Influence of stationary components on unsteady flow in industrial centrifugal compressors

An experimental investigation was performed to determine the characteristics of the onset and the growth of rotating nonuniform flow in a standard low specific speed stage, normally utilized in high pressure applications, in relation to change of stationary component geometry. Four configurations, differing only in the return channel and crossover geometry were tested on an atmospheric pressure open loop test rig. Experimental results make conspicious the effect of return channel geometry and give the possibility of shifting the unstable zone onset varying such geometry. An attempt was made to interpret the experimental results in the Emmons - Stenning's rotating stall theory

Unsteady flow phenomena in industrial centrifugal compressor stage

The results of an experimental investigation on a typical centrifugal compressor stage running on an atmospheric pressure test rig are shown. Unsteady flow was invariably observed at low flow well before surge. In order to determine the influence of the statoric components, the same impeller was repeatedly tested with the same vaneless diffuser, but varying return channel geometry. Experimental results show the strong effect exerted by the return channel, both on onset and on the behavior of unsteady flow. Observed phenomena have been found to confirm well the observed dynamic behavior of full load tested machines when gas density is high enough to cause appreciable mechanical vibrations. Therefore, testing of single stages at atmospheric pressure may provide a fairly accurate prediction of this kind of aerodynamic excitation

The resummed quark form factor in dimensional regularization

The resummed expression for the quark form factor illustrates the fact that dimensional continuation provides a regularization not only for ultraviolet and infrared singularities of fixed order QCD amplitudes, but also for the Landau pole arising in resummed calculations. Explicit renormalization group invariant analytic expressions for the logarithm of the form factor are given up to two-loop order in the QCD beta function.Comment: 5 pages, LaTeX with espcrc2.sty, talk given at QCD 00, Montpellier (France), 6-13/7/200

Next-to-next-to-leading soft-gluon corrections for the top quark cross section and transverse momentum distribution

I present results for top quark production in hadronic collisions at LHC and Tevatron energies. The soft-gluon corrections to the differential cross section are resummed at next-to-next-to-leading-logarithm (NNLL) accuracy via the two-loop soft anomalous dimension matrices. Approximate next-to-next-to-leading-order (NNLO) differential and total cross sections are calculated. Detailed theoretical predictions are shown for the t tbar cross section and the top quark p_T distribution at the Tevatron and the LHC.Comment: 23 pages, 14 figures; additional results and figure

New Bound States of Heavy Quarks at LHC and Tevatron

The present paper is based on the assumption that heavy quarks bound states exist in the Standard Model (SM). Considering New Bound States (NBS) of top-anti-top quarks (named T-balls) we have shown that: 1) there exists the scalar 1S--bound state of $6t+6\bar t$; 2) the forces which bind the top-quarks are very strong and almost completely compensate the mass of the twelve top-anti-top-quarks in the scalar NBS; 3) such strong forces are produced by the Higgs-top-quarks interaction with a large value of the top-quark Yukawa coupling constant $g_t\simeq 1$. Theory also predicts the existence of the NBS $6t + 5\bar t$, which is a color triplet and a fermion similar to the $t'$-quark of the fourth generation. We have also considered the "b-quark-replaced" NBS, estimated the masses of the lightest fermionic NBS: $M_{NBS}\gtrsim 300$ GeV, and discussed the larger masses of T-balls. We have developed a theory of the scalar T-ball's condensate and predicted the existence of three SM phases. Searching for heavy quark bound states at the Tevatron and LHC is discussed. We have constructed the possible form-factors of T-balls, and estimated the charge multiplicity coming from the T-ball's decays.Comment: 25 pages 12 figure

The Two Loop Crossed Ladder Vertex Diagram with Two Massive Exchanges

We compute the (three) master integrals for the crossed ladder diagram with two exchanged quanta of equal mass. The differential equations obeyed by the master integrals are used to generate power series expansions centered around all the singular (plus some regular) points, which are then matched numerically with high accuracy. The expansions allow a fast and precise numerical calculation of the three master integrals (better than 15 digits with less than 30 terms in the whole real axis). A conspicuous relation with the equal-mass sunrise in two dimensions is found. Comparison with a previous large momentum expansion is made finding complete agreement.Comment: 42 pages, 1 figur

Calculation of the Two-Loop Heavy-Flavor Contribution to Bhabha Scattering

We describe in detail the calculation of the two-loop corrections to the QED Bhabha scattering cross section due to the vacuum polarization by heavy fermions. Our approach eliminates one mass scale from the most challenging part of the calculation and allows us to obtain the corrections in a closed analytical form. The result is valid for arbitrary values of the heavy fermion mass and the Mandelstam invariants, as long as s,t,u >> m_e^2.Comment: 43 pages, 8 figures; added reference

3-point off-shell vertex in scalar QED in arbitrary gauge and dimension

We calculate the complete one-loop off-shell three-point scalar-photon vertex in arbitrary gauge and dimension for Scalar Quantum Electrodynamics. Explicit results are presented for the particular cases of dimensions 3 and 4 both for massive and massless scalars. We then propose non-perturbative forms of this vertex that coincide with the perturbative answer to order $e^2$.Comment: Uses axodra

Sudakov resummation of multiparton QCD cross sections

We present the general expressions for the resummation, up to next-to-leading logarithmic accuracy, of Sudakov-type logarithms in processes with an arbirtrary number of hard-scattering partons. These results document the formulae used by the authors in several previous phenomenological studies. The resummation formulae presented here, which are valid for phase-space factorizable observables, determine the resummation correction in a process-independent fashion. All process dependence is encoded in the colour and flavour structure of the leading order and virtual one-loop amplitudes, and in Sudakov weights associated to the cross section kinematics. We explicitly illustrate the application to the case of Drell--Yan and prompt-photon production.Comment: 13 pages, LaTe

What are the strategies for implementing primary care models in maternity? A systematic review on midwifery units

Background Implementation depth, the extent to which innovations are implemented successfully, is a matter of great interest in healthcare practice. Yet, the way implementation depth is conceptualised varies between different studies, settings and contexts. The aim of this study is to report on the clarification and re-conceptualisation of implementation depth in healthcare, by synthesising the theoretic scientific literature from multiple disciplinary backgrounds. Method We applied a pragmatic utility concept analysis approach, a metaanalytic and interpretative method aiming at providing new insights of partially mature concepts using literature as data source. We followed the BeHEMoTh (Behaviour or phenomenon of interest, Health context, Exclusions, Models and Theories) approach for systematically searching for and identifying a comprehensive compilation of concepts from the scientific literature. The following databases were searched: Medline, Embase, CINAHL, PsychInfo, Global Health, HMIC, Business Source Complete, and Social Policy and Practice. In addition to handsearching references of selected publications, key textbooks and citation tracking. First order-concepts’ definitions, characteristics/attributes and boundaries/allied concepts were extracted and analysed to derive second-order concepts of implementation depth. Results We identified 66 publications that met our eligibility criteria. The preliminary results reveal the consolidated conceptualisation of implementation depth encompasses five concepts: low implementation depth (abandonment), high implementation depth (assimilation), normalising and sustaining innovation over time (sustainability), removal/reduction or substitution of an existing practice (deimplementation), and progression of implementation stages (stickiness of implementation stages). The second-order concepts of implementation depth clarify a unified structure to conceptualise the dynamic successes and/or failures of implementation efforts. Conclusion The consolidated framework of implementation depth delineates the type of implementation ‘success’. It offers a useful heuristic for operationalising shallow to deep implementation, that may be better suited for understanding challenge