The Behavior of Kasner Cosmologies with Induced Matter

We extend the induced matter model, previously applied to a variety of isotropic cases, to a generalization of Bianchi type-I anisotropic cosmologies. The induced matter model is a 5D Kaluza-Klein approach in which assumptions of compactness are relaxed for the fifth coordinate, leading to extra geometric terms. One interpretation of these extra terms is to identify them as an ``induced matter'' contribution to the stress-energy tensor. In similar spirit, we construct a five dimensional metric in which the spatial slices possess Bianchi type-I geometry. We find a set of solutions for the five dimensional Einstein equations, and determine the pressure and density of induced matter. We comment on the long-term dynamics of the model, showing that the assumption of positive density leads to the contraction over time of the fifth scale factor.Comment: 14 page

Solutions of Higher Dimensional Gauss-Bonnet FRW Cosmology

We examine the effect on cosmological evolution of adding a Gauss-Bonnet term to the standard Einstein-Hilbert action for a (1 + 3)+ d dimensional Friedman-Robertson-Walker (FRW) metric. By assuming that the additional dimensions compactify as a power law as the usual 3 spatial dimensions expand, we solve the resulting dynamical equations and find that the solution may be of either de Sitter or Kasner form depending upon whether the Gauss-Bonnet term or the Einstein term dominates.Comment: 10 pages, references added/corrected, accepted for publication in General Relativity and Gravitatio

A new experiment for the determination of the 18F(p,alpha) reaction rate at nova temperatures

The 18F(p,alpha) reaction was recognized as one of the most important for gamma ray astronomy in novae as it governs the early 511 keV emission. However, its rate remains largely uncertain at nova temperatures. A direct measurement of the cross section over the full range of nova energies is impossible because of its vanishing value at low energy and of the short 18F lifetime. Therefore, in order to better constrain this reaction rate, we have performed an indirect experiment taking advantage of the availability of a high purity and intense radioactive 18F beam at the Louvain La Neuve RIB facility. We present here the first results of the data analysis and discuss the consequences.Comment: Contribution to the Classical Novae Explosions conference, Sitges, Spain, 20-24 May 2002, 5 pages, 3 figure

Kasner and Mixmaster behavior in universes with equation of state w \ge 1

We consider cosmological models with a scalar field with equation of state $w\ge 1$ that contract towards a big crunch singularity, as in recent cyclic and ekpyrotic scenarios. We show that chaotic mixmaster oscillations due to anisotropy and curvature are suppressed, and the contraction is described by a homogeneous and isotropic Friedmann equation if $w>1$. We generalize the results to theories where the scalar field couples to p-forms and show that there exists a finite value of $w$, depending on the p-forms, such that chaotic oscillations are suppressed. We show that $Z_2$ orbifold compactification also contributes to suppressing chaotic behavior. In particular, chaos is avoided in contracting heterotic M-theory models if $w>1$ at the crunch.Comment: 25 pages, 2 figures, minor changes, references adde

Minimal information for studies of extracellular vesicles 2018 (MISEV2018):a position statement of the International Society for Extracellular Vesicles and update of the MISEV2014 guidelines

The last decade has seen a sharp increase in the number of scientific publications describing physiological and pathological functions of extracellular vesicles (EVs), a collective term covering various subtypes of cell-released, membranous structures, called exosomes, microvesicles, microparticles, ectosomes, oncosomes, apoptotic bodies, and many other names. However, specific issues arise when working with these entities, whose size and amount often make them difficult to obtain as relatively pure preparations, and to characterize properly. The International Society for Extracellular Vesicles (ISEV) proposed Minimal Information for Studies of Extracellular Vesicles (“MISEV”) guidelines for the field in 2014. We now update these “MISEV2014” guidelines based on evolution of the collective knowledge in the last four years. An important point to consider is that ascribing a specific function to EVs in general, or to subtypes of EVs, requires reporting of specific information beyond mere description of function in a crude, potentially contaminated, and heterogeneous preparation. For example, claims that exosomes are endowed with exquisite and specific activities remain difficult to support experimentally, given our still limited knowledge of their specific molecular machineries of biogenesis and release, as compared with other biophysically similar EVs. The MISEV2018 guidelines include tables and outlines of suggested protocols and steps to follow to document specific EV-associated functional activities. Finally, a checklist is provided with summaries of key points

Lawson criterion for ignition exceeded in an inertial fusion experiment

For more than half a century, researchers around the world have been engaged in attempts to achieve fusion ignition as a proof of principle of various fusion concepts. Following the Lawson criterion, an ignited plasma is one where the fusion heating power is high enough to overcome all the physical processes that cool the fusion plasma, creating a positive thermodynamic feedback loop with rapidly increasing temperature. In inertially confined fusion, ignition is a state where the fusion plasma can begin "burn propagation" into surrounding cold fuel, enabling the possibility of high energy gain. While "scientific breakeven" (i.e., unity target gain) has not yet been achieved (here target gain is 0.72, 1.37 MJ of fusion for 1.92 MJ of laser energy), this Letter reports the first controlled fusion experiment, using laser indirect drive, on the National Ignition Facility to produce capsule gain (here 5.8) and reach ignition by nine different formulations of the Lawson criterion

Chebyshev pseudospectral solution of the Stokes equations using finite element preconditioning

The Stokes equations are solved by a Chebyshev pseudospectral method on a rectangular domain. As the resulting system of algebraic equations is very difficult to factorize, a preconditioning is designed using a finite element technique. The FEM solver constitutes the masterpiece of a Richardson iteration process. Several finite elements are investigated: the 9-nodes Lagrangian element /b Q/2-/b Q/1, the /b Q/1-/b Q/0 element, and the /b Q/1-/b Q/1 element due to Brezzi and Pitkaranta. An eigenvalue analysis is carried out in order to pinpoint the characteristic features of each precondition. It is shown that the /b Q/2-/b Q/1 element yields the best convergence results. The power of this choice is demonstrated on theoretical solutions and on the regularized square cavity problem.Anglai