2,194 research outputs found
Forage Quality of Cool Season Pasture Species Under Two Rotational Grazing Height Regimes
To optimize animal and pasture performance in management intensive grazing systems, pasture production and quality often must be compromised. Rotationally-stocking pastures at slightly taller grazing heights can increase pasture productivity, but lower forage quality may limit animal performance. Our objective was to compare the forage quality of common cool season pasture species in the Northeastern U.S., under two rotational grazing regimes defined by slightly different grass heights
Min-oscillations in Escherichia coli induced by interactions of membrane-bound proteins
During division it is of primary importance for a cell to correctly determine
the site of cleavage. The bacterium Escherichia coli divides in the center,
producing two daughter cells of equal size. Selection of the center as the
correct division site is in part achieved by the Min-proteins. They oscillate
between the two cell poles and thereby prevent division at these locations.
Here, a phenomenological description for these oscillations is presented, where
lateral interactions between proteins on the cell membrane play a key role.
Solutions to the dynamic equations are compared to experimental findings. In
particular, the temporal period of the oscillations is measured as a function
of the cell length and found to be compatible with the theoretical prediction.Comment: 17 pages, 5 figures. Submitted to Physical Biolog
Constraints on the Existence of Chiral Fermions in Interacting Lattice Theories
It is shown that an interacting theory, defined on a regular lattice, must
have a vector-like spectrum if the following conditions are satisfied:
(a)~locality, (b)~relativistic continuum limit without massless bosons, and
(c)~pole-free effective vertex functions for conserved currents.
The proof exploits the zero frequency inverse retarded propagator of an
appropriate set of interpolating fields as an effective quadratic hamiltonian,
to which the Nielsen-Ninomiya theorem is applied.Comment: LaTeX, 9 pages, WIS--93/56--JUNE--P
The steady-state of heterogeneous catalysis, studied by first-principles statistical mechanics
The turn-over frequency of the catalytic oxidation of CO at RuO2(110) was
calculated as function of temperature and partial pressures using ab initio
statistical mechanics. The underlying energetics of the gas-phase molecules,
dissociation, adsorption, surface diffusion, surface chemical reactions, and
desorption were obtained by all-electron density-functional theory. The
resulting CO2 formation rate [in the full (T, p_CO, p_O2)-space], the movies
displaying the atomic motion and reactions over times scales from picoseconds
to seconds, and the statistical analyses provide insights into the concerted
actions ruling heterogeneous catalysis and open thermodynamic systems in
general.Comment: 4 pages including 3 figures, Related publications can be found at
http://www.fhi-berlin.mpg.de/th/paper.htm
Response to Drought of White Clover Lines Selected for Different Stolon Morphologies
White clover (Trifolium repens L.) lines were selected from within large and small-leaved cultivars of Grasslands Kopu and Grasslands Tahora, respectively, for long or short internodes, and for high or low branching frequency from plants grown in sun and shade (50% full sunlight). Lines were compared for drought tolerance in a perennial ryegrass (Lolium perenne L.) sward in boxes. Prior to imposing drought branching frequency selections did not differ in branching frequency, although the low branching frequency selection had a higher percentage of rooted nodes. After an imposed drought treatment sun-selected lines grew better than shade-selected lines relative to their non-stressed controls suggesting that white clover selected under full-sun may be more drought-tolerant than lines selected in shade. Selections for different stolon morphologies did not differ in stolon and root growth at the end of the drought
Nonlocal lattice fermion models on the 2d torus
Abelian fermion models described by the SLAC action are considered on a
finite 2d lattice. It is shown that modification of these models by introducing
additional Pauli - Villars regularization supresses nonlocal effects and
provides agreement with the continuum results in vectorial U(1) models. In the
case of chiral fermions the phase of the determinant differs from the continuum
one.Comment: 16 pages, LaTeX, 5 eps figures, uses epsf.sty, rotate.st
Hamiltonian domain wall fermions at strong coupling
We apply strong-coupling perturbation theory to gauge theories containing
domain-wall fermions in Shamir's surface version. We construct the effective
Hamiltonian for the color-singlet degrees of freedom that constitute the
low-lying spectrum at strong coupling. We show that the effective theory is
identical to that derived from naive, doubled fermions with a mass term, and
hence that domain-wall fermions at strong coupling suffer both doubling and
explicit breaking of chiral symmetry. Since we employ a continuous fifth
dimension whose extent tends to infinity, our result applies to overlap
fermions as well.Comment: Revtex, 21 pp. Some changes in Introduction, dealing with consistency
with previous wor
Josephson current through a molecular transistor in a dissipative environment
We study the Josephson coupling between two superconductors through a single
correlated molecular level, including Coulomb interaction on the level and
coupling to a bosonic environment. All calculations are done to the lowest,
i.e., the fourth, order in the tunneling coupling and we find a suppression of
the supercurrent due to the combined effect of the Coulomb interaction and the
coupling to environmental degrees of freedom. Both analytic and numerical
results are presented.Comment: 11 pages, 6 figures, to appear in Phys. Rev. B; v3: several misprints
corrected - in particular, sign inconsistencies throughout the paper should
be fixe
The Evolution of Cosmic Magnetic Fields: From the Very Early Universe, to Recombination, to the Present
(abridged) A detailed examination of the evolution of stochastic magnetic
fields between high cosmic temperatures and the present epoch is presented. A
simple analytical model matching the results of the 3D MHD simulations allows
for the prediction of present day magnetic field correlation lengths and
energy. Our conclusions are multi fold. (a) Initial primordial fields with only
a small amount of helicity are evolving into maximally helical fields. (b)
There exists a correlation between the strength of the magnetic field, B, at
the peak of it's spectrum and the location of the peak, given at the present
epoch by: B ~ 5x10^{-12} (L/kpc) Gauss, where L is the correlation length
determined by the initial magnetic field. (c) Concerning studies of generation
of cosmic microwave background (CMBR) anisotropies due to primordial magnetic
fields of B~10^{-9} Gauss on ~ 10 Mpc scales, such fields are not only
impossible to generate in early causal magnetogenesis scenarios but also
seemingly ruled out by distortions of the CMBR spectrum due to magnetic field
dissipation on smaller scales and the overproduction of cluster magnetic
fields. (d) The most promising detection possibility of CMBR distortions due to
primordial magnetic fields may be on much smaller scales at higher multipoles
l~10^6 where the signal is predicted to be the strongest. (e) It seems possible
that magnetic fields in clusters of galaxies are entirely of primordial origin,
without invoking dynamo amplification. Such fields would be of (pre-collapse)
strength 10^{-12} - 10^{-11} Gauss with correlation lengths in the kpc range,
and would also exist in voids of galaxies.Comment: 35 pages, 22 figures, revtex style, submitted to PR
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