Transport coefficients for inelastic Maxwell mixtures

The Boltzmann equation for inelastic Maxwell models is used to determine the Navier-Stokes transport coefficients of a granular binary mixture in $d$ dimensions. The Chapman-Enskog method is applied to solve the Boltzmann equation for states near the (local) homogeneous cooling state. The mass, heat, and momentum fluxes are obtained to first order in the spatial gradients of the hydrodynamic fields, and the corresponding transport coefficients are identified. There are seven relevant transport coefficients: the mutual diffusion, the pressure diffusion, the thermal diffusion, the shear viscosity, the Dufour coefficient, the pressure energy coefficient, and the thermal conductivity. All these coefficients are {\em exactly} obtained in terms of the coefficients of restitution and the ratios of mass, concentration, and particle sizes. The results are compared with known transport coefficients of inelastic hard spheres obtained analytically in the leading Sonine approximation and by means of Monte Carlo simulations. The comparison shows a reasonably good agreement between both interaction models for not too strong dissipation, especially in the case of the transport coefficients associated with the mass flux.Comment: 9 figures, to be published in J. Stat. Phy

MRI phenotyping of underlying cerebral small vessel disease in mixed hemorrhage patients

Objective: To investigate underlying cerebral small vessel disease (CSVD) in patients with mixed cerebral hemorrhages patterns and phenotype them according to the contribution of the two most common sporadic CSVD subtypes: cerebral amyloid angiopathy (CAA) vs. hypertensive arteriopathy (HA). Methods: Brain MRIs of patients with intracerebral hemorrhages (ICHs) and/or cerebral microbleeds (CMBs) were assessed for the full spectrum of CSVD markers using validated scales: ICHs, CMBs, cortical superficial siderosis (cSS), white matter hyperintensities, MRI-visible perivascular spaces (PVS). PVS predominance pattern was grouped as centrum-semiovale (CSO)-PVS predominance, basal-ganglia (BG)-PVS predominance, CSO-PVS and BG-PVS equality. Patients with mixed cerebral hemorrhages were classified into mixed CAA-pattern or mixed HA-pattern according to the existence of cSS and/or a CSO-PVS predominance pattern and comparisons were performed. Results: We included 110 patients with CAA (strictly lobar ICHs/CMBs), 33 with HA (strictly deep ICHs/CMBs) and 97 with mixed lobar/deep ICHs/CMBs. Mixed patients were more similar to HA with respect to their MRI-CSVD markers, vascular risk profile and cerebrospinal fluid (CSF) measures. In the mixed patients, 33 (34%) had cSS, a CSO-PVS predominance pattern, or both, and were defined as mixed CAA-pattern cases. The mixed CAA-pattern patients were more alike CAA patients regarding their MRI-CSVD markers, CSF and genetic profile. Conclusion: Our findings suggest that the heterogeneous group of patients with mixed cerebral hemorrhages distribution can be further phenotyped according to the predominant underlying CSVD. cSS presence and a CSO-PVS predominance pattern could serve as strongly suggestive markers of a contribution from CAA among patients with mixed hemorrhages

High Resolution Optical Spectroscopy of the F Supergiant Proto-Planetary Nebula V887 Her=IRAS 18095+2704

An abundance analysis is presented for IRAS 18095+2704 (V887 Her), a post-AGB star and proto-planetary nebula. The analysis is based on high-resolution optical spectra from the McDonald Observatory and the Special Astrophysical Observatory. Standard analysis using a classical Kurucz model atmosphere and the line analysis program MOOG provides the atmospheric parameters: Teff = 6500 K, log g = +0.5, and a microturbulent velocity Vt = 4.7 km/s and [Fe/H] = -0.9. Extraction of these parameters is based on excitation of FeI lines, ionization equilibrium between neutral and ions of Mg, Ca, Ti, Cr, and Fe, and the wings of hydrogen Paschen lines. Elemental abundances are obtained for 22 elements and upper limits for an additional four elements. These results show that the star's atmosphere has not experienced a significant number of C- and s-process enriching thermal pulses. Abundance anomalies as judged relative to the compositions of unevolved and less-evolved normal stars of a similar metallicity include Al, Y, and Zr deficiencies with respect to Fe of about 0.5 dex. Judged by composition, the star resembles a RV Tauri variable that has been mildly affected by dust-gas separation reducing the abundances of the elements of highest condensation temperature. This separation may occur in the stellar wind. There are indications that the standard 1D LTE analysis is not entirely appropriate for IRAS 18095+2704. These include a supersonic macroturbulent velocity of 23 km/s, emission in H-alpha and the failure of predicted profiles to fit observed profiles of H-beta and H-gamma.Comment: Accepted for publication in MNRA

