115 research outputs found
Collective stochastic resonance in shear-induced melting of sliding bilayers
The far-from-equilibrium dynamics of two crystalline two-dimensional
monolayers driven past each other is studied using Brownian dynamics
simulations. While at very high and low driving rates the layers slide past one
another retaining their crystalline order, for intermediate range of drives the
system alternates irregularly between the crystalline and fluid-like phases. A
dynamical phase diagram in the space of interlayer coupling and drive is
obtained. A qualitative understanding of this stochastic alternation between
the liquid-like and crystalline phases is proposed in terms of a reduced model
within which it can be understood as a stochastic resonance for the dynamics of
collective order parameter variables. This remarkable example of stochastic
resonance in a spatially extended system should be seen in experiments which we
propose in the paper.Comment: 12 pages, 18 eps figures, minor changes in text and labelling of
figures, accepted for publication in Phys. Rev.
Flow-induced currents in nanotubes: a Brownian dynamics approach
Motivated by recent experiments [Science {\bf 299}, 1042 (2003)] reporting
that carbon nanotubes immersed in a flowing fluid displayed an electric current
and voltage, we numerically study the behaviour of a collection of Brownian
particles in a channel, in the presence of a flow field applied on similar but
slower particles in a wide chamber in contact with the channel. For a suitable
range of shear rates, we find that the flow field induces a unidirectional
drift in the confined particles, and is stronger for narrower channels. The
average drift velocity initially rises with increasing shear rate, then shows
saturation for a while, thereafter starts decreasing, in qualitative agreement
with recent theoretical studies [Phys. Rev. B {\bf 70}, 205423 (2004)] based on
Brownian drag and ``loss of grip''. Interestingly, if the sign of the
interspecies interaction is reversed, the direction of the induced drift
remains the same, but the flow-rate at which loss of grip occurs is lower, and
the level of fluctuations is higher.Comment: 7 pages, 9 figure
Transport of aerosols and nanoparticles through respirators and masks
In several countries wearing multiple surgical masks or N95 respirators was
mandatory in public during the COVID pandemic. In this study, we investigated
the transportation and filtering mechanism of heterogeneous nanoparticles and
viruses through surgical masks and N95 respirators. We conducted experiments in
vitro using aerosol spray paints containing nanoparticles and validated the
findings in vivo on a human volunteer. Scanning electron microscopy was
employed to analyse the transportation and distribution of nanoparticles in
different mask layers and on pristine silicon substrates placed on human skin.
We provide analytical insights into the pressure distribution and fluid
velocity profiles within the complex polymer network. Remarkably, our results
showed that both single surgical masks and N95 respirators demonstrated similar
efficiency in filtering colloidal and jet-stream nanoparticles in the air.
These comprehensive findings have significant implications for policymakers in
defining regulations for airborne pandemics and air pollution control
Spatiotemporal rheochaos in nematic hydrodynamics
Motivated by the observation of rheochaos in sheared wormlike micelles
[Bandyopadhyay et al., Phys. Rev. Lett, 84 2022, (2000); Europhys. Lett. 56,
447 (2001); Pramana 53, 223 (1999)] we study the coupled nonlinear partial
differential equations for the hydrodynamic velocity and order parameter fields
in a sheared nematogenic fluid. In a suitable parameter range, we find
irregular, dynamic shear-banding and establish by decisive numerical tests that
the chaos we observe in the model is spatiotemporal in nature.Comment: Slight changes in text, references and Fig. 5 inset; 6 eps figures
(figs 2,3,4 at lower resolution to reduce file size; full files available on
request); accepted for publication in Phys Rev Let
Statistical Isotropy violation of the CMB brightness fluctuations
Certain anomalies at large angular scales in the cosmic microwave background
measured by WMAP have been suggested as possible evidence of breakdown of
statistical isotropy(SI). Most CMB photons free-stream to the present from the
surface of last scattering. It is thus reasonable to expect statistical
isotropy violation in the CMB photon distribution observed now to have
originated from SI violation in the baryon-photon fluid at last scattering, in
addition to anisotropy of the primordial power spectrum studied earlier in
literature.
