First investigation of noble gases in the Dengli H3,8 chondrite

The Dengli (H3,8) meteorite, which weighs 243.5 g, is a find from the Karakum desert. It is a complex microbreccia containing unusual clasts which are more typical for regolithic breccias than for H-chondrites. Based on comparisons of Xe and Kr content and isotopic composition, the Dengli does not differ significantly from other H-chondrites. Its exposure age is 7.6 Ma. That is in agreement with common data for the exposure age (6.2 + 0.2 Ma) of 350 H-chondrites. Dengli's K/Ar age (4.01 Ga) coincides with the same ages of many other H-chondrites. Thus the Dengli is not regolithic breccia, and it probably formed during accretion of its parent body

Excess <SUP>36</SUP>Ar in the Efremovka meteorite: a strong hint for the presence of <SUP>36</SUP>Cl in the early solar system

Noble gas studies of fine-grained silicate material of the Efremovka carbonaceous chondrite revealed the presence of excess 36Ar over and above the level expected due to contributions from the trapped and cosmic-ray-produced, both spallogenic and secondary neutron-induced, components. The observed excess in 36Ar can be best explained as due to in situ decay of 36Cl (&#964; = 0.43 Ma) in the analyzed samples and provides a strong hint for the presence of this now-extinct nuclide in the early solar system. Additional experiments that will confirm our observation are proposed. A conservative estimate of an initial 36Cl/35Cl of (1.4 &#177; 0.2) &#215; 10-6 at the time of formation of Efremovka silicates can be made from our data. If we consider a nucleosynthetic origin of 36Cl, the time interval between the last addition of freshly synthesized 36Cl to the solar nebula and the formation of some of the first silicate grains in the nebula could be estimated to be approximately 1 Ma

Natural Nuclear Reactor Oklo and Variation of Fundamental Constants Part 1: Computation of Neutronics of Fresh Core

Using modern methods of reactor physics we have performed full-scale calculations of the natural reactor Oklo. For reliability we have used recent version of two Monte Carlo codes: Russian code MCU REA and world wide known code MCNP (USA). Both codes produce similar results. We have constructed a computer model of the reactor Oklo zone RZ2 which takes into account all details of design and composition. The calculations were performed for three fresh cores with different uranium contents. Multiplication factors, reactivities and neutron fluxes were calculated. We have estimated also the temperature and void effects for the fresh core. As would be expected, we have found for the fresh core a significant difference between reactor and Maxwell spectra, which was used before for averaging cross sections in the Oklo reactor. The averaged cross section of Sm-149 and its dependence on the shift of resonance position (due to variation of fundamental constants) are significantly different from previous results. Contrary to results of some previous papers we find no evidence for the change of the fine structure constant in the past and obtain new, most accurate limits on its variation with time: -4 10^{-17}year^{-1} < d alpha/dt/alpha < 3 10^{-17} year^{-1} A further improvement in the accuracy of the limits can be achieved by taking account of the core burnup. These calculations are in progress.Comment: 25 pages, 14 figures, 12 tables, minor corrections, typos correcte

Visual Cycle: Dependence of Retinol Production and Removal on Photoproduct Decay and Cell Morphology

The visual cycle is a chain of biochemical reactions that regenerate visual pigment following exposure to light. Initial steps, the liberation of all-trans retinal and its reduction to all-trans retinol by retinol dehydrogenase (RDH), take place in photoreceptors. We performed comparative microspectrophotometric and microfluorometric measurements on a variety of rod and cone photoreceptors isolated from salamander retinae to correlate the rates of photoproduct decay and retinol production. Metapigment decay rate was spatially uniform within outer segments and 50–70 times faster in the cells that contained cone-type pigment (SWS2 and M/LWS) compared to cells with rod-type pigment (RH1). Retinol production rate was strongly position dependent, fastest at the base of outer segments. Retinol production rate was 10–40 times faster in cones with cone pigments (SWS2 and M/LWS) than in the basal OS of rods containing rod pigment (RH1). Production rate was approximately five times faster in rods containing cone pigment (SWS2) than the rate in basal OS of rods containing the rod pigment (RH1). We show that retinol production is defined either by metapigment decay rate or RDH reaction rate, depending on cell type or outer segment region, whereas retinol removal is defined by the surface-to-volume ratio of the outer segment and the availability of retinoid binding protein (IRBP). The more rapid rates of retinol production in cones compared to rods are consistent with the more rapid operation of the visual cycle in these cells

Magnetic flaring in the pre-main sequence Sun and implications for the early solar system

