Keele University

About: Keele University is a education organization based out in Newcastle-under-Lyme, United Kingdom. It is known for research contribution in the topics: Population & Stars. The organization has 11318 authors who have published 26323 publications receiving 894671 citations. The organization is also known as: Keele University.

Maximum likelihood estimation of endogenous switching and sample selection models for binary, ordinal, and count variables

Abstract: Studying behavior in economics, sociology, and statistics often involves fitting models in which the response variable depends on a dummy variable—also known as a regime-switch variable—or in which...

Spectroscopy of $A0620-00$: the mass of the black hole and an image of its accretion disc

Abstract: We present spectra of the black hole binary A0620-00 taken at Hα and Hβ to study the distribution of emission-line flux from its accretion disc. Using the spectra of Hα, we have measured the K-type companion star's radial velocity semi-amplitude and rotational broadening to be K 2 =433±3 km s −1 and v sin i=83±5 km s −1 . Accounting for the Roche-lobe geometry of the companion, the rotational broadening gives the mass ratio q=M 2 /M 1 =0.06 7±0.01. The disc contributes 6±3 per cent of the light at Hα and 17±3 per cent at Hβ, with the K star providing the rest. The masses of the compact object and K star derived from our values of K 2 and q are M 1 =(3.09±0.09)sin −3 i M ○. and M 2 =(0.21±0.04)sin −3 i M ○.

Structure-Activity Relationship Analysis of Pd-PEPPSI Complexes in Cross-Couplings: A Close Inspection of the Catalytic Cycle and the Precatalyst Activation Model

Abstract: A series of Pd-N-heterocyclic carbene (Pd-NHC) complexes with various NHC, halide and pyridine ligands (PEPPSI (pyridine, enhanced, precatalyst, preparation, stabilisation and initiation) precatalysts) were prepared, and the effects of these ligands on catalyst activation and performance were studied in the Kumada-Tamao-Corriu (KTC), Negishi, and Suzuki-Miyaura cross-coupling reactions. The lowered reactivity of more hindered 2,6-dimethylpyridyl complex 4 in the Negishi and KTC reactions is consistent with slow reductive dimerisation of the organometallic reaction partner during precatalyst activation. Comparative rate studies of complexes 1, 4 and 5 in the KTC and Suzuki-Miyaura reactions verify that 4 activated more slowly than the others. A potential on/ off mechanism of pyridine coordination to NHC-Pd 0 is also plausible, in which the more basic pyridine stays bound for longer.

An absorption origin for the X-ray spectral variability of MCG-6-30-15

Abstract: Context. The Seyfert I galaxy MCG–6-30-15 shows one of the best examples of a broad “red wing” of emission in its X-ray spectrum at energies 2 20 keV. Methods. We compiled all the available long-exposure, high-quality data for MCG–6-30-15: 522 ks of Chandra hetgs, 282 ks of XMM-Newton pn/rgs and 253 ks of Suzaku xis/pin data. This is the first analysis of this full dataset. We investigated the spectral variability on timescales >20 ks using principal components analysis and fitted spectral models to “flux state” and mean spectra over the energy range 0.5−45 keV (depending on detector). The absorber model was based on the zones previously identified in the highresolution grating data. Joint fits were carried out to any data that were simultaneous. Results. Multiple absorbing zones covering a wide range of ionisation are required by the grating data, including a highly ionised outflowing zone. A variable partial-covering zone plus absorbed low-ionisation reflection, distant from the source, provides a complete description of the variable X-ray spectrum. A single model fits all the data. We conclude that these zones are responsible for the red wing, its apparent lack of variability, the absorption structure around the Fe Kα line, the soft-band “excess” and the high flux seen in the hard X-ray band. A relativistically-blurred Fe line is not required in this model. We suggest the partial covering zone is a clumpy wind from the accretion disk.