4,575 research outputs found
Causes of Stillbirth and Time of Death in Swedish Holstein Calves Examined Post Mortem
This study was initiated due to the observation of increasing and rather high levels of stillbirths, especially in first-calving Swedish Holstein cows (10.3%, 2002). Seventy-six Swedish Holstein calves born to heifers at 41 different farms were post mortem examined in order to investigate possible reasons for stillbirth and at what time in relation to full-term gestation they had occurred. The definition of a stillborn calf was dead at birth or within 24 h after birth after at least 260 days of gestation. Eight calves were considered as having died already in uterus. Slightly less than half of the examined calves (46.1%) were classified as having died due to a difficult calving. Four calves (5.3%) had different kinds of malformations (heart defects, enlarged thymus, urine bladder defect). Approximately one third of the calves (31.6%) were clinically normal at full-term with no signs of malformation and born with no indication of difficulties at parturition or any other reason that could explain the stillbirth. The numbers of male and female calves were rather equally distributed within the groups. A wide variation in post mortem weights was seen in all groups, although a number of the calves in the group of clinically normal calves with unexplained reason of death were rather small and, compared with e.g. those calves categorised as having died due to a difficult calving, their average birth weight was 6 kg lower (39.9 ± 1.7 kg vs. 45.9 ± 1.5 kg, p ≤ 0.01). It was concluded that the cause of stillbirth with a non-infectious aetiology is likely to be multifactorial and difficult calving may explain only about half of the stillbirths. As much as one third of the calves seemed clinically normal with no obvious reason for death. This is a target group of calves that warrants a more thorough investigation in further studies
Relating the Cosmological Constant and Supersymmetry Breaking in Warped Compactifications of IIB String Theory
It has been suggested that the observed value of the cosmological constant is
related to the supersymmetry breaking scale M_{susy} through the formula Lambda
\sim M_p^4 (M_{susy}/M_p)^8. We point out that a similar relation naturally
arises in the codimension two solutions of warped space-time varying
compactifications of string theory in which non-isotropic stringy moduli induce
a small but positive cosmological constant.Comment: 7 pages, LaTeX, references added and minor changes made, (v3) map
between deSitter and global cosmic brane solutions clarified, supersymmetry
breaking discussion improved and references adde
Phase-Dependent Spontaneous Spin Polarization and Bifurcation Delay in Coupled Two-Component Bose-Einstein Condensates
The spontaneous spin polarization and bifurcation delay in two-component
Bose-Einstein condensates coupled with laser or/and radio-frequency pulses are
investigated. We find that the bifurcation and the spontaneous spin
polarization are determined by both physical parameters and relative phase
between two condensates. Through bifurcations, the system enters into the
spontaneous spin polarization regime from the Rabi regime. We also find that
bifurcation delay appears when the parameter is swept through a static
bifurcation point. This bifurcation delay is responsible for metastability
leading to hysteresis.Comment: Improved version for cond-mat/021157
Patterns of quark mass matrices in a class of Calabi-Yau models
We study a class of superstring models compactified in the 3-generation
Calabi-Yau manifold of Tian and Yau. Our analysis includes the complete
-singlet sector, which has been recently evaluated using techniques of
spectral and exact sequences. We use the discrete symmetries of the models to
find flat directions of symmetry breaking that leave unbroken a low energy
matter parity and make all leptoquarks heavy while preserving light Higgs
fields. Then we classify the patterns of ordinary quark mass matrices and show
that (without invoking effects due to nonrenormalizable terms) only one
structure can accommodate the observed value of fermion masses and mixing
angles, with preference for a heavy {\it top} quark ( GeV for
). The model, which unifies perturbatively and predicts a
realistic structure of quark mass matrices with texture zeroes, is one of the
many possible string vacua. However, in contrast with what is often assumed in
the search for realistic unified scenarios, it is highly nonminimal near the
unification scale and the predicted mass matrices have no simple symmetry
properties.Comment: 30 (including Tables and Figures), UG-FT-38/9
Liquid-jet target for laser-plasma soft x-ray generation
We describe a new liquid-target system for low-debris laser-plasma soft x-ray sources. The system is based on a microscopic liquid jet and is experimentally evaluated for 0.7-1 keV proximity lithography and water-window x-ray microscopy applications. Compared to an existing liquid-droplet target, this target system has the same low debris emission, high x-ray photon flux, and narrow spectral bandwidth. The advantages of the liquid-jet target include improved x-ray flux stability, increased range of suitable target liquids, and elimination of the need for temporal synchronization, thereby allowing less complex laser systems to be used. (C) 1996 American Institute of Physics
Beyond the Fokker-Planck equation: Pathwise control of noisy bistable systems
We introduce a new method, allowing to describe slowly time-dependent
Langevin equations through the behaviour of individual paths. This approach
yields considerably more information than the computation of the probability
density. The main idea is to show that for sufficiently small noise intensity
and slow time dependence, the vast majority of paths remain in small space-time
sets, typically in the neighbourhood of potential wells. The size of these sets
often has a power-law dependence on the small parameters, with universal
exponents. The overall probability of exceptional paths is exponentially small,
with an exponent also showing power-law behaviour. The results cover time spans
up to the maximal Kramers time of the system. We apply our method to three
phenomena characteristic for bistable systems: stochastic resonance, dynamical
hysteresis and bifurcation delay, where it yields precise bounds on transition
probabilities, and the distribution of hysteresis areas and first-exit times.
