A New Limit on the Antiproton Lifetime

Measurements of the cosmic ray pbar/p ratio are compared to predictions from an inhomogeneous disk-diffusion model of pbar production and propagation within the Galaxy, combined with a calculation of the modulation of the interstellar cosmic ray spectra as the particles propagate through the heliosphere to the Earth. The predictions agree with the observed pbar/p spectrum. Adding a finite pbar lifetime to the model, we obtain the limit tau_pbar > 0.8 Myr (90 % C.L.).Comment: 13 pages, 3 encapsulated Postscript figures, uses AASTeX; accepted by Astrophysical Journal; minor change

Properties of quasi-periodic pulsations in solar flares from a single active region

We investigate the properties of a set of solar flares originating from a single active region (AR) that exhibit QPPs, and look for signs of the QPP periods relating to AR properties. The AR studied, best known as NOAA 12192, was unusually long-lived and produced 181 flares. Data from the GOES, EVE, Fermi, Vernov and NoRH observatories were used to determine if QPPs were present in the flares. For the soft X-ray GOES and EVE data, the time derivative of the signal was used. Power spectra of the time series data (without any form of detrending) were inspected, and flares with a peak above the 95% confidence level in the spectrum were labelled as having candidate QPPs. The confidence levels were determined taking account of uncertainties and the possible presence of red noise. AR properties were determined using HMI line of sight magnetograms. A total of 37 flares (20% of the sample) show good evidence of having QPPs, and some of the pulsations can be seen in data from multiple instruments and in different wavebands. The QPP periods show a weak correlation with the flare amplitude and duration, but this may be due to an observational bias. A stronger correlation was found between the QPP period and duration of the QPP signal, which can be partially but not entirely explained by observational constraints. No correlations were found with the AR area, bipole separation, or average magnetic field strength. The fact that a substantial fraction of the flare sample showed evidence of QPPs using a strict detection method with minimal processing of the data demonstrates that these QPPs are a real phenomenon, which cannot be explained by the presence of red noise or the superposition of multiple unrelated flares. The lack of correlation between the QPP periods and AR properties implies that the small-scale structure of the AR is important, and/or that different QPP mechanisms act in different cases.Comment: 23 pages, 57 figures. Accepted for publication by Astronomy & Astrophysic

Diffusion and Transport Coefficients in Synthetic Opals

Opals are structures composed of the closed packing of spheres in the size range of nano-to-micro meter. They are sintered to create small necks at the points of contact. We have solved the diffusion problem in such structures. The relation between the diffusion coefficient and the termal and electrical conductivity makes possible to estimate the transport coefficients of opal structures. We estimate this changes as function of the neck size and the mean-free path of the carriers. The theory presented is also applicable to the diffusion problem in other periodic structures.Comment: Submitted to PR

Plasma hardening of heavily loaded parts of soil-cutting machines

The influence of plasma hardening on hardening processes of heavy-duty and, therefore, wear parts of working elements of soil-cutting machines has been studied. It is shown that surface plasma hardening of ploughshare made of structural steel 65Mn in the hardened zone with thickness of 0,8 mm leads to formation of gradient-layered (mixed) structure consisting of finely dispersed mixture decay products of fine-grained austenite with variable microhardness in the range of 760 – 395 HV. It is confirmed that the creation of gradient-layered structure and features of its formation after the surface plasma treatment are explained by ultrahigh heating and cooling rates, unattainable with traditional methods of heat treatment

Metallic Xenon, Molecular Condensates, and Superconductivity

A possibility of explaining the light absorption observed to occur under pressure-induced xenon metallization as due to the transition to the superconducting state is analyzed. The mechanism of the van der Waals bonding is discussed.Comment: LaTeX 2.09 (RevTeX), 4 pages, 4 PostScript figures included in tex

Antimatter research in Space

Two of the most compelling issues facing astrophysics and cosmology today are to understand the nature of the dark matter that pervades the universe and to understand the apparent absence of cosmological antimatter. For both issues, sensitive measurements of cosmic-ray antiprotons and positrons, in a wide energy range, are crucial. Many different mechanisms can contribute to antiprotons and positrons production, ranging from conventional reactions up to exotic processes like neutralino annihilation. The open problems are so fundamental (i.e.: is the universe symmetric in matter and antimatter ?) that experiments in this field will probably be of the greatest interest in the next years. Here we will summarize the present situation, showing the different hypothesis and models and the experimental measurements needed to lead to a more established scenario.Comment: 10 pages, 7 figures, Invited talk at the 18th European Cosmic Ray Symposium, Moscow, July 2002, submitted to Journal of Physics

Gain limits of a Thick GEM in high-purity Ne, Ar and Xe

The dependence of the avalanche charge gain in Thick Gas Electron Multipliers (THGEM) on the purity of Ne, Ar and Xe filling gases was investigated. The gain, measured with alpha-particles in standard conditions (atmospheric pressure, room temperature), was found to considerably drop in gases purified by non-evaporable getters. On the other hand, small N2 admixtures to noble gases resulted in high reachable gains. The results are of general relevance in the operation of gas-avalanche detectors in noble gases, particularly that of two-phase cryogenic detectors for rare events.Comment: 15 pages, 6 figures, submitted to JINS

Polaron Transport in the Paramagnetic Phase of Electron-Doped Manganites

The electrical resistivity, Hall coefficient, and thermopower as functions of temperature are reported for lightly electron-doped Ca(1-x)La(x)MnO(3)(0 <= x <= 0.10). Unlike the case of hole-doped ferromagnetic manganites, the magnitude and temperature dependence of the Hall mobility for these compounds is found to be inconsistent with small-polaron theory. The transport data are better described by the Feynman polaron theory and imply intermediate coupling (alpha \~ 5.4) with a band effective mass, m*~4.3 m_0, and a polaron mass, m_p ~ 10 m_0.Comment: 7 pp., 7 Fig.s, to be published, PR

Organization and Management of the International Space Station (ISS) Multilateral Medical Operations

The goal of this work is to review the principles, design, and function of the ISS multilateral medical authority and the medical support system of the ISS Program. Multilateral boards and panels provide operational framework, direct, and supervise the ISS joint medical operational activities. The Integrated Medical Group (IMG) provides front-line medical support of the crews. Results of ongoing activities are reviewed weekly by physician managers. A broader status review is conducted monthly to project the state of crew health and medical support for the following month. All boards, panels, and groups function effectively and without interruptions. Consensus prevails as the primary nature of decisions made by all ISS medical groups, including the ISS medical certification board. The sustained efforts of all partners have resulted in favorable medical outcomes of the initial fourteen long-duration expeditions. The medical support system appears to be mature and ready for further expansion of the roles of all Partners, and for the anticipated increase in the size of ISS crews