3,541 research outputs found
Conicoid Mirrors
The first order equation relating object and image location for a mirror of
arbitrary conic-sectional shape is derived. It is also shown that the parabolic
reflecting surface is the only one free of aberration and only in the limiting
case of distant sources.Comment: 9 page
Organisational interventions designed to reduce caesarean section rates: a systematic review protocol.
INTRODUCTION: There is a growing body of evidence to indicate that both primary and subsequent caesarean sections are associated with increased maternal and perinatal morbidity. Efforts to reduce the number of clinically unnecessary caesarean sections are urgently required. Our objective is to systematically review published evidence on the effectiveness of maternity service organisational interventions, such as models of maternity care, that aim to reduce caesarean section rates. METHODS AND ANALYSIS: Databases will be searched, including the Cochrane Central Register of Controlled Trials, Cumulative Index to Nursing and Allied Health Literature, MEDLINE, Maternity and Infant Care, EMBASE and SCOPUS. Search terms related to caesarean section and organisational intervention will be used. Research published before 1980 will be excluded and only randomised controlled trials, cluster-randomised controlled trials, quasi-randomised controlled trials, controlled before and after studies and interrupted time series studies will be included. Data extraction and quality assessments will be undertaken by two authors. ETHICS AND DISSEMINATION: Ethics approval is not required for this systematic review. The results of this study will be disseminated via peer-reviewed publication and presentation at professional conferences. PROSPERO REGISTRATION NUMBER: CRD42016039458
Families of Graphs with W_r({G},q) Functions That Are Nonanalytic at 1/q=0
Denoting as the chromatic polynomial for coloring an -vertex
graph with colors, and considering the limiting function , a fundamental question in graph theory is the
following: is analytic or not at the origin
of the plane? (where the complex generalization of is assumed). This
question is also relevant in statistical mechanics because
, where is the ground state entropy of the
-state Potts antiferromagnet on the lattice graph , and the
analyticity of at is necessary for the large- series
expansions of . Although is analytic at for many
, there are some for which it is not; for these, has no
large- series expansion. It is important to understand the reason for this
nonanalyticity. Here we give a general condition that determines whether or not
a particular is analytic at and explains the
nonanalyticity where it occurs. We also construct infinite families of graphs
with functions that are non-analytic at and investigate the
properties of these functions. Our results are consistent with the conjecture
that a sufficient condition for to be analytic at is
that is a regular lattice graph . (This is known not to be a
necessary condition).Comment: 22 pages, Revtex, 4 encapsulated postscript figures, to appear in
Phys. Rev.
Geometric Parameterization of Absorption in Heavy Ion Collisions
We calculate the survival probability of particles in various
colliding systems using a Glauber model. An analysis of recent data has
reported a -nucleon breakup cross section of 6.20.7 mb derived
from an exponential fit to the ratio of to Drell-Yan yields as a
function of a simple, linearly-averaged mean path length through the nuclear
medium. Our calculations indicate that, due to the nature of the calculation,
this approach yields an apparent breakup cross section which is systematically
lower than the actual value.Comment: LaTex, 7 pages, 2 figure
Topological Phase Transitions and Holonomies in the Dimer Model
We demonstrate that the classical dimer model defined on a toroidal hexagonal
lattice acquires holonomy phases in the thermodynamic limit. When all
activities are equal the lattice sizes must be considered mod 6 in which case
the finite size corrections to the bulk partition function correspond to a
massless Dirac Fermion in the presence of a flat connection with nontrivial
holonomy. For general bond activities we find that the phase transition in this
model is a topological one, where the torus degenerates and its modular
parameter becomes real at the critical temperature. We argue that these
features are generic to bipartite dimer models and we present a more general
lattice whose continuum partition function is that of a massive Dirac Fermion.Comment: 7 pages, 4 figures. Minor corrections with additional figure
The Kasteleyn model and a cellular automaton approach to traffic flow
We propose a bridge between the theory of exactly solvable models and the
investigation of traffic flow. By choosing the activities in an apropriate way
the dimer configurations of the Kasteleyn model on a hexagonal lattice can be
interpreted as space-time trajectories of cars. This then allows for a
calculation of the flow-density relationship (fundamental diagram). We further
introduce a closely-related cellular automaton model. This model can be viewed
as a variant of the Nagel-Schreckenberg model in which the cars do not have a
velocity memory. It is also exactly solvable and the fundamental diagram is
