856 research outputs found
New sub-millimeter heterodyne observations of CO and HCN in Titan's atmosphere with the APEX Swedish Heterodyne Facility Instrument
The origin of the atmosphere of the largest moon of Saturn, Titan, is poorly
understood and its chemistry is rather complicated. Ground-based
millimeter/sub-millimeter heterodyne spectroscopy resolves line shapes
sufficiently to determine information in Titan's atmospheric composition (on
vertical profiles and isotopic ratios). We test the capabilities of the Swedish
Heterodyne Facility Instrument (SHFI), Receiver APEX-1, together with the
Atacama Pathfinder EXperiment APEX 12-m telescope for Titan's atmospheric
observations. In particular we present sub-millimeter observations of the
CO(2-1) and HCN(3-2) lines of the Titan stratosphere with APEX, and with SHFI
taken during the Science Verification (SV) instrument phase on March and June
2008. With the help of appropriate radiative transfer calculations we
investigate the possibility to constrain the chemical concentrations and
optimize the performance of the APEX-1 instrument for inferring vertical
profiles of molecular components of the atmosphere of Titan.Comment: 13 pages, 5 figures, to appear in Advances in Geosciences (a refereed
publication of papers presented at Asia Oceanic Geophysical Society 6th
annual meeting 2009 in Singapore, a publication of World Scientific
Publication Company
HHSMT Observations of the Venusian Mesospheric Temperature, Winds, and CO abundance around the MESSENGER Flyby
We present submillimeter observations of 12CO J=3-2 and J=2-1, and 13CO J =
2-1 lines of the Venusian mesosphere and lower thermosphere with the Heinrich
Hertz Submillimeter Telescope (HHSMT) taken around the second MESSENGER flyby
of Venus on 5 June 2007. The observations cover a range of Venus solar
elongations with different fractional disk illuminations. Preliminary results
like temperature and CO abundance profiles are presented.These data are part of
a coordinated observational campaign in support of the ESA Venus Express
mission. Furthermore, this study attempts to contribute to cross-calibrate
space- and ground-based observations, to constrain radiative transfer and
retrieval algorithms for planetary atmospheres, and to a more thorough
understanding of the global patters of circulation of the Venusian atmosphere.Comment: 12 pages, 8 figures. Latex, uses elsart.cls (included). Higher
resolution figures in original article. Planetary and Space Science, in pres
Modeling of the Terminal Velocities of the Dust Ejected Material by the Impact
We compute the distribution of velocities of the particles ejected by the
impact of the projectile released from NASA Deep Impact spacecraft on the
nucleus of comet 9P/Tempel 1 on the successive 20 hours following the
collision. This is performed by the development and use of an ill-conditioned
inverse problem approach, whose main ingredients are a set of observations
taken by the Narrow Angle Camera (NAC) of OSIRIS onboard the Rosetta
spacecraft, and a set of simple models of the expansion of the dust ejecta
plume for different velocities. Terminal velocities are derived using a maximum
likelihood estimator.
We compare our results with published estimates of the expansion velocity of
the dust cloud. Our approach and models reproduce well the velocity
distribution of the ejected particles. We consider these successful comparisons
of the velocities as an evidence for the appropriateness of the approach. This
analysis provides a more thorough understanding of the properties of the Deep
Impact dust cloud.Comment: Comments: 6 pages, 2 Postscript figures, To appear in the proceedings
of "Deep Impact as a World Observatory Event - Synergies in Space, Time", ed.
Hans Ulrich Kaeufl and Chris Sterken, Springer-Verla
Hot carrier and hot phonon coupling during ultrafast relaxation of photoexcited electrons in graphene
We study, by means of a Monte Carlo simulator, the hot phonon effect on the
relaxation dynamics in photoexcited graphene and its quantitative impact as
compared to considering an equilibrium phonon distribution. Our multi-particle
approach indicates that neglecting the hot phonon effect significantly
underestimates the relaxation times in photoexcited graphene. The hot phonon
effect is more important for a higher energy of the excitation pulse and
photocarrier densities between and .
Acoustic intervalley phonons play a non-negligible role, and emitted phonons
with wavelengths limited up by a maximum (determined by the carrier
concentration) induce a slower carrier cooling rate. Intrinsic phonon heating
is damped in graphene on a substrate due to additional cooling pathways, with
the hot phonon effect showing a strong inverse dependence with the carrier
density.Comment: 12 pages, 5 figure
Early stages of LDL oxidation: apolipoprotein B structural changes monitored by infrared spectroscopy.
