Nucleosynthesis in Advective Accretion Disks Around Galactic and Extra-Galactic Black Holes

We compute the nucleosynthesis of materials inside advective disks around black holes. We show that composition of incoming matter can change significantly depending on the accretion rate and accretion disks. These works are improvements on the earlier works in thick accretion disks of Chakrabarti, Jin & Arnett (1987) in presence of advection in the flow.Comment: Latex pages including figures. Kluwer Style files included. Appearing in `Observational Evidence for Black Holes in the Universe', ed. Sandip K. Chakrabarti, Kluwer Academic Publishers (DORDRECHT: Holland

Microflares in accretion disks

We have investigated the phenomenon of explosive chromospheric evaporation from an accretion disk as a mechanism for fast variability in accreting sources such as low mass X-ray binaries and active galactic nuclei. This has been done in the context of advection dominated accretion flows, allowing both high and low states to be considered. This mechanism can in principle produce sub-millisecond timescales in binaries and sub-minute timescales in active galaxies. However, even considering the possibility that large numbers of these microflares may be present simultaneously, the power emitted from these microflares probably amounts to only a small fraction of the total X-ray luminosity.Comment: 5 pages, 1 figure, uses older A&A class file; accepted for publication in A&

The effects of discreteness of galactic cosmic rays sources

Most studies of GeV Galactic Cosmic Rays (GCR) nuclei assume a steady state/continuous distribution for the sources of cosmic rays, but this distribution is actually discrete in time and in space. The current progress in our understanding of cosmic ray physics (acceleration, propagation), the required consistency in explaining several GCRs manifestation (nuclei, $\gamma$,...) as well as the precision of present and future space missions (e.g. INTEGRAL, AMS, AGILE, GLAST) point towards the necessity to go beyond this approximation. A steady state semi-analytical model that describes well many nuclei data has been developed in the past years based on this approximation, as well as others. We wish to extend it to a time dependent version, including discrete sources. As a first step, the validity of several approximations of the model we use are checked to validate the approach: i) the effect of the radial variation of the interstellar gas density is inspected and ii) the effect of a specific modeling for the galactic wind (linear vs constant) is discussed. In a second step, the approximation of using continuous sources in space is considered. This is completed by a study of time discreteness through the time-dependent version of the propagation equation. A new analytical solution of this equation for instantaneous point-like sources, including the effect of escape, galactic wind and spallation, is presented. Application of time and space discretness to definite propagation conditions and realistic distributions of sources will be presented in a future paper.Comment: final version, 8 figures, accepted in ApJ. A misprint in fig 8 labels has been correcte

An elastic second skin

We report the synthesis and application of an elastic, wearable crosslinked polymer layer (XPL) that mimics the properties of normal, youthful skin. XPL is made of a tunable polysiloxane-based material that can be engineered with specific elasticity, contractility, adhesion, tensile strength and occlusivity. XPL can be topically applied, rapidly curing at the skin interface without the need for heat- or light-mediated activation. In a pilot human study, we examined the performance of a prototype XPL that has a tensile modulus matching normal skin responses at low strain (<40%), and that withstands elongations exceeding 250%, elastically recoiling with minimal strain-energy loss on repeated deformation. The application of XPL to the herniated lower eyelid fat pads of 12 subjects resulted in an average 2-grade decrease in herniation appearance in a 5-point severity scale. The XPL platform may offer advanced solutions to compromised skin barrier function, pharmaceutical delivery and wound dressings

Membranes by the Numbers

Many of the most important processes in cells take place on and across membranes. With the rise of an impressive array of powerful quantitative methods for characterizing these membranes, it is an opportune time to reflect on the structure and function of membranes from the point of view of biological numeracy. To that end, in this article, I review the quantitative parameters that characterize the mechanical, electrical and transport properties of membranes and carry out a number of corresponding order of magnitude estimates that help us understand the values of those parameters.Comment: 27 pages, 12 figure

The spin dependence of high energy proton scattering

Motivated by the need for an absolute polarimeter to determine the beam polarization for the forthcoming RHIC spin program, we study the spin dependence of the proton-proton elastic scattering amplitudes at high energy and small momentum transfer.We examine experimental evidence for the existence of an asymptotic part of the helicity-flip amplitude phi_5 which is not negligible relative to the largely imaginary average non-flip amplitude phi_+. We discuss theoretical estimates of r_5, essentially the ratio of phi_5 to phi_+, based upon extrapolation of low and medium energy Regge phenomenological results to high energies, models based on a hybrid of perturbative QCD and non-relativistic quark models, and models based on eikonalization techniques. We also apply the model-independent methods of analyticity and unitarity.The preponderence of evidence at available energy indicates that r_5 is small, probably less than 10%. The best available experimental limit comes from Fermilab E704:those data indicate that |r_5|<15%. These bounds are important because rigorous methods allow much larger values. In contradiction to a widely-held prejudice that r_5 decreases with energy, general principles allow it to grow as fast as ln(s) asymptotically, and some models show an even faster growth in the RHIC range. One needs a more precise measurement of r_5 or to bound it to be smaller than 5% in order to use the classical Coulomb-nuclear interference technique for RHIC polarimetry. As part of this study, we demonstrate the surprising result that proton-proton elastic scattering is self-analysing, in the sense that all the helicity amplitudes can, in principle, be determined experimentally at small momentum transfer without a knowledge of the magnitude of the beam and target polarization

<SUP>3</SUP>He-rich solar flares

A new subgroup of3He rich solar flares is found on reanalysing the global data.3He/H ratio as a function of maximum proton flux at an energy of about 10 MeV shows a break-up of the data into two groups. The first group follows the anticorrelation of 3He/H ratio with the proton flux, as expected in the plasma process acceleration models. But the second group has a constant 3He/H ratio as a function of maximum proton flux. This is not in conformity with the plasma process models. But this is expected in models where the nuclear spallation reactions are responsible for the production of 3He. It is also found that the same break-up into two distinct groups follows if one plots the location of the flares in the solar disc. The first group is more or less confined to the west limb of the Sun, whereas the second group is more widely spread out across the solar disk

Mobility as a Resource (MaaR) for resilient human-centric automation: a vision paper

With technological advances, mobility has been moving from a product (i.e., traditional modes and vehicles), to a service (i.e., Mobility as a Service, MaaS). However, as observed in other fields (e.g. cloud computing resource management) we argue that mobility will evolve from a service to a resource (i.e., Mobility as a Resource, MaaR). Further, due to increasing scarcity of shared mobility spaces across traditional and emerging modes, the transition must be viewed within the critical need for ethical and equitable solutions for the traveling public (i.e., research is needed to avoid hyper-market driven outcomes for society). The evolution of mobility into a resource requires novel conceptual frameworks, technologies, processes and perspectives of analysis. A key component of the future MaaR system is the technological capacity to observe, allocate and manage (in real-time) the smallest envisionable units of mobility (i.e., atomic units of mobility capacity) while providing prioritized attention to human movement and ethical metrics related to access, consumption and impact. To facilitate research into the envisioned future system, this paper proposes initial frameworks which synthesize and advance methodologies relating to highly dynamic capacity reservation systems. Future research requires synthesis across transport network management, demand behavior, mixed-mode usage, and equitable mobility