118 research outputs found
Non-Gaussianities in Multifield Inflation: Superhorizon Evolution, Adiabaticity, and the Fate of fnl
We explore the superhorizon generation of large fnl of the local form in two
field inflation. We calculate the two- and three-point observables in a general
class of potentials which allow for an analytic treatment using the delta N
formalism. Motivated by the conservation of the curvature perturbation outside
the horizon in the adiabatic mode and also by the observed adiabaticity of the
power spectrum, we follow the evolution of fnl^{local} until it is driven into
the adibatic solution by passing through a phase of effectively single field
inflation. We find that although large fnl^{local} may be generated during
inflation, such non-gaussianities are transitory and will be exponentially
damped as the cosmological fluctuations approach adiabaticity.Comment: v3: Typos corrected, minor changes to match published version,
references added, 18 pages, 1 figure. v2: Changed sign of fnl to match WMAP
convention, minor changes throughout, references added, 18 pages, 1 figure.
v1: 17 pages, 1 figur
Growth abnormalities of fetuses and infants
The objective of this special issue is to address recent research trends and developments about the advancements of image processing and vision in healthcare. A substantial number of papers were submitted, and after a thorough peer review process, some of these were selected to be included in this special issue. Growth abnormalities (either growth restriction or large for gestational age) during perinatal and postnatal life are a hot topic issue, since they are often linked to alteration of uterine environment caused by placental insufficiency, maternal metabolic syndrome, and in general under- or overnutrition of the fetus. These fetal abnormalities account for the leading causes of perinatal morbidity and mortality. Moreover, under the hypothesis of developmental origin of adult diseases, they bear consequences in later life, programming the infant physiology for a higher risk of noncommunicable diseases, cardiovascular adult diseases, and neurodevelopment delay. Low birth weight, caused either by preterm birth and/or by intrauterine growth restriction, is recently known to be associated with increased rates of cardiovascular disease and noninsulin dependent diabetes in adult life. The “developmental origins of adult disease” hypothesis, often called “the Barker hypothesis,” proposes that these diseases originate through adaptations of the fetus when it is undernourished. These adaptations may be cardiovascular, metabolic, or endocrine and they may permanently change the structure and function of the body, increasing coronary heart disease risk factors, such as hypertension, type 2 diabetes mellitus, insulin resistance, and hyperlipidaemia. This hypothesis originally involved from observation by Barker and colleagues that the regions in England with the highest rates of infant mortality in the early 20th century also had the highest rates of mortality from coronary heart disease decades later. As the most commonly registered cause of infant death at the start of 20th century was low birth weight, these observations led to the hypothesis that low birth weight babies who survived infancy and childhood might be at increased risk of coronary heart disease in later life. There is an increased evidence of the link between intrauterine and perinatal alterations and adult diseases. Although the main focus so far has been the timing of delivery and follow-up, the study of the pathophysiology and of possible recovery is of paramount importance and needs the contributions of physicians from several fields, biologists, bioinformaticians, and engineers
The Type Ia Supernova Rate in Redshift 0.5--0.9 Galaxy Clusters
Supernova (SN) rates are potentially powerful diagnostics of metal enrichment
and SN physics, particularly in galaxy clusters with their deep,
metal-retaining potentials and relatively simple star-formation histories. We
have carried out a survey for supernovae (SNe) in galaxy clusters, at a
redshift range 0.5<z<0.9, using the Advanced Camera for Surveys (ACS) on the
Hubble Space Telescope. We reimaged a sample of 15 clusters that were
previously imaged by ACS, thus obtaining two to three epochs per cluster, in
which we discovered five likely cluster SNe, six possible cluster SNe Ia, two
hostless SN candidates, and several background and foreground events. Keck
spectra of the host galaxies were obtained to establish cluster membership. We
conducted detailed efficiency simulations, and measured the stellar
luminosities of the clusters using Subaru images. We derive a cluster SN rate
of 0.35 SNuB +0.17/-0.12 (statistical) \pm0.13 (classification) \pm0.01
(systematic) [where SNuB = SNe (100 yr 10^10 L_B_sun)^-1] and 0.112 SNuM
+0.055/-0.039 (statistical) \pm0.042 (classification) \pm0.005 (systematic)
[where SNuM = SNe (100 yr 10^10 M_sun)^-1]. As in previous measurements of
cluster SN rates, the uncertainties are dominated by small-number statistics.
