274 research outputs found
Langevin equation with scale-dependent noise
A new wavelet based technique for the perturbative solution of the Langevin
equation is proposed. It is shown that for the random force acting in a limited
band of scales the proposed method directly leads to a finite result with no
renormalization required. The one-loop contribution to the Kardar-Parisi-Zhang
equation Green function for the interface growth is calculated as an example.Comment: LaTeX, 5 page
Dispersion Coefficients by a Field-Theoretic Renormalization of Fluid Mechanics
We consider subtle correlations in the scattering of fluid by randomly placed
obstacles, which have been suggested to lead to a diverging dispersion
coefficient at long times for high Peclet numbers, in contrast to finite
mean-field predictions. We develop a new master equation description of the
fluid mechanics that incorporates the physically relevant fluctuations, and we
treat those fluctuations by a renormalization group procedure. We find a finite
dispersion coefficient at low volume fraction of disorder and high Peclet
numbers.Comment: 4 pages, 1 figure; to appear in Phys. Rev. Let
Numerical study of the spherically-symmetric Gross-Pitaevskii equation in two space dimensions
We present a numerical study of the time-dependent and time-independent
Gross-Pitaevskii (GP) equation in two space dimensions, which describes the
Bose-Einstein condensate of trapped bosons at ultralow temperature with both
attractive and repulsive interatomic interactions. Both time-dependent and
time-independent GP equations are used to study the stationary problems. In
addition the time-dependent approach is used to study some evolution problems
of the condensate. Specifically, we study the evolution problem where the trap
energy is suddenly changed in a stable preformed condensate. In this case the
system oscillates with increasing amplitude and does not remain limited between
two stable configurations. Good convergence is obtained in all cases studied.Comment: 9 latex pages, 7 postscript figures, To appear in Phys. Rev.
Defect generation and deconfinement on corrugated topographies
We investigate topography-driven generation of defects in liquid crystals
films coating frozen surfaces of spatially varying Gaussian curvature whose
topology does not automatically require defects in the ground state. We study
in particular disclination-unbinding transitions with increasing aspect ratio
for a surface shaped as a Gaussian bump with an hexatic phase draped over it.
The instability of a smooth ground state texture to the generation of a single
defect is also discussed. Free boundary conditions for a single bump are
considered as well as periodic arrays of bumps. Finally, we argue that defects
on a bump encircled by an aligning wall undergo sharp deconfinement transitions
as the aspect ratio of the surface is lowered.Comment: 24 page
Adjuvant chemotherapy for breast cancer in older women: an analysis of retrospective English cancer registration data
Aims
Adjuvant chemotherapy is recommended as a treatment for women with high recurrence risk early breast cancer. Older women are less likely to receive chemotherapy than younger women. This study investigated the impact of chemotherapy on breast cancer-specific survival in women aged 70 + years using English registry data.
Materials and methods
Cancer registration data were obtained from two English regions from 2002 to 2012 (n = 29 728). The impact of patient-level characteristics on the probability of receiving adjuvant chemotherapy was explored using logistic regression. Survival modelling was undertaken to show the effect of chemotherapy and age/health status on breast cancer-specific survival. Missing data were handled using multiple imputation.
Results
In total, 11 735 surgically treated early breast cancer patients were identified. Use of adjuvant chemotherapy has increased over time. Younger age at diagnosis, increased nodal involvement, tumour size and grade, oestrogen receptor-negative or human epidermal growth factor receptor 2-positive disease were all associated with increased probability of receiving chemotherapy. Chemotherapy was associated with a significant reduction in the hazard of breast cancer-specific mortality in women with high risk cancer, after adjusting for patient-level characteristics (hazard ratio 0.74, 95% confidence interval 0.67–0.81).
