The X-ray luminosity function of AGN at z~3

We combine Lyman-break colour selection with ultradeep (> 200 ks) Chandra X-ray imaging over a survey area of ~0.35 deg^2 to select high redshift AGN. Applying careful corrections for both the optical and X-ray selection functions, the data allow us to make the most accurate determination to date of the faint end of the X-ray luminosity function (XLF) at z~3. Our methodology recovers a number density of X-ray sources at this redshift which is at least as high as previous surveys, demonstrating that it is an effective way of selecting high z AGN. Comparing to results at z=1, we find no evidence that the faint slope of the XLF flattens at high z, but we do find significant (factor ~3.6) negative evolution of the space density of low luminosity AGN. Combining with bright end data from very wide surveys we also see marginal evidence for continued positive evolution of the characteristic break luminosity L*. Our data therefore support models of luminosity-dependent density evolution between z=1 and z=3. A sharp upturn in the the XLF is seen at the very lowest luminosities (Lx < 10^42.5 erg s^-1), most likely due to the contribution of pure X-ray starburst galaxies at very faint fluxes.Comment: 16 pages, 9 figures, accepted for publication in MNRA

Injection-Locked Dye Laser Pumped By A Xenon-lon Laser

Injection locking of a dye laser is reported for a 4-minor ring-cavity dye User pumped by a xenon-ion laser. Both a He-Ne laser and tunable CW dye laser were used as the injection sources. Copyright © 1980 by The Institute of Electrical and Electronics Engineers, Inc

Direct calculation of the hard-sphere crystal/melt interfacial free energy

We present a direct calculation by molecular-dynamics computer simulation of the crystal/melt interfacial free energy, $\gamma$, for a system of hard spheres of diameter $\sigma$. The calculation is performed by thermodynamic integration along a reversible path defined by cleaving, using specially constructed movable hard-sphere walls, separate bulk crystal and fluid systems, which are then merged to form an interface. We find the interfacial free energy to be slightly anisotropic with $\gamma$ = 0.62$\pm 0.01$, 0.64$\pm 0.01$ and 0.58$\pm 0.01 k_BT/\sigma^2$ for the (100), (110) and (111) fcc crystal/fluid interfaces, respectively. These values are consistent with earlier density functional calculations and recent experiments measuring the crystal nucleation rates from colloidal fluids of polystyrene spheres that have been interpreted [Marr and Gast, Langmuir {\bf 10}, 1348 (1994)] to give an estimate of $\gamma$ for the hard-sphere system of $0.55 \pm 0.02 k_BT/\sigma^2$, slightly lower than the directly determined value reported here.Comment: 4 pages, 4 figures, submitted to Physical Review Letter

External field control of donor electron exchange at the Si/SiO2 interface

We analyze several important issues for the single- and two-qubit operations in Si quantum computer architectures involving P donors close to a SiO2 interface. For a single donor, we investigate the donor-bound electron manipulation (i.e. 1-qubit operation) between the donor and the interface by electric and magnetic fields. We establish conditions to keep a donor-bound state at the interface in the absence of local surface gates, and estimate the maximum planar density of donors allowed to avoid the formation of a 2-dimensional electron gas at the interface. We also calculate the times involved in single electron shuttling between the donor and the interface. For a donor pair, we find that under certain conditions the exchange coupling (i.e. 2-qubit operation) between the respective electron pair at the interface may be of the same order of magnitude as the coupling in GaAs-based two-electron double quantum dots where coherent spin manipulation and control has been recently demonstrated (for example for donors ~10 nm below the interface and \~40 nm apart, J~10^{-4} meV), opening the perspective for similar experiments to be performed in Si.Comment: 11 pages, 15 figures. Changes in Eq. 24 plus minor typo

Interplay between distribution of live cells and growth dynamics of solid tumours

Experiments show that simple diffusion of nutrients and waste molecules is not sufficient to explain the typical multilayered structure of solid tumours, where an outer rim of proliferating cells surrounds a layer of quiescent but viable cells and a central necrotic region. These experiments challenge models of tumour growth based exclusively on diffusion. Here we propose a model of tumour growth that incorporates the volume dynamics and the distribution of cells within the viable cell rim. The model is suggested by in silico experiments and is validated using in vitro data. The results correlate with in vivo data as well, and the model can be used to support experimental and clinical oncology

Pyomo - Optimization Modeling in Python

INFORMS Journal of Computing, November 2012The article of record as published may be located at http://dx.doi.org/10.1287/ijoc.2012.4.brIf a simple, intuitive tool for a task exists, the task is done more often, by more people. This basic principle is as true for gardening and gadgets, as it is for computation in operations research. The book, Pyomo { Optimization Modeling in Python, documents a simple, yet versatile tool for modeling and solving optimization problems

