75,053 research outputs found
The removal of methyl violet 2B dye using palm kernel activated carbon: thermodynamic and kinetics model
No full textThe Benefits of Being Economics Professor A (and not Z)
No full textAlphabetic name ordering on multi-authored academic papers, which is the convention in the economics discipline and various other disciplines, is to the advantage of people whose last name initials are placed early in the alphabet. As it turns out, Professor A, who has been a first author more often than Professor Z, will have published more articles and experienced afaster growth rate over the course of her career as a result of reputation and visibility. Moreover, authors know that name ordering matters and indeed take ordering seriously: Several characteristics of an author group composition determine the decision to deviate from the default alphabetic name order to a significant extent.performance measurement, incentives, economists, name ordering
Final word on Jersey Dutch
No full textIn this article, William Z. Shetter compares and contrasts the dialects that developed between different Dutch colonies in the New World. He explores in-depth the nuances of Jersey Dutch, and provides theories to explain how Dutch and colonial languages blended. The article is reprinted from American Speech, December 1958, Volum XXXIII, No. 4
Material model characterization of a Ti/SiC metal matrix nanocomposite coating subjected to hypervelocity impact
No full textTitanium alloys have been extensively used in the aerospace industry because of their outstanding properties, such as high strength-to-weight ratios, high corrosion resistances, and high melting points. However, it is hypothesized that the performance of titanium alloys can be further enhanced to be more resistant to hypervelocity impact by coating them. Earlier experimental investigations showed that coating a Ti-6Al-4V substrate by Ti/SiC Metal Matrix Nanocomposite (MMNC) improved hypervelocity impact resistance of the composite. The coating had 7% SiC by volume. These experiments were simulated using the Smoothed Particle Hydrodynamics (SPH) modeling approach. Johnson-Cook material models were used for the Ti-6Al-4V substrate and the Lexan projectile. Due to the lack of detailed mechanical characterization of the MMNC, a bilinear elastic plastic material model was used to model the coating. In this study, single-parameter sensitivity analyses were conducted to understand the sensitivity of the SPH model based on comparison with the experimental crater volume. The parameters of the bilinear elastic plastic material model were modulus of elasticity, Poisson's ratio, yield strength, tangent modulus, and the failure strain. These parameters were varied by ±5%, and ±10% of their respective base values for a Ti/SiC Metal Matrix Nanocomposite (MMNC) with 35% SiC by volume for which stress-strain curves under various strain rates were available. These values were applied to the full range of tested velocities. Exploiting the parameters from sensitivity analyses, the results show that the accuracy of SPH modeling of MMNC can be enhanced when experimental data is not available. The results also show that bilinear elastic plastic material model can be used for MMNC coating under elevated strain rates
Effect of gamma rays on magnetic and linear/nonlinear optical properties of pristine and modified nickel ferrite nanoparticles
No full textIn this study, pure and surfactant-added nickel ferrite nanoparticles are successfully synthesized using the co-precipitation method. The prepared samples are investigated before and after irradiation of gamma ray and compared. The linear and nonlinear optical responses, morphological, magnetic, and structural properties are examined using the photoluminescence, ultraviolet-visible spectroscopy, z-scan technique, field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), vibrating-sample magnetometer (VSM), and Raman spectroscopy analysis. The XRD analyses of the samples showed their crystallinity with no significant change after gamma irradiation. The grain sizes of the irradiated and surfactant-added nickel ferrites are decreased. According to the FE-SEM images, the synthesized particles are spherical. Based on the VSM results, the nanoparticles displayed superparamagnetic properties. However, after gamma irradiation and adding the surfactant, the magnetic saturation is reduced. The band gap of unmodified samples is measured in the range of 2.05-3.92 eV before and after gamma irradiation. Moreover, the band gap of the nickel ferrite samples modified with cetyltrimethylammonium bromide-tartaric acid is in the range of 2.07-3.84 eV. The closed- and open-aperture z-scans are used to measure the nonlinear refractive index and absorption coefficient, respectively. Based on analysis and data, our synthesized nanoparticles can be a good candidate for various applications such as hyperthermia, catalysis, and optical switches.This project is supported by Sahand University of Technology with contract number 23681
Logarithmic variance profiles and the corresponding f-1 spectra of temperature fluctuations in turbulent Rayleigh-Bénard convection
