758 research outputs found
Reexamination of a multisetting Bell inequality for qudits
The class of d-setting, d-outcome Bell inequalities proposed by Ji and
collaborators [Phys. Rev. A 78, 052103] are reexamined. For every positive
integer d > 2, we show that the corresponding non-trivial Bell inequality for
probabilities provides the maximum classical winning probability of the
Clauser-Horne-Shimony-Holt-like game with d inputs and d outputs. We also
demonstrate that the general classical upper bounds given by Ji et al. are
underestimated, which invalidates many of the corresponding correlation
inequalities presented thereof. We remedy this problem, partially, by providing
the actual classical upper bound for d less than or equal to 13 (including
non-prime values of d). We further determine that for prime value d in this
range, most of these probability and correlation inequalities are tight, i.e.,
facet-inducing for the respective classical correlation polytope. Stronger
lower and upper bounds on the quantum violation of these inequalities are
obtained. In particular, we prove that once the probability inequalities are
given, their correlation counterparts given by Ji and co-workers are no longer
relevant in terms of detecting the entanglement of a quantum state.Comment: v3: Published version (minor rewordings, typos corrected, upper
bounds in Table III improved/corrected); v2: 7 pages, 1 figure, 4 tables
(substantially revised with new results on the tightness of the correlation
inequalities included); v1: 7.5 pages, 1 figure, 4 tables (Comments are
welcome
Temperature analysis in the shock waves regime for gas-filled plasma capillaries in plasma-based accelerators
Plasma confinement represents a crucial point for plasma-based accelerators and plasma lenses because it can strongly affect the beam properties. For this reason, an accurate measurement of the plasma parameters, as plasma temperature, pressure and electron density, must be performed. In this paper, we introduce a novel method to detect the plasma temperature and the pressure for gas-filled capillaries in use at the SPARC-LAB test facility. The proposed method is based on the shock waves produced at the ends of the capillary during the gas discharge and the subsequent plasma formation inside it. By measuring the supersonic speed of the plasma outflow, the thermodynamic parameters have been obtained both outside and inside the capillary. A plasma temperature around 1.4 eV has been measured, that depends on the geometric properties and the operating conditions of the capillary
Changes in children’s cognitive development at the Start of School in England 2001–2008.
Since 1997, England has seen massive changes in the Early Years including the introduction of an early childhood curriculum, free pre-school education for three-year-olds and local programmes for disadvantaged communities. Many of these initiatives took time to introduce and become established. Beginning in 2001, and each year thereafter until 2008, the authors collected consistent data from thousands of children when they started school at the age of four on a range of variables, chosen because they are good predictors of later success. These included vocabulary, early reading and early mathematics. Children from the same set of 472 state primary schools in England were assessed each year. This paper contributes to the existing studies of educational trends over time by examining the extent to which children's scores on these measures changed over that period; in general, they were found to have remained stable
Longitudinal phase-space manipulation with beam-driven plasma wakefields
The development of compact accelerator facilities providing high-brightness
beams is one of the most challenging tasks in field of next-generation compact
and cost affordable particle accelerators, to be used in many fields for
industrial, medical and research applications. The ability to shape the beam
longitudinal phase-space, in particular, plays a key role to achieve high-peak
brightness. Here we present a new approach that allows to tune the longitudinal
phase-space of a high-brightness beam by means of a plasma wakefields. The
electron beam passing through the plasma drives large wakefields that are used
to manipulate the time-energy correlation of particles along the beam itself.
