8,917 research outputs found
Cosmological Constraints on Dissipative Models of Inflation
(Abridged) We study dissipative inflation in the regime where the dissipative
term takes a specific form, \Gamma=\Gamma(\phi), analyzing two models in the
weak and strong dissipative regimes with a SUSY breaking potential. After
developing intuition about the predictions from these models through analytic
approximations, we compute the predicted cosmological observables through full
numerical evolution of the equations of motion, relating the mass scale and
scale of dissipation to the characteristic amplitude and shape of the
primordial power spectrum. We then use Markov Chain Monte Carlo techniques to
constrain a subset of the models with cosmological data from the cosmic
microwave background (WMAP three-year data) and large scale structure (SDSS
Luminous Red Galaxy power spectrum). We find that the posterior distributions
of the dissipative parameters are highly non-Gaussian and their allowed ranges
agree well with the expectations obtained using analytic approximations. In the
weak regime, only the mass scale is tightly constrained; conversely, in the
strong regime, only the dissipative coefficient is tightly constrained. A lower
limit is seen on the inflation scale: a sub-Planckian inflaton is disfavoured
by the data. In both weak and strong regimes, we reconstruct the limits on the
primordial power spectrum and show that these models prefer a {\it red}
spectrum, with no significant running of the index. We calculate the reheat
temperature and show that the gravitino problem can be overcome with large
dissipation, which in turn leads to large levels of non-Gaussianity: if
dissipative inflation is to evade the gravitino problem, the predicted level of
non-Gaussianity might be seen by the Planck satellite.Comment: 14 pages, 9 figures, Accepted by JCAP without text changes,
References adde
Analysis of noise-induced transitions from regular to chaotic oscillations in the Chen system
The stochastically perturbed Chen system is studied within the parameter region which permits both regular and chaotic oscillations. As noise intensity increases and passes some threshold value, noise-induced hopping between close portions of the stochastic cycle can be observed. Through these transitions, the stochastic cycle is deformed to be a stochastic attractor that looks like chaotic. In this paper for investigation of these transitions, a constructive method based on the stochastic sensitivity function technique with confidence ellipses is suggested and discussed in detail. Analyzing a mutual arrangement of these ellipses, we estimate the threshold noise intensity corresponding to chaotization of the stochastic attractor. Capabilities of this geometric method for detailed analysis of the noise-induced hopping which generates chaos are demonstrated on the stochastic Chen system. © 2012 American Institute of Physics
Theory of temperature dependence of the Fermi surface-induced splitting of the alloy diffuse-scattering intensity peak
The explanation is presented for the temperature dependence of the fourfold
intensity peak splitting found recently in diffuse scattering from the
disordered Cu3Au alloy. The wavevector and temperature dependence of the
self-energy is identified as the origin of the observed behaviour. Two
approaches for the calculation of the self-energy, the high-temperature
expansion and the alpha-expansion, are proposed. Applied to the Cu3Au alloy,
both methods predict the increase of the splitting with temperature, in
agreement with the experimental results.Comment: 4 pages, 3 EPS figures, RevTeX, submitted to J. Phys. Condens. Matter
(Letter to the Editor
An optical view of the filament region of Abell 85
We compare the distribution of optically and Halpha (Ha) selected galaxies in
the Southern half of the nearby Abell 85 (A85) cluster with the recently
discovered X-ray filament (XRF). We search for galaxies where star formation
(SF) may have been triggered by interactions with intracluster gas or tidal
pressure due to the cluster potential when entering the cluster. Our analysis
is based on images obtained with CFHT MegaPrime/MegaCam (1x1 deg2 field) in
four bands (ugri) and ESO 2.2mWFI (38'x36' field) in a narrow band filter
corresponding to the redshifted Halpha (Ha) line and in a broad R-band filter.
The LFs are estimated by statistically subtracting a reference field.
Background contamination is minimized by cutting out galaxies redder than the
observed red sequence in the g-i vs. i colour-magnitude diagram. The galaxy
distribution shows a significantly flattened cluster, whose principal axis is
slightly offset from the XRF. The analysis of the broad band LFs shows that the
filament region is well populated. The filament is also independently detected
as a gravitationally bound structure by the Serna & Gerbal hierarchical method.
101 galaxies are detected in Ha, among which 23 have spectroscopic redshifts in
the cluster, 2 have spectroscopic redshifts higher than the cluster and 58 have
photometric redshifts that tend to indicate that they are background
objects.The 23 galaxies with spectroscopic redshifts in the cluster are mostly
concentrated in the South part of the cluster and along the filament. We find a
number of galaxies showing evidence for SF in the XRF, and all our results are
consistent with the previous hypothesis that the XRF in A85 is a
gravitationally bound structure made of groups falling on to the main cluster.Comment: Accepted in A&A. 39 pages, 107 figures. Full resolution images
available at ftp://ftp.iap.fr/pub/from_users/gam/A85
Item-specific proactive interference in olfactory working memory.
