3,916 research outputs found
Three-phase coexistence with sequence partitioning in symmetric random block copolymers
We inquire about the possible coexistence of macroscopic and microstructured
phases in random Q-block copolymers built of incompatible monomer types A and B
with equal average concentrations. In our microscopic model, one block
comprises M identical monomers. The block-type sequence distribution is
Markovian and characterized by the correlation \lambda. Upon increasing the
incompatibility \chi\ (by decreasing temperature) in the disordered state, the
known ordered phases form: for \lambda\ > \lambda_c, two coexisting macroscopic
A- and B-rich phases, for \lambda\ < \lambda_c, a microstructured (lamellar)
phase with wave number k(\lambda). In addition, we find a fourth region in the
\lambda-\chi\ plane where these three phases coexist, with different,
non-Markovian sequence distributions (fractionation). Fractionation is revealed
by our analytically derived multiphase free energy, which explicitly accounts
for the exchange of individual sequences between the coexisting phases. The
three-phase region is reached, either, from the macroscopic phases, via a third
lamellar phase that is rich in alternating sequences, or, starting from the
lamellar state, via two additional homogeneous, homopolymer-enriched phases.
These incipient phases emerge with zero volume fraction. The four regions of
the phase diagram meet in a multicritical point (\lambda_c, \chi_c), at which
A-B segregation vanishes. The analytical method, which for the lamellar phase
assumes weak segregation, thus proves reliable particularly in the vicinity of
(\lambda_c, \chi_c). For random triblock copolymers, Q=3, we find the character
of this point and the critical exponents to change substantially with the
number M of monomers per block. The results for Q=3 in the continuous-chain
limit M -> \infty are compared to numerical self-consistent field theory
(SCFT), which is accurate at larger segregation.Comment: 24 pages, 19 figures, version published in PRE, main changes: Sec.
IIIA, Fig. 14, Discussio
Three Bead Rotating Chain model shows universality in the stretching of proteins
We introduce a model of proteins in which all of the key atoms in the protein
backbone are accounted for, thus extending the Freely Rotating Chain model. We
use average bond lengths and average angles from the Protein Databank as input
parameters, leaving the number of residues as a single variable. The model is
used to study the stretching of proteins in the entropic regime. The results of
our Monte Carlo simulations are found to agree well with experimental data,
suggesting that the force extension plot is universal and does not depend on
the side chains or primary structure of proteins
Quantum Quenches in a Holographic Kondo Model
We study non-equilibrium dynamics and quantum quenches in a recent
gauge/gravity duality model for a strongly coupled system interacting with a
magnetic impurity with spin. At large , it is convenient to write
the impurity spin as a bilinear in Abrikosov fermions. The model describes an
RG flow triggered by the marginally relevant Kondo operator. There is a phase
transition at a critical temperature, below which an operator condenses which
involves both an electron and an Abrikosov fermion field. This corresponds to a
holographic superconductor in AdS and models the impurity screening. We
study the time dependence of the condensate induced by quenches of the Kondo
coupling. The timescale for equilibration is generically given by the
lowest-lying quasinormal mode of the dual gravity model. This mode also governs
the formation of the screening cloud, which is obtained as the decrease of
impurity degrees of freedom with time. In the condensed phase, the leading
quasinormal mode is imaginary and the relaxation of the condensate is
over-damped. For quenches whose final state is close to the critical point of
the large phase transition, we study the critical slowing down and obtain
the combination of critical exponents . When the final state is exactly
at the phase transition, we find that the exponential ringing of the
quasinormal modes is replaced by a power-law behaviour of the form . This indicates the emergence of a discrete scale
invariance.Comment: 23 pages + appendices, 11 figure
Universal Formulae for Percolation Thresholds
A power law is postulated for both site and bond percolation thresholds. The
formula writes , where is the space
dimension and the coordination number. All thresholds up to are found to belong to only three universality classes. For first two
classes for site dilution while for bond dilution. The last one
associated to high dimensions is characterized by for both sites and
bonds. Classes are defined by a set of value for . Deviations
from available numerical estimates at are within and
for high dimensional hypercubic expansions at . The
formula is found to be also valid for Ising critical temperatures.Comment: 11 pages, latex, 3 figures not include
Use dry skim milk for drinking, for cooking
"Dry skim milk is skim milk with the water taken out. Some dry milk is called instant dry milk. It is made so it will dissolve easier. Nearly all skim milk you buy in the store is instant. To make fluid milk from dry skim milk follow the directions on the package. Then use it as fresh milk for drinking or cooking. Dry skim milk may also be used for many cooked foods just as it comes from the box."--Page 1."MP-20, 7,66"4 unnumbered pages ; illustrationsJosephine Flory, Mildred S. Bradshe
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