Changes in the conformation of apoliprotein B-100 in the early stages of copper-mediated low density lipoprotein oxidation have been monitored by infrared spectroscopy. During the lag phase no variation in structure is observed, indicating that copper binding to the protein does not significantly affect its structure. In the propagation phase, while hydroperoxides are formed but the protein is not modified, no changes in secondary structure are observed, but the thermal profile of the band corresponding to alpha-helix is displaced in frequency, indicating changes in tertiary structure associated with this conformation but not with beta-sheet components. When aldehyde formation starts, a decrease of approximately 3% in the area of bands corresponding to alpha-helix and beta-sheet is produced, concomitantly with an increase in beta-turns and unordered structure. The two bands corresponding to beta-turns vary as well under these conditions, indicating changes in these structures. Also at this stage the thermal profile shows variations in frequency for the bands corresponding to both alpha-helix and beta-sheet.The results are consistent with the hypothesis that as soon as the polyunsaturated fatty acids from the particle core are modified, this change is reflected at the surface, in the alpha-helical components contacting the monolayer.Fil: Chehin, Rosana Nieves. Consejo Superior de Investigaciones CientÃficas; España. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico Conicet - Tucumán. Instituto Superior de Investigaciones Biológicas. Universidad Nacional de Tucumán. Instituto Superior de Investigaciones Biológicas; Argentina. Universidad del PaÃs Vasco; EspañaFil: Rengel, David. Consejo Superior de Investigaciones CientÃficas; España. Universidad del PaÃs Vasco; EspañaFil: Milicua, José Carlos G.. Universidad del PaÃs Vasco; España. Consejo Superior de Investigaciones CientÃficas; EspañaFil: Goñi, Félix M.. Universidad del PaÃs Vasco; España. Consejo Superior de Investigaciones CientÃficas; EspañaFil: Arrondo JL. Consejo Superior de Investigaciones CientÃficas; España. Universidad del PaÃs Vasco; EspañaFil: Pifat, Greta. Rudjer BoÅ¡ković Institute; Croaci
Submillimetric spectroscopic observations of volatiles in comet C/2004 Q2 (Machholz)
We aim to determine the production rates of several parent and product
volatiles and the 12C/13C isotopic carbon ratio in the long-period comet C/2004
Q2 (Machholz), which is likely to originate from the Oort Cloud. The line
emission from several molecules in the coma was measured with high
signal-to-noise ratio in January 2005 at heliocentric distance of 1.2 AU by
means of high-resolution spectroscopic observations using the Submillimeter
Telescope (SMT). We have obtained production rates of several volatiles (CH3OH,
HCN, H13CN, HNC, H2CO, CO and CS) by comparing the observed and simulated
line-integrated intensities. Furthermore, multiline observations of the CH3OH
(7-6) series allow us to estimate the rotational temperature using the rotation
diagram technique. We find that the CH3OH population distribution of the levels
sampled by these lines can be described by a rotational temperature of 40 \pm 3
K. Derived mixing ratios relative to hydrogen cyanide are
CO/CH3OH/H2CO/CS/HNC/H13CN/HCN = 30.9/24.6/4.8/0.57/0.031/0.013/1 assuming a
pointing offset of 8" due to the uncertain ephemeris at the time of the
observations and the telescope pointing error. The measured relative molecular
abundances in C/2004 Q2 (Machholz) are between low- to typical values of those
obtained in Oort Cloud comets, suggesting that it has visited the inner solar
system previously and undergone thermal processing. The HNC/HCN abundance ratio
of ~3.1% is comparable to that found in other comets, accounting for the
dependence on the heliocentric distance, and could possibly be explained by
ion-molecule chemical processes in the low-temperature atmosphere. From a
tentative H13CN detection, the measured value of 97 \pm 30 for the H12CN/H13CN
isotopologue pair is consistent with a telluric value.Comment: 14 pages with 11 figures, abridged abstrac
Stellar impact on disequilibrium chemistry and on observed spectra of hot Jupiter atmospheres
In this work we study the effect of disequilibrium processes on mixing ratio
profiles of neutral species and on the simulated spectra of a hot Jupiter
exoplanet that orbits stars of different spectral types. We also address the
impact of stellar activity that should be present to a different degree in all
stars with convective envelopes. We used the VULCAN chemical kinetic code to
compute number densities of species. The temperature-pressure profile of the
atmosphere was computed with the HELIOS code. We also utilized the -ReX
forward model to predict the spectra of planets in primary and secondary
eclipses. In order to account for the stellar activity we made use of the
observed solar XUV spectrum taken from Virtual Planetary Laboratory (VPL) as a
proxy for an active sun-like star. We find large changes in mixing ratios of
most chemical species in planets orbiting A-type stars that radiate strong XUV
flux inducing a very effective photodissociation. For some species, these
changes can propagate very deep into the planetary atmosphere to pressures of
around 1 bar. To observe disequilibrium chemistry we favor hot Jupiters with
temperatures Teq=1000 K and ultra-hot Jupiters with Teq=3000$ K that also have
temperature inversion in their atmospheres. On the other hand, disequilibrium
calculations predict little changes in spectra of planets with intermediate
temperatures. We also show that stellar activity similar to the one of the
modern Sun drives important changes in mixing ratio profiles of atmospheric
species. However, these changes take place at very high atmospheric altitudes
and thus do not affect predicted spectra. We estimate that the effect of
disequilibrium chemistry in planets orbiting nearby bright stars could be
robustly detected and studied with future missions with spectroscopic
capabilities in infrared such as, e.g., JWST and ARIEL.Comment: 17 pages, 12 figure
Estratégia competitiva de uma multinacional estrangeira na avicultura de postura no Brasil.
Este estudo aborda a questão das estratégias envolvidas no processo de importação de gaiolas para aves de postura, direcionadas ao centro de distribuição de uma multinacional estrangeira localizada em Araraquara, São Paulo. Identifica as razões que levam uma empresa multinacional a aumentar seus investimentos no Brasil, onde está implantando um centro de distribuição (CD). Para estudar as estratégias envolvidas no processo, realizou-se pesquisa exploratória sobre o atual processo logÃstico da empresa, buscando identificar tais estratégias e as vantagens do novo processo. O trabalho apoia-se nas cinco forças competitivas de Porter, na análise SWOT, nas estratégias genéricas adotadas para obtenção de retorno sobre os investimentos e ainda, fundamenta-se em temas como, importação, logÃstica, armazenagem e centro de distribuição. A pesquisa demonstra que a implantação do CD envolve a estratégia de inserção do produto no mercado nacional, especificamente em São Paulo, onde está o maior mercado de aves de postura do PaÃs. Para obter vantagem competitiva, a multinacional adota ainda a estratégia genérica da diferenciação, com foco em tecnologia e qualidade do produto. Apesar dos altos custos da construção e manutenção do CD representarem uma barreira de entrada no mercado, o investimento não representa risco financeiro, já que aumentará a demanda pelo produto, resultando maior retorno sobre o capital investido
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