Analytical solution for the evolution of a binary with stable mass transfer from a giant

We derive a simple analytical solution for the evolution of a close binary with nuclear time-scale driven mass transfer from a giant. This solution is based on the well-known fact that the luminosity and the radius of a giant scale to a good approximation as simple power laws of the mass M_c of the degenerate helium core. Comparison with results of numerical calculations by Webbink, Rappaport & Savonije (1983) show the analytical solution and the power law approximation to be quite accurate. The analytical solution presented does also allow (in parametrized form) for non-conservative mass transfer. Furthermore it is shown that the near constancy of the mass transfer rate over most of the mass transfer phase seen in the results by Webbink, Rappaport & Savonije is not a generic feature of this type of evolution but rather a consequence of a particular choice of parameters. The analytical solution also demonstrates that the level of mass transfer is largely set by the core mass of the giant at the onset of mass transfer. Finally we show that the model is selfconsistent and discuss its applicability to low-mass X-ray binaries.Comment: 13 pages, 5 encapsulated figures, LaTeX, minor revisions, accepted by MNRA

The Ritter-Kolb Catalogue and its Impact on Research into CVs, LMXBs and related Objects

In the first part of this paper, the Ritter-Kolb catalogue (RKcat for short), its history and a few examples of its application to research in the field of cataclysmic variables are briefly described. In a second part we look forward to possible future applications of RKcat for the study of cataclysmic variables, low-mass X-ray binaries and related objects. Last but not least we also briefly comment on the future of the RKcat service itself

Illumination in binaries

We give a simple, but accurate method that can be used to account for illumination in compact binary systems which have a low-mass companion, even if spherically symmetric illumination of the secondary star (not necessarily on the main sequence) is not assumed. This is done by introducing a multiplicative factor Phi in the Stefan-Boltzmann surface boundary condition, which accounts for the blocking of the intrinsic secondary flux by X-ray heating of the photospheric layers. Numerical fits and tables for Phi are given for unperturbed effective temperatures in the range 2500 - 5600 K and log g in the range 1.0 - 5.0Comment: 5 pages, 3 figures. Accepted for publication in Astronomy and Astrophysics Supplement Serie

What Does the NAEP Tell Us About Student Achievement in Arkansas?

This brief discusses the most recent and historical NAEP data in math, science, reading, and writing. Arkansas’ NAEP results are compared to national and border state averages. Based on the most recent NAEP exams, Arkansas is performing slightly below the national average in reading, math, science, and writing. There is also data to support that Arkansas students perform less well in Grade 8 than in Grade 4 when compared to the national and border state averages. Arkansas, however, is among the highest performing states with regard to change over the last decade. Since 1992, Arkansas has gained on the national and border state averages. In addition, Arkansas’ black-white and Hispanic-white achievement gaps in reading and math are lower than over half of participating states

Spectrophotometric studies of the photolysis of diazido-bis(phosphine)-metal(II) complexes

The photolysis of mixed ligand complexes of the type MLn(N3)2 (M=Ni, Pd, Pt; L = phosphane and diphosphane ligands, respectively; n = 1, 2) was monitored by electronic spectroscopy in absorption, emission and excitation. Initial quantum yields of these complexes were measured in CH2Cl2 and EtOH in dependence on the irradiation wavelength. Photochemically formed MOIn fragments of Pd and Pt are distinguished by an intensive emission detected at 77 K. No emission was observed with respect to the appropriate NiO fragments. An initial emission at 615 nm detected by irradiating Pd(PPh3)2(N3)2 at 77 K is explained by assuming a photochemical cis/trans isomerization Quenching experiments have been performed by using Ru(bpy)3Cl2, Os(bpy)3Cl2, Re(CO)3(phen)Cl and Cr(bpy)3(ClO4)3 as sensitizers and the mixed-ligand complexes under discussion as quenchers

Direct determination of the spin structure of Nd2_2Ir2_2O7_7 by means of neutron diffraction

We report on the spin structure of the pyrochlore iridate Nd$_2$Ir$_2$O$_7$ that could be directly determined by means of powder neutron diffraction. Our magnetic structure refinement unravels a so-called all-in/all-out magnetic structure that appears in both, the Nd and the Ir sublattice. The ordered magnetic moments at 1.8 K amount to 0.34(1) $\mu_\mathrm{B}$/Ir$^{4+}$ and 1.27(1) $\mu_\mathrm{B}$/Nd$^{3+}$. The Nd$^{3+}$ moment size at 1.8 K is smaller than that expected for the Nd$^{3+}$ ground state doublet. On the other hand, the size of the ordered moments of the Ir$^{4+}$ ions at 1.8 K agrees very well with the value expected for a $J_\mathrm{eff}$ = 1/2 state based on the presence of strong spin-orbit coupling in this system. Finally, our measurements reveal a parallel alignment of the Nd$^{3+}$ moments with the net moment of its six nearest neighboring Ir$^{4+}$ ions.Comment: http://journals.aps.org/prb/pdf/10.1103/PhysRevB.94.16110

Investigation of topographical stability of the concave and convex Self-Organizing Map variant

We investigate, by a systematic numerical study, the parameter dependence of the stability of the Kohonen Self-Organizing Map and the Zheng and Greenleaf concave and convex learning with respect to different input distributions, input and output dimensions

Commitment as investment under uncertainty

Irreversible investment and the techniques associated with pricing real options have led to significant advances many areas. We broaden this range of applications, showing how the techniques can apply to many policy problems in finance, macroeconomics, and trade policy. With small changes, standard techniques can handle a broad range of strategic problems related to policy. The decision to commit is like the decision to make an irreversible investment. Explicitly considering and correctly valuing the option to wait makes discretion relatively more attractive, implies that increased uncertainty increases the gain to discretion, and results in policy which displays hysteresis.Investments