No full textWe report experimental results for the temperature variance 2(z) and the corresponding frequency spectra P(f) in turbulent Rayleigh-Bénard convection (RBC) in a cylindrical sample of aspect ratioT= D/L = 1:00 (D = 1:12 m is the diameter and L = 1:12 m the height). The measurements were conducted in the Rayleigh-number range 1011 < Ra < 1:35 1014 and Pr ' 0:8. For Ra = 1:35x1014, 2(z) could be described well by a logarithmic dependence on the vertical position z in a range of z 1 < z < z 2 with z 1 ' 70 and z 2 = 0:1L. Here L=(2Nu) is the thickness of a thin thermal sublayer adjacent to the horizontal plate where the heat flux (denoted by the Nusselt number Nu) is carried mostly by thermal diffusion. In the log layer, we found that the temperature spectra had a significant frequency range over which P(f) f with close to 1. As Ra decreased, increased so that the log layer became thinner. At Ra = 2:05 1011, z 2 < z 1 and therefore there was no range for a log layer. Correspondingly, the temperature spectrum near the horizontal plate did not have the f1 scaling form either
Statistics of the subgrid scales after the shock-turbulence interaction
No full textThe interaction of a normal shock with isotropic turbulence (IT) represents a basic problem for studying some of the phenomena associated with high speed flows, such as hypersonic flight, supersonic combustion and Inertial Confinement Fusion (ICF). In general, in practical applications, the shock width is much smaller than the turbulence scales and the upstream turbulent Mach number is modest. In this case, recent high resolution shock-resolved Direct Numerical Simulations (DNS) (Ryu and Livescu, J. Fluid Mech., 756, R1, 2014) show that the interaction can be described by the Linear Interaction Approximation (LIA). By using LIA to alleviate the need to solve the shock, DNS post-shock data can be generated at much higher Reynolds numbers than previously possible. Here, such results with Taylor Reynolds number around are used to investigate the properties of the subgrid scales (SGS). In particular, it is shown that the shock interaction decreases the asymmetry of the SGS dissipation PDF as the shock Mach number increases, with a significant enhancement in size of the regions and magnitude of backscatter
Transition to turbulence in a qblique shock-wave/boundary-layer interaction at M=15
No full textDirect numerical simulations are carried out for different forcing techniques to trigger transition during the interaction between an oblique shock-wave and a laminar boundary-layer at M = 1.5. Three forcing methods are used: a) forcing of oblique unstable modes, whose shape and behaviour are determined by the local linear stability theory, b) broadband free-stream acoustic disturbances, and c) a cold plasma flow control device. While the oblique-mode breakdown is dominant for low-amplitude forcing, long streaky structures drive the transition process in a high-amplitude disturbance environment. LES are also performed on the experimental setup by the Institute of Theoretical and Applied Mechanics (ITAM) from Novosibirsk State University with cold plasma actuation. As well as the disturbance type, the effect of Reynolds number and forcing amplitude will be investigated
Triangular Constellations in Flows
No full textParticles advected on the surface of a fluid can exhibit fractal clustering. The local structure of a fractal set is described by its dimension , which is the exponent of a power-law relating the mass in a ball to its radius : . It is desirable to characterise the {\em shapes} of constellations of points sampling a fractal measure, as well as their masses. The simplest example is the distribution of shapes of triangles formed by triplets of points, which we investigate for fractals generated by chaotic dynamical systems. The most significant parameter describing the triangle shape is the ratio of its area to the radius of gyration squared. We show that the probability density of has a phase transition: is independent of and approximately uniform below a critical flow compressibility , which we estimate. For the distribution appears to be described by two power laws: when , and when
Preferential concentration of particles in compressible turbulence
No full textThe behavior of particles in compressible turbulence has been seldom investigated to date despite its importance in many natural and industrial flows. Direct numerical simulations of particle-laden compressible isotropic turbulence are performed to study the preferential concentration of particles and the underling mechanisms. It turns out that heavy particles tend to concentrate in regions of low enstrophy and high fluid density (i.e, strain regions between vortex rings), especially the particles of Kolmogorov scale, which show the largest number density. Due to the compressibility, fluid particles do not distribute uniformly as in incompressible case, but show a tendency to bunch up in high density zones. The preliminary result might give some insights into compressible turbulent transport, dispersion and mixing as well as the subgrid-scale modeling for large-eddy simulation of particle-laden compressible flows
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