26,394 research outputs found
Starobinsky-like inflation from induced gravity
We derive a general criterion that defines all single-field models leading to
Starobinsky-like inflation and to universal predictions for the spectral index
and tensor-to-scalar ratio, which are in agreement with Planck data. Out of all
the theories that satisfy this criterion, we single out a special class of
models with the interesting property of retaining perturbative unitarity up to
the Planck scale. These models are based on induced gravity, with the Planck
mass determined by the vacuum expectation value of the inflaton.Comment: 13 pages; some references added; version published in PL
Anxiety and Learning in Dynamic and Static Clock Game Experiments
In clock games, agents receive differently-timed private signals when an asset value is above its fundamental. The price crashes to
the fundamental when K of N agents have decided to sell. If selling decisions are private, bubbles can be sustained because people
delay selling, after receiving signals, knowing that others will delay too. Our results replicate the main features of the one previous
experimental study of clock game (in two subject pools): Selling delays are shorter than predicted, but converge toward equilibrium
predictions over repeated trials. We also find that delays are shorter in a dynamic game in which selling decisions unfold over time,
compared to a static equivalent in which subjects precommit to selling decisions. A model of learning with growing anxiety after
signal arrival can reproduce the empirical observations of shorter-than-predicted delay, smaller delay after later signal arrival, and
shorter delays in dynamic games
Accurate and efficient algorithm for Bader charge integration
We propose an efficient, accurate method to integrate the basins of
attraction of a smooth function defined on a general discrete grid, and apply
it to the Bader charge partitioning for the electron charge density. Starting
with the evolution of trajectories in space following the gradient of charge
density, we derive an expression for the fraction of space neighboring each
grid point that flows to its neighbors. This serves as the basis to compute the
fraction of each grid volume that belongs to a basin (Bader volume), and as a
weight for the discrete integration of functions over the Bader volume.
Compared with other grid-based algorithms, our approach is robust, more
computationally efficient with linear computational effort, accurate, and has
quadratic convergence. Moreover, it is straightforward to extend to non-uniform
grids, such as from a mesh-refinement approach, and can be used to both
identify basins of attraction of fixed points and integrate functions over the
basins.Comment: 19 pages, 8 figure
A Recursive Method for Determining the One-Dimensional Submodules of Laurent-Ore Modules
We present a method for determining the one-dimensional submodules of a
Laurent-Ore module. The method is based on a correspondence between
hyperexponential solutions of associated systems and one-dimensional
submodules. The hyperexponential solutions are computed recursively by solving
a sequence of first-order ordinary matrix equations. As the recursion proceeds,
the matrix equations will have constant coefficients with respect to the
operators that have been considered.Comment: To appear in the Proceedings of ISSAC 200
Spectroscopic diagnostic for the mineralogy of large dust grains
We examine the thermal infrared spectra of large dust grains of different
chemical composition and mineralogy. Strong resonances in the optical
properties result in detectable spectral structure even when the grain is much
larger than the wavelength at which it radiates. We apply this to the thermal
infrared spectra of compact amorphous and crystalline silicates. The weak
resonances of amorphous silicates at 9.7 and 18 micron virtually disappear for
grains larger than about 10 micron. In contrast, the strong resonances of
crystalline silicates produce emission dips in the infrared spectra of large
grains; these emission dips are shifted in wavelength compared to the emission
peaks commonly seen in small crystalline silicate grains. We discuss the effect
of a fluffy or compact grain structure on the infrared emission spectra of
large grains, and apply our theory to the dust shell surrounding Vega.Comment: Submitted to A&A Letter
Hypothetical and Real Choice Differentially Activate Common Valuation Areas
Hypothetical reports of intended behavior are commonly used to draw conclusions about real choices. A fundamental question in decision neuroscience is whether the same type of valuation and choice computations are performed in hypothetical and real decisions. We investigated this question using functional magnetic resonance imaging while human subjects made real and hypothetical choices about purchases of consumer goods. We found that activity in common areas of the orbitofrontal cortex and the ventral striatum correlated with behavioral measures of the stimulus value of the goods in both types of decision. Furthermore, we found that activity in these regions was stronger in response to the stimulus value signals in the real choice condition. The findings suggest that the difference between real and hypothetical choice is primarily attributable to variations in the value computations of the medial orbitofrontal cortex and the ventral striatum, and not attributable to the use of different valuation systems, or to the computation of stronger stimulus value signals in the hypothetical condition
