1,317 research outputs found
Effect of endurance training on lung function: A one year study
The official published version can be accessed from the link below.Objective: To identify in a follow up study airway changes occurring during the course of a sport season in healthy endurance athletes training in a Mediterranean region.
Methods: Respiratory pattern and function were analysed in 13 healthy endurance trained athletes, either during a maximal exercise test, or at rest and during recovery through respiratory manoeuvres (spirometry and closing volume tests). The exercise test was conducted on three different occasions: during basic endurance training and then during the precompetition and competitive periods.
Results: During the competitive period, a slight but non-clinically significant decrease was found in forced vital capacity (−3.5%, p = 0.0001) and an increase in slope of phase III (+25%, p = 0.0029), both at rest and after exercise. No concomitant reduction in expiratory flow rates was noticed. During maximal exercise there was a tachypnoeic shift over the course of the year (mean (SEM) breathing frequency and tidal volume were respectively 50 (2) cycles/min and 3.13 (0.09) litres during basic endurance training v 55 (3) cycles/min and 2.98 (0.10) litres during the competitive period; p<0.05).
Conclusions: This study does not provide significant evidence of lung function impairment in healthy Mediterranean athletes after one year of endurance training
Mantle formation, coagulation and the origin of cloud/core-shine: II. Comparison with observations
Many dense interstellar clouds are observable in emission in the near-IR,
commonly referred to as "Cloudshine", and in the mid-IR, the so-called
"Coreshine". These C-shine observations have usually been explained with grain
growth but no model has yet been able to self-consistently explain the dust
spectral energy distribution from the near-IR to the submm. We want to
demonstrate the ability of our new core/mantle evolutionary dust model THEMIS
(The Heterogeneous dust Evolution Model at the IaS), which has been shown to be
valid in the far-IR and submm, to reproduce the C-shine observations. Our
starting point is a physically motivated core/mantle dust model. It consists of
3 dust populations: small aromatic-rich carbon grains; bigger core/mantle
grains with mantles of aromatic-rich carbon and cores either made of amorphous
aliphatic-rich carbon or amorphous silicate. We assume an evolutionary path
where these grains, when entering denser regions, may first form a second
aliphatic-rich carbon mantle (coagulation of small grains, accretion of carbon
from the gas phase), second coagulate together to form large aggregates, and
third accrete gas phase molecules coating them with an ice mantle. To compute
the corresponding dust emission and scattering, we use a 3D Monte-Carlo
radiative transfer code. We show that our global evolutionary dust modelling
approach THEMIS allows us to reproduce C-shine observations towards dense
starless clouds. Dust scattering and emission is most sensitive to the cloud
central density and to the steepness of the cloud density profile. Varying
these two parameters leads to changes, which are stronger in the near-IR, in
both the C-shine intensity and profile. With a combination of aliphatic-rich
mantle formation and low-level coagulation into aggregates, we can
self-consistently explain the observed C-shine and far-IR/submm emission
towards dense starless clouds.Comment: Paper accepted for publication in A&A with companion paper "Mantle
formation, coagulation and the origin of cloud/core-shine: I. Dust scattering
and absorption in the IR", A.P Jones, M. Koehler, N. Ysard, E. Dartois, M.
Godard, L. Gavila
Discovery of interstellar mercapto radicals (SH) with the GREAT instrument on SOFIA
We report the first detection of interstellar mercapto radicals, obtained
along the sight-line to the submillimeter continuum source W49N. We have used
the GREAT instrument on SOFIA to observe the 1383 GHz Doublet Pi 3/2 J = 5/2 -
3/2 lambda doublet in the upper sideband of the L1 receiver. The resultant
spectrum reveals SH absorption in material local to W49N, as well as in
foreground gas, unassociated with W49N, that is located along the sight-line.
For the foreground material at velocities in the range 37 - 44 km/s with
respect to the local standard of rest, we infer a total SH column density ~ 2.6
E+12 cm-2, corresponding to an abundance of ~ 7 E-9 relative to H2, and
yielding an SH/H2S abundance ratio ~ 0.13. The observed SH/H2S abundance ratio
is much smaller than that predicted by standard models for the production of SH
and H2S in turbulent dissipation regions and shocks, and suggests that the
endothermic neutral-neutral reaction SH + H2 -> H2S + H must be enhanced along
with the ion-neutral reactions believed to produce CH+ and SH+ in diffuse
molecular clouds.Comment: Accepted for publication in Astronomy and Astrophysics (SOFIA/GREAT
special issue
Sulphur-bearing molecules in diffuse molecular clouds: new results from SOFIA/GREAT and the IRAM 30 m telescope
We have observed five sulphur-bearing molecules in foreground diffuse
molecular clouds lying along the sight-lines to five bright continuum sources.
