Superconductivity in the η\eta-carbide-type oxides Zr4Rh2Ox

We report on the synthesis and the superconductivity of Zr$_4$Rh$_2$O$_{x}$ ($x$ = 0.4, 0.5, 0.6, 0.7, 1.0). These compounds crystallize in the $\eta$-carbide structure, which is a filled version of the complex intermetallic Ti$_2$Ni structure. We find that in the system Zr$_4$Rh$_2$O$_{x}$, already a small amount ($x$ $\geq$ 0.4) of oxygen addition stabilizes the $\eta$-carbide structure over the more common intermetallic CuAl$_2$ structure-type, in which Zr$_2$Rh crystallizes. We show that Zr$_4$Rh$_2$O$_{0.7}$ and Zr$_4$Rh$_2$O are bulk superconductors with critical temperatures of $T_c \approx$ 2.8 K and 4.7 K in the resistivity, respectively. Our analysis of the superconducting properties reveal both compounds to be strongly type-II superconductors with critical fields up to $\mu_0 H_{c1}$(0) $\approx$ 8.8 mT and $\mu_0 H_{c2}$(0) $\approx$ 6.08 T. Our results support that the $\eta$-carbides are a versatile family of compounds for the investigation of the interplay of interstitial doping on physical properties, especially for superconductivity

Do nuclear starbursts obscure the X-ray background?

We propose a model for the source of the X-ray background (XRB) in which low luminosity active nuclei (L<10^43 erg/s) are obscured by nuclear starbursts within the inner 100pc. The obscuring material covers most of the sky as seen from the central source, rather than being distributed in a toroidal structure, and hardens the averaged X-ray spectrum by photoelectric absorption. The gas is turbulent with velocity dispersion of a few 100 km/s and cloud-cloud collisions lead to copious star formation. Although supernovae tend to produce outflows, most of the gas is trapped in the gravity field of the starforming cluster itself and the central black hole. A hot (T=10^6-10^7 K) virialised phase of this gas, comprising a few per cent of the total obscuring material, feeds the central engine of 10^7 solar masses through Bondi accretion, at a sub-Eddington rate appropriate for the luminosity of these objects. If starburst-obscured objects give rise to the residual XRB, then only 10 per cent of the accretion in active galaxies occurs close to the Eddington limit in unabsorbed objects.Comment: 5 pages, 2 PS figures included in the text, MNRAS in the press. Also at http://www.ifca.unican.es/~barcons/preprints.htm

Efficient sympathetic motional ground-state cooling of a molecular ion

Cold molecular ions are promising candidates in various fields ranging from precision spectroscopy and test of fundamental physics to ultra-cold chemistry. Control of internal and external degrees of freedom is a prerequisite for many of these applications. Motional ground state cooling represents the starting point for quantum logic-assisted internal state preparation, detection, and spectroscopy protocols. Robust and fast cooling is crucial to maximize the fraction of time available for the actual experiment. We optimize the cooling rate of ground state cooling schemes for single $^{25}\mathrm{Mg}^{+}$ ions and sympathetic ground state cooling of $^{24}\mathrm{MgH}^{+}$. In particular, we show that robust cooling is achieved by combining pulsed Raman sideband cooling with continuous quench cooling. Furthermore, we experimentally demonstrate an efficient strategy for ground state cooling outside the Lamb-Dicke regime.Comment: 11 pages, 11 figure

The effects of a comptonizing corona on the appearance of the reflection components in accreting black hole spectra

We discuss the effects of a comptonizing corona on the appearance of the reflection components, and in particular of the reflection hump, in the X-rays spectra of accreting black holes. Indeed, in the framework of a thermal corona model, we expect that part (or even all, depending on the coronal covering factor) of the reflection features should cross the hot plasma, and thus suffer Compton scattering, before being observed. We have studied in detail the dependence of these effects on the physical (i.e. temperature and optical depth) and geometrical (i.e. inclination angle) parameters of the corona, concentrating on the slab geometry . Due to the smoothing and shifting towards high energies of the comptonized reflection hump, the main effects on the emerging spectra appear above 100 keV. We have also investigated the importance of such effects on the interpretation of the results obtained with the standard fitting procedures. We found that fitting Comptonization models, taking into account comptonized reflection, by the usual cut-off power law + uncomptonized reflection model, may lead to an underestimation of the reflection normalization and an overestimation of the high energy cut-off. We discuss and illustrate the importance of these effects by analysing recent observational results as those of the galaxy NGC 4258. We also find that the comptonizing corona can produce and/or emphasize correlations between the reflection features characteristics (like the iron line equivalent width or the covering fraction) and the X-ray spectral index similar to those recently reported in the literature. We also underline the importance of these effects when dealing with accurate spectral fitting of the X-ray background.Comment: 11 pages, 14 figures accepted for publication in MNRAS. Version printable on US 8.5x11 pape