We examine item-specific olfactory proactive interference (PI) effects and undertake comparisons with verbal and non-verbal visual stimuli. Using a sequential recent-probes task, we show no evidence for PI with hard-to-name odours (Experiment 1). However, verbalisable odours do exhibit PI effects (Experiment 2). These findings occur despite above chance performance and similar serial position functions across both tasks. Experiments 3 and 4 apply words and faces, respectively, to our modified procedure, and show that methodological differences cannot explain the null finding in Experiment 1. The extent to which odours exhibit analogous PI effects to that of other modalities is, we argue, contingent on the characteristics of the odours employed
Neural Network Diagnosis of Malignant Melanoma from Color Images
Malignant melanoma is the deadliest form of all skin cancers. Approximately 32,000 new cases of malignant melanoma were diagnosed in 1991, with approximately 80 percent of patients expected to survive five years [1]. Fortunately, if detected early, even malignant melanoma may be treated successfully. Thus, in recent years, there has been a rising interest in the automated detection and diagnosis of skin cancer, particularly malignant melanoma [2]. In this paper, we present a novel neural network approach for the automated separation of melanoma from three other benign categories of tumors which exhibit melanoma-like characteristics. Our approach is based on devising new and discriminant features which are used as inputs to an artificial neural network for classification of tumor images as malignant or benign. We have obtained promising results using our method on real skin cancer images
Mobility gap in intermediate valent TmSe
The infrared optical conductivity of intermediate valence compound TmSe
reveals clear signatures for hybridization of light - and heavy f-electronic
states with m* ~ 1.6 m_0 and m* ~ 16 m_0, respectively. At moderate and high
temperatures, the metal-like character of the heavy carriers dominate the
low-frequency response while at low temperatures (T_N < T < 100 K) a gap-like
feature is observed in the conductivity spectra below 10 meV which is assigned
to be a mobility gap due to localization of electrons on local Kondo singlets,
rather than a hybridization gap in the density of states
Neutrino Dark Energy and Moduli Stabilization in a BPS Braneworld Scenario
A braneworld model for neutrino Dark Energy (DE) is presented. We consider a
five dimensional two-branes set up with a bulk scalar field motivated by
supergravity. Its low-energy effective theory is derived with a moduli space
approximation (MSA). The position of the two branes are parametrized by two
scalar degrees of freedom (moduli). After detuning the brane tensions a
classical potential for the moduli is generated. This potential is unstable for
dS branes and we suggest to consider as a stabilizing contribution the Casimir
energy of bulk fields. In particular we add a massive spinor (neutrino) field
in the bulk and then evaluate the Casimir contribution of the bulk neutrino
with the help of zeta function regularization techniques. We construct an
explicit form of the 4D neutrino mass as function of the two moduli. To recover
the correct DE scale for the moduli potential the usual cosmological constant
fine-tuning is necessary, but, once accepted, this model suggests a stronger
connection between DE and neutrino physics.Comment: 26 pages, 1 EPS figur
Incorporating parent, former patient, and clinician perspectives in the design of a national UK double-cluster, randomised controlled trial addressing uncertainties in preterm nutrition
Background: Comparative effectiveness randomised controlled trials are powerful tools to resolve uncertainties in existing treatments and care processes. We sought parent and patient perspectives on the design of a planned national, double-cluster randomised controlled trial (COLLABORATE) to resolve two longstanding uncertainties in preterm nutrition. Methods: We used qualitative focus groups and interviews with parents, former patients and clinicians. We followed the Consolidated Criteria for Reporting Qualitative Research checklist and conducted framework analysis, a specific methodology within thematic analysis. Results: We identified support for the trial’s methodology and vision, and elicited themes illustrating parents’ emotional needs in relation to clinical research. These were: relieving the pressure on mothers to breastfeed; opt-out consent as reducing parent stress; the desire for research to be a partnership between clinicians, parents and researchers; the value of presenting trial information in a collaborative tone; and in a format that allows assimilation by parents at their own pace. We identified anxiety and cognitive dissonance among some clinicians in which they recognised the uncertainties that justify the trial but felt unable to participate because of their strongly held views. Conclusions: The early involvement of parents and former patients identified the centrality of parents’ emotional needs in the design of comparative effectiveness research. These insights have been incorporated into trial enrolment processes and information provided to participants. Specific outputs were a two-sided leaflet providing very brief as well as more detailed information, and use of language that parents perceive as inclusive and participatory. Further work is warranted to support clinicians to address personal biases that inhibit trial participation
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