promoted surface changes and higher silver nitrate penetration when compared to the control group. Conclusions: It may be concluded that different bleaching agents might alter the topography and roughness of enamel surface. Moreover, the higher infiltration of silver nitrate suggests an easier penetration path for the oxygen molecules into the dentin substrate.10116Nathoo, S.A., The chemistry and mechanisms of extrinsic and intrinsic discoloration (1997) J Am Dent Assoc, 128 (SUPPL.), pp. 6S-10SMcEvoy, S.A., Chemical agents for removing intrinsic stains from vital teeth. II. Current techniques and their clinical application (1989) Quintessence Int, 20, pp. 379-384Ben-Amar, A., Liberman, R., Gorfil, C., Bernstein, Y., Effect of mouthguard bleaching on enamel surface (1995) Am J Dent, 8, pp. 29-32Lynch, E., Sheerin, A., Samarawickrama, D.Y., Atherton, M.A., Claxson, A.W., Hawkes, J., Molecular mechanisms of the bleaching actions associated with commercially-available whitening oral health care products (1995) J Ir Dent Assoc, 41, pp. 94-102Bowles, W.H., Ugwuneri, Z., Pulp chamber penetration by hydrogen peroxide following vital bleaching procedures (1987) J Endod, 13, pp. 375-377Sun, G., The role of lasers in cosmetic dentistry (2000) Dent Clin North Am, 44, pp. 831-850Hegedus, C., Bistey, T., Flora-Nagy, E., Keszthelyi, G., Jenei, A., An atomic force microscopy study on the effect of bleaching agents on enamel surface (1999) J Dent, 27, pp. 509-515Park, H.J., Kwon, T.Y., Nam, S.H., Kim, H.J., Kim, K.H., Kim, Y.J., Changes in bovine enamel after treatment with a 30% hydrogen peroxide bleaching agent (2004) Dent Mater J, 23, pp. 517-521Iwamoto, N., Shimada, Y., Tagami, J., Penetration of silver nitrate into bleached enamel, dentin, and cementum (2007) Quintessence Int, 38, pp. e183-e188Cavalli, V., Arrais, C.A., Giannini, M., Ambrosano, G.M., High-concentrated carbamide peroxide bleaching agents effects on enamel surface (2004) J Oral Rehabil, 31, pp. 155-159Hosoya, N., Honda, K., Iino, F., Arai, T., Changes in enamel surface roughness and adhesion of Streptococcus mutans to enamel after vital bleaching (2003) J Dent, 31, pp. 543-548Josey, A.L., Meyers, I.A., Romaniuk, K., Symons, A.L., The effect of a vital bleaching technique on enamel surface morphology and the bonding of composite resin to enamel (1996) J Oral Rehabil, 23, pp. 244-250Lee, C.Q., Cobb, C.M., Zargartalebi, F., Hu, N., Effect of bleaching on microhardness, morphology, and color of enamel (1995) Gen Dent, 43, pp. 158-160McGuckin, R.S., Babin, J.F., Meyer, B.J., Alterations in human enamel surface morphology following vital bleaching (1992) J Prosthet Dent, 68, pp. 754-760Pinto, C.F., Oliveira, R., Cavalli, V., Giannini, M., Peroxide bleaching agent effects on enamel surface microhardness, roughness and morphology (2004) Braz Oral Res, 18, pp. 306-311Shannon, H., Spencer, P., Gross, K., Tira, D., Characterization of enamel exposed to 10% carbamide peroxide bleaching agents (1993) Quintessence Int, 24, pp. 39-44Zalkind, M., Arwaz, J.R., Goldman, A., Rotstein, I., Surface morphology changes in human enamel, dentin and cementum following bleaching: a scanning electron microscopy study (1996) Endod Dent Traumatol, 12, pp. 82-88Ernst, C.P., Marroquin, B.B., Willershausen-Zonnchen, B., Effects of hydrogen peroxide-containing bleaching agents on the morphology of human enamel (1996) Quintessence Int, 27, pp. 53-56Gultz, J., Kaim, J., Scherer, W., Gupta, H., Two