Jupiter's polar ionospheric flows: measured intensity and velocity variations poleward of the main auroral oval

Recent analysis of high-resolution spectra of Doppler-shifted H3+ emission from the auroral/polar regions of Jupiter revealed a complex wind system, with a persistent auroral electrojet and strong anti-sunward flows in a region of lesser intensity centred around the magnetic pole [ Stallard et al., 2001 ]. This region, which we have called the Dark Polar Region (DPR), is re-investigated, transforming the observed line-of-sight velocities into a frame of reference fixed with respect to the magnetic pole. The DPR is shown to include a region essentially stagnant in this frame of reference (the f-DPR). We identify it as a region coupled to open magnetotail field lines. There is also a transition region in which the ion velocity returns to corotation (the r-DPR)

Partial Identification of the Average Treatment Effect Using Instrumental Variables: Review of Methods for Binary Instruments, Treatments, and Outcomes

Several methods have been proposed for partially or point identifying the average treatment effect (ATE) using instrumental variable (IV) type assumptions. The descriptions of these methods are widespread across the statistical, economic, epidemiologic, and computer science literature, and the connections between the methods have not been readily apparent. In the setting of a binary instrument, treatment, and outcome, we review proposed methods for partial and point identification of the ATE under IV assumptions, express the identification results in a common notation and terminology, and propose a taxonomy that is based on sets of identifying assumptions. We further demonstrate and provide software for the application of these methods to estimate bounds. Supplementary materials for this article are available online

Estimating the feasibility of transition paths in extended finite state machines

There has been significant interest in automating testing on the basis of an extended finite state machine (EFSM) model of the required behaviour of the implementation under test (IUT). Many test criteria require that certain parts of the EFSM are executed. For example, we may want to execute every transition of the EFSM. In order to find a test suite (set of input sequences) that achieves this we might first derive a set of paths through the EFSM that satisfy the criterion using, for example, algorithms from graph theory. We then attempt to produce input sequences that trigger these paths. Unfortunately, however, the EFSM might have infeasible paths and the problem of determining whether a path is feasible is generally undecidable. This paper describes an approach in which a fitness function is used to estimate how easy it is to find an input sequence to trigger a given path through an EFSM. Such a fitness function could be used in a search-based approach in which we search for a path with good fitness that achieves a test objective, such as executing a particular transition, and then search for an input sequence that triggers the path. If this second search fails then we search for another path with good fitness and repeat the process. We give a computationally inexpensive approach (fitness function) that estimates the feasibility of a path. In order to evaluate this fitness function we compared the fitness of a path with the ease with which an input sequence can be produced using search to trigger the path and we used random sampling in order to estimate this. The empirical evidence suggests that a reasonably good correlation (0.72 and 0.62) exists between the fitness of a path, produced using the proposed fitness function, and an estimate of the ease with which we can randomly generate an input sequence to trigger the path

A comparison of aerosol chemical and optical properties from the 1st and 2nd Aerosol Characterization Experiments

Shipboard measurements of aerosol chemical composition and optical properties were made during both ACE-1 and ACE-2. ACE-1 focused on remote marine aerosol minimally perturbed by continental sources. ACE-2 studied the outflow of European aerosol into the NE Atlantic atmosphere. A variety of air masses were sampled during ACE-2 including Atlantic, polar, Iberian Peninsula, Mediterranean, and Western European. Reported here are mass size distributions of non-sea salt (nss) sulfate, sea salt, and methanesulfonate and submicron and supermicron concentrations of black and organic carbon. Optical parameters include submicron and supermicron aerosol scattering and backscattering coefficients at 550 nm, the absorption coefficient at 550±20 nm, the Ångström exponent for the 550 and 700 nm wavelength pair, and single scattering albedo at 550 nm. All data are reported at the measurement relative humidity of 55%. Measured concentrations of nss sulfate aerosol indicate that, relative to ACE-1, ACE-2 aerosol during both marine and continental flow was impacted by continental sources. Thus, while sea salt controlled the aerosol chemical composition and optical properties of both the submicron and supermicron aerosol during ACE-1, it played a relatively smaller role in ACE-2. This is confirmed by the larger average Ångström exponent for ACE-2 continental aerosol of 1.2±0.26 compared to the ACE-1 average of -0.03±0.38. The depletion of chloride from sea salt aerosol in ACE-2 continental air masses averaged 55±25% over all particle sizes. This compares to the ACE-2 marine average of 4.8±18% and indicates the enhanced interaction of anthropogenic acids with sea salt as continental air masses are transported into the marine atmosphere. Single scattering albedos averaged 0.95±0.03 for ACE-2 continental air masses. Averages for ACE-2 and ACE-1 marine air masses were 0.98±0.01 and 0.99±0.01, respectively

