183,019 research outputs found
Free radially expanding liquid sheet in air: time- and space-resolved measurement of the thickness field
The collision of a liquid drop against a small target results in the
formation of a thin liquid sheet that extends radially until it reaches a
maximum diameter. The subsequent retraction is due to the air-liquid surface
tension. We have used a time- and space-resolved technique to measure the
thickness field of this class of liquid sheet, based on the grey level
measurement of the image of a dyed liquid sheet recorded using a fast camera.
This method enables a precise measurement of the thickness in the range
, with a temporal resolution equal to that of the
camera. We have measured the evolution with time since impact, , and radial
position, , of the thickness, , for various drop volumes and impact
velocities. Two asymptotic regimes for the expansion of the sheet are
evidenced. The scalings of the thickness with and measured in the two
regimes are those that were predicted in \citet{Rozhkov2004} fort the
short-time regime and \citet{Villermaux2011} for the long time regime, but
never experimentally measured before. Interestingly, our experimental data also
evidence the existence of a maximum of the film thickness at
a radial position corresponding to the crossover of these
two asymptotic regimes. The maximum moves with a constant velocity of the order
of the drop impact velocity, as expected theoretically. Thanks to our
visualization technique, we also evidence an azimuthal thickness modulation of
the liquid sheets.Comment: accepted for publication in Journal of Fluid Mechanic
Is the Value Added Tax Reform in India Poverty-Improving? An Analysis of Data from Two Major States
The Value Added Tax (VAT) was introduced in India in place of Sales Tax, taking effect in April 1, 2005. These taxes are in the domain of different state governments within the country's federal set up. Although VAT is widely acclaimed to be a better system than the sales tax on grounds of efficiency in tax collection, no study has been undertaken to assess the impact of this reform measure on social equity. This paper addresses this need with the use of concentration curves and consumption dominance curves of various orders. The simulations were done on two major states in India, namely Maharashtra and West Bengal, using National Sample Survey Unit Level data for the 55th round. The results show that the reform is largely pro-poor, although there are ways to improve it with respect to some items predominantly consumed by the relatively poorer groups.Value added tax, Marginal tax reform, public distribution system, concentration curve, Lorenz curve, marginal efficiency cost of funds, consumption dominance
The Ascent of America's High-Growth Companies: An Analysis of the Geography of Entrepreneurship
This report offers the first-ever deep dive into the geographic trends of America's fastest growing private companies -- the Inc. 500. Inc. magazine's annual ranking, which began in 1982, has become an important point of pride for high-achieving companies and a source of research for economists. Not until now, however, has anyone dissected the past thirty years of comprehensive data from these high-growth companies. Through a partnership with Inc. magazine, the Ewing Marion Kauffman Foundation has done just that. In this, one of a set of studies examining Inc. 500 data over time, we offer a geographic analysis of how regional characteristics are associated with fast-growing companies and innovations. Tracing hundreds of Inc. firms per year and thousands per decade, we have captured a range of innovations and analyzed the regions that continuously produce fast-growing companies. Knowing that very little is understood about the geography of high-growth companies, we approached this analysis with a range of questions: where are the fast-growing Inc. firms located at the state and metropolitan levels? How have they shifted over time? Do we find greater geographic concentration of Inc. firms over time? How is the geography of Inc. firms different from commonly associated growth factors, such as high-tech industries, venture capital firms, and research universities?As you review the findings of this report, keep in mind that the creation of another ranking is not our primary objective. It is more important to demonstrate different regions with different sectors and strengths, in contrast to previously identified areas that have been highlighted as strong producers of high-tech companies. Thus, our objective is to shed light on formerly understudied areas of economic development
The distribution of red and blue galaxies in groups: an empirical test of the halo model
The popular halo model predicts that the power spectrum of the galaxy
fluctuations is simply the sum of the large scale linear halo-halo power
spectrum and the weighted power spectrum of the halo profile. Previous studies
have derived halo parameters from the observed galaxy correlation function.
Here we test the halo model directly for self-consistency with a minimal set of
theoretical assumptions by utilising the 2dF Galaxy Redshift Survey (2dFGRS).
