5,476 research outputs found
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
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
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
Stated choice valuation of traffic related noise
This paper reports a novel application of the stated choice method to the valuation of road traffic noise. The innovative context used is that of choice between apartments with different levels of traffic noise, view, sunlight and cost with which respondents would be familiar. Stated choice models were developed on both perceived and objective measures of traffic noise, with the former statistically superior, and an extensive econometric analysis has been conducted to assess the nature and extent of householdersâ heterogeneity of preferences for noise. This found that random taste variation is appreciable but also identified considerable systematic variation in valuations according to income level, household composition and exposure to noise. Self-selectivity is apparent, whereby those with higher marginal values of noise tend to live in quieter apartments. Sign and reference effects were apparent in the relationship between ratings and objective noise measures, presumably reflecting the non-linear nature of the latter. However, there was no strong support for sign, size or reference effects in the valuations of perceived noise levels
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
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
The effect of classical noise on a quantum two-level system
We consider a quantum two-level system perturbed by classical noise. The
noise is implemented as a stationary diffusion process in the off-diagonal
matrix elements of the Hamiltonian, representing a transverse magnetic field.
We determine the invariant measure of the system and prove its uniqueness. In
the case of Ornstein-Uhlenbeck noise, we determine the speed of convergence to
the invariant measure. Finally, we determine an approximate one-dimensional
diffusion equation for the transition probabilities. The proofs use both
spectral-theoretic and probabilistic methods.Comment: 25 page
Green and Fire Resistant Nanocellulose/Hemicellulose/Clay Foams
Lightweight polymer foams from synthetic polymers are commonly used in a wide-spread spectrum of application fields. Their intrinsic flammability coupled with restrictions on flame retardant chemicals poses a severe threat to safety. Here, fire resistant foams comprising biobased components capable of replacing petroleum-based foams are investigated. Cellulose nanofibers are combined with 2D montmorillonite nanoplatelets and a native xyloglucan hemicellulose binder, using a water-based freeze casting approach. Due to the silicate nanoplatelets, these lightweight foams self-extinguish the flame during flammability tests. The limiting oxygen index is as high as 31.5% and in the same range as the best fire-retardant synthetic foams available. In cone calorimetry, the foams display extremely low combustion rates. Smoke release is near the detection limit of the instrument. In addition, the foams are withstanding the penetration of a flame torch focused on one side of the specimen (T on surface 800 °C) and structural integrity is maintained. At the same time, the unexposed side is insulated, as demonstrated by a through-thickness temperature drop of 680 °C cmâ1. The results represent a tremendous opportunity for the development of fire-safe foams combining excellent sustainability with multifunctional performance
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 âabdominal heightâ 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 âŒ22âcm (95%CI; 21.6 to 22.8) and in women âŒ20âcm (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 âmetabolically obeseâ men who would benefit from lifestyle and pharmacological interventions. These results need to be verified in younger age groups
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