Classical and quantum properties of a 2-sphere singularity

Recently Boehmer and Lobo have shown that a metric due to Florides, which has been used as an interior Schwarzschild solution, can be extended to reveal a classical singularity that has the form of a two-sphere. Here the singularity is shown to be a scalar curvature singularity that is both timelike and gravitationally weak. It is also shown to be a quantum singularity because the Klein-Gordon operator associated with quantum mechanical particles approaching the singularity is not essentially self-adjoint.Comment: 10 pages, 1 figure, minor corrections, final versio

Magnetized Particle Capture Cross Section for Braneworld Black Hole

Capture cross section of magnetized particle (with nonzero magnetic moment) by braneworld black hole in uniform magnetic field is considered. The magnetic moment of particle was chosen as it was done by \citet{rs99} and for the simplicity particle with zero electric charge is chosen. It is shown that the spin of particle as well as the brane parameter are to sustain the stability of particles circularly orbiting around the black hole in braneworld i.e. spin of particles and brane parameter try to prevent the capture by black hole.Comment: 7 pages, 4 figures, Accepted for publication in Astrophysics & Space Scienc

Two-step cell-death kinetics in vitro during cis-platinum, hydroxyurea and mitomycin incubation.

A human leukaemic cell line (REH) growing in suspension was incubated with cis-platinum, hydroxyurea and mitomycin C at various concentrations causing complete cell-cycle arrest. At different times the cell suspensions were harvested, diluted 1:1 with a buffer solution, stained without further treatment with a mixture of acridine orange (AO) and ethidium bromide (EB) and analysed with a biparametrical flow cytometer. Fluorescent plastic beads were introduced into the suspensions to provide an internal numerical reference for the control of cell loss. The fluorescence distributions showed three groups of cells: vital cells (V) which were only stained with AO; dead cells in which EB stained cytoplasmic components but not the nuclear DNA (D1), and dead cells which allowed EB to stain both cytoplasm and nuclear DNA (D2). The kinetics of cells entering D1 depended on drug concentration and showed equal characteristics for cis-platinum and mitomycin, but were different for hydroxyurea. The subsequent entry into D2 occurred about 15 hr later and showed no pronounced dependence on drug concentration. Parallel trypan-blue (TB) exclusion tests revealed that TB only stained D2 cells and therefore is not useful for investigating cell-death kinetics exposure to cell-killing agents

Cell-cycle-dependent and -independent damage to rat haemopoiesis by hydroxyurea.

The generally accepted cell-killing effect of hydroxyurea (HU) on S-phase cells, as well as its potential to arrest cells at the G1/S boundary, hardly explain its benefit for application in human chronic myelogenous leukaemia. Studies were therefore performed in rat haemopoiesis in order to quantify the cell-killing effect on various phases of the cell cycle. For this purpose, the [3H]thymidine ([3H]TdR) labelling index and the specific activity of [3H]TdR in the DNA-synthesizing fraction of cells were determined after a non-cytoreductive dose of 25 mg/kg HU, as well as a medium cytoreductive dose of 100 mg/kg. Furthermore, flow cytometric DNA histograms and absolute as well as differential cell counts of femoral bone marrow were performed after 100 mg/kg HU. The results indicate a predominant cell kill in G1 encompassing almost all 2c cells in the proliferative pool, while the S-phase fraction is not even reduced to half its initial value. The specific activity of [3H]TdR in cell synthesizing DNA, as well as the labelling index after HU show an initial dip and a tendency to recovery, as has been observed in many other cell systems. Instead of a complete restoration, however, there is a second depression of these parameters lasting for at least one cell cycle. The results are interpreted as a partly cell-cycle-dependent and partly independent action of HU in this cell system. The independent component may be attributed to the repeatedly described direct interference of HU with DNA. In rat haemopoiesis, therefore, this direct effect of HU on the DNA strands appears to be much more pronounced than in cell-culture systems and other mammalian tissues. In view of these findings, some caution should be taken in using HU for the determination of the S-phase fraction by way of a suicide experiment

Modeling of ultrasound propagation through contrast agents

In the past years many advances have been made in the detection of ultrasound contrast agents (UCA) by exploiting their nonlinear behavior. However, little attention has been paid to the nonlinear distortion of ultrasound (US) waves propagating through contrast media. The aim of this study is to model the nonlinear propagation of low pressure US waves through contrast media. The Burgers’ equation (approximated to the second order) is used to model the nonlinear US propagation. In addition, the results are compared to a numerical approximation of forward scattering, combining the linear-wave and modified Rayleigh-Plesset Noltingk Neppiras and Poritsky (RPNNP) equations. Measurements are performed for the model validation. Using a single element transducer, a Hanning-windowed 20 cycle US pulse was transmitted through water. An acoustically transparent tube (22 mm diameter) was positioned in the transducer focus containing different UCA concentrations up to 0.2%. All measurements were performed with an US mechanical index of 0.1 to prevent bubble collapse. The adopted frequency range was 0.5 to 3.5 MHz, which is around the UCA resonance frequency. The waves were measured by a hydrophone placed in line with the transducer. For low concentrations of UCA, the propagation of US waves can be described using the Burgers’ equation. For higher concentrations and frequencies close to the UCA resonance frequency a phase shift arises in the measurements which can be predicted by combining the modified RPNNP and the linear-wave equations

Author Correction: Study of 300,486 individuals identifies 148 independent genetic loci influencing general cognitive function

These authors contributed equally: Gail Davies, Max Lam. These authors jointly supervised this work: Todd Lencz, Ian J. Deary