428 research outputs found
Integrable Multicomponent Perfect Fluid Multidimensional Cosmology II: Scalar Fields
We consider anisotropic cosmological models with an universe of dimension 4
or more, factorized into n>1 Ricci-flat spaces, containing an m-component
perfect fluid of m non-interacting homogeneous minimally coupled scalar fields
under special conditions. We describe the dynamics of the universe: It has a
Kasner-like behaviour near the singularity and isotropizes during the expansion
to infinity.
Some of the considered models are integrable, and classical as well as
quantum solutions are found. Some solutions produce inflation from "nothing".
There exist classical asymptotically anti-de Sitter wormholes, and quantum
wormholes with discrete spectrum.Comment: 28 pages, LaTeX, subm. to Gen. Rel. Gra
Einstein and Brans-Dicke frames in multidimensional cosmology
Inhomogeneous multidimensional cosmological models with a higher dimensional
space-time manifold M= M_0 x M_1 ...x M_n are investigated under dimensional
reduction to a D_0-dimensional effective non-minimally coupled sigma-model
which generalizes the familiar Brans-Dicke model.
It is argued that the Einstein frame should be considered as the physical
one. The general prescription for the Einstein frame reformulation of known
solutions in the Brans-Dicke frame is given. As an example, the reformulation
is demonstrated explicitly for the generalized Kasner solutions where it is
shown that in the Einstein frame there are no solutions with inflation of the
external space.Comment: 27 pages, Revte
Evidence of changes in regional blood perfusion in human intracranial tumours during conductive interstitial hyperthermia
Human intracranial tumours were treated using local heat therapy produced by surgically implanted catheters containing local resistive heating elements. Changes in local tumor blood flow were assessed indirectly from an algorithm based on the bioheat transfer equation. The algorithm used the ratio of catheter power to catheter temperature rise to estimate regional blood perfusion. Local heat therapy produced consistent reductions in local apparent perfusion. Changes in apparent regional perfusion occurred in intriguing patterns that gave clues to possible vascular events of therapeutic significance
Effective Estimation and Computer Control of Minimum Tumour Temperature During Conductive Interstitial Hyperthermia
The goal of heat therapy in the treatment of malignant disease is to raise the temperature of all neoplastic tissue to a cytotoxic temperature for a predetermined period of time. This seemingly simple task has proved difficult in-vivo, in part because of nonuniform power absorption and in part because of nonhomogeneous and time varying tumour blood flow. We have addressed this difficulty first by utilizing the conceptually simple technique of conductive interstitial hyperthermia, in which the tumour is warmed by multiple, electrically heated catheters, and second by implementing on-line conu·ol of minimum tumour temperatures near each catheter, estimated on the basis of the steadystate ratio of catheter power to catheter temperature rise. This report presents an analysis of the accuracy, precision, and stability of the on-line minimum temperature estimation/conu·ol technique for 22 patients who received 31 separate courses of conductive interstitial hyperthermia for the treatment of malignant brain tumours, and in whom temperature was monitored independently by 12 to 16 independent sensors per patient. In all patients, the technique was found to accurately and precisely estimate and control the local minimum temperatures. Comparison of measured and estimated temperatures revealed a mean difference of 0.0 ±0.4 °C for those sensors within 1.0 mm of the expected location for minimum temperatures. This technique, therefore, offers an attractive method for controlling hyperthermia therapy -- even in the presence of time varying local blood flow
Integration of D-dimensional 2-factor spaces cosmological models by reducing to the generalized Emden-Fowler equation
The D-dimensional cosmological model on the manifold describing the evolution of 2 Einsteinian factor spaces,
and , in the presence of multicomponent perfect fluid source is
considered. The barotropic equation of state for mass-energy densities and the
pressures of the components is assumed in each space. When the number of the
non Ricci-flat factor spaces and the number of the perfect fluid components are
both equal to 2, the Einstein equations for the model are reduced to the
generalized Emden-Fowler (second-order ordinary differential) equation, which
has been recently investigated by Zaitsev and Polyanin within discrete-group
analysis. Using the integrable classes of this equation one generates the
integrable cosmological models. The corresponding metrics are presented. The
method is demonstrated for the special model with Ricci-flat spaces
and the 2-component perfect fluid source.Comment: LaTeX file, no figure
Toda chains with type A_m Lie algebra for multidimensional m-component perfect fluid cosmology
We consider a D-dimensional cosmological model describing an evolution of
Ricci-flat factor spaces, M_1,...M_n (n > 2), in the presence of an m-component
perfect fluid source (n > m > 1). We find characteristic vectors, related to
the matter constants in the barotropic equations of state for fluid components
of all factor spaces.
We show that, in the case where we can interpret these vectors as the root
vectors of a Lie algebra of Cartan type A_m=sl(m+1,C), the model reduces to the
classical open m-body Toda chain.
