Morse Boundaries of Proper Geodesic Metric Spaces

We introduce a new type of boundary for proper geodesic spaces, called the Morse boundary, that is constructed with rays that identify the "hyperbolic directions" in that space. This boundary is a quasi-isometry invariant and thus produces a well-defined boundary for any finitely generated group. In the case of a proper $\mathrm{CAT}(0)$ space this boundary is the contracting boundary of Charney and Sultan and in the case of a proper Gromov hyperbolic space this boundary is the Gromov boundary. We prove three results about the Morse boundary of Teichm\"uller space. First, we show that the Morse boundary of the mapping class group of a surface is homeomorphic to the Morse boundary of the Teichm\"uller space of that surface. Second, using a result of Leininger and Schleimer, we show that Morse boundaries of Teichm\"uller space can contain spheres of arbitrarily high dimension. Finally, we show that there is an injective continuous map of the Morse boundary of Teichm\"uller space into the Thurston compactification of Teichm\"uller space by projective measured foliations.Comment: Corrected some proofs and slightly reorganized with comments from referee. To appear in Groups, Geometry, and Dynamic

Illegal, Unreported and Unregulated (IUU) Fishing: A Whitepaper

Illegal, unregulated and unreported (IUU) fishing refers to fishing activities that do not comply with regional, national, or international fisheries conservation or management measures. This whitepaper characterizes the status of Illegal, unregulated, and unreported fishing, the philanthropic community's current efforts to help reduce it, and potential opportunities for the Packard Foundation to become more actively engaged. The paper was drafted between March and June 2015, following a combination of desk research and a handful of select interviews

Litigating abroad : merchant’s expectations regarding procedure before foreign courts according to the hanseatic privileges (12th - 16th c.)

Between the 12th and 16th centuries the Hanseatic merchants obtained extremely important privileges from the rulers of the countries with whom they traded. These secured their commercial and legal status and the autonomy of their staples in Flanders, England, Norway, Denmark and Russia. Within these privileges no other subject receives so extensive a treatment as court procedure. Here, the single most important concern of the Hanseatic merchants was their position in front of alien courts. The article analyses the great attention given to court procedure in the twenty main Hanseatic privileges: What did the merchants require? Which procedural rules were necessary to encourage them to submit their disputes to alien public court instead of taking the matter into their own hands and turning to extra-judicial methods to resolve matters, e.g. cancellation of business relations, boycotts or even trade wars? This analysis suggests that the two most important concerns reflected in the procedural rules were to avoid delay to the next trading trip and to ensure a rational law of proof. The former was addressed by pressing for short-term scheduling and swift judgment and by the dispensation from appearing before the court in person. The latter included avoidance of duels and other ordeals and the attempt to obtain parity by appointing half of the jurors from Hanseatic cities

Pulsar State Switching from Markov Transitions and Stochastic Resonance

Markov processes are shown to be consistent with metastable states seen in pulsar phenomena, including intensity nulling, pulse-shape mode changes, subpulse drift rates, spindown rates, and X-ray emission, based on the typically broad and monotonic distributions of state lifetimes. Markovianity implies a nonlinear magnetospheric system in which state changes occur stochastically, corresponding to transitions between local minima in an effective potential. State durations (though not transition times) are thus largely decoupled from the characteristic time scales of various magnetospheric processes. Dyadic states are common but some objects show at least four states with some transitions forbidden. Another case is the long-term intermittent pulsar B1931+24 that has binary radio-emission and torque states with wide, but non-monotonic duration distributions. It also shows a quasi-period of $38\pm5$ days in a 13-yr time sequence, suggesting stochastic resonance in a Markov system with a forcing function that could be strictly periodic or quasi-periodic. Nonlinear phenomena are associated with time-dependent activity in the acceleration region near each magnetic polar cap. The polar-cap diode is altered by feedback from the outer magnetosphere and by return currents from an equatorial disk that may also cause the neutron star to episodically charge and discharge. Orbital perturbations in the disk provide a natural periodicity for the forcing function in the stochastic resonance interpretation of B1931+24. Disk dynamics may introduce additional time scales in observed phenomena. Future work can test the Markov interpretation, identify which pulsar types have a propensity for state changes, and clarify the role of selection effects.Comment: 25 pages, 6 figures, submitted to the Astrophysical Journa

