19,743 research outputs found
Ambiguous Dependence Of Minimal Plant Generation Time On Nuclear DNA Content
AMBIGUOUS DEPENDENCE OF MINIMAL PLANT GENERATION TIME ON NUCLEAR DNA CONTENT Victor B. Ivanov The minimum generation time (MGT) of plant development was suggested to depend on nuclear DNA content, which varies in plants over wide limits1. In ephemeral species with the shortest MGT, the average C values were significantly lower than in annual species, whereas the average C values in annual species were lower than those in perennial plants. However, nobody has paid attention to the ratio of annual to perennial species number as a function of C values. Here I show that with increasing C the ratio of annual to perennial species increases to C values equal to 7-8 pg (monocots) and 6-7 pg (eudicots) and then decreases and that the fraction of annuals is abundant not at the lowest, but at some higher C levels. Hence, C value increase exerts an ambiguous effect on MGT. The C value is not the only factor, which determines the duration of the plant development. Nevertheless, the nuclear DNA content exerts a pronounced effect on MGT together with other diverse factors affecting the rate of plant development, especially at higher C values
Skewed Sudakov Regime, Harmonic Numbers, and Multiple Polylogarithms
On the example of massless QED we study an asymptotic of the vertex when only
one of the two virtualities of the external fermions is sent to zero. We call
this regime the skewed Sudakov regime. First, we show that the asymptotic is
described with a single form factor, for which we derive a linear evolution
equation. The linear operator involved in this equation has a discrete
spectrum. Its eigenfunctions and eigenvalues are found. The spectrum is a
shifted sequence of harmonic numbers. With the spectrum found, we represent the
expansion of the asymptotic in the fine structure constant in terms of multiple
polylogarithms. Using this representation, the exponentiation of the doubly
logarithmic corrections of the Sudakov form factor is recovered. It is pointed
out that the form factor of the skewed Sudakov regime is growing with the
virtuality of a fermion decreasing at a fixed virtuality of another fermion.Comment: 6 page
Space medicine considerations: Skeletal and calcium homeostasis
Based on the information obtained from space missions, particularly Skylab and the longer Salyut missions, it is clear that bone and mineral metabolism is substantially altered during space flight. Calcium balance becomes increasingly more negative throughout the flight, and the bone mineral content of the os calcis declines. The major health hazards associated with skeletal changes include the signs and symptoms of hypercalcemia with rapid bone turnover, the risk of kidney stones because of hypercalciuria, the lengthy recovery of lost bone mass after flight, the possibility of irreversible bone loss (particularly the trabecular bone), the possible effects of metastated calcification in the soft tissues, and the possible increase in fracture potential. For these reasons, major efforts need to be directed toward elucidating the fundamental mechanisms by which bone is lost in space and developing more effective countermeasures to prevent both short-term and long-term complications
Instability of magnetic fields in electroweak plasma driven by neutrino asymmetries
The magnetohydrodynamics (MHD) is modified to incorporate the parity
violation in the Standard Model leading to a new instability of magnetic fields
in the electroweak plasma in the presence of nonzero neutrino asymmetries. The
main ingredient for such a modified MHD is the antisymmetric part of the photon
polarization tensor in plasma, where the parity violating neutrino interaction
with charged leptons is present. We calculate this contribution to the
polarization tensor connected with the Chern-Simons term in effective
Lagrangian of the electromagnetic field. The general expression for such a
contribution which depends on the temperature and the chemical potential of
plasma as well as on the photon's momentum is derived. The instability of a
magnetic field driven by the electron neutrino asymmetry for the -burst
during the first second of a supernova explosion can amplify a seed magnetic
field of a protostar, and, perhaps, can explain the generation of strongest
magnetic fields in magnetars. The growth of a cosmological magnetic field
driven by the neutrino asymmetry density is provided by a lower bound on
which is consistent with the well-known Big
Bang nucleosynthesis (upper) bound on neutrino asymmetries in a hot universe
plasma.Comment: 22 pages in JCAP latex style, 3 eps figures; paper was significantly
revised, title was changed, some details of the calculation of the
polarization tensor were removed, 2 appendixes were included; version to be
published in JCA
Magnetic field instability in a neutron star driven by the electroweak electron-nucleon interaction versus the chiral magnetic effect
We show that the Standard Model electroweak interaction of ultrarelativistic
electrons with nucleons ( interaction) in a neutron star (NS) permeated by
a seed large-scale helical magnetic field provides its growth up to during a time comparable with the ages of young
magnetars . The magnetic field instability
originates from the parity violation in the interaction entering the
generalized Dirac equation for right and left massless electrons in an external
uniform magnetic field. We calculate the averaged electric current given by the
solution of the modified Dirac equation containing an extra current for right
and left electrons (positrons), which turns out to be directed along the
magnetic field. Such current includes both a changing chiral imbalance of
electrons and the potential given by a constant neutron density in NS.
