5,254 research outputs found
Contribution of Scalar Loops to the Three-Photon Decay of the Z
I corrected 3 mistakes from the first version: that were an omitted Feynman
integration in the function f^3_{ij}, a factor of 2 in front of log f^3_{ij} in
eq.2 and an overall factor of 2 in Fig.1 c). The final result is changed
drastically. Doing an expansion in the Higgs mass I show that the matrix
element is identically 0 in the order (MZ/MH)^2, which is due to gauge
invariance. Left with an amplitude of the order (MZ/MH)^4 the final result is
that the scalar contribution to this decay rate is several orders of magnitude
smaller than those of the W boson and fermions.Comment: 6 pages, plain Tex, 1 figure available under request via fax or mail,
OCIP/C-93-5, UQAM-PHE-93/0
Discrete Event Simulation for Decision Modeling in Health Care: Lessons from Abdominal Aortic Aneurysm Screening
Markov models are often used to evaluate the cost-effectiveness of new healthcare interventions but they are sometimes not flexible enough to allow accurate modeling or investigation of alternative scenarios and policies. A Markov model previously demonstrated that a one-off invitation to screening for abdominal aortic aneurysm (AAA) for men aged 65 y in the UK and subsequent follow-up of identified AAAs was likely to be highly cost-effective at thresholds commonly adopted in the UK (£20,000 to £30,000 per quality adjusted life-year). However, new evidence has emerged and the decision problem has evolved to include exploration of the circumstances under which AAA screening may be cost-effective, which the Markov model is not easily able to address. A new model to handle this more complex decision problem was needed, and the case of AAA screening thus provides an illustration of the relative merits of Markov models and discrete event simulation (DES) models. An individual-level DES model was built using the R programming language to reflect possible events and pathways of individuals invited to screening v. those not invited. The model was validated against key events and cost-effectiveness, as observed in a large, randomized trial. Different screening protocol scenarios were investigated to demonstrate the flexibility of the DES. The case of AAA screening highlights the benefits of DES, particularly in the context of screening studies
Frequency-Dependent Streaming Potential of Porous Media—Part 2: Experimental Measurement of Unconsolidated Materials
Frequency-dependent streaming potential coefficient measurements have been made upon Ottawa sand and glass bead packs using a new apparatus that is based on an electromagnetic drive. The apparatus operates in the range 1 Hz to 1 kHz with samples of 25.4 mm diameter up to 150 mm long. The results have been analysed using theoretical models that are either (i) based upon vibrational mechanics, (ii) treat the geological material as a bundle of capillary tubes, or (iii) treat the material as a porous medium. The best fit was provided by the Pride model and its simplification, which is satisfying as this model was conceived for porous media rather than capillary tube bundles. Values for the transition frequency were derived from each of the models for each sample and were found to be in good agreement with those expected from the independently measured effective pore radius of each material. The fit to the Pride model for all four samples was also found to be consistent with the independently measured steady-state permeability, while the value of the streaming potential coefficient in the low-frequency limit was found to be in good agreement with other steady-state streaming potential coefficient data
Inclusive Prompt Photon Production in Hadronic Final States of Annihilation
We provide complete analytic expressions for the inclusive prompt photon
production cross section in hadronic final states of annihilation
reactions through one-loop order in quantum chromodynamics perturbation theory.