in-office bleaching systems: a scanning electron microscope study (1999) Compend Contin Educ Dent, 20, pp. 965-968. , 70quiz 72Haywood, V.B., Heymann, H.O., Nightguard vital bleaching: how safe is it? (1991) Quintessence Int, 22, pp. 515-523Haywood, V.B., Leech, T., Heymann, H.O., Crumpler, D., Bruggers, K., Nightguard vital bleaching: effects on enamel surface texture and diffusion (1990) Quintessence Int, 21, pp. 801-804Oltu, U., Gurgan, S., Effects of three concentrations of carbamide peroxide on the structure of enamel (2000) J Oral Rehabil, 27, pp. 332-340Spalding, M., Taveira, L.A., de Assis, G.F., Scanning electron microscopy study of dental enamel surface exposed to 35% hydrogen peroxide: alone, with saliva, and with 10% carbamide peroxide (2003) J Esthet Restor Dent, 15, pp. 154-165Sulieman, M., Addy, M., Macdonald, E., Rees, J.S., A safety study in vitro for the effects of an in-office bleaching system on the integrity of enamel and dentine (2004) J Dent, 32, pp. 581-590Tong, L.S., Pang, M.K., Mok, N.Y., King, N.M., Wei, S.H., The effects of etching, micro-abrasion, and bleaching on surface enamel (1993) J Dent Res, 72, pp. 67-71Bagheri, R., Tyas, M.J., Burrow, M.F., Subsurface degradation of resin-based composites (2007) Dent Mater, 23, pp. 944-951Reis, A., Grande, R.H., Oliveira, G.M., Lopes, G.C., Loguercio, A.D., A 2-year evaluation of moisture on microtensile bond strength and nanoleakage (2007) Dent Mater, 23, pp. 862-870Ritter, A.V., Ghaname, E., Leonard, R.H., The influence of dental unit waterline cleaners on composite-to-dentin bond strengths (2007) J Am Dent Assoc, 138, pp. 985-991. , quiz 1022-3Sano, H., Shono, T., Takatsu, T., Hosoda, H., Microporous dentin zone beneath resin-impregnated layer (1994) Oper Dent, 19, pp. 59-64Nanci, A., (2007) Ten Cate's oral histology: development, structure, and function, , 7th ed. Saint Louis: Mosby-ElsevierCeliberti, P., Pazera, P., Lussi, A., The impact of ozone treatment on enamel physical properties (2006) Am J Dent, 19, pp. 67-72Chen, J.H., Xu, J.W., Shing, C.X., Decomposition rate of hydrogen peroxide bleaching agents under various chemical and physical conditions (1993) J Prosthet Dent, 69, pp. 46-48Reyto, R., Laser tooth whitening (1998) Dent Clin North Am., 42, pp. 755-762. , xiBitter, N.C., Sanders, J.L., The effects of four bleaching agents on the enamel surface: a scanning electron microscopic study (1993) Quintessence Int, 24, pp. 817-824Leonard Jr., R.H., Austin, S.M., Haywood, V.B., Bentley, C.D., Change in pH of plaque and 10% carbamide peroxide solution during nightguard vital bleaching treatment (1994) Quintessence Int, 25, pp. 819-823Leonard Jr., R.H., Bentley, C.D., Haywood, V.B., Salivary pH changes during 10% carbamide peroxide bleaching (1994) Quintessence Int, 25, pp. 547-550Li, Y., Biological properties of peroxide-containing tooth whiteners (1996) Food Chem Toxicol, 34, pp. 887-904Price, R.B., Sedarous, M., Hiltz, G.S., The pH of tooth-whitening products (2000) J Can Dent Assoc, 66, pp. 421-426Yeh, S.T., Su, Y., Lu, Y.C., Lee, S.Y., Surface changes and acid dissolution of enamel after carbamide peroxide bleach treatment (2005) Oper Dent, 30, pp. 507-515Justino, L.M., Tames, D.R., Demarco, F.F., In situ and in vitro effects of bleaching with carbamide peroxide on human enamel (2004) Oper Dent, 29, pp. 219-22

Traversable Wormholes Construction in 2+1 Dimensions