The SN rate in this redshift bin is consistent with the SN rate in clusters at
lower redshifts (to within the uncertainties), and shows that there is, at
most, only a slight increase of cluster SN rate with increasing redshift. The
low and fairly constant SN Ia rate out to z~1 implies that the bulk of the iron
mass in clusters was already in place by z~1. The recently observed doubling of
iron abundances in the intracluster medium between z=1 and 0, if real, is
likely the result of redistribution of existing iron, rather than new
production of iron.Comment: Accepted to ApJ. Full resolution version available at
http://kicp.uchicago.edu/~kerens/HSTclusterSNe
Accidental Inflation in String Theory
We show that inflation in type IIB string theory driven by the volume modulus
can be realized in the context of the racetrack-based Kallosh-Linde model (KL)
of moduli stabilization. Inflation here arises through the volume modulus
slow-rolling down from a flat hill-top or inflection point of the scalar
potential. This situation can be quite generic in the landscape, where by
uplifting one of the two adjacent minima one can turn the barrier either to a
flat saddle point or to an inflection point supporting eternal inflation. The
resulting spectral index is tunable in the range of 0.93 < n_s < 1, and there
is only negligible production of primordial gravitational waves r < 10^{-6}.
The flatness of the potential in this scenario requires fine-tuning, which may
be justified taking into account the exponential reward by volume factors
preferring the regions of the universe with the maximal amount of slow-roll
inflation. This consideration leads to a tentative prediction of the spectral
index or depending on whether the
potential has a symmetry phi -> - phi or not.Comment: 15 pages, 6 figures, LaTeX, uses RevTex
Neuroinflammation, Mast Cells, and Glia: Dangerous Liaisons
The perspective of neuroinflammation as an epiphenomenon following neuron damage is being replaced by the awareness of glia and their importance in neural functions and disorders. Systemic inflammation generates signals that communicate with the brain and leads to changes in metabolism and behavior, with microglia assuming a pro-inflammatory phenotype. Identification of potential peripheral-to-central cellular links is thus a critical step in designing effective therapeutics. Mast cells may fulfill such a role. These resident immune cells are found close to and within peripheral nerves and in brain parenchyma/meninges, where they exercise a key role in orchestrating the inflammatory process from initiation through chronic activation. Mast cells and glia engage in crosstalk that contributes to accelerate disease progression; such interactions become exaggerated with aging and increased cell sensitivity to stress. Emerging evidence for oligodendrocytes, independent of myelin and support of axonal integrity, points to their having strong immune functions, innate immune receptor expression, and production/response to chemokines and cytokines that modulate immune responses in the central nervous system while engaging in crosstalk with microglia and astrocytes. In this review, we summarize the findings related to our understanding of the biology and cellular signaling mechanisms of neuroinflammation, with emphasis on mast cell-glia interactions
Artificial intelligence for photovoltaic systems
Photovoltaic systems have gained an extraordinary popularity in the energy generation industry. Despite the benefits, photovoltaic systems still suffer from four main drawbacks, which include low conversion efficiency, intermittent power supply, high fabrication costs and the nonlinearity of the PV system output power. To overcome these issues, various optimization and control techniques have been proposed. However, many authors relied on classical techniques, which were based on intuitive, numerical or analytical methods. More efficient optimization strategies would enhance the performance of the PV systems and decrease the cost of the energy generated. In this chapter, we provide an overview of how Artificial Intelligence (AI) techniques can provide value to photovoltaic systems. Particular attention is devoted to three main areas: (1) Forecasting and modelling of meteorological data, (2) Basic modelling of solar cells and (3) Sizing of photovoltaic systems. This chapter will aim to provide a comparison between conventional techniques and the added benefits of using machine learning methods
A SPITZER -SELECTED GALAXY CLUSTER AT z = 1.62
We report the discovery of a galaxy cluster at z = 1.62 located in the Spitzer Wide-Area Infrared Extragalactic survey XMM-LSS field. This structure was selected solely as an overdensity of galaxies with red Spitzer/Infrared Array Camera colors, satisfying ([3.6] - [4.5])AB> - 0.1 mag. Photometric redshifts derived from the Subaru XMM Deep Survey (BViz bands), the UKIRT Infrared Deep Survey-Ultra-Deep Survey (UKIDSS-UDS, JK bands), and from the Spitzer Public UDS survey (3.6-8.0 μm) show that this cluster corresponds to a surface density of galaxies at z ≈ 1.6 that is >20σ above the mean at this redshift. We obtained optical spectroscopic observations of galaxies in the cluster region using IMACS on the Magellan telescope. We measured redshifts for seven galaxies in the range z = 1.62-1.63 within 2.8 arcmin (1.7 mag. The photometric-redshift probability distributions for the red galaxies are strongly peaked at z = 1.62, coincident with the spectroscopically confirmed galaxies. The rest-frame (U - B) color and scatter of galaxies on the red sequence are consistent with a mean luminosity-weighted age of 1.2 ± 0.1 Gyr, yielding a formation redshift \overline{z_f}=2.35 \, \pm \, 0.10, and corresponding to the last significant star formation period in these galaxies.
