1,133 research outputs found
On generation of metric perturbations during preheating
We consider the generation of the scalar mode of the metric perturbations
during preheating stage in a two field model with the potential . We discuss two possible
sources of such perturbations: a) due to the coupling between the perturbation
of the matter field and the background part of the matter field
, b) due to non-linear fluctuations in a condensate of
``particles'' of the field . Both types of the metric perturbations are
assumed to be small, and estimated using the linear theory of the metric
perturbations. We estimate analytically the upper limit of the amplitude of the
metric perturbations for all scales in the limit of so-called broad resonance,
and show that the large scale metric perturbations are very small, and taking
them into account does not influence the standard picture of the production of
the metric perturbations in inflationary scenario.Comment: This version is to be published in PRD, new references added and
typos correcte
Dynamics of a small neutrally buoyant sphere in a fluid and targeting in Hamiltonian systems
We show that, even in the most favorable case, the motion of a small
spherical tracer suspended in a fluid of the same density may differ from the
corresponding motion of an ideal passive particle. We demonstrate furthermore
how its dynamics may be applied to target trajectories in Hamiltonian systems.Comment: See home page http://lec.ugr.es/~julya
Molecular Mechanisms Leading from Periodontal Disease to Cancer
Periodontitis is prevalent in half of the adult population and raises critical health concerns as it has been recently associated with an increased risk of cancer. While information about the topic remains somewhat scarce, a deeper understanding of the underlying mechanistic pathways promoting neoplasia in periodontitis patients is of fundamental importance. This manuscript presents the literature as well as a panel of tables and figures on the molecular mechanisms of Porphyromonas gingivalis and Fusobacterium nucleatum, two main oral pathogens in periodontitis pathology, involved in instigating tumorigenesis. We also present evidence for potential links between the RANKL–RANK signaling axis as well as circulating cytokines/leukocytes and carcinogenesis. Due to the nonconclusive data associating periodontitis and cancer reported in the case and cohort studies, we examine clinical trials relevant to the topic and summarize their outcome
Heat Shock Proteins Alterations in Rheumatoid Arthritis
Rheumatoid arthritis (RA) is a chronic inflammatory and autoimmune disease characterized by the attack of the immune system on the body’s healthy joint lining and degeneration of articular structures. This disease involves an increased release of inflammatory mediators in the affected joint that sensitize sensory neurons and create a positive feedback loop to further enhance their release. Among these mediators, the cytokines and neuropeptides are responsible for the crippling pain and the persistent neurogenic inflammation associated with RA. More importantly, specific proteins released either centrally or peripherally have been shown to play opposing roles in the pathogenesis of this disease: an inflammatory role that mediates and increases the severity of inflammatory response and/or an anti-inflammatory and protective role that modulates the process of inflammation. In this review, we will shed light on the neuroimmune function of different members of the heat shock protein (HSPs) family and the complex manifold actions that they exert during the course of RA. Specifically, we will focus our discussion on the duality in the mechanism of action of Hsp27, Hsp60, Hsp70, and Hsp90
Fresh inflation: a warm inflationary model from a zero temperature initial state
A two-components mixture fluid which complies with the gamma law is
considered in the framework of inflation with finite temperature. The model is
developed for a quartic scalar potential without symmetry breaking. The
radiation energy density is assumed to be zero when inflation starts and
remains below the GUT temperature during the inflationary stage. Furthermore,
provides the necessary number of e-folds and sufficient radiation energy
density to GUT baryogenesis can take place near the minimum energetic
configuration.Comment: 11 pages, no figures, to be published in Phys. Rev.
Patterned Irradiation of YBa_2Cu_3O_(7-x) Thin Films
We present a new experiment on YBa_2Cu_3O_{7-x} (YBCO) thin films using
spatially resolved heavy ion irradiation. Structures consisting of a periodic
array of strong and weak pinning channels were created with the help of metal
masks. The channels formed an angle of +/-45 Deg with respect to the symmetry
axis of the photolithographically patterned structures. Investigations of the
anisotropic transport properties of these structures were performed. We found
striking resemblance to guided vortex motion as it was observed in YBCO single
crystals containing an array of unidirected twin boundaries. The use of two
additional test bridges allowed to determine in parallel the resistivities of
the irradiated and unirradiated parts as well as the respective current-voltage
characteristics. These measurements provided the input parameters for a
numerical simulation of the potential distribution of the Hall patterning. In
contrast to the unidirected twin boundaries in our experiment both strong and
weak pinning regions are spatially extended. The interfaces between
unirradiated and irradiated regions therefore form a Bose-glass contact. The
experimentally observed magnetic field dependence of the transverse voltage
vanishes faster than expected from the numerical simulation and we interpret
this as a hydrodynamical interaction between a Bose-glass phase and a vortex
liquid.Comment: 7 pages, 8 Eps figures included. Submitted to PR
Position statement on classification of basal cell carcinomas. Part 1: unsupervised clustering of experts as a way to build an operational classification of advanced basal cell carcinoma based on pattern recognition
Background No simple classification system has emerged for 'advanced basal cell carcinomas', and more generally for all difficult-to-treat BCCs (DTT-BCCs), due to the heterogeneity of situations, TNM inappropriateness to BCCs, and different approaches of different specialists. Objective To generate an operational classification, using the unconscious ability of experts to simplify the great heterogeneity of the clinical situations into a few relevant groups, which drive their treatment decisions. Method Non-supervised independent and blinded clustering of real clinical cases of DTT-BCCs was used. Fourteen international experts from different specialties independently partitioned 199 patient cases considered 'difficult to treat' into as many clusters they want (<= 10), choosing their own criteria for partitioning. Convergences and divergences between the individual partitions were analyzed using the similarity matrix, K-mean approach, and average silhouette method. Results There was a rather consensual clustering of cases, regardless of the specialty and nationality of the experts. Mathematical analysis showed that consensus between experts was best represented by a partition of DTT-BCCs into five clusters, easily recognized a posteriori as five clear-cut patterns of clinical situations. The concept of 'locally advanced' did not appear consistent between experts. Conclusion Although convergence between experts was not granted, this experiment shows that clinicians dealing with BCCs all tend to work by a similar pattern recognition based on the overall analysis of the situation. This study thus provides the first consensual classification of DTT-BCCs. This experimental approach using mathematical analysis of independent and blinded clustering of cases by experts can probably be applied to many other situations in dermatology and oncology
The acceleration of the universe and the physics behind it
Using a general classification of dark enegy models in four classes, we
discuss the complementarity of cosmological observations to tackle down the
physics beyond the acceleration of our universe. We discuss the tests
distinguishing the four classes and then focus on the dynamics of the
perturbations in the Newtonian regime. We also exhibit explicitely models that
have identical predictions for a subset of observations.Comment: 18 pages, 18 figure
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