21,801 research outputs found
Herbage intake in Danish Jersey and Danish Holstein steers on perennial ryegrass/white clover pasture
The objective of this study was to estimate herbage intake in Danish Friesian and Danish Jersey steers at an age of 8-9 months on ryegrass / white clover pasture. The steers were turned out on pasture in late April and herbage intake was estimated in June in steers of a mean live weight (± S.D.) of 264 ± 14 kg and 185 ± 25 kg for Danish Friesian and Danish Jersey respectively. Faeces and herbage samples were analysed for alkanes to estimate herbage dry matter intake, dry matter digestibility (DMD) and botanical composition of intake. The weight gains at the time of herbage intake estimation in June (kg/day) were 1.142 ± 265 kg/day and 0.927 ± 168 kg/day for Danish Friesian and Danish Jersey respectively. Daily herbage intake (kg dry matter (DM)) estimated by alkanes C32 /C33 was 8.33 ± 0.97 and 6.28 ± 0.61 per day (P<0.001) and 3.15 ± 0.32 and 3.43 ± 0.30 per 100 kg liveweight (LW) (P<0.05) for Danish Friesian and Danish Jersey respectively. The botanical composition of the diet was the same for Danish Friesian and Danish Jersey with about half of the diet being grass leaves and the other half clover leaves. It is concluded that Danish Jersey steers have higher herbage intake per 100 kg LW than Danish Friesian steers of the same age, but herbage intake per kg metabolic LW is not different between the two breeds
Time-Dependent Random Walks and the Theory of Complex Adaptive Systems
Motivated by novel results in the theory of complex adaptive systems, we
analyze the dynamics of random walks in which the jumping probabilities are
{\it time-dependent}. We determine the survival probability in the presence of
an absorbing boundary. For an unbiased walk the survival probability is
maximized in the case of large temporal oscillations in the jumping
probabilities. On the other hand, a random walker who is drifted towards the
absorbing boundary performs best with a constant jumping probability. We use
the results to reveal the underlying dynamics responsible for the phenomenon of
self-segregation and clustering observed in the evolutionary minority game.Comment: 5 pages, 2 figure
The role of binaries in the enrichment of the early Galactic halo. I. r-process-enhanced metal-poor stars
The detailed chemical composition of most metal-poor halo stars has been
found to be highly uniform, but a minority of stars exhibit dramatic
enhancements in their abundances of heavy neutron-capture elements and/or of
carbon. The key question for Galactic chemical evolution models is whether
these peculiarities reflect the composition of the natal clouds, or if they are
due to later mass transfer of processed material from a binary companion. If
the former case applies, the observed excess of certain elements was implanted
within selected clouds in the early ISM from a production site at interstellar
distances. Our aim is to determine the frequency and orbital properties of
binaries among these chemically peculiar stars. This information provides the
basis for deciding whether mass transfer from a binary companion is necessary
and sufficient to explain their unusual compositions. This paper discusses our
study of a sample of 17 moderately (r-I) and highly (r-II) r-process-element
enhanced VMP and EMP stars. High-resolution, low signal-to-noise spectra of the
stars were obtained at roughly monthly intervals over 8 years with the FIES
spectrograph at the Nordic Optical Telescope. From these spectra, radial
velocities with an accuracy of ~100 m/s were determined by cross-correlation
against an optimized template. 14 of the programme stars exhibit no significant
RV variation over this period, while 3 are binaries with orbits of typical
eccentricity for their periods, resulting in a normal binary frequency of
~18+-6% for the sample. Our results confirm our preliminary conclusion from
2011, based on partial data, that the chemical peculiarity of the r-I and r-II
stars is not caused by any putative binary companions. Instead, it was
imprinted on the natal molecular clouds of these stars by an external, distant
source. Models of the ISM in early galaxies should account for such mechanisms.Comment: 14 pages, 3 figures, accepted for publication in Astronomy and
Astrophysic
Superconducting phase diagram of itinerant antiferromagnets
We study the phase diagram of the Hubbard model in the weak-coupling limit
for coexisting spin-density-wave order and spin-fluctuation-mediated
superconductivity. Both longitudinal and transverse spin fluctuations
contribute significantly to the effective interaction potential, which creates
Cooper pairs of the quasi-particles of the antiferromagnetic metallic state. We
find a dominant -wave solution in both electron- and hole-doped
cases. In the quasi-spin triplet channel, the longitudinal fluctuations give
rise to an effective attraction supporting a -wave gap, but are overcome by
repulsive contributions from the transverse fluctuations which disfavor
-wave pairing compared to . The sub-leading pair instability is
found to be in the -wave channel, but complex admixtures of and are
not energetically favored since their nodal structures coincide. Inclusion of
interband pairing, in which each fermion in the Cooper pair belongs to a
different spin-density-wave band, is considered for a range of electron dopings
in the regime of well-developed magnetic order. We demonstrate that these
interband pairing gaps, which are non-zero in the magnetic state, must have the
same parity under inversion as the normal intraband gaps. The self-consistent
solution to the full system of five coupled gap equations give intraband and
interband pairing gaps of structure and similar gap magnitude. In
conclusion, the gap dominates for both hole and electron doping
inside the spin-density-wave phase.Comment: 14 pages, 9 figure
Local modulations of the spin-fluctuation mediated pairing interaction by impurities in d-wave superconductors
We present a self-consistent real space formulation of spin-fluctuation
mediated d-wave pairing. By calculating all relevant inhomogeneous spin and
charge susceptibilities in real space within the random phase approximation
(RPA), we obtain the effective pairing interaction and study its spatial
dependence near both local potential and hopping impurities. A remarkably large
enhancement of the pairing interaction may be obtained near the impurity site.
