1,891 research outputs found
Non-standard connections in classical mechanics
In the jet-bundle description of first-order classical field theories there
are some elements, such as the lagrangian energy and the construction of the
hamiltonian formalism, which require the prior choice of a connection. Bearing
these facts in mind, we analyze the situation in the jet-bundle description of
time-dependent classical mechanics. So we prove that this connection-dependence
also occurs in this case, although it is usually hidden by the use of the
``natural'' connection given by the trivial bundle structure of the phase
spaces in consideration. However, we also prove that this dependence is
dynamically irrelevant, except where the dynamical variation of the energy is
concerned. In addition, the relationship between first integrals and
connections is shown for a large enough class of lagrangians.Comment: 17 pages, Latex fil
Towards a more complete description of nucleon distortion in lepton-induced single-pion production at low-
Theoretical predictions for lepton-induced single-pion production (SPP) on
C are revisited in order to assess the effect of different treatments of
the current operator. On one hand we have the asymptotic approximation, which
consists in replacing the particle four-vectors that enter in the operator by
their asymptotic values, i.e., their values out of the nucleus. On the other
hand we have the full calculation, which is a more accurate approach to the
problem. We also compare with results in which the final nucleon is described
by a relativistic plane wave, to rate the effect of the nucleon distortion. The
study is performed for several lepton kinematics, reproducing inclusive and
semi-inclusive cross sections belonging to the low- region (between 0.05
and 1 GeV), which is of special interest in charged-current (CC)
neutrino-nucleus 1 production. Inclusive electron results are compared
with experimental data. We find non-trivial corrections comparable in size with
the effect of the nucleon distortion, namely, corrections up to 6\%, either
increasing or diminishing the asymptotic prediction, and a shift of the
distributions towards higher energy transfer. For the semi-inclusive cross
sections, we observe the correction to be prominent mainly at low values of the
outgoing nucleon kinetic energy. Finally, for CC neutrino-induced 1
production, we find a reduction at low- with respect to both the
plane-wave approach and the asymptotic case
Ab initio evaluation of the charge-ordering in
We report {\it ab initio} calculations of the charge ordering in
using large configurations interaction methods on
embedded fragments. Our major result is that the electrons of the
bridging oxygen of the rungs present a very strong magnetic character and
should thus be explicitly considered in any relevant effective model. The most
striking consequence of this result is that the spin and charge ordering differ
substantially, as differ the experimental results depending on whether they are
sensitive to the spin or charge density.Comment: 4 page
Unbounded violation of tripartite Bell inequalities
We prove that there are tripartite quantum states (constructed from random
unitaries) that can lead to arbitrarily large violations of Bell inequalities
for dichotomic observables. As a consequence these states can withstand an
arbitrary amount of white noise before they admit a description within a local
hidden variable model. This is in sharp contrast with the bipartite case, where
all violations are bounded by Grothendieck's constant. We will discuss the
possibility of determining the Hilbert space dimension from the obtained
violation and comment on implications for communication complexity theory.
Moreover, we show that the violation obtained from generalized GHZ states is
always bounded so that, in contrast to many other contexts, GHZ states do in
this case not lead to extremal quantum correlations. The results are based on
tools from the theories of operator spaces and tensor norms which we exploit to
prove the existence of bounded but not completely bounded trilinear forms from
commutative C*-algebras.Comment: Substantial changes in the presentation to make the paper more
accessible for a non-specialized reade
The A-cation deficient perovskite series La<sub>2-x</sub>CoTiO<sub>6-Ύ</sub> (0 †x †0.20): new components for potential SOFC composite cathodes
The best performances are obtained for low x due to a compromise between sufficiently high amount of defects, but not so high to induce defect clustering.</p
Carbon-encapsulated iron nanoparticles as reusable adsorbents for micropollutants removal from water
Adsorption represents the most plausible technology for micropollutants removal from water nowadays. Nevertheless, the regeneration of the saturated carbon materials is still an important challenge, being these solids in practice commonly disposed. This work aims at overcoming this issue by using innovative carbonencapsulated iron nanoparticles (CE-nFe). This material was synthesized by a low-cost and green method viz. hydrothermal carbonization (HTC), using olive mill wastewater as carbonaceous source. The solid was fully characterized by different techniques (magnetic properties, elemental analyses, N2-sorption isotherms, pHPZC, ICP, XRD and TEM). It showed a clear core-shell structure of around 40 nm in diameter. The core was mainly formed by zero-valent iron and the shell by graphitized carbon. Accordingly, it showed an essentially mesoporous structure, with a specific surface area of 169 m2 gâ1 , and a clear hydrophobic character (pHPZC = 10). Its adsorption performance was investigated using three relevant micropollutants (diclofenac (DCF), sulfamethoxazole (SMX) and metronidazole (MNZ)). A very fast removal of the micropollutants was achieved (30 min at the most, with rate constants in the range of 0.11â0.41 g mgâ1 minâ1 ). The adsorption isotherms revealed the vertical packing of the adsorbate