High-Throughput 3D Cellular Imaging

Extended abstract of a paper presented at Microscopy and Microanalysis 2009 in Richmond, Virginia, USA, July 26 - July 30, 200

Planning assistance for the 30/20 GHz program, volume 3

The three basic experiment categories and consolidated experiments proposed by members of the Carrier Working Group are defined by category and by carrier. The three experiment categories are: (1) Possible Service (PS); (2) Possible Service and Technology (PSAT); and (3) Possible Technology (PT). Under Task 9 Western Union provided review, recommendations and critique of the NASA generated Statement of Work (SOW) defining the technical requirements governing design, launch and operation of the 30/20 GHz experimental systems

Planning assistance for the 30/20 GHz program, volume 1

Functional requirements for the 30/20 GHz communication system, planning assistance for the 30/20 GHz program, and a review of specified conceptual designs and recommendations are provided

Improved shaping approach to the preliminary design of low-thrust trajectories

This paper presents a general framework for the development of shape-based approaches to low-thrust trajectory design. A novel shaping method, based on a three-dimensional description of the trajectory in spherical coordinates, is developed within this general framework. Both the exponential sinusoid and the inverse polynomial shaping are demonstrated to be particular two-dimensional cases of the spherical one. The pseudoequinoctial shaping is revisited within the new framework, and the nonosculating nature of the pseudoequinoctial elements is analyzed. A two step approach is introduced to solve the time of flight constraint, related to the design of low-thrust arcs with boundary constraints for both spherical and pseudoequinoctial shaping. The solution derived from the shaping approach is improved with a feedback linear-quadratic controller and compared against a direct collocation method based on finite elements in time. The new shaping approach and the combination of shaping and linear-quadratic controller are tested on three case studies: a mission to Mars, a mission to asteroid 1989ML, a mission to comet Tempel-1, and a mission to Neptune

Mesoscopic Effects in Quantum Phases of Ultracold Quantum Gases in Optical Lattices

We present a wide array of quantum measures on numerical solutions of 1D Bose- and Fermi-Hubbard Hamiltonians for finite-size systems with open boundary conditions. Finite size effects are highly relevant to ultracold quantum gases in optical lattices, where an external trap creates smaller effective regions in the form of the celebrated "wedding cake" structure and the local density approximation is often not applicable. Specifically, for the Bose-Hubbard Hamiltonian we calculate number, quantum depletion, local von-Neumann entropy, generalized entanglement or Q-measure, fidelity, and fidelity susceptibility; for the Fermi-Hubbard Hamiltonian we also calculate the pairing correlations, magnetization, charge-density correlations, and antiferromagnetic structure factor. Our numerical method is imaginary time propagation via time-evolving block decimation. As part of our study we provide a careful comparison of canonical vs. grand canonical ensembles and Gutzwiller vs. entangled simulations. The most striking effect of finite size occurs for bosons: we observe a strong blurring of the tips of the Mott lobes accompanied by higher depletion, and show how the location of the first Mott lobe tip approaches the thermodynamic value as a function of system size.Comment: 13 pages, 10 figure

A reliable Pade analytical continuation method based on a high accuracy symbolic computation algorithm

We critique a Pade analytic continuation method whereby a rational polynomial function is fit to a set of input points by means of a single matrix inversion. This procedure is accomplished to an extremely high accuracy using a novel symbolic computation algorithm. As an example of this method in action we apply it to the problem of determining the spectral function of a one-particle thermal Green's function known only at a finite number of Matsubara frequencies with two example self energies drawn from the T-matrix theory of the Hubbard model. We present a systematic analysis of the effects of error in the input points on the analytic continuation, and this leads us to propose a procedure to test quantitatively the reliability of the resulting continuation, thus eliminating the black magic label frequently attached to this procedure.Comment: 11 pages, 8 eps figs, revtex format; revised version includes reference to anonymous ftp site containing example codes (MapleVr5.1 worksheets) displaying the implementation of the algorithm, including the padematinv.m library packag

Imprints of the nuclear symmetry energy on gravitational waves from the axial w-modes of neutron stars

The eigen-frequencies of the axial w-modes of oscillating neutron stars are studied using the continued fraction method with an Equation of State (EOS) partially constrained by the recent terrestrial nuclear laboratory data. It is shown that the density dependence of the nuclear symmetry energy $E_{sym}(\rho)$ affects significantly both the frequencies and the damping times of these modes. Besides confirming the previously found universal behavior of the mass-scaled eigen-frequencies as functions of the compactness of neutron stars, we explored several alternative universal scaling functions. Moreover, the $w_{II}$-mode is found to exist only for neutron stars having a compactness of $M/R\geq 0.1078$ independent of the EOS used.Comment: Version appeared in Phys. Rev. C80, 025801 (2009

A trap-based pulsed positron beam optimised for positronium laser spectroscopy

We describe a pulsed positron beam that is optimised for positronium (Ps) laser-spectroscopy experiments. The system is based on a two-stage Surko-type buffer gas trap that produces 4 ns wide pulses containing up to 5 × 105 positrons at a rate of 0.5-10 Hz. By implanting positrons from the trap into a suitable target material, a dilute positronium gas with an initial density of the order of 107 cm−3 is created in vacuum. This is then probed with pulsed (ns) laser systems, where various Ps-laser interactions have been observed via changes in Ps annihilation rates using a fast gamma ray detector. We demonstrate the capabilities of the apparatus and detection methodology via the observation of Rydberg positronium atoms with principal quantum numbers ranging from 11 to 22 and the Stark broadening of the n = 2 → 11 transition in electric fields

Isochronal annealing effects on local structure, crystalline fraction, and undamaged region size of radiation damage in Ga-stabilized δ\delta-Pu

The effects on the local structure due to self-irradiation damage of Ga stabilized $\delta$-Pu stored at cryogenic temperatures have been examined using extended x-ray absorption fine structure (EXAFS) experiments. Extensive damage, seen as a loss of local order, was evident after 72 days of storage below 15 K. The effect was observed from both the Pu and Ga sites, although less pronounced around Ga. Isochronal annealing was performed on this sample to study the annealing processes that occur between cryogenic and room temperature storage conditions, where damage is mostly reversed. Damage fractions at various points along the annealing curve have been determined using an amplitude-ratio method, standard EXAFS fitting, and a spherical crystallite model, and provide information complementary to previous electrical resistivity- and susceptibility-based isochronal annealing studies. The use of a spherical crystallite model accounts for the changes in EXAFS spectra using just two parameters, namely, the crystalline fraction and the particle radius. Together, these results are discussed in terms of changes to the local structure around Ga and Pu throughout the annealing process and highlight the unusual role of Ga in the behavior of the lowest temperature anneals.Comment: 13 pages, 10 figure