Internal shocks in the jets of radio-loud quasars

The central engine causing the production of jets in radio sources may work intermittently, accelerating shells of plasma with different mass, energy and velocity. Faster but later shells can then catch up slower earlier ones. In the resulting collisions shocks develop, converting some of the ordered bulk kinetic energy into magnetic field and random energy of the electrons which then radiate. We propose that this internal shock scenario, which is the scenario generally thought to explain the observed gamma-ray burst radiation, can work also for radio sources in general, and for blazar in particular. We investigate in detail this idea, simulating the birth, propagation and collision of shells, calculating the spectrum produced in each collision, and summing the locally produced spectra from those regions of the jet which are simultaneously active in the observer's frame. We can thus construct snapshots of the overall spectral energy distribution as well as time dependent spectra and light curves. This allows us to characterize the predicted variability at any frequency, study correlations among the emission at different frequencies, specify the contribution of each region of the jet to the total emission, find correlations between flares at high energies and the birth of superluminal radio knots and/or radio flares. The model has been applied to qualitatively reproduce the observed properties of 3C 279. Global agreement in terms of both spectra and temporal evolution is found. In a forthcoming work, we explore the constraints which this scenario sets on the initial conditions of the plasma injected in the jet and the shock dissipation for different classes of blazars.Comment: 12 pages, 10 postscript figures, submitted to MNRA

Relationships among lying and standing behaviour, body condition score and milk production in primiparous cows

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Diagnostic accuracy of intracranial translucency in detecting spina bifida: a systematic review and meta-analysis

OBJECTIVE: To evaluate the diagnostic accuracy of intracranial translucency (IT) in the detection of spina bifida (SB) in the first trimester of pregnancy. METHODS: We included study assessing the accuracy of sonographic measurements of IT in a mid-sagittal view of the fetal face in prediction of SB in the first trimester of pregnancy. The primary outcome was the accuracy of IT in prediction of spina bifida. Summary estimates of sensitivity, specificity, positive and negative likelihood ratios (LR), and diagnostic odds ratio for the overall predictive accuracy of IT were computed. RESULTS: Nine studies (21 070 fetuses) were included in the analysis. IT was successfully assessed in the majority of fetuses 97.8% (95% CI 97.6-98.0). The diagnostic performance of IT in detecting SB was as follows: sensitivity: 53.5% (95% CI 42.4-64.3), specificity: 99.7% (95% CI 99.6-99.8), positive LR: 62.1 (95% CI 12.2-317), negative LR:0.55 (95% CI 0.45-0.68), and diagnostic odds ratio: 223 (95% CI 25-2039). CONCLUSIONS: Intracranial translucency had low diagnostic accuracy in prediction of open spina bifida, thus questioning its role as a screening marker for open SB in an unselected population. When looking at the individual study data, it appears that IT assessment for open SB prediction can be affected by a high rate of false positive results potentially leading to unnecessary parental anxiet

A radiochemistry laboratory exercise: determination of uranium in tap water by solvent extraction and liquid scintillation counting

Environmental radiochemistry is a key pillar of the education of nuclear engineering students and young professionals. Teaching the fundamentals of this multidisciplinary field is best performed also through well-designed hands-on experiments. A simple and fast radiochemical procedure has been developed to determine uranium in tap water by liquid scintillation counting. The proposed method provides reliable and repeatable results, with accuracy and precision within 5%. It can be proficiently executed by undergraduate students, who have appreciated the engagement and got acquainted with standard analysis protocols, from sample collection and manipulation to radiometric measure and data analysis

Inverted Ligand Field in a Pentanuclear Bow Tie Au/Fe Carbonyl Cluster

Gold chemistry has experienced in the last decades exponential attention for a wide spectrum of chemical applications, but the +3 oxidation state, traditionally assigned to gold, remains somewhat questionable. Herein, we present a detailed analysis of the electronic structure of the pentanuclear bow tie Au/Fe carbonyl cluster [Au{η2-Fe2(CO)8}2]- together with its two one-electron reversible reductions. A new interpretation of the bonding pattern is provided with the help of inverted ligand field theory. The classical view of a central gold(III) interacting with two [Fe2(CO)8]2- units is replaced by Au(I), with a d10 gold configuration, with two interacting [Fe2(CO)8]- fragments. A d10 configuration for the gold center in the compound [Au{η2-Fe2(CO)8}2]- is confirmed by the LUMO orbital composition, which is mainly localized on the iron carbonyl fragments rather than on a d gold orbital, as expected for a d8 configuration. Upon one-electron stepwise reduction, the spectroelectrochemical measurements show a progressive red shift in the carbonyl stretching, in agreement with the increased population of the LUMO centered on the iron units. Such a trend is also confirmed by the X-ray structure of the direduced compound [Au{η1-Fe2(CO)8}{η2-Fe2(CO)6(μ-CO)2}]3-, featuring the cleavage of one Au-Fe bond

Short-term cardiac outcome in survivors of COVID-19: a systematic study after hospital discharge

Background COVID-19 has caused considerable morbidity and mortality worldwide and cardiac involvement has been reported during infection. The short-term cardiac outcome in survivors of COVID-19 is not known.Objective To examine the heart of patients who survived COVID-19 and to compare the cardiac outcome between patients who recovered from mild-to-moderate or severe illness.Methods With use of ECG and echocardiography, we examined the heart of 105 patients who had been hospitalized with COVID-19 and were consecutively recruited after hospital discharge while attending follow-up visits. Survivors of COVID-19 were compared with 105 matched controls. We also compared the cardiac outcome and lung ultrasound scan between COVID-19 patients who had mild-to-moderate or severe illness.Results Cardiac data were collected a median of 41 days from the first detection of COVID-19. Symptoms were present in a low percentage of patients. In comparison with matched controls, no considerable structural or functional differences were observed in the heart of survivors of COVID-19. Lung ultrasound scan detected significantly greater residual pulmonary involvement in COVID-19 patients who had recovered from severe than mild-to-moderate illness. No significant differences were detected in ECG tracings nor were found in the left and right ventricular function of patients who had recovered from mild-to-moderate or severe illness.Conclusions In a short-term follow-up, no abnormalities were identified in the heart of survivors of COVID-19, nor cardiac differences were detected between patients who had different severity of illness. With the limitations of a cross-sectional study, these findings suggest that patients who recover from COVID-19 do not have considerable cardiac sequelae.[GRAPHICS]