385 research outputs found
Compact x-ray source based on burst-mode inverse Compton scattering at 100 kHz
A design for a compact x-ray light source (CXLS) with flux and brilliance
orders of magnitude beyond existing laboratory scale sources is presented. The
source is based on inverse Compton scattering of a high brightness electron
bunch on a picosecond laser pulse. The accelerator is a novel high-efficiency
standing-wave linac and RF photoinjector powered by a single ultrastable RF
transmitter at x-band RF frequency. The high efficiency permits operation at
repetition rates up to 1 kHz, which is further boosted to 100 kHz by operating
with trains of 100 bunches of 100 pC charge, each separated by 5 ns. The entire
accelerator is approximately 1 meter long and produces hard x-rays tunable over
a wide range of photon energies. The colliding laser is a Yb:YAG solid-state
amplifier producing 1030 nm, 100 mJ pulses at the same 1 kHz repetition rate as
the accelerator. The laser pulse is frequency-doubled and stored for many
passes in a ringdown cavity to match the linac pulse structure. At a photon
energy of 12.4 keV, the predicted x-ray flux is
photons/second in a 5% bandwidth and the brilliance is in pulses with RMS pulse
length of 490 fs. The nominal electron beam parameters are 18 MeV kinetic
energy, 10 microamp average current, 0.5 microsecond macropulse length,
resulting in average electron beam power of 180 W. Optimization of the x-ray
output is presented along with design of the accelerator, laser, and x-ray
optic components that are specific to the particular characteristics of the
Compton scattered x-ray pulses.Comment: 25 pages, 24 figures, 54 reference
Cycloidal Domains in the Magnetization Reversal Process of Ni80Fe20/Nd16Co84/Gd12Co88 Trilayers
The magnetization reversal of each individual layer in magnetic trilayers (
permalloy
/
Nd
Co
/
Gd
Co
) is investigated in detail with x-ray microscopy and micromagnetic calculations. Two sequential inversion mechanisms are identified. First, magnetic vortex-antivortex pairs move along the field direction while inverting the magnetization of magnetic stripes until they are pinned by defects. The vortex-antivortex displacements are reversible within a field interval which allows their controlled motion. Second, as the reversed magnetic field increases, cycloidal domains appear in the permalloy layer as a consequence of the dissociation of vortex-antivortex pairs due to pinning. The field range where magnetic vortices and antivortices are effectively guided by the stripe pattern is of the order of tens of mT for the
Ni
Fe
layer, as estimated from the stability of cycloid domains in the sample
Electron beam shaping via laser heater temporal shaping
Active longitudinal beam optics can help FEL facilities achieve cutting edge
performance by optimizing the beam to: produce multi-color pulses, suppress
caustics, or support attosecond lasing. As the next generation of
superconducting accelerators comes online, there is a need to find new elements
which can both operate at high beam power and which offer multiplexing
capabilities at Mhz repetition rate. Laser heater shaping promises to satisfy
both criteria by imparting a programmable slice-energy spread on a shot-by-shot
basis. We use a simple kinetic analysis to show how control of the slice energy
spread translates into control of the bunch current profile, and then we
present a collection of start-to-end simulations at LCLS-II in order to
illustrate the technique.Comment: 12 pages, 11 figure
One Anastomosis/Mini-Gastric Bypass (OAGB/MGB) as Revisional Surgery Following Primary Restrictive Bariatric Procedures: a Systematic Review and Meta-Analysis
One anastomosis gastric bypass (OAGB/MGB) has gained popularity in the past decade. International databases were searched for articles published by September 10, 2020, on OAGB/MGB as a revisional procedure after restrictive procedures. Twenty-six studies examining a total of 1771 patients were included. The mean initial BMI was 45.70 kg/m2, which decreased to 31.52, 31.40, and 30.54 kg/m2 at 1, 3, and 5-year follow-ups, respectively. Remission of type-2 diabetes mellitus (T2DM) following OAGB/MGB at 1-, 3-, and 5-year follow-up was 65.16 ± 24.43, 65.37 ± 36.07, and 78.10 ± 14.19%, respectively. Remission/improvement rate from gastroesophageal reflux disease (GERD). Also, 7.4% of the patients developed de novo GERD following OAGB/MGB. Leakage was the most common major complication. OAGB/MGB appears to be feasible and effective as a revisional procedure after failed restrictive bariatric procedures
The first survey addressing patients with BMI over 50: a survey of 789 bariatric surgeons
Background: Bariatric surgery in patients with BMI over 50 kg/m2 is a challenging task. The aim of this study was to address main issues regarding perioperative management of these patients by using a worldwide survey. Methods: An online 48-item questionnaire-based survey on perioperative management of patients with a BMI superior to 50 kg/m2 was ideated by 15 bariatric surgeons from 9 different countries. The questionnaire was emailed to all members of the International Federation of Surgery for Obesity (IFSO). Responses were collected and analyzed by the authors. Results: 789 bariatric surgeons from 73 countries participated in the survey. Most surgeons (89.9%) believed that metabolic/bariatric surgery (MBS) on patients with BMI over 50 kg/m2 should only be performed by expert bariatric surgeons. Half of the participants (55.3%) believed that weight loss must be encouraged before surgery and 42.6% of surgeons recommended an excess weight loss of at least 10%. However, only 3.6% of surgeons recommended the insertion of an Intragastric Balloon as bridge therapy before surgery. Sleeve Gastrectomy (SG) was considered the best choice for patients younger than 18 or older than 65 years old. SG and One Anastomosis Gastric Bypass were the most common procedures for individuals between 18 and 65 years. Half of the surgeons believed that a 2-stage approach should be offered to patients with BMI > 50 kg/m2, with SG being the first step. Postoperative thromboprophylaxis was recommended for 2 and 4 weeks by 37.8% and 37.7% of participants, respectively. Conclusion: This survey demonstrated worldwide variations in bariatric surgery practice regarding patients with a BMI superior to 50 kg/m2. Careful analysis of these results is useful for identifying several areas for future research and consensus building