To address the role of energetic processes in the solar nebula, we provide a detailed characterization of magnetic flaring in stellar analogs of the pre-main sequence Sun based on 23 hours observations of 43 analogs of the young Sun in the Orion Nebula Cluster obtained with the Chandra X-ray Observatory. We find the X-ray luminosities are strongly elevated over main sequence levels with average = 30.3 erg/s and = -3.9 (0.5-8 keV), and dozens of flares are present. Analogs of the <= 1 My old pre-main sequence Sun exhibit X-ray flares 10^{1.5} times more powerful and 10^{2.5} times more frequent than the most powerful flares seen on the contemporary Sun. Extrapolating the solar relationship between X-ray luminosity and proton fluence, we infer that the young Sun exhibited a 10^5-fold enhancement in energetic protons compared to contemporary levels. Unless the flare geometries are unfavorable, this inferred proton flux on the disk is sufficient to produce the observed meteoritic abundances of several important short-lived radioactive isotopes. Our study thus strengthens the astronomical foundation for local proton spallation models of isotopic anomalies in carbonaceous chondritic meteorites. The radiation, particles and shocks produced by the magnetic reconnection flares seen with Chandra may also have flash melted meteoritic chondrules and produced excess 21-Ne seen in meteoritic grains.Comment: 36 pages, 3 figures. Accepted for publication in the Astrophysical Journa

Molybdenum Evidence for Inherited Planetary Scale Isotope Heterogeneity of the Protosolar Nebula

Isotope anomalies provide important information about early solar system evolution. Here we report molybdenum isotope abundances determined in samples of various meteorite classes. There is no fractionation of molybdenum isotopes in our sample set within 0.1 permil and no contribution from the extinct radionuclide 97Tc at mass 97 (97Tc/92Mo<3E-6). Instead, we observe clear anomalies in bulk iron meteorites, mesosiderites, pallasites, and chondrites characterized by a coupled excess in p- and r- or a mirror deficit in s-process nuclides (Mo-HL). This large scale isotope heterogeneity of the solar system observed for molybdenum must have been inherited from the interstellar environment where the sun was born, illustrating the concept of ``cosmic chemical memory''. The presence of molybdenum anomalies is used to discuss the filiation between planetesimals.Comment: 7 pages, 2 figures, 1 table, accepted in Ap

Bottom-Water Conditions in a Marine Basin after the Cretaceous–Paleogene Impact Event: Timing the Recovery of Oxygen Levels and Productivity

An ultra-high-resolution analysis of major and trace element contents from the Cretaceous–Paleogene boundary interval in the Caravaca section, southeast Spain, reveals a quick recovery of depositional conditions after the impact event. Enrichment/depletion profiles of redox sensitive elements indicate significant geochemical anomalies just within the boundary ejecta layer, supporting an instantaneous recovery –some 102 years– of pre-impact conditions in terms of oxygenation. Geochemical redox proxies point to oxygen levels comparable to those at the end of the Cretaceous shortly after impact, which is further evidenced by the contemporary macrobenthic colonization of opportunistic tracemakers. Recovery of the oxygen conditions was therefore several orders shorter than traditional proposals (104–105 years), suggesting a probable rapid recovery of deep-sea ecosystems at bottom and in intermediate waters.This research was supported by Projects CGL2009-07603, CGL2008-03007, CGL2012-33281 and CGL2012-32659 (Secretaría de Estado de I+D+I, Spain), Projects RNM-3715 and RNM 05212, and Research Groups RNM-178 and 0179 (Junta de Andalucía)

Inactivation of VCP/ter94 Suppresses Retinal Pathology Caused by Misfolded Rhodopsin in Drosophila

The most common Rhodopsin (Rh) mutation associated with autosomal dominant retinitis pigmentosa (ADRP) in North America is the substitution of proline 23 by histidine (RhP23H). Unlike the wild-type Rh, mutant RhP23H exhibits folding defects and forms intracellular aggregates. The mechanisms responsible for the recognition and clearance of misfolded RhP23H and their relevance to photoreceptor neuron (PN) degeneration are poorly understood. Folding-deficient membrane proteins are subjected to Endoplasmic Reticulum (ER) quality control, and we have recently shown that RhP23H is a substrate of the ER–associated degradation (ERAD) effector VCP/ter94, a chaperone that extracts misfolded proteins from the ER (a process called retrotranslocation) and facilitates their proteasomal degradation. Here, we used Drosophila, in which Rh1P37H (the equivalent of mammalian RhP23H) is expressed in PNs, and found that the endogenous Rh1 is required for Rh1P37H toxicity. Genetic inactivation of VCP increased the levels of misfolded Rh1P37H and further activated the Ire1/Xbp1 ER stress pathway in the Rh1P37H retina. Despite this, Rh1P37H flies with decreased VCP function displayed a potent suppression of retinal degeneration and blindness, indicating that VCP activity promotes neurodegeneration in the Rh1P37H retina. Pharmacological treatment of Rh1P37H flies with the VCP/ERAD inhibitor Eeyarestatin I or with the proteasome inhibitor MG132 also led to a strong suppression of retinal degeneration. Collectively, our findings raise the possibility that excessive retrotranslocation and/or degradation of visual pigment is a primary cause of PN degeneration