89 research outputs found
Photoevaporation of Jeans-unstable molecular clumps
We study the photoevaporation of Jeans-unstable molecular clumps by isotropic FUV (6 eV < h\u3bd < 13.6 eV) radiation, through 3D radiative transfer hydrodynamical simulations implementing a non-equilibrium chemical network that includes the formation and dissociation of H2. We run a set of simulations considering different clump masses (M=10 - 200 M_{odot }) and impinging fluxes (G0 = 2
7 103 to 8
7 104 in Habing units). In the initial phase, the radiation sweeps the clump as an R-type dissociation front, reducing the H2 mass by a factor 40 - 90{{ per cent}}. Then, a weak (M 3ceq 2) shock develops and travels towards the centre of the clump, which collapses while losing mass from its surface. All considered clumps remain gravitationally unstable even if radiation rips off most of the clump mass, showing that external FUV radiation is not able to stop clump collapse. However, the FUV intensity regulates the final H2 mass available for star formation: for example, for G0 < 104 more than 10 per cent of the initial clump mass survives. Finally, for massive clumps ({ 73 } 100 M_{odot }) the H2 mass increases by 25 - 50{{ per cent}} during the collapse, mostly because of the rapid density growth that implies a more efficient H2 self-shielding
Deep into the structure of the first galaxies: SERRA views
We study the formation and evolution of a sample of Lyman Break Galaxies in
the Epoch of Reionization by using high-resolution (),
cosmological zoom-in simulations part of the SERRA suite. In SERRA, we follow
the interstellar medium (ISM) thermo-chemical non-equilibrium evolution, and
perform on-the-fly radiative transfer of the interstellar radiation field
(ISRF). The simulation outputs are post-processed to compute the emission of
far infrared lines ([CII], [NII], and [OIII]). At , the most massive
galaxy, `Freesia', has an age , stellar mass
, and a star formation rate
, due to a recent burst.
Freesia has two stellar components (A and B) separated by ; other 11 galaxies are found within . The
mean ISRF in the Habing band is and is spatially uniform; in
contrast, the ionisation parameter is , and
has a patchy distribution peaked at the location of star-forming sites. The
resulting ionising escape fraction from Freesia is .
While [CII] emission is extended (radius 1.54 kpc), [OIII] is concentrated in
Freesia-A (0.85 kpc), where the ratio . As many high- galaxies, Freesia lies below the local [CII]-SFR
relation. We show that this is the general consequence of a starburst phase
(pushing the galaxy above the Kennicutt-Schmidt relation) which
disrupts/photodissociates the emitting molecular clouds around star-forming
sites. Metallicity has a sub-dominant impact on the amplitude of [CII]-SFR
deviations.Comment: 22 pages, 14 figures, accepted by MNRA
Warm dust in high-z galaxies: origin and implications
ALMA observations have revealed the presence of dust in galaxies in the Epoch
of Reionization (redshift ). However, the dust temperature, , remains
unconstrained, and this introduces large uncertainties, particularly in the
dust mass determinations. Using an analytical and physically-motivated model,
we show that dust in high-, star-forming giant molecular clouds (GMC),
largely dominating the observed far-infrared luminosity, is warmer ($T_d > 60\
\mathrm{K}\sim 40\%T_dz\beta$ relation, (b) alleviates the
problem of the uncomfortably large dust masses deduced from observations of
some EoR galaxies.Comment: 14 pages, 6 figures, accepted for publication in MNRA
Selective detection of liposoluble vitamins using an organic electrochemical transistor
Accurate quantification of vitamins content is essential in food analysis, with direct impact on the quality of our diet and, therefore, on our health. Current research interest is devoted to the design of robust and versatile devices able to perform real-time analyses that do not strictly rely on laboratory facilities. Here, we report the first organic electrochemical transistor (OECT) based sensor working in organic environment for the detection of a fat-soluble vitamin (Vitamin A). The OECT behaviour in organic solvents was thoroughly characterized and its structure was optimised allowing both potentiostatic and potentiodynamic detections. On one hand, the potentiostatic approach provided a gain of 100 and the detection limit was as low as 115 nM, but it did not address selectivity issues. On the other hand, the potentiodynamic approach showed a higher detection limit, but allowed the selective detection of Vitamin A in the presence of & alpha;-Tocopherol. Analyses of randomized solutions revealed that a pre-calibrated sensor can estimate Vitamin A concentration with a 3% error. Moreover, the robustness of our sensor was demonstrated by analysing commercial food fortifiers without any sample pretreatment
A wearable electrochemical gas sensor for ammonia detection