We have used the GREAT instrument on SOFIA to observe the 1383 GHz transitions of SH towards the star-forming regions W31C,
G29.96-0.02, G34.3+0.1, W49N and W51, detecting foreground absorption towards
all five sources; and the EMIR receivers on the IRAM 30m telescope at Pico
Veleta to detect the HS 1(10)-1(01), CS J=2-1 and SO 3(2)-2(1) transitions.
In nine foreground absorption components detected towards these sources, the
inferred column densities of the four detected molecules showed relatively
constant ratios, with N(SH)/N(HS) in the range 1.1 - 3.0, N(CS)/N(HS)
in the range 0.32 - 0.61, and N(SO)/N(HS) in the range 0.08 - 0.30. The
observed SH/H ratios - in the range (0.5-2.6) - indicate
that SH (and other sulphur-bearing molecules) account for << 1% of the
gas-phase sulphur nuclei. The observed abundances of sulphur-bearing molecules,
however, greatly exceed those predicted by standard models of cold diffuse
molecular clouds, providing further evidence for the enhancement of endothermic
reaction rates by elevated temperatures or ion-neutral drift. We have
considered the observed abundance ratios in the context of shock and turbulent
dissipation region (TDR) models. Using the TDR model, we find that the
turbulent energy available at large scale in the diffuse ISM is sufficient to
explain the observed column densities of SH and CS. Standard shock and TDR
models, however, fail to reproduce the column densities of HS and SO by a
factor of about 10; more elaborate shock models - in which account is taken of
the velocity drift, relative to H, of SH molecules produced by the
dissociative recombination of HS - reduce this discrepancy to a factor
~ 3.Comment: 30 pages, accepted for publication in A&
Spatial distribution of far-infrared rotationally excited CH<sup>+</sup> and OH emission lines in the Orion Bar photodissociation region
Context. The methylidyne cation (CH+) and hydroxyl (OH) are key molecules in the warm interstellar chemistry, but their formation and excitation mechanisms are not well understood. Their abundance and excitation are predicted to be enhanced by the presence of vibrationally excited H2 or hot gas (~500−1000 K) in photodissociation regions (PDRs) with high incident far-ultraviolet (FUV) radiation field. The excitation may also originate in dense gas (>105 cm-3) followed by nonreactive collisions with H2, H, and electrons. Previous observations of the Orion Bar suggest that the rotationally excited CH+ and OH correlate with the excited CO, which is a tracer of dense and warm gas, and that formation pumping contributes to CH+ excitation.Aims. Our goal is to examine the spatial distribution of the rotationally excited CH+ and OH emission lines in the Orion Bar to establish their physical origin and main formation and excitation mechanisms.Methods. We present spatially sampled maps of the CH+ J = 3–2 transition at 119.8 μm and the OH Λ doublet at 84 μm in the Orion Bar over an area of 110″× 110″ with Herschel/PACS. We compare the spatial distribution of these molecules with those of their chemical precursors, C+ , O and H2, and tracers of warm and dense gas (high-
J CO). We assess the spatial variation of the CH+ J = 2–1 velocity-resolved line profile at 1669 GHz with Herschel/HIFI spectrometer observations.Results. The OH and especially CH+ lines correlate well with the high-J CO emission and delineate the warm and dense molecular region at the edge of the Bar. While notably similar, the differences in the CH+ and OH morphologies indicate that CH+ formation and excitation are strongly related to the observed vibrationally excited H2. This, together with the observed broad CH+ line widths, indicates that formation pumping contributes to the excitation of this reactive molecular ion. Interestingly, the peak of the rotationally excited OH 84 μm emission coincides with a bright young object, proplyd 244–440, which shows that OH can be an excellent tracer of UV-irradiated dense gas.Conclusions. The spatial distribution of CH+ and OH revealed in our maps is consistent with previous modeling studies. Both formation pumping and nonreactive collisions in a UV-irradiated dense gas are important CH+ J = 3–2 excitation processes. The excitation of the OH Λ doublet at 84 μm is mainly sensitive to the temperature and density
A milestone toward understanding PDR properties in the extreme environment of LMC-30Dor
More complete knowledge of galaxy evolution requires understanding the
process of star formation and interaction between the interstellar radiation
field and the interstellar medium in galactic environments traversing a wide
range of physical parameter space. Here we focus on the impact of massive star
formation on the surrounding low metallicity ISM in 30 Doradus in the Large
Magellanic Cloud. A low metal abundance, as is the case of some galaxies of the
early universe, results in less ultra-violet shielding for the formation of the
molecular gas necessary for star formation to proceed. The half-solar
metallicity gas in this region is strongly irradiated by the super star cluster
R136, making it an ideal laboratory to study the structure of the ISM in an
extreme environment. Our spatially resolved study investigates the gas heating
and cooling mechanisms, particularly in the photo-dissociation regions where
the chemistry and thermal balance are regulated by far-ultraviolet photons (6
eV< h\nu <13.6 eV).
