1,241 research outputs found
Longitudinal phase space manipulation in energy recovering linac-driven free-electron lasers
Energy recovering an electron beam after it has participated in a
free-electron laser (FEL) interaction can be quite challenging because of the
substantial FEL-induced energy spread and the energy anti-damping that occurs
during deceleration. In the Jefferson Lab infrared FEL driver-accelerator, such
an energy recovery scheme was implemented by properly matching the longitudinal
phase space throughout the recirculation transport by employing the so-called
energy compression scheme. In the present paper,after presenting a
single-particle dynamics approach of the method used to energy-recover the
electron beam, we report on experimental validation of the method obtained by
measurements of the so-called "compression efficiency" and "momentum
compaction" lattice transfer maps at different locations in the recirculation
transport line. We also compare these measurements with numerical tracking
simulations.Comment: 31 pages, 13 figures, submitted to Phys. Rev. Special Topics A&
Geotraceability: an innovative concept to enhance conventional traceability in the agri-food chain
With the globalization of trade, people have become enlightened and demanding consumers as regards the origin of their food and the environment in which it is produced. The concept of geotraceability described in this article responds to that requirement by combining geographical information with conventional traceability data. The inclusion of geographical information relating to the environment of the production plots is based not only on exploiting some functionalities of spatial analysis tools that exist in geographical information systems (GIS) but also on developing specific tools such as a geoidentifier and geoindicators. This article also describes the characteristics and methods of implementing a geographical information management system linked with traceability information. Lastly, the potential for using geotraceability systems in supply chains is analyzed, in particular for consumer warnings in cases of food crisis and assistance for certification of differentiated quality agricultural products
Evaluation des Nationalen Programms ErnĂ€hrung und Bewegung 2008â2012 [Evaluation NPEB 2008-2012]
Le PNAAP 2008â2012 dĂ©finit la stratĂ©gie nationale pour la promotion dâune alimentation
équilibrée et d'une activité physique suffisante. Le 18 juin 2008, le Conseil fédéral adoptait le
programme et chargeait le DFI de sa mise en pratique. Ce programme définit des objectifs à long
terme ainsi que des champs dâaction prioritaires pour la marche Ă suivre au plan national ; câest
aussi sur ce programme que se base la collaboration des différents acteurs impliqués. Sa mise en
Ćuvre a Ă©tĂ© confiĂ©e Ă lâOffice fĂ©dĂ©ral de la santĂ© publique (OFSP), en collaboration avec lâOffice
fédéral du sport (OFSPO) et en coordination avec les cantons et Promotion Santé Suisse (PSS). Le
PNAAP a une vision: motiver la population et plus particuliĂšrement les jeunes Ă se nourrir de
maniĂšre Ă©quilibrĂ©e et Ă bouger suffisamment, car ces mesures sont Ă mĂȘme de lutter efficacement
contre la surcharge pondĂ©rale, lâobĂ©sitĂ©, les troubles du comportement alimentaire et les
maladies non transmissibles qui y sont liées. Le programme a cinq objectifs:
1. Assurer la coordination nationale
2. Promouvoir une alimentation équilibrée
3. Promouvoir lâactivitĂ© physique et le sport
4. RĂ©aliser des modĂšles intĂ©grĂ©s de promotion dâun poids corporel sain
5. Optimiser le conseil et la thérapi
High Power Test of RF Separator for 12 GEV Upgrade of CEBAF at Jefferson Lab
CEBAF at JLab is in the process of an energy upgrade from 6 GeV to 12 GeV. The existing setup of the RF separator cavities in the 5th pass will not be adequate enough to extract the highest energy (11 GeV) beam to any two existing halls (A, B or C) while simultaneously delivering to the new hall D in the case of the proposed 12 GeV upgrade of the machine. To restore this capability, several options including the extension of existing normal conducting (NC) and a potential 499 MHz TEM-type superconducting (SC) cavity design have been investigated using computer simulations. Detailed numerical studies suggest that six 2-cell normal conducting structures meet the requirements; each 2-cell structure will require up to 4 kW RF input power in contrast with the current nominal operating power of 1.0 to 2.0 kW. A high power test to 4 kW is required to confirm the cavityâs operate-ability at these elevated gradient and power levels. We have assembled a 2-cell cavity, pumped down to 2.0·10-9 torr using ion pump and confirmed the low level RF performance. A high power test is in progress and will be completed soon. The detailed numerical and experimental results will be discussed in the paper
