Computing the Photometric and Polarimetric Variability of Be Stars

We investigate variations in the linear polarization as well as in the V-band and B-band colour-magnitudes for classical Be star disks. We present two models: disks with enhanced disk density and disks that are tilted or warped from the stellar equatorial plane. In both cases, we predict variation in observable properties of the system as the disk rotates. We use a non-LTE radiative transfer code BEDISK (Sigut & Jones) in combination with a Monte Carlo routine that includes multiple scattering (Halonen et al.) to model classical Be star systems. We find that a disk with an enhanced density region that is one order of magnitude denser than the disk's base density shows as much as $\sim$0.2% variability in the polarization while the polarization position angle varies by $\sim$8\deg. The $\Delta$V magnitude for the same system shows variations of up to $\sim$0.4 magnitude while the $\Delta$(B-V) colour varies by at most $\sim$0.01 magnitude. We find that disks tilted from the equatorial plane at small angles of $\sim$30\deg more strongly reflect the values of polarization and colour-magnitudes reported in the literature than disks tilted at larger angles. For this model, the linear polarization varies by $\sim$0.3%, the polarization position angle varies by $\sim$60\deg, the $\Delta$V magnitude varies up to 0.35 magnitude, and the $\Delta$(B-V) colour varies up to 0.1 magnitude. We find that the enhanced disk density models show ranges of polarization and colour-magnitudes that are commensurate with what is reported in the literature for all sizes of the density enhanced regions. From this, we cannot determine any preference for small or large density enhanced regions.Comment: Accepted in ApJ. 11 pages, 9 figures. The University of Western Ontari

Wave function engineering in quantum dot-ring nanostructures

Modern nanotechnology allows producing, depending on application, various quantum nanostructures with the desired properties. These properties are strongly influenced by the confinement potential which can be modified, e.g., by electrical gating. In this paper we analyze a nanostructure composed of a quantum dot surrounded by a quantum ring. We show that depending on the details of the confining potential the electron wave functions can be located in different parts of the structure. Since the properties of such a nanostructure strongly depend on the distribution of the wave functions, varying the applied gate voltage one can easily control them. In particular, we illustrate the high controllability of the nanostructure by demonstrating how its coherent, optical, and conducting properties can be drastically changed by a small modification of the confining potential.Comment: 8 pages, 10 figures, 2 tables, revte

Coulomb matrix elements of bilayers of confined charge carriers with arbitrary spatial separation

We describe a practical procedure to calculate the Coulomb matrix elements of 2D spatially separated and confined charge carriers, which are needed for detailed theoretical descriptions of important condensed matter finite systems. We derive an analytical expression, for arbitrary separations, in terms of a single infinite series and apply a u-type Levin transform in order to accelerate the resulting infinite series. This procedure has proven to be efficient and accurate. Direct consequences concerning the functional dependence of the matrix elements on the separation distance, transition amplitudes and the diagonalization of a single electron-hole pair in vertically stacked parabolic quantum dots are presented.Comment: 8 page

Energy levels and far-infrared spectroscopy for two electrons in a semiconductor nanoring

The effects of electron-electron interaction of a two-electron nanoring on the energy levels and far-infrared (FIR) spectroscopy have been investigated based on a model calculation which is performed within the exactly numerical diagonalization. It is found that the interaction changes the energy spectra dramatically, and also shows significant influence on the FIR spectroscopy. The crossings between the lowest spin-singlet and triplet states induced by the coulomb interaction are clearly revealed. Our results are related to the experiment recently carried out by A. Lorke et al. [Phys. Rev. Lett. 84, 2223 (2000)].Comment: 17 pages, 6 figures, revised and accepted by Phys. Rev. B (Dec. 15

Infrared Excess in the Be Star Delta Scorpii

We present infrared photometric observations of the Be binary system delta Scorpii obtained in 2006. The J,H and K magnitudes are the same within the errors compared to observations taken 10 months earlier. We derive the infrared excess from the observation and compare this to the color excess predicted by a radiative equilibrium model of the primary star and its circumstellar disk. We use a non-LTE computational code to model the gaseous envelope concentrated in the star's equatorial plane and calculate the expected spectral energy distribution and Halpha emission profile of the star with its circumstellar disk. Using the observed infrared excess of delta Sco, as well as Halpha spectroscopy bracketing the IR observations in time, we place constraints on the radial density distribution in the circumstellar disk. Because the disk exhibits variability in its density distribution, this work will be helpful in understanding its dynamics.Comment: 12 pages, 14 figures, to be published in PASP May 200

Measurements and Variability of Arterial Blood Pressure and Heart Interval in Conscious and Anesthetized Dogs

No abstract availabl

An agenda for rethinking mid-career master programs in public administration

The pace of societal change and the development of societal challenges have speeded up considerably during the last couple of decades, with substantial impact on different levels, i.e. ranging from global to local, or from business to government. When focusing on the public domain, these changes and challenges have had a major impact on public professionals, who face different and frequently changing questions. Mid-career programs in Public Administration (MPA) have the mission to support enrolled professionals in dealing with these changes and challenges. This article is about the development of such MPAs. Both substantive and didactic development is needed. To counter institutional inertia it seems vital to institutionalize a regular rethinking and adaptation of curricula and didactic strategies. This article identified some important points of attention and some options to deal with these in order to continuously improve the contribution of MPA programs to relevant and effective professional development and ongoing professional learning