97 research outputs found
The complex behaviour of the microquasar GRS 1915+105 in the rho class observed with BeppoSAX. I: Timing analysis
GRS 1915+105 was observed by BeppoSAX for about 10 days in October 2000. For
about 80% of the time, the source was in the variability class ,
characterised by a series of recurrent bursts. We describe the results of the
timing analysis performed on the MECS (1.6--10 keV) and PDS (15--100 keV) data.
The X-ray count rate from \grss showed an increasing trend with different
characteristics in the various energy bands. Fourier and wavelet analyses
detect a variation in the recurrence time of the bursts, from 45--50 s to about
75 s, which appear well correlated with the count rate. From the power
distribution of peaks in Fourier periodograms and wavelet spectra, we
distinguished between the {\it regular} and {\it irregular} variability modes
of the class, which are related to variations in the count rate in the
3--10 keV range. We identified two components in the burst structure: the slow
leading trail, and the pulse, superimposed on a rather stable level. We found
that the change in the recurrence time of the regular mode is caused by the
slow leading trails, while the duration of the pulse phase remains far more
stable. The evolution in the mean count rates shows that the time behaviour of
both the leading trail and the baseline level are very similar to those
observed in the 1.6--3 and 15--100 keV ranges, while that of the pulse follows
the peak number. These differences in the time behaviour and count rates at
different energies indicate that the process responsible for the pulses must
produce the strongest emission between 3 and 10 keV, while that associated with
both the leading trail and the baseline dominates at lower and higher energiesComment: Astronomy and Astrophysics, in pres
First-Principles Study of the Electronic and Magnetic Properties of Defects in Carbon Nanostructures
Understanding the magnetic properties of graphenic nanostructures is
instrumental in future spintronics applications. These magnetic properties are
known to depend crucially on the presence of defects. Here we review our recent
theoretical studies using density functional calculations on two types of
defects in carbon nanostructures: Substitutional doping with transition metals,
and sp-type defects created by covalent functionalization with organic and
inorganic molecules. We focus on such defects because they can be used to
create and control magnetism in graphene-based materials. Our main results are
summarized as follows: i)Substitutional metal impurities are fully understood
using a model based on the hybridization between the states of the metal
atom and the defect levels associated with an unreconstructed D carbon
vacancy. We identify three different regimes, associated with the occupation of
distinct hybridization levels, which determine the magnetic properties obtained
with this type of doping; ii) A spin moment of 1.0 is always induced by
chemical functionalization when a molecule chemisorbs on a graphene layer via a
single C-C (or other weakly polar) covalent bond. The magnetic coupling between
adsorbates shows a key dependence on the sublattice adsorption site. This
effect is similar to that of H adsorption, however, with universal character;
iii) The spin moment of substitutional metal impurities can be controlled using
strain. In particular, we show that although Ni substitutionals are
non-magnetic in flat and unstrained graphene, the magnetism of these defects
can be activated by applying either uniaxial strain or curvature to the
graphene layer. All these results provide key information about formation and
control of defect-induced magnetism in graphene and related materials.Comment: 40 pages, 17 Figures, 62 References; Chapter 2 in Topological
Modelling of Nanostructures and Extended Systems (2013) - Springer, edited by
A. R. Ashrafi, F. Cataldo, A. Iranmanesh, and O. Or
The complex behaviour of the microquasar GRS 1915+105 in the rho class observed with BeppoSAX. II: Time-resolved spectral analysis
BeppoSAX observed GRS 1915+105 on October 2000 with a long pointing lasting
about ten days. During this observation, the source was mainly in the rho class
characterized by bursts with a recurrence time of between 40 and 100 s. We
identify five segments in the burst structure and accumulate the average
spectra of these segments during each satellite orbit. We present a detailed
spectral analysis aimed at determining variations that occur during the burst
and understanding the physical process that produces them. We compare MECS,
HPGSPC, and PDS spectra with several models. Under the assumption that a single
model is able to fit all spectra, we find that the combination of a
multi-temperature black-body disk and a hybrid corona is able to give a
consistent physical explanation of the source behaviour. Our measured
variations in KT_el, tau, KT_in, and R_in appear to be either correlated or
anti-correlated with the count rate in the energy range 1.6-10 keV. The
strongest variations are detected along the burst segments: almost all
parameters exhibit significant variations in the segments that have the highest
fluxes (pulse) with the exception of R_in, which varies continuously and
reaches a maximum just before the peak. The flux of the multi-temperature disk
strongly increases in the pulse and simultaneously the corona contribution is
significantly reduced. The disk luminosity increases in the pulse and the
R_in-T_in correlation can be most successfully interpreted in term of the slim
disk model. In addition, the reduction in the corona luminosity at the bursts
might represent the condensation of the corona onto the disk.Comment: accepted for publication in A&A, added references, version after
language editin
Gender Difference in the Effects of COVID-19 Pandemic on Mechanical Reperfusion and 30-Day Mortality for STEMI: Results of the ISACS-STEMI COVID-19 Registry