The next future strategies for improved occupational safety and health management could largely benefit from wearable and Internet of Things technologies, enabling the real-time monitoring of health-related and environmental information to the wearer, to emergency responders, and to inspectors. The aim of this study is the development of a wearable gas sensor for the detection of NH3 at room temperature based on the organic semiconductor poly(3,4-ethylenedioxythiophene) (PEDOT), electrochemically deposited iridium oxide particles, and a hydrogel film. The hydrogel composition was finely optimised to obtain self-healing properties, as well as the desired porosity, adhesion to the substrate, and stability in humidity variations. Its chemical structure and morphology were characterised by infrared spectroscopy and scanning electron microscopy, respectively, and were found to play a key role in the transduction process and in the achievement of a reversible and selective response. The sensing properties rely on a potentiometric-like mechanism that significantly differs from most of the state-of-the-art NH3 gas sensors and provides superior robustness to the final device. Thanks to the reliability of the analytical response, the simple two-terminal configuration and the low power consumption, the PEDOT:PSS/IrOx Ps/hydrogel sensor was realised on a flexible plastic foil and successfully tested in a wearable configuration with wireless connectivity to a smartphone. The wearable sensor showed stability to mechanical deformations and good analytical performances, with a sensitivity of 60 ± 8 µA decade−1 in a wide concentration range (17–7899 ppm), which includes the safety limits set by law for NH3 exposure
Fast and real-time electrical transistor assay for quantifying SARS-CoV-2 neutralizing antibodies
Due to the SARS-CoV-2 pandemic renewed attention has been directed towards viral neutralization assays and neutralizing antibodies quantification, for vaccine pre-clinical trials and determining vaccine efficacy over time. The gold standard to assess antibody titer is the plaque reduction neutralization test, an end-point assay which evaluates the highest serum antibody dilution that neutralizes viral replication, by inspecting the cytopathic effect induced on cell cultures. Here, we use planar, PEDOT:PSS-based organic electrochemical transistors for real-time, remote-controlled, reliable and fast electrical monitoring of the cytopathic effect induced by SARS29 CoV-2 on Vero E6 cell lines, allowing the quantification of serum neutralizing titer. Our low-cost and scalable device has the potential to speed-up large-scale viral neutralization screening without the need for cancerous staining or highly specialized operators. Finally, the technology could be easily transferred to assess neutralizing antibody response towards different viruses in their permissive cell substrates
SEARCH FOR SLOWLY MOVING MAGNETIC MONOPOLES WITH THE MACRO DETECTOR
A search for slowly moving magnetic monopoles in the cosmic radiation was conducted from October 1989 to November 1991 using the large liquid scintillator detector subsystem of the first supermodule of the MACRO detector at the Gran Sasso underground laboratory. The absence of candidates established an upper limit on the monopole flux of 5.6 x 10(-15) cm-2 sr-1 s-1 at 90% confidence level in the velocity range of 10(-4) less than or similar to beta < 4 x 10(-3). This result places a new constraint on the abundance of monopoles trapped in our solar system
Shaping the structure of a GMC with radiation and winds
We study the effect of stellar feedback (photodissociation/ionization, radiation pressure and winds) on the evolution of a Giant Molecular Cloud (GMC), by means of a 3D radiative transfer, hydro-simulation implementing a complex chemical network featuring H2 formation and destruction. We track the formation of individual stars with mass M > 1 M⊙ with a stochastic recipe. Each star emits radiation according to its spectrum, sampled with 10 photon bins from near-infrared to extreme ultra-violet bands; winds are implemented by energy injection in the neighbouring cells. We run a simulation of a GMC with mass M = 105 M⊙, following the evolution of different gas phases. Thanks to the simultaneous inclusion of different stellar feedback mechanisms, we identify two stages in the cloud evolution: (1) radiation and winds carve ionized, low-density bubbles around massive stars, while FUV radiation dissociates most H2 in the cloud, apart from dense, self-shielded clumps; (2) rapid star formation (SFR≃ 0.1 M⊙  − 1) consumes molecular gas in the dense clumps, so that UV radiation escapes and ionizes the remaining HI gas in the GMC. H2 is exhausted in 1.6 Myr, yielding a final star formation efficiency of 36 per cent. The average intensity of FUV and ionizing fields increases almost steadily with time; by the end of the simulation (t = 2.5 Myr) we find 〈G0〉 ≃ 103 (in Habing units), and a ionization parameter 〈Uion〉 ≃ 102, respectively. The ionization field has also a more patchy distribution than the FUV one within the GMC. Throughout the evolution, the escape fraction of ionizing photons from the cloud is fion, esc ≲ 0.03
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