Required precision of mass and half-life measurements for r-process nuclei planned at future RI-beam facilities

In order to understand the r-process nucleosynthesis, we suggest precision required for mass and beta-decay half-life measurements planned at future RI-beam facilities. To satisfy a simple requirement that we put on nuclear model predictions, it is concluded that the detectors for the mass measurements must have a precision of 1sigma ~< 250 keV, and that the detectors for the half-life measurements demand a precision of 1sigma ~< 0.15 ms. Both the above precisions are required at the neutron richness of A/Z = 3.0 at the N=82 shell closure and A/Z = 2.9 at the N=50 shell closure. For the doubly magic nuclide 78Ni, a precision of 1sigma ~< 300 keV and 1sigma ~< 5 ms are required, respectively, for mass and half-life measurements. This analysis aims to provide a first rough guide for ongoing detector developments.Comment: 8 pages, 2 figures. in Proceedings of Int. conf. The Future Astronuclear Physics, From microscopic puzzles to macroscopic nightmares, Eds. H.M.J. Boffin et al., EAS Publication Series, EDP Sciences, in press (2004

Fabrication and superconductivity of NaxTaS2 crystals

In this paper we report the growth and superconductivity of $Na_xTaS_2$ crystals. The structural data deduced from X-ray diffraction pattern shows that the sample has the same structure as $2H-TaS_2$. A series of crystals with different superconducting transition temperatures ($T_c$) ranging from 2.5 K to 4.4 K were obtained. It is found that the $T_c$ rises with the increase of $Na$ content determined by Energy-Dispersive x-ray microanalysis(EDX) of Scanning Electron Microscope (SEM) on these crystals. Compared with the resistivity curve of un-intercalated sample $2H-TaS_2$ ($T_c$ = 0.8 K, $T_{CDW} \approx$ 70 K), no signal of charge density wave (CDW) was observed in samples $Na_{0.1}TaS_2$ and $Na_{0.05}TaS_2$. However, in some samples with lower $T_c$, the CDW appears again at about 65 K. Comparison between the anisotropic resistivity indicates that the anisotropy becomes smaller in samples with more $Na$ intercalation (albeit a weak semiconducting behavior along c-axis) and thus higher $T_c$. It is thus concluded that there is a competition between the superconductivity and the CDW. With the increase of sodium content, the rise of $T_c$ in $Na_xTaS_2$ is caused mainly by the suppression to the CDW in $2H-TaS_2$, and the conventional rigid band model for layered dichalcogenide may be inadequate to explain the changes induced by the slight intercalation of sodium in $2H-TaS_2$.Comment: 8 pages, 13 figures, To appear in Physical Review

Fermi Surface Nesting and the Origin of the Charge Density Wave in NbSe2_2

We use highly accurate density functional calculations to study the band structure and Fermi surfaces of NbSe2. We calculate the real part of the non-interacting susceptibility, Re chi_0(q), which is the relevant quantity for a charge density wave (CDW) instability and the imaginary part, Im chi_0(q), which directly shows Fermi surface (FS) nesting. We show that there are very weak peaks in Re chi_0(q) near the CDW wave vector, but that no such peaks are visible in Im chi_0(q), definitively eliminating FS nesting as a factor in CDW formation. Because the peak in Re chi_0(q) is broad and shallow, it is unlikely to be the direct cause of the CDW instability. We briefly address the possibility that electron-electron interactions (local field effects) produce additional structure in the total (renormalized) susceptibility, and we discuss the role of electron-ion matrix elements.Comment: Replacement of Table II values, minor changes to tex

Constraints on the luminosity of the stellar remnant in SNR1987A

We obtain photometric constraints on the luminosity of the stellar remnant in SNR1987A using XMM-Newton and INTEGRAL data. The upper limit in the 2--10 keV band based on the XMM-Newton data is L<5*10^{34}erg/s. We note, however, that the optical depth of the envelope is still high in the XMM-Newton band, therefore, this upper limit does not constrain the true unabsorbed luminosity of the central source. The optical depth is expected to be small in the hard X-ray band of the IBIS telescope aboard the INTEGRAL observatory, therefore it provides an unobscured look at the stellar remnant. We did not detect statistically significant emission from SN1987A in the 20-60 keV band with the upper limit of L<1.1*10^{36}erg/s. We also obtained an upper limit on the mass of radioactive 44Ti M(44Ti)<10^{-3}Msun.Comment: 5 pages, 3 figures, accepted for publication in Astronomy Letter

Are Ti44-Producing Supernovae Exceptional?

According to standard models supernovae produce radioactive $^{44}$Ti, which should be visible in gamma-rays following decay to $^{44}$Ca for a few centuries. $^{44}Ti production is believed to be the source of cosmic$^{44}$Ca, whose abundance is well established. Yet, gamma-ray telescopes have not seen the expected young remnants of core collapse events. The$^{44}$Ti mean life of$\tau \simeq$89 y and the Galactic supernova rate of$\simeq$3/100 y imply$\simeq$several detectable$^{44}Ti gamma-ray sources, but only one is clearly seen, the 340-year-old Cas A SNR. Furthermore, supernovae which produce much $^{44}Ti are expected to occur primarily in the inner part of the Galaxy, where young massive stars are most abundant. Because the Galaxy is transparent to gamma-rays, this should be the dominant location of expected gamma-ray sources. Yet the Cas A SNR as the only one source is located far from the inner Galaxy (at longitude 112 degree). We evaluate the surprising absence of detectable supernovae from the past three centuries. We discuss whether our understanding of SN explosions, their$^{44}Ti yields, their spatial distributions, and statistical arguments can be stretched so that this apparent disagreement may be accommodated within reasonable expectations, or if we have to revise some or all of the above aspects to bring expectations in agreement with the observations. We conclude that either core collapse supernovae have been improbably rare in the Galaxy during the past few centuries, or $^{44}Ti-producing supernovae are atypical supernovae. We also present a new argument based on$^{44}$Ca/$^{40}$Ca ratios in mainstream SiC stardust grains that may cast doubt on massive-He-cap Type I supernovae as the source of most galactic$^{44}$Ca.Comment: 23 pages, 14 figures, accepted for publication in Astronomy and Astrophysics 2006. Correcting the SN type of Tycho in Table B.1. and add its associated reference

