Microelectrophoresis of selected mineral particles

Particle mobilities of ilmenite, labradorite plagioclase, enstatite pyroxene, and olivine were measured with a Rank microelectrophoresis system to evaluate indicated mineral separability. Sodium bicarbonate buffer suspension media with and without additives (0.0001 M DTAB and 5 percent v/v ethylene glycol) were used to determine differential adsorption by mineral particles and modification of relative mobilities. Good separability between some minerals was indicated; additives did not enhance separability

Computer model calibration with large non-stationary spatial outputs: application to the calibration of a climate model

Bayesian calibration of computer models tunes unknown input parameters by comparing outputs with observations. For model outputs that are distributed over space, this becomes computationally expensive because of the output size. To overcome this challenge, we employ a basis representation of the model outputs and observations: we match these decompositions to carry out the calibration efficiently. In the second step, we incorporate the non-stationary behaviour, in terms of spatial variations of both variance and correlations, in the calibration. We insert two integrated nested Laplace approximation-stochastic partial differential equation parameters into the calibration. A synthetic example and a climate model illustration highlight the benefits of our approach

Pulsar Polar Cap Heating and Surface Thermal X-Ray Emission I. Curvature Radiation Pair Fronts

We investigate the effect of pulsar polar cap (PC) heating produced by positrons returning from the upper pair formation front. Our calculations are based on a self-consistent treatment of the pair dynamics and the effect of electric field screening by the returning positrons. We calculate the resultant X-ray luminosities, and discuss the dependence of the PC heating efficiencies on pulsar parameters, such as characteristic spin-down age, spin period, and surface magnetic field strength. In this study we concentrate on the regime where the pairs are produced in a magnetic field by curvature photons emitted by accelerating electrons. Our theoretical results are not in conflict with the available observational X-ray data and suggest that the effect of PC heating should significantly contribute to the thermal X-ray fluxes from middle-aged and old pulsars. The implications for current and future X-ray observations of pulsars are briefly outlined.Comment: 28 pages, 7 figures, accepted for publication in Ap

Direct measurements of the polarization of terrestrial kilometric radiation from Voyagers 1 and 2

Terrestrial radiation measurements obtained with planetary radio astronomy experiments on Voyager-1 and 2 during the early portions of each flight show the signals to be predominantly left-hand circularly polarized. Since these emissions were most probably generated above the Northern Hemisphere auroral zone, it is concluded that the radiation is emitted primarily in the extraordinary mode

Solar electric propulsion for Mars transport vehicles

Solar electric propulsion (SEP) is an alternative to chemical and nuclear powered propulsion systems for both piloted and unpiloted Mars transport vehicles. Photovoltaic solar cell and array technologies were evaluated as components of SEP power systems. Of the systems considered, the SEP power system composed of multijunction solar cells in an ENTECH domed fresnel concentrator array had the least array mass and area. Trip times to Mars optimized for minimum propellant mass were calculated. Additionally, a preliminary vehicle concept was designed

Radio Jupiter after Voyager: An overview of the Planetary Radio Astronomy observations

Jupiter's low frequency radio emission morphology as observed by the Planetary Radio Astronomy (PRA) instrument onboard the Voyager spacecraft is reviewed. The PRA measurement capabilities and limitations are summarized following over two years of experience with the instrument. As a direct consequence of the PRA spacecraft observations, unprecedented in terms of their sensitivity and frequency coverage, at least three previous unrecognized emission components were discovered: broadband and narrow band kilometric emission and the lesser arc decametric emission. Their properties are reviewed. In addition, the fundamental structure of the decameter and hectometer wavelength emission, which is believed to be almost exclusively in the form of complex but repeating arc structures in the frequency time domain, is described. Dramatic changes in the emission morphology of some components as a function of Sun-Jupiter-spacecraft angle (local time) are described. Finally, the PRA in suit measurements of the Io plasma torus hot to cold electron density and temperature ratios are summarized

Ground-State and Domain-Wall Energies in the Spin-Glass Region of the 2D ±J\pm J Random-Bond Ising Model

The statistics of the ground-state and domain-wall energies for the two-dimensional random-bond Ising model on square lattices with independent, identically distributed bonds of probability $p$ of $J_{ij}= -1$ and $(1-p)$ of $J_{ij}= +1$ are studied. We are able to consider large samples of up to $320^2$ spins by using sophisticated matching algorithms. We study $L \times L$ systems, but we also consider $L \times M$ samples, for different aspect ratios $R = L / M$. We find that the scaling behavior of the ground-state energy and its sample-to-sample fluctuations inside the spin-glass region ($p_c \le p \le 1 - p_c$) are characterized by simple scaling functions. In particular, the fluctuations exhibit a cusp-like singularity at $p_c$. Inside the spin-glass region the average domain-wall energy converges to a finite nonzero value as the sample size becomes infinite, holding $R$ fixed. Here, large finite-size effects are visible, which can be explained for all $p$ by a single exponent $\omega\approx 2/3$, provided higher-order corrections to scaling are included. Finally, we confirm the validity of aspect-ratio scaling for $R \to 0$: the distribution of the domain-wall energies converges to a Gaussian for $R \to 0$, although the domain walls of neighboring subsystems of size $L \times L$ are not independent.Comment: 11 pages with 15 figures, extensively revise

Secants of Lagrangian Grassmannians

We study the dimensions of secant varieties of the Grassmannian of Lagrangian subspaces in a symplectic vector space. We calculate these dimensions for third and fourth secant varieties. Our result is obtained by providing a normal form for four general points on such a Grassmannian and by explicitly calculating the tangent spaces at these four points

Massive scalar field quasi-normal modes of higher dimensional black holes

We study quasinormal spectrum of massive scalar field in the $D$-dimensional black hole background. We found the qualitatively different dependence on the field mass of the fundamental modes for $D\geq6$. The behaviour of higher modes is qualitatively the same for all $D$. Thus for some particular values of mass (of the field and of the black hole) the spectrum has two dominating oscillations with a very long lifetime. Also we show that the asymptotically high overtones do not depend on the field mass. In addition, we present the generalisation of the Nollert improvement of the continued fraction technique for the numerical calculation of quasi-normal frequencies of $D$-dimensional black holes.Comment: 8 pages, 4 figures, misprints corrected, version to appear in Phys. Rev.