We study traversable Lorentzian wormholes in the three-dimensional low energy string theory by adding some matter source involving a dilaton field. It will be shown that there are two-different types of wormhole solutions such as BTZ and black string wormholes depending on the dilaton backgrounds, respectively. We finally obtain the desirable solutions which confine exotic matter near the throat of wormhole by adjusting NS charge.Comment: 12 pages, 4 figures, JHEP style, one reference adde

Optical And Physical Properties Of Er3+-yb3+ Co-doped Tellurite Fibers

In this work we present results of physical and optical properties of Er3+-Yb3+ co-doped tellurite glasses and fibers. The Double Clad Tellurite Fibers (DCTFs) are based on glasses with the composition: TeO2-WO3-Nb2O5-Na 2O-Al2O3-Er2O3-Yb 2O3. The DCTFs were fabricated by using the rod-in-tube technique and a Heathway drawing tower. The optical absorption spectra (ranging from 350 to 1750 nm) of these fibers were measured using an Optical Spectrum Analyzer (OSA). The emission spectra, around 1550 nm band, of these fibers (lengths varying from 1 to 60 cm) were obtained by using a 980nm diode laser pump. The optimal Amplified Spontaneous Emission (ASE) spectra were observed for fiber lengths ranging from 2 to 6 cm. The Er 3+/Yb3+ co-doped DCTFs show an efficient up-conversion process in comparison with the Er3+-doped DCTF. © 2011 Copyright Society of Photo-Optical Instrumentation Engineers (SPIE).8120The Society of Photo-Optical Instrumentation Engineers (SPIE)Murugan, G.S., Suzuki, T., Ohishi, Y., Raman characteristics and nonlinear optical properties of tellurite and phosphotellurite glasses containing heavy metal oxides with ultrabroad Raman bands (2006) J. of Appl. Phys., 100, p. 023107Nandi, P., Jose, G., Ytterbium-doped P2O5-TeO2 glass for laser applications (2006) IEEE J. of Quat. Electron., 42, pp. 1115-1121Man, S.Q., Pun, E.Y.B., Chung, P.S., Tellurite glasses for 1.3 mm optical amplifiers" (1999) Opt. Comm., 168, pp. 369-373Wang, J.S., Vogel, E.M., Snitzer, E., Tellurite Glass: A New Candidate for Fiber Devices" (1994) Opt. Mat., 3, pp. 187-203Xu, S., Sun, H., Dai, S., Zhang, J., Jiang, Z., Upconversion luminescence of Tm3+/Yb3+-codoped oxyhalide tellurite glasses" (2005) Sol. St. Comm., 133, pp. 89-92Bookey, H.T., Lousteau, J., Jha, A., Gayraud, N., Thomson, R.R., Psaila, N.D., Li, H., Kar, A.K., Multiple rare earth emissions in a multicore tellurite fiber with a single pump wavelength" (2007) Opt. Express, 15, pp. 17554-17561Qin, G., Mori, A., Ohishi, Y., Brillouin lasing in a single-mode tellurite fiber" (2007) Opt. Lett., 32, pp. 2179-2181Zweig, A.D., Frenz, M., Romano, V., Weber, H.P., A comparative study of laser tissue interaction at 2.94 μm and 10.6 μm" (1988) Appl. Phys. B, 47, pp. 259-265Zhang, J., Dai, S., Wang, G., Sun, H., Zhang, L., Hu, L., Fabrication and emission properties of Er3+/Yb3+ codoped tellurite glass fiber for broadband optical amplification (2005) J. of Lum., 115, pp. 45-52Shixun, D., Tiefeng, X., Qiuhua, N., Xiang, S., Xunsi, W., Fabrication and gain performance of Er3+/Yb3+-codoped tellurite glass fiber (2008) J. of Rare Earths, 26, pp. 915-918Jakutis, J., Gomes, L., Amancio, C.T., Kassab, L.R.P., Martinelli, J.R., Wetter, N.U., Increased Er3+ upconversion in tellurite fibers and glasses by co-doping with Yb3+ (2010) Opt. Mat., 33, pp. 107-111Hruby, A., Evaluation of glass-forming tendency by means of DTA (1972) Czech J. Phys B, 22, pp. 1187-119