32,241 research outputs found
General practitioners’ perceptions of asynchronous telemedicine in a randomized controlled trial of teledermatology.
Background: Telemedicine is viewed as having a key role to play in the Government’s plans to modernise the NHS.1 However, to date there are few studies which have explored the views and acceptability of GPs towards telemedicine in primary care.
Aim: To elicit the perceptions of GPs towards teledermatology (TD) before and after it’s introduction into their Practices and to observe whether GP views of TD had changed over the course of the study.
Design of study: A postal questionnaire administered as part of a wider randomised controlled trial of telemedicine in dermatology.
Setting: A locality group of eight General Practices in Sheffield and a single teaching hospital in Sheffield that provided the local dermatology referral service.
Method: A postal questionnaire circulated to all GPs from the eight participating Practices.
Results: A 85.7% (36/42) response rate was achieved. Only 21% (n=7; 95% CI: 10-37%) of respondents felt satisfied/very satisfied with TD in their Practice, 47% (n=16) said that they were dissatisfied or very dissatisfied. Thirty one per cent (n=10; 95% CI: 18-49%) said that they felt confident about diagnosis and management of care through TD, with 28% (n=9) reporting that they were unconfident. Only 23% (n=8; 95% CI: 12-39%) of respondents said that they would consider using a telemedicine system in the future, 34% (n=12) said they would probably or definitely not and 43% (n=15) were unsure. There was some evidence that GPs views about TD became more negative over the course of the study. Conclusions: The study reports less favourable GP responses to telemedicine than observed in previous studies, and suggests that the model of telemedicine described in this study paper would not be widely acceptable to GPs
Renormalization-group anatomy of transverse-momentum dependent parton distribution functions in QCD
The ultraviolet and rapidity divergences of transverse-momentum dependent
parton distribution functions with lightlike and transverse gauge links is
studied, also incorporating a soft eikonal factor. We find that in the
light-cone gauge with -independent pole prescriptions extra divergences
appear which amount, at one-loop, to a cusp-like anomalous dimension. We show
that such contributions are absent when the Mandelstam-Leibbrandt prescription
is used. In the first case, the soft factor cancels the anomalous-dimension
defect, while in the second case its ultraviolet-divergent part reduces to
unity.Comment: 10 pages, 3 figures; needs ws-mpla-hep.cls (supplied). Talk presented
by the first author at Workshop on "Recent Advances in Perturbative QCD and
Hadronic Physics", 20--25 July 2009, ECT*, Trento, Italy, in Honor of Prof.
Anatoly Efremov's 75th birthda
Random quantum channels I: graphical calculus and the Bell state phenomenon
This paper is the first of a series where we study quantum channels from the
random matrix point of view. We develop a graphical tool that allows us to
compute the expected moments of the output of a random quantum channel. As an
application, we study variations of random matrix models introduced by Hayden
\cite{hayden}, and show that their eigenvalues converge almost surely. In
particular we obtain for some models sharp improvements on the value of the
largest eigenvalue, and this is shown in a further work to have new
applications to minimal output entropy inequalities.Comment: Several typos were correcte
Factorization theorems for exclusive heavy-quarkonium production
We outline the proofs of the factorization theorems for exclusive two-body
charmonium production in B-meson decay and e^+e^- annihilation to all orders in
perturbation theory in quantum chromodynamics. We find that factorized
expressions hold up to corrections of order m_c/m_b in B-meson decay and
corrections of order m_c^2/s in e^+e^- annihilation, where m_c is the
charm-quark mass, m_b is the bottom-quark mass, and root-s is the e^+e^-
center-of-momentum energy.Comment: 4 pages, 2 figure
Factorization of low-energy gluons in exclusive processes
We outline a proof of factorization in exclusive processes, taking into
account the presence of soft and collinear modes of arbitrarily low energy,
which arise when the external lines of the process are taken on shell.
Specifically, we examine the process of e^+e^- annihilation through a virtual
photon into two light mesons. In an intermediate step, we establish a
factorized form that contains a soft function that is free of collinear
divergences. In contrast, in soft-collinear effective theory, the low-energy
collinear modes factor most straightforwardly into the soft function. We point
out that the cancellation of the soft function, which relies on the
color-singlet nature of the external hadrons, fails when the soft function
contains low-energy collinear modes.Comment: 18 pages, 10 figures, 2 tables, version published in Physical Review
Factorization in exclusive quarkonium production
We present factorization theorems for two exclusive heavy-quarkonium
production processes: production of two quarkonia in e^+e^- annihilation and
production of a quarkonium and a light meson in B-meson decays. We describe the
general proofs of factorization and supplement them with explicit one-loop
analyses, which illustrate some of the features of the soft-gluon
cancellations. We find that violations of factorization are generally
suppressed relative to the factorized contributions by a factor v^2m_c/Q for
each S-wave charmonium and a factor m_c/Q for each L-wave charmonium with L>0.