molecules onto the adsorbent active centers, being the data successfully described by the GAB model. The saturated adsorbents were effectively regenerated by heterogeneous Fenton oxidation, taking advantage of the iron core of CE-nFe and the opened mesoporous carbon shell. The regeneration efficiency increased with increasing the operating temperature (25â75 âŠC) and contact time (1â4 h), as well as the H2O2 dose up to 6 g L-1. The micropollutant nature affected the adsorbent regeneration yield in the order: SMX > DCF > MNZ, consistent with their reactivity towards Fenton oxidationThis research has been supported by the Spanish MINECO through the project CTM-2016-76454-R and by the CM through the project P2018/EMT-4341. M. Munoz and J. Nieto-Sandoval thank the Spanish MINECO for the RamĂłn y Cajal postdoctoral contract (RYC-2016-20648) and the FPI predoctoral grant (BES-2017-081346), respectivel
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Cool stars in the Galactic center as seen by APOGEE : M giants, AGB stars, and supergiant stars and candidates
The Galactic center region, including the nuclear disk, has until recently been largely avoided in chemical census studies because of extreme extinction and stellar crowding. Large, near-IR spectroscopic surveys, such as the Apache Point Observatory Galactic Evolution Experiment (APOGEE), allow the measurement of metallicities in the inner region of our Galaxy. Making use of the latest APOGEE data release (DR16), we are able for the first time to study cool Asymptotic Giant branch (AGB) stars and supergiants in this region. The stellar parameters of five known AGB stars and one supergiant star (VR 5-7) show that their location is well above the tip of the red giant branch. We studied metallicities of 157 M giants situated within 150 pc of the Galactic center from observations obtained by the APOGEE survey with reliable stellar parameters from the APOGEE pipeline making use of the cool star grid down to 3200 K. Distances, interstellar extinction values, and radial velocities were checked to confirm that these stars are indeed situated in the Galactic center region. We detect a clear bimodal structure in the metallicity distribution function, with a dominant metal-rich peak of [Fe/H] ⌠+0.3 dex and a metal-poor peak around {Fe/H] = â0.5 dex, which is 0.2 dex poorer than Baadeâs Window. The α-elements Mg, Si, Ca, and O show a similar trend to the Galactic bulge. The metal-poor component is enhanced in the α-elements, suggesting that this population could be associated with the classical bulge and a fast formation scenario. We find a clear signature of a rotating nuclear stellar disk and a significant fraction of high-velocity stars with vgalâ> â300 km sâ1; the metal-rich stars show a much higher rotation velocity (âŒ200 km sâ1) with respect to the metal-poor stars (âŒ140 km sâ1). The chemical abundances as well as the metallicity distribution function suggest that the nuclear stellar disk and the nuclear star cluster show distinct chemical signatures and might be formed differently
Total quality management practices, competitive strategies and financial performance: the case of the Palestinian industrial SMEs
"This is an Accepted Manuscript of an article published by Taylor & Francis in Total Quality Management and Business Excellence on 19 Aug 2013, available online: http://wwww.tandfonline.com/10.1080/14783363.2013.824714."The purpose of this paper is to examine the relationship between Total Quality Management (TQM) practices, competitive strategies - cost leadership and differentiation- and firm performance in the Palestinian economy. Within this study total quality management has been conceptualized as soft and hard practices, in congruence with the literature. An empirical analysis based upon an extensive validation process was applied to refine TQM, competitive strategies and financial performance scales. Data were collected through surveying 202 in Palestinian industrial small and medium enterprises (SMEs). Structural Equation Modeling was carried out to test the anticipated relationships. Results derived from this study show that TQM practices have indirect, positive and significant relationship with financial performance through competitive strategies. In addition, a direct, positive and significant relationship between competitive strategies and financial performance was observed. Results derived from this study might help managers to implement TQM practices in order to effectively allocate resources and improve financial performance
Tomography of fast-ion velocity-space distributions from synthetic CTS and FIDA measurements
We compute tomographies of 2D fast-ion velocity distribution functions from synthetic collective Thomson scattering (CTS) and fast-ion D-alpha (FIDA) 1D measurements using a new reconstruction prescription. Contradicting conventional wisdom we demonstrate that one single 1D CTS or FIDA view suffices to compute accurate tomographies of arbitrary 2D functions under idealized conditions. Under simulated experimental conditions, single-view tomographies do not resemble the original fast-ion velocity distribution functions but nevertheless show their coarsest features. For CTS or FIDA systems with many simultaneous views on the same measurement volume, the resemblance improves with the number of available views, even if the resolution in each view is varied inversely proportional to the number of views, so that the total number of measurements in all views is the same. With a realistic four-view system, tomographies of a beam ion velocity distribution function at ASDEX Upgrade reproduce the general shape of the function and the location of the maxima at full and half injection energy of the beam ions. By applying our method to real many-view CTS or FIDA measurements, one could determine tomographies of 2D fast-ion velocity distribution functions experimentally
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