2,235 research outputs found
ECUT: Energy Conversion and utilization Technologies program biocatalysis research activity. Generation of chemical intermediates by catalytic oxidative decarboxylation of dilute organic acids
A rhodium-based catalyst was prepared and preliminary experiments were completed where the catalyst appeared to decarboxylate dilute acids at concentrations of 1 to 10 vol%. Electron spin resonance spectroscoy was used to characterize the catalyst as a first step leading toward modeling and optimization of rhodium catalysts. Also, a hybrid chemical/biological process for the production of hydrocarbons has been assessed. These types of catalysts could greatly increase energy efficiency of this process
Activity cycles in members of young loose stellar associations
Magnetic cycles have been detected in tens of solar-like stars. The
relationship between the cycle properties and global stellar parameters is not
fully understood yet.
We searched for activity cycles in 90 solar-like stars with ages between 4
and 95 Myr aiming to investigate the properties of activity cycles in this age
range.
We measured the length of a given cycle by analyzing the long-term
time-series of three activity indexes. For each star, we computed also the
global magnetic activity index that is proportional to the amplitude of
the rotational modulation and is a proxy of the mean level of the surface
magnetic activity. We detected activity cycles in 67 stars. Secondary cycles
were also detected in 32 stars. The lack of correlation between and
suggest that these stars belong to the Transitional Branch and that
the dynamo acting in these stars is different from the solar one. This
statement is also supported by the analysis of the butterfly diagrams.
We computed the Spearman correlation coefficient between ,
and different stellar parameters. We found that is
uncorrelated with all the investigated parameters. The index is
positively correlated with the convective turn-over time-scale, the magnetic
diffusivity time-scale , and the dynamo number , whereas
it is anti-correlated with the effective temperature , the
photometric shear and the radius at which
the convective zone is located.
We found that is about constant and that decreases with the
stellare age in the range 4-95 Myr. We investigated the magnetic activity of AB
Dor A by merging ASAS time-series with previous long-term photometric data. We
estimated the length of the AB Dor A primary cycle as .Comment: 19 pages , 15 figures, accepte
Lower limit for differential rotation in members of young loose stellar associations
Surface differential rotation (SDR) plays a key role in dynamo models. SDR
estimates are therefore essential for constraining theoretical models. We
measure a lower limit to SDR in a sample of solar-like stars belonging to young
associations with the aim of investigating how SDR depends on global stellar
parameters in the age range (4-95 Myr). The rotation period of a solar-like
star can be recovered by analyzing the flux modulation caused by dark spots and
stellar rotation. The SDR and the latitude migration of dark-spots induce a
modulation of the detected rotation period. We employ long-term photometry to
measure the amplitude of such a modulation and to compute the quantity
DeltaOmega_phot =2p/P_min -2pi/P_max that is a lower limit to SDR. We find that
DeltaOmega_phot increases with the stellar effective temperature and with the
global convective turn-over time-scale tau_c. We find that DeltaOmega_phot is
proportional to Teff^2.18pm 0.65 in stars recently settled on the ZAMS. This
power law is less steep than those found by previous authors, but closest to
recent theoretical models. We find that DeltaOmega_phot steeply increases
between 4 and 30 Myr and that itis almost constant between 30 and 95 Myr in a 1
M_sun star. We find also that the relative shear increases with the Rossby
number Ro. Although our results are qualitatively in agreement with
hydrodynamical mean-field models, our measurements are systematically higher
than the values predicted by these models. The discrepancy between
DeltaOmega_phot measurements and theoretical models is particularly large in
stars with periods between 0.7 and 2 d. Such a discrepancy, together with the
anomalous SDR measured by other authors for HD 171488 (rotating in 1.31 d),
suggests that the rotation period could influence SDR more than predicted by
the models.Comment: 23 pages, 15 figures, 5 tables,accepted by Astronomy and Astrophysic
Evidence of New Magnetic Transitions in Late-Type Dwarfs from Gaia DR2
The second Gaia data release contains the identification of 147 535 low-mass
() rotational modulation variable candidates on (or close
to) the main sequence, together with their rotation period and modulation
amplitude. The richness, the period and amplitude range, and the photometric
precision of this sample make it possible to unveil, for the first time,
signatures of different surface inhomogeneity regimes in the amplitude-period
density diagram. The modulation amplitude distribution shows a clear
bimodality, with an evident gap at periods d. The low amplitude
branch, in turn, shows a period bimodality with a main clustering at periods 5 - 10 d and a secondary clustering of ultra-fast rotators at d. The amplitude-period multimodality is correlated with the position in
the period-absolute magnitude (or period-color) diagram, with the low- and
high-amplitude stars occupying different preferential locations. Here we argue
that such a multimodality represents a further evidence of the existence of
different regimes of surface inhomogeneities in young and middle-age low-mass
stars and we lay out possible scenarios for their evolution, which manifestly
include rapid transitions from one regime to another. In particular, the data
indicate that stars spinning up close to break-up velocity undergo a very rapid
change in their surface inhomogeneities configuration, which is revealed here
for the first time. The multimodality can be exploited to identify field stars
of age 100 -- 600 Myr belonging to the slow-rotator low-amplitude
sequence, for which age can be estimated from the rotation period via
gyrochronology relationships.Comment: 15 pages, 6 figures, Accepted by Ap
Neutrino flux predictions for known Galactic microquasars
It has been proposed recently that Galactic microquasars may be prodigious
emitters of TeV neutrinos that can be detected by upcoming km^2 neutrino
telescopes. In this paper we consider a sample of identified microquasars and
