9,121 research outputs found
AGB and SAGB stars: modelling dust production at solar metallicity
We present dust yields for asymptotic giant branch (AGB) and
super--asymptotic giant branch (SAGB) stars of solar metallicity. Stars with
initial mass reach the carbon
star stage during the AGB phase and produce mainly solid carbon and SiC. The
size and the amount of the carbon particles formed follows a positive trend
with themass of the star; the carbon grains with the largest size (m) are produced by AGB stars with ,
as these stars are those achieving the largest enrichment of carbon in the
surface regions. The size of SiC grains, being sensitive to the surface silicon
abundance, keeps around m. The mass of carbonaceous
dust formed is in the range , whereas the
amount of SiC produced is . Massive
AGB/SAGB stars with experience HBB, that inhibits
formation of carbon stars. The most relevant dust species formed in these stars
are silicates and alumina dust, with grain sizes in the range m and m, respectively. The
mass of silicates produced spans the interval and increases with the initial
mass of the star.Comment: Accepted for publication in MNRA
Dynamic density functional study of a driven colloidal particle in polymer solutions
The Dynamic Density Functional (DDF) theory and standard Brownian dynamics
simulations (BDS) are used to study the drifting effects of a colloidal
particle in a polymer solution, both for ideal and interacting polymers. The
structure of the stationary density distributions and the total induced current
are analyzed for different drifting rates. We find good agreement with the BDS,
which gives support to the assumptions of the DDF theory. The qualitative
aspect of the density distribution are discussed and compared to recent results
for driven colloids in one-dimensional channels and to analytical expansions
for the ideal solution limit
Biogeochemical processes in sediments of the Manfredonia Gulf (Southern Adriatic Sea): early diagenesis of carbon and nutrient and benthic exchange
In order to understand the mechanisms responsible of the recycle of carbon and nutrients at the sediment-water interface and to understand the role of sediments in nutrients mass balance in coastal water, cores were collected (pore waters and solid phases) and benthic fluxes (oxygen, dissolved nutrients, dissolved iron and manganese, alkalinity and TCO2) were measured in two stations in the Gulf of Manfredonia (Southern Adriatic Sea). Stations were chosen to include a site, in the offshore part of the gulf, under the influence of western Adriatic current and another site, in the inner part of the gulf, under influence of gyres occurring inside the gulf. Both stations were placed in areas characterized by high sedimentation rate. Fluxes at sediment water interface show higher values in S2 site during the summer. Bio-irrigation seems to be the main transport mechanism characterizing both sites, with more evident effects during summer in S1 site
Spatial and temporal biochemical variation in the Norther Adriatic Sea during summer 2001
Nel giugno e nel settembre del 2001 sono state effettuate due crociere oceanografiche nel nord Adriatico, da Numana (An) a Chioggia (Ve), dall\u27Italia alla Croazia, con misurazioni di temperatura, salinit?, fluorescenza, irradianza, ossigeno disciolto e nutrienti. Nel lavoro vengono posti in relazione tra loro l\u27ossigeno disciolto, la fluorescenza, i nutrienti, l\u27irradianza e le portate del Po, con lo scopo di osservare le loro variazioni biochimiche nello spazio e nel tempo. Dallo studio risulta che gli inputs del Po e l\u27irradianza sono fattori importanti nella distribuzione della clorofilla a e dell\u27ossigeno disciolto in superficie, e che i processi di mineralizzazione determinano una marcata ipossia in un\u27ampia area al largo della foce del Po.Nel giugno e nel settembre del 2001 sono state effettuate due crociere oceanografiche nel nord Adriatico, da Numana (An) a Chioggia (Ve), dall\u27Italia alla Croazia, con misurazioni di temperatura, salinit?, fluorescenza, irradianza, ossigeno disciolto e nutrienti. Nel lavoro vengono posti in relazione tra loro l\u27ossigeno disciolto, la fluorescenza, i nutrienti, l\u27irradianza e le portate del Po, con lo scopo di osservare le loro variazioni biochimiche nello spazio e nel tempo. Dallo studio risulta che gli inputs del Po e l\u27irradianza sono fattori importanti nella distribuzione della clorofilla a e dell\u27ossigeno disciolto in superficie, e che i processi di mineralizzazione determinano una marcata ipossia in un\u27ampia area al largo della foce del Po
Maturity related differences in body composition assessed by classic and specific bioimpedance vector analysis among male elite youth soccer players
