[en] Short communication

[en] We have shown that after global myocardial ischemia, reperfusion injury may be related to platelet deposition in the coronary microcirculation. The purpose of this study was to determine whether multidose hypothermic potassium cardioplegia suppresses platelet deposition during postischemic reperfusion. Platelets labeled with ¹¹¹In and erythrocytes labeled with ⁵¹Cr were injected into dogs subjected to either 120 min of continuous cardiopulmonary bypass (control, n . 4), 60 min of global normothermic myocardial ischemia followed by 50 min of reperfusion (n . 6), or global ischemia with cardioplegia (n . 5). Intracoronary platelet deposition was determined by comparing the double-labeled isotope activity of myocardial biopsy specimens to peripheral blood. Reperfusion after global myocardial ischemia resulted in substantial deposition of platelets within the coronary vasculature in both the cardioplegia-treated (215 +/- 40 platelets/mg) and untreated (269 +/- 95 platelets/mg) groups. These increases were significantly greater than those measured during continuous bypass (48 +/- 2 platelets/mg; p less than .01). Cardioplegia, despite apparent washout of the microcirculation, does not alter platelet deposition. Thus other platelet-stabilizing measures must be used to prevent platelet deposition-induced reperfusion injury after surgical global ischemia

[en] We compute the temperature and IR signal of particles of radius a and albedo α at heliocentric distance R, taking into account the emissivity effect, and give an interpolating formula for the result. We compare with analyses of COBE DIRBE data by others (including recent detection of the cosmic IR background) for various values of heliocentric distance R, particle radius a, and particle albedo α. We then apply these results to a recently developed picture of the Kuiper belt as a two-sector disk with a nearby, low-density sector (40< R<50 endash 90 AU) and a more distant sector with a higher density. We consider the case in which passage through a molecular cloud essentially cleans the solar system of dust. We apply a simple model of dust production by comet collisions and removal by the Poynting-Robertson effect to find limits on total and dust masses in the near and far sectors as a function of time since such a passage. Finally, we compare Kuiper belt IR spectra for various parameter values. Results of this work include: (1) numerical limits on Kuiper belt dust as a function of (R, a, α) on the basis of four alternative sets of constraints, including those following from recent discovery of the cosmic IR background by Hauser et al.; (2) application to the two-sector Kuiper belt model, finding mass limits and spectrum shape for different values of relevant parameters including dependence on time elapsed since last passage through a molecular cloud cleared the outer solar system of dust; and (3) potential use of spectral information to determine time since last passage of the Sun through a giant molecular cloud. copyright copyright 1999. The American Astronomical Society

[en] We have computed the charge that develops on an SQN in space as a result of balance between the rates of ionization by ambient gammas and capture of ambient electrons. We have also computed the times for achieving that equilibrium and binding energy of the least bound SQN electrons. We have done this for seven different settings. We sketch the calculations here and give their results in the Figure and Table II; details are in the Physical Review D.79.023513 (2009).

[en] Since Witten's seminal 1984 paper on the subject, searches for evidence of strange quark nuggets (SQNs) have proven unsuccessful. In the absence of experimental evidence ruling out SQNs, the validity of theories introducing mechanisms that increase their stability should continue to be tested. To stimulate electromagnetic SQN searches, particularly space searches, we estimate the net charge that would develop on a SQN in space exposed to various radiation baths (and showers) capable of liberating the SQN's less strongly bound electrons, taking into account recombination with ambient electrons. We consider, in particular, the cosmic microwave background, radiation from the sun, and diffuse galactic and extragalactic ultraviolet backgrounds. The largest charge, for the settings considered, develops on a solar system SQN exposed to a solar X-ray flare. A possible dramatic signal of SQNs in explosive astrophysical events is noted.

[en] We consider the implications of fermionic asymmetric dark matter (ADM) for a “mixed neutron star” composed of ordinary baryons and dark fermions. We find examples, where for a certain range of dark fermion mass – when it is less than that of ordinary baryons – such systems can reach higher masses than the maximal values allowed for ordinary (“pure”) neutron stars. This is shown both within a simplified, heuristic Newtonian analytic framework with non-interacting particles and via a general relativistic numerical calculation, under certain assumptions for the dark matter equation of state. Our work applies to various dark fermion models such as mirror matter models and to other models where the dark fermions have self-interactions