Dynamic arterial elastance (Eadyn), the relationship between pulse pressure variation (PPV) and stroke volume variation (SVV), has been suggested as a functional assessment of arterial load. The aim ...of this study was to evaluate the impact of arterial load changes during acute pharmacological changes, fluid administration, and haemorrhage on Eadyn.
Eighteen anaesthetized, mechanically ventilated New Zealand rabbits were studied. Arterial load changes were induced by phenylephrine (n=9) or nitroprusside (n=9). Thereafter, animals received a fluid bolus (10 ml kg−1), followed by stepwise bleeding (blood loss: 15 ml kg−1). The influence of arterial load and cardiac variables on PPV, SVV, and Eadyn was analysed using a linear mixed-effects model analysis.
After phenylephrine infusion, mean (sd) Eadyn decreased from 0.89 (0.14) to 0.49 (0.12), P<0.001; whereas after administration of nitroprusside, Eadyn increased from 0.80 (0.23) to 1.28 (0.21), P<0.0001. Overall, the fluid bolus decreased Eadyn from 0.89 (0.44) to 0.73 (0.35); P<0.01, and haemorrhage increased it from 0.78 (0.23) to 0.95 (0.26), P=0.03. Both PPV and SVV were associated with similar arterial factors (effective arterial elastance, arterial compliance, and resistance) and heart rate. Furthermore, PPV was also related to the acceleration and peak velocity of aortic blood flow. Both arterial and cardiac factors contributed to the evolution of Eadyn throughout the experiment.
Acute modifications of arterial load induced significant changes on Eadyn; vasodilatation increased Eadyn, whereas vasoconstriction decreased it. The Eadyn was associated with both arterial load and cardiac factors, suggesting that Eadyn should be more properly considered as a ventriculo-arterial coupling index.
ABSTRACT
The evolution of molecular clouds in galactic centres is thought to differ from that in galactic discs due to a significant influence of the external gravitational potential. We present a ...set of numerical simulations of molecular clouds orbiting on the 100-pc stream of the Central Molecular Zone (the central ${\sim }500\,{{\rm pc}}$ of the Galaxy) and characterize their morphological and kinematic evolution in response to the background potential and eccentric orbital motion. We find that the clouds are shaped by strong shear and torques, by tidal and geometric deformation, and by their passage through the orbital pericentre. Within our simulations, these mechanisms control cloud sizes, aspect ratios, position angles, filamentary structure, column densities, velocity dispersions, line-of-sight velocity gradients, spin angular momenta, and kinematic complexity. By comparing these predictions to observations of clouds on the Galactic Centre ‘dust ridge’, we find that our simulations naturally reproduce a broad range of key observed morphological and kinematic features, which can be explained in terms of well-understood physical mechanisms. We argue that the accretion of gas clouds on to the central regions of galaxies, where the rotation curve turns over and the tidal field is fully compressive, is accompanied by transformative dynamical changes to the clouds, leading to collapse and star formation. This can generate an evolutionary progression of cloud collapse with a common starting point, which either marks the time of accretion on to the tidally compressive region or of the most recent pericentre passage. Together, these processes may naturally produce the synchronized starbursts observed in numerous (extra)galactic nuclei.
Chasing discs around O-type (proto)stars Maud, L. T.; Cesaroni, R.; Kumar, M. S. N. ...
