Effects of Differential Rotation on the Maximum Mass of Neutron Stars

The merger of binary neutron stars is likely to lead to differentially rotating remnants. In this paper we numerically construct models of differentially rotating neutron stars in general relativity and determine their maximum allowed mass. We model the stars adopting a polytropic equation of state and tabulate maximum allowed masses as a function of differential rotation and stiffness of the equation of state. We also provide a crude argument that yields a qualitative estimate of the effect of stiffness and differential rotation on the maximum allowed mass.Comment: 6 pages, to appear in Ap

Using constraint preconditioners with regularized saddle-point problems

The problem of finding good preconditioners for the numerical solution of a certain important class of indefinite linear systems is considered. These systems are of a 2 by 2 block (KKT) structure in which the (2,2) block (denoted by -C) is assumed to be nonzero. In Constraint preconditioning for indefinite linear systems , SIAM J. Matrix Anal. Appl., 21 (2000), Keller, Gould and Wathen introduced the idea of using constraint preconditioners that have a specific 2 by 2 block structure for the case of C being zero. We shall give results concerning the spectrum and form of the eigenvectors when a preconditioner of the form considered by Keller, Gould and Wathen is used but the system we wish to solve may have C \neq 0 . In particular, the results presented here indicate clustering of eigenvalues and, hence, faster convergence of Krylov subspace iterative methods when the entries of C are small; such situations arise naturally in interior point methods for optimization and we present results for such problems which validate our conclusions.\ud \ud The first author's work was supported by the OUCL Doctorial Training Accoun

iResilience of science pre-service teachers through digital storytelling

© 2015. We live in a multimodal world where communication enabled by digital media supports the expression of ideas, opinions, instructions and experiences in a variety of formats that empower the individual to convey thoughts and emotions persuasively. In education, digital storytelling as a pedagogical strategy can be embedded in student-generated videos of narratives of personal learning experiences or in teacher-constructed stories that inform or instruct. The aim of this qualitative research was to investigate how a group of science pre-service teachers created digital stories to elicit resiliency (risk and protective factors) during their teaching practicum and how their peers responded to the digital stories, uploaded and shared on VoiceThread. The results showed that the digital stories were able to convey thinking and emotions successfully at a deeper level. A range of issues (risk factors) and strategies (protective factors) to overcome them could be identified in the digital stories. As reducing the risk of attrition in teachers' early professional careers is important for maintaining teacher numbers and quality in teaching, this research is significant in understanding how pre-service teachers view resiliency in their education. Digital stories are able to provide teacher educators and researchers with richer data for this purpose. Australasian Journal of Educational Technolog

Reflective Ghost Imaging through Turbulence

Recent work has indicated that ghost imaging may have applications in standoff sensing. However, most theoretical work has addressed transmission-based ghost imaging. To be a viable remote-sensing system, the ghost imager needs to image rough-surfaced targets in reflection through long, turbulent optical paths. We develop, within a Gaussian-state framework, expressions for the spatial resolution, image contrast, and signal-to-noise ratio of such a system. We consider rough-surfaced targets that create fully developed speckle in their returns, and Kolmogorov-spectrum turbulence that is uniformly distributed along all propagation paths. We address both classical and nonclassical optical sources, as well as a computational ghost imager.Comment: 13 pages, 3 figure

The effect of terminal group modification on the solution properties of dendrimers: A molecular dynamics simulation study

We study the static and dynamic properties of amphiphilic dendrimers of generation 3 through 7 in an explicitly modeled solvent with molecular dynamics. All interior monomers are solvophobic while the terminal monomers are varied from all solvophobic to all solvophilic, with a number of nonuniform solvophobic/ solvophilic terminal monomer arrangements investigated. For generations 6 and 7, crowding at the dendrimer surface forces some solvophilic monomers into the interior of the molecule. The nonuniformly surface-modified dendrimers are studied to examine how different arrangements of terminal monomers might affect dendrimer conformation. In all cases with solvophilic terminal monomers we find the solvophilic monomers congregating at the surface; thus, the dendrimer adopts the form of a unimolecular micelle. For generation 5 and smaller, the terminal monomer arrangement has no effect on the static or dynamic properties. For generations 6 and 7, a minimum number of bonds between the two types of terminal monomers is required to observe all solvophilic terminal monomers at the surface of the molecule. Lowering the simulation temperature, which effectively increases the interaction strength between solvophilic monomers and solvent, eliminates the backfolding tendencies of the solvophilic monomers and increases the asphericity of the generation 6 and 7 dendrimers

State detection using coherent Raman repumping and two-color Raman transfers

We demonstrate state detection based on coherent Raman repumping and a two-color Raman state transfer. The Raman coupling during detection selectively eliminates unwanted dark states in the fluorescence cycle without compromising the immunity of the desired dark state to off-resonant scattering. We demonstrate this technique using $^{137}\mathrm{Ba}^+$ where a combination of Raman coupling and optical pumping leaves the $D_{3/2}$ $\ket{F"=3,m_F"=3}$ metastable state optically dark and immune to off-resonant scattering. All other states are strongly coupled to the upper $P_{1/2}$ levels. We achieve a single shot state-detection efficiency of $89.6(3)$ in a $1\mathrm{ms}$ integration time, limited almost entirely by technical imperfections. Shelving to the $\ket{F"=3,m_F"=3}$ state before detection is performed via a two-color Raman transfer with a fidelity of $1.00(3)$