4,673 research outputs found
A High Current Proton Linac with 352 MHz SC Cavities
A proposal for a 10-120 mA proton linac employing superconducting
beta-graded, CERN type, four cell cavities at 352 MHz is presented. The high
energy part (100 MeV-1 GeV) of the machine is split in three beta-graded
sections, and transverse focusing is provided via a periodic doublet array. All
the parameters, like power in the couplers and accelerating fields in the
cavities, are within the state of the art, achieved in operating machines. A
first stage of operation at 30 mA beam current is proposed, while the upgrade
of the machine to 120 mA operation can be obtained increasing the number of
klystrons and couplers per cavity. The additional coupler ports, up to four,
will be integrated in the cavity design. Preliminary calculations indicate that
beam transport is feasible, given the wide aperture of the 352 MHz structures.
A capital cost of less than 100 M for the 120
mA extension, has been estimated for the superconducting high energy section
(100 MeV-1 GeV). The high efficiency of the proposed machine, reaching 50% at
15 mA, makes it a good candidate for proposed nuclear waste incineration
facilities and Energy Amplifier studies.Comment: 9 Pages, 4 figures, LaTeX2e, html version found from
http://hptesla.mi.infn.it/~pierini/publication_list.html . To Appear in the
Proceedings of the 1996 LINAC Conference, Geneve, August 26-30 199
The Benefit of Being Non-Lazy in Probabilistic λ-calculus: Applicative Bisimulation is Fully Abstract for Non-Lazy Probabilistic Call-by-Name
Leaders\u2019 competence and warmth: Their relationships with employees\u2019 well-being and organizational effectiveness
The aim of this work was to investigate competence and warmth \u2014 the two basic dimensions of social judgment \u2014 as dimensions employees use to evaluate their supervisors. A mediation model was tested in which supervisor\u2019s perceived competence and warmth were associated with relevant outcomes (lower burnout, weaker turnover intentions, more frequent citizenship behaviors) through the mediation of affective organizational commitment (AOC). In Study 1, data were collected from employees of a company in the water service sector. In Study 2, participants were financial promoters. In Study 3, the sample included employees from different organizations. As hypothesized, the perception of one\u2019s supervisor as competent (Studies 1-3) and warm (Study 3) was related to employees\u2019 lower burnout, weaker turnover intentions, more frequent prosocial behaviors through the mediation of AOC. Theoretical and practical implications of findings are discussed
Selective mass scaling for distorted solid-shell elements in explicit dynamics: optimal scaling factor and stable time step estimate
The use of solid-shell elements in explicit dynamics has been so far limited by the small critical time step resulting from the small thickness of these elements in comparison with the in-plane dimensions. To reduce the element highest eigenfrequency in inertia dominated problems, the selective mass scaling approach previously proposed in [G. Cocchetti, M. Pagani and U. Perego, Comp. \& Struct. 2013; 127:39-52.] for parallelepiped elements is here reformulated for distorted solid-shell elements. The two following objectives are achieved: the critical time step is governed by the smallest element in-plane dimension and not anymore by the thickness; the mass matrix remains diagonal after the selective mass scaling. The proposed approach makes reference to one Gauss point, trilinear brick element, for which the maximum eigenfrequency can be computed analytically. For this element, it is shown that the proposed mass scaling can be interpreted as a geometric thickness scaling, obtaining in this way a simple criterion for the definition of the optimal mass scaling factor. A strategy for the effective computation of the element maximum eigenfrequency is also proposed. The considered mass scaling preserves the element translational inertia, while it modifies the rotational one, leading to errors in the kinetic energy when the motion rotational component is dominant. The error has been rigorously assessed for an individual element, and a simple formula for its estimate has been derived. Numerical tests, both in small and large displacements and rotations, using a state-of-the-art solid-shell element taken from the literature, confirm the effectiveness and accuracy of the proposed approach. Copyright {\copyright} 2014 John Wiley \& Sons, Ltd
Functional imaging in neurodegenerative disorders: past, present and future
The present monographic issue of the Quarterly Journal of Nuclear Medicine and Molecular Imaging is dedicated to the role of functional imaging in the broad field of neurodegenerative disorders, with a special focus on some of the most relevant topics of the last decades, of the present time and of the near future. Functional neuroimaging is close to reach the time in which it will be routinely implemented in clinical practice and in which the principles of "molecular imaging" will aid clinical diagnosis disclosing the fine extra- and intracellular deposit of protein aggregates and neuroinflammation markers. The almost simultaneous advancement in nuclear medicine techniques, i.e., PET-MRI, along with the development of new tracers and the implementation of more and more sophisticated image analysis software will assign to neuroimaging a preeminent role in the diagnostic algorithm both in neurological and psychiatric practice
The electroweak contribution to the top quark forward-backward asymmetry at the Tevatron
The electroweak contributions to the forward-backward asymmetry in the
production of top-quark pairs at the Tevatron are evaluated at O(alpha^2) and
O(alpha*alphas^2). We perform a detailed analysis of all partonic channels that
produce an asymmetry and combine them with the QCD contributions. They provide
a non-negligible fraction of the QCD-induced asymmetry with the same overall
sign, thus enlarging the Standard Model prediction and diminishing the observed
deviation. For the observed mass-dependent forward-backward asymmetry a 3-sigma
deviation still remains at an invariant-mass cut of M_(t-tbar) > 450 GeV.Comment: 14 pages, 8 figure
Host Galaxies of low z Radio-loud Quasars: A search of HST archives
We searched the HST archives for unpublished WFPC2 images of low redshift
(z<0.5) radio loud quasars (RLQ). This led to the identification of 11 objects.
