76,770 research outputs found
The Benefits of Being Economics Professor A (and not Z)
Get PDFAlphabetic 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
Robust estimation with latin hypercube sampling: a central limit theorem for Z-estimators
No full textLatin hypercube sampling (LHS) is a widely used stratified sampling method in computer experiments. In this work, we extend the existing convergence results for the sample mean under LHS to the broader class of -estimators, estimators defined as the zeros of a sample mean function. We derive the asymptotic variance of these estimators and demonstrate that it is smaller when using LHS compared to traditional independent and identically distributed (i.i.d.) sampling. Furthermore, we establish a Central Limit Theorem for -estimators under LHS, providing a theoretical foundation for its improved efficiency
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
Robust estimation with latin hypercube sampling: a central limit theorem for Z-estimators
No full textLatin hypercube sampling (LHS) is a widely used stratified sampling method in computer experiments. In this work, we extend the existing convergence results for the sample mean under LHS to the broader class of -estimators — estimators defined as the zeros of a sample mean function. We derive the asymptotic variance of these estimators and demonstrate that it is smaller when using LHS compared to traditional independent and identically distributed (i.i.d.) sampling. Furthermore, we establish a Central Limit Theorem for -estimators under LHS, providing a theoretical foundation for its improved efficiency
Prototype Development of Simple Boost Control Technique For Z-Source Inverter
No full textThis paper explains about Z-source inverter (ZSI), which is part Z-source converter. As traditional converter such as voltage-source converter and current-source converter have their major disadvantages that can poorly effect on electrical system, Z-source converter has been chosen as the most suitable alternative. Z-source converter can be applied to all kind of conversion, which are dc-dc, dc-ac, ac-ac and ac-dc. However, this research project mainly stresses about the dc-ac or inverting part. Z-source inverter has different kind of topologies, such as Improved Z-Source Inverter (IZSI), depend on the usage and its efficiency demand. IZSI has two major advantages compared to conventional ZSI, which are the ability to compress the capacitor voltage stress and also to surpass the inrush current ability. Based on these variables, both ZSI and IZSI will be compared in simulation mode, by using Matlab/SIMULINK software. One of the methods to control the switches in ZSI and IZSI is by using simple boost control method. Using this method, it allows the any two or more legs of the switches to be short-0circuited at the same time without creating any damage to the circuit. This situation then leads to the existence of active and non-active state. In this research project, simulation of z-source inverter had been conducted and all of the result will be presented at the end of the project, in term of comparison of both ZSI and IZSI outputs using simple boost control method
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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