2,123 research outputs found
Penetrative Convection at High Rayleigh Numbers
We study penetrative convection of a fluid confined between two horizontal
plates, the temperatures of which are such that a temperature of maximum
density lies between them. The range of Rayleigh numbers studied is and the Prandtl numbers are and . An
evolution equation for the growth of the convecting region is obtained through
an integral energy balance. We identify a new non-dimensional parameter,
, which is the ratio of temperature difference between the stable and
unstable regions of the flow; larger values of denote increased
stability of the upper stable layer. We study the effects of on the
flow field using well-resolved lattice Boltzmann simulations, and show that the
characteristics of the flow depend sensitively upon it. For the range , we find that for a fixed the Nusselt number,
, increases with decreasing . We also investigate the effects of
on the vertical variation of convective heat flux and the
Brunt-V\"{a}is\"{a}l\"{a} frequency. Our results clearly indicate that in the
limit the problem reduces to that of the classical
Rayleigh-B\'enard convection.Comment: 12 pages, 19 figure
Jamming transitions in amorphous packings of frictionless spheres occur over a continuous range of volume fractions
We numerically produce fully amorphous assemblies of frictionless spheres in
three dimensions and study the jamming transition these packings undergo at
large volume fractions. We specify four protocols yielding a critical value for
the jamming volume fraction which is sharply defined in the limit of large
system size, but is different for each protocol. Thus, we directly establish
the existence of a continuous range of volume fraction where nonequilibrium
jamming transitions occur. However, these jamming transitions share the same
critical behaviour. Our results suggest that, even in the absence of partial
crystalline ordering, a unique location of a random close packing does not
exist, and that volume fraction alone is not sufficient to describe the
properties of jammed states.Comment: 5 pages, 3 fig
Dynamic Radio-Frequency Transverse Susceptibility in Magnetic Nanoparticle Systems
A novel resonant method based on a tunnel-diode oscillator (TDO) is used to
study the dynamic transverse susceptibility in a Fe nanoparticle system. The
magnetic system consists of an aggregate of nanometer-size core (Au)-shell (Fe)
structure, synthesized by reverse micelle methods. Static and dynamic
magnetization measurements carried out in order to characterize the system
reveal a superparamagnetic behavior at high temperature. The field-dependent
transverse susceptibility at radio-frequencies (RF), for different temperatures
reveals distinct peak structure at characteristics fields (H_k, H_c) which
changes with temperature. It is proposed that relaxation processes could
explain the influence of the temperature on the field dependence of the
transverse susceptibility on the MI.Comment: 3 pages, 2-column, 3 figures, To be published in J. Appl. Phys. 2000
(44th Annual MMM proceedings
Recommended from our members
Naga Resistance Movement and the Peace Process in Northeast India
Occasional Papers in Sociology and Anthropology - Peace and Democracy in South Asia, Volume 1, Issue 2, 200
Computer Simulation Study of the Phase Behavior and Structural Relaxation in a Gel-Former Modeled by Three Body Interactions
We report a computer simulation study of a model gel-former obtained by
modifying the three-body interactions of the Stillinger-Weber potential for
silicon. This modification reduces the average coordination number and
consequently shifts the liquid-gas phase coexistence curve to low densities,
thus facilitating the formation of gels without phase separation. At low
temperatures and densities, the structure of the system is characterized by the
presence of long linear chains interconnected by a small number of three
coordinated junctions at random locations. At small wave-vectors the static
structure factor shows a non-monotonic dependence on temperature, a behavior
which is due to the competition between the percolation transition of the
particles and the stiffening of the formed chains. We compare in detail the
relaxation dynamics of the system as obtained from molecular dynamics with the
one obtained from Monte Carlo dynamics. We find that the bond correlation
function displays stretched exponential behavior at moderately low temperatures
and densities, but exponential relaxation at low temperatures. The bond
lifetime shows an Arrhenius behavior, independent of the microscopic dynamics.
For the molecular dynamics at low temperatures, the mean squared displacement
and the (coherent and incoherent) intermediate scattering function display at
intermediate times a dynamics with ballistic character and we show that this
leads to compressed exponential relaxation. For the Monte Carlo dynamics we
find always an exponential or stretched exponential relaxation. Thus we
conclude that the compressed exponential relaxation observed in experiments is
due to the out-of-equilibrium dynamics
Prospecting for scarabid specific Bacillus thuringiensis crystal toxin cry8 gene in sugarcane ecosystem of Tamil Nadu, India
In the present study, we report the occurrence of cry8 positive isolates of Bacillus thuringiensis (Bt) in selected white grub, Holotrichia serrata F. (Coleoptera: Scarabaeidae), endemic soils of sugarcane ecosystem and other places in Tamil Nadu. Out of the 66 soil samples collected and screened for white grub specific Bt, 74 isolates of the bacterium, all containing only spherical crystal toxin, were identified. PCR screening of these isolates with cry8 gene universal primer revealed six isolates to be positive. Further, the amplicon of a 370 bp band, amplified with another set of degenerate primer designed based on the conserved sequence of cry8 genes, was sequenced from four isolates. Multiple sequence alignment revealed the gene sequences to be the same for all the isolates. The present report of the availability of cry8 positive Bt isolates opens the avenue for controlling white grubs through transgenic research
- …