74,979 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
Fluorescencja oleju smarnego wzbudzana światłem ultrafioletowym
No full textThe paper describes the study on relationship between the engine lubricate oil quality and fluorescence phenomenon. In order to determine the Excitation-Emission spectra (EEMs) of oil samples, a spectrofluorometer combined with an optical fiber system were applied. Two methods of fluorescence measurement: when oil diluted in non-fluorescent solvent (n-hexane) is placed in the quartz-cuvette inside the spectrofluorometer, and when oil sample is placed outside the spectrofluorometer (then EEMs is measured through the optical fiber sensor) were utilized to analyze the shape of EEMs of lubricate oil. Moreover in the second case of measurement, the optical fiber sensor was placed at an angle of 45 degrees to the oil surface, similarly above the oil surface and beneath the oil surface directly submerged in oil. Preliminary measurement results presented in this paper – on one hand – indicate diversity in the shape of EEMs depending on the method of fluorescence measurement, on the other hand – indicate possibility to measure fluorescence of oil directly in engine lubricate oil circuit.W artykule przedstawiono wyniki badań związku pomiędzy jakością oleju smarnego a zjawiskiem fluorescencji. W celu wyznaczenia widm zupełnych fluorescencji próbek oleju wykorzystano spektrofluorymetr połączony ze światłowodowym systemem pomiarowym. Zanalizowano kształt widm odnoszących się do oleju smarnego w dwóch sytuacjach, gdy: olej jest rozpuszczony w niefluoryzującym medium (n-hexan) i umieszczony jest w przyrządzie w kwarcowej kuwecie oraz gdy próbka oleju znajduje się na zewnątrz przyrządu, sygnał jest przenoszony światłowodem. Ponadto przy pomiarach z zastosowaniem światłowodu ustawiona pod kątem 45° głowica pomiarowa zestawu światłowodowego znajduje się, odpowiednio: w powietrzu nad powierzchnią oleju albo pod powierzchnię oleju. Przedstawione w niniejszym artykule wstępne wyniki badań z jednej strony wskazują na zróżnicowanie kształtów widm zupełnych fluorescencji względem metody pomiarowej, z drugiej strony – wskazują na możliwość wyznaczania fluorescencji bez wstępnej obróbki laboratoryjnej, bezpośrednio w silnikowym obiegu oleju smarnego
Spektrofluorymetryczna charakterystyka zużytego oleju smarnego
No full textDeterioration of lubricate oil in combustion engines enforces measurements of parameters essential for proper operation of define driving system or to certain engine malfunctions indicate. Since the fluorescence phenomenon is known for oil excited by ultraviolet light - the question arises whether fluorescence spectra evolving with the time of exploitation of oil in the engine. In this paper the introductory studies of excitation-emission spectra (EEMs) for chosen lubricate oil are described. Both fresh and used oil (after 593 h of work in a ship engine), was used to measure EEMs. As a result of comparison of EEMs for both fresh and used lubricate oils more significant transformations in fluorescence spectra of oil caused by their exploitation are indicated. Obtained results allow to predict that spectrofluorimetry method could supplement present methods of used lubricating oil testing.Pogarszanie się właściwości oleju smarnego w silniku spalinowym skutkuje koniecznością monitorowania jego eksploatacyjnych parametrów. Z racji wykazywania przez oleje fluorescencji w świetle ultrafioletowym - powstaje pytanie, czy widma fluorescencji ewoluują wraz z czasem przebywania oleju w obiegu smarnym silnika. W artykule opisane są wstępne analizy zmian zupełnych widm fluorescencji (EEMs) dla różnych stężeń wybranego oleju smarnego. Do pomiaru EEMs oleju użyto dwóch form oleju – świeżego i przepracowanego w silniku okrętowym w czasie 593 h. W następstwie porównania widm uzyskanych dla świeżego i przepracowanego oleju wskazano na zachodzące najbardziej znaczące zmiany we fluorescencji oleju smarnego. Uzyskane wyniki pozwalają sądzić, że spektrofluorymetria mogłaby uzupełnić obecne metody testowania przepracowanego oleju
Modelling the bidirectional reflectance distribution functions (BRDF) of sea areas polluted by oil
No full textThe paper discusses the possibilities of modelling the bi-directional reflectance distribution function (BRDF) in sea areas polluted by oil. Three sea basin models are considered: a coastal one free of oil, one polluted by an oil film and one polluted by an oil emulsion. The following concentrations of oil were compared: for the film, 1 cm3 of oil per 1 m2 water surface, for the emulsion 1 cm3 of oil in 1 m3 of water. The optical properties of Romashkino crude oil were taken into consideration, as were various angles of incident solar light. The conversion of BRDFs into a directional distribution of the optical contrast of polluted areas is demonstrated
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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