Predictions of LDEF radioactivity and comparison with measurements

As part of the program to utilize LDEF data for evaluation and improvement of current ionizing radiation environmental models and related predictive methods for future LEO missions, calculations have been carried out to compare with the induced radioactivity measured in metal samples placed on LDEF. The predicted activation is about a factor of two lower than observed, which is attributed to deficiencies in the AP8 trapped proton model. It is shown that this finding based on activation sample data is consistent with comparisons made with other LDEF activation and dose data. Plans for confirming these results utilizing additional LDEF data sets, and plans for model modifications to improve the agreement with LDEF data, are discussed

Adjusting the melting point of a model system via Gibbs-Duhem integration: application to a model of Aluminum

Model interaction potentials for real materials are generally optimized with respect to only those experimental properties that are easily evaluated as mechanical averages (e.g., elastic constants (at T=0 K), static lattice energies and liquid structure). For such potentials, agreement with experiment for the non-mechanical properties, such as the melting point, is not guaranteed and such values can deviate significantly from experiment. We present a method for re-parameterizing any model interaction potential of a real material to adjust its melting temperature to a value that is closer to its experimental melting temperature. This is done without significantly affecting the mechanical properties for which the potential was modeled. This method is an application of Gibbs-Duhem integration [D. Kofke, Mol. Phys.78, 1331 (1993)]. As a test we apply the method to an embedded atom model of aluminum [J. Mei and J.W. Davenport, Phys. Rev. B 46, 21 (1992)] for which the melting temperature for the thermodynamic limit is 826.4 +/- 1.3K - somewhat below the experimental value of 933K. After re-parameterization, the melting temperature of the modified potential is found to be 931.5K +/- 1.5K.Comment: 9 pages, 5 figures, 4 table

Global deletion of Panx3 produces multiple phenotypic effects in mouse humeri and femora

© 2016 Anatomical Society. Pannexins form single-membrane channels that allow passage of small molecules between the intracellular and extracellular compartments. Of the three pannexin family members, Pannexin3 (Panx3) is the least studied but is highly expressed in skeletal tissues and is thought to play a role in the regulation of chondrocyte and osteoblast proliferation and differentiation. The purpose of our study is to closely examine the in vivo effects of Panx3 ablation on long bone morphology using micro-computed tomography. Using Panx3 knockout (KO) and wildtype (WT) adult mice, we measured and compared aspects of phenotypic shape, bone mineral density (BMD), cross-sectional geometric properties of right femora and humeri, and lean mass. We found that KO mice have absolutely and relatively shorter diaphyseal shafts compared with WT mice, and relatively larger areas of muscle attachment sites. No differences in BMD or lean mass were found between WT and KO mice. Interestingly, KO mice had more robust femora and humeri compared with WT mice when assessed in cross-section at the midshaft. Our results clearly show that Panx3 ablation produces phenotypic effects in mouse femora and humeri, and support the premise that Panx3 has a role in regulating long bone growth and development

The TWA 3 Young Triple System: Orbits, Disks, Evolution

We have characterized the spectroscopic orbit of the TWA 3A binary and provide preliminary families of probable solutions for the TWA 3A visual orbit as well as for the wide TWA 3A--B orbit. TWA 3 is a hierarchical triple located at 34 pc in the $\sim$10 Myr old TW Hya association. The wide component separation is 1."55; the close pair was first identified as a possible binary almost 20 years ago. We initially identified the 35-day period orbital solution using high-resolution infrared spectroscopy which angularly resolved the A and B components. We then refined the preliminary orbit by combining the infrared data with a re-analysis of our high-resolution optical spectroscopy. The orbital period from the combined spectroscopic solution is $\sim$35 days, the eccentricity is $\sim$0.63, and the mass ratio is $\sim$0.84; although this high mass ratio would suggest that optical spectroscopy alone should be sufficient to identify the orbital solution, the presence of the tertiary B component likely introduced confusion in the blended optical spectra. Using millimeter imaging from the literature, we also estimate the inclinations of the stellar orbital planes with respect to the TWA 3A circumbinary disk inclination and find that all three planes are likely misaligned by at least $\sim$30 degrees. The TWA 3A spectroscopic binary components have spectral types of M4.0 and M4.5; TWA 3B is an M3. We speculate that the system formed as a triple, is bound, and that its properties were shaped by dynamical interactions between the inclined orbits and disk.Comment: Accepted to Ap