2,987 research outputs found
Volatile organic compounds in the atmosphere of Mexico City
The Mexico City Metropolitan Area (MCMA) is one of the most polluted megacities in North America. Therefore, it is an excellent benchmark city to understand atmospheric chemistry and to implement pilot countermeasures. Air quality in the MCMA is not within acceptable levels, mainly due to high ground levels of ozone (O3). Tropospheric O3 is a secondary pollutant formed from the oxidation of volatile organic compounds (VOCs) in the presence of nitrogen oxides and sunlight. To gain a better understanding of O3 formation in megacities, evaluate the effectiveness of already-implemented countermeasures, and identify new cost-effective alternatives to reduce tropospheric O3 concentrations, researchers and environmental authorities require updated concentrations for a broader range of VOCs. Moreover, in an effort to protect human health and the environment, it is important to understand which VOCs exceed reference safe values or most contribute to O3 formation, as well as to identify the most probable emission sources of those VOCs. In this work, 64 VOCs, including 36 toxic VOCs, were measured at four sites in the MCMA during 2011-2012. VOCs related to liquefied petroleum gas leakages exhibited the highest concentrations. Toxic VOCs with the highest average concentrations were acetone and ethanol. The toxic VOC benzene represented the highest risk to Mexican citizens, and toluene contributed the most to O3 formation. Correlation analysis indicated that the measured VOCs come from vehicular emissions and solvent-related industrial sources. VOC measurements revealed that compounds related to liquefied petroleum gas leakages are the most abundant, the toxic VOC benzene represents the highest risk to citizens, and toluene is the greatest VOC contributor to O3 formation in Mexico City. © 2015 Elsevier Ltd.Japan Science and Technology Agency, Science and Technology Research Partnership for Sustainable Development, Japan International Cooperation Agency1,3 butadiene, 106-99-0, 25339-57-5; 1,4 dichlorobenzene, 106-46-7; acetone, 67-64-1; alcohol, 64-17-5; benzene, 71-43-2; ethylbenzene, 100-41-4; gasoline, 86290-81-5; methyl chloride, 74-87-3; ozone, 10028-15-6; propane, 74-98-6; styrene, 100-42-5; toluene, 108-88-3; xylene, 1330-20-
Clinical value of cortical bursting in preterm infants with intraventricular haemorrhage
Background: In healthy preterm infants, cortical burst rate and temporal dynamics predict important measures such as brain growth. We hypothesised that in preterm infants with germinal matrix-intraventricular haemorrhage (GM-IVH), cortical bursting could provide prognostic information. / Aims: We determined how cortical bursting was influenced by the injury, and whether this was related to developmental outcome. / Study design: Single-centre retrospective cohort study at University College London Hospitals, UK. / Subjects: 33 infants with GM-IVH ≥ grade II (median gestational age: 25 weeks). / Outcome measures: We identified 47 EEGs acquired between 24 and 40 weeks corrected gestational age as part of routine clinical care. In a subset of 33 EEGs from 25 infants with asymmetric injury, we used the least-affected hemisphere as an internal comparison. We tested whether cortical burst rate predicted survival without severe impairment (median 2 years follow-up). / Results: In asymmetric injury, cortical burst rate was lower over the worst- than least-affected hemisphere, and bursts over the worst-affected hemisphere were less likely to immediately follow bursts over the least-affected hemisphere than vice versa. Overall, burst rate was lower in cases of GM-IVH with parenchymal involvement, relative to milder structural injury grades. Higher burst rate modestly predicted survival without severe language (AUC 0.673) or motor impairment (AUC 0.667), which was partly mediated by structural injury grade. / Conclusions: Cortical bursting can index the functional injury after GM-IVH: perturbed burst initiation (rate) and propagation (inter-hemispheric dynamics) likely reflect associated grey matter and white matter damage. Higher cortical burst rate is reassuring for a positive outcome
Dynamic exchange coupling and Gilbert damping in magnetic multilayers
We theoretically study dynamic properties of thin ferromagnetic films in
