519 research outputs found
Recommended from our members
Functional nanoparticles
Functional nanoparticles may be formed using at least one nano-lithography step. In one embodiment, sacrificial material may be patterned on a multi-layer substrate using an imprint lithography system. The pattern may be further etched into the multi-layer substrate. Functional material may then be deposited on multi-layer substrate and solidified. At least a portion of the functional material may then be removed to provide a crown surface exposing pillars. Pillars may be removed from multi-layer substrate forming functional nanoparticles.Board of Regents, University of Texas Syste
Plume motion and large-scale circulation in a cylindrical Rayleigh-B\'enard cell
We used the time correlation of shadowgraph images to determine the angle
of the horizontal component of the plume velocity above (below) the
center of the bottom (top) plate of a cylindrical Rayleigh-B\'enard cell of
aspect ratio ( is the diameter and mm
the height) in the Rayleigh-number range for a Prandtl number . We expect that gives the
direction of the large-scale circulation. It oscillates time-periodically. Near
the top and bottom plates has the same frequency but is
anti-correlated.Comment: 4 pages, 6 figure
Gonad differentiation in zebrafish is regulated by the canonical Wnt signalling pathway
Zebrafish males undergo a ‘‘juvenile ovary-to-testis’’ gonadal transformation process. Several genes, including nuclear receptor subfamily 5, group A (nr5a) and anti-Mu¨ llerian hormone (amh), and pathways such as Tp53-mediated germ-cell apoptosis have been implicated in zebrafish testis formation. However, our knowledge of the regulation of this complex process is incomplete, and much remains to be investigated about the molecular pathways and network of genes that control it. Using a microarray-based analysis of transforming zebrafish male
gonads, we demonstrated that their transcriptomes undergo transition from an ovary-like pattern to an ovotestis to a testislike profile. Microarray results also validated the previous histological and immunohistochemical observation that there
is high variation in the duration and extent of commitment to the juvenile ovary phase among individuals. Interestingly, global gene expression profiling of diverging zebrafish juvenile ovaries and transforming ovotestes revealed that some members of the canonical Wnt/beta-catenin signaling pathway were differentially expressed between these two phases. To investigate whether Wnt/beta-catenin signaling plays a role in zebrafish gonad differentiation, we used the Tg (hsp70l:dkk1b-GFP)w32 line to inhibit Wnt/beta-catenin signaling during gonad differentiation. Activation of dkk1b-GFP expression by heat shock resulted in an increased proportion of males and corresponding decrease in gonadal aromatase gene (cyp19a1a) expression. The Wnt target gene, lymphocyte enhancer binding factor 1 (lef1), was also down-regulated in the process. Together, these results provide the first functional evidence that, similarly to mammals,
Wnt/beta-catenin signaling is a ‘‘pro-female’’ pathway that regulates gonad differentiation in zebrafish.Web of Scienc
Scaling relation for determining the critical threshold for continuum percolation of overlapping discs of two sizes
We study continuum percolation of overlapping circular discs of two sizes. We
propose a phenomenological scaling equation for the increase in the effective
size of the larger discs due to the presence of the smaller discs. The critical
percolation threshold as a function of the ratio of sizes of discs, for
different values of the relative areal densities of two discs, can be described
in terms of a scaling function of only one variable. The recent accurate Monte
Carlo estimates of critical threshold by Quintanilla and Ziff [Phys. Rev. E, 76
051115 (2007)] are in very good agreement with the proposed scaling relation.Comment: 4 pages, 3 figure
An improved \eps expansion for three-dimensional turbulence: summation of nearest dimensional singularities
An improved \eps expansion in the -dimensional () stochastic
theory of turbulence is constructed by taking into account pole singularities
at in coefficients of the \eps expansion of universal quantities.
Effectiveness of the method is illustrated by a two-loop calculation of the
Kolmogorov constant in three dimensions.Comment: 4 page
Hysteresis at low Reynolds number: the onset of 2D vortex shedding
Hysteresis has been observed in a study of the transition between laminar
flow and vortex shedding in a quasi-two dimensional system. The system is a
vertical, rapidly flowing soap film which is penetrated by a rod oriented
perpendicular to the film plane. Our experiments show that the transition from
laminar flow to a periodic K\'arm\'an vortex street can be hysteretic, i.e.
vortices can survive at velocities lower than the velocity needed to generate
them.Comment: RevTeX file 4 pages + 5 (encapsulated postscript) figures. to appear
in Phys.Rev.E, Rapid Communicatio
Effect of large-scale intermittency and mean shear on scaling-range exponents in a turbulent jet
The present study investigates the combined impact of the intermittency associated with the turbulent-nonturbulent interface and the mean shear rate in an axisymmetric jet on the structure of turbulence in the scaling range, where the spectrum exhibits a power-law behavior. Second-order structure functions, autocorrelations of the dissipation rate, and spectra of both the longitudinal velocity fluctuation and the passive temperature fluctuation are measured at a distance of 40 diameter downstream from the nozzle exit. All the scaling range exponents are influenced by the large-scale intermittency and the mean shear. The scalar fluctuation is much more sensitive to the variation in large-scale intermittency than the velocity fluctuation.J. Mi and R. A. Antoni
Bottleneck effects in turbulence: Scaling phenomena in r- versus p-space
We (analytically) calculate the energy spectrum corresponding to various
experimental and numerical turbulence data analyzed by Benzi et al.. We find
two bottleneck phenomena: While the local scaling exponent of the
structure function decreases monotonically, the local scaling exponent
of the corresponding spectrum has a minimum of
at and a maximum
of at . A physical
argument starting from the constant energy flux in p--space reveals the general
mechanism underlying the energy pileups at both ends of the p--space scaling
range. In the case studied here, they are induced by viscous dissipation and
the reduced spectral strength on the scale of the system size, respectively.Comment: 9 pages, 3figures on reques
Turbulence and Multiscaling in the Randomly Forced Navier Stokes Equation
We present an extensive pseudospectral study of the randomly forced
Navier-Stokes equation (RFNSE) stirred by a stochastic force with zero mean and
a variance , where is the wavevector and the dimension . We present the first evidence for multiscaling of velocity structure
functions in this model for . We extract the multiscaling exponent
ratios by using extended self similarity (ESS), examine their
dependence on , and show that, if , they are in agreement with those
obtained for the deterministically forced Navier-Stokes equation (NSE). We
also show that well-defined vortex filaments, which appear clearly in studies
of the NSE, are absent in the RFNSE.Comment: 4 pages (revtex), 6 figures (postscript
- …