1,284 research outputs found

    Entanglement Dynamics in 1D Quantum Cellular Automata

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    Several proposed schemes for the physical realization of a quantum computer consist of qubits arranged in a cellular array. In the quantum circuit model of quantum computation, an often complex series of two-qubit gate operations is required between arbitrarily distant pairs of lattice qubits. An alternative model of quantum computation based on quantum cellular automata (QCA) requires only homogeneous local interactions that can be implemented in parallel. This would be a huge simplification in an actual experiment. We find some minimal physical requirements for the construction of unitary QCA in a 1 dimensional Ising spin chain and demonstrate optimal pulse sequences for information transport and entanglement distribution. We also introduce the theory of non-unitary QCA and show by example that non-unitary rules can generate environment assisted entanglement.Comment: 12 pages, 8 figures, submitted to Physical Review

    Vector boson production at hadron colliders: hard-collinear coefficients at the NNLO

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    We consider QCD radiative corrections to vector-boson production in hadron collisions. We present the next-to-next-to-leading order (NNLO) result of the hard-collinear coefficient function for the all-order resummation of logarithmically-enhanced contributions at small transverse momenta. The coefficient function controls NNLO contributions in resummed calculations at full next-to-next-to-leading logarithmic accuracy. The same coefficient function is used in applications of the subtraction method to perform fully-exclusive perturbative calculations up to NNLO.Comment: 13, pages, no figures. arXiv admin note: text overlap with arXiv:1106.465

    Impact of Scottish vocational qualifications on residential child care : have they fulfilled the promise?

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    This article will present findings from a doctoral study exploring the impact of 'SVQ Care: Promoting Independence (level III)' within children's homes. The study focuses on the extent to which SVQs enhance practice and their function within a 'learning society'. A total of 30 staff were selected from seven children's homes in two different local authority social work departments in Scotland. Each member of staff was interviewed on four separate occasions over a period of 9 months. Interviews were structured using a combination of repertory grids and questions. Particular focus was given to the assessment process, the extent to which SVQs enhance practice and the learning experiences of staff. The findings suggest that there are considerable deficiencies both in terms of the SVQ format and the way in which children's homes are structured for the assessment of competence. Rather than address the history of failure within residential care, it appears that SVQs have enabled the status quo to be maintained whilst creating an 'illusion' of change within a learning society

    Frequency of Aspirating Gastric Tubes for Patients Receiving Enteral Nutrition in the ICU: A Randomised Controlled Trial

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    Background: Enteral nutrition (EN) tolerance is often monitored by aspirating stomach contents by syringe at prescribed intervals. No studies have been conducted to assess the most appropriate time interval for aspirating gastric tubes. We compared gastric tube aspirations every 4 hours (usual care) with a variable regimen (up to every 8 hours aspirations).Methods: This randomized controlled trial (RCT) enrolled patients who stayed in the intensive care unit (ICU) for >48 hours, had a gastric tube, and were likely to receive EN for 3 or more days. Patients were randomized (computer-generated randomization) to either the control (every 4 hours) or intervention group (variable regimen). The primary outcome was number of gastric tube aspirations per day from randomization until EN was ceased or up to 2 weeks postrandomization.Results: Following Institutional Ethics Committee approval, 357 patients were recruited (control group, n = 179; intervention group, n = 178). No differences were found in age, sex, worst APACHE II score, or time to start of EN. In the intention-to-treat analysis, the intervention group had fewer tube aspirations per day (3.4 versus 5.4 in the control group, P < .001). Vomiting/regurgitation was increased in the intervention group (2.1% versus 3.6%, P = .02). There were no other differences in complications.Conclusion: This is the first RCT to examine the frequency of gastric tube aspirations. The frequency of gastric tube aspirations was reduced in the variable-regimen group with no increase in risk to the patient. Reducing the frequency of aspirations saves nursing time, decreases risk of contamination of feeding circuit, and minimizes risk of body fluid exposure

    Nuclear dependence coefficient α(A,qT)\alpha(A,q_T) for the Drell-Yan and J/ψ\psi production

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    Define the nuclear dependence coefficient α(A,qT)\alpha(A,q_T) in terms of ratio of transverse momentum spectrum in hadron-nucleus and in hadron-nucleon collisions: dσhAdqT2/dσhNdqT2Aα(A,qT)\frac{d\sigma^{hA}}{dq_T^2}/ \frac{d\sigma^{hN}}{dq_T^2}\equiv A^{\alpha(A,q_T)}. We argue that in small qTq_T region, the α(A,qT)\alpha(A,q_T) for the Drell-Yan and J/ψ\psi production is given by a universal function:\ a+bqT2a+b q_T^2, where parameters a and b are completely determined by either calculable quantities or independently measurable physical observables. We demonstrate that this universal function α(A,qT)\alpha(A,q_T) is insensitive to the A for normal nuclear targets. For a color deconfined nuclear medium, the α(A,qT)\alpha(A,q_T) becomes strongly dependent on the A. We also show that our α(A,qT)\alpha(A,q_T) for the Drell-Yan process is naturally linked to perturbatively calculated α(A,qT)\alpha(A,q_T) at large qTq_T without any free parameters, and the α(A,qT)\alpha(A,q_T) is consistent with E772 data for all qTq_T.Comment: latex, 28 pages, 10 figures, updated two figures, and add more discussion

    Antiproton Production in 11.5 A GeV/c Au+Pb Nucleus-Nucleus Collisions

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    We present the first results from the E864 collaboration on the production of antiprotons in 10% central 11.5 A GeV/c Au+Pb nucleus collisions at the Brookhaven AGS. We report invariant multiplicities for antiproton production in the kinematic region 1.4<y<2.2 and 50<p_T<300 MeV/c, and compare our data with a first collision scaling model and previously published results from the E878 collaboration. The differences between the E864 and E878 antiproton measurements and the implications for antihyperon production are discussed.Comment: 4 pages, 4 figures; accepted for publication in Physical Review Letter