The aim of this study was to analyze the efficiency of classic and specific bioelectrical impedance vector analysis (BIVA) in the assessment of maturity related differences in body composition among male elite youth soccer players, and to provide bioelectrical impedance reference data for this category. A group of 178 players (aged 12.1 \ub1 1.6 years) were registered in a professional Italian soccer team participating in the first division (Serie A). They were divided into three groups according to their maturity status while bioelectrical resistance and reactance were obtained. The classic and specific BIVA procedures were applied, which correct bioelectrical values for body height and body geometry, respectively. Percentage of fat mass (FM%) and total body water (TBW (L)) were estimated from bioelectrical values. Age-specific z-scores of the predicted age at peak height velocity identified 29 players as earlier-, 126 as on time-, and 23 as later-maturing. TBW was higher (p < 0.01) in adolescents classified as \u201cearly\u201d maturity status compared to the other two groups and classic BIVA confirmed these results. Conversely, no differences in FM% were found among the groups. Specific vector length showed a higher correlation (r = 0.748) with FM% compared with the classic approach (r = 0.493). Classic vector length showed a stronger association (r = 120.955) with TBW compared with specific (r = 120.263). Specific BIVA turns out to be accurate for the analysis of FM% in athletes, while classic BIVA shows to be a valid approach to evaluate TBW. An original data set of bioelectric impedance reference values of male elite youth soccer players was provided
The middle-southern Adriatic basin in February 1999: the chemical and physical characteristics of the water column.
In the Southern Adriatic depression nitrogen and phosphorous salts are concentrated in the bottom water. The Redfield ratio, same 29, is higher at Pomo and D transect, mostly on the bottom, because phosphorous is limiting and nitrogen is abundant. Northern waters influence this southern area, together with surface and intermediate waters coming from Ionian sea, and western shelf waters which tend to sink to the bottom. Key-words: Adriatic Sea, thermohaline characteristics, nutrient salts, Redfield rati
Vibrational spectrum of solid picene (C_22H_14)
Recently, Mitsuhashi et al., have observed superconductivity with transition
temperature up to 18 K in potassium doped picene (C22H14), a polycyclic
aromatic hydrocarbon compound [Nature 464 (2010) 76]. Theoretical analysis
indicate the importance of electron-phonon coupling in the superconducting
mechanisms of these systems, with different emphasis on inter- and
intra-molecular vibrations, depending on the approximations used. Here we
present a combined experimental and ab-initio study of the Raman and infrared
spectrum of undoped solid picene, which allows us to unanbiguously assign the
vibrational modes. This combined study enables the identification of the modes
which couple strongly to electrons and hence can play an important role in the
superconducting properties of the doped samples
An insight into Capella (alpha Aurigae): from the extent of core overshoot to its evolutionary history
The binary star alpha Aurigae (otherwise known as Capella) is extremely
important to understand the core hydrogen and helium burning phases of the
stars, as the primary star is likely evolving through the core helium burning
phase, and the masses of the two components are 2.5 Msun and 2.6 Msun, which
fall into a mass range for which the extention of the core overshoot during the
main sequence phase is uncertain. We aim at deriving the extent of the core
overshoot experienced during the core burning phases and testing the efficiency
of the convective transport of energy in the external envelope, by comparing
results from stellar evolution modelling with the results from the
observations. We consider evolutionary tracks calculated on purpose for the
present work, for the primary and secondary star of Capella. We determine the
extent of the extra-mixing from the core during the main sequence evolution and
the age of the system, by requiring that the effective temperatures and surface
gravities of the model stars reproduce those derived from the observations at
the same epoch. We further check consistency between the observed and predicted
surface chemistry of the stars. Consistency between results from stellar
evolution modelling and the observations of Capella is found when extra-mixing
from the core is assumed, the extent of the extra-mixed zone being of the order
of 0.25 H_P. The age of the system is estimated to be 710 Myr. These results
allow to nicely reproduce the observed surface chemistry, particularly the
recent determination of the 12C/13C ratio based on LBT (Large Binocular
Telescope) and VATT (Vatican Advanced Technology Telescope) observation
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