Generating Survival Times to Simulate Cox Proportional Hazards Models

This paper discusses techniques to generate survival times for simulation studies regarding Cox proportional hazards models. In linear regression models, the response variable is directly connected with the considered covariates, the regression coefficients and the simulated random errors. Thus, the response variable can be generated from the regression function, once the regression coefficients and the error distribution are specified. However, in the Cox model, which is formulated via the hazard function, the effect of the covariates have to be translated from the hazards to the survival times, because the usual software packages for estimation of Cox models require the individual survival time data. A general formula describing the relation between the hazard and the corresponding survival time of the Cox model is derived. It is shown how the exponential, the Weibull and the Gompertz distribution can be used to generate appropriate survival times for simulation studies. Additionally, the general relation between hazard and survival time can be used to develop own distributions for special situations and to handle flexibly parameterized proportional hazards models. The use of other distributions than the exponential distribution only is indispensable to investigate the characteristics of the Cox proportional hazards model, especially in non-standard situations, where the partial likelihood depends on the baseline hazard

Roll convection of binary fluid mixtures in porous media

We investigate theoretically the nonlinear state of ideal straight rolls in the Rayleigh-B\'enard system of a fluid layer heated from below with a porous medium using a Galerkin method. Applying the Oberbeck-Boussinesq approximation, binary mixtures with positive separation ratio are studied and compared to one-component fluids. Our results for the structural properties of roll convection resemble qualitatively the situation in the Rayleigh--B\'enard system without porous medium except for the fact that the streamlines of binary mixtures are deformed in the so-called Soret regime. The deformation of the streamlines is explained by means of the Darcy equation which is used to describe the transport of momentum. In addition to the properties of the rolls, their stability against arbitrary infinitesimal perturbations is investigated. We compute stability balloons for the pure fluid case as well as for a wide parameter range of Lewis numbers and separation ratios which are typical for binary gas and fluid mixtures. The stability regions of rolls are found to be restricted by a crossroll, a zigzag and a new type of oscillatory instability mechanism, which can be related to the crossroll mechanism

Cox's Proportional Hazards Model under Covariate Measurement Error - A Review and Comparison of Methods

This contribution studies the Cox model under covariate measurement error. Methods proposed in the literature to adjust for measurement error are reviewed. The basic structural and functional approaches are discussed in some detail, important modifications and further developments are briefly sketched. Then the basic methods are compared in a simulation study

Measurement of the Blackbody Radiation Shift of the 133Cs Hyperfine Transition in an Atomic Fountain

We used a Cs atomic fountain frequency standard to measure the Stark shift on the ground state hyperfine transiton frequency in cesium (9.2 GHz) due to the electric field generated by the blackbody radiation. The measures relative shift at 300 K is -1.43(11)e-14 and agrees with our theoretical evaluation -1.49(07)e-14. This value differs from the currently accepted one -1.69(04)e-14. The difference has a significant implication on the accuracy of frequency standards, in clocks comparison, and in a variety of high precision physics tests such as the time stability of fundamental constants.Comment: 4 pages, 2 figures, 2 table

Detecting Gluino-Containing Hadrons

When SUSY breaking produces only dimension-2 operators, gluino and photino masses are of order 1 GeV or less. The gluon-gluino bound state has mass 1.3-2.2 GeV and lifetime > 10^{-5} - 10^{-10} s. This range of mass and lifetime is largely unconstrained because missing energy and beam dump techniques are ineffective. With only small modifications, upcoming K^0 decay experiments can study most of the interesting range. The lightest gluino-containing baryon (uds-gluino) is long-lived or stable; experiments to find it and the uud-gluino are also discussed.Comment: 13 pp, 1 figure (uuencoded). Descendant of hep-ph/9504295, hep-ph/9508291, and hep-ph/9508292, focused on experimental search techniques. To be published in Phys Rev Let

Safety and efficacy of methylene blue combined with artesunate or amodiaquine for uncomplicated falciparum malaria

Besides existing artemisinin-based combination therapies, alternative safe, effective and affordable drug combinations against falciparum malaria are needed. Methylene blue (MB) was the first synthetic antimalarial drug ever used, and recent studies have been promising with regard to its revival in malaria therapy. The objective of this study was to assess the safety and efficacy of two MB-based malaria combination therapies, MB-artesunate (AS) and MB-amodiaquine (AQ), compared to the local standard of care, AS-AQ, in Burkina Faso. Open-label randomised controlled phase II study in 180 children aged 6-10 years with uncomplicated falciparum malaria in Nouna, north-western Burkina Faso. Follow-up was for 28 days and analysis by intention-to-treat. The treatment groups were similar in baseline characteristics and there was only one loss to follow-up. No drug-related serious adverse events and no deaths occurred. MB-containing regimens were associated with mild vomiting and dysuria. No early treatment failures were observed. Parasite clearance time differed significantly among groups and was the shortest with MB-AS. By day 14, the rates of adequate clinical and parasitological response after PCR-based correction for recrudescence were 87% for MB-AS, 100% for MB-AQ (p = 0.004), and 100% for AS-AQ (p = 0.003). By day 28, the respective figure was lowest for MB-AS (62%), intermediate for the standard treatment AS-AQ (82%; p = 0.015), and highest for MB-AQ (95%; p<0.001; p = 0.03). MB-AQ is a promising alternative drug combination against malaria in Africa. Moreover, MB has the potential to further accelerate the rapid parasite clearance of artemisinin-based combination therapies. More than a century after the antimalarial properties of MB had been described, its role in malaria control deserves closer attention. ClinicalTrials.gov NCT00354380

Strong gametocytocidal effect of methylene blue-based combination therapy against falciparum malaria

With the availability of new preventive and curative interventions, global malaria control has been strengthened significantly in recent years. Drugs effective in reducing malaria gametocytaemia might contribute to local elimination and possible long-term eradication. We here report on the effects of methylene blue (MB)-based malaria combination therapy on gametocytaemia during a randomised-controlled trial in Burkina Faso. An open-label randomised controlled phase II study in 180 children aged 6-10 years with uncomplicated falciparum malaria was conducted in Nouna, north-western Burkina Faso. Children were randomised to MB-artesunate (AS), MB-amodiaquine (AQ), and AS-AQ (local standard of care). Overall follow-up was for 28 days, follow-up for gametocytaemia was for 14 days. The treatment groups were similar in baseline characteristics and there was only one loss to follow-up. Compared to AS-AQ, both MB-containing regimens were associated with significantly reduced gametocyte carrier rates during follow-up days 3, 7, and 14. This effect was seen both in patients with and without P. falciparum gametocytaemia at baseline. MB reveals pronounced gametocytocidal activity which appears to act against both existing and developing P. falciparum gametocytes. MB-based combination therapy thus has the potential to reduce transmission of P. falciparum malaria in endemic regions, which has important implications for future elimination and eradication strategies

Angular dependences in electroweak semi-inclusive leptoproduction

We present the leading order unpolarized and polarized cross sections in electroweak semi-inclusive deep inelastic leptoproduction. The azimuthal dependences in the cross section differential in the transverse momentum of the vector boson arise due to intrinsic transverse momenta of the quarks. However, the presented asymmetries are not suppressed by inverse powers of the hard scale. We discuss the different opportunities to measure specific asymmetries as offered by neutral compared to charged current processes and point out the optimal kinematical regions. The present and (proposed) future HERA collider experiments would be most suitable for measuring some of the asymmetries discussed here, especially in case of Lambda production.Comment: 10 pages, Revtex, 5 Postscript figures, uses aps.sty, epsfig.st