4,032 research outputs found
A nomogram to determine required seed air kerma strength in planar 131 Cesium permanent seed implant brachytherapy
Purpose: Intraoperatively implanted Cesium-131 ( 131 Cs) permanent seed brachytherapy is used to deliver highly localized re-irradiation in recurrent head and neck cancers. A single planar implant of uniform air kerma strength (AKS) seeds and 10 mm seed-to-seed spacing is used to deliver the prescribed dose to a point 5 mm or 10 mm perpendicular to the center of the implant plane. Nomogram tables to quickly determine the required AKS for rectangular and irregularly shaped implants were created and dosimetrically verified. By eliminating the need for a full treatment planning system plan, nomogram tables allow for fast dose calculation for intraoperative re-planning and for a second check method.
Material and methods: TG-43U1 recommended parameters were used to create a point-source model in MATLAB. The dose delivered to the prescription point from a single 1 U seed at each possible location in the implant plane was calculated. Implant tables were verified using an independent seed model in MIM Symphony LDR™. Implant tables were used to retrospectively determine seed AKS for previous cases: three rectangular and three irregular.
Results: For rectangular implants, the percent difference between required seed AKS calculated using MATLAB and MIM was at most 0.6%. For irregular implants, the percent difference between MATLAB and MIM calculations for individual seed locations was within 1.5% with outliers of less than 3.1% at two distal locations (10.6 cm and 8.8 cm), which have minimal dose contribution to the prescription point. The retrospectively determined AKS for patient implants using nomogram tables agreed with previous calculations within 5% for all six cases.
Conclusions: Nomogram tables were created to determine required AKS per seed for planar uniform AKS 131 Cs implants. Comparison with the treatment planning system confirms dosimetric accuracy that is acceptable for use as a second check or for dose calculation in cases of intraoperative re-planning
Market and regional segmentation and risk premia in the first era of financial globalization
We study market segmentation effects using data on U.S. railroads that list their bonds in New York and London between 1873 and 1913. This sample provides a unique setting for such analysis because of the precision offered by bond yields in cost of capital estimation, the geography-specific nature of railroad assets, and ongoing substantial technological change. We document a significant
reduction in market segmentation over time. Whilst New York bond yields exceeded those in London in the 1870s, this premium disappeared by the early 1900s. However, the segmentation premium persisted in the more remote regions of the United States.Chambers acknowledges financial support from his Keynes Fellowship, the Newton Centre for Endowment Asset Management and the Cambridge Endowment for Research in Finance, Sarkissian acknowledges financial support from the Social Sciences & Humanities Research Council of Canada, and Schill acknowledges financial support from the Darden School Foundation
Artistic representations of infectious disease
Artistic representations of disease are widespread yet largely ignored in health psychology research. In this paper we use two infectious diseases, tuberculosis and the plague, as tracers to study how infectious diseases are represented in novels, films, paintings, and songs. They were represented especially in terms of their causes and seriousness. Studying how diseases are represented in various art forms extends our understanding of how they are socially constructed. This knowledge can also be incorporated into the training of health care providers to sensitize them to issues in patient care
Regulation of pancreatic cancer aggressiveness by stromal stiffening
No abstract available
A unified hyperbolic formulation for viscous fluids and elastoplastic solids
We discuss a unified flow theory which in a single system of hyperbolic
partial differential equations (PDEs) can describe the two main branches of
continuum mechanics, fluid dynamics, and solid dynamics. The fundamental
difference from the classical continuum models, such as the Navier-Stokes for
example, is that the finite length scale of the continuum particles is not
ignored but kept in the model in order to semi-explicitly describe the essence
of any flows, that is the process of continuum particles rearrangements. To
allow the continuum particle rearrangements, we admit the deformability of
particle which is described by the distortion field. The ability of media to
flow is characterized by the strain dissipation time which is a characteristic
time necessary for a continuum particle to rearrange with one of its
neighboring particles. It is shown that the continuum particle length scale is
intimately connected with the dissipation time. The governing equations are
represented by a system of first order hyperbolic PDEs with source terms
modeling the dissipation due to particle rearrangements. Numerical examples
justifying the reliability of the proposed approach are demonstrated.Comment: 6 figure
Orometric methods in bounded metric data
A large amount of data accommodated in knowledge graphs (KG) is metric. For example, the Wikidata KG contains a plenitude of metric facts about geographic entities like cities or celestial objects. In this paper, we propose a novel approach that transfers orometric (topographic) measures to bounded metric spaces. While these methods were originally designed to identify relevant mountain peaks on the surface of the earth, we demonstrate a notion to use them for metric data sets in general. Notably, metric sets of items enclosed in knowledge graphs. Based on this we present a method for identifying outstanding items using the transferred valuations functions isolation and prominence. Building up on this we imagine an item recommendation process. To demonstrate the relevance of the valuations for such processes, we evaluate the usefulness of isolation and prominence empirically in a machine learning setting. In particular, we find structurally relevant items in the geographic population distributions of Germany and France. © 2020, The Author(s)
The CMB and the measure of the multiverse
In the context of eternal inflation, cosmological predictions depend on the
choice of measure to regulate the diverging spacetime volume. The spectrum of
inflationary perturbations is no exception, as we demonstrate by comparing the
predictions of the fat geodesic and causal patch measures. To highlight the
effect of the measure---as opposed to any effects related to a possible
landscape of vacua---we take the cosmological model, including the model of
inflation, to be fixed. We also condition on the average CMB temperature
accompanying the measurement. Both measures predict a 1-point expectation value
for the gauge-invariant Newtonian potential, which takes the form of a
(scale-dependent) monopole, in addition to a related contribution to the
3-point correlation function, with the detailed form of these quantities
differing between the measures. However, for both measures both effects are
well within cosmic variance. Our results make clear the theoretical relevance
of the measure, and at the same time validate the standard inflationary
predictions in the context of eternal inflation.Comment: 28 pages; v2: reference added, some clarification
Single spontaneous photon as a coherent beamsplitter for an atomic matterwave
In spontaneous emission an atom in an excited state undergoes a transition to
the ground state and emits a single photon. Associated with the emission is a
change of the atomic momentum due to photon recoil. Photon emission can be
modified close to surfaces and in cavities. For an ion, localized in front of a
mirror, coherence of the emitted resonance fluorescence has been reported. In
free space experiments demonstrated that spontaneous emission destroys motional
coherence. Here we report on motional coherence created by a single spontaneous
emission event close to a mirror surface. The coherence in the free atomic
motion is verified by atom interferometry. The photon can be regarded as a
beamsplitter for an atomic matterwave and consequently our experiment extends
the original recoiling slit Gedanken experiment by Einstein to the case where
the slit is in a robust coherent superposition of the two recoils associated
with the two paths of the quanta.Comment: main text: 5 pages, 4 figure; supplementary information: 8 pages, 1
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