Measuring and Controlling the Energy Spread in CEBAF
As compared to electron storage rings, one advantage of recirculating linear
accelerators is that the beam properties at target are no longer dominated by
the equilibrium between quantum radiative diffusion and radiation damping
because new beam is continually injected into the accelerator. This allows the
energy spread from a CEBAF-type machine to be relatively small; the measured
energy spread from CEBAF at 4 GeV is less than 100 parts per million
accumulated over times of order several days. In this paper, the various
subsystems contributing to the energy spread of a CEBAF-type accelerator are
reviewed, as well as the machine diagnostics and controls that are used in
CEBAF to ensure that a small energy spread is provided during routine running.
Examples of relevant developments are (1) stable short bunches emerging from
the injector, (2) precision timing and phasing of the linacs with respect to
the centroid of the beam bunches on all passes, (3) implementing 2 kHz sampling
rate feedback systems for final energy stabilization, and (4) continuous beam
energy spread monitoring with optical transition radiation devices. We present
measurement results showing that small energy spreads are achieved over
extended periods.Comment: 5 pages, 5 figures, Invited Paper TH205 at 2000 International Linac
Conferenc
The influence of the Great Recession on perinatal healthâan ecological study on the trend changes and regional differences in Portugal
Background: Few studies examine the relationship between socioeconomic factors and trends in mortality in high-income European countries. Due to the lack of regional-level data, most recent studies on social inequality in Portugal do not investigate regional differences. This study analyses time trends and regional disparities in the evolution of perinatal mortality (PMR) and infant mortality (IMR) associated with demographic and socioeconomic indicators following Portugal's 2008 economic and financial crisis. Methods: Associations were assessed using generalised linear models. A Poisson joinpoint regression model was applied to identify relevant PMR and IMR changes between 2000 and 2018. Country regional disparities were analysed using Mixed Effect Multilevel models. Findings: IMR and PMR significantly decreased in the pre-crisis period but not in the post-crisis period. The significant differences between regions in IMR and PMR in 2000 were followed by a different evolution of regional IMR after 2008. PMR and IMR were not significantly associated with socioeconomic indicators. A significant positive association with maternal age at first birth was identified. Interpretation: Results confirm the influence of the crisis on PMR and IMR trends in Portugal, taking into account recurring associations between macroeconomic cycles, variations in mortality trends, macroeconomic volatility, and stagnation of IMR and PMR. Regional inequalities confirm the internal variability of the crisis influence and persistent spatial inequalities affecting IMR patterns. Funding: FCT, under the Institute of Public Health of the University of Porto (ISPUP)â EPIUnit ( UIDB/04750/2020) and ITR ( LA/P/0064/2020), Maastricht University's external PhD programme under the Care and Public Health Research Institute ( CAPHRI), and the RECAP preterm project (grant agreement no 733280). © 2023 The Author(s)FCT, under the Institute of Public Health of the University of Porto (ISPUP)âEPIUnit (UIDB/04750/2020) and ITR (LA/P/0064/2020), Maastricht University's external PhD programme under the Care and Public Health Research Institute (CAPHRI), and the RECAP preterm project (grant agreement no 733280)
Potential application of hydrogen in traumatic and surgical brain injury, stroke and neonatal hypoxia-ischemia
This article summarized findings of current preclinical studies that implemented hydrogen administration, either in the gas or liquid form, as treatment application for neurological disorders including traumatic brain injury (TBI), surgically induced brain injury (SBI), stroke, and neonatal hypoxic-ischemic brain insult (HI). Most reviewed studies demonstrated neuroprotective effects of hydrogen administration. Even though anti-oxidative potentials have been reported in several studies, further neuroprotective mechanisms of hydrogen therapy remain to be elucidated. Hydrogen may serve as an adjunct treatment for neurological disorders
(Towards) Spin-polarized scanning tunneling microscopy of NiFe films on a chromium001 single crystal: Growth and electronic structure of Permalloy
This paper shows spin-polarized tunneling on the terraces of antiferromagnetic chromiums001d.
