Giant collimated gamma-ray flashes

Bright sources of high energy electromagnetic radiation are widely employed in fundamental research as well as in industry and medicine. This steadily growing interest motivated the construction of several facilities aiming at the realisation of sources of intense X- and gamma-ray pulses. To date, free electron lasers and synchrotrons provide intense sources of photons with energies up to 10-100 keV. Facilities under construction based on incoherent Compton back scattering of an optical laser pulse off an electron beam are expected to yield photon beams with energy up to 19.5 MeV and peak brilliance in the range 10$^{20}$-10$^{23}$ photons s$^{-1}$ mrad$^{-2}$ mm$^{-2}$ per 0.1% bandwidth. Here, we demonstrate a novel mechanism based on the strongly amplified synchrotron emission which occurs when a sufficiently dense electron beam interacts with a millimetre thickness solid target. For electron beam densities exceeding approximately 3\times10^{19}\text{ cm^{-3}} filamentation instability occurs with the self-generation of 10$^{7}$-10$^{8}$ gauss magnetic fields where the electrons of the beam are trapped. This results into a giant amplification of synchrotron emission with the production of collimated gamma-ray pulses with peak brilliance above $10^{25}$ photons s$^{-1}$ mrad$^{-2}$ mm$^{-2}$ per 0.1% bandwidth and photon energies ranging from 200 keV up to several hundreds MeV. These findings pave the way to compact, high-repetition-rate (kHz) sources of short (30 fs), collimated (mrad) and high flux ($>10^{12}$ photons/s) gamma-ray pulses.Comment: Full-text access to a view-only version of the published paper by the following SharedIt link: https://rdcu.be/LGtC This is part of the Springer Nature Content Sharing Initiative (https://www.springernature.com/gp/researchers/sharedit). Enhanced PDF features such as annotation tools, one-click supplements, citation file exports and article metrics are freely availabl

Feeding behaviour, digestibility, energy balance and productive performance of lactating goats fed forage-based and forage-free diets

Six lactating Saanen goats have been used in a Latin Square design to evaluate a grass-based diet (G), a hay-based diet(H) and a nonforage diet (NF). On dry matter, grass and hay contributed for 55% of the diets and had 13.7 and 16.1%CP, 55.4 and 49.4% NDF, 38.0 and 31.6% ADF, respectively. Diet NF had beet pulp, cracked carob beans and whole cottonseedas main ingredients, with more than 75% of the particles greater than 2 mm.Independently of the dietary treatment, the goats spent more time eating than ruminating. Diet NF proved to be effectivein stimulating chewing activity, despite a trend for a lower chewing activity for eating (178, 185, 125 min/kg DMIfor diets G, H and NF, respectively), but not for ruminating (84, 80, 80 min/kg DMI for diets G, H and NF, respectively).Feed intake did not differ among diets, while regarding digestibility diet NF had the highest values for DM (74.1%), OM(75.7%) and non-fibrous carbohydrates (92.0%), but the lowest for ADF (44.5%). For treatments G, H and NF milk yieldswere 3011, 3688 and 3212 g/d (P<0.05 between H and G), while milk fat and protein were respectively 3.37, 3.24,2.96% (P<0.05 between G and NF) and 3.11, 3.32, 3.29%. Milk urea N was lower for diet NF (18.8, 18.6, 12.7 mg/100ml, P<0.001). Diet NF increased the concentration of the short chain fatty acids of milk fat and decreased the content ofC18:0, C18:1 and C18:3 in comparison to the other two diets. No difference among treatments was recorded for CLA.Intake energy was digested to a lesser extent for diet G (68.9, 70.0, 72.7%, P<0.05 between G and NF) due to its poorquality forage. Urinary energy losses reflected the corresponding protein contents of the diets, while no difference wasrecorded for methane production. ME resulted higher for diet NF (60.0, 60.7, 65.1% of the intake energy, P<0.01), whileheat production and milk energy yield were similar in the three treatments. Diet NF had a higher ME content (11.13,11.26, 11.93 MJ/kg DM, P<0.05), while no significant difference among the diets was recorded in terms of kl (0.64, 0.70,0.69) and NEl (7.20, 7.93, 8.30 MJ/kg DM).It is concluded from the study that a nonforage diet with an adequate amount of structured fibre could substitute a rationbased on poor quality forage in lactating goats; however, good forage seems to enhance milk performance to a greaterextent

Influence of drag and turbulence modelling on CFD predictions of solid liquid suspensions in stirred vessels

Suspensions of solid particles into liquids within industrial stirred tanks are frequently carried out at an impeller speed lower than the minimum required for complete suspension conditions. This choice allows power savings which usually overcome the drawback of a smaller particle-liquid interfacial area. Despite this attractive economical perspective, only limited attention has been paid so far to the modelling of the partial suspension regime. In the present work two different baffled tanks stirred by Rushton turbines were simulated by employing the Eulerian-Eulerian Multi Fluid Model (MFM) along with either the Sliding Grid algorithm (transient simulations) or the Multiple Reference Frame technique (steady state simulations). In particular, a comparison of alternative modelling approaches for inter-phase drag force and turbulence closure is presented. The results are evaluated against a number of experimental data concerning sediment features (amount and shape) and local axial profiles of solids concentration, with emphasis on the partial suspension regime. Results show that some of the approaches commonly adopted to account for dense particle effects or turbulent fluctuations of the volumetric fractions may actually lead to substantial discrepancies from the experimental data. Conversely simpler models which do not include such additional effects give the best overall predictions in the whole range of partial to complete suspension conditions