Psychological Ownership, Hope, Resilience and Employee Work Engagement among Teachers in Selected Mission Schools

Since the quality of education in Nigeria has continued to progressively decline in standard, there has been a sustained public outcry and suggestions on the possible ways to save the Nigerian education from total collapse. As a result many schools, especially the post primary schools (public) have undergone transformation. Teachers’ level of engagement has been suggested as one of the factors that may be responsible for this decline in education in Nigeria. The current study adopted the cross-sectional survey design to explore whether psychological ownership, hope and resilience could predict work engagement behaviour among teachers in selected mission schools. Contrary to speculation and in conflict with previous studies, results showed that psychological ownership did not predict work engagement behavior among teachers whereas hope and resilience significantly predicted work engagement behaviour among the teachers. The study’s implications point to the fact that since psychological ownership is seen as a vital organisational behavior, managers should endeavor to build a culture that will promote such ownership for the good of the organisation. Keywords: Psychological ownership, hope, resilience, employee work engagemen

Detection of motional ground state population of a trapped ion using delayed pulses

Efficient preparation and detection of the motional state of trapped ions is important in many experiments ranging from quantum computation to precision spectroscopy. We investigate the stimulated Raman adiabatic passage (STIRAP) technique for the manipulation of motional states in a trapped ion system. The presented technique uses a Raman coupling between two hyperfine ground states in $^{25}$Mg$^+$, implemented with delayed pulses, which removes a single phonon independent of the initial motional state. We show that for a thermal state the STIRAP population transfer is more efficient than a stimulated Raman Rabi pulse on a motional sideband. In contrast to previous implementations, a large detuning of more than 200 times the natural linewidth of the transition is used. This approach renders STIRAP suitable for atoms in which resonant laser fields would populate fluorescing excited states and thus impede the STIRAP process. We use the technique to measure the wavefunction overlap of excited motional states with the motional ground state. This is an important application for photon recoil spectroscopy and other force sensing applications that utilize the high sensitivity of the motional state of trapped ions to external fields. Furthermore, a determination of the ground state population enables a simple measurement of the ion's temperature.Comment: 17 pages, 7 figure

Ethnicity and self-esteem as predictors of work-family conflict among Nigerian workers

This study investigated the impact of ethnicity and self-esteem on work-family conflict of Nigerian employees. Five hundred and three volunteered workers (202 Hausa ethnic group workers and 301 Igbo ethnic group workers) drawn from four Federal institutions in Nigeria participated in the study. A multiple regression analysis showed that ethnicity significantly predicted work-family conflict of Nigerian employees. The result further revealed that self-esteem significantly predicted work-family conflict. It was concluded that shared values and beliefs about work and family, as well as immediate socio-contextual circumstances, shape the potential for individuals to experience work-family conflict. Keywords: Ethnicity, self-esteem, work-family conflict and Nigerian workers

Threshold Singularities in the One Dimensional Hubbard Model

We consider excitations with the quantum numbers of a hole in the one dimensional Hubbard model below half-filling. We calculate the finite-size corrections to the energy. The results are then used to determine threshold singularities in the single-particle Green's function for commensurate fillings. We present the analogous results for the Yang-Gaudin model (electron gas with delta-function interactions).Comment: 26 pages, 12 figures version to appear in Phys Rev

Compactness in Banach space theory - selected problems

We list a number of problems in several topics related to compactness in nonseparable Banach spaces. Namely, about the Hilbertian ball in its weak topology, spaces of continuous functions on Eberlein compacta, WCG Banach spaces, Valdivia compacta and Radon-Nikod\'{y}m compacta

AXJ1749+684: a narrow emission-line galaxy with a flat X-ray spectrum

We report the serendipitous detection of an X-ray source, AXJ1749+684, with the ASCA Gas Imaging Spectrometer. AXJ1749+684 is identified with a LINER/starburst-type spiral galaxy KUG 1750+683A at a redshift z = 0.05. It has a hard X-ray spectrum, consistent with that of the X-ray background (XRB) in the 1-10 keV band. Despite the optical classification, the X-ray luminosity cannot be explained by starburst activity. Combined with spatial variations in the optical emission line ratios, this suggests the presence of an obscured Seyfert nucleus embedded within a starforming galaxy. Similar behaviour could explain the ambiguous properties of the faint narrow-line X-ray galaxies (NLXGs) emerging from deep X-ray surveys.Comment: MNRAS Letters in press, 6 pages, 7 figures in MNRAS LaTex styl