ELM triggering conditions for the integrated modeling of H-mode plasmas

Recent advances in the integrated modeling of ELMy H-mode plasmas are presented. A model for the H-mode pedestal and for the triggering of ELMs predicts the height, width, and shape of the H-mode pedestal and the frequency and width of ELMs. Formation of the pedestal and the L-H transition is the direct result of ExB flow shear suppression of anomalous transport. The periodic ELM crashes are triggered by either the ballooning or peeling MHD instabilities. The BALOO, DCON, and ELITE ideal MHD stability codes are used to derive a new parametric expression for the peeling-ballooning threshold. The new dependence for the peeling-ballooning threshold is implemented in the ASTRA transport code. Results of integrated modeling of DIII-D like discharges are presented and compared with experimental observations. The results from the ideal MHD stability codes are compared with results from the resistive MHD stability code NIMROD.Comment: 12th International Congress on Plasma Physics, 25-29 October 2004, Nice (France

Nucleation versus Spinodal decomposition in a first order quark hadron phase transition

We investigate the scenario of homogeneous nucleation for a first order quark-hadron phase transition in a rapidly expanding background of quark gluon plasma. Using an improved preexponential factor for homogeneous nucleation rate, we solve a set of coupled equations to study the hadronization and the hydrodynamical evolution of the matter. It is found that significant supercooling is possible before hadronization begins. This study also suggests that spinodal decomposition competes with nucleation and may provide an alternative mechanism for phase conversion particularly if the transition is strong enough and the medium is nonviscous. For weak enough transition, the phase conversion may still proceed via homogeneous nucleation.Comment: LaTeX, 10 pages with 7 Postscript figures, more discussions and referencese added, typos correcte

Metal-oxide interactions for infiltrated Ni nanoparticles on A-site deficient LaxSr1 − 3x/2TiO3

The authors would like to thank EPSRC Platform (Grant EP/K015540/1) and the Royal Society for Wolfson Merit Award (WRMA 2012/R2) for funding. We also acknowledge support from China Scholarship Council (No. 201406690029).Enhancing the stability of introduced metal catalysts on oxide surfaces is a major issue for infiltrated anodes in Solid Oxide Cells (SOC) and other related catalysis field. Stoichiometric SrTiO3 (STO) and A-site cation deficient LaxSr1 − 3x/2TiO3 (LST) were compared to investigate the influence of stoichiometry upon the contact between metal and oxide, in order to improve the bonding of catalyst and substrate. Optimization of oxidizing and reducing temperatures for Ni infiltration processes was performed to get good nanoparticles distribution on the perovskite surface. Thermogravimetry (TG) and X-ray diffraction (XRD) analysis showed the formation of NiO, Ni after oxidation and reduction, respectively. Energy Dispersive Spectroscopy (EDS) on a Transmission Electron Microscopy (TEM) was employed to characterize the nickel nanoparticles on the LST surface. No obvious elemental transfer happened between Ni and LST. The TEM images showed Ni nanoparticles bonded well to the A-site deficient perovskite with large contact area. TG analysis in reducing atmosphere indicates interactions between metal-oxide interactions in deficient samples. This may improve the Ni distribution on perovskite surface and further control the growth of Ni particles when heated at extreme temperature.PostprintPeer reviewe

Kinetic theory of point vortices: diffusion coefficient and systematic drift

We develop a kinetic theory for point vortices in two-dimensional hydrodynamics. Using standard projection operator technics, we derive a Fokker-Planck equation describing the relaxation of a ``test'' vortex in a bath of ``field'' vortices at statistical equilibrium. The relaxation is due to the combined effect of a diffusion and a drift. The drift is shown to be responsible for the organization of point vortices at negative temperatures. A description that goes beyond the thermal bath approximation is attempted. A new kinetic equation is obtained which respects all conservation laws of the point vortex system and satisfies a H-theorem. Close to equilibrium this equation reduces to the ordinary Fokker-Planck equation.Comment: 50 pages. To appear in Phys. Rev.

A pilgrimage to gravity on GPUs

In this short review we present the developments over the last 5 decades that have led to the use of Graphics Processing Units (GPUs) for astrophysical simulations. Since the introduction of NVIDIA's Compute Unified Device Architecture (CUDA) in 2007 the GPU has become a valuable tool for N-body simulations and is so popular these days that almost all papers about high precision N-body simulations use methods that are accelerated by GPUs. With the GPU hardware becoming more advanced and being used for more advanced algorithms like gravitational tree-codes we see a bright future for GPU like hardware in computational astrophysics.Comment: To appear in: European Physical Journal "Special Topics" : "Computer Simulations on Graphics Processing Units" . 18 pages, 8 figure