43 research outputs found
Exact results for the reactivity of a single-file system
We derive analytical expressions for the reactivity of a Single-File System
with fast diffusion and adsorption and desorption at one end. If the conversion
reaction is fast, then the reactivity depends only very weakly on the system
size, and the conversion is about 100%. If the reaction is slow, then the
reactivity becomes proportional to the system size, the loading, and the
reaction rate constant. If the system size increases the reactivity goes to the
geometric mean of the reaction rate constant and the rate of adsorption and
desorption. For large systems the number of nonconverted particles decreases
exponentially with distance from the adsorption/desorption end.Comment: 4 pages, 2 figure
Interacting Growth Walk - a model for hyperquenched homopolymer glass?
We show that the compact self avoiding walk configurations, kinetically
generated by the recently introduced Interacting Growth Walk (IGW) model, can
be considered as members of a canonical ensemble if they are assigned random
values of energy. Such a mapping is necessary for studying the thermodynamic
behaviour of this system. We have presented the specific heat data for the IGW,
obtained from extensive simulations on a square lattice; we observe a broad
hump in the specific heat above the -point, contrary to expectation.Comment: 4 figures; Submitted to PR
Steady-State Properties of Single-File Systems with Conversion
We have used Monte-Carlo methods and analytical techniques to investigate the
influence of the characteristic parameters, such as pipe length, diffusion,
adsorption, desorption and reaction rate constants on the steady-state
properties of Single-File Systems with a reaction. We looked at cases when all
the sites are reactive and when only some of them are reactive. Comparisons
between Mean-Field predictions and Monte-Carlo simulations for the occupancy
profiles and reactivity are made. Substantial differences between Mean-Field
and the simulations are found when rates of diffusion are high. Mean-Field
results only include Single-File behavior by changing the diffusion rate
constant, but it effectively allows passing of particles. Reactivity converges
to a limit value if more reactive sites are added: sites in the middle of the
system have little or no effect on the kinetics. Occupancy profiles show
approximately exponential behavior from the ends to the middle of the system.Comment: 15 pages, 20 figure
UHECR Acceleration in Dark Matter Filaments of Cosmological Structure Formation
A mechanism for proton acceleration to ~10^21eV is suggested. It may operate
in accretion flows onto thin dark matter filaments of cosmic structure
formation. The flow compresses the ambient magnetic field to strongly increase
and align it with the filament. Particles begin the acceleration by the ExB
drift with the accretion flow. The energy gain in the drift regime is limited
by the conservation of the adiabatic invariant p_perp^2/B. Upon approaching the
filament, the drift turns into the gyro-motion around the filament so that the
particle moves parallel to the azimuthal electric field. In this 'betatron'
regime the acceleration speeds up to rapidly reach the electrodynamic limit
for an accelerator with magnetic field and the orbit radius
(Larmor radius). The periodic orbit becomes unstable and the particle
slings out of the filament to the region of a weak (uncompressed) magnetic
field, which terminates the acceleration.
The mechanism requires pre-acceleration that is likely to occur in structure
formation shocks upstream or nearby the filament accretion flow. Previous
studies identify such shocks as efficient proton accelerators to a firm upper
limit ~10^19.5 eV placed by the catastrophic photo-pion losses. The present
mechanism combines explosive energy gain in its final (betatron) phase with
prompt particle release from the region of strong magnetic field. It is this
combination that allows protons to overcome both the photo-pion and the
synchrotron-Compton losses and therefore attain energy 10^21 eV. A requirement
on accelerator to reach a given E_max placed by the accelerator energy
dissipation \propto E_{max}^{2}/Z_0 due to the finite vacuum impedance Z_0 is
circumvented by the cyclic operation of the accelerator.Comment: 34 pages, 10 figures, to be published in JCA
Multiwavelength studies of MHD waves in the solar chromosphere: An overview of recent results
The chromosphere is a thin layer of the solar atmosphere that bridges the
relatively cool photosphere and the intensely heated transition region and
corona. Compressible and incompressible waves propagating through the
chromosphere can supply significant amounts of energy to the interface region
and corona. In recent years an abundance of high-resolution observations from
state-of-the-art facilities have provided new and exciting ways of
disentangling the characteristics of oscillatory phenomena propagating through
the dynamic chromosphere. Coupled with rapid advancements in
magnetohydrodynamic wave theory, we are now in an ideal position to thoroughly
investigate the role waves play in supplying energy to sustain chromospheric
and coronal heating. Here, we review the recent progress made in
characterising, categorising and interpreting oscillations manifesting in the
solar chromosphere, with an impetus placed on their intrinsic energetics.Comment: 48 pages, 25 figures, accepted into Space Science Review
Reproductive ecology of <i>Syzygium alternifolium</i> (Myrtaceae), an endemic and endangered tropical tree species in the southern Eastern Ghats of India
Syzygium alternifolium is a semi-evergreen mass-flowering tree species of dry deciduous forest in the southern Eastern Ghats of India. It is a mass bloomer with flowering during dry season. The floral traits suggest a mixed pollination syndrome involving entomophily and anemophily together called as ambophily. Further, the floral traits suggest generalist pollination system adapted for a guild of pollinating insects. The plant is self-incompatible and obligate out-crosser. The flowers are many-ovuled but only a single ovule forms seed and hence, fruit and seed set rates are the same. Natural fruit set stands at 11%. Bud infestation by a moth, flower predation by the beetle, Popillia impressipyga and bud and flower mounds significantly limit fruit set rate. The ability of the plant to repopulate itself is limited by the collection of fruits by locals due to their edible nature, short viability of seeds, high seedling mortality due to water stress, nutrient deficiency and erratic rainfall or interval of drought within the rainy season. Therefore, S. alternifolium is struggling to populate itself under various intrinsic and extrinsic factors. Further studies should focus on how to assist the plant to increase its population size in its natural area taking into account the information provided in this paper