Discussion
Chemotherapy is associated with an improved breast cancer-specific survival in older women with early breast cancer at high risk of recurrence . Lower rates of chemotherapy use in older women may, therefore, contribute to inferior cancer outcomes. Decisions on potential benefits for individual patients should be made on the basis of life expectancy, treatment tolerance and patient preference
Stability of scaling regimes in developed turbulence with weak anisotropy
The fully developed turbulence with weak anisotropy is investigated by means
of renormalization group approach (RG) and double expansion regularization for
dimensions . Some modification of the standard minimal substraction
scheme has been used to analyze stability of the Kolmogorov scaling regime
which is governed by the renormalization group fixed point. This fixed point is
unstable at ; thus, the infinitesimally weak anisotropy destroyes above
scaling regime in two-dimensional space. The restoration of the stability of
this fixed point, under transition from to has been demonstrated
at borderline dimension . The results are in qualitative agreement
with ones obtained recently in the framework of the usual analytical
regularization scheme.Comment: 23 pages, 2 figure
ALA- and ALA-hexylester-induced protoporphyrin IX fluorescence and distribution in multicell tumour spheroids
Synthesis of protoporphyrin IX (PpIX) in intact murine mammary cancer cell spheroids is reported from optical sections obtained using a laser scanning confocal fluorescence microscope. EMT6 spheroids 275–350 μ m in diameter were incubated in 0.1–15 mM aminolevulinic acid (ALA) or 0.001–2 mM ALA-hexylester (h-ALA) to test the ability of both pro-drugs to diffuse into the spheroids and induce PpIX production. Spheroids incubated with ALA show significant fluorescence nonuniformity for all concentrations, with the outermost cells exhibiting greater porphyrin fluorescence. Comparable levels of fluorescence throughout the optical section are achieved with approximately 100-fold lower h-ALA concentrations, indicating that the interior cells maintain esterase activity and porphyrin synthesis and that h-ALA diffuses efficiently to the spheroid interior. Fluorescence gradients are less pronounced with h-ALA incubation, in part because of apparent saturation of esterase activity in the spheroid perimeter. Proliferating (Ki67 positive) and quiescent cell populations exhibit remarkably different h-ALA concentration dependencies. The incubation concentration resulting in maximum fluorescence with ALA is 10 mM, while the optimal concentration for h-ALA is 200-fold lower at 0.05 mM. Exceeding these optimal concentrations for both pro-drugs leads to an overall loss of fluorescence. © 2001 Cancer Research Campaign
http://www.bjcancer.co
Circulation Statistics in Three-Dimensional Turbulent Flows
We study the large limit of the loop-dependent characteristic
functional , related
to the probability density function (PDF) of the circulation around a closed
contour . The analysis is carried out in the framework of the
Martin-Siggia-Rose field theory formulation of the turbulence problem, by means
of the saddle-point technique. Axisymmetric instantons, labelled by the
component of the strain field -- a partially annealed variable in
our formalism -- are obtained for a circular loop in the plane, with
radius defined in the inertial range. Fluctuations of the velocity field around
the saddle-point solutions are relevant, leading to the lorentzian asymptotic
behavior . The
subleading correction and the asymmetry between right and left PDF tails due to
parity breaking mechanisms are also investigated.Comment: Computations are discussed in a more detailed way; accepted for
publication in Physical Review
The use of surgery in the treatment of ER+ early stage breast cancer in England: variation by time, age and patient characteristics
AIM: To assess whether the proportion of patients aged 70 and over with ER+ operable breast cancer in England who are treated with surgery has changed since 2002, and to determine whether age and individual level factors including tumour characteristics and co-morbidity
influence treatment choice.
METHODS: A retrospective cohort analysis of routinely collected cancer registration data from two English regions (West Midlands, Northern & Yorkshire) was carried out (n = 17,129). Trends in surgical use over time for different age groups were assessed graphically and with linear regression. Uni- and multivariable logistic regressions were used to assess the effects of age, comorbidity, deprivation and disease characteristics on treatment choice. Missing data was handled using multiple imputation.
RESULTS: There is no evidence of a change in the proportion of patients treated surgically over time. The multivariable model shows that age remains an important predictor of whether or not a woman with ER+ operable breast cancer receives surgery after covariate adjustment (Odds
ratio of surgery vs no surgery, 0.82 (per year over 70)). Co-morbidity, deprivation, symptomatic presentation, later stage at diagnosis and low grade are also associated with increased probability of non-surgical treatment.
CONCLUSION: Contrary to current NICE guidance in England, age appears to be an important factor in the decision to treat operable ER+ breast cancer non-surgically. Further research is needed to assess the role of other age-related factors on treatment choice, and the effect that current practice has on survival and mortality from breast cancer for older women
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