1,595 research outputs found
Echelle long-slit optical spectroscopy of evolved stars
We present echelle long-slit optical spectra of a sample of objects evolving
off the AGB, most of them in the pre-planetary nebula (pPN) phase, obtained
with the ESI and MIKE spectrographs at Keck-II and Magellan-I, respectively.
The total wavelength range covered with ESI (MIKE) is ~3900 to 10900 A (~3600
to 7200A). In this paper, we focus our analysis mainly on the Halpha profiles.
Prominent Halpha emission is detected in half of the objects, most of which
show broad Halpha wings (up to ~4000 km/s). In the majority of the
Halpha-emission sources, fast, post-AGB winds are revealed by P-Cygni profiles.
In ~37% of the objects Halpha is observed in absorption. In almost all cases,
the absorption profile is partially filled with emission, leading to complex,
structured profiles that are interpreted as an indication of incipient post-AGB
mass-loss. All sources in which Halpha is seen mainly in absorption have F-G
type central stars, whereas sources with intense Halpha emission span a larger
range of spectral types from O to G. Shocks may be an important excitation
agent of the close stellar surroundings for objects with late type central
stars. Sources with pure emission or P Cygni Halpha profiles have larger J-K
color excess than objects with Halpha mainly in absorption, which suggests the
presence of warm dust near the star in the former. The two classes of profile
sources also segregate in the IRAS color-color diagram in a way that intense
Halpha-emitters have dust grains with a larger range of temperatures.
(abridged)Comment: 68 pages, 14 figures, accepted for publication in ApJS (abstract
abridged
Traversable wormholes coupled to nonlinear electrodynamics
In this work we explore the possible existence of static, spherically
symmetric and stationary, axisymmetric traversable wormholes coupled to
nonlinear electrodynamics. Considering static and spherically symmetric (2+1)
and (3+1)-dimensional wormhole spacetimes, we verify the presence of an event
horizon and the non-violation of the null energy condition at the throat. For
the former spacetime, the principle of finiteness is imposed, in order to
obtain regular physical fields at the throat. Next, we analyze the
(2+1)-dimensional stationary and axisymmetric wormhole, and also verify the
presence of an event horizon, rendering the geometry non-traversable.
Relatively to the (3+1)-dimensional stationary and axisymmetric wormhole
geometry, we find that the field equations impose specific conditions that are
incompatible with the properties of wormholes. Thus, we prove the non-existence
of the general class of traversable wormhole solutions, outlined above, within
the context of nonlinear electrodynamics.Comment: 9 pages, Revtex4. V2: major change in title; considerable additions
in the Introduction and in the rotating solution, no physics changes;
correction of a reference, one reference added; now 10 pages. This version to
appear in Classical and Quantum Gravit
Full-Folding Optical Potentials for Elastic Nucleon-Nucleus Scattering based on Realistic Densities
Optical model potentials for elastic nucleon nucleus scattering are
calculated for a number of target nuclides from a full-folding integral of two
different realistic target density matrices together with full off-shell
nucleon-nucleon t-matrices derived from two different Bonn meson exchange
models. Elastic proton and neutron scattering observables calculated from these
full-folding optical potentials are compared to those obtained from `optimum
factorized' approximations in the energy regime between 65 and 400 MeV
projectile energy. The optimum factorized form is found to provide a good
approximation to elastic scattering observables obtained from the full-folding
optical potentials, although the potentials differ somewhat in the structure of
their nonlocality.Comment: 21 pages, LaTeX, 17 postscript figure
Pulsational instability of yellow hypergiants
Instability of population I (X=0.7, Y=0.02) massive stars against radial
oscillations during the post-main sequence gravitational contraction of the
helium core is investigated. Initial stellar masses are in the range from
65M_\odot to 90M_\odot. In hydrodynamic computations of self-exciting stellar
oscillations we assumed that energy transfer in the envelope of the pulsating
star is due to radiative heat conduction and convection. The convective heat
transfer was treated in the framework of the theory of time-dependent turbulent
convection. During evolutionary expansion of outer layers after hydrogen
exhaustion in the stellar core the star is shown to be unstable against radial
oscillations while its effective temperature is Teff > 6700K for
Mzams=65M_\odot and Teff > 7200K for mzams=90M_\odot. Pulsational instability
is due to the \kappa-mechanism in helium ionization zones and at lower
effective temperature oscillations decay because of significantly increasing
convection. The upper limit of the period of radial pulsations on this stage of
evolution does not exceed 200 day. Radial oscillations of the hypergiant resume
during evolutionary contraction of outer layers when the effective temperature
is Teff > 7300K for Mzams=65M_\odot and Teff > 7600K for Mzams=90M_\odot.
Initially radial oscillations are due to instability of the first overtone and
transition to fundamental mode pulsations takes place at higher effective
temperatures (Teff > 7700K for Mzams=65M_\odot and Teff > 8200K for
Mzams=90M_\odot). The upper limit of the period of radial oscillations of
evolving blueward yellow hypergiants does not exceed 130 day. Thus, yellow
hypergiants are stable against radial stellar pulsations during the major part
of their evolutionary stage.Comment: 20 pages, 7 gigures. Accepted for publication in Astronomy Letter
Evaluation of inflammatory cytokine secretion by human alveolar macrophages.