Chemical stratification in the atmosphere of Ap star HD 133792. Regularized solution of the vertical inversion problem

High spectral resolution studies of cool Ap stars reveal conspicuous anomalies of the shape and strength of many absorption lines. This is a signature of large atmospheric chemical gradients produced by the selective radiative levitation and gravitational settling of chemical species. Here we present a new approach to mapping the vertical chemical structures in stellar atmospheres. We have developed a regularized chemical inversion procedure that uses all information available in high-resolution stellar spectra. The new technique for the first time allowed us to recover chemical profiles without making a priori assumptions about the shape of chemical distributions. We have derived average abundances and applied the vertical inversion procedure to the high-resolution VLT UVES spectra of the weakly magnetic, cool Ap star HD 133792. Our analysis yielded improved estimates of the atmospheric parameters of HD 133792. We show that this star has negligible vsini and the mean magnetic field modulus =1.1+/-0.1 kG. We have derived average abundances for 43 ions and obtained vertical distributions of Ca, Si, Mg, Fe, Cr, and Sr. All these elements except Mg show high overabundance in the deep layers and solar or sub-solar composition in the upper atmosphere of HD 133792. In contrast, the Mg abundance increases with height. We find that transition from the metal-enhanced to metal-depleted zones typically occurs in a rather narrow range of depths in the atmosphere of HD 133792. Based on the derived photospheric abundances, we conclude that HD 133792 belongs to the rare group of evolved cool Ap stars, which possesses very large Fe-peak enhancement, but lacks a prominent overabundance of the rare-earth elements.Comment: Accepted by A&A; 12 pages, 9 figure

Search for the standard model Higgs boson decaying to a bbˉb\bar{b} pair in events with no charged leptons and large missing transverse energy using the full CDF data set

We report on a search for the standard model Higgs boson produced in association with a vector boson in the full data set of proton-antiproton collisions at $\sqrt{s} = 1.96$ TeV recorded by the CDF II detector at the Tevatron, corresponding to an integrated luminosity of 9.45 fb$^{-1}$. We consider events having no identified charged lepton, a transverse energy imbalance, and two or three jets, of which at least one is consistent with originating from the decay of a $b$ quark. We place 95% credibility level upper limits on the production cross section times standard model branching fraction for several mass hypotheses between 90 and $150 \mathrm{GeV}/c^2$. For a Higgs boson mass of $125 \mathrm{GeV}/c^2$, the observed (expected) limit is 6.7 (3.6) times the standard model prediction.Comment: Accepted by Phys. Rev. Let

Search for the standard model Higgs boson decaying to a bb pair in events with one charged lepton and large missing transverse energy using the full CDF data set

We present a search for the standard model Higgs boson produced in association with a W boson in sqrt(s) = 1.96 TeV p-pbar collision data collected with the CDF II detector at the Tevatron corresponding to an integrated luminosity of 9.45 fb-1. In events consistent with the decay of the Higgs boson to a bottom-quark pair and the W boson to an electron or muon and a neutrino, we set 95% credibility level upper limits on the WH production cross section times the H->bb branching ratio as a function of Higgs boson mass. At a Higgs boson mass of 125 GeV/c2 we observe (expect) a limit of 4.9 (2.8) times the standard model value.Comment: Submitted to Phys. Rev. Lett (v2 contains clarifications suggested by PRL

Search for the standard model Higgs boson decaying to a bb pair in events with two oppositely-charged leptons using the full CDF data set

We present a search for the standard model Higgs boson produced in association with a Z boson in data collected with the CDF II detector at the Tevatron, corresponding to an integrated luminosity of 9.45/fb. In events consistent with the decay of the Higgs boson to a bottom-quark pair and the Z boson to electron or muon pairs, we set 95% credibility level upper limits on the ZH production cross section times the H -> bb branching ratio as a function of Higgs boson mass. At a Higgs boson mass of 125 GeV/c^2 we observe (expect) a limit of 7.1 (3.9) times the standard model value.Comment: To be submitted to Phys. Rev. Let

