Boron Abundances in Diffuse Interstellar Clouds

We present a comprehensive survey of B abundances in diffuse interstellar clouds from HST/STIS observations along 56 Galactic sight lines. Our sample is the result of a complete search of archival STIS data for the B II resonance line at 1362 angstroms, with each detection confirmed by the presence of absorption from other dominant ions at the same velocity. The data probe a range of astrophysical environments including both high-density regions of massive star formation as well as low-density paths through the Galactic halo, allowing us to clearly define the trend of B depletion onto interstellar grains as a function of gas density. Many extended sight lines exhibit complex absorption profiles that trace both local gas and gas associated with either the Sagittarius-Carina or Perseus spiral arm. Our analysis indicates a higher B/O ratio in the inner Sagittarius-Carina spiral arm than in the vicinity of the Sun, which may suggest that B production in the current epoch is dominated by a secondary process. The average gas-phase B abundance in the warm diffuse ISM is consistent with the abundances determined for a variety of Galactic disk stars, but is depleted by 60 percent relative to the solar system value. Our survey also reveals sight lines with enhanced B abundances that potentially trace recent production of B-11 either by cosmic-ray or neutrino-induced spallation. Such sight lines will be key to discerning the relative importance of the two production routes for B-11 synthesis.Comment: To be published in the proceedings of the IAU Symposium 268, Light Elements in the Universe, C. Charbonnel, M. Tosi, F. Primas & C. Chiappini, ed

Can Galactic Cosmic Rays Account for Solar 6Li Without Overproducing Gamma Rays?

Cosmic-ray interactions with interstellar gas produces both 6Li, which accumulates in the interstellar medium (ISM), and $\pi^0$ mesons, which decay to gamma-rays which propagate throughout the cosmos. Local 6Li abundances and extragalactic gamma-rays thus have a common origin which tightly links them. We exploit this connection to use gamma-ray observations to infer the contribution to 6Li nucleosynthesis by standard Galactic cosmic-ray (GCR) interactions with the ISM. Our calculation uses a carefully propagated cosmic-ray spectrum and accounts for 6Li production from both fusion reactions ($\alpha \alpha \to ^6Li$) as well as from spallation channels ({p,\alpha+CNO \to ^6Li). We find that although extreme assumptions yield a consistent picture, more realistic ones indicate that solar 6Li cannot be produced by standard GCRs alone without overproducing the hadronic gamma rays. Implications for the primordial 6Li production by decaying dark matter and cosmic rays from cosmological structure formation are discussed. Upcoming gamma-ray observations by GLAST will be crucial for determining the resolution of this problem.Comment: 4 pages, 1 figure To be published in ApJ

Evolution of Beryllium and Boron in the Inhomogeneous Early Galaxy

A model of supernova-driven chemical evolution of the Galactic halo, recently proposed by Tsujimoto, Shigeyama, & Yoshii (1999, ApJL, 519, 64), is extended in order to investigate the evolution of light elements such as Be and B (BeB), which are produced mainly through spallative reactions with Galactic cosmic rays. In this model each supernova sweeps up the surrounding interstellar gas into a dense shell and directly enriches it with ejecta which consist of heavy elements produced in each Type II supernova with different progenitor masses. We propose a two-component source for GCRs such that both interstellar gas and fresh SN ejecta engulfed in the shell are accelerated by the shock wave. Our model results include: (1) a prediction of the intrinsic scatter in BeB and [Fe/H] abundances within the model, (2) a successful prediction of the observed linear trend between BeB and [Fe/H], (3) a proposal for using BeB as a cosmic clock, as an alternative to [Fe/H], and (4) a method for possibly constraining the BBN model from future observations of metal-poor stars.Comment: 3 color figures in 7 pages, accepted by ApJ Letter