Astronomy and astrophysics (Berlin),
12/2018, Letnik:
620
Journal Article
Recenzirano
Odprti dostop
We present high angular resolution (~0.2″) continuum and molecular emission line Atacama Large Millimeter/sub-millimeter Array (ALMA) observations of G17.64+0.16 in Band 6 (220−230 GHz) taken as part ...of a campaign in search of circumstellar discs around (proto)-O-stars. At a resolution of ~400 au the main continuum core is essentially unresolved and isolated from other strong and compact emission peaks. We detect SiO (5–4) emission that is marginally resolved and elongated in a direction perpendicular to the large-scale outflow seen in the 13 CO (2−1) line using the main ALMA array in conjunction with the Atacama Compact Array (ACA). Morphologically, the SiO appearsto represent a disc-like structure. Using parametric models we show that the position-velocity profile of the SiO is consistent with the Keplerian rotation of a disc around an object between 10 and 30 M⊙ in mass, only if there is also radial expansion from a separate structure. The radial motion component can be interpreted as a disc wind from the disc surface. Models with a central stellar object mass between 20 and 30 M⊙ are the most consistent with the stellar luminosity (1 × 105 L⊙) and indicative of an O-type star. The H30α millimetre recombination line (231.9 GHz) is also detected, but spatially unresolved, and is indicative of a very compact, hot, ionised region co-spatial with the dust continuum core. The broad line-width of the H30α emission (full-width-half-maximum = 81.9 km s−1) is not dominated by pressure-broadening but is consistent with underlying bulk motions. These velocities match those required for shocks to release silicon from dust grains into the gas phase. CH3 CN and CH3 OH thermal emission also shows two arc shaped plumes that curve away from the disc plane. Their coincidence with OH maser emission suggests that they could trace the inner working surfaces of a wide-angle wind driven by G17.64 which impacts the diffuse remnant natal cloud before being redirected into the large-scale outflow direction. Accounting for all observables, we suggest that G17.64 is consistent with a O-type young stellar object in the final stages of protostellar assembly, driving a wind, but that has not yet developed into a compact H II region. The existance and detection of the disc in G17.64 is likely related to its isolated and possibly more evolved nature, traits which may underpin discs in similar sources.
We present the highest angular resolution (∼20 × 15 mas–44 × 33 au) Atacama Large Millimeter/sub-millimeter Array (ALMA) observations that are currently possible of the proto-O-star G17.64+0.16 in ...Band 6. The Cycle 5 observations with baselines out to 16 km probe scales < 50 au and reveal the rotating disc around G17.64+0.16, a massive forming O-type star. The disc has a ring-like enhancement in the dust emission that is especially visible as arc structures to the north and south. The Keplerian kinematics are most prominently seen in the vibrationally excited water line, H2O 55, 0−64, 3 ν2 = 1 (Eu = 3461.9 K). The mass of the central source found by modelling the Keplerian rotation is consistent with 45 ± 10 M⊙. The H30α (231.9 GHz) radio-recombination line and the SiO (5-4) molecular line were detected at up to the ∼10σ level. The estimated disc mass is 0.6 − 2.6 M⊙ under the optically thin assumption. Analysis of the Toomre Q parameter in the optically thin regime indicates that the disc stability is highly dependent on temperature. The disc currently appears stable for temperatures > 150 K; this does not preclude that the substructures formed earlier through disc fragmentation.
Abstract
The HyGAL Stratospheric Observatory for Infrared Astronomy legacy program surveys six hydride molecules—ArH
+
, OH
+
, H
2
O
+
, SH, OH, and CH—and two atomic constituents—C
+
and O—within ...the diffuse interstellar medium (ISM) by means of absorption-line spectroscopy toward 25 bright Galactic background continuum sources. This detailed spectroscopic study is designed to exploit the unique value of specific hydrides as tracers and probes of different phases of the ISM, as demonstrated by recent studies with the Herschel Space Observatory. The observations performed under the HyGAL program will allow us to address several questions related to the life cycle of molecular material in the ISM and the physical processes that impact the phase transition from atomic to molecular gas, such as: (1) What is the distribution function of the H
2
fraction in the ISM? (2) How does the ionization rate due to low-energy cosmic rays vary within the Galaxy? (3) What is the nature of interstellar turbulence (e.g., typical shear or shock velocities), and what mechanisms lead to its dissipation? In this overview, we discuss the observing strategy, the synergies with ancillary and archival observations of other small molecules, and the data reduction and analysis schemes we adopted; and we present the first results obtained toward three of the survey targets, W3(OH), W3 IRS5, and NGC 7538 IRS1. Robust measurements of the column densities of these hydrides—obtained through widespread observations of absorption lines—help address the questions raised, and there is a very timely synergy between these observations and the development of theoretical models, particularly pertaining to the formation of H
2
within the turbulent ISM. The provision of enhanced HyGAL data products will therefore serve as a legacy for future ISM studies.