We also discuss the effect of coloured noise.Comment: 37 pages, 11 figure
Sagittal Abdominal Diameter as a Screening Tool in Clinical Research: Cutoffs for Cardiometabolic Risk
Background. Waist girth and BMI are commonly used as markers of cardiometabolic risk. Accumulating data however suggest that sagittal abdominal diameter (SAD) or “abdominal height” may be a better marker of intra-abdominal adiposity and cardiometabolic risk. We aimed to identify cutoffs for SAD using a cardiometabolic risk score. Design. A population-based cross-sectional study. Methods. In 4032 subjects (1936 men and 2096 women) at age 60, different anthropometric variables (SAD, BMI, waist girth, and waist-to-hip ratio) were measured and cardiometabolic risk score calculated. ROC curves were used to assess cutoffs. Results. Among men SAD showed the strongest correlations to the majority of the individual risk factors; whereas in women SAD was equal to that of waist girth. In the whole sample, the area under the ROC curve was highest for SAD. The optimal SAD cutoff for an elevated cardiometabolic risk score in men was ∼22 cm (95%CI; 21.6 to 22.8) and in women ∼20 cm (95%CI; 19.4 to 20.8). These cutoffs were similar if the Framingham risk score was used. Conclusions. These cutoffs may be used in research and screening to identify “metabolically obese” men who would benefit from lifestyle and pharmacological interventions. These results need to be verified in younger age groups
Mixed-mode oscillations and interspike interval statistics in the stochastic FitzHugh-Nagumo model
We study the stochastic FitzHugh-Nagumo equations, modelling the dynamics of
neuronal action potentials, in parameter regimes characterised by mixed-mode
oscillations. The interspike time interval is related to the random number of
small-amplitude oscillations separating consecutive spikes. We prove that this
number has an asymptotically geometric distribution, whose parameter is related
to the principal eigenvalue of a substochastic Markov chain. We provide
rigorous bounds on this eigenvalue in the small-noise regime, and derive an
approximation of its dependence on the system's parameters for a large range of
noise intensities. This yields a precise description of the probability
distribution of observed mixed-mode patterns and interspike intervals.Comment: 36 page
A mathematical framework for critical transitions: normal forms, variance and applications
Critical transitions occur in a wide variety of applications including
mathematical biology, climate change, human physiology and economics. Therefore
it is highly desirable to find early-warning signs. We show that it is possible
to classify critical transitions by using bifurcation theory and normal forms
in the singular limit. Based on this elementary classification, we analyze
stochastic fluctuations and calculate scaling laws of the variance of
stochastic sample paths near critical transitions for fast subsystem
bifurcations up to codimension two. The theory is applied to several models:
the Stommel-Cessi box model for the thermohaline circulation from geoscience,
an epidemic-spreading model on an adaptive network, an activator-inhibitor
switch from systems biology, a predator-prey system from ecology and to the
Euler buckling problem from classical mechanics. For the Stommel-Cessi model we
compare different detrending techniques to calculate early-warning signs. In
the epidemics model we show that link densities could be better variables for
prediction than population densities. The activator-inhibitor switch
demonstrates effects in three time-scale systems and points out that excitable
cells and molecular units have information for subthreshold prediction. In the
predator-prey model explosive population growth near a codimension two
bifurcation is investigated and we show that early-warnings from normal forms
can be misleading in this context. In the biomechanical model we demonstrate
that early-warning signs for buckling depend crucially on the control strategy
near the instability which illustrates the effect of multiplicative noise.Comment: minor corrections to previous versio
A repulsive trap for two electrons in a magnetic field
We study numerically and analytically the dynamics of two classical electrons
with Coulomb interaction in a two dimensional antidot superlattice potential in
the presence of crossed electric and magnetic fields. It is found that near one
antidot the electron pair can be trapped for a long time and the escape rate
from such a trap is proportional to the square of a weak electric field. This
is qualitatively different from the case of noninteracting electrons which are
trapped forever by the antidot. For the pair propagation in the antidot
superlattice we found a broad parameter regime for which the pair is stable and
where two repulsive electrons propagate together on an enormously large
distance.Comment: revtex, 5 pages, 6 figure
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