We discuss the relevance of our result to inhomogeneities observed by scanning
tunneling spectroscopy on the surface of cuprate superconductors.Comment: 8 pages, 7 figure
Competing Ordered Phases in URu2Si2: Hydrostatic Pressure and Re-substitution
A persistent kink in the pressure dependence of the \hidden order" (HO)
transition temperature of URu2-xRexSi2 is observed at a critical pressure Pc=15
kbar for 0 < x < 0.08. In URu2Si2, the kink at Pc is accompanied by the
destruction of superconductivity; a change in the magnitude of a spin
excitation gap, determined from electrical resistivity measurements; and a
complete gapping of a portion of the Fermi surface (FS), inferred from a change
in scattering and the competition between the HO state and superconductivity
for FS fraction
The role of binaries in the enrichment of the early Galactic halo. II. Carbon-Enhanced Metal-Poor Stars - CEMP-no stars
The detailed composition of most metal-poor halo stars has been found to be
very uniform. However, a fraction of 20-70% (increasing with decreasing
metallicity) exhibit dramatic enhancements in their abundances of carbon - the
so-called carbon-enhanced metal-poor (CEMP) stars. A key question for Galactic
chemical evolution models is whether this non-standard composition reflects
that of the stellar natal clouds, or is due to local, post-birth mass transfer
of chemically processed material from a binary companion; CEMP stars should
then all be members of binary systems. Our aim is to determine the frequency
and orbital parameters of binaries among CEMP stars with and without
over-abundances of neutron-capture elements - CEMP-s and CEMP-no stars,
respectively - as a test of this local mass-transfer scenario. This paper
discusses a sample of 24 CEMP-no stars, while a subsequent paper will consider
a similar sample of CEMP-s stars. Most programme stars exhibit no statistically
significant radial-velocit variation over this period and appear to be single,
while four are found to be binaries with orbital periods of 300-2,000 days and
normal eccentricity; the binary frequency for the sample is 17+-9%. The single
stars mostly belong to the recently-identified ``low-C band'', while the
binaries have higher absolute carbon abundances. We conclude that the
nucleosynthetic process responsible for the strong carbon excess in these
ancient stars is unrelated to their binary status; the carbon was imprinted on
their natal molecular clouds in the early Galactic ISM by an even earlier,
external source, strongly indicating that the CEMP-no stars are likely bona
fide second-generation stars. We discuss potential production sites for carbon
and its transfer across interstellar distances in the early ISM, and
implications for the composition of high-redshift DLA systems. Abridged.Comment: 16 pages, 5 figures, accepted for publication in Astronomy and
Astrophysic
Maps of complex motion selectivity in the superior temporal cortex of the alert macaque monkey: a double-label 2-deoxyglucose study
The superior temporal sulcus (STS) of the macaque monkey contains multiple visual areas. Many neurons within these regions respond selectively to motion direction and to more complex motion patterns, such as expansion, contraction and rotation. Single-unit recording and optical recording studies in MT/MST suggest that cells with similar tuning properties are clustered into columns extending through multiple cortical layers. In this study, we used a double-label 2-deoxyglucose technique in awake, behaving macaque monkeys to clarify this functional organization. This technique allowed us to label, in a single animal, two populations of neurons responding to two different visual stimuli. In one monkey we compared expansion with contraction; in a second monkey we compared expansion with clockwise rotation. Within the STS we found a patchy arrangement of cortical columns with alternating stimulus selectivity: columns of neurons preferring expansion versus contraction were more widely separated than those selective for expansion versus rotation. This mosaic of interdigitating columns on the floor and posterior bank of the STS included area MT and some neighboring regions of cortex, perhaps including area MST
Interpretation of scanning tunneling quasiparticle interference and impurity states in cuprates
We apply a recently developed method combining first principles based Wannier
functions with solutions to the Bogoliubov-de Gennes equations to the problem
of interpreting STM data in cuprate superconductors. We show that the observed
images of Zn on the surface of BiSrCaCuO can only be understood
by accounting for the tails of the Cu Wannier functions, which include
significant weight on apical O sites in neighboring unit cells. This
calculation thus puts earlier crude "filter" theories on a microscopic
foundation and solves a long standing puzzle. We then study quasiparticle
interference phenomena induced by out-of-plane weak potential scatterers, and
show how patterns long observed in cuprates can be understood in terms of the
interference of Wannier functions above the surface. Our results show excellent
agreement with experiment and enable a better understanding of novel phenomena
in the cuprates via STM imaging.Comment: 5 pages, 5 figures, published version (Supplemental Material: 5
pages, 11 figures) for associated video file, see
http://itp.uni-frankfurt.de/~kreisel/QPI_BSCCO_BdG_p_W.mp
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