microquasar candiates, for which available data enables rough determination of
the jet parameters. By employing the parameters inferred from radio
observations of various jet ejection events, we determine the neutrino fluxes
that should have been produced during these events by photopion production in
the jet. Despite the large uncertainties in our analysis, we demonstrate that
in several of the sources considered, the neutrino flux at Earth, produced in
events similar to those observed, would exceed the detection threshold of a
km^2 neutrino detector. The class of microquasars may contain also sources with
bulk Lorentz factors larger than those characteristic of the sample considered
here, directed along our line of sight. Such sources, which may be very
difficult to resolve at radio wavelengths and hence may be difficult to
identify as microqusar candidates, may emit neutrinos with fluxes significantly
larger than typically obtained in the present analysis. These sources may
eventually be identified through their neutrino and gamma-ray emission.Comment: 17 pages. Submitted to Ap
Cluster of legionnaires’ disease in an Italian prison
Background: Legionella pneumophila (Lp) is the most common etiologic agent causing Legionnaires’ Disease (LD). Water systems offer the best growth conditions for Lp and support its spread by producing aerosols. From 2015 to 2017, the Regional Reference Laboratory of Clinical and Environmental Surveillance of Legionellosis of Palermo monitored the presence of Lp in nine prisons in Western Sicily. During this investigation, we compared Lp isolates from environmental samples in a prison located in Palermo with isolates from two prisoners in the same prison. Methods: We collected 93 water samples from nine Sicilian prisons and the bronchoalveolar lavages (BALs) of two prisoners considered cases of LD. These samples were processed following the procedures described in the Italian Guidelines for the Prevention and Control of Legionellosis of 2015. Then, genotyping was performed on 19 Lp colonies (17 from water samples and 2 from clinical samples) using the Sequence-Based Typing (SBT) method, according to European Study Group for Legionella Infections (ESGLI) protocols. Results: Lp serogroup (sg) 6 was the most prevalent serogroup isolated from the prisons analyzed (40%), followed by Lp sg 1 (16%). Most of all, in four penitentiary institutions, we detected a high concentration of Lp >104 Colony Forming Unit/Liter (CFU/L). The environmental molecular investigation found the following Sequence Types (STs) in Lp sg 6: ST 93, ST 292, ST 461, ST 728, ST 1317 and ST 1362, while most of the isolates in sg 1 belonged to ST 1. We also found a new ST that has since been assigned the number 2451 in the ESGLI-SBT database. From the several Lp sg 1 colonies isolated from the two BALs, we identified ST 2451. Conclusions: In this article, we described the results obtained from environmental and epidemiological investigations of Lp isolated from prisons in Western Sicily. Furthermore, we reported the first cluster of Legionnaires’ in an Italian prison and the molecular typing of Lp sg 1 from one prison’s water system and two BALs, identified the source of the contamination, and discovered a new ST
Resonant Scattering and Recombination in CAL 87
The eclipsing supersoft X-ray binary CAL 87 has been observed with Chandra on
August 13/14, 2001 for nearly 100 ksec, covering two full orbital cycles and
three eclipses. The shape of the eclipse light curve derived from the
zeroth-order photons indicates that the size of the X-ray emission region is
about 1.5 solar radii. The ACIS/LETG spectrum is completely dominated by
emission lines without any noticeable continuum. The brightest emission lines
are significantly redshifted and double-peaked, suggestive of emanating in a
2000 km/s wind. We model the X-ray spectrum by a mixture of recombination and
resonant scattering. This allows us to deduce the temperature and luminosity of
the ionizing source to be kT = 50-100 eV and L_X = 5E37 erg/s.Comment: To appear in Proceedings of IAU Coll. 194 "Compact binaries in the
Galaxy and beyond" (Rev. Mex. A&A Conf. Series), eds. G. Tovmassian and E.
Sio
Feasible alternatives to green growth
Climate change and increasing income inequality have emerged as twin threats to contemporary standards of living, peace and democracy. These two problems are usually tackled separately in the policy agenda. A new breed of radical proposals have been advanced to manage a fair low-carbon transition. In this spirit, we develop a dynamic macrosimulation model to investigate the long-term effects of three scenarios: green growth, policies for social equity, and degrowth. The green growth scenario, based on technological progress and environmental policies, achieves a significant reduction in greenhouse gas emissions at the cost of increasing income inequality and unemployment. The policies for social equity scenario adds direct labour market interventions that result in an environmental performance similar to green growth while improving social conditions at the cost of increasing public deficit. The degrowth scenario further adds a reduction in consumption and exports, and achieves a greater reduction in emissions and inequality with higher public deficit, despite the introduction of a wealth tax. We argue that new radical social policies can combine social prosperity and low-carbon emissions and are economically and politically feasible
Spatial Interpolants
We propose Splinter, a new technique for proving properties of
heap-manipulating programs that marries (1) a new separation logic-based
analysis for heap reasoning with (2) an interpolation-based technique for
refining heap-shape invariants with data invariants. Splinter is property
directed, precise, and produces counterexample traces when a property does not
hold. Using the novel notion of spatial interpolants modulo theories, Splinter
can infer complex invariants over general recursive predicates, e.g., of the
form all elements in a linked list are even or a binary tree is sorted.
Furthermore, we treat interpolation as a black box, which gives us the freedom
to encode data manipulation in any suitable theory for a given program (e.g.,
bit vectors, arrays, or linear arithmetic), so that our technique immediately
benefits from any future advances in SMT solving and interpolation.Comment: Short version published in ESOP 201
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