Environmental evolution and archaeological record of Barrancas river basin, Jujuy province, Argentina
Since 2012 our research team started the “Barrancas Archaeological Project” which main goal is to study the history of the people that dwelled this locality and neighbouring areas during the last 10000 years and yo put in value the cultural heritage of these societies. This paper have two aims: 1) to characterize the general environmental evolution of the Barrancas river basin since the end of Pleistocene and to discuss its impact on the human groups that used it: and 2) to briefly describe the archaeological record recovered in the upper and mid-section of the Barrancas river, mainly the chronology and general characteristics of the archaeological sites under study and the relative chronology and placement of the currently documented rock art. Barrancas archaeological evidence conjoined with the paleoenvironmental data obtained in this basin shows that substantial changes in local habitats have had a relevant role in the way in what human groups used this spaces through time, allowing to characterize them alternatively as a nodal or inter-nodal area through Holocene.Introducción El área de estudio - Antecedentes paleoambientales suprarregionales y regionales Evolución ambiental de Barrancas - Los registros paleoambientales de Barrancas - Tendencias paleoambientales - Evolución de la capacidad de carga en la cuenca desde los 7300 cal AP Síntesis de los sitios arqueológicos y ocupaciones humanas en Barrancas - Ocupaciones humanas del Holoceno Temprano y Medio (10.000-3750 años cal. AP) - Ocupaciones humanas entre 3500-1550 años cal. AP - Ocupaciones humanas ente 1200 y 200 cal AP - Manifestaciones rupestres Discusión y Conclusió
One Star to Tag Them All (OSTTA): I. Radial velocities and chemical abundances for 20 poorly studied open clusters
Context: Open clusters are ideal laboratories to investigate a variety of
astrophysical topics, from the properties of the Galactic disc to stellar
evolution models. For this purpose, we need to know their chemical composition
in detail. Unfortunately, the number of systems with chemical abundances
determined from high resolution spectroscopy remains small. Aims: Our aim is to
increase the number of open clusters with radial velocities and chemical
abundances determined from high resolution spectroscopy by sampling a few stars
in clusters not studied previously. Methods: We obtained high resolution
spectra with the FIES spectrograph at NOT for 41 stars belonging to 20 open
clusters. These stars have high astrometric membership probabilities,
determined from the Gaia second data release. Results: We derived radial
velocities for all the observed stars, which were used to confirm their
membership to the corresponding clusters. For Gulliver\,37 we cannot be sure
the observed star is a real member. We derived atmospheric parameters for the
32 stars considered real cluster members. We discarded five stars because they
have very low gravity or atmospheric parameters were not properly constrained
due to low signal-to-noise ratio spectra. Therefore, detailed chemical
abundances were determined for 28 stars belonging to 17 clusters. For most of
them, this is the first chemical analysis available in the literature. Finally,
we compared the clusters in our sample to a large population of well studied
clusters. The studied systems follow the trends, both chemical and kinematical,
described by the majority of open clusters. Worth noticing that the three most
metal-poor studied clusters (NGC\,1027, NGC\,1750 and Trumpler 2) are enhanced
in Si but not in the other alpha-elements studied (Mg, Ca and Ti).Comment: 19 pages Accepted for publication on A&
Nitrate removal in saline water by photo-reduction using natural FeTiO as catalyst
As climate change progresses, there is an increasing interest on the use of non-conventional water sources such as brackish or saline waters. Nowadays, the main threat in Europe detected in these waterbodies is nitrate contamination. Within the multiple available methods studied for nitrate reduction, photocatalysis presents promising results, but this technology has not yet been tested in saline water. This work tackles the elimination of nitrate ([NO3−] =50 mg/L) in brackish and saline water ([sea salt] = 5–33 g/L) using ilmenite as photocatalyst and oxalic acid as an environmental-friendly reducing agent. The main challenge when working in saline water is to overcome oxalic acid scavenging by Ca2+ present in the water matrix. This can be solved either working at over stoichiometric concentrations of oxalic acid (≈300% stoich. dose) or acidifying the reaction media. The addition of hydrochloric acid ensures the protonation of oxalic acid, reducing drastically its precipitation as CaC2O4. Working at [C2O42−] = 180 mg/L, [FeTiO3] = 450 mg/L and [HCl 37%] = 13 mM, 73% total nitrogen (TN) elimination was reached after 420 min. Reaction temperature was also evaluated in the range of 20–80 °C, which allowed to calculate the Ea=9.8 kJ/mol. Finally, the effect of dissolved O2 on the TN reduction was assessed. Overall, photocatalytic nitrate reduction presents itself as a feasible technology regardless of the water salinit
Price and service competition with maintenance service bundling
In many equipment manufacturing industries, firms compete with each other not only on products price, but also on maintenance service. More and more traditional products oriented firms are offering their customers products bundled with maintenance service (P&S bundles). In this study, we examine firms’ incentive to offer customers products bundling with long-term maintenance or repair support service in a duopoly competitive environment. When providing P&S bundles, a firm need to determine the service level (in terms of average response time guarantee for the service in this paper) to offer and needs to build a service facility to handle the maintenance service requirements. Based on the analysis of three sub-game models, we characterize the market conditions in which only one firm, both firms or neither firm will offer P&S bundles. Finally, we analyze the affects of several market factors on firms’ strategy choices
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