We consider the generalized anisotropic brightness distribution fluctuations,
(at conformal time ) in contrast to the
SI case where it is simply a function of and . The brightness fluctuations expanded in Bipolar Spherical Harmonic
(BipoSH) series, can then be written as where terms encode deviations from statistical isotropy. We
study the evolution of from
non-zero terms at last
scattering. Similar to the SI case, power at small spherical harmonic (SH)
multipoles of at the last
scattering, is transferred to at
larger SH multipoles. The structural similarity is more apparent in the
asymptotic expression for large values of the final SH multipoles. This
formalism allows an elegant identification of any SI violation observed today
to a possible origin in the SI violation present in the baryon-photon fluid
(eg., due to the presence of significant magnetic field).Comment: 14 pages, 4 figures, added illustrative example of SI violation in
baryon-photon fluid, matches version accepted for publication in Phys. Rev.
Curvature condensation and bifurcation in an elastic shell
We study the formation and evolution of localized geometrical defects in an
indented cylindrical elastic shell using a combination of experiment and
numerical simulation. We find that as a symmetric localized indentation on a
semi-cylindrical shell increases, there is a transition from a global mode of
deformation to a localized one which leads to the condensation of curvature
along a symmetric parabolic crease. This process introduces a soft mode in the
system, converting a load-bearing structure into a hinged, kinematic mechanism.
Further indentation leads to twinning wherein the parabolic crease bifurcates
into two creases that move apart on either side of the line of symmetry. A
qualitative theory captures the main features of the phenomena and leads to
sharper questions about the nucleation of these defects.Comment: 4 pages, 5 figures, submitted to Physical Review Letter
Memecylon macneillianum (Melastomataceae), a new species from South Andaman, India
Memecylon macneillianum M. Das Das, G. S. Giri, A. Pramanik and D. Maity, a new species from the southern Andaman Islands in India, is described and illustrated. It differs from its closely related species M. oleifolium Blume by having both terminal and axillary inflorescences, a higher number (mostly 3–7) inflorescences per node, longer and acutely quadrangular, distinctly furrowed primary inflorescence axes, distinct calyx lobes, and globose fruits. Moreover, in M. macneillianum the leaves are thicker, coriaceous and yellowish on both surfaces when dry, whereas in M. oleifolium the leaves are thin, chartaceous and olive green with a distinctive rusty-red blush around the midvein on drying
An attempt to explore the production routes of Astatine radionuclides: Theoretical approach
In order to fulfil the recent thrust of Astatine radionuclides in the field
of nuclear medicine various production routes have been explored in the present
work. The possible production routes of At comprise both light and
heavy ion induced reactions at the bombarding energy range starting from
threshold to maximum 100 MeV energy. For this purpose, we have used the nuclear
reaction model codes TALYS, ALICE91 and PACE-II. Excitation functions of those
radionuclides, produced through various production routes, have been calculated
using nuclear reaction model codes and compared with the available measured
data. Contribution of various reaction mechanisms, like, direct, preequilibrium
and equilibrium reactions, to the total reaction cross section has been studied
using the codes. Result shows that equilibrium reaction mechanism dominates in
all cases over other reaction mechanisms
Buckling and force propagation along intracellular microtubules
Motivated by recent experiments showing the compressive buckling of microtubules in cells, we study theoretically the mechanical response of and force propagation along elastic filaments embedded in a non-linear elastic medium. We find that embedded microtubules buckle when their compressive load exceeds a critical value
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Towards Real-Time Oxygen Sensing: From Nanomaterials to Plasma
A significantly large scope is available for the scientific and engineering developments of high-throughput ultra-high sensitive oxygen sensors. We give a perspective of oxygen sensing for two physical states of matters—solid-state nanomaterials and plasma. From single-molecule experiments to material selection, we reviewed various aspects of sensing, such as capacitance, photophysics, electron mobility, response time, and a yearly progress. Towards miniaturization, we have highlighted the benefit of lab-on-chip-based devices and showed exemplary measurements of fast real-time oxygen sensing. From the physical–chemistry perspective, plasma holds a strong potential in the application of oxygen sensing. We investigated the current state-of-the-art of electron density, temperature, and design issues of plasma systems. We also show numerical aspects of a low-cost approach towards developing plasma-based oxygen sensor from household candle flame. In this perspective, we give an opinion about a diverse range of scientific insight together, identify the short comings, and open the path for new physical–chemistry device developments of oxygen sensor along with providing a guideline for innovators in oxygen sensing
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