Are Quasar Jets Matter or Poynting Flux Dominated?

If quasar jets are accelerated by magnetic fields but terminate as matter dominated, where and how does the transition occur between the Poynting-dominated and matter-dominated regimes? To address this question, we study constraints which are imposed on the jet structure by observations at different spatial scales. We demonstrate that observational data are consistent with a scenario where the acceleration of a jet occurs within 10^{3-4} R_g. In this picture, the non-thermal flares -- important defining attributes of the blazar phenomenon - are produced by strong shocks formed in the region where the jet inertia becomes dominated by matter. Such shocks may be formed due to collisions between the portions of a jet accelerated to different velocities, and the acceleration differentiation is very likely to be related to global MHD instabilities.Comment: to appear in "Astrophysical Sources of High Energy Particles and Radiation", AIP Proceedings Series, eds. T. Bulik, G. Madejski, and B. Rudak (20-24 June 2005, Torun, Poland

Large-scale bottleneck effect in two-dimensional turbulence

The bottleneck phenomenon in three-dimensional turbulence is generally associated with the dissipation range of the energy spectrum. In the present work, it is shown by using a two-point closure theory, that in two-dimensional turbulence it is possible to observe a bottleneck at the large scales, due to the effect of friction on the inverse energy cascade. This large-scale bottleneck is directly related to the process of energy condensation, the pile-up of energy at wavenumbers corresponding to the domain size. The link between the use of friction and the creation of space-filling structures is discussed and it is concluded that the careless use of hypofriction might reduce the inertial range of the energy spectrum

Two case studies of severe storms in the Mediterranean using AMSU

International audienceMediterranean storms and their associated upper level features are diagnosed here using Advanced Microwave Sounding Unit (AMSU) observations. AMSU-A channel 8 is used to identify upper-level intrusions of stratospheric air, which are often present upstream of heavy precipitating areas, while a combination of AMSU-B channels 3 and 5 is chosen to discriminate moderate to heavily precipitating areas. This precipitation detection method provides results that are in good agreement with TRMM rainfall product and independent ground-based precipitation data. These tools allow us to follow the concomitant evolution of two severe rainfall events in the Mediterranean region and associated upper-level features

Comparison of ten packages that compute ocean carbonate chemistry

International audienceMarine scientists often use two measured or modeled carbonate system variables to compute others. These carbonate chemistry calculations, based on well-known thermodynamic equilibria, are now available in a dozen public packages. Ten of those were compared using common input data and the set of equilibrium constants recommended for best practices. Current versions of all 10 packages agree within 0.2 μatm for pCO2, 0.0002 units for pH, and 0.1 μmol kg−1 for CO32− in terms of surface zonal-mean values. That represents more than a 10-fold improvement relative to outdated versions of the same packages. Differences between packages grow with depth for some computed variables but remain small. Discrepancies derive largely from differences in equilibrium constants. Analysis of the sensitivity of each computed variable to changes in each constant reveals the general dominance of K1 and K2 but also the comparable sensitivity to KB for the AT–CT input pair. Best-practice formulations for K1 and K2 are implemented consistently among packages. Yet with more recent formulations designed to cover a wider range of salinity, packages disagree by up to 8 μatm in pCO2, 0.006 units in pH, and 1 μmol kg−1 in CO32− under typical surface conditions. They use different proposed sets of coefficients for these formulations, all of which are inconsistent. Users would do well to use up-to-date versions of packages and the constants recommended for best practices

Early phrenic motor neuron loss and transient respiratory abnormalities following unilateral cervical spinal cord contusion