New Analyses of Star-to-Star Abundance Variations Among Bright Giants in the Mildly Metal-Poor Globular Cluster M5

We present a chemical composition analysis of 36 giant stars in the mildly metal-poor globular cluster M5 (NGC 5904). The analysis makes use of high resolution data acquired at the Keck I telescope as well as a re-analysis of high resolution spectra acquired for an earlier study at Lick Observatory. We employed two analysis techniques: one, adopting standard spectroscopic constraints, and two, adopting an analysis consistent with the non-LTE precepts as recently described by Thevenin & Idiart. The abundance ratios we derive for magnesium, silicon, calcium, scandium, titanium, vanadium, nickel, barium and europium in M5 show no significant abundance variations and the ratios are comparable to those of halo field stars. However, large variations are seen in the abundances of oxygen, sodium and aluminum, the elements that are sensitive to proton-capture nucleosynthesis. In comparing the abundances of M5 and M4 (NGC 6121), another mildly metal-poor globular cluster, we find that silicon, aluminum, barium and lanthanum are overabundant in M4 with respect to what is seen in M5, confirming and expanding the results of previous studies. In comparing the abundances between these two clusters and others having comparable metallicities, we find that the anti-correlations observed in M5 are similar to those found in more metal-poor clusters, M3, M10 and M13, whereas the behavior in M4 is more like that of the more metal-rich globular cluster M71. We conclude that among stars in Galactic globular clusters, there is no definitive ``single'' value of [el/Fe] at a given [Fe/H] for at least some alpha-capture, odd-Z and slow neutron-capture process elements, in this case, silicon, aluminum, barium and lanthanum.Comment: 31 pages + 16 figures + 11 tables; accepted for publication in Sept.2001 Astronomical Journa

Chemical Compositions of Red Giant Stars in Old Large Magellanic Cloud Globular Clusters

We have observed ten red giant stars in four old Large Magellanic Cloud globular clusters with the high-resolution spectrograph MIKE on the Magellan Landon Clay 6.5-m telescope. The stars in our sample have up to 20 elemental abundance determinations for the alpha-, iron-peak, and neutron-capture element groups. We have also derived abundances for the light odd-Z elements Na and Al. We find NGC 2005 and NGC 2019 to be more metal-rich than previous estimates from the Ca II triplet, and we derive [Fe/H] values closer to those obtained from the slope of the red giant branch. However, we confirm previous determinations for Hodge 11 and NGC 1898 to within 0.2 dex. The LMC cluster [Mg/Fe] and [Si/Fe] ratios are comparable to the values observed in old Galactic globular cluster stars, as are the abundances [Y/Fe], [Ba/Fe], and [Eu/Fe]. The LMC clusters do not share the low-Y behavior observed in some dwarf spheroidal galaxies. [Ca/Fe], [Ti/Fe], and [V/Fe] in the LMC, however, are significantly lower than what is seen in the Galactic globular cluster system. Neither does the behavior of [Cu/Fe] as a function of [Fe/H] in our LMC clusters match the trend seen in the Galaxy, staying instead at a constant value of ~0.8. Because not all [alpha/Fe] ratios are suppressed, these abundance ratios cannot be attributed solely to the injection of Type Ia SNe material, and instead reflect the differences in star formation history of the LMC vs. the Milky Way. We conclude that many of the abundances in the LMC globular clusters we observed are distinct from those observed in the Milky Way, and these differences are intrinsic to the stars in those systems.Comment: To be published in ApJ, 21 pages, 12 figures. Tables 2 (equivalent widths) and 3 (hyperfine splitting information) included separatel

Measurement of the difference of CP-violating asymmetries in D0 -> K+K- and D0 ->pi+pi- decays at CDF

We report a measurement of the difference (Delta Acp) between time-integrated CP--violating asymmetries in D0-> K+ K- and D0-> pi+pi- decays reconstructed in the full data set of proton-antiproton collisions collected by the Collider Detector at Fermilab, corresponding to 9.7 fb-1 of integrated luminosity. The strong decay D*+->D0 pi+ is used to identify the charm meson at production as D0 or anti-D0. We measure Delta Acp = [-0.62 +- 0.21 (stat) +- 0.10 (syst)] %, which differs from zero by 2.7 Gaussian standard deviations.This result supports similar evidence for CP violation in charm-quark decays obtained in proton-proton collisions.Comment: Phys. Rev. Lett. 109, 111801 (2012