Large magnetic entropy change near room temperature in antipervoskite SnCMn3

We report the observation of large magnetocaloric effect near room temperature in antipervoskite SnCMn3. The maximal magnetic entropy change at the first-order ferrimagnetic-paramagnetic transition temperature (TC 279 K) is about 80.69mJ/cm3 K and 133mJ/cm3 K under the magnetic field of 20 kOe and 48 kOe, respectively. These values are close to those of typical magnetocaloric materials. The large magnetocaloric effect is associated with the sharp change of lattice, resistivity and magnetization in the vicinity of TC. Through the measurements of Seebeck coefficient and normal Hall effect, the title system is found to undergo a reconstruction of electronic structure at TC. Considering its low-cost and innocuous raw materials, Mn-based antiperovskite compounds are suggested to be appropriate for pursuing new materials with larger magnetocaloric effect.Comment: 11 pages, 8 figure

Vibrio parahaemolyticus, enterotoxigenic Escherichia coli, enterohemorrhagic Escherichia coli and Vibrio cholerae

This review highlighted the following: (i) pathogenic mechanism of the thermostable direct hemolysin produced by Vibrio parahaemolyticus, especially on its cardiotoxicity, (ii) heat-labile and heat-stable enterotoxins produced by enterotoxigenic Escherichia coli, especially structure–activity relationship of heat-stable enterotoxin, (iii) RNA N-glycosidase activity of Vero toxins (VT1 and VT2) produced by enterohemorrhagic Escherichia coli O157:H7, (iv) discovery of Vibrio cholerae O139, (v) isolation of new variant of Vibrio cholerae O1 El Tor that carries classical ctxB, and production of high concentration of cholera toxin by these strains, and (vi) conversion of viable but nonculturable (VBNC) Vibrio cholerae to culturable state by co-culture with eukaryotic cells

Prion Formation and Polyglutamine Aggregation Are Controlled by Two Classes of Genes

Prions are self-perpetuating aggregated proteins that are not limited to mammalian systems but also exist in lower eukaryotes including yeast. While much work has focused around chaperones involved in prion maintenance, including Hsp104, little is known about factors involved in the appearance of prions. De novo appearance of the [PSI+] prion, which is the aggregated form of the Sup35 protein, is dramatically enhanced by transient overexpression of SUP35 in the presence of the prion form of the Rnq1 protein, [PIN+]. When fused to GFP and overexpressed in [ps−] [PIN+] cells, Sup35 forms fluorescent rings, and cells with these rings bud off [PSI+] daughters. We investigated the effects of over 400 gene deletions on this de novo induction of [PSI+]. Two classes of gene deletions were identified. Class I deletions (bug1Δ, bem1Δ, arf1Δ, and hog1Δ) reduced the efficiency of [PSI+] induction, but formed rings normally. Class II deletions (las17Δ, vps5Δ, and sac6Δ) inhibited both [PSI+] induction and ring formation. Furthermore, class II deletions reduced, while class I deletions enhanced, toxicity associated with the expanded glutamine repeats of the huntingtin protein exon 1 that causes Huntington's disease. This suggests that prion formation and polyglutamine aggregation involve a multi-phase process that can be inhibited at different steps.National Institutes of Health (U.S.) (grant GM56350)National Institutes of Health (U.S.) (NSRA F32 postdoctoral fellowship GM072340)National Institutes of Health (U.S.) (grant GM25874)Howard Hughes Medical Institut

Enhancement of Cell Membrane Invaginations, Vesiculation and Uptake of Macromolecules by Protonation of the Cell Surface

The different pathways of endocytosis share an initial step involving local inward curvature of the cell’s lipid bilayer. It has been shown that to generate membrane curvature, proteins or lipids enforce transversal asymmetry of the plasma membrane. Thus it emerges as a general phenomenon that transversal membrane asymmetry is the common required element for the formation of membrane curvature. The present study demonstrates that elevating proton concentration at the cell surface stimulates the formation of membrane invaginations and vesiculation accompanied by efficient uptake of macromolecules (Dextran-FITC, 70 kD), relative to the constitutive one. The insensitivity of proton induced uptake to inhibiting treatments and agents of the known endocytic pathways suggests the entry of macromolecules to proceeds via a yet undefined route. This is in line with the fact that neither ATP depletion, nor the lowering of temperature, abolishes the uptake process. In addition, fusion mechanism such as associated with low pH uptake of toxins and viral proteins can be disregarded by employing the polysaccharide dextran as the uptake molecule. The proton induced uptake increases linearly in the extracellular pH range of 6.5 to 4.5, and possesses a steep increase at the range of 4> pH>3, reaching a plateau at pH≤3. The kinetics of the uptake implies that the induced vesicles release their content to the cytosol and undergo rapid recycling to the plasma membrane. We suggest that protonation of the cell’s surface induces local charge asymmetries across the cell membrane bilayer, inducing inward curvature of the cell membrane and consequent vesiculation and uptake