We experimentally demonstrate that such solution is highly tunable by simply
adjusting the density of the plasma and can be used to imprint or remove any
correlation onto the beam. This is a fundamental requirement when dealing with
largely time-energy correlated beams coming from future plasma accelerators
Focusing of high-brightness electron beams with active-plasma lenses
Plasma-based technology promises a tremendous reduction in size of accelerators used for research, medical, and industrial applications, making it possible to develop tabletop machines accessible for a broader scientific community. By overcoming current limits of conventional accelerators and pushing particles to larger and larger energies, the availability of strong and tunable focusing optics is mandatory also because plasma-accelerated beams usually have large angular divergences. In this regard, active-plasma lenses represent a compact and affordable tool to generate radially symmetric magnetic fields several orders of magnitude larger than conventional quadrupoles and solenoids. However, it has been recently proved that the focusing can be highly nonlinear and induce a dramatic emittance growth. Here, we present experimental results showing how these nonlinearities can be minimized and lensing improved. These achievements represent a major breakthrough toward the miniaturization of next-generation focusing devices
Total disc replacement surgery for symptomatic degenerative lumbar disc disease: a systematic review of the literature
The objective of this study is to evaluate the effectiveness and safety of total disc replacement surgery compared with spinal fusion in patients with symptomatic lumbar disc degeneration. Low back pain (LBP), a major health problem in Western countries, can be caused by a variety of pathologies, one of which is degenerative disc disease (DDD). When conservative treatment fails, surgery might be considered. For a long time, lumbar fusion has been the “gold standard” of surgical treatment for DDD. Total disc replacement (TDR) has increased in popularity as an alternative for lumbar fusion. A comprehensive systematic literature search was performed up to October 2008. Two reviewers independently checked all retrieved titles and abstracts, and relevant full text articles for inclusion. Two reviewers independently assessed the risk of bias of included studies and extracted relevant data and outcomes. Three randomized controlled trials and 16 prospective cohort studies were identified. In all three trials, the total disc replacement was compared with lumbar fusion techniques. The Charité trial (designed as a non-inferiority trail) was considered to have a low risk of bias for the 2-year follow up, but a high risk of bias for the 5-year follow up. The Charité artificial disc was non-inferior to the BAK® Interbody Fusion System on a composite outcome of “clinical success” (57.1 vs. 46.5%, for the 2-year follow up; 57.8 vs. 51.2% for the 5-year follow up). There were no statistically significant differences in mean pain and physical function scores. The Prodisc artificial disc (also designed as a non-inferiority trail) was found to be statistically significant more effective when compared with the lumbar circumferential fusion on the composite outcome of “clinical success” (53.4 vs. 40.8%), but the risk of bias of this study was high. Moreover, there were no statistically significant differences in mean pain and physical function scores. The Flexicore trial, with a high risk of bias, found no clinical relevant differences on pain and physical function when compared with circumferential spinal fusion at 2-year follow up. Because these are preliminary results, in addition to the high risk of bias, no conclusions can be drawn based on this study. In general, these results suggest that no clinical relevant differences between the total disc replacement and fusion techniques. The overall success rates in both treatment groups were small. Complications related to the surgical approach ranged from 2.1 to 18.7%, prosthesis related complications from 2.0 to 39.3%, treatment related complications from 1.9 to 62.0% and general complications from 1.0 to 14.0%. Reoperation at the index level was reported in 1.0 to 28.6% of the patients. In the three trials published, overall complication rates ranged from 7.3 to 29.1% in the TDR group and from 6.3 to 50.2% in the fusion group. The overall reoperation rate at index-level ranged from 3.7 to 11.4% in the TDR group and from 5.4 to 26.1% in the fusion group. In conclusion, there is low quality evidence that the Charité is non-inferior to the BAK cage at the 2-year follow up on the primary outcome measures. For the 5-year follow up, the same conclusion is supported only by very low quality evidence. For the ProDisc, there is very low quality evidence for contradictory results on the primary outcome measures when compared with anterior lumbar circumferential fusion. High quality randomized controlled trials with relevant control group and long-term follow-up is needed to evaluate the effectiveness and safety of TDR
A review of spatial causal inference methods for environmental and epidemiological applications
The scientific rigor and computational methods of causal inference have had
great impacts on many disciplines, but have only recently begun to take hold in
spatial applications. Spatial casual inference poses analytic challenges due to
complex correlation structures and interference between the treatment at one
location and the outcomes at others. In this paper, we review the current
literature on spatial causal inference and identify areas of future work. We
first discuss methods that exploit spatial structure to account for unmeasured
confounding variables. We then discuss causal analysis in the presence of
spatial interference including several common assumptions used to reduce the
complexity of the interference patterns under consideration. These methods are
extended to the spatiotemporal case where we compare and contrast the potential
outcomes framework with Granger causality, and to geostatistical analyses
involving spatial random fields of treatments and responses. The methods are
introduced in the context of observational environmental and epidemiological
studies, and are compared using both a simulation study and analysis of the
effect of ambient air pollution on COVID-19 mortality rate. Code to implement
many of the methods using the popular Bayesian software OpenBUGS is provided
Recent results at SPARC_LAB
The current activity of the SPARC_LAB test-facility is focused on the
realization of plasma-based acceleration experiments with the aim to provide
accelerating field of the order of several GV/m while maintaining the overall
quality (in terms of energy spread and emittance) of the accelerated electron
bunch. In the following, the current status of such an activity is presented.
We also show results related to the usability of plasmas as focusing lenses in
view of a complete plasma-based focusing and accelerating system
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