RFI Identification and Mitigation Using Simultaneous Dual Station Observations

RFI mitigation is a critically important issue in radio astronomy using existing instruments as well as in the development of next-generation radio telescopes, such as the Square Kilometer Array (SKA). Most designs for the SKA involve multiple stations with spacings of up to a few thousands of kilometers and thus can exploit the drastically different RFI environments at different stations. As demonstrator observations and analysis for SKA-like instruments, and to develop RFI mitigation schemes that will be useful in the near term, we recently conducted simultaneous observations with Arecibo Observatory and the Green Bank Telescope (GBT). The observations were aimed at diagnosing RFI and using the mostly uncorrelated RFI between the two sites to excise RFI from several generic kinds of measurements such as giant pulses from Crab-like pulsars and weak HI emission from galaxies in bands heavily contaminated by RFI. This paper presents observations, analysis, and RFI identification and excision procedures that are effective for both time series and spectroscopy applications using multi-station data.Comment: 12 pages, 9 figures (4 in ps and 5 in jpg formats), Accepted for publication in Radio Scienc

National launch strategy vehicle data management system

The national launch strategy vehicle data management system (NLS/VDMS) was developed as part of the 1990 NASA Summer Faculty Fellowship Program. The system was developed under the guidance of the Engineering Systems Branch of the Information Systems Office, and is intended for use within the Program Development Branch PD34. The NLS/VDMS is an on-line database system that permits the tracking of various launch vehicle configurations within the program development office. The system is designed to permit the definition of new launch vehicles, as well as the ability to display and edit existing launch vehicles. Vehicles can be grouped in logical architectures within the system. Reports generated from this package include vehicle data sheets, architecture data sheets, and vehicle flight rate reports. The topics covered include: (1) system overview; (2) initial system development; (3) supercard hypermedia authoring system; (4) the ORACLE database; and (5) system evaluation

Low Frequency Interstellar Scattering and Pulsar Observations

Radio astronomy at frequencies from 2 to 30 MHz challenges time tested methods for extracting usable information from observations. One fundamental reason for this is that propagation effects due to the magnetoionic ionosphere, interplanetary medium, and interstellar matter (ISM) increase strongly with wavelength. The problems associated with interstellar scattering off of small scale irregularities in the electron density are addressed. What is known about interstellar scattering is summarized on the basis of high frequency observations, including scintillation and temporal broadening of pulsars and angular broadening of various galactic and extragalactic radio sources. Then those high frequency phenomena are addressed that are important or detectable at low frequencies. The radio sky becomes much simpler at low frequencies, most pulsars will not be seen as time varying sources, intensity variations will be quenched or will occur on time scales much longer than a human lifetime, and many sources will be angularly broadened and/or absorbed into the noise. Angular broadening measurements will help delineate the galactic distribution and power spectrum of small scale electron density irregularities

Spin Evolution of Pulsars with Weakly Coupled Superfluid Interiors

We discuss the spin evolution of pulsars in the case where a superfluid component of the star is coupled to the observable crust on long, spindown timescales. The momentum transfer from the superfluid interior results in an apparent decay of the external torque and, after a dramatic increase, to an asymptotic decrease of the generic value of the braking index, e.g. $n=3$, to values $n\sim 2.5$ if the magnetic field of the star does not decay over its lifetime. In the case where an exponential decay of the magnetic field towards a residual value occurs, the star undergoes a spin-up phase after which it could emerge in the millisecond sector of the $P$-$\dot P$ diagram.Comment: 11 pages, 3 figures, Latex, uses aaspp4.sty; ApJ in pres