Flow and aerodynamic noise control of a circular cylinder by local blowing

In this experimental study, the impact of symmetric local blowing on suppressing the vortex-induced noise of a circular cylinder was investigated. A highly instrumented cylinder with pressure taps and a series of blowing chambers was used to inject air along the span (seven times the cylinder diameter) at circumferential anglesθb=±41∘, ±90∘ and ±131∘ corresponding to the boundary layer, shear layers on the cylinder and separated shear layers, respectively. The investigation aimed to understand the noise reduction mechanism of local blowing by conducting near-field pressure and far-field noise measurements in synchronisation with flow field velocity measurements. Near-field pressure was measured around the circumference of the cylinder using a remote-sensing technique and planar particle image velocimetry was implemented to measure the velocity of the wake flow field at a diameter-based Reynolds number of Re=7×104. The results revealed that the interaction of the rolling up separated shear layers, under the influence of high-momentum fluid travelling from the free stream to the wake, induced significant vertical flow movement in the vortex-formation region. This movement led to strong alternating surface pressure fluctuations at the cylinder's shoulders, contributing to the scattering of noise. It was demonstrated that local blowing delayed vortex shedding for all cases, except at θb=±90∘, , which elongated the shear layers and pushed the high-momentum transfer area farther downstream. The application of local blowing at θb=±41∘ was particularly effective in increasing the vortex formation size due to reduced entrainment of fluid-bearing vorticity

Extrusion properties of a Zr-based bulk metallic glass

The extrusion behavior of Zr41.2Ti13.8Cu12.5Ni10Be22.5 metallic glasses in the supercooled liquid region was investigated. Good extrusion formability was observed under low strain rates at temperatures higher than 395 &deg;C. The metallic glasses were fully extruded without crystallization and failure within the range of T=395&ndash;415 &deg;C under strain rates from 5&times;10&minus;3 s&minus;1 to 5&times;10&minus;2 s&minus;1, and the deformation behavior of the metallic glasses during the extrusion was found to be in a Newtonian viscous flow mode by a strain rate sensitivity of 1.0.<br /

1/f Noise in Electron Glasses

We show that 1/f noise is produced in a 3D electron glass by charge fluctuations due to electrons hopping between isolated sites and a percolating network at low temperatures. The low frequency noise spectrum goes as \omega^{-\alpha} with \alpha slightly larger than 1. This result together with the temperature dependence of \alpha and the noise amplitude are in good agreement with the recent experiments. These results hold true both with a flat, noninteracting density of states and with a density of states that includes Coulomb interactions. In the latter case, the density of states has a Coulomb gap that fills in with increasing temperature. For a large Coulomb gap width, this density of states gives a dc conductivity with a hopping exponent of approximately 0.75 which has been observed in recent experiments. For a small Coulomb gap width, the hopping exponent approximately 0.5.Comment: 8 pages, Latex, 6 encapsulated postscript figures, to be published in Phys. Rev.

Symbolic Automata: The Toolkit

Abstract. The symbolic automata toolkit lifts classical automata anal-ysis to work modulo rich alphabet theories. It uses the power of state-of-the-art constraint solvers for automata analysis that is both expres-sive and efficient, even for automata over large finite alphabets. The toolkit supports analysis of finite symbolic automata and transducers over strings. It also handles transducers with registers. Constraint solving is used when composing and minimizing automata, and a much deeper and powerful integration is also obtained by internalizing automata as theories. The toolkit, freely available from Microsoft Research1, has re-cently been used in the context of web security for analysis of potentially malicious data over Unicode characters. Introduction. The distinguishing feature of the toolkit is the use and oper-ations with symbolic labels. This is unlike classical automata algorithms that mostly work assuming a finite alphabet. Adtantages of a symbolic representa-tion are examined in [4], where it is shown that the symbolic algorithms con

Experimental investigation of active local blowing on the aerodynamic noise reduction of a circular cylinder