We present here the results of the analysis of these images from which we
derive the properties of their host galaxies. All objects are clearly resolved
and their surrounding nebulosity is consistent with an elliptical galaxy model.
These new data, together with previous published HST observations, form a
sample of 34 sources which significantly expands all previous studies of low
redshift RLQ based on HST data. For this full sample we derive the average
absolute magnitude of the host galaxies =-24.01+/-0.48, and the effective
radius =10.5+/-3.7kpc. No significant correlation is found between the
nucleus and the host galaxy luminosity. Using the relationship between black
hole mass (M_BH) and bulge luminosity we investigate the relation between M_BH
and total radio power for RLQ and compare with other classes of radio sources.
The overall distribution of AGN in the plane M_BH-P(radio) exhibits a trend for
increasing M_BH with increasing P(radio) but with a substantial spread. RLQ
occupy the region of most powerful sources and most massive BH. The quasars
appear to emit over a wide range of power with respect to their Eddington
luminosity as deduced by the estimated M_BH.Comment: 23 pages, 8 figures, ApJ in pres
Detection of doubly-deuterated methanol in the solar-type protostar IRAS16293-2422
We report the first detection of doubly-deuterated methanol (CHD2OH), as well
as firm detections of the two singly-deuterated isotopomers of methanol (CH2DOH
and CH3OD), towards the solar-type protostar IRAS16293-2422. From the present
multifrequency observations, we derive the following abundance ratios:
[CHD2OH]/[CH3OH] = 0.2 +/- 0.1, [CH2DOH]/[CH3OH] = 0.9 +/- 0.3, [CH3OD]/[CH3OH]
= 0.04 +/- 0.02. The total abundance of the deuterated forms of methanol is
greater than that of its normal hydrogenated counterpart in the circumstellar
material of IRAS16293-2422, a circumstance not previously encountered.
Formaldehyde, which is thought to be the chemical precursor of methanol,
possesses a much lower fraction of deuterated isotopomers (~ 20%) with respect
to the main isotopic form in IRAS16293-2422. The observed fractionation of
methanol and formaldehyde provides a severe challenge to both gas-phase and
grain-surface models of deuteration. Two examples of the latter model are
roughly in agreement with our observations of CHD2OH and CH2DOH if the
accreting gas has a large (0.2-0.3) atomic D/H ratio. However, no gas-phase
model predicts such a high atomic D/H ratio, and hence some key ingredient
seems to be missing.Comment: 5 pages, 3 figure
Nitrogen chemistry and depletion in starless cores
We investigated the chemistry of nitrogen--containing species, principally
isotopomers of CN, HCN, and HNC, in a sample of pre-protostellar cores. We used
the IRAM 30 m telescope to measure the emission in rotational and hyperfine
transitions of CN, HCN, 13CN, H13CN, HN13C, and HC15N, in L 1544, L 183, Oph D,
L 1517B, L 310. The observations were made along axial cuts through the dust
emission peak, at a number of regularly--spaced offset positions. The
observations were reduced and analyzed to obtain the column densities, using
the measurements of the less abundant isotopic variants in order to minimize
the consequences of finite optical depths in the lines. The observations were
compared with the predictions of a free--fall gravitational collapse model,
which incorporates a non-equilibrium treatment of the relevant chemistry. We
found that CN, HCN, and HNC remain present in the gas phase at densities well
above that at which CO depletes on to grains. The CN:HCN and the HNC:HCN
abundance ratios are larger than unity in all the objects of our sample.
Furthermore, there is no observational evidence for large variations of these
ratios with increasing offset from the dust emission peak and hence with
density. Whilst the differential freeze--out of CN and CO can be understood in
terms of the current chemistry, the behaviour of the CN:HCN ratio is more
difficult to explain. Models suggest that most nitrogen is not in the gas phase
but may be locked in ices. Unambiguous conclusions require measurements of the
rate coefficients of the key neutral--neutral reactions at low temperatures
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