We derive empirically the halo occupation and galaxy radial distributions in
the haloes of the 2dF Percolation-Inferred Galaxy Group (2PIGG) catalogue. The
mean halo occupation number is found to be well-fitted by a power-law, ~
M^b, at high masses, with b = 1.05, 0.88, 0.99 for red, blue and all galaxies
respectively (with 1-sigma errors of 15-19%). We find that the truncated NFW
profile provides a good fit to the galaxy radial distributions, with
concentration parameters c=3.9, 1.3, 2.4 for red, blue and all galaxies
respectively (with 1-sigma errors of 8-15%). Adding the observed linear power
spectrum to these results, we compare these empirical predictions of the halo
model with the observed correlation functions for these same 2dF galaxy
populations. We conclude that subject to some fine tuning it is an acceptable
model for the two-point correlations. Our analysis also explains why the
correlation function slope of the red galaxies is steeper than that of the blue
galaxies. It is mainly due to the number of red and blue galaxies per halo,
rather than the radial distribution within the haloes of the two galaxy
species.Comment: 15 pages, 15 figures. MNRAS accepted version. Adds appx. on profile
fitting; now use truncated NF
Preferential concentration of inertial sub-kolmogorov particles. The roles of mass loading of particles, Stokes and Reynolds numbers
Turbulent flows laden with inertial particles present multiple open questions
and are a subject of great interest in current research. Due to their higher
density compared to the carrier fluid, inertial particles tend to form high
concentration regions, i.e. clusters, and low concentration regions, i.e.
voids, due to the interaction with the turbulence. In this work, we present an
experimental investigation of the clustering phenomenon of heavy sub-Kolmogorov
particles in homogeneous isotropic turbulent flows. Three control parameters
have been varied over significant ranges: ,
and volume fraction . The scaling of clustering characteristics, such as the distribution
of Vorono\"i areas and the dimensions of cluster and void regions, with the
three parameters are discussed. In particular, for the polydispersed size
distributions considered here, clustering is found to be enhanced strongly
(quasi-linearly) by and noticeably (with a square-root
dependency) with , while the cluster and void sizes, scaled with the
Kolmogorov lengthscale , are driven primarily by . Cluster
length scales up to , measured
at the highest , while void length
scaled also with is typically two times larger ().
The lack of sensitivity of the above characteristics to the Stokes number lends
support to the "sweep-stick" particle accumulation scenario. The non-negligible
influence of the volume fraction, however, is not considered by that model and
can be connected with collective effects
The impact of Early Dark Energy on non-linear structure formation
We study non-linear structure formation in high-resolution simulations of
Early Dark Energy (EDE) cosmologies and compare their evolution with the
standard LCDM model. Extensions of the spherical top-hat collapse model predict
that the virial overdensity and linear threshold density for collapse should be
modified in EDE model, yielding significant modifications in the expected halo
mass function. Here we present numerical simulations that directly test these
expectations. Interestingly, we find that the Sheth & Tormen formalism for
estimating the abundance of dark matter halos continues to work very well in
its standard form for the Early Dark Energy cosmologies, contrary to analytic
predictions. The residuals are even slightly smaller than for LCDM. We also
study the virial relationship between mass and dark matter velocity dispersion
in different dark energy cosmologies, finding excellent agreement with the
normalization for Lambda as calibrated by Evrard et al.(2008). The earlier
growth of structure in EDE models relative to LCDM produces large differences
in the mass functions at high redshift. This could be measured directly by
counting groups as a function of the line-of-sight velocity dispersion,
skirting the ambiguous problem of assigning a mass to the halo. Using dark
matter substructures as a proxy for member galaxies, we demonstrate that even
with 3-5 members sufficiently accurate measurements of the halo velocity
dispersion function are possible. Finally, we determine the concentration-mass
relationship for our EDE cosmologies. Consistent with the earlier formation
time, the EDE halos show higher concentrations at a given halo mass. We find
that the magnitude of the difference in concentration is well described by the
prescription of Eke et al.(2001) for estimating halo concentrations.Comment: 17 pages,17 figure
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