Pregalactic LiBeB Production by Supernova Cosmic Rays

I calculate the evolution of Be and B abundances produced by cosmic rays generated by massive stars in the pregalactic phase of the universe. The inputs for calculation, i.e. the star formation rate and the nuclear abundances of cosmic rays, which I assume to be the same as those of the ISM, are taken from the results of a detailed cosmic chemical evolution model with its parameters best fitted from several items of observational information including an early reionization of the IGM by $z\sim 15$. I found that when the $^6$Li plateau abundance observed in metal-poor halo stars originated in the pregalactic cosmological cosmic ray nucleosynthesis, Be and B simultaneously produced with $^6$Li amount to the lowest levels ever detected in metal-poor halo stars. It is desirable to observe Be and B abundances in metal-poor halo stars with [Fe/H]$\leq -3$ in order to elucidate the possibility of early $^6$LiBeB production by pregalactic supernova cosmic ray nucleosynthesis.Comment: 13 pages, 8 figures, ApJ accepte

An inertial range length scale in structure functions

It is shown using experimental and numerical data that within the traditional inertial subrange defined by where the third order structure function is linear that the higher order structure function scaling exponents for longitudinal and transverse structure functions converge only over larger scales, $r>r_S$, where $r_S$ has scaling intermediate between $\eta$ and $\lambda$ as a function of $R_\lambda$. Below these scales, scaling exponents cannot be determined for any of the structure functions without resorting to procedures such as extended self-similarity (ESS). With ESS, different longitudinal and transverse higher order exponents are obtained that are consistent with earlier results. The relationship of these statistics to derivative and pressure statistics, to turbulent structures and to length scales is discussed.Comment: 25 pages, 9 figure

Roles of Supernova Ejecta in Nucleosynthesis of Light Elements, Li, Be, and B

Explosions of type Ic supernovae (SNe Ic) are investigated using a relativistic hydrodynamic code to study roles of their outermost layers of the ejecta in light element nucleosynthesis through spallation reactions as a possible mechanism of the "primary" process. We have confirmed that the energy distribution of the outermost layers with a mass fraction of only 0.001 % follows the empirical formula proposed by previous work when the explosion is furious. In such explosions, a significant fraction of the ejecta ($>$0.1 % in mass) have the energy greater than the threshold energy for spallation reactions. On the other hand, it is found that the outermost layers of ejecta become more energetic than the empirical formula would predict when the explosion energy per unit ejecta mass is smaller than \sim 1.3\times 10^{51}{ergs/}\Msun. As a consequence, it is necessary to numerically calculate explosions to estimate light element yields from SNe Ic. The usage of the empirical formula would overestimate the yields by a factor of \gtsim 3 for energetic explosions such as SN 1998bw and underestimate the yields by a similar factor for less energetic explosions like SN 1994I. The yields of light elements Li, Be, and B (LiBeB) from SNe Ic are estimated by solving the transfer equation of cosmic rays originated from ejecta of SNe Ic and compared with observations.Comment: 10 pages, 6 figures, 2 tables, to appear in The Astrophysical Journa

Cosmic Ray Production of Lithium-6 by Structure Formation Shocks in the Early Milky Way: A Fossil Record of Dissipative Processes during Galaxy Formation

While the abundances of Be and B observed in metal-poor halo stars are well explained as resulting from spallation of CNO-enriched cosmic rays (CRs) accelerated by supernova shocks, accounting for the observed $^6$Li in such stars with supernova CRs is more problematic. Here we propose that gravitational shocks induced by infalling and merging sub-Galactic clumps during hierarchical structure formation of the Galaxy should dissipate enough energy at early epochs, and CRs accelerated by such shocks can provide a natural explanation of the observed $^6$Li. In clear constrast to supernovae, structure formation shocks do not eject freshly synthesized CNO nor Fe, so that the only effective production channel at low metallicity is $\alpha-\alpha$ fusion, capable of generating sufficient $^6$Li with no accompanying Be or B and no direct correspondence with Fe. Correlations between the $^6$Li abundance and the kinematic properties of the halo stars may also be expected in this scenario. Further, more extensive observations of $^6$Li in metal-poor halo stars, e.g. by the Subaru HDS or VLT/UVES, may offer us an invaluable fossil record of dissipative dynamical processes which occurred during the formation of our Galaxy.Comment: Ap.J. in press; 6 pages, 1 figur

Light Element Production in the Circumstellar Matter of Energetic Type Ic Supernovae

