2,776 research outputs found
Conformational transitions of heteropolymers in dilute solutions
In this paper we extend the Gaussian self-consistent method to permit study
of the equilibrium and kinetics of conformational transitions for
heteropolymers with any given primary sequence. The kinetic equations earlier
derived by us are transformed to a form containing only the mean squared
distances between pairs of monomers. These equations are further expressed in
terms of instantaneous gradients of the variational free energy. The method
allowed us to study exhaustively the stability and conformational structure of
some periodic and random aperiodic sequences. A typical phase diagram of a
fairly long amphiphilic heteropolymer chain is found to contain phases of the
extended coil, the homogeneous globule, the micro-phase separated globule, and
a large number of frustrated states, which result in conformational phases of
the random coil and the frozen globule. We have also found that for a certain
class of sequences the frustrated phases are suppressed. The kinetics of
folding from the extended coil to the globule proceeds through non-equilibrium
states possessing locally compacted, but partially misfolded and frustrated,
structure. This results in a rather complicated multistep kinetic process
typical of glassy systems.Comment: 15 pages, RevTeX, 20 ps figures, accepted for publication in Phys.
Rev.
Hydration of a B-DNA Fragment in the Method of Atom-atom Correlation Functions with the Reference Interaction Site Model Approximation
We propose an efficient numerical algorithm for solving integral equations of
the theory of liquids in the Reference Interaction Site Model (RISM)
approximation for infinitely dilute solution of macromolecules with a large
number of atoms. The algorithm is based on applying the nonstationary iterative
methods for solving systems of linear algebraic equations. We calculate the
solvent-solute atom-atom correlation functions for a fragment of the B-DNA
duplex d(GGGGG).d(CCCCC) in infinitely dilute aqueous solution. The obtained
results are compared with available experimental data and results from computer
simulations.Comment: 9 pages, RevTeX, 9 pages of ps figures, accepted for publications in
JC
Aggregation number distributions and mesoglobules in dilute solutions of diblock and triblock copolymers
We investigate the aggregation number and size distributions for
inter-molecular clusters of amphiphilic diblock and triblock copolymers in poor
solvent at very low concentrations. Diblocks and triblocks with hydrophilic
ends are shown to possess narrow distributions corresponding to formation of
monodispersed mesoglobules. Diblocks with hydrophobic ends are found to produce
inter-cluster multimers due to bridging by the hydrophilic middle blocks,
resulting in polydisperse distributions. Implications of these observations for
preparation of monodispersed nanoparticles and, potentially, understanding of
the quaternary structure of proteins are discussed.Comment: 4 pages, 4 PS figures. Accepted for publication in EP
In-vivo Studies of Ultrasound-activated Drug-loaded Porous Silicon Nanoparticles for Cancer Therapy Application
It is investigated the therapeutic efficacy of combined action of ultrasound and porous silicon nanoparticles loaded with anticancer drug doxorubicin by using an experimental cancer model of lung Lewis carcinoma in vivo. Time dependences of growth of the primary tumor with introduced nanoparticles and without them, as well as the life span of mice after exposure to therapeutic ultrasound with intensity of 1W/cm2 and frequency of 1 MHz were studied. The obtained results show the effectiveness of inhibiting the growth of primary tumor site, as well as slowing the process of metastasis, in the case of combined action of ultrasound and drug-loaded porous silicon nanoparticles that indicates the prospect of latter as sonosensitizers and nanocontainers for the delivery and controlled release of drugs in sonodynamic therapy of malignant tumors.
Keywords: silicon nanoparticles, nanocontainers, medical ultrasound, sonodynamic therapy, sonosensitizer
Drained cavity expansion analysis with a unified state parameter model for clay and sand
This paper presents an analytical solution for drained expansion in both spherical and cylindrical cavities with a unified state parameter model for clay and sand (CASM). The solution developed here provides the stress and strain fields during the expansion of a cavity from an initial to an arbitrary final radius. Small strains are assumed for the elastic region and large strains are applied to soil in the plastic region by using logarithmic strain definitions. Since its development, the unified CASM model has been demonstrated by many researchers to be able to capture the overall soil behaviour for both clay and sand under both drained and undrained loading conditions. In this study, the CASM model is used to model soil behaviour whilst a drained cavity expansion solution is developed with the aid of an auxiliary variable. This is an extension of the undrained solution presented by the authors in 2017. The parametric study investigates the effects of various model constants including the stress-state coefficient and the spacing ratio on soil stress paths and cavity expansion curves. Both London clay and Ticino sand are modelled under various initial stress conditions and initial state parameters. The newly developed analytical solution highlights the potential applications in geotechnical practice (e.g., for the interpretation of cone penetration test data) and also provides useful benchmarks for numerical simulations of cavity expansion problems in critical state soils
The UA9 experimental layout
The UA9 experimental equipment was installed in the CERN-SPS in March '09
with the aim of investigating crystal assisted collimation in coasting mode.
Its basic layout comprises silicon bent crystals acting as primary
collimators mounted inside two vacuum vessels. A movable 60 cm long block of
tungsten located downstream at about 90 degrees phase advance intercepts the
deflected beam.
Scintillators, Gas Electron Multiplier chambers and other beam loss monitors
measure nuclear loss rates induced by the interaction of the beam halo in the
crystal. Roman pots are installed in the path of the deflected particles and
are equipped with a Medipix detector to reconstruct the transverse distribution
of the impinging beam. Finally UA9 takes advantage of an LHC-collimator
prototype installed close to the Roman pot to help in setting the beam
conditions and to analyze the efficiency to deflect the beam. This paper
describes in details the hardware installed to study the crystal collimation
during 2010.Comment: 15pages, 11 figure, submitted to JINS
Study of the process in the energy range GeV with SND
The process is studied in
the center-of-mass energy region GeV using data with an integral
luminosity of about 35 pb collected with the SND detector at the
VEPP-2000 collider. In the energy range under study, the value of the
measured Born cross section varies from 0.7 to 18 nb. The statistical
uncertainty of the cross section is %, while the systematic uncertainty
is in the range of %. The results are consistent with previous
measurements but have better accuracy.Comment: 13 pages, 11 figure
Study of the process in the energy range \sqrt{s} = \mbox{1.05-2.00} GeV with the SND detector
The process is studied in the center-of-mass
energy range 1.05-2.00 GeV using data with an integrated luminosity of 94.5
pb collected by the SND detector at the VEPP-2000 collider. The
cross section is measured for the first time. It is
shown that the dominant mechanism of this reaction is the transition through
the intermediate state. The measured cross section of the
subprocess is consistent with previous
measurements in the mode. It is found, with a
significance of 5.6, that the process is not
completely described by hadronic vector-pseudoscalar intermediate states. The
cross section of this missing contribution, which can originate from radiation
processes, e. g. , is measured. It is found to be
15-20 pb in the wide energy range from 1.3 to 1.9 GeV.Comment: 10 pages, 6 figures, to be submitted to European Physical Journal
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