Contusion-type cervical spinal cord injury (SCI) is one of the most common forms of SCI observed in patients. In particular, injuries targeting the C3-C5 region affect the pool of phrenic motor neurons (PhMNs) that innervates the diaphragm, resulting in significant and often chronic respiratory dysfunction. Using a previously described rat model of unilateral midcervical C4 contusion with the Infinite Horizon Impactor, we have characterized the early time course of PhMN degeneration and consequent respiratory deficits following injury, as this knowledge is important for designing relevant treatment strategies targeting protection and plasticity of PhMN circuitry. PhMN loss (48% of the ipsilateral pool) occurred almost entirely during the first 24 h post-injury, resulting in persistent phrenic nerve axonal degeneration and denervation at the diaphragm neuromuscular junction (NMJ). Reduced diaphragm compound muscle action potential amplitudes following phrenic nerve stimulation were observed as early as the first day post-injury (30% of pre-injury maximum amplitude), with slow functional improvement over time that was associated with partial reinnervation at the diaphragm NMJ. Consistent with ipsilateral diaphragmatic compromise, the injury resulted in rapid, yet only transient, changes in overall ventilatory parameters measured via whole-body plethysmography, including increased respiratory rate, decreased tidal volume, and decreased peak inspiratory flow. Despite significant ipsilateral PhMN loss, the respiratory system has the capacity to quickly compensate for partially impaired hemidiaphragm function, suggesting that C4 hemicontusion in rats is a model of SCI that manifests subacute respiratory abnormalities. Collectively, these findings demonstrate significant and persistent diaphragm compromise in a clinically relevant model of midcervical contusion SCI; however, the therapeutic window for PhMN protection is restricted to early time points post-injury. On the contrary, preventing loss of innervation by PhMNs and/or inducing plasticity in spared PhMN axons at the diaphragm NMJ are relevant long-term targets

Characterization and Cradiovascular Effects of (13S)-9α,13α-epoxylabda-6β(19),15(14)diol dilactone, a Diterpenoid Isolated from Leonotis leonurus

A new diterpenoid, (13S)-9 ,13 -epoxylabda-6 (19),15(14)diol dilactone (1), was isolated from Leonotis leonurus and the structure determined via NMR analysis. The compound causes significant changes in blood pressure of anaesthetized normotensive rats and exhibits a negative chronotropic effect.Web of Scienc

Spatial distribution and abondance of freshwater snails in Lake Kivu, DR Congo side

               The main goal of this investigation was to study the distribution of freshwater molluscs in Lake Kivu located in DR Congo side. Mollusca play important role in the public and veterinary health and thus need to be study their distribution continuously. The semi-quantitative surveys carried out during the period of January 2019 to December 2019 has focused on sites selected in lake covering the dry and wet seasons. The choice of these sites was based on the molluscan data available, physical structure of the littoral and structure associated vegetation. The harvesting of snails in the littoral zone of Lake Kivu was done using a plankton net and pliers. The physicochemical parameters of the water at each site were carried out using the standard water quality analysis method. The collected snails were morphologically identified using different identification keys. Biomphalaria species were analyzed for trematode infestation. One thousand three hundred and thirty-six (1,356) snails belonging to seven genera and seven species were recorded during the study. The overall relative percentage of the various snail species recorded was: Biomphalaria pfeifferi (50.8 %), Biomphalaria smithi (13.1 %), Gabbielle spirilosa (11.2 %), Bulinus tuncatus (10.2 %), Lymnea natalensis (5.7 %), Helisoma duryi (2.5 %), Pila ovata (1.4), Melanoides tuberculata (1.2%), Lymnea columella (0.7 %), Tomchia hendrexyx (0.6 %), Bulinus forskalii (0.5 %), Tomchia ventricosa and Physa acuta (0.4 %), Tomchia zwellandanensis, Corbicula fluminalis and Hydrobia accrensis  (0.3 %), Lymnae palutris (0.2 %), Tomchia kivuensis and Segmentorbis kempi (0.1 %). The present clarified the distribution and seasonal abundance of freshwater snails in Lake Kivu, DRCongo side. Eighteen species of freshwater snails were collected in the malacological survey in the Lake Kivu, DRC side. The observed snail distribution can provide insight into some aspects of the epidemiology of trematode infection in the study area and the potential risks to humans and animals. The implications of these findings for the control of snail-borne trematodes are also discussed