The strategic implementation of local blowing (LB) around a circular cylinder within a uniformflow has demonstrated its capacity to effectively suppress aerodynamic noise under specific blowingconditions. This study aimed to comprehend the underlying mechanism driving noise reductionthrough the synchronisation of far-field noise with surface pressure fluctuations, which were measured at various peripheral angles. The parameters under examination for LB were the angle of blowing in relation to the freestream flow (θb) and the equivalent momentum coefficient (Cµ). A dedicated series of chambers were employed to facilitate LB at θb = ±41◦, ±90◦, ±131◦, and 180◦across the ranges of Cµ = 0.007–0.036 (Re = 0.7 × 105) and Cµ = 0.003–0.016 (Re = 1.04 × 105).Notably, LB at θb = ±41◦ and 180◦exhibited a remarkable reduction in tonal noise within theCµ range of 0.007 to 0.036. Despite this achievement, the most optimal overall sound pressurelevel was achieved at θb = 180◦. It was determined that the dissimilarity in noise reductionamong these LB cases was attributed to additional high-frequency noise generated by the blowing technique. The connection between the near- and far-field signals was established through recordedcoherence values. The investigation highlighted that surface pressure fluctuations initiated byvortex shedding in the pre- and post-separation regions, particularly at the fundamental vortexshedding frequency, had the most significant impact on far-field noise. The attenuation of suchsurface pressure fluctuations played a pivotal role in tonal noise reduction by LB, as evidenced bynotable reductions in lift fluctuations and the absence of amplitude modulation in both the time and frequency domains

Parton distribution function uncertainties and nuclear corrections for the LHC

We study nuclear effects of charged current deep inelastic neutrino-iron scattering in the framework of a chi^2 analysis of parton distribution functions (PDFs). We extract a set of iron PDFs which are used to compute x_Bj-dependent and Q^2-dependent nuclear correction factors for iron structure functions which are required in global analyses of free nucleon PDFs. We compare our results with nuclear correction factors from neutrino-nucleus scattering models and correction factors for charged lepton-iron scattering. We find that, except for very high x_Bj, our correction factors differ in both shape and magnitude from the correction factors of the models and charged-lepton scattering

Kink propagation in a two-dimensional curved Josephson junction

We consider the propagation of sine-Gordon kinks in a planar curved strip as a model of nonlinear wave propagation in curved wave guides. The homogeneous Neumann transverse boundary conditions, in the curvilinear coordinates, allow to assume a homogeneous kink solution. Using a simple collective variable approach based on the kink coordinate, we show that curved regions act as potential barriers for the wave and determine the threshold velocity for the kink to cross. The analysis is confirmed by numerical solution of the 2D sine-Gordon equation.Comment: 8 pages, 4 figures (2 in color

Translucency of Human Dental Enamel

Translucency of human dental enamel was determined by total transmittance of wavelengths from 400 to 700 nm. The transmission coefficient at 525 nm was 0.481 mm-1. Total transmission of light through human dental enamel increased with increasing wavelength. Human tooth enamel is more translucent at higher wavelengths. The translucency of wet human enamel and enamel after dehydration was also measured by total transmittance. The transmission coefficient at 525 nm decreased from 0.482 to 0.313 mm-1 after dehydration and was reversed on rehydration. The decrease in translucency occurred as a result of the replacement of water around the enamel prisms by air during dehydration.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/68115/2/10.1177_00220345810600100401.pd

Numerical renormalization group study of the 1D t-J model

The one-dimensional (1D) $t-J$ model is investigated using the density matrix renormalization group (DMRG) method. We report for the first time a generalization of the DMRG method to the case of arbitrary band filling and prove a theorem with respect to the reduced density matrix that accelerates the numerical computation. Lastly, using the extended DMRG method, we present the ground state electron momentum distribution, spin and charge correlation functions. The $3k_F$ anomaly of the momentum distribution function first discussed by Ogata and Shiba is shown to disappear as $J$ increases. We also argue that there exists a density-independent $J_c$ beyond which the system becomes an electron solid.Comment: Wrong set of figures were put in the orginal submissio

Nuclear Parton Distribution Functions

We study nuclear effects of charged current deep inelastic neutrino-iron scattering in the framework of a chi^2 analysis of parton distribution functions (PDFs). We extract a set of iron PDFs which are used to compute x_Bj-dependent and Q^2-dependent nuclear correction factors for iron structure functions which are required in global analyses of free nucleon PDFs. We compare our results with nuclear correction factors from neutrino-nucleus scattering models and correction factors for charged-lepton--iron scattering. We find that, except for very high x_Bj, our correction factors differ in both shape and magnitude from the correction factors of the models and charged-lepton scattering.Comment: 11 pages, 6 figures, to appear in the proceedings of the Ringberg Workshop "New Trends in HERA Physics 2008