Computed explicitly are direct photon production through first order in the
electromagnetic strength and the quark-to-photon and
gluon-to-photon fragmentation contributions through first order in the strong
coupling . The full angular dependence of the cross sections is
displayed, separated into transverse and
longitudinal components, where
specifies the direction of the photon with respect to the collision
axis. We discuss extraction of fragmentation functions from data.Comment: 40 pages, RevTex, 30 figures in postscript available in a separate
fil
Isolated Prompt Photon Production in Hadronic Final States of Annihilation
We provide complete analytic expressions for the isolated prompt photon
production cross section in annihilation reactions through one-loop
order in quantum chromodynamics (QCD) perturbation theory. Functional
dependences on the isolation cone size and isolation energy parameter
are derived. The energy dependence as well as the full angular
dependence of the cross section on are displayed, where
specifies the direction of the photon with respect to the
collision axis. We point out that conventional perturbative QCD
factorization breaks down for isolated photon production in
annihilation reactions in a specific region of phase space. We discuss the
implications of this breakdown for the extraction of fragmentation functions
from annihilation data and for computations of prompt photon
production in hadron-hadron reactions.Comment: 54 pages RevTeX plus 19 postscript figures submitted together in one
compressed fil
Effects of Parent Implemented Visual Schedule Routines for African American Children with ASD in Low-Income Home Settings
Low-income, minority families are underrepresented in the literature on parent training for school-aged children with autism spectrum disorder (ASD). Although the use of visual supports, such as visual schedules, is considered to be an evidence-based practice for children with ASD in school, it is not known whether this strategy is effective for minority, low-income families when implemented by the parent in the home setting. This study used a multiple-baseline across routines design replicated across two African American child-mother dyads to examine the effects of a parent-implemented visual schedule procedure on child independent schedule use and between-activity transitions. Parent participants were trained to implement a visual schedule intervention during home routines. Although a functional relation was demonstrated across routines for one mother-child dyad, results varied across participants, highlighting the importance of treatment fidelity. Implications for future research, including the challenges involved in parent-implemented interventions in low-income settings for minority children with ASD, are addressed
Carbon in different phases ([CII], [CI], and CO) in infrared dark clouds: Cloud formation signatures and carbon gas fractions
Context: How do molecular clouds form out of the atomic phase? And what are
the relative fractions of carbon in the ionized, atomic and molecular phase?
These are questions at the heart of cloud and star formation. Methods: Using
multiple observatories from Herschel and SOFIA to APEX and the IRAM 30m
telescope, we mapped the ionized, atomic and molecular carbon ([CII]@1900GHz,
[CI]@492GHz and C18O(2-1)@220GHz) at high spatial resolution (12"-25") in four
young massive infrared dark clouds (IRDCs). Results: The three carbon phases
were successfully mapped in all four regions, only in one source the [CII] line
remained a non-detection. Both the molecular and atomic phases trace the dense
structures well, with [CI] also tracing material at lower column densities.
[CII] exhibits diverse morphologies in our sample, from compact to diffuse
structures probing the cloud environment. In at least two out of the four
regions, we find kinematic signatures strongly indicating that the dense gas
filaments have formed out of a dynamically active and turbulent
atomic/molecular cloud, potentially from converging gas flows. The
atomic-to-molecular carbon gas mass ratios are low between 7% and 12% with the
lowest values found toward the most quiescent region. In the three regions
where [CII] is detected, its mass is always higher by a factor of a few than
that of the atomic carbon. The ionized carbon emission depends as well on the
radiation field, however, we also find strong [CII] emission in a region
without significant external sources, indicating that other processes, e.g.,
energetic gas flows can contribute to the [CII] excitation as well.Comment: 15 pages, 18 figures, accepted by Astronomy & Astrophysics, a higher
resolution version can be found at
http://www.mpia.de/homes/beuther/papers.htm
Factorization and soft-gluon divergences in isolated-photon cross sections
We study the production of isolated photons in annihilation and give
the proof of the all-order factorization of the collinear singularities. These
singularities are absorbed in the standard fragmentation functions of partons
into a photon, while the effects of the isolation are consistently included in
the short-distance cross section. We compute this cross section at order \as
and show that it contains large double logarithms of the isolation parameters.
We explain the physical origin of these logarithms and discuss the possibility
to resum them to all orders in \as.Comment: 18 pages, LaTex, 2 eps figures, few modifications in the text,
results unchange
Color-Octet Fragmentation and the psi' Surplus at the Tevatron
The production rate of prompt 's at large transverse momentum at the
Tevatron is larger than theoretical expectations by about a factor of 30. As a
solution to this puzzle, we suggest that the dominant production
mechanism is the fragmentation of a gluon into a pair in a pointlike
color-octet S-wave state, which subsequently evolves nonperturbatively into a
plus light hadrons. The contribution to the fragmentation function from
this process is enhanced by a short-distance factor of relative
to the conventional color-singlet contribution. This may compensate for the
suppression by , where is the relative momentum of the charm quark in
the . If this is indeed the dominant production mechanism at large
, then the prompt 's that are observed at the Tevatron should
almost always be associated with a jet of light hadrons.Comment: 9 pages, LaTe
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