143,473 research outputs found
Inhibition of DNA ejection from bacteriophage by Mg+2 counterions
The problem of inhibiting viral DNA ejection from bacteriophages by
multivalent counterions, specifically Mg counterions, is studied.
Experimentally, it is known that MgSO salt has a strong and non-monotonic
effect on the amount of DNA ejected. There exists an optimal concentration at
which the minimum amount of DNA is ejected from the virus. At lower or higher
concentrations, more DNA is ejected from the capsid. We propose that this
phenomenon is the result of DNA overcharging by Mg multivalent
counterions. As Mg concentration increases from zero, the net charge of
DNA changes from negative to positive. The optimal inhibition corresponds to
the Mg concentration where DNA is neutral. At lower/higher
concentrations, DNA genome is charged. It prefers to be in solution to lower
its electrostatic self-energy, which consequently leads to an increase in DNA
ejection. By fitting our theory to available experimental data, the strength of
DNADNA short range attraction energies, mediated by Mg, is found to
be 0.004 per nucleotide base. This and other fitted parameters agree
well with known values from other experiments and computer simulations. The
parameters are also in aggreement qualitatively with values for tri- and
tetra-valent counterions.Comment: 17 pages, 4 figures, improved manuscript. Submitted to J. Chem. Phys
(2010
Effects of translational and rotational degrees of freedom on the properties of model water
Molecular dynamics simulations with separate thermostats for rotational and
translational motions were used to study the effects of these degrees of
freedom on the structure of water at a fixed density. To describe water
molecules, we used the SPC/E model. The results indicate that an increase of
the rotational temperature, , causes a significant breaking of
the hydrogen bonds. This is not the case, at least not to such an extent, when
the translational temperature, , is raised. The probability of
finding an empty spherical cavity (no water molecule present) of a given size,
strongly decreases with an increase of , but this only marginally
affects the free energy of the hydrophobe insertion. The excess internal energy
increases proportionally with an increase of , while an increase
of yields a much smaller effect at high temperatures. The
diffusion coefficient of water exhibits a non-monotonous behaviour with an
increase of the rotational temperature.Comment: 9 pages, 9 figure
Double charmonium production at B-factories within light cone formalism
This paper is devoted to the study of the processes e^+e^- \to J/\Psi \eta_c,
J/\Psi \eta_c', \psi' \eta_c, \psi' \eta_c' within light cone formalism. It is
shown that if one disregards the contribution of higher fock states, the
twist-3 distribution amplitudes needed in the calculation can be unambiguously
determined from the twist-2 distribution amplitudes and equations of motion.
Using models of the twist-2 distribution amplitudes the cross sections of the
processes under study have been calculated. The results of the calculation are
in agreement with Belle and BaBar experiments. It is also shown that
relativistic and radiative corrections to the cross sections play crucial role
in the achievement of the agreement between the theory and experiments. The
comparison of the results of this paper with the results obtained in other
papers has been carried out. In particular, it is shown that the results of
papers where relativistic and radiative corrections were calculated within
NRQCD are overestimated by a factor of ~1.5.Comment: 14 pages, 1 figur
Quasi-dark Mode in a Metamaterial for Analogous Electromagnetically-induced Transparency
We study a planar metamaterial supporting electromagnetically-induced
transparency (EIT)-like effect by exploiting the coupling between bright and
quasi-dark eigenmodes. The specific design of such a metamaterial consists of a
cut-wire (CW) and a single-gap split-ring resonator (SRR). From the numerical
and the analytical results we demonstrate that the response of SRR, which is
weakly excited by external electric field, is mitigated to be a quasi-dark
eigenmode in the presence of strongly radiative CW. This result suggests more
relaxed conditions for the realization of devices utilizing the EIT-like
effects in metamaterial, and thereby widens the possibilities for many
different structural implementations.Comment: 11 pages, 4 figure
Fluorine in a Carbon-Enhanced Metal-Poor Star
The fluorine abundance of the Carbon-Enhanced Metal-Poor (CEMP) star HE
1305+0132 has been derived by analysis of the molecular HF (1-0) R9 line at
2.3357 microns in a high-resolution (R = 50,000) spectrum obtained with the
Phoenix spectrometer and Gemini-South telescope. Our abundance analysis makes
use of a CNO-enhanced ATLAS12 model atmosphere characterized by a metallicity
and CNO enhancements determined utilizing medium-resolution (R = 3,000) optical
and near-IR spectra. The effective iron abundance is found to be [Fe/H] = -2.5,
making HE 1305+0132 the most Fe-deficient star, by more than an order of
magnitude, for which the abundance of fluorine has been measured. Using
spectral synthesis, we derive a super-solar fluorine abundance of A(19F) = 4.96
+/- 0.21, corresponding to a relative abundance of [F/Fe] = 2.90. A single line
of the Phillips C_2 system is identified in our Phoenix spectrum, and along
with multiple lines of the first-overtone vibration-rotation CO (3-1) band
head, C and O abundances of A(12C) = 8.57 +/- 0.11 and A(16O) = 7.04 +/- 0.14
are derived. We consider the striking fluorine overabundance in the framework
of the nucleosynthetic processes thought to be responsible for the
C-enhancement of CEMP stars and conclude that the atmosphere of HE 1305+0132
was polluted via mass transfer by a primary companion during its asymptotic
giant branch phase. This is the first study of fluorine in a CEMP star, and it
demonstrates that this rare nuclide can be a key diagnostic of nucleosynthetic
processes in the early Galaxy.Comment: 13 pages, 3 figures; Accepted for publication in ApJ Letter
Vibrational state dependence of ionic rotational branching ratios in resonance enhanced multiphoton ionization of CH
We show that rapid evolution of a Rydberg orbital with internuclear distance in a resonance enhanced multiphoton ionization (REMPI) process can have a profound influence on the production of molecular ions in alternative rotational states. This is illustrated by calculations of ionic rotational branching ratios for (2+1′) REMPI via the O11 (20.5) branch of the E′ ^2Σ^+(3pσ) Rydberg state of CH. The rotational propensity rule for ionization changes from ΔN=odd (ΔN=N_+−N_i) at lower vibrational excitation, as expected from the ΔN+l=odd selection rule, to ΔN=even at higher vibrational levels. This effect is expected to be quite general and should be most readily observable in diatomic hydrides
Three-Species Diffusion-Limited Reaction with Continuous Density-Decay Exponents
We introduce a model of three-species two-particle diffusion-limited
reactions A+B -> A or B, B+C -> B or C, and C+A -> C or A, with three
persistence parameters (survival probabilities in reaction) of the hopping
particle. We consider isotropic and anisotropic diffusion (hopping with a
drift) in 1d. We find that the particle density decays as a power-law for
certain choices of the persistence parameter values. In the anisotropic case,
on one symmetric line in the parameter space, the decay exponent is
monotonically varying between the values close to 1/3 and 1/2. On another, less
symmetric line, the exponent is constant. For most parameter values, the
density does not follow a power-law. We also calculated various characteristic
exponents for the distance of nearest particles and domain structure. Our
results support the recently proposed possibility that 1d diffusion-limited
reactions with a drift do not fall within a limited number of distinct
universality classes.Comment: 12 pages in plain LaTeX and four Postscript files with figure
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