106,025 research outputs found
Turbulence Time Series Data Hole Filling using Karhunen-Loeve and ARIMA methods
Measurements of optical turbulence time series data using unattended
instruments over long time intervals inevitably lead to data drop-outs or
degraded signals. We present a comparison of methods using both Principal
Component Analysis, which is also known as the Karhunen--Loeve decomposition,
and ARIMA that seek to correct for these event-induced and mechanically-induced
signal drop-outs and degradations. We report on the quality of the correction
by examining the Intrinsic Mode Functions generated by Empirical Mode
Decomposition. The data studied are optical turbulence parameter time series
from a commercial long path length optical anemometer/scintillometer, measured
over several hundred metres in outdoor environments.Comment: 8 pages, 9 figures, submitted to ICOLAD 2007, City University,
London, U
Combustion: Structural interaction in a viscoelastic material
The effect of interaction between combustion processes and structural deformation of solid propellant was considered. The combustion analysis was performed on the basis of deformed crack geometry, which was determined from the structural analysis. On the other hand, input data for the structural analysis, such as pressure distribution along the crack boundary and ablation velocity of the crack, were determined from the combustion analysis. The interaction analysis was conducted by combining two computer codes, a combustion analysis code and a general purpose finite element structural analysis code
Allergic fetal priming leads to developmental, behavioral and neurobiological changes in mice.
The state of the mother's immune system during pregnancy has an important role in fetal development and disruptions in the balance of this system are associated with a range of neurologic, neuropsychiatric and neurodevelopmental disorders. Epidemiological and clinical reports reveal various clues that suggest a possible association between developmental neuropsychiatric disorders and family history of immune system dysfunction. Over the past three decades, analogous increases have been reported in both the incidence of neurodevelopmental disorders and immune-related disorders, particularly allergy and asthma, raising the question of whether allergic asthma and characteristics of various neurodevelopmental disorders share common causal links. We used a mouse model of maternal allergic asthma to test this novel hypothesis that early fetal priming with an allergenic exposure during gestation produces behavioral deficits in offspring. Mothers were primed with an exposure to ovalbumin (OVA) before pregnancy, then exposed to either aerosolized OVA or vehicle during gestation. Both male and female mice born to mothers exposed to aerosolized OVA during gestation exhibited altered developmental trajectories in weight and length, decreased sociability and increased marble-burying behavior. Moreover, offspring of OVA-exposed mothers were observed to have increased serotonin transporter protein levels in the cortex. These data demonstrate that behavioral and neurobiological effects can be elicited following early fetal priming with maternal allergic asthma and provide support that maternal allergic asthma may, in some cases, be a contributing factor to neurodevelopmental disorders
Reptile scale paradigm: Evo-Devo, pattern formation and regeneration
The purpose of this perspective is to highlight the merit of the reptile integument as an experimental model. Reptiles represent the first amniotes. From stem reptiles, extant reptiles, birds and mammals have evolved. Mammal hairs and feathers evolved from Therapsid and Sauropsid reptiles, respectively. The early reptilian integument had to adapt to the challenges of terrestrial life, developing a multi-layered stratum corneum capable of barrier function and ultraviolet protection. For better mechanical protection, diverse reptilian scale types have evolved. The evolution of endothermy has driven the convergent evolution of hair and feather follicles: both form multiple localized growth units with stem cells and transient amplifying cells protected in the proximal follicle. This topological arrangement allows them to elongate, molt and regenerate without structural constraints. Another unique feature of reptile skin is the exquisite arrangement of scales and pigment patterns, making them testable models for mechanisms of pattern formation. Since they face the constant threat of damage on land, different strategies were developed to accommodate skin homeostasis and regeneration. Temporally, they can be under continuous renewal or sloughing cycles. Spatially, they can be diffuse or form discrete localized growth units (follicles). To understand how gene regulatory networks evolved to produce increasingly complex ectodermal organs, we have to study how prototypic scale-forming pathways in reptiles are modulated to produce appendage novelties. Despite the fact that there are numerous studies of reptile scales, molecular analyses have lagged behind. Here, we underscore how further development of this novel experimental model will be valuable in filling the gaps of our understanding of the Evo-Devo of amniote integuments
The weakly perturbed Schwarzschild lens in the strong deflection limit
We investigate the strong deflection limit of gravitational lensing by a
Schwarzschild black hole embedded in an external gravitational field. The study
of this model, analogous to the Chang & Refsdal lens in the weak deflection
limit, is important to evaluate the gravitational perturbations on the
relativistic images that appear in proximity of supermassive black holes hosted
in galactic centers. By a simple dimensional argument, we prove that the tidal
effect on the light ray propagation mainly occurs in the weak field region far
away from the black hole and that the external perturbation can be treated as a
weak field quadrupole term. We provide a description of relativistic critical
curves and caustics and discuss the inversion of the lens mapping. Relativistic
caustics are shifted and acquire a finite diamond shape. Sources inside the
caustics produce four sequences of relativistic images. On the other hand,
retro-lensing caustics are only shifted while remaining point-like to the
lowest order.Comment: 12 pages, 1 figure
Exploring Dark Matter with Milky Way substructure
The unambiguous detection of Galactic dark matter annihilation would unravel
one of the most outstanding puzzles in particle physics and cosmology. Recent
observations have motivated models in which the annihilation rate is boosted by
the Sommerfeld effect, a non-perturbative enhancement arising from a long range
attractive force. Here we apply the Sommerfeld correction to Via Lactea II, a
high resolution N-body simulation of a Milky-Way-size galaxy, to investigate
the phase-space structure of the Galactic halo. We show that the annihilation
luminosity from kinematically cold substructure can be enhanced by orders of
magnitude relative to previous calculations, leading to the prediction of
gamma-ray fluxes from up to hundreds of dark clumps that should be detectable
by the Fermi satellite.Comment: 23 pages, 9 figures (includes Supporting Online Material), accepted
for publication in Science, v2: added reference, fixed typo
- …