546 research outputs found

    A Case for 802.11B

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    Stochastic technology and active networks have garnered improbable interest from both analysts and system administrators in the last several years. Given the trends in robust configurations, physicists daringly note the study of congestion control. We explore new distributed technology, which we call PureZonar

    The Academic Achievement Gap of Black American Students Vis-à-vis Whites and Asians

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    In response to the academic achievement gap of black American students� vis-�-vis whites and Asians, Paul C. Mocombe developed his Mocombeian Strategy and Reading Room Curriculum, which posit a comprehensive mentoring program of educated black professionals and the restructuring of the linguistic structure of black American inner-city students via phonetic and language arts instructions, as the solutions to resolving the gap. The two approaches are based on Mocombe�s hypothesis that the academic underachievement of black American students, vis-�-vis their white and Asian counterparts, on standardized tests is grounded in what he refers to as �a mismatch of linguistic structure and social class function.� This work explores the theoretical, practical, and pedagogical relationships between Mocombe�s �mismatch of linguistic structure and social class function hypothesis,� The Mocombeian Strategy, and Reading Room Curriculum (published as Mocombe�s Reading Room Series)

    Constraint algebra in LQG reloaded : Toy model of a U(1)^{3} Gauge Theory I

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    We analyze the issue of anomaly-free representations of the constraint algebra in Loop Quantum Gravity (LQG) in the context of a diffeomorphism-invariant gauge theory in three spacetime dimensions. We construct a Hamiltonian constraint operator whose commutator matches with a quantization of the classical Poisson bracket involving structure functions. Our quantization scheme is based on a geometric interpretation of the Hamiltonian constraint as a generator of phase space-dependent diffeomorphisms. The resulting Hamiltonian constraint at finite triangulation has a conceptual similarity with the "mu-bar"-scheme in loop quantum cosmology and highly intricate action on the spin-network states of the theory. We construct a subspace of non-normalizable states (distributions) on which the continuum Hamiltonian constraint is defined which leads to an anomaly-free representation of the Poisson bracket of two Hamiltonian constraints in loop quantized framework.Comment: 60 pages, 6 figure

    Half-life and spin of 60Mn^g

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    A value of 0.28 +/- 0.02 s has been deduced for the half-life of the ground state of 60Mn, in sharp contrast to the previously adopted value of 51 +/- 6 s. Access to the low-spin 60Mn ground state was accomplished via beta decay of the 0+ 60Cr parent nuclide. New, low-energy states in 60Mn have been identified from beta-delayed gamma-ray spectroscopy. The new, shorter half-life of 60Mn^g is not suggestive of isospin forbidden beta decay, and new spin and parity assignments of 1+ and 4+ have been adopted for the ground and isomeric beta-decaying states, respectively, of 60Mn.Comment: 13 pages, 5 figures, Accepted for publication in Phys. Rev.

    Sources and magnitude of error in preparing morphine infusions for nurse-patient controlled analgesia in a UK paediatric hospital

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    Background Administering nurse/patient controlled analgesia (N/PCA) to children requires complex dose calculations and multiple manipulations to prepare morphine solutions in 50 mL syringes for administration by continuous infusion with additional boluses. Objective To investigate current practice and accuracy during preparation of morphine N/PCA infusions in hospital theatres and wards at a UK children's hospital. Methods Direct observation of infusion preparation methods and morphine concentration quantification using UV-Vis spectrophotometry. The British Pharmacopoeia specification for morphine sulphate injection drug content (±7.5 %) was used as a reference limit. Results Preparation of 153 morphine infusions for 128 paediatric patients was observed. Differences in preparation method were identified, with selection of inappropriate syringe size noted. Lack of appreciation of the existence of a volume overage (i.e. volume in excess of the nominal volume) in morphine ampoules was identified. Final volume of the infusion was greater than the target (50 mL) in 33.3 % of preparations. Of 78 infusions analysed, 61.5 % had a morphine concentration outside 92.5-107.5 % of label strength. Ten infusions deviated by more than 20 %, with one by 100 %. Conclusions Variation in morphine infusion preparation method was identified. Lack of appreciation of the volume overage in ampoules, volumetric accuracy of different syringe sizes and ability to perform large dilutions of small volumes were sources of inaccuracy in infusion concentration, resulting in patients receiving morphine doses higher or lower than prescribed

    Global sensitivity analysis of detailed chemical kinetic schemes for DME oxidation in premixed flames

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    Detailed chemical kinetic investigations on dimethylether oxidation in one-dimensional premixed flat flames were performed. Local and global sensitivities of the reaction rate constants within selected chemical kinetic schemes were studied using maximum flame temperature, and peak methane and formaldehyde concentrations as predictive target quantities. The global sensitivity analysis was based on the application of high dimensional model representations using quasi-random sampling. First- and second-order sensitivity indices of important reaction steps were determined for fuel rich (Φ = 1.49) and fuel lean (Φ = 0.67) conditions. Differences in the importance ranking for key reactions were found to exist between the selected schemes, highlighting the influence of differences in the key rate constants. Whilst the peak flame temperature was predicted with fairly low uncertainty by both schemes, significant uncertainties were identified in the prediction of the target minor species. Key reaction rates requiring better quantification in order to improve the prediction of methane and formaldehyde concentrations are identified

    Spherically symmetric Einstein-Maxwell theory and loop quantum gravity corrections

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    Effects of inverse triad corrections and (point) holonomy corrections, occuring in loop quantum gravity, are considered on the properties of Reissner-Nordstr\"om black holes. The version of inverse triad corrections with unmodified constraint algebra reveals the possibility of occurrence of three horizons (over a finite range of mass) and also shows a mass threshold beyond which the inner horizon disappears. For the version with modified constraint algebra, coordinate transformations are no longer a good symmetry. The covariance property of spacetime is regained by using a \emph{quantum} notion of mapping from phase space to spacetime. The resulting quantum effects in both versions of these corrections can be associated with renormalization of either mass, charge or wave function. In neither of the versions, Newton's constant is renormalized. (Point) Holonomy corrections are shown to preclude the undeformed version of constraint algebra as also a static solution, though time-independent solutions exist. A possible reason for difficulty in constructing a covariant metric for these corrections is highlighted. Furthermore, the deformed algebra with holonomy corrections is shown to imply signature change.Comment: 38 pages, 9 figures, matches published versio

    Proton Drip-Line Calculations and the Rp-process

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    One-proton and two-proton separation energies are calculated for proton-rich nuclei in the region A=4175 A=41-75 . The method is based on Skyrme Hartree-Fock calculations of Coulomb displacement energies of mirror nuclei in combination with the experimental masses of the neutron-rich nuclei. The implications for the proton drip line and the astrophysical rp-process are discussed. This is done within the framework of a detailed analysis of the sensitivity of rp process calculations in type I X-ray burst models on nuclear masses. We find that the remaining mass uncertainties, in particular for some nuclei with N=ZN=Z, still lead to large uncertainties in calculations of X-ray burst light curves. Further experimental or theoretical improvements of nuclear mass data are necessary before observed X-ray burst light curves can be used to obtain quantitative constraints on ignition conditions and neutron star properties. We identify a list of nuclei for which improved mass data would be most important.Comment: 20 pages, 9 figures, 2 table
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