1,130 research outputs found
Hie-Isolde High Beta Cavity Study and Measurements
The upgrade of the ISOLDE machine at CERN foresees a superconducting linac
based on two gap independently phased Nb sputtered Quarter Wave Resonators
(QWRs) working at 101.28MHz and producing an accelerating field of 6MV/m on
axis. A careful study of the fields in the cavity has been carried out in order
to pin down the crucial e-m parameters of the structure such as peak fields,
quality factor and e-m power dissipated on the cavity wall. A tuning system
with about 200kHz frequency range has been developed in order to cope with
fabrication tolerances. In this paper we will report on the cavity simulations.
The tuning plate design will be described. Finally the frequency measurements
on a cavity prototype at room temperature will be presented.Comment: 5 pages, SRF09 Conference in Berli
The exit-time problem for a Markov jump process
The purpose of this paper is to consider the exit-time problem for a
finite-range Markov jump process, i.e, the distance the particle can jump is
bounded independent of its location. Such jump diffusions are expedient models
for anomalous transport exhibiting super-diffusion or nonstandard normal
diffusion. We refer to the associated deterministic equation as a
volume-constrained nonlocal diffusion equation. The volume constraint is the
nonlocal analogue of a boundary condition necessary to demonstrate that the
nonlocal diffusion equation is well-posed and is consistent with the jump
process. A critical aspect of the analysis is a variational formulation and a
recently developed nonlocal vector calculus. This calculus allows us to pose
nonlocal backward and forward Kolmogorov equations, the former equation
granting the various moments of the exit-time distribution.Comment: 15 pages, 7 figure
A High Phase Advance Damped and Detuned Structure for the Main Linacs of Clic
The main accelerating structures for the CLIC are designed to operate at an
average accelerating gradient of 100 MV/m. The accelerating frequency has been
optimised to 11.994 GHz with a phase advance of 2{\pi}/3 of the main
accelerating mode. The moderately damped and detuned structure (DDS) design is
being studied as an alternative to the strongly damped WDS design. Both these
designs are based on the nominal accelerating phase advance. Here we explore
high phase advance (HPA) structures in which the group velocity of the rf
fields is reduced compared to that of standard (2{\pi}/3) structures. The
electrical breakdown strongly depends on the fundamental mode group velocity.
Hence it is expected that electrical breakdown is less likely to occur in the
HPA structures. We report on a study of both the fundamental and dipole modes
in a CLIC_DDS_HPA structure, designed to operate at 5{\pi}/6 phase advance per
cell. Higher order dipole modes in both the standard and HPA structures are
also studied
Deep carbon storage potential of buried floodplain soils.
Soils account for the largest terrestrial pool of carbon and have the potential for even greater quantities of carbon sequestration. Typical soil carbon (C) stocks used in global carbon models only account for the upper 1 meter of soil. Previously unaccounted for deep carbon pools (>1 m) were generally considered to provide a negligible input to total C contents and represent less dynamic C pools. Here we assess deep soil C pools associated with an alluvial floodplain ecosystem transitioning from agricultural production to restoration of native vegetation. We analyzed the soil organic carbon (SOC) concentrations of 87 surface soil samples (0-15 cm) and 23 subsurface boreholes (0-3 m). We evaluated the quantitative importance of the burial process in the sequestration of subsurface C and found our subsurface soils (0-3 m) contained considerably more C than typical C stocks of 0-1 m. This deep unaccounted soil C could have considerable implications for global C accounting. We compared differences in surface soil C related to vegetation and land use history and determined that flooding restoration could promote greater C accumulation in surface soils. We conclude deep floodplain soils may store substantial quantities of C and floodplain restoration should promote active C sequestration
High Bandwidth Wall Current Monitor for CTF3
Wall Current Monitors (WCM) are commonly used to observe the time profile and spectra of a particle beam by detecting its image current. Within the framework of the EUROTeV Programme, a WCM for CLIC and ILC having a very large bandwidth (100kHz-20GHz) is required and has been developed. A deep study of the field configuration for the device has been necessary. Consequently, the geometrical parameters crucial for a proper functioning of the structure have been found. Furthermore, the very stringent initial requests (bandwidth from 100kHz to 20GHz) were reviewed in a more critical way showing that the low frequency cutoff can be sensibly increased, thus avoiding any ferrite in the structure
Dust properties at z=6.3 in the host galaxy of GRB 050904
We investigate the dust extinction properties in the host galaxy of the
Gamma-Ray Burst (GRB) GRB 050904 at z=6.29 by analyzing simultaneous broad band
observations of the optical and UV afterglow at three different epochs. We show
that the peculiar afterglow spectral energy distribution (SED) observed at 0.5
days and at 1 day after the burst (1.6 and 3 hours rest frame) cannot be
explained with dust reddening with any of the extinction curves observed at low
redshift. Yet, the extinction curve recently inferred for the most distant BAL
QSO at z=6.2 nicely reproduces the SED of GRB 050904 at both epochs. Our result
provides an additional, independent indication that the properties of dust