Power requirements for complete suspension and aeration in an unbaffled bioslurry reactor

Remediation of contaminated soils is spreading as a matter of crucial importance nowadays. Bioremediation via bioslurry reactors of sites polluted by recalcitrant pollutants has been proved to be a valuable option, although optimization is needed to reduce process costs. Free-surface unbaffled stirred tanks (with central air vortex) have been recently proposed as a promising alternative to the more common systems provided with baffles. In a bioslurry reactor solid-liquid interfacial area, oxygen supply, solid loading per reactor unit volume should be maximized, and, at the same time, operation costs have to be kept low. In this regard, the minimum impeller speeds for complete suspension Njs (suspension of all solid particles) and aeration Nca (air vortex ingested by the turbine and dispersed as bubbles in the system) represents a reasonable compromise between process yield and power requirements. To this purpose, a flat bottomed unbaffled tank with diameter T=0.19 m was investigated. The tank was filled with water up to a height H=T. It was stirred by a radial sixbladed Rushton turbines (RT) with diameter D=T/3 and H=T/3. Mono-dispersed particles with diameter dp=250-300μm and density p≈2500 kg/m3 were employed. Solid loadings B% ranging from 2.5% (weight of solid/weight of liquid) up to the very high 160% w/w were tested. The visual Zwietering criterion along with the aid of a digital camera was employed to evaluate Njs values. An acoustic criterion was adopted to assess Nca. A static frictionless granite turntable was employed to measure the impeller torque at Njs and Nca and to assess the relevant specific power requirements js and ca. Results show that the dependence of Njs and Nca on B% is much lower at low solids loading (B30%). The relevant specific powers per unit mass of solids (i.e. js and ca) were found to exhibit a minimum, at B≈20% for js and B≈60% for ca. On overall, data collected suggest that operating a radially stirred unbaffled bioslurry reactor loaded with a concentration B≈30% could be the best compromise to minimize the costs for achieving complete suspension and aeration conditions

Bipolar disorder and antithyroid antibodies: review and case series

Mood disorders and circulating thyroid antibodies are very prevalent in the population and their concomitant occurrence may be due to chance. However, thyroid antibodies have been repeatedly hypothesized to play a role in specific forms of mood disorders. Potentially related forms include treatment-refractory cases, severe or atypical depression, and depression at specific phases of a woman's life (early gestation, postpartum depression, perimenopausal). With regard to bipolar disorder, studies of specific subgroups (rapid cycling, mixed, or depressive bipolar) have reported associations with thyroid antibodies. Offspring of bipolar subjects were found more vulnerable to develop thyroid antibodies independently from the vulnerability to develop psychiatric disorders. A twin study suggested thyroid antibodies among possible endophenotypes for bipolar disorder. Severe encephalopathies have been reported in association with Hashimoto's thyroiditis. Cases with pure psychiatric presentation are being reported, the antithyroid antibodies being probably markers of some other autoimmune disorders affecting the brain. Vasculitis resulting in abnormalities in cortical perfusion is one of the possible mechanisms

Dense Solid-Liquid Off-Bottom Suspension Dynamics: Simulation and Experiment

Dense solid-liquid off-bottom suspension inside a baffled mechanically agitated stirred tank equipped with a standard Rushton turbine is investigated. Dynamic evolution of the suspension from start up to steady state conditions has been inspected by both visual experiments and computational fluid dynamics. A classical Eulerian-Eulerian Multi Fluid Model along with the “homogeneous” k-epsilon turbulence model is adopted to simulate suspension dynamics. In these systems the drag inter-phase force affects both solids suspension and distribution. Therefore, different computational approaches are tested in order to compute this term. Simulation results are compared with images acquired on the real system and a good agreement is found

CFD prediction of solid particle distribution in baffled stirred vessels under partial to complete suspension conditions

Solid-liquid mixing within tanks agitated by stirrers can be easily encountered in many industrial processes. It is common to find an industrial tank operating at an impeller speed N lower than the minimum agitation speed for the suspension of solid particles: under such conditions the distribution of solid-particles is very far from being homogeneous and very significant concentration gradients exist. The present work evaluates the capability of a Computational Fluid Dynamics (CFD) model to reliably predict the particle distribution throughout the tank under either partial or complete suspension conditions. A flat bottomed baffled tank stirred by a Rushton turbine was investigated. Both transient and steady state RANS simulations of the stirred tank were performed with the commercial code CFX4.4. The Eulerian-Eulerian Multi Fluid Model along with the k-ε turbulence model was adopted. Either the Sliding Grid or the Multiple Reference Frame technique was employed to simulate the impeller to baffle relative rotation. Inter-phase momentum exchange terms were approximated only by the inter-phase drag forces. Literature experimental data were used for the model validation. Results show that the model along with the Sliding Grid technique can reliably predict the experimental particle distribution at all investigated impeller speeds. Radial gradients of solids concentration, usually neglected in the literature, where found to be significant in the presence of unsuspended solid particles (partial suspension conditions)