Here, v is the velocity of the heavy quark or antiquark in the quarkonium rest
frame, Q=sqrt{s} for e^+e^- annihilation, Q=m_B for B-meson decays, sqrt{s} is
the e^+e^- center-of-momentum energy, m_c is the charm-quark mass, and m_B is
the B-meson mass. There are modifications to the suppression factors if
quantum-number restrictions apply for the specific process.Comment: 69 pages, 12 figures, 2 tables. v2: Version published in Physical
Review
Dark matter cores all the way down
We use high resolution simulations of isolated dwarf galaxies to study the
physics of dark matter cusp-core transformations at the edge of galaxy
formation: M200 = 10^7 - 10^9 Msun. We work at a resolution (~4 pc minimum cell
size; ~250 Msun per particle) at which the impact from individual supernovae
explosions can be resolved, becoming insensitive to even large changes in our
numerical 'sub-grid' parameters. We find that our dwarf galaxies give a
remarkable match to the stellar light profile; star formation history;
metallicity distribution function; and star/gas kinematics of isolated dwarf
irregular galaxies. Our key result is that dark matter cores of size comparable
to the stellar half mass radius (r_1/2) always form if star formation proceeds
for long enough. Cores fully form in less than 4 Gyrs for the M200 = 10^8 Msun
and 14 Gyrs for the 10^9 Msun dwarf. We provide a convenient two parameter
'coreNFW' fitting function that captures this dark matter core growth as a
function of star formation time and the projected stellar half mass radius.
Our results have several implications: (i) we make a strong prediction that
if LCDM is correct, then 'pristine' dark matter cusps will be found either in
systems that have truncated star formation and/or at radii r > r_1/2; (ii)
complete core formation lowers the projected velocity dispersion at r_1/2 by a
factor ~2, which is sufficient to fully explain the 'too big to fail problem';
and (iii) cored dwarfs will be much more susceptible to tides, leading to a
dramatic scouring of the subhalo mass function inside galaxies and groups.Comment: 20 pages; 9 figures; final version to appear in MNRAS including typos
corrected in proo
Fully Unintegrated Parton Correlation Functions and Factorization in Lowest Order Hard Scattering
Motivated by the need to correct the potentially large kinematic errors in
approximations used in the standard formulation of perturbative QCD, we
reformulate deeply inelastic lepton-proton scattering in terms of gauge
invariant, universal parton correlation functions which depend on all
components of parton four-momentum. Currently, different hard QCD processes are
described by very different perturbative formalisms, each relying on its own
set of kinematical approximations. In this paper we show how to set up
formalism that avoids approximations on final-state momenta, and thus has a
very general domain of applicability. The use of exact kinematics introduces a
number of significant conceptual shifts already at leading order, and tightly
constrains the formalism. We show how to define parton correlation functions
that generalize the concepts of parton density, fragmentation function, and
soft factor. After setting up a general subtraction formalism, we obtain a
factorization theorem. To avoid complications with Ward identities the full
derivation is restricted to abelian gauge theories; even so the resulting
structure is highly suggestive of a similar treatment for non-abelian gauge
theories.Comment: 44 pages, 69 figures typos fixed, clarifications and second appendix
adde
Quantization effects in Viterbi decoding rate 1/n convolutional codes
A Viterbi decoder's performance loss due to quantizing data from the additive white Gaussian noise (AWGN) channel is studied. An optimal quantization scheme and branch metric calculation method are presented. The uniformly quantized channel capacity C(sub u)(q) is used to determine the smallest number of quantization bits q that does not cause a significant loss. The quantizer stepsize which maximizes C(sub u)(q) almost minimizes the decoder bit error rate (BER). However, a slightly larger stepsize is better, like the value that minimizes the Bhattacharyya bound. The range and renormalization of state metrics is analyzed, in particular for K = 15 decoders such as the Big Viterbi Decoder (BVD) for the Galileo mission. These results are required to design reduced hardware complexity Viterbi decoders with a negligible quantization loss
Next-to-Leading Order Hard Scattering Using Fully Unintegrated Parton Distribution Functions
We calculate the next-to-leading order fully unintegrated hard scattering
coefficient for unpolarized gluon-induced deep inelastic scattering using the
logical framework of parton correlation functions developed in previous work.
In our approach, exact four-momentum conservation is maintained throughout the
calculation. Hence, all non-perturbative functions, like parton distribution
functions, depend on all components of parton four-momentum. In contrast to the
usual collinear factorization approach where the hard scattering coefficient
involves generalized functions (such as Dirac -functions), the fully
unintegrated hard scattering coefficient is an ordinary function. Gluon-induced
deep inelastic scattering provides a simple illustration of the application of
the fully unintegrated factorization formalism with a non-trivial hard
scattering coefficient, applied to a phenomenologically interesting case.
Furthermore, the gluon-induced process allows for a parameterization of the
fully unintegrated gluon distribution function.Comment: 22 pages, Typos Fixed, Reference Added, Minor Clarification Adde
- …