This work is based in part on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under NASA contract 1407. This paper also includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile. This work is based in part on data collected at Subaru Telescope, which is operated by the National Astronomical Observatory of Japan
Three New Eclipsing White-dwarf - M-dwarf Binaries Discovered in a Search for Transiting Planets Around M-dwarfs
We present three new eclipsing white-dwarf / M-dwarf binary systems
discovered during a search for transiting planets around M-dwarfs. Unlike most
known eclipsing systems of this type, the optical and infrared emission is
dominated by the M-dwarf components, and the systems have optical colors and
discovery light curves consistent with being Jupiter-radius transiting planets
around early M-dwarfs. We detail the PTF/M-dwarf transiting planet survey, part
of the Palomar Transient Factory (PTF). We present a Graphics Processing Unit
(GPU)-based box-least-squares search for transits that runs approximately 8X
faster than similar algorithms implemented on general purpose systems. For the
discovered systems, we decompose low-resolution spectra of the systems into
white-dwarf and M-dwarf components, and use radial velocity measurements and
cooling models to estimate masses and radii for the white dwarfs. The systems
are compact, with periods between 0.35 and 0.45 days and semimajor axes of
approximately 2 solar radii (0.01 AU). We use the Robo-AO laser guide star
adaptive optics system to tentatively identify one of the objects as a triple
system. We also use high-cadence photometry to put an upper limit on the white
dwarf radius of 0.025 solar radii (95% confidence) in one of the systems. We
estimate that 0.08% (90% confidence) of M-dwarfs are in these short-period,
post-common-envelope white-dwarf / M-dwarf binaries where the optical light is
dominated by the M-dwarf. Similar eclipsing binary systems can have arbitrarily
small eclipse depths in red bands and generate plausible small-planet-transit
light curves. As such, these systems are a source of false positives for
M-dwarf transiting planet searches. We present several ways to rapidly
distinguish these binaries from transiting planet systems.Comment: 14 pages, 14 figures, submitted to Ap
ANDES, the high resolution spectrograph for the ELT: science case, baseline design and path to construction
Free vibration analysis and design optimization of SMA/Graphite/Epoxy composite shells in thermal environments
Composite shells, which are being widely used in engineering applications, are often under thermal loads. Thermal loads usually bring thermal stresses in the structure which can significantly affect its static and dynamic behaviors. One of the possible solutions for this matter is embedding Shape Memory Alloy (SMA) wires into the structure. In the present study, thermal buckling and free vibration of laminated composite cylindrical shells reinforced by SMA wires are analyzed. Brinson model is implemented to predict the thermo-mechanical behavior of SMA wires. The natural frequencies and buckling temperatures of the structure are obtained by employing Generalized Differential Quadrature (GDQ) method. GDQ is a powerful numerical approach which can solve partial differential equations. A comparative study is carried out to show the accuracy and efficiency of the applied numerical method for both free vibration and buckling analysis of composite shells in thermal environment. A parametric study is also provided to indicate the effects of like SMA volume fraction, dependency of material properties on temperature, lay-up orientation, and pre-strain of SMA wires on the natural frequency and buckling of Shape Memory Alloy Hybrid Composite (SMAHC) cylindrical shells. Results represent the fact that SMAs can play a significant role in thermal vibration of composite shells. The second goal of present work is optimization of SMAHC cylindrical shells in order to maximize the fundamental frequency parameter at a certain temperature. To this end, an eight-layer composite shell with four SMA-reinforced layers is considered for optimization. The primary optimization variables are the values of SMA angles in the four layers. Since the optimization process is complicated and time consuming, Genetic Algorithm (GA) is performed to obtain the orientations of SMA layers to maximize the first natural frequency of structure. The optimization results show that using an optimum stacking sequence for SMAHC shells can increase the fundamental frequency of the structure by a considerable amount
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