3,268 research outputs found
Local Loop Unbundling in Europe: Experience, Prospects and Policy Challenges
This paper discusses the development of local loop unbundling in telecommunications markets throughout the European Union. It elaborates on the regulatory framework in Europe and provides an overview of recent experiences in Europe. Different types of unbundling, allowing for different types of entry and services provided by entrants, are discussed. This paper also explores the challenges for policy and regulation that arise because of unbundling and recent, related technological developments in the markets for fixed voice telephony and broadband internet access, particularly the emergence of packet-switched telephony such as VoIP.local-loop unbundling; VoIP; telecommunications; regulation
Uniformity in Association schemes and Coherent Configurations: Cometric Q-Antipodal Schemes and Linked Systems
2010 Mathematics Subject Classification. Primary 05E30, Secondary 05B25, 05C50, 51E12
Production of Jet Pairs at Large Relative Rapidity in Hadron-Hadron Collisions as a Probe of the Perturbative Pomeron
The production of jet pairs with small transverse momentum and large relative
rapidity in high energy hadron-hadron collisions is studied. The rise of the
parton-level cross section with increasing rapidity gap is a fundamental
prediction of the BFKL `perturbative pomeron' equation of Quantum
Chromodynamics. However, at fixed collider energy it is difficult to
disentangle this effect from variations in the cross section due to the parton
distributions. It is proposed to study instead the distribution in the
azimuthal angle difference of the jets as a function of the rapidity gap. The
flattening of this distribution with increasing dijet rapidity gap is shown to
be a characteristic feature of the BFKL behaviour. Predictions for the Fermilab
proton-antiproton collider are presented.Comment: 17 pages, 11 figures, preprint DTP/94/0
Blood-feeding in the young adult filarial worms litomosoides sigmodontis
In this study with the filarial model Litomosoides sigmodontis, we demonstrate that the worms ingest host red blood cells at a precise moment of their life-cycle, immediately after the fourth moult. The red blood cells (RBC) were identified microscopically in live worms immobilized in PBS at 4 degrees C, and their density assessed. Two hosts were used: Mongolian gerbils, where microfilaraemia is high, and susceptible BALB/c mice with lower microfilaraemia. Gerbils were studied at 12 time-points, between day 9 post-inoculation (the worms were young 4th stage larvae) and day 330 p.i. (worms were old adults). Only the very young adult filarial worms had red blood cells in their gut. Haematophagy was observed between days 25 and 56 p.i. and peaked between day 28 and day 30 p.i. in female worms. In males, haematophagy was less frequent and intense. Similar kinetics of haematophagy were found in BALB/c mice, but frequency and intensity tended to be lower. Haematophagy seems useful to optimize adult maturation. These observations suggest that haematophagy is an important step in the life-cycle of L. sigmodontis. This hitherto undescribed phenomenon might be characteristic of other filarial species including human parasites
J/psi production at the Tevatron and HERA: the effect of k_T smearing
We study the effects of intrinsic transverse momentum smearing on J/psi
production both at the Tevatron and at HERA. For the case of large-p_T J/psi
production at the Tevatron, the effects due to k_T smearing are mild. On the
other hand, inelastic J/psi photoproduction at HERA is very sensitive to the
k_T smearing and, in fact, with a reasonable value of it is possible to
resolve the large-z discrepancy seen by comparing non-relativistic QCD (NRQCD)
predictions with the HERA data. We conclude that, with the present kinematic
cuts, photoproduction at HERA is not a good test of NRQCD.Comment: 11 pages, LaTeX, 2 figures, uses epsfi
CD4 count and tuberculosis risk in HIV-positive adults not on ART: a systematic review and meta-analysis
