4,720 research outputs found
Renormalization group approach to vibrational energy transfer in protein
Renormalization group method is applied to the study of vibrational energy
transfer in protein molecule. An effective Lagrangian and associated equations
of motion to describe the resonant energy transfer are analyzed in terms of the
first-order perturbative renormalization group theory that has been developed
as a unified tool for global asymptotic analysis. After the elimination of
singular terms associated with the Fermi resonance, amplitude equations to
describe the slow dynamics of vibrational energy transfer are derived, which
recover the result obtained by a technique developed in nonlinear optics [S.J.
Lade, Y.S. Kivshar, Phys. Lett. A 372 (2008) 1077].Comment: 11 page
Ac conductivity and dielectric properties of CuFe1−xCrxO2 : Mg delafossite
The electrical and dielectric properties of CuFe(1−x)Cr(x)O(2) (0 ≤ x ≤ 1) powders, doped with 3% of Mg and prepared by solid-state reaction, were studied by broadband dielectric spectroscopy in the temperature range from −100 to 150 °C. The frequency-dependent electrical and dielectric data have been discussed in the framework of a power law conductivity and complex impedance and dielectric modulus. At room temperature, the ac conductivity behaviour is characteristic of the charge transport in CuFe1−xCrxO2 powders. The substitution of Fe3+ by Cr3+ results in an increase in dc conductivity and a decrease in the Cu+–Cu+ distance. Dc conductivity, characteristic onset frequency and Havriliak–Negami characteristics relaxation times are thermally activated above −40 °C for x = 0.835. The associated activation energies obtained from dc and ac conductivity and from impedance and modulus losses are similar and show that CuFe1−xCrxO2 delafossite powders satisfy the BNN relation. Dc and ac conductivities have the same transport mechanism, namely thermally activated nearest neighbour hopping and tunnelling hopping above and below −40 °C, respectively
Experimental evidence of stochastic resonance without tuning due to non Gaussian noises
In order to test theoretical predictions, we have studied the phenomenon of
stochastic resonance in an electronic experimental system driven by white non
Gaussian noise. In agreement with the theoretical predictions our main findings
are: an enhancement of the sensibility of the system together with a remarkable
widening of the response (robustness). This implies that even a single resonant
unit can reach a marked reduction in the need of noise tuning.Comment: 4 pages, 3 figure
Molecular Identification of Rickettsial Endosymbionts in the Non-Phagotrophic Volvocalean Green Algae
Background: The order Rickettsiales comprises Gram-negative obligate intracellular bacteria (also called rickettsias) that are mainly associated with arthropod hosts. This group is medically important because it contains human-pathogenic species that cause dangerous diseases. Until now, there has been no report of non-phagotrophic photosynthetic eukaryotes, such as green plants, harboring rickettsias. Methodology/Principal Findings: We examined the bacterial endosymbionts of two freshwater volvocalean green algae: unicellular Carteria cerasiformis and colonial Pleodorina japonica. Epifluorescence microscopy using 49-6-deamidino-2phenylindole staining revealed the presence of endosymbionts in all C. cerasiformis NIES-425 cells, and demonstrated a positive correlation between host cell size and the number of endosymbionts. Strains both containing and lacking endosymbionts of C. cerasiformis (NIES-425 and NIES-424) showed a.10-fold increase in cell number and typical sigmoid growth curves over 192 h. A phylogenetic analysis of 16 S ribosomal (r)RNA gene sequences from the endosymbionts of C. cerasiformis and P. japonica demonstrated that they formed a robust clade (hydra group) with endosymbionts of various non-arthropod hosts within the family Rickettsiaceae. There were significantly fewer differences in the 16 S rRNA sequences of the rickettsiacean endosymbionts between C. cerasiformis and P. japonica than in the chloroplast 16 S rRNA or 18 S rRNA of the host volvocalean cells. Fluorescence in situ hybridization demonstrated the existence of the rickettsiacea
Flagellate green algae from four water bodies in the state of Rio de Janeiro, Southeast Brazil
Magnetic Ordering in V-Layers of the Superconducting System of Sr2VFeAsO3
Results of transport, magnetic, thermal, and 75As-NMR measurements are
presented for superconducting Sr2VFeAsO3 with an alternating stack of FeAs and
perovskite-like block layers. Although apparent anomalies in magnetic and
thermal properties have been observed at ~150 K, no anomaly in transport
behaviors has been observed at around the same temperature. These results
indicate that V ions in the Sr2VO3-block layers have localized magnetic moments
and that V-electrons do not contribute to the Fermi surface. The electronic
characteristics of Sr2VFeAsO3 are considered to be common to those of other
superconducting systems with Fe-pnictogen layers.Comment: 4 pages, 4 figures, To appear in JPSJ 79 (2010) 12371
Pattern formation of reaction-diffusion system having self-determined flow in the amoeboid organism of Physarum plasmodium
The amoeboid organism, the plasmodium of Physarum polycephalum, behaves on
the basis of spatio-temporal pattern formation by local
contraction-oscillators. This biological system can be regarded as a
reaction-diffusion system which has spatial interaction by active flow of
protoplasmic sol in the cell. Paying attention to the physiological evidence
that the flow is determined by contraction pattern in the plasmodium, a
reaction-diffusion system having self-determined flow arises. Such a coupling
of reaction-diffusion-advection is a characteristic of the biological system,
and is expected to relate with control mechanism of amoeboid behaviours. Hence,
we have studied effects of the self-determined flow on pattern formation of
simple reaction-diffusion systems. By weakly nonlinear analysis near a trivial
solution, the envelope dynamics follows the complex Ginzburg-Landau type
equation just after bifurcation occurs at finite wave number. The flow term
affects the nonlinear term of the equation through the critical wave number
squared. Contrary to this, wave number isn't explicitly effective with lack of
flow or constant flow. Thus, spatial size of pattern is especially important
for regulating pattern formation in the plasmodium. On the other hand, the flow
term is negligible in the vicinity of bifurcation at infinitely small wave
number, and therefore the pattern formation by simple reaction-diffusion will
also hold. A physiological role of pattern formation as above is discussed.Comment: REVTeX, one column, 7 pages, no figur
Development of continuous flow type hydrothermal reactor for hemicellulose fraction recovery from corncob
ArticleBioresource Technology. 100(11):2842-2848 (2009)journal articl
Extended parametric resonances in nonlinear Schrodinger systems
We study an example of exact parametric resonance in a extended system ruled
by nonlinear partial differential equations of nonlinear Schr\"odinger type. It
is also conjectured how related models not exactly solvable should behave in
the same way. The results have applicability in recent experiments in
Bose-Einstein condensation and to classical problems in Nonlinear Optics.Comment: 1 figur
The Complex Ginzburg-Landau Equation in the Presence of Walls and Corners
We investigate the influence of walls and corners (with Dirichlet and Neumann
boundary conditions) in the evolution of twodimensional autooscillating fields
described by the complex Ginzburg-Landau equation. Analytical solutions are
found, and arguments provided, to show that Dirichlet walls introduce strong
selection mechanisms for the wave pattern. Corners between walls provide
additional synchronization mechanisms and associated selection criteria. The
numerical results fit well with the theoretical predictions in the parameter
range studied.Comment: 10 pages, 9 figures; for related work visit
http://www.nbi.dk/~martine
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