contact with normal metals. Moving magnetizations cause a flow of spins into
adjacent conductors, which relax by spin flip, scatter back into the
ferromagnet, or are absorbed by another ferromagnet. Relaxation of spins
outside the moving magnetization enhances the overall damping of the
magnetization dynamics in accordance with the Gilbert phenomenology. Transfer
of spins between different ferromagnets by these nonequilibrium spin currents
leads to a long-ranged dynamic exchange interaction and novel collective
excitation modes. Our predictions agree well with recent
ferromagnetic-resonance experiments on ultrathin magnetic films.Comment: 15 pages, 3 figures, for MMM'02 proceeding
More New Records of Spider Wasps from Colombia (Hymenoptera, Pompilidae)
Aporinellus Banks, Austrochares Banks and Dicranoplius Haupt are new generic records for Colombia, as well as the species Dipogon ariel Banks, Evagetes peruana Banks, and Euplaniceps notabilis (Smith). Five new combinations are formally endorsed: Aimatocare argentinica (Banks), comb. n.;Aimatocare longula (Banks), comb. n.; Aimatocare imitator (Evans), comb. n.; Aimatocare impensa (Evans), comb. n.; Aimato-care vitrea (Fox), comb. n. Although these names have been used in Pompilidae, no formal nomenclatural act had been proposed. The presence of Chirodamus paramicola Roig-Alsina, previously reported with uncertainty, is confirmed. Finally, a new combination for Euplaniceps notabilis (Smith), comb. n. is proposed based on molecular phylogenetics and morphological data.The Colombian fauna of Pompilidae sums up to 38 genera and approximately 150 species
Star-galaxy separation in the AKARI NEP Deep Field
Context: It is crucial to develop a method for classifying objects detected
in deep surveys at infrared wavelengths. We specifically need a method to
separate galaxies from stars using only the infrared information to study the
properties of galaxies, e.g., to estimate the angular correlation function,
without introducing any additional bias. Aims. We aim to separate stars and
galaxies in the data from the AKARI North Ecliptic Pole (NEP) Deep survey
collected in nine AKARI / IRC bands from 2 to 24 {\mu}m that cover the near-
and mid-infrared wavelengths (hereafter NIR and MIR). We plan to estimate the
correlation function for NIR and MIR galaxies from a sample selected according
to our criteria in future research. Methods: We used support vector machines
(SVM) to study the distribution of stars and galaxies in the AKARIs multicolor
space. We defined the training samples of these objects by calculating their
infrared stellarity parameter (sgc). We created the most efficient classifier
and then tested it on the whole sample. We confirmed the developed separation
with auxiliary optical data obtained by the Subaru telescope and by creating
Euclidean normalized number count plots. Results: We obtain a 90% accuracy in
pinpointing galaxies and 98% accuracy for stars in infrared multicolor space
with the infrared SVM classifier. The source counts and comparison with the
optical data (with a consistency of 65% for selecting stars and 96% for
galaxies) confirm that our star/galaxy separation methods are reliable.
Conclusions: The infrared classifier derived with the SVM method based on
infrared sgc- selected training samples proves to be very efficient and
accurate in selecting stars and galaxies in deep surveys at infrared
wavelengths carried out without any previous target object selection.Comment: 8 pages, 8 figure
Ask The Machine: Systematic detection of wind-type outflows in low-mass X-ray binaries
The systematic discovery of outflows in the optical spectra of low-mass X-ray
binaries opened a new avenue for the study of the outburst evolution in these
extreme systems. However, the efficient detection of such features in a
continuously growing database requires the development of new analysis
techniques with a particular focus on scalability, adaptability, and
automatization. In this pilot study, we explore the use of machine learning
algorithms to perform the identification of outflows in spectral line profiles
observed in the optical range. We train and test the classifier on a simulated
database, constructed through a combination of disc emission line profiles and
outflow signatures, emulating typical observations of low-mass X-ray binaries.