evolve beyond z~6. We discuss the implications of this finding within the
context of the dust production mechanisms through the cosmic ages.Comment: 4 pages, 2 figures, accepted for publication in ApJ
UVES/VLT high resolution absorption spectroscopy of the GRB080330 afterglow: a study of the GRB host galaxy and intervening absorbers
We study the Gamma Ray Burst (GRB) environment and intervening absorbers by
analyzing the optical absorption features produced by gas surrounding the GRB
or along its line of sight. We analyzed high resolution spectroscopic
observations (R=40000, S/N=3 - 6) of the optical afterglow of GRB080330, taken
with UVES at the VLT ~ 1.5 hours after the GRB trigger. The spectrum
illustrates the complexity of the ISM of the GRB host galaxy at z = 1.51 which
has at least four components in the main absorption system. We detect strong
FeII, SiII, and NiII excited absorption lines associated with the bluemost
component only. In addition to the host galaxy, at least two more absorbers
lying along the line of sight to the afterglow have been detected in the
redshift range 0.8 < z < 1.1, each exhibiting MgII absorption. For the bluemost
component in the host galaxy, we derive information about its distance from the
site of the GRB explosion. We do so by assuming that the excited absorption
lines are produced by indirect UV pumping, and compare the data with a time
dependent photo-excitation code. The distance of this component is found to be
280+40-50 pc, which is lower than found for other GRBs (1 - 6 kpc). We identify
two additional MgII absorbers, one of them with a rest frame equivalent width
larger than 1A. The distance between the GRB and the absorber measured in this
paper confirms that the power of the GRB radiation can influence the conditions
of the interstellar medium up to a distance of at least several hundred pc. For
the intervening absorbers, we confirm the trend that on average one strong
intervening system is found per afterglow, as has been noted in studies
exhibiting an excess of strong MgII absorbers along GRB sightlines compared to
quasars.Comment: 8 Pages, 7 ps figures, A&A in pres
Compensation of Transverse Field Asymmetry in the High-beta Quarter-wave Resonator of the HIE-ISOLDE Linac at CERN
The superconducting upgrade of the REX-ISOLDE radioactive ion beam (RIB)
post-accelerator at CERN will utilise a compact lattice comprising quarter-wave
resonators (QWRs) and solenoids, accelerating beams in the mass range 2.5 < A/q
< 4.5 to over 10 MeV/u. The short and independently phased quarter-wave
structures allow for the acceleration of RIBs over a variable velocity profile
and provide an unrivalled longitudinal acceptance when coupled with solenoid
focusing. The incorporation of the solenoids into the cryomodule shortens the
linac, whilst maximising the acceptance, but the application of solenoid
focusing in the presence of asymmetric QWR fields can have consequences for the
beam quality. The rotation of an asymmetric beam produces an effective
emittance growth in the laboratory reference system. We present modifications
of the cavity geometry to optimise the symmetry of the transverse fields in the
high-beta QWR. A racetrack shaped beam port is analysed and a modification made
to the inner conductor with a geometry that will enable a niobium film to be
effectively sputtered onto the cavity surface.Comment: 5 pages, 9 figures, presented at the 14th international conference on
RF superconductivit
Physical education teaching in Italian primary school: theoretical lines and operational proposals
Background and Study Aim For the new reform to be applied in the best possible way, it is a priority and useful to promote the development of knowledge on the organization and methods of teaching/learning in physical education in primary school. This study aims to search for a new didactic organizational model for physical education in primary school, starting from the theoretical lines, showing the contrasts of the significant aspects and the uniqueness of heuristic learning, with a consequent theoretical and argumentative elaboration of operational proposals.Material and Methods For this purpose, an accurate survey of the scientific literature has been analyzed, highlighting the critical issues that characterized the various proposals and attempt to implement physical activity and sports education courses in primary school over the years, up to the recent legislative innovation.Results The path of the definition of physical education in primary school was marked by stages that did not always enhance the educational and training dimension of the motor and sports experience, making the school discipline assume a marginal and optional role in the face of an extracurricular practice characterized by a widespread organization and more capable of intercepting and responding to the physical exercise and sport needs of society. This complex situation has only generated confusion without solving the problem of the absence of physical and sporting activity in the 5-10 age group, as required by the World Health Organization and the European Union, by adequately and uniquely qualified teachers. It is now useful to promote the development of knowledge on the didactic organization of the primary school, on the different teaching/learning methods in physical education, to contextualize the scope of the new legal provision to the current legal framework.Conclusions The study highlights the value of a new approach in teacher training that aims to ensure the acquisition of key competence, according to the Recommendation of the European Parliament. This perspective can be easily realized by using a core curriculum uniformly applied at the national level
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