Late evolution of cataclysmic variables: the loss of AM Her systems

The white dwarf in AM Her systems is strongly magnetic and keeps in synchronous rotation with the orbit by magnetic coupling to the secondary star. As the latter evolves through mass loss to a cool, degenerate brown dwarf it can no longer sustain its own magnetic field and coupling is lost. Angular momentum accreted then spins up the white dwarf and the system no longer appears as an AM Her system. Possible consequences are run-away mass transfer and mass ejection from the system. Some of the unusual cataclysmic variable systems at low orbital periods may be the outcome of this evolution.Comment: 6 pages, 1 figure, Proceedings of "Cataclysmic Variables", Symposium in Honour of Brian Warner, Oxford 1999, eds. P.Charles, A.King, O'Donoghue, to appea

The relation between radio and X-ray luminosity of black hole binaries: affected by inner cool disks?

Observations of the black hole X-ray binaries GX 339-4 and V404 Cygni have brought evidence of a strong correlation between radio and X-ray emission during the hard spectral state; however, now more and more sources, the so-called `outliers', are found with a radio emission noticeably below the established `standard' relation. Several explanations have already been considered, but the existence of dual tracks is not yet fully understood. We suggest that in the hard spectral state re-condensation of gas from the corona into a cool, weak inner disk can provide additional soft photons for Comptonization, leading to a higher X-ray luminosity in combination with rather unchanged radio emission, which presumably traces the mass accretion rate. As an example, we determined how much additional luminosity due to photons from an underlying disk would be needed to explain the data from the representative outlier source H1743-322. From the comparison with calculations of Compton spectra with and without the photons from an underlying disk, we find that the required additional X-ray luminosity lies well in the range obtained from theoretical models of the accretion flow. The radio/X-ray luminosity relation resulting from Comptonization of additional photons from a weak, cool inner disk during the hard spectral state can explain the observations of the outlier sources, especially the data for H1743-322, the source with the most detailed observations. The existence or non-existence of weak inner disks on the two tracks might point to a difference in the magnetic fields of the companion stars. These could affect the effective viscosity and the thermal conductivity, hence also the re-condensation process.Comment: 7 pages, 2 figures. Accepted for publication in A &

From EMT to HSC to AML: ZEB2 is a cell fate switch.

In this issue of Blood, complimentary studies by J. Li et al1 and H. Li et al2 identify the transcription factor ZEB2 as a critical regulator of multilineage differentiation in both normal and malignant hematopoiesis. In particular, these studies show that ZEB2 is an inhibitor of normal granulocyte production, and in acute myeloid leukemia (AML), antagonizing ZEB2 function releases the granulocytic differentiation block, creating an antileukemic therapeutic effect

A Rank Minrelation - Majrelation Coefficient

Improving the detection of relevant variables using a new bivariate measure could importantly impact variable selection and large network inference methods. In this paper, we propose a new statistical coefficient that we call the rank minrelation coefficient. We define a minrelation of X to Y (or equivalently a majrelation of Y to X) as a measure that estimate p(Y > X) when X and Y are continuous random variables. The approach is similar to Lin's concordance coefficient that rather focuses on estimating p(X = Y). In other words, if a variable X exhibits a minrelation to Y then, as X increases, Y is likely to increases too. However, on the contrary to concordance or correlation, the minrelation is not symmetric. More explicitly, if X decreases, little can be said on Y values (except that the uncertainty on Y actually increases). In this paper, we formally define this new kind of bivariate dependencies and propose a new statistical coefficient in order to detect those dependencies. We show through several key examples that this new coefficient has many interesting properties in order to select relevant variables, in particular when compared to correlation