Then we derive the system of the kinetic equations for the chiral imbalance and
the magnetic helicity which accounts for the interaction. By solving this
system, we show that a sizable chiral imbalance arising in a neutron protostar
due to the Urca-process diminishes
very rapidly because of a huge chirality flip rate. Thus the term prevails
the chiral effect providing a huge growth of the magnetic helicity and the
helical magnetic field.Comment: 6 pages in Revtex4.1, two columns, 2 eps figures; text was slightly
extended, multiple misprints were corrected, some references were added;
version published in Phys.Rev.D as a Rapid Communicatio
Chiral magnetic effect in the presence of electroweak interactions as a quasiclassical phenomenon
We elaborate the quasiclassical approach to obtain the modified chiral
magnetic effect in the case when massless charged fermions interact with
electromagnetic fields and the background matter by the electroweak forces. The
derivation of the anomalous current along the external magnetic field involves
the study of the energy density evolution of chiral particles in parallel
electric and magnetic fields. We consider both the particle acceleration by the
external electric field and the contribution of the Adler anomaly. The
condition of the validity of this method for the derivation of the chiral
magnetic effect is formulated. We obtain the expression for the electric
current along the external magnetic field, which appears to coincide with our
previous results based on the purely quantum approach. Our results are compared
with findings of other authors.Comment: 13 pages in LaTeX2e, 1 table; Appendix is added, we compare different
methods to derive CM
Permanent mean spin source of the chiral magnetic effect in neutron stars
We suggest the generalization of the Anomalous Magneto-Hydro-Dynamics (AMHD)
in the chiral plasma of a neutron star (NS) accounting for the mean spin in the
ultrarelativistic degenerate electron gas within the magnetized NS core as a
continuing source of the chiral magnetic effect. Using the mean field dynamo
model generalized in AMHD, one can obtain the growth of a seed magnetic field
up to for an old non-superfluid NS at its neutrino cooling
era , while neglecting any matter turbulence within its
core and assuming the rigid NS rotation. The application of the suggested
approach to the evolution of magnetic fields observed in magnetars, , should be self-consistent with all approximations used in
the suggested laminar dynamo, at least, up to the jumps of growing fields.Comment: 15 pages, 9 eps figures, JCAP latex style; title is modified, minimal
changes in the text; version published in JCA
Generation of the relic neutrino asymmetry in a hot plasma of the early Universe
The neutrino asymmetry in the early universe plasma, ,
is calculated both before and after the electroweak phase transition (EWPT). In
the Standard Model before EWPT, the leptogenesis is well known to be driven by
the abelian anomaly in a massless hypercharge field. The generation of the
neutrino asymmetry in the Higgs phase after EWPT, in its turn, has not been
considered previously because of the absence of any quantum anomaly in an
external electromagnetic field for such electroneutral particles as neutrino,
unlike the Adler-Bell-Jackiw anomaly for charged left and right polarized
massless electrons in the same electromagnetic field. Using the neutrino
Boltzmann equation, modified by the Berry curvature term in the momentum space,
we establish the violation of the macroscopic neutrino current in plasma after
EWPT and exactly reproduce the nonconservation of the lepton current in the
symmetric phase before EWPT arising in quantum field theory due to the nonzero
lepton hypercharge and corresponding triangle anomaly in an external
hypercharge field. In the last case, the non-conservation of the lepton current
is derived through the kinetic approach without a computation of corresponding
Feynman diagrams. Then the new kinetic equation is applied for the calculation
of the neutrino asymmetry accounting for the Berry curvature and the
electroweak interaction with background fermions in the Higgs phase. Such an
interaction generates a neutrino asymmetry through the electroweak coupling of
neutrino currents with electromagnetic fields in plasma, which is . It turns out that this effect is especially efficient for
maximally helical magnetic fields.Comment: 18 pages in LaTeX2e, 4 eps figures; based on talk given on the 3rd
International Conference on Particle Physics and Astrophysics ICPPA-2017
(October 2-5, 2017, Moscow, Russia); to be published in the special issue of
Int.J.Mod.Phys.
- …