Atomistic Hydrodynamics and the Dynamical Hydrophobic Effect in Porous Graphene

Mirroring their role in electrical and optical physics, two-dimensional crystals are emerging as novel platforms for fluid separations and water desalination, which are hydrodynamic processes that occur in nanoscale environments. For numerical simulation to play a predictive and descriptive role, one must have theoretically sound methods that span orders of magnitude in physical scales, from the atomistic motions of particles inside the channels to the large-scale hydrodynamic gradients that drive transport. Here, we use constraint dynamics to derive a nonequilibrium molecular dynamics method for simulating steady-state mass flow of a fluid moving through the nanoscopic spaces of a porous solid. After validating our method on a model system, we use it to study the hydrophobic effect of water moving through pores of electrically doped single-layer graphene. The trend in permeability that we calculate does not follow the hydrophobicity of the membrane, but is instead governed by a crossover between two competing molecular transport mechanisms.Comment: 6 pages, 3 figure

Balloon telescope studies of Venus

Determination of ice clouds and water vapor in Venus atmosphere from balloon observation

Preparation, analysis and release of simulated interplanetary grains into low Earth orbit

Astronomical observations which reflect the optical and dynamical properties of interstellar and interplanetary grains are the primary means of identifying the shape, size, and the chemistry of extraterrestrial grain materials. Except for recent samplings of extraterrestrial particles in near-Earth orbit and in the stratosphere observations were the only method of deducing the properties of extraterrestrial particles. In order to elucidate the detailed characteristics of observed dust, the observations must be compared with theoretical studies, some of which are discussed in this volume, or compared with terrestrial laboratory experiments. The formation and optical characterization of simulated interstellar and interplanetary dust with particular emphasis on studying the properties on irregularly shaped particles were discussed. Efforts to develop the techniques to allow dust experiments to be carried out in low-Earth orbit were discussed, thus extending the conditions under which dust experiments may be performed

Parameterization of the Angular Distribution of Gamma Rays Produced by p-p Interaction in Astronomical Environment

We present the angular distribution of gamma rays produced by proton-proton interactions in parameterized formulae to facilitate calculations in astrophysical environments. The parameterization is derived from Monte Carlo simulations of the up-to-date proton-proton interaction model by Kamae et al. (2005) and its extension by Kamae et al. (2006). This model includes the logarithmically rising inelastic cross section, the diffraction dissociation process and Feynman scaling violation. The extension adds two baryon resonance contributions: one representing the Delta(1232) and the other representing multiple resonances around 1600 MeV/c^2. We demonstrate the use of the formulae by calculating the predicted gamma-ray spectrum for two different cases: the first is a pencil beam of protons following a power law and the second is a fanned proton jet with a Gaussian intensity profile impinging on the surrounding material. In both cases we find that the predicted gamma-ray spectrum to be dependent on the viewing angle.Comment: 8 pages, 7 figures, figure 7 updated, accepted for publication in ApJ, text updated to match changes by the editor, two refs updated from preprints to full journal

Frequency-Tunable Josephson Junction Resonator for Quantum Computing

We have fabricated and measured a high-Q Josephson junction resonator with a tunable resonance frequency. A dc magnetic flux allows the resonance frequency to be changed by over 10 %. Weak coupling to the environment allows a quality factor of $\thicksim$7000 when on average less than one photon is stored in the resonator. At large photon numbers, the nonlinearity of the Josephson junction creates two stable oscillation states. This resonator can be used as a tool for investigating the quality of Josephson junctions in qubits below the single photon limit, and can be used as a microwave qubit readout at high photon numbers.Comment: 3 pages, 5 figure

Evidence for a Galactic gamma ray halo

We present quantitative statistical evidence for a $\gamma$-ray emission halo surrounding the Galaxy. Maps of the emission are derived. EGRET data were analyzed in a wavelet-based non-parametric hypothesis testing framework, using a model of expected diffuse (Galactic + isotropic) emission as a null hypothesis. The results show a statistically significant large scale halo surrounding the center of the Milky Way as seen from Earth. The halo flux at high latitudes is somewhat smaller than the isotropic gamma-ray flux at the same energy, though of the same order (O(10^(-7)--10^(-6)) ph/cm^2/s/sr above 1 GeV).Comment: Final version accepted for publication in New Astronomy. Some additional results/discussion included, along with entirely revised figures. 19 pages, 15 figures, AASTeX. Better quality figs (PS and JPEG) are available at http://tigre.ucr.edu/halo/paper.htm