1,547 research outputs found
An Estimate of the Vibrational Frequencies of Spherical Virus Particles
The possible normal modes of vibration of a nearly spherical virus particle
are discussed. Two simple models for the particle are treated, a liquid drop
model and an elastic sphere model. Some estimates for the lowest vibrational
frequency are given for each model. It is concluded that this frequency is
likely to be of the order of a few GHz for particles with a radius of the order
of 50 nm.Comment: 6 pages, 1 figur
Lack of effect of sex on pig embryonic development in vivo
The effect of sex on pig conceptus development to day 12 of gestation was investigated. On day 2 of gestation, reciprocal embryo transfers were performed resulting in four groups (Yorkshire–Yorkshire, Yorkshire–Meishan, Meishan–Yorkshire and Meishan–Meishan). Conceptuses at day 12 were recovered from each recipient and diameter, as well as DNA, protein and oestradiol content were determined for individual conceptuses. The sex of individual conceptuses at day 12 was determined by amplification of a fragment of the pig SRY gene, using the polymerase chain reaction. Embryos developed more rapidly to day 12 in Yorkshire recipients, but there was no detectable effect of sex on the diameter, DNA, protein or oestradiol content of conceptuses from any transfer group. Thus, no sex effect was apparent under conditions either promoting or retarding the rate of early pig blastocyst growth. These results provide strong evidence that pig embryonic development occurs at a rate determined by uterine environment and not by sex of the conceptus
Information and entropy in quantum Brownian motion: Thermodynamic entropy versus von Neumann entropy
We compare the thermodynamic entropy of a quantum Brownian oscillator derived
from the partition function of the subsystem with the von Neumann entropy of
its reduced density matrix. At low temperatures we find deviations between
these two entropies which are due to the fact that the Brownian particle and
its environment are entangled. We give an explanation for these findings and
point out that these deviations become important in cases where statements
about the information capacity of the subsystem are associated with
thermodynamic properties, as it is the case for the Landauer principle.Comment: 8 pages, 7 figure
On The Low Frequency Quasi Periodic Oscillations of X-ray Sources
Based on the interpretation of the twin kilohertz Quasi Periodic Oscillations
(kHz QPOs) of X-ray spectra of Low Mass X-Ray Binaries
(LMXBs) to the Keplerian and the periastron precession frequencies at the
magnetosphere-disk of X-ray neutron star (NS) respectively, we ascribe the low
frequency Quasi Periodic Oscillations (LFQPO) and HBO (15-60 Hz QPO for Z
sources or Atoll sources) to the periastron precession at some outer disk
radius.
The obtained conclusions include: all QPO frequencies increase with
increasing the accretion rate. The obtained theoretical relations between HBO
(LFQPO) frequency and the kHz QPO frequency are similar to the measured
empirical formula. Further, the possible dynamical mechanism for QPO production
is discussed.Comment: 6 pages, 2 figures, accepted by APSS, 200
Phase Space Transport in Noisy Hamiltonian Systems
This paper analyses the effect of low amplitude friction and noise in
accelerating phase space transport in time-independent Hamiltonian systems that
exhibit global stochasticity. Numerical experiments reveal that even very weak
non-Hamiltonian perturbations can dramatically increase the rate at which an
ensemble of orbits penetrates obstructions like cantori or Arnold webs, thus
accelerating the approach towards an invariant measure, i.e., a
near-microcanonical population of the accessible phase space region. An
investigation of first passage times through cantori leads to three
conclusions, namely: (i) that, at least for white noise, the detailed form of
the perturbation is unimportant, (ii) that the presence or absence of friction
is largely irrelevant, and (iii) that, overall, the amplitude of the response
to weak noise scales logarithmically in the amplitude of the noise.Comment: 13 pages, 3 Postscript figures, latex, no macors. Annals of the New
York Academy of Sciences, in pres
A preliminary investigation into the apparent abhesive effect of stearic acid on cured silicone elastomer
The effect of addition of small amounts of stearic acid on the adhesive properties of
polydimethylsiloxane (PDMS) was investigated. Stearic acid reduced the peel strength of bonded aluminium samples with the joint weakening effect increasing with increased loadings. Surface analysis of the peeled surfaces was carried out using XPS, SSIMS and FTIR. This showed that stearic acid did not form a weak boundary
layer at the metal-polymer interface as would traditionally be expected. Local Force
Microscopy confirmed this, as the surface adhesion of the PDMS increased, rather
than decreased, on addition of stearic acid
Higher spin fields and the problem of cosmological constant
The cosmological evolution of free massless vector or tensor (but not gauge)
fields minimally coupled to gravity is analyzed. It is shown that there are
some unstable solutions for these fields in De Sitter background. The back
reaction of the energy-momentum tensor of such solutions to the original
cosmological constant exactly cancels the latter and the expansion regime
changes from the exponential to the power law one. In contrast to the
adjustment mechanism realized by a scalar field the gravitational coupling
constant in this model is time-independent and the resulting cosmology may
resemble the realistic one.Comment: 15 pages, Latex twic
- …