The alveolar macrophage (AM) secretes interleukin 1beta (IL-1beta), tumour necrosis factor-alpha (TNF-alpha), interleukin-6 (IL-6) and interleukin-8 (IL-8), all of them inflammatory cytokines involved in the pathogenesis of many lung diseases. The aim of the present work was to evaluate the basal and stimulated secretion of these cytokines by human AMs. Human AMs were collected by bronchoalveolar lavage (BAL) from four healthy controls and 13 patients with diffuse interstitial lung disease (five cases of sarcoidosis, three of hypersensitivity pneumonitis and five of idiopathic pulmonary fibrosis). AMs were cultured in the presence or absence of different concentrations of lipopolysaccharide (LPS), phorbolmyristate and gamma-interferon. IL-1beta, TNF-alpha, IL-6 and IL-8 levels were measured in BAL fluid and culture supernatant using specific enzyme-linked immunosorbent assays. The substance found to stimulate the secretion of inflammatory cytokines to the greatest extent was LPS at a concentration of 10 microg/ml. Regarding the secretion of IL-1beta, four observations were of interest: basal secretion was very low; LPS exerted a potent stimulatory effect; considerable within-group variability was observed; and there were no significant differences in the comparisons among groups. With respect to TNF-alpha secretion, the results were similar. The only striking finding was the higher basal secretion of this cytokine with respect to that of IL-1beta. Regarding the secretion of IL-6, the same pattern followed by TNF-alpha was found. However, it should be stressed that the increase induced by LPS was smaller than in the two previous cytokines. Regarding the secretion of IL-8, three findings were patent: the strong basal secretion of this cytokine; the moderate increase induced by LPS; and the existence of significant differences among the different groups with respect to the stimulated secretion of this cytokine, which reached maximum values in patients with idiopathic pulmonary fibrosis. Finally, it should be noted that the pattern of cytokines observed in the BAL fluid was similar to that found in cultured AM supernatants. The pattern of inflammatory cytokine secretion by AMs differs from that of other cells of the mononuclear phagocyte system (MPS). In this sense. AMs secrete low amounts of IL-1, moderate amounts of TNF-alpha and IL-6, and high quantities of IL-8. Adherence is an important stimulus in the secretion of these molecules and LPS elicits an increased secretion inverse to the basal secretion. There is considerable individual variability in the secretion of inflammatory cytokines by the AMs of patients with interstitial lung disease and the AMs of these patients are primed in vivo for the secretion of these cytokines. The results of our study, carried out in vitro, can be extrapolated to the in vivo setting
Is the New Mayo Clinic Quadratic Equation Useful for the Estimation of Glomerular Filtration Rate in Type 2 Diabetic Patients?
OBJECTIVE—To test the Mayo Clinic Quadratic (MCQ) equation against isotopic glomerular filtration rate, compared with the Modification of Diet in Renal Disease (MDRD) and the Cockcroft-Gault formulas, in type 2 diabetes
Controle de Orthezia praelonga com o fungo Colletotrichum gloeosporioides isolado Orthezia, na região de Limeira, SP.
A Orthezia praelonga e uma praga encontrada na maioria dos pomares visitados na Região de Limeira. O seu combate tem sido feito através de produtos químicos de pouca eficiência e de efeitos danosos ao ambiente. Tem sido procurado alternativas no seu controle. Testes de eficiência de controle em campo, com uma cepa de Colletotrichum gloeosporioides isolado Orthesia foram realizados em um experimento tomando-se ao acaso 34 plantas de citros com alta infestação, em reboleiras de cinco propriedades na Região de Limeira, das seguintes variedades: Lima, Natal e Pêra (laranjas) e Cravo e Ponkan (tangerinas). Foram amostradas 10 folhas de cada planta em 3 alturas e 4 faces, totalizando 120 folhas por planta. Anotou-se o numero de insetos adultos e a porcentagem da área infestada antes da pulverização com o fungo entomopatogênico C. gloeosporioides numa suspensão de concêntricas 1,34 x 10 6 de esporos por ml na dose de um litro por planta, e após 35, 70 e 100 dias da aplicação. Foi observada uma redução significativa (Teste de Dunnett, 5%) da infestação da praga de 66 a 84% e do numero de insetos de 43 a 82% aos 35 dias. Uma redução da praga de 80 a 96% e do numero de adultos de 85 a 96% aos 70 dias. Após 100 dias da aplicação houve uma leve tendência de reinfestação da praga. Observou-se uma correlação positiva significativa entre a altura da planta e a porcentagem de infestação nas variedades Natal e Cravo. Não houve interação entre a altura e a época de avaliação em todas as variedades
3D-printed structured catalysts for CO methanation reaction: Advancing of gyroid-based geometries
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