70,333 research outputs found

    Entanglement and entropy engineering of atomic two-qubit states

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    We propose a scheme employing quantum-reservoir engineering to controllably entangle the internal states of two atoms trapped in a high finesse optical cavity. Using laser and cavity fields to drive two separate Raman transitions between metastable atomic ground states, a system is realized corresponding to a pair of two-state atoms coupled collectively to a squeezed reservoir. Phase-sensitive reservoir correlations lead to entanglement between the atoms, and, via local unitary transformations and adjustment of the degree and purity of squeezing, one can prepare entangled mixed states with any allowed combination of linear entropy and entanglement of formation.Comment: 4 pages, 5 figures, REVTe

    Understanding best practices in control engineering education using the concept of TPACK

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    This study aimed to design an integrated pedagogical approach to advance introductory Process Control Engineering Education through the application of the Technological Pedagogical Content Knowledge (TPACK) framework, and evaluating its impact on student learning. The research is initially being undertaken at Nottingham Trent University, UK but we will next adapt it to a case study in Libya. This paper aims to strengthen the teaching of introductory Process Control by using appropriate approach es in universities to improve the learning outcomes for students. From this work a new schematic for teaching Process Control ha s be en developed and, moreover, a thoughtful best practice in introducing Process Control in engineering education can be developed

    Polarizabilities of Si^{2+}: a benchmark test of theory and experiment

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    We have calculated electric-dipole polarizabilities of the 3s^2 ^1S_0, 3s3p ^3P_0, and 3s3p ^1P_1 states of the Si^{2+} ion using recently developed configuration interaction + all-order method. Detailed evaluation of the uncertainties of the final results is carried out. Our value for the ground state electric-dipole polarizability 11.670(13) a.u. is in excellent agreement with the resonant excitation Stark ionization spectroscopy value 11.669(9) a.u. [Komara et al., J. Phys. B 38, 87 (2005); Mitroy, Phys. Rev. A 78, 052515 (2008)]. This work represents the most precise benchmark test to date of theory and experiment in divalent atoms. The near cancellation of the ns^2 ^1S_0 ground state and the lowest nsnp ^3P_0 polarizabilities previously observed in B+, Al+, In+, Tl+, and Pb^{2+} is also found in Si^{2+} ion.Comment: 6 page

    Milton Keynes - preliminary estimates of regional traffic flows in 1981

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    The Milton Keynes Development Corporation and their planning consultants have asked the College Transport Group to investigate the scale of likely regional traffic flows into and out of Milton Keynes. At this stage the emphasis is on providing information for the preparation of a Master Plan for the city itself, rather than detailed traffic estimates for planning transport systems in the surrounding region. Population estimates for 1981 have been obtained from County Councils for areas within a 20 mile radius of the new city, and the proportions attracted to Milton Keynes for work and shopping assessed using gravity model techniques. Separate estimates have been made of work journeys from the city to regional employment and to London. Possible upper and lower limits to these forecasts are included to account for many uncertainties in the absolute and relative growth of population, employment and shopping opportunities in the city itself and in the surrounding region. The results are presented as traffic flews into and out of octant sectors around the city. Flows to the east are greater than to the west with work trip flows of the order of 2,500 person trips each way in the most heavily loaded sectors. A 1981 city population of 150,000 is likely to produce at least 1,500 daily commuters to London using the fast rail service, with an additional 200 commuters from the region using Milton Keynes railway station

    Distortion of genealogical properties when the sample is very large

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    Study sample sizes in human genetics are growing rapidly, and in due course it will become routine to analyze samples with hundreds of thousands if not millions of individuals. In addition to posing computational challenges, such large sample sizes call for carefully re-examining the theoretical foundation underlying commonly-used analytical tools. Here, we study the accuracy of the coalescent, a central model for studying the ancestry of a sample of individuals. The coalescent arises as a limit of a large class of random mating models and it is an accurate approximation to the original model provided that the population size is sufficiently larger than the sample size. We develop a method for performing exact computation in the discrete-time Wright-Fisher (DTWF) model and compare several key genealogical quantities of interest with the coalescent predictions. For realistic demographic scenarios, we find that there are a significant number of multiple- and simultaneous-merger events under the DTWF model, which are absent in the coalescent by construction. Furthermore, for large sample sizes, there are noticeable differences in the expected number of rare variants between the coalescent and the DTWF model. To balance the tradeoff between accuracy and computational efficiency, we propose a hybrid algorithm that utilizes the DTWF model for the recent past and the coalescent for the more distant past. Our results demonstrate that the hybrid method with only a handful of generations of the DTWF model leads to a frequency spectrum that is quite close to the prediction of the full DTWF model.Comment: 27 pages, 2 tables, 14 figure

    1^{1}H-NMR spin-echo measurements of the static and dynamic spin properties in λ\lambda-(BETS)2_{2}FeCl4_{4}

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    1^{1}H-NMR spin-echo measurements of the spin-echo decay M(2τ)M(2\tau) with a decay rate 1/T2T_{2} and the frequency shift Δν/ν0\Delta\nu/\nu_{0} under applied magnetic field B\mathbf{B}0_{0} = 9 T along the a-axis over a temperature range 2.0-180 K are reported for a single crystal of the organic conductor λ\lambda-(BETS)2_{2}FeCl4_{4}. It provides the spin dynamic and static properties in the paramagnetic metal (PM) and antiferromagnetic insulator (AFI) states as well as across the PM-AFI phase transition. A large slow beat structure in the spin-echo decay is observed with a typical beat frequency of ff \sim 7 kHz and it varies across the spectrum. Its origin is attributed to the 1^{1}H-1^{1}H dipole interactions rather than to the much larger dipolar field contribution from the Fe3+^{3+} electrons (spin SS = 5/2). A simple phenomenological model provides an excellent fit to the data. The dominant 1^{1}H-NMR frequency shift comes from the dipolar field from the 3d Fe3+^{3+} ions, and the Fe3+^{3+} - Fe3+^{3+} exchange interactions (J0J_{0}) (J0J_{0} includes the d-d exchange interactions through the π\pi-electrons) have a substantial effect to the local field at the proton sites expecially at low temperatures. A good fit is obtained with J0J_{0} = - 1.7 K. The data of the spin-echo decay rate 1/T2T_{2} indicates that there is a significant change in the slow fluctuations of the local magnetic field at the 1^{1}H-sites on traversing the PM to AFI phase. This evidence supports earlier reports that the PM-AFI phase transition in λ\lambda-(BETS)2_{2}% FeCl4_{4} is driven magnetically and first order.Comment: 9 pages, 10 figures, resubmitted to Phys. Rev. B in response to comments of Editor and reviewers on March 23, 200
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