Background. Several reports have demonstrated the impact of the COVID-19 pandemic on the management and outcome of patients with ST-segment elevation myocardial infarction (STEMI). The aim of the current analysis is to investigate the potential gender difference in the effects of the COVID-19 pandemic on mechanical reperfusion and 30-day mortality for STEMI patients within the ISACS-STEMI COVID-19 Registry. Methods. This retrospective multicenter registry was performed in high-volume primary percutaneous coronary intervention (PPCI) centers on four continents and included STEMI patients undergoing PPCIs in MarchâJune 2019 and 2020. Patients were divided according to gender. The main outcomes were the incidence and timing of the PPCI, (ischemia time â„ 12 h and door-to-balloon â„ 30 min) and in-hospital or 30-day mortality. Results. We included 16683 STEMI patients undergoing PPCIs in 109 centers. In 2020 during the pandemic, there was a significant reduction in PPCIs compared to 2019 (IRR 0.843 (95% CI: 0.825â0.861, p < 0.0001). We did not find a significant gender difference in the effects of the COVID-19 pandemic on the numbers of STEMI patients, which were similarly reduced from 2019 to 2020 in both groups, or in the mortality rates. Compared to prepandemia, 30-day mortality was significantly higher during the pandemic period among female (12.1% vs. 8.7%; adjusted HR [95% CI] = 1.66 [1.31â2.11], p < 0.001) but not male patients (5.8% vs. 6.7%; adjusted HR [95% CI] = 1.14 [0.96â1.34], p = 0.12). Conclusions. The COVID-19 pandemic had a significant impact on the treatment of patients with STEMI, with a 16% reduction in PPCI procedures similarly observed in both genders. Furthermore, we observed significantly increased in-hospital and 30-day mortality rates during the pandemic only among females. Trial registration number: NCT 04412655
Impact of chronic obstructive pulmonary disease on short-term outcome in patients with ST-elevation myocardial infarction during COVID-19 pandemic: insights from the international multicenter ISACS-STEMI registry
Background: Chronic obstructive pulmonary disease (COPD) is projected to become the third cause of mortality worldwide. COPD shares several pathophysiological mechanisms with cardiovascular disease, especially atherosclerosis. However, no definite answers are available on the prognostic role of COPD in the setting of ST elevation myocardial infarction (STEMI), especially during COVID-19 pandemic, among patients undergoing primary angioplasty, that is therefore the aim of the current study. Methods: In the ISACS-STEMI COVID-19 registry we included retrospectively patients with STEMI treated with primary percutaneous coronary intervention (PCI) between March and June of 2019 and 2020 from 109 high-volume primary PCI centers in 4 continents. Results: A total of 15,686 patients were included in this analysis. Of them, 810 (5.2%) subjects had a COPD diagnosis. They were more often elderly and with a more pronounced cardiovascular risk profile. No preminent procedural dissimilarities were noticed except for a lower proportion of dual antiplatelet therapy at discharge among COPD patients (98.9% vs. 98.1%, P = 0.038). With regards to short-term fatal outcomes, both in-hospital and 30-days mortality occurred more frequently among COPD patients, similarly in pre-COVID-19 and COVID-19 era. However, after adjustment for main baseline differences, COPD did not result as independent predictor for in-hospital death (adjusted OR [95% CI] = 0.913[0.658â1.266], P = 0.585) nor for 30-days mortality (adjusted OR [95% CI] = 0.850 [0.620â1.164], P = 0.310). No significant differences were detected in terms of SARS-CoV-2 positivity between the two groups. Conclusion: This is one of the largest studies investigating characteristics and outcome of COPD patients with STEMI undergoing primary angioplasty, especially during COVID pandemic. COPD was associated with significantly higher rates of in-hospital and 30-days mortality. However, this association disappeared after adjustment for baseline characteristics. Furthermore, COPD did not significantly affect SARS-CoV-2 positivity. Trial registration number: NCT 04412655 (2nd June 2020)
Simple Dip-Coating Process for the Synthesis of Small Diameter Single-Walled Carbon NanotubesâEffect of Catalyst Composition and Catalyst Particle Size on Chirality and Diameter
The importance of a Biosphere Reserve of Atlantic Forest for the conservation of stream fauna
Assessment of phenolic herbicide toxicity and mode of action by different assays
A phytotoxicity assay based on seed germination/root elongation has been optimized and used to evaluate the toxic effects of some phenolic herbicides. The method has been improved by investigating the influence of experimental conditions. Lepidium sativum was chosen as the most suitable species, showing high germinability, good repeatability of root length measurements, and low sensitivity to seed pretreatment. DMSO was the most appropriate solvent carrier for less water-soluble compounds. Three dinitrophenols and three hydroxybenzonitriles were tested: dinoterb, DNOC, 2,4-dinitrophenol, chloroxynil, bromoxynil, and ioxynil. Toxicity was also determined using the Vibrio fischeri MicrotoxA (R) test, and a highly significant correlation was found between EC50 values obtained by the two assays. Dinoterb was the most toxic compound. The toxicity of hydroxybenzonitriles followed the order: ioxynil > bromoxynil > chloroxynil; L. sativum exhibited a slightly higher sensitivity than V. fischeri to these compounds. A QSAR analysis highlighted the importance of hydrophobic, electronic, and hydrogen-bonding interactions, in accordance with a mechanism of toxic action based on protonophoric uncoupling of oxidative phosphorylation. The results suggest that the seed germination/root elongation assay with L. sativum is a valid tool for the assessment of xenobiotic toxicity and can be recommended as part of a test battery
Application of the ReaxFF Reactive Force Field to Reactive Dynamics of Hydrocarbon Chemisorption and Decomposition
Can We Optimize Arc Discharge and Laser Ablation for Well-Controlled Carbon Nanotube Synthesis?
- âŠ