We investigate energetic type Ic supernovae as production sites for Li6 and Be in the early stages of the Milky Way. Recent observations have revealed that some very metal-poor stars with [Fe/H]<-2.5 possess unexpectedly high abundances of Li6. Some also exbihit enhanced abundances of Be as well as N. From a theoretical point of view, recent studies of the evolution of metal-poor massive stars show that rotation-induced mixing can enrich the outer H and He layers with C, N, and O (CNO) elements, particularly N, and at the same time cause intense mass loss of these layers. Here we consider energetic supernova explosions occurring after the progeniter star has lost all but a small fraction of the He layer. The fastest portion of the supernova ejecta can interact directly with the circumstellar matter (CSM), both composed of He and CNO, and induce light element production through spallation and He-He fusion reactions. The CSM should be sufficiently thick to energetic particles so that the interactions terminate within its innermost regions. We calculate the resulting Li6/O and Be9/O ratios in the ejecta+CSM material out of which the very metal-poor stars may form. We find that they are consistent with the observed values if the mass of the He layer remaining on the pre-explosion core is 0.01-0.1 solar mass, and the mass fraction of N mixed in the He layer is about 0.01. Further observations of Li6, Be and N at low metallicity should provide critical tests of this production scenario.Comment: 12 pages, 2 figures, revised with referee suggestions, final version accepted in ApJ Letter

The Revival of Galactic Cosmic Ray Nucleosynthesis?

Because of the roughly linear correlation between Be/H and Fe/H in low metallicity halo stars, it has been argued that a ``primary'' component in the nucleosynthesis of Be must be present in addition to the ``secondary'' component from standard Galactic cosmic ray nucleosynthesis. In this paper we critically re-evaluate the evidence for the primary versus secondary character of Li, Be, and B evolution, analyzing both in the observations and in Galactic chemical evolution models. While it appears that [Be/H] versus [Fe/H] has a logarithmic slope near 1, it is rather the Be-O trend that directly arises from the physics of spallation production. Using new abundances for oxygen in halo stars based on UV OH lines, we find that the Be-O slope has a large uncertainty due to systematic effects, rendering it difficult to distinguish from the data between the secondary slope of 2 and the primary slope of 1. The possible difference between the Be-Fe and Be-O slopes is a consequence of the variation in O/Fe versus Fe: recent data suggests a negative slope rather than zero (i.e., Fe $\propto$ O) as is often assumed. In addition to a phenomenological analysis of Be and B evolution, we have also examined the predicted LiBeB, O, and Fe trends in Galactic chemical evolution models which include outflow. Based on our results, it is possible that a good fit to the LiBeB evolution requires only traditional the Galactic cosmic ray spallation, and the (primary) neutrino-process contribution to B11. We thus suggest that these two processes might be sufficient to explain Li6, Be, and B evolution in the Galaxy, without the need for an additional primary source of Be and B.Comment: 25 pages, latex, 8 ps figures, figure 1 correcte

O aumento da frequência de salmonella clínica Brasil.

A atividade suinícola é um expoente econômico e cultural que gera renda para famílias de agricultores, emprego direto nas agroindústrias e indireto nas atividades relacionadas, também contribui sobremaneira para o balanço comercial e PIB do país. A manutenção e acesso a mercados exigem a superação de desafios dentre os quais merecem atenção a sustentabilidade das propriedades, o bem estar dos animais, a melhoria da biosseguridade das granjas e o status sanitário do rebanho. O maior obstáculo sanitário deriva do crescente número de animais nos plantéis suinícolas aliado ao reaparecimento de enfermidades de grande impacto na cadeia de produção. Dentre as inúmeras patologias que afetam os suínos, a salmonelose clínica desponta com grande importância nos últimos anos. A contaminação por salmonelas na suinocultura se caracteriza por dois problemas: a presença de sorovares patogênicos, adaptados ao suíno, que provocam gastroenterites e septicemias e a presença de sorovares que não causam doença nos animais, mas são as principais fontes de contaminação das carcaças nos abatedouros e que podem infectar seres humanos. Porém, o foco deste relato é o aumento e caracterização da salmonelose clínica que vem ocorrendo nos últimos anos no Brasil