calculated.Comment: Latex, 13 pages including 3 ps-figure
Resonant tunneling diodes as sources for millimeter and submillimeter wavelengths
High-quality Resonant Tunneling Diodes have been fabricated and tested as sources for millimeter and submillimeter wavelengths. The devices have shown excellent I-V characteristics with peak-to-valley current ratios as high as 6:1 and current densities in the range of 50-150 kA/cm(exp 2) at 300 K. Used as local oscillators, the diodes are capable of state of the art output power delivered by AlGaAs-based tunneling devices. As harmonic multipliers, a frequency of 320 GHz has been achieved by quintupling the fundamental oscillation of a klystron source
The local electronic structure of alpha-Li3N
New theoretical and experimental investigation of the occupied and unoccupied
local electronic density of states (DOS) are reported for alpha-Li3N. Band
structure and density functional theory calculations confirm the absence of
covalent bonding character. However, real-space full-multiple-scattering
(RSFMS) calculations of the occupied local DOS finds less extreme nominal
valences than have previously been proposed. Nonresonant inelastic x-ray
scattering (NRIXS), RSFMS calculations, and calculations based on the
Bethe-Salpeter equation are used to characterize the unoccupied electronic
final states local to both the Li and N sites. There is good agreement between
experiment and theory. Throughout the Li 1s near-edge region, both experiment
and theory find strong similarities in the s- and p-type components of the
unoccupied local final density of states projected onto an orbital angular
momentum basis (l-DOS). An unexpected, significant correspondence exists
between the near-edge spectra for the Li 1s and N 1s initial states. We argue
that both spectra are sampling essentially the same final density of states due
to the combination of long core-hole lifetimes, long photoelectron lifetimes,
and the fact that orbital angular momentum is the same for all relevant initial
states. Such considerations may be generically applicable for low atomic number
compounds.Comment: 34 pages, 7 figures, 1 tabl
Maternity service organisational interventions that aim to reduce caesarean section: a systematic review and meta-analyses
Background
Caesarean sections (CSs) are associated with increased maternal and perinatal morbidity, yet rates continue to increase within most countries. Effective interventions are required to reduce the number of non-medically indicated CSs and improve outcomes for women and infants. This paper reports findings of a systematic review of literature related to maternity service organisational interventions that have a primary intention of improving CS rates.
Method
A three-phase search strategy was implemented to identify studies utilising organisational interventions to improve CS rates in maternity services. The database search (including Cochrane CENTRAL, CINAHL, MEDLINE, Maternity and Infant Care, EMBASE and SCOPUS) was restricted to peer-reviewed journal articles published from 1 January 1980 to 31 December 2017. Reference lists of relevant reviews and included studies were also searched. Primary outcomes were overall, planned, and unplanned CS rates. Secondary outcomes included a suite of birth outcomes. A series of meta-analyses were performed in RevMan, separated by type of organisational intervention and outcome of interest. Summary risk ratios with 95% confidence intervals were presented as the effect measure. Effect sizes were pooled using a random-effects model.
Results
Fifteen articles were included in the systematic review, nine of which were included in at least one meta-analysis. Results indicated that, compared with women allocated to usual care, women allocated to midwife-led models of care implemented across pregnancy, labour and birth, and the postnatal period were, on average, less likely to experience CS (overall) (average RR 0.83, 95% CI 0.73 to 0.96), planned CS (average RR 0.75, 95% CI 0.61 to 0.93), and episiotomy (average RR 0.84, 95% CI 0.74 to 0.95). Narratively, audit and feedback, and a hospital policy of mandatory second opinion for CS, were identified as interventions that have potential to reduce CS rates.
Conclusion
Maternity service leaders should consider the adoption of midwife-led models of care across the maternity episode within their organisations, particularly for women classified as low-risk. Additional studies are required that utilise either audit and feedback, or a hospital policy of mandatory second opinion for CS, to facilitate the quantification of intervention effects within future reviews
Particle correlations at RHIC from parton coalescence dynamics -- first results
A new dynamical approach that combines covariant parton transport theory with
hadronization channels via parton coalescence and fragmentation is applied to
Au+Au at RHIC. Basic consequences of the simple coalescence formulas, such as
elliptic flow scaling and enhanced proton/pion ratio, turn out to be rather
sensitive to the spacetime aspects of coalescence dynamics.Comment: Contribution to Quark Matter 2004 (January 11-17, 2004, Oakland, CA).
4 pages, 2 EPS figs, IOP style fil
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