3,378 research outputs found
Semiclassical quantization of multidimensional systems
Low order classical perturbation theory is used to obtain semiclassical eigenvalues for a system of three anharmonically coupled oscillators. The results in the low energy region studied here agree well with the "exact" quantum values. The latter had been calculated by matrix diagonalization using a large basis set
How Do Glassy Domains Grow?
We construct the equations for the growth kinetics of a structural glass
within mode-coupling theory, through a non-stationary variant of the 3-density
correlator defined in Phys. Rev. Lett. 97}, 195701 (2006). We solve a schematic
form of the resulting equations to obtain the coarsening of the 3-point
correlator as a function of waiting time . For a quench
into the glass, we find that attains a peak value at
, providing a theoretical basis for the numerical
observations of Parisi [J. Phys. Chem. B 103, 4128 (1999)] and Kob and Barrat
[Phys. Rev. Lett. 78, 4581 (1997)]. The aging is not "simple": the
dependence cannot be attributed to an evolving effective temperature.Comment: 6 pages, 5 figure
Instabilities and waves in thin films of living fluids
We formulate the thin-film hydrodynamics of a suspension of polar self-driven
particles and show that it is prone to several instabilities through the
interplay of activity, polarity and the existence of a free surface. Our
approach extends, to self-propelling systems, the work of Ben Amar and Cummings
[Phys Fluids 13 (2001) 1160] on thin-film nematics. Based on our estimates the
instabilities should be seen in bacterial suspensions and the lamellipodium,
and are potentially relevant to the morphology of biofilms. We suggest several
experimental tests of our theory.Comment: 4 pages, pdflatex, accepted for publication in Phys Rev Let
Influence of Mineralogical Nature of Aggregates on Acid Resistance of Mortar
Cement-based materials being alkaline in nature are often subjected to rapid deterioration on exposure to the aggressive acidic environments. Acids penetrate into the cement matrix causing calcium leaching and deterioration of phases leading to alteration in the microstructure. Currently, there are hardly any codes or standards available for evaluating the durability of materials to acid attack. Moreover, the literature addressing the material resistance is quite inconclusive. This paper aims to evaluate the influence of mineralogical nature of aggregates on the degradation kinetics of cement mortar when exposed to inorganic and organic acid solutions by performing a static accelerated leaching test. Cement mortar (1: 3) specimens of size 10 × 10 × 60 mm were prepared using Ordinary Portland Cement (OPC), using limestone (calcareous) aggregates and siliceous aggregates with a water to cement ratio of 0.40. After 28 days of initial curing in saturated lime water, the specimens were exposed to various concentrations of sulphuric (1 % and 3 %) and acetic acid solutions (0.25 M and 0.5 M) for a testing period of 4 months. The acid solution was replenished on a periodic basis to maintain the aggressiveness of the solution. The degradation kinetics was investigated by measuring mass changes, thickness changes, changes in pH of the acid solution and imaging using X-ray micro-tomography. Additionally, periodic abrasive action applied manually (using soft nylon brush) was used to accelerate the degradation process in case of sulphuric acid exposure and its effect was compared with the testing without the abrasive action. An attempt was also made to evaluate the changes in compressive strength and changes in dynamic modulus of elasticity of cylindrical mortar specimens (25 mm diameter and 50 mm height) on exposure to the acid solutions. The test results indicate that the performance of limestone aggregates is better on exposure to sulphuric acid and worse in case of acetic acid when compared to siliceous aggregates
Structure based de novo design of IspD inhibitors as anti-tubercular agents
Tuberculosis is one of the leading contagious diseases, caused by Mycobacterium tuberculosis. Despite improvements in anti-tubercular agents, it remains one of the most prevalent infectious diseases worldwide, responsible for a total of 1.6 million deaths annually. The emergence of multidrug resistant strains highlighted the need of discovering novel drug targets for the development of anti-tubercular agents. 2-C-methyl-D-erythritol-4-phosphate cytidyltransferase (IspD) is an enzyme involved in MEP pathway for isoprenoid biosynthesis, which is considered an attractive target for the discovery of novel antibiotics for its essentiality in bacteria and absence in mammals. In the present study, we have employed structure based drug design approach to develop novel and potent inhibitors for IspD receptor. To explore binding affinity and hydrogen bond interaction between the ligand and active site of IspD receptor, docking studies were performed. ADMET and synthetic accessibility filters were used to screen designed molecules. Finally, ten compounds were selected and subsequently submitted for the synthesis and in vitro studies as IspD inhibitors
Power spectrum of mass and activity fluctuations in a sandpile
We consider a directed abelian sandpile on a strip of size ,
driven by adding a grain randomly at the left boundary after every
time-steps. We establish the exact equivalence of the problem of mass
fluctuations in the steady state and the number of zeroes in the ternary-base
representation of the position of a random walker on a ring of size . We
find that while the fluctuations of mass have a power spectrum that varies as
for frequencies in the range , the activity
fluctuations in the same frequency range have a power spectrum that is linear
in .Comment: 8 pages, 10 figure
A Dynamic Renormalization Group Study of Active Nematics
We carry out a systematic construction of the coarse-grained dynamical
equation of motion for the orientational order parameter for a two-dimensional
active nematic, that is a nonequilibrium steady state with uniaxial, apolar
orientational order. Using the dynamical renormalization group, we show that
the leading nonlinearities in this equation are marginally \textit{irrelevant}.
We discover a special limit of parameters in which the equation of motion for
the angle field of bears a close relation to the 2d stochastic Burgers
equation. We find nevertheless that, unlike for the Burgers problem, the
nonlinearity is marginally irrelevant even in this special limit, as a result
of of a hidden fluctuation-dissipation relation. 2d active nematics therefore
have quasi-long-range order, just like their equilibrium counterpartsComment: 31 pages 6 figure
Processing of china clay by super-conducting high gradient magnetic separation
Super-conducting high gradient magnetic separation tests on a typical china clay from the western part of India showed that the brightness of the clay can be enhanced from 72.8% to 79% ISO by suitably manipulating the process variables. Important variables studied are feed solid content, retention time, production rate (nummber of canister volumes), number of passes etc. keeping the magnetic field srength constant. The secondary magnet (wire wool matrix) and its packing volume were also not changed during these tests. A brightness of 79%
was achieved with a two pass operation for 5 canister volume feed slurry having 15% solid content and with retention rime of about 20 secs. The overall clay recovery is 86%(94%_for the first pass and 92% for the second pass). Understandably, the feed solid content of second
pass was lower than 15% while the iron (Fe201) could be reduced by about 55% the reduction in TiO2 was about 12% indicating that there still exists scope for removing Ti02 from this clay and enhancing brightness further. All the SC-HGMS tests were conducted at Bhabha Atomic Research Centre, Trombay, Bombay. India
Elasticity-mediated self-organization and colloidal interactions of solid spheres with tangential anchoring in a nematic liquid crystal
Using laser tweezers and fluorescence confocal polarizing microscopy, we
study colloidal interactions of solid microspheres in the nematic bulk caused
by elastic distortions around the particles with strong tangential surface
anchoring. The particles aggregate into chains directed at about 30 degrees to
the far field director and, at higher concentrations, form complex kinetically
trapped structures. We characterize the distance and angular dependencies of
the colloidal interaction forces.Comment: 6 pages, 5 figure
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