We present Herschel observations of far-infrared fine-structure lines
obtained with PACS and SPIRE/FTS. We have combined atomic fine-structure lines
from Herschel and Spitzer observations with ground-based CO data to provide
diagnostics on the properties and the structure of the gas by modeling it with
the Meudon PDR code. We derive the spatial distribution of the radiation field,
the pressure, the size, and the filling factor of the photodissociated gas and
molecular clouds. We find a range of pressure of ~ 10^5 - 1.7x10^6 cm^{-3} K
and a range of incident radiation field G_UV ~ 10^2 - 2.5x10^4 through PDR
modeling. Assuming a plane-parallel geometry and a uniform medium, we find a
total extinction of 1-3 mag , which correspond to a PDR cloud size of 0.2 to
3pc, with small CO depth scale of 0.06 to 0.5pc. We also determine the three
dimensional structure of the gas. (Abridged)Comment: 20 pages, 23 figures, accepted in A&
Ligurian pyroxenite-peridotite sequences (Italy) and the role of melt-rock reaction in creating enriched-MORB mantle sources
Deep melt intrusion and melt-peridotite interaction may introduce small-scale heterogeneity in the MORB mantle. These processes generate pyroxenite-bearing veined mantle that represent potential mantle sources of oceanic basalts. Natural proxies of such veined mantle are very rare and our understanding of mechanisms governing the chemical modification of mantle peridotite by MORB-type pyroxenite emplacement is very limited. We report the results of detailed spatially-controlled chemical profiles in pyroxenite-peridotite associations from the Northern Apennine ophiolitic mantle sequences (External Liguride Units, Italy), and investigate the extent and mechanism driving the local modification of peridotite by the interaction with pyroxenite-derived melt. Pyroxenites occur as cm-thick layers parallel to mantle tectonite foliation and show diffuse orthopyroxene-rich reaction rims along the pyroxenite-peridotite contact. Relative to distal unmodified peridotites, wall-rock peridotites show i) modal orthopyroxene enrichment at the expense of olivine, ii) higher Al, Ca, Si contents and slightly lower XMg, iii) Al-richer spinel and lower-XMg pyroxenes. Clinopyroxenes from wall-rock peridotites exhibit variable LREE-MREE fractionation, always resulting in SmN/NdN ratios lower than distal peridotites. From the contact with pyroxenite layers, peridotite clinopyroxenes record a REE compositional gradient up to about 15\u202fcm marked by an overall REE increase away from the pyroxenite. Beyond 15\u202fcm, and up to 23\u202fcm, the MREE and HREE content decreases while the LREEs remain at nearly constant abundances. This REE gradient is well reproduced by a two-step numerical simulation of reactive melt percolation assuming variable amounts of olivine assimilation and pyroxene crystallization. Percolative reactive flow at decreasing melt mass and rather high instantaneous melt/peridotite ratio (initial porosity of 30%), combined with high extents of fractional crystallization (i.e. relatively low Ma/Mc ratio), accounts for the overall REE enrichment in the first 15\u202fcm. Change of melt-rock reaction regime, mostly determined by the drastic decrease of porosity (\u3a6i\u202f=\u202f0.01) due to increasing crystallization rates, results in more efficient chemical buffering of the host peridotite on the HREE composition of the differentiated liquids through ion-exchange chromatographic-type processes, determining the observed increase of the LREE/HREE ratio. Emplacement of thin (cm-sized) pyroxenite veins by deep melt infiltration is able to metasomatize a much larger volume of the host peridotite. Hybrid mantle domains made by pyroxenite, metasomatized peridotite and unmodified peridotite potentially represent mantle sources of E-MORB. Results of this work stress the key role of melt-peridotite reactions in modifying the upwelling mantle prior to oceanic basalts production
Mantle formation, coagulation and the origin of cloud/core shine: I. Modelling dust scattering and absorption in the infra-red
Context. The observed cloudshine and coreshine (C-shine) have been explained
in terms of grain growth leading to enhanced scatter- ing from clouds in the J,
H and K photometric bands and the Spitzer IRAC 3.6 and 4.5 {\mu}m bands. Aims.