Details on the morphological and chemical composition are shown as a function of various stages
of surface preparation, and protocols for obtaining Crs001d that reveal spin-polarized contrast are
reported. On the clean crystal the chromium surface state at the Fermi level could be observed. The
spin splitting of the state was measured by using an iron coated tungsten tip. A spin polarization of
10% was observed. The properties of NiFe grown on Crs001d measured using nonpolarized
tunneling spectroscopy are also reported. Monolayer thick permalloy grows in VolmerâWeber
mode, exhibiting pyramidal islands oriented along the chromium k110l direction. Spectroscopic data
reveal that NiFe alloying is preserved
Redesign of the Jefferson Lab -300 kV DC Photo-Gun for High Bunch Charge Operations
Production of high bunch charge beams for the ElectronIon Collider (EIC) is a challenging task. High bunch charge (a few nC) electron beam studies at Jefferson Lab using an inverted insulator DC high voltage photo-gun showed evidence of space charge limitations starting at 0.3 nC, limiting the maximum delivered bunch charge to 0.7 nC for beam at -225 kV, 75 ps (FWHM) pulse width, and 1.64 mm (rms) laser spot size. The low extracted charge is due to the modest longitudinal electric field (Ez) at the photocathode leading to beam loss at the anode and downstream beam pipe. To reach the few nC high bunch charge goal, and to correct the beam deflection exerted by the non-symmetric nature of the inverted insulator photo-gun the existing photo-gun was modified. This contribution discusses the electrostatic design of the modified photo-gun obtained using CST Studio Suiteâs electromagnetic field solver. Beam dynamics simulations performed using General Particle Tracer (GPT) with the resulting electrostatic field map obtained from the modified electrodes confirmed the validity of the new design
Spin states of asteroids in the Eos collisional family
Eos family was created during a catastrophic impact about 1.3 Gyr ago.
Rotation states of individual family members contain information about the
history of the whole population. We aim to increase the number of asteroid
shape models and rotation states within the Eos collision family, as well as to
revise previously published shape models from the literature. Such results can
be used to constrain theoretical collisional and evolution models of the
family, or to estimate other physical parameters by a thermophysical modeling
of the thermal infrared data. We use all available disk-integrated optical data
(i.e., classical dense-in-time photometry obtained from public databases and
through a large collaboration network as well as sparse-in-time individual
measurements from a few sky surveys) as input for the convex inversion method,
and derive 3D shape models of asteroids together with their rotation periods
and orientations of rotation axes. We present updated shape models for 15
asteroids and new shape model determinations for 16 asteroids. Together with
the already published models from the publicly available DAMIT database, we
compiled a sample of 56 Eos family members with known shape models that we used
in our analysis of physical properties within the family. Rotation states of
asteroids smaller than ~20 km are heavily influenced by the YORP effect, whilst
the large objects more or less retained their rotation state properties since
the family creation. Moreover, we also present a shape model and bulk density
of asteroid (423) Diotima, an interloper in the Eos family, based on the
disk-resolved data obtained by the Near InfraRed Camera (Nirc2) mounted on the
W.M. Keck II telescope.Comment: Accepted for publication in ICARUS Special Issue - Asteroids: Origin,
Evolution & Characterizatio
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