1,795 research outputs found
Dynamics of Diblock Copolymers in Dilute Solutions
We consider the dynamics of freely translating and rotating diblock (A-B),
Gaussian copolymers, in dilute solutions. Using the multiple scattering
technique, we have computed the diffusion and the friction coefficients D_AB
and Zeta_AB, and the change Eta_AB in the viscosity of the solution as
functions of x = N_A/N and t = l_B/l_A, where N_A, N are the number of segments
of the A block and of the whole copolymer, respectively, and l_A, l_B are the
Kuhn lengths of the A and B blocks. Specific regimes that maximize the
efficiency of separation of copolymers with distinct "t" values, have been
identified.Comment: 20 pages Revtex, 7 eps figures, needs epsf.tex and amssymb.sty,
submitted to Macromolecule
Origin of translocation barriers for polyelectrolyte chains
For single-file translocations of a charged macromolecule through a narrow
pore, the crucial step of arrival of an end at the pore suffers from free
energy barriers, arising from changes in intrachain electrostatic interaction,
distribution of ionic clouds and solvent molecules, and conformational entropy
of the chain. All contributing factors to the barrier in the initial stage of
translocation are evaluated by using the self-consistent field theory for the
polyelectrolyte and the coupled Poisson-Boltzmann description for ions, without
radial symmetry. The barrier is found to be essentially entropic, due to
conformational changes. For moderate and high salt concentrations, the barriers
for the polyelectrolyte chain are quantitatively equivalent to that of
uncharged self-avoiding walks. Electrostatic effects are shown to increase the
free energy barriers, but only slightly. The degree of ionization,
electrostatic interaction strength, decreasing salt concentration and the
solvent quality all result in increases in the barrier.Comment: J.Chem. Phys. 131, 21 (2009) - to be appeare
Polymers pushing Polymers: Polymer Mixtures in Thermodynamic Equilibrium with a Pore
We investigate polymer partitioning from polymer mixtures into nanometer size
cavities by formulating an equation of state for a binary polymer mixture
assuming that only one (smaller) of the two polymer components can penetrate
the cavity. Deriving the partitioning equilibrium equations and solving them
numerically allows us to introduce the concept of "polymers-pushing-polymers"
for the action of non-penetrating polymers on the partitioning of the
penetrating polymers. Polymer partitioning into a pore even within a very
simple model of a binary polymer mixture is shown to depend in a complicated
way on the composition of the polymer mixture and/or the pore-penetration
penalty. This can lead to enhanced as well as diminished partitioning, due to
two separate energy scales that we analyse in detail.Comment: 10 pages, 6 figure
DETECTION OF SPATIOTEMPORAL CHANGES IN PALAR - PORUNDALAR DAM, DINDIGUL DISTRICT, TAMIL NADU, INDIA USING GEOMATICS TECHNOLOGIES
Water is an essential natural resource which indicates the economic growth of a region along with its various sustainable development plans. However, the rapid development on demographic, economic, and technological trends results in demolishing the favorable environment condition for water availability and results it scarcity. Though, the global warming condition and the anthropogenic activities affects the climatic conditions, the natural water resources and its sustainability need to maintain for future generations. The impacts of global warming, climate change and manmade activities affects water resource availability and its quality. It is mandatory to monitor the water resources in order to manage the resource. So, it is important to detect the surface water bodies and to analyze the Spatio-temporal changes of water bodies. It helps to provide sustainable development plans in water resource management. In the recent researches, remote sensing is one of the cost effective technology which used to detect and analyze the changes of spatial features and also to monitor the natural resources present on the earth surface. The study area chosen for the analysis is the Palar- Porundalar Dam which is the largest water body present in Palani Taluk, Dindigul District, Tamil Nadu, India. The present study, strives to detect the water spread of the Palar-Porundalar Dam for the years 1997, 2009 and 2021 using multi temporal satellite images with the help of Normalized Difference Water Index (NDWI) and to identify the changes over the above said periods. The result indicates that for the year 1997 the surface water spread detected upto 4.84 sqkm, for the year 2009 the surface water spread detected upto 4.81 sqkm and in the year 2021 the surface water spread detected upto 4.88 sqkm. Finally, the validation of the result carried out using accuracy assessment method manually by using kappa coefficient formula. The validation result indicates that there is 85.08% of the match detected among the classified and the reference data. The overall accuracy is 92.59%
Continuum Theory of Polymer Crystallization
We present a kinetic model of crystal growth of polymers of finite molecular
weight. Experiments help to classify polymer crystallization broadly into two
kinetic regimes. One is observed in melts or in high molar mass polymer
solutions and is dominated by nucleation control with , where is the growth rate and is the super-cooling. The
other is observed in low molar mass solutions (as well as for small molecules)
and is diffusion controlled with , for small . Our
model unifies these two regimes in a single formalism. The model accounts for
the accumulation of polymer chains near the growth front and invokes an
entropic barrier theory to recover both limits of nucleation and diffusion
control. The basic theory applies to both melts and solutions, and we
numerically calculate the growth details of a single crystal in a dilute
solution. The effects of molecular weight and concentration are also determined
considering conventional polymer dynamics. Our theory shows that entropic
considerations, in addition to the traditional energetic arguments, can capture
general trends of a vast range of phenomenology. Unifying ideas on
crystallization from small molecules and from flexible polymer chains emerge
from our theory.Comment: 37 double-spaced pages including 8 figures, submitted to the Journal
of Chemical Physic
Efficient Set Sharing Using ZBDDs
Set sharing is an abstract domain in which each concrete object is represented by the set of local variables from which it might be reachable. It is a useful abstraction to detect parallelism opportunities, since it contains definite information about which variables do not share in memory, i.e., about when the memory regions reachable from those variables are disjoint. Set sharing is a more precise alternative to pair sharing, in which each domain element is a set of all pairs of local variables from which a common object may be reachable. However, the exponential complexity of some set sharing operations has limited its wider application. This work introduces an efficient implementation of the set sharing domain using Zero-suppressed Binary Decision Diagrams (ZBDDs). Because ZBDDs were designed to represent sets of combinations (i.e., sets of sets), they naturally represent elements of the set sharing domain. We show how to synthesize the operations needed in the set sharing transfer functions from basic ZBDD operations. For some of the operations, we devise custom ZBDD algorithms that perform better in practice. We also compare our implementation of the abstract domain with an efficient, compact, bit set-based alternative, and show that the ZBDD version scales better in terms of both memory usage and running time
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