Using our global dust modelling approach THEMIS (The Heterogeneous dust
Evolution Model at the IaS) we explore the effects of dust evolution in dense
clouds, through aliphatic-rich carbonaceous mantle formation and grain-grain
coagulation. Methods. We model the effects of wide band gap a-C:H mantle
formation and the low-level aggregation of diffuse interstellar medium dust in
the moderately-extinguished outer regions of molecular clouds. Results. The
formation of wide band gap a-C:H mantles on amorphous silicate and amorphous
carbon (a-C) grains leads to a decrease in their absorption cross-sections but
no change in their scattering cross-sections at near-IR wavelengths, resulting
in higher albedos. Conclusions. The evolution of dust, with increasing density
and extinction in the diffuse to dense molecular cloud transition, through
mantle formation and grain aggregation, appears to be a likely explanation for
the observed C-shine.Comment: 12 pages, 15 figures, accepted for publication in A&A along with the
companion paper entitled, Mantle formation, coagulation and the origin of
cloud/core shine: II Comparison with observations, by Ysard et al. (also
accepted for publication in A&A
Shock excitation of H in the James Webb Space Telescope era
(Abridged) H2 is the most abundant molecule in the Universe. Thanks to its
widely spaced energy levels, it predominantly lights up in warm gas, T > 100 K,
such as shocked regions, and it is one of the key targets of JWST observations.
These include shocks from protostellar outflows, all the way up to starburst
galaxies and AGN. Shock models are able to simulate H2 emission. We aim to
explore H2 excitation using such models, and to test over which parameter space
distinct signatures are produced in H2 emission. We present simulated H2
emission using the Paris-Durham shock code over an extensive grid of 14,000
plane-parallel stationary shock models, a large subset of which are exposed to
an external UV radiation field. The grid samples 6 input parameters: preshock
density, shock velocity, transverse magnetic field strength, UV radiation field
strength, cosmic-ray-ionization rate, and PAH abundance. Physical quantities,
such as temperature, density, and width, have been extracted along with H2
integrated line intensities. The strength of the transverse magnetic field, set
by the scaling factor, b, plays a key role in the excitation of H2. At low
values of b (<~ 0.3, J-type shocks), H2 excitation is dominated by
vibrationally excited lines; at higher values (b >~ 1, C-type shocks),
rotational lines dominate the spectrum for shocks with an external radiation
field comparable to (or lower than) the solar neighborhood. Shocks with b >= 1
can be spatially resolved with JWST for nearby objects. When the input kinetic
energy flux increases, the excitation and integrated intensity of H2 increases
similarly. An external UV field mainly serves to increase the excitation,
particularly for shocks where the input radiation energy is comparable to the
input kinetic energy flux. These results provide an overview of the energetic
reprocessing of input kinetic energy flux and the resulting H2 line emission.Comment: Published in A&
Low-velocity shocks: signatures of turbulent dissipation in diffuse irradiated gas
Context. Large-scale motions in galaxies (supernovae explosions, galaxy collisions, galactic shear etc.) generate turbulence, which allows a fraction of the available kinetic energy to cascade down to small scales before it is dissipated.
Aims. We establish and quantify the diagnostics of turbulent dissipation in mildly irradiated diffuse gas in the specific context of shock structures.
Methods. We incorporated the basic physics of photon-dominated regions into a state-of-the-art steady-state shock code. We examined the chemical and emission properties of mildly irradiated (G_0 = 1) magnetised shocks in diffuse media (n_H = 10^2 to 10^4 cm^(-3)) at low- to moderate velocities (from 3 to 40 km s^(-1)).
Results. The formation of some molecules relies on endoergic reactions. Their abundances in J-type shocks are enhanced by several orders of magnitude for shock velocities as low as 7 km s^(-1). Otherwise most chemical properties of J-type shocks vary over less than an order of magnitude between velocities from about 7 to about 30 km s^(-1), where H_2 dissociation sets in. C-type shocks display a more gradual molecular enhancement with increasing shock velocity.
We quantified the energy flux budget (fluxes of kinetic, radiated and magnetic energies) with emphasis on the main cooling lines of the cold interstellar medium. Their sensitivity to shock velocity is such that it allows observations to constrain statistical distributions of shock velocities.
We fitted various probability distribution functions (PDFs) of shock velocities to spectroscopic observations of the galaxy-wide shock in Stephan’s Quintet and of a Galactic line of sight which samples diffuse molecular gas in Chamaeleon. In both cases, low velocities bear the greatest statistical weight and the PDF is consistent with a bimodal distribution. In the very low velocity shocks (below 5 km s^(-1)), dissipation is due to ion-neutral friction and it powers H_2 low-energy transitions and atomic lines. In moderate velocity shocks (20 km s^(-1) and above), the dissipation is due to viscous heating and accounts for most of the molecular emission. In our interpretation a significant fraction of the gas in the line of sight is shocked (from 4% to 66%). For example, C^+ emission may trace shocks in UV irradiated gas where C^+ is the dominant carbon species.
Conclusions. Low- and moderate velocity shocks are important in shaping the chemical composition and excitation state of the interstellar gas. This allows one to probe the statistical distribution of shock velocities in interstellar turbulence
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