Association of PET-measured myocardial flow reserve with echocardiography-estimated pulmonary artery systolic pressure in patients with hypertrophic cardiomyopathy
BackgroundPulmonary hypertension (PH) is a known complication of HCM and is a strong predictor of mortality. We aim to investigate the relationship between microvascular dysfunction measured by quantitative PET and PH in HCM patients.MethodsEighty-nine symptomatic HCM patients were included in the study. Each patient underwent two 20-min 13N-NH3 dynamic PET scans for rest and stress conditions, respectively. A 2-tissue irreversible compartmental model was used to fit the segments time activity curves for estimating segmental and global myocardial blood flow (MBF) and myocardial flow reserve (MFR). Echocardiographic derived PASP was utilized to estimate PH.ResultsPatients were categorized into two groups across PASP: PH (PASP > 36 mmHg) and no-PH (PASP ≤ 36 mmHg). patients with PH had larger left atrium, ratio of higher inflow early diastole (E) and atrial contraction (A) waves, E/A, and ratio of inflow and peak early diastolic waves, E/e', significantly reduced global stress MBF (1.85 ± 0.52 vs. 2.13 ± 0.56 ml/min/g; p = 0.024) and MFR (2.21 ± 0.57 vs. 2.62 ± 0.75; p = 0.005), while the MBFs at rest between the two groups were similar. There were significant negative correlations between global stress MBF/MFR and PASP (stress MBF: r = -0.23, p = 0.03; MFR: r = -0.32, p = 0.002); for regional MBF and MFR measurements, the highest linear correlation coefficients were observed in the septal wall (stress MBF: r = -0.27, p = 0.01; MFR: r = -0.31, p = 0.003). Global MFR was identified to be independent predictor for PH in multivariate regression analysis.ConclusionEchocardiography-derived PASP is negatively correlated with global MFR measured by 13N-NH3 dynamic PET. Global MFR is suggested to be an index of PH in HCM patients.</div
The energy spectrum symmetry of Heisenberg model in Fock space
We prove strictly that one dimension spin 1/2 Heisenberg model has a symmetry
of energy spectrum between its subspace and the subspace of the Fock
space. Our proof is completed by introducing two general quantum operations.
One is a flip operation of spin direction and another is a mirror reflection of
spin sites.Comment: Revising version, 7 preprint pages, no figures; Published version
contains some revisions in Languag
The LHC di-photon Higgs signal predicted by little Higgs models
Little Higgs theory naturally predicts a light Higgs boson whose most
important discovery channel at the LHC is the di-photon signal . In this work we perform a comparative study for this signal in
some typical little Higgs models, namely the littlest Higgs model (LH), two
littlest Higgs models with T-parity (named LHT-I and LHT-II) and the simplest
little Higgs modes (SLH). We find that compared with the Standard Model
prediction, the di-photon signal rate is always suppressed and the suppression
extent can be quite different for different models. The suppression is mild
(\lsim 10%) in the LH model but can be quite severe () in other
three models. This means that discovering the light Higgs boson predicted by
the little Higgs theory through the di-photon channel at the LHC will be more
difficult than discovering the SM Higgs boson.Comment: 17 pages, 4 figures, 1 tabl
The lunar phases of dust grains orbiting Fomalhaut
Optical images of the nearby star Fomalhaut show a ring of dust orbiting the
central star. This dust is in many respects expected to be similar to the
zodiacal dust in the solar system. The ring displays a clear brightness
asymmetry, attributed to asymmetric scattering of the central starlight by the
circumstellar dust grains. Recent measurements show that the bright side of the
Fomalhaut ring is oriented away from us. This implies that the grains in this
system scatter most of the light in the backward direction, in sharp contrast
to the forward-scattering nature of the grains in the solar system. In this
letter, we show that grains considerably larger than those dominating the solar
system zodiacal dust cloud provide a natural explanation for the apparent
backward scattering behavior. In fact, we see the phases of the dust grains in
the same way as we can observe the phases of the Moon and other large solar
system bodies. We outline how the theory of the scattering behavior of
planetesimals can be used to explain the Fomalhaut dust properties. This
indicates that the Fomalhaut dust ring is dominated by very large grains. The
material orbiting Fomalhaut, which is at the transition between dust and
planetesimals, can, with respect to their optical behavior, best be described
as micro-asteroids.Comment: Accepted for publication in A&
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