5,558 research outputs found
Pulse confinement in optical fibers with random dispersion
Short range correlated uniform noise in the dispersion coefficient, inherent
in many types of optical fibers, broadens and eventually destroys all initially
ultra-short pulses. However, under the constraint that the integral of the
random component of the dispersion coefficient is set to zero, or pinned,
periodically or quasi-periodically along the fiber, the nature of the pulse
propagation changes dramatically. For the case that randomness is added to
constant positive dispersion, the pinning restriction significantly reduces
pulse broadening. If the randomness is added to piecewise constant periodic
dispersion, the pinning may even provide probability distributions of pulse
parameters that are numerically indistinguishable from the statistically steady
case. The pinning method can be used to both manufacture better fibers and
upgrade existing fiber links.Comment: 4 pages, 2 figure
The a-function in six dimensions
The a-function is a proposed quantity defined in even dimensions which has a
monotonic behaviour along RG flows, related to the beta-functions via a
gradient flow equation. We study the a-function for a general scalar theory in
six dimensions, using the beta-functions up to three-loop order for both the
MSbar and MOM schemes (the latter presented here for the first time at three
loops).Comment: 27 pages, seven figures, uses axodraw. Minor improvements in wordin
The accurate staging of ovarian cancer using 3T magnetic resonance imaging - a realistic option
Objectives: The aim of the study was to determine whether staging primary ovarian cancer using 3.0 Tesla (3T) magnetic resonance imaging (MRI) is comparable to surgical staging of the disease. Design: A retrospective study consisting of a search of the pathology database to identify women with ovarian pathology from May 2004 to January 2007. Setting: All women treated for suspected ovarian cancer in our cancer centre region. Sample: All women suspected of ovarian pathology who underwent 3T MRI prior to primary surgical intervention between May 2004 and January 2007. Methods: All women found to have ovarian pathology, both benign and malignant, were then cross checked with the magnetic resonance (MR) database to identify those who had undergone 3T MRI prior to surgery. The resulting group of women underwent comparison of the MR, surgical and histopathological findings for each individual including diagnosis of benign or malignant disease and International Federation of Gynecology and Obstetrics (FIGO) staging where appropriate. Main outcome measures: Comparisons were made between the staging accuracy of 3T MRI and surgical staging compared with histopathological findings and FIGO stage using weighted kappa. Sensitivity, specificity and accuracy were calculated for diagnosing malignant ovarian disease with 3T MRI. Results: A total of 191 women identified as having ovarian pathology underwent imaging with 3T MR and primary surgical intervention. In 19 of these women, the ovarian disease was an incidental finding. The group for which staging methods were compared consisted of 77 women of primary ovarian malignancy (20 of whom had borderline tumours). 3T MRI was able to detect ovarian malignancy with a sensitivity of 92% and a specificity of 76%. The overall accuracy in detecting malignancy with 3T MRI was 84%, with a positive predictive value of 80% and negative predictive value of 90%. Statistical analysis of the two methods of staging using weighted kappa, gave a K value of 0.926 (SE ±0.121) for surgical staging and 0.866 (SE ±0.119) for MR staging. A further analysis of the staging data for ovarian cancers alone, excluding borderline tumours resulted in a K value of 0.931 (SE ±0.136) for histopathological staging versus MR staging and 0.958 (±0.140) for histopathological stage versus surgical staging. Conclusion: Our study has shown that MRI can achieve staging of ovarian cancer comparable with the accuracy seen with surgical staging. No previous studies comparing different modalities have used the higher field strength 3T MRI. In addition, all other studies comparing radiological assessment of ovarian cancer have grouped the stages into I, II, III and IV rather than the more clinically appropriate a, b and c subgroups. © 2008 The Authors
Miniature spectrally selective dosimeter
A miniature spectrally selective dosimeter capable of measuring selected bandwidths of radiation exposure on small mobile areas is described. This is achieved by the combination of photovoltaic detectors, electrochemical integrators (E-cells) and filters in a small compact case which can be easily attached in close proximity to and substantially parallel to the surface being measured. In one embodiment two photovoltaic detectors, two E-cells, and three filters are packaged in a small case with attaching means consisting of a safety pin. In another embodiment, two detectors, one E-cell, three filters are packaged in a small case with attaching means consisting of a clip to clip over a side piece of an eye glass frame
<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>a</mml:mi></mml:math> -function in three dimensions: Beyond the leading order
Recently, evidence was provided for the existence of an -function for
renormalisable quantum field theories in three dimensions. An explicit
expression was given at lowest order for general theories involving scalars and
fermions, and shown to be related to the beta-functions by a gradient flow
equation with positive-definite metric as in four dimensions. Here, we extend
this lowest-order calculation to a general abelian Chern-Simons gauge theory
coupled to fermions and scalars, and derive a prediction for part of the
four-loop Yukawa beta-function. We also compute the complete four-loop Yukawa
beta-function for the scalar-fermion theory and show that it is entirely
consistent with the gradient flow equations at next-to-leading order.Comment: 24 pages; uses Axodraw. Revised version with typos correcte
The a-function for gauge theories
The a-function is a proposed quantity defined for quantum field theories
which has a monotonic behaviour along renormalisation group flows, being
related to the beta-functions via a gradient flow equation involving a positive
definite metric. We construct the a-function at four loop order for a general
gauge theory with fermions and scalars, using only one and two loop
beta-functions; we are then able to provide a stringent consistency check on
the general three-loop gauge beta-function. In the case of an N=1
supersymmetric gauge theory, we present a general condition on the chiral field
anomalous dimension which guarantees an exact all-orders expression for the
a-function; and we verify this up to fifth order (corresponding to the
three-loop anomalous dimension).Comment: 28 pages; uses axodraw; typos corrected, also some sign errors
corrected in Sect
CP-nets: A Tool for Representing and Reasoning withConditional Ceteris Paribus Preference Statements
Information about user preferences plays a key role in automated decision
making. In many domains it is desirable to assess such preferences in a
qualitative rather than quantitative way. In this paper, we propose a
qualitative graphical representation of preferences that reflects conditional
dependence and independence of preference statements under a ceteris paribus
(all else being equal) interpretation. Such a representation is often compact
and arguably quite natural in many circumstances. We provide a formal semantics
for this model, and describe how the structure of the network can be exploited
in several inference tasks, such as determining whether one outcome dominates
(is preferred to) another, ordering a set outcomes according to the preference
relation, and constructing the best outcome subject to available evidence
- …