Using an elegant technique by Anderson (J. Math. Phys. 37 (1996) 1349) for
solving this system, we integrate the Einstein equations for the model and
present the metric in a Kasner-like form.Comment: LaTeX, 2 ps figure
Rates of inclusion of teenagers and young adults in England into National Cancer Research Network clinical trials: Report from the National Cancer Research Institute (NCRI) Teenage and Young Adult Clinical Studies Development Group
Poor inclusion rates into clinical trials for teenagers and young adults (TYA; aged 13–24 years) have been assumed but not systematically investigated in England. We analysed accrual rates (AR) from 1 April 2005 up to 31 March 2007 to National Cancer Research Network (NCRN) Phase III trials for the commonest tumour types occurring in TYA and children: leukaemia, lymphoma, brain and central nervous system, bone sarcomas and male germ cell tumours. AR for 2005–2007 were 43.2% for patients aged 10–14 years, 25.2% for patients aged 15–19 years, and 13.1% for patients aged 20–24 years in the tumour types analysed. Compared with accrual from 1 April 2005 to 31 March 2006, AR between 1 April 2006 and 31 March 2007 increased for those aged 10–14 and 15–19 years, but fell for those aged 20–24 years. AR varied considerably among cancer types. Despite four trials being available, patients over 16 years with central nervous system tumours were not recruited. Rates of participation in clinical trials in England from 2005 to 2007 were much lower for TYA older than 15 years compared with children and younger teenagers. The variations in open trials, trial age eligibility criteria and extent of trial activation in treatment centres in part explain this observation. Other possible influences, such as difficulties associated with the consent of TYA require further evaluation. Closer dialogue between those involved in planning and running trials for children and for adults is necessary to improve trial availability and recruitment. Further research is required to identify trends in trial availability and accrual for those tumours constituting the remaining 26% of TYA cancers
Cancer Survival and Excess Mortality Estimates among Adolescents and Young Adults in Western Australia, 1982-2004: A Population-Based Study
Background: Data are limited on cancer outcomes in adolescents and young adults. Methods: Based on data from the Western Australian Data Linkage System, this study modelled survival and excess mortality in all adolescents and young adults aged 15-39 years in Western Australia who had a diagnosis of cancer in the period 1982-2004. Relative survival and excess all-cause mortality for all cancers combined and for principal tumour subgroups were estimated, using the Ederer II method and generalised linear Poisson modelling, respectively. Results: A cancer diagnosis in adolescents and young adults conferred substantial survival decrement. However, overall outcomes improved over calendar period (excess mortality hazard ratio [HR], latest versus earliest diagnostic period: 0.52, trend <0.0001). Case fatality varied according to age group (HR, oldest versus youngest: 1.38, trend <0.0001), sex (HR, female versus male: 0.66, 95% confidence interval [CI] 0.62-0.71), ethnicity (HR, Aboriginal versus others: 1.47, CI 1.23-1.76), geographical area (HR, rural/remote versus urban: 1.13, CI 1.04-1.23) and residential socioeconomic status (HR, lowest versus highest quartile: 1.14, trend <0.05). Tumour subgroups differed substantially in frequency according to age group and sex, and were critical outcome determinants. Conclusions: Marked progressive calendar-time improvement in overall outcomes was evident. Further research is required to disentangle the contributions of tumour biology and health service factors to outcome disparities between ethno-demographic, geographic and socioeconomic subgroups of adolescents and young adults with cancer. © 2013 Haggar et al
Recruitment and follow-up of adolescent and young adult cancer survivors: the AYA HOPE Study
IntroductionCancer is rare in adolescents and young adults (AYA), but these patients have seen little improvement in survival in contrast to most other age groups. Furthermore, participation in research by AYAs is typically low. We conducted a study to examine the feasibility of recruiting a population-based sample of AYA survivors to examine issues of treatment and health outcomes.MethodsIndividuals diagnosed in 2007-08 and age 15-39 at the time of diagnosis with acute lymphocytic leukemia, Hodgkin lymphoma, non-Hodgkin lymphoma, germ cell cancer or sarcoma were identified by 7 Surveillance, Epidemiology, and End-Results (SEER) cancer registries, mailed surveys within 14 months after diagnosis and again a year later, and had medical records reviewed.Results525 (43%) of the eligible patients responded, 39% refused and 17% were lost to follow-up. Extensive efforts were required for most potential respondents (87%). 76% of respondents completed the paper rather than online survey version. In a multivariate model, age, cancer site, education and months from diagnosis to the first mailing of the survey were not associated with participation, although males (p  <  0.01), Hispanics and non-Hispanic blacks (p  <  0.001) were less likely to participate. 91% of survivors completing the initial survey completed the subsequent survey.DiscussionDespite the response rate, those who participated adequately reflected the population of AYA cancer survivors. The study demonstrates that cancer registries are valuable foundations for conducting observational, longitudinal population-based research on AYA cancer survivors.Implications for cancer survivorsAchieving a reasonable response rate in this population is possible, but requires extensive resources
Multidimensional cosmological models: cosmological and astrophysical implications and constraints
We investigate four-dimensional effective theories which are obtained by
dimensional reduction of multidimensional cosmological models with factorizable
geometry and consider the interaction between conformal excitations of the
internal space (geometrical moduli excitations) and Abelian gauge fields. It is
assumed that the internal space background can be stabilized by minima of an
effective potential. The conformal excitations over such a background have the
form of massive scalar fields (gravitational excitons) propagating in the
external spacetime. We discuss cosmological and astrophysical implications of
the interaction between gravexcitons and four-dimensional photons as well as
constraints arising on multidimensional models of the type considered in our
paper. In particular, we show that due to the experimental bounds on the
variation of the fine structure constant, gravexcitons should decay before
nucleosynthesis starts. For a successful nucleosynthesis the masses of the
decaying gravexcitons should be m>10^4 GeV. Furthermore, we discuss the
possible contribution of gravexcitons to UHECR. It is shown that, at energies
of about 10^{20}eV, the decay length of gravexcitons with masses m>10^4 GeV is
very small, but that for m <10^2 GeV it becomes much larger than the
Greisen-Zatsepin-Kuzmin cut-off distance. Finally, we investigate the
possibility for gravexciton-photon oscillations in strong magnetic fields of
astrophysical objects. The corresponding estimates indicate that even the high
magnetic field strengths of magnetars are not sufficient for an efficient and
copious production of gravexcitons.Comment: 16 pages, LaTeX2e, minor changes, improved references, to appear in
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