3,630 research outputs found
A model study of cooperative binding of ionic surfactants to oppositely charged flexible polyions
A novel statistical model for the cooperative binding of monomeric ligands to
a linear lattice is developed to study the interaction of ionic surfactant
molecules with flexible polyion chain in dilute solution. Electrostatic binding
of a ligand to a site on the polyion and hydrophobic associations between the
neighboring bound ligands are assumed to be stochastic processes. Ligand
association separated by several lattice points within defined width is
introduced for the flexible polyion. Model calculations by the Monte Carlo
method are carried out to investigate the binding behavior. The hypothesis on
the ligand association and its width on the chain are of importance in
determining critical aggregation concentration and binding isotherm. The
results are reasonable for the interpretations of several surfactant-flexible
polyion binding experiments. The implications of the approach are presented and
discussed.Comment: 11 pages, 9 figure
Dynamical approach to heavy-ion induced fission using actinide target nuclei at energies around the Coulomb barrier
In order to describe heavy-ion fusion reactions around the Coulomb barrier
with an actinide target nucleus, we propose a model which combines the
coupled-channels approach and a fluctuation-dissipation model for dynamical
calculations. This model takes into account couplings to the collective states
of the interacting nuclei in the penetration of the Coulomb barrier and the
subsequent dynamical evolution of a nuclear shape from the contact
configuration. In the fluctuation-dissipation model with a Langevin equation,
the effect of nuclear orientation at the initial impact on the prolately
deformed target nucleus is considered. Fusion-fission, quasi-fission and deep
quasi-fission are separated as different Langevin trajectories on the potential
energy surface. Using this model, we analyze the experimental data for the mass
distribution of fission fragments (MDFF) in the reactions of
S+U and Si+U at several incident energies
around the Coulomb barrier. We find that the time scale in the quasi-fission as
well as the deformation of fission fragments at the scission point are
different between the Si+U and S+U systems,
causing different mass asymmetries of the quasi-fission.Comment: 11 figure
Extra-large crystal emulsion detectors for future large-scale experiments
Photographic emulsion is a particle tracking device which features the best
spatial resolution among particle detectors. For certain applications, for
example muon radiography, large-scale detectors are required. Therefore, a huge
surface has to be analyzed by means of automated optical microscopes. An
improvement of the readout speed is then a crucial point to make these
applications possible and the availability of a new type of photographic
emulsions featuring crystals of larger size is a way to pursue this program.
This would allow a lower magnification for the microscopes, a consequent larger
field of view resulting in a faster data analysis. In this framework, we
developed new kinds of emulsion detectors with a crystal size of 600-1000 nm,
namely 3-5 times larger than conventional ones, allowing a 25 times faster data
readout. The new photographic emulsions have shown a sufficient sensitivity and
a good signal to noise ratio. The proposed development opens the way to future
large-scale applications of the technology, e.g. 3D imaging of glacier bedrocks
or future neutrino experiments.Comment: Version accepted for publication in JINS
Matemática e meio ambiente : uma proposta de atividade interdisciplinar
É importante frisar que no ensino da Matemática, destacam-se duas abordagens centrais, relacionar , por um lado, observações do mundo real com representações (esquemas, tabelas, figuras ); por outro, com princípios, estruturas e conceitos matemáticos. Assim, interligar temas transversais, meio ambiente, especificamente, consumo de água e energia, representam o desafio desta investigação. Os dados indicam que os alunos ficaram estimulados pelo estudo de funções; e apresentaram melhor compreensão na utilização de gráficos e do estudo da poluição do Rio Sarapuí. Percebemos que a investigação de dados sobre o consumo e a tradução deles, em gráficos estimula a conscientização sobre o meio ambiente. Isso se tornou possível, ao estabelecer vínculo com o mundo real e um ensino que tenha significado com a vida do estudante
Static and Dynamic Phases for Vortex Matter with Attractive Interactions
Exotic vortex states with long range attraction and short range repulsion
have recently been proposed to arise in superconducting hybrid structures and
multi-band superconductors. Using large scale simulations we examine the static
and dynamic properties of such vortex states interacting with random and
periodic pinning. In the absence of pinning this system does not form patterns
but instead completely phase separates. When pinning is present there is a
transition from inhomogeneous to homogeneous vortex configurations similar to a
wetting phenomenon. Under an applied drive, a dynamical dewetting process can
occur from a strongly pinned homogeneous state into pattern forming states. We
show that a signature of the exotic vortex interactions under transport
measurements is a robust double peak feature in the differential conductivity
curves.Comment: 5 pages, 4 postscript figure
Development of Nuclear Emulsion Detector for Muon Radiography
AbstractMuon radiography is the non-destructive testing technique of large-scale constructions with cosmic ray muon. Cosmic ray muon has high penetrating power and it always comes from the whole sky. In the same way of taking a X-ray photograph, we can obtain integrated density of constructions which thickness are several tens to several hundreds. We had ever applied this technique to nuclear reactors, volcanos, and so on. Nuclear emulsion is three dimensional track detector with micrometric position accuracy. Thanks to high position resolution, Nuclear emulsion has mrad angular resolution. In addition, the features which require no power supply and can observe in a large area suitable for muon radiography. In Nagoya University, we launched emulsion manufacturing equipment at 2010. It has become possible to flexible development of our detector and succeeded to development of high sensitive nuclear emulsion film (Nagoya emulsion). An important factor is the temperature characteristic to withstand the outdoor observation as a detector to be used in the muon radiography. There is a phenomenon of a latent image fading, whichit is well known in the photographic industry, and this phenomenon is known that temperature and water are involved. So we examined temperature and humidity characteristic of latent image fading about Nagoya emulsion. As a result, we found latent image fading is strongly depends on both temperature and humidity. By dehydrating emulsion film in RH8%, over 95% (Grain Density>40) detection efficiency of muon track keeps over 3months in 25degree, for 2months in 35degree. Additionally it was showed in this test that increasing back ground noise “fog”, which may have occurred by sealing emulsion film in a narrow space, is reduced by buffer space in the bag
Type-1.5 Superconductors
We demonstrate the existence of a novel superconducting state in high quality
two-component MgB2 single crystalline superconductors where a unique
combination of both type-1 (kappa_1 0.707)
superconductor conditions is realized for the two components of the order
parameter. This condition leads to a vortex-vortex interaction attractive at
long distances and repulsive at short distances, which stabilizes
unconventional stripe- and gossamer-like vortex patterns that we have
visualized in this type-1.5 superconductor using Bitter decoration and also
reproduced in numerical simulations.Comment: accepted in Phys. Rev. Let
Quasi-Particle Spectra, Charge-Density-Wave, Superconductivity and Electron-Phonon Coupling in 2H-NbSe2
High-resolution photoemission has been used to study the electronic structure
of the charge density wave (CDW) and superconducting (SC) dichalcogenide, 2H-
NbSe2. From the extracted self-energies, important components of the
quasiparticle (QP) interactions have been identified. In contrast to previously
studied TaSe2, the CDW transition does not affect the electronic properties
significantly. The electron-phonon coupling is identified as a dominant
contribution to the QP self-energy and is shown to be very anisotropic
(k-dependent) and much stronger than in TaSe2.Comment: 4 pages, 3 figures, minor changes, to appear in PR
- …