Background: CD4 cell count in adults with human immunodeficiency virus (HIV) infection (PLHIV) not receiving antiretroviral therapy (ART) influences tuberculosis (TB) risk. Despite widespread use in models informing resource allocation, this relationship has not been systematically reviewed. Methods: We systematically searched MEDLINE, Aidsinfo, Cochrane review database and Google Scholar for reports in English describing TB incidence stratified by updated CD4 cell count in cohorts of HIV-positive adults (age ≥15 years) not on ART (PROSPERO protocol no: CRD42016048888). Among inclusion criteria were: reporting precision for TB incidence, repeated CD4 measurements, and TB incidence reported for those not on ART or monotherapy. Study quality was assessed via the Newcastle-Ottawa tool for cohort studies. A Bayesian hierarchical model was fitted to estimate the pooled factor increase in TB incidence with respect to CD4 cell count decrement. Results: A total of 1,555 distinct records were identified from which 164 full text articles were obtained. Common reasons for exclusion of full texts were: no valid TB incidence, no repeat CD4 measurements, and not reporting TB incidence by ART status. The seven studies included reported on 1,206 TB cases among 41,271 individuals, with a typical median follow-up of four years. Studies were generally rated as moderate or high quality. Our meta-analysis estimated a 1.43 (95% credible interval: 1.16-1.88)-fold increase in TB incidence per 100 cells per mm3 decrease in CD4 cell count. Discussion: Our analysis confirms previous estimates of exponential increase in TB incidence with declining CD4 cell count in adults, emphasizing the importance of early ART initiation to reduce TB risk in PLHIV
Width and dual width of subsets in polynomial association schemes
AbstractThe width of a subset C of the vertices of a distance-regular graph is the maximum distance which occurs between elements of C. Dually, the dual width of a subset in a cometric association scheme is the index of the “last” eigenspace in the Q-polynomial ordering to which the characteristic vector of C is not orthogonal. Elementary bounds are derived on these two new parameters. We show that any subset of minimal width is a completely regular code and that any subset of minimal dual width induces a cometric association scheme in the original. A variety of examples and applications are considered
MRST2001: partons and α <SUB>S</SUB> from precise deep inelastic scattering and Tevatron jet data
We use all the available new precise data for deep inelastic and related hard scattering processes to perform NLO global parton analyses. These new data allow an improved determination of partons and, in particular, the inclusion of the recent measurements of the structure functions at HERA and of the inclusive jets at the Tevatron help to determine the gluon distribution and aS better than ever before. We find a somewhat smaller gluon at low x than previous determinations and that aS (MZ2) = 0.119 ±0.002 (expt.) ±0.003 (theory)
Uncertainties of predictions from parton distributions I: experimental errors
We determine the uncertainties on observables arising from the errors on the experimental data that are fitted in the global MRST2001 parton analysis. By diagonalizing the error matrix we produce sets of partons suitable for use within the framework of linear propagation of errors, which is the most convenient method for calculating the uncertainties. Despite the potential limitations of this approach we find that it can be made to work well in practice. This is confirmed by our alternative approach of using the more rigorous Lagrange multiplier method to determine the errors on physical quantities directly. As particular examples we determine the uncertainties on the predictions of the charged-current deep-inelastic structure functions, on the cross-sections for W production and for Higgs boson production via gluon-gluon fusion at the Tevatron and the LHC, on the ratio of W- to W+ production at the LHC and on the moments of the non-singlet quark distributions. We discuss the corresponding uncertainties on the parton distributions in the relevant x,Q2 domains. Finally, we briefly look at uncertainties related to the fit procedure, stressing their importance and using sW, sH and extractions of aS(MZ2) as examples. As a by-product of this last point we present a slightly updated set of parton distributions, MRST2002
The wave-vector power spectrum of the local tunnelling density of states: ripples in a d-wave sea
A weak scattering potential imposed on a layer of a cuprate
superconductor modulates the local density of states . In recently
reported experimental studies scanning-tunneling maps of have
been Fourier transformed to obtain a wave-vector power spectrum. Here, for the
case of a weak scattering potential, we discuss the structure of this power
spectrum and its relationship to the quasi-particle spectrum and the structure
factor of the scattering potential. Examples of quasi-particle interferences in
normal metals and - and d-wave superconductors are discussed.Comment: 22 pages, 21 figures; enlarged discussion of the d-wave response, to
be published in Physical Review
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