The final, trained classifier is applied to two sets of spectra taken during
two bright outbursts that were particularly well covered, those of V404 Cyg
(2015) and MAXI J1820+070 (2018). The resulting classification gained by this
novel approach is overall consistent with that obtained through traditional
techniques, while it simultaneously provides a number of key advantages over
the latter, including the access to low velocity outflows. This study sets the
foundations for future studies on large samples of spectra from low-mass X-ray
binaries and other compact binaries.Comment: Accepted for publication in MNRAS. 13 pages, 6 figure
Morphological evolution of z~1 galaxies from deep K-band AO imaging in the COSMOS deep field
We present the results of an imaging programme of distant galaxies (z~0.8) at
high spatial resolution (~0.1").We observed 7 fields of 1'*1' with the NACO
Adaptive Optics system (VLT) in Ks (2.16um) band with typical V ~ 14 guide
stars and 3h integration time per field. Observed fields are selected within
the COSMOS survey area. High angular resolution K-band data have the advantage
to probe old stellar populations in the rest-frame, enabling to determine
galaxy morphological types unaffected by recent star formation, better linked
to the underlying mass than classical optical morphology studies (HST).
Adaptive optics on ground based telescopes is the only method today to obtain
such high resolution in the K-band. In this paper we show that reliable results
can be obtained and establish a first basis for larger observing programmes. We
analyze the morphologies by means of B/D (Bulge/Disk) decomposition with GIM2D
and CAS (Concentration-Asymmetry) estimators for 79 galaxies with magnitudes
between Ks = 17-23 and classify them in three main morphological types (Late
Type, Early Type and Irregulars). We obtain for the first time an estimate of
the distribution of galaxy types at redshift z ~ 1 as measured from the near
infrared at high spatial resolution. We show that galactic parameters (disk
scale length, bulge effective radius and bulge fraction) can be estimated with
a random error lower than 20% for the bulge fraction up to Ks = 19 (AB = 21)
and that classification into the three main morphological types can be done up
to Ks = 20 (AB = 22) with at least 70% of correct identifications. We used the
known photometric redshifts to obtain a redshift distribution over 2 redshift
bins (z < 0.8, 0.8 < z < 1.5) for each morphological type.Comment: 19 pages, 19 figures, 5 tables, Accepted for publication in A&A,
typos corrected, referee's suggestions added, figure 3 has been strongly
degrade
Real Time Electron Tunneling and Pulse Spectroscopy in Carbon Nanotube Quantum Dots
We investigate a Quantum Dot (QD) in a Carbon Nanotube (CNT) in the regime
where the QD is nearly isolated from the leads. An aluminum single electron
transistor (SET) serves as a charge detector for the QD. We precisely measure
and tune the tunnel rates into the QD in the range between 1 kHz and 1 Hz,
using both pulse spectroscopy and real - time charge detection and measure the
excitation spectrum of the isolated QD.Comment: 12 pages, 5 figure
Early-type Galaxies at z ~ 1.3. II. Masses and Ages of Early-type Galaxies in Different Environments and Their Dependence on Stellar Population Model Assumptions
We have derived masses and ages for 79 early-type galaxies (ETGs) in different environments at z ~ 1.3 in the Lynx supercluster and in the GOODS/CDF-S field using multi-wavelength (0.6-4.5 μm; KPNO, Palomar, Keck, Hubble Space Telescope, Spitzer) data sets. At this redshift the contribution of the thermally pulsing asymptotic giant branch (TP-AGB) phase is important for ETGs, and the mass and age estimates depend on the choice of the stellar population model used in the spectral energy distribution fits. We describe in detail the differences among model predictions for a large range of galaxy ages, showing the dependence of these differences on age. Current models still yield large uncertainties. While recent models from Maraston and Charlot & Bruzual offer better modeling of the TP-AGB phase with respect to less recent Bruzual & Charlot models, their predictions do not often match. The modeling of this TP-AGB phase has a significant impact on the derived parameters for galaxies observed at high redshift. Some of our results do not depend on the choice of the model: for all models, the most massive galaxies are the oldest ones, independent of the environment. When using the Maraston and Charlot & Bruzual models, the mass distribution is similar in the clusters and in the groups, whereas in our field sample there is a deficit of massive (M ≳ 10^(11) M_☉) ETGs. According to those last models, ETGs belonging to the cluster environment host on average older stars with respect to group and field populations. This difference is less significant than the age difference in galaxies of different masses
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