Recent astrophysical and terrestrial experiments have motivated the proposal of a dark sector with GeV-scale gauge boson force carriers and new Higgs bosons. We present a search for a dark Higgs ...boson using 516 fb(-1) of data collected with the BABAR detector. We do not observe a significant signal and we set 90% confidence level upper limits on the product of the standard model-dark-sector mixing angle and the dark-sector coupling constant.
Chasing discs around O-type (proto)stars Maud, L. T.; Cesaroni, R.; Kumar, M. S. N. ...
Astronomy and astrophysics (Berlin),
12/2018, Letnik:
620
Journal Article
Recenzirano
We present high angular resolution (~0.2″) continuum and molecular emission line Atacama Large Millimeter/sub-millimeter Array (ALMA) observations of G17.64+0.16 in Band 6 (220−230 GHz) taken as part ...of a campaign in search of circumstellar discs around (proto)-O-stars. At a resolution of ~400 au the main continuum core is essentially unresolved and isolated from other strong and compact emission peaks. We detect SiO (5–4) emission that is marginally resolved and elongated in a direction perpendicular to the large-scale outflow seen in the
13
CO (2−1) line using the main ALMA array in conjunction with the Atacama Compact Array (ACA). Morphologically, the SiO appearsto represent a disc-like structure. Using parametric models we show that the position-velocity profile of the SiO is consistent with the Keplerian rotation of a disc around an object between 10 and 30
M
⊙
in mass, only if there is also radial expansion from a separate structure. The radial motion component can be interpreted as a disc wind from the disc surface. Models with a central stellar object mass between 20 and 30
M
⊙
are the most consistent with the stellar luminosity (1 × 10
5
L
⊙
) and indicative of an O-type star. The H30
α
millimetre recombination line (231.9 GHz) is also detected, but spatially unresolved, and is indicative of a very compact, hot, ionised region co-spatial with the dust continuum core. The broad line-width of the H30
α
emission (full-width-half-maximum = 81.9 km s
−1
) is not dominated by pressure-broadening but is consistent with underlying bulk motions. These velocities match those required for shocks to release silicon from dust grains into the gas phase. CH
3
CN and CH
3
OH thermal emission also shows two arc shaped plumes that curve away from the disc plane. Their coincidence with OH maser emission suggests that they could trace the inner working surfaces of a wide-angle wind driven by G17.64 which impacts the diffuse remnant natal cloud before being redirected into the large-scale outflow direction. Accounting for all observables, we suggest that G17.64 is consistent with a O-type young stellar object in the final stages of protostellar assembly, driving a wind, but that has not yet developed into a compact H
II
region. The existance and detection of the disc in G17.64 is likely related to its isolated and possibly more evolved nature, traits which may underpin discs in similar sources.
Catalysis under harsh environmental conditions requires robust nanoparticles that can resist leaching of the organic shell and possess significant resistance to aggregation. Robust gold core-carbon ...shell gold-aryl nanoparticles (AuNPs-COOH) were fabricated by mild reduction of the water-soluble aryldiazonium salt HOOC-4-C
6
H
4
N&z.tbd;NAuCl
4
, and were fully characterized in solution and solid state. The nanoparticles showed high stability in the presence of 0.01-1.00 M NaCl salt, acidic and basic pH values (1-13) and moderate temperatures (20-90 °C). DFT calculations of the optimized model system Au
38
-C
6
H
4
-COOH show an Au-C (aryl) distance of 2.04 Å, which is related to a binding energy of −59.2 kcal mol
−1
. The 4-nitrophenol (4-NPh) reduction model was used to study the viability of AuNPs-COOH as a catalyst. Nitrophenols are among the most common organic pollutants in industrial and agricultural wastewaters due to their toxicity, anthropogenic and inhibitory nature. The AuNPs-COOH show high catalytic activity, where the reduction of 80 μM 4-NPh was complete in less than five minutes with a high
k
app
(2.26 × 10
−2
s
−1
) and a relatively low
E
a
(25 kJ mol
−1
) compared to literature values. Catalytic activity decreases with subsequent cycles of the reaction, along with a decrease in intensity and red shift in the LSPR band, and an increase in aggregation of nanoparticles in the TEM following each reaction cycle.
In-depth kinetic insight into the catalytic reduction of nitrophenol pollutant using gold-carbon nanoparticles is described.
PDF
