65 research outputs found

    Reverse Bisimulations on Stable Configuration Structures

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    The relationships between various equivalences on configuration structures, including interleaving bisimulation (IB), step bisimulation (SB) and hereditary history-preserving (HH) bisimulation, have been investigated by van Glabbeek and Goltz (and later Fecher). Since HH bisimulation may be characterised by the use of reverse as well as forward transitions, it is of interest to investigate forms of IB and SB where both forward and reverse transitions are allowed. We give various characterisations of reverse SB, showing that forward steps do not add extra power. We strengthen Bednarczyk's result that, in the absence of auto-concurrency, reverse IB is as strong as HH bisimulation, by showing that we need only exclude auto-concurrent events at the same depth in the configuration

    A Logic with Reverse Modalities for History-preserving Bisimulations

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    We introduce event identifier logic (EIL) which extends Hennessy-Milner logic by the addition of (1) reverse as well as forward modalities, and (2) identifiers to keep track of events. We show that this logic corresponds to hereditary history-preserving (HH) bisimulation equivalence within a particular true-concurrency model, namely stable configuration structures. We furthermore show how natural sublogics of EIL correspond to coarser equivalences. In particular we provide logical characterisations of weak history-preserving (WH) and history-preserving (H) bisimulation. Logics corresponding to HH and H bisimulation have been given previously, but not to WH bisimulation (when autoconcurrency is allowed), as far as we are aware. We also present characteristic formulas which characterise individual structures with respect to history-preserving equivalences.Comment: In Proceedings EXPRESS 2011, arXiv:1108.407

    SRGeJ045359.9+622444: A 55-min Period Eclipsing AM CVn Discovered from a Joint SRG/eROSITA + ZTF Search

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    AM CVn systems are ultra-compact binaries where a white dwarf accretes from a helium-rich degenerate or semi-degenerate donor. Some AM CVn systems will be among the loudest sources of gravitational waves for the upcoming Laser Interferometer Space Antenna (LISA), yet the formation channel of AM CVns remains uncertain. We report the study and characterisation of a new eclipsing AM CVn, SRGeJ045359.9+622444 (hereafter SRGeJ0453), discovered from a joint SRG/eROSITA and ZTF program to identify cataclysmic variables (CVs). We obtained optical photometry to confirm the eclipse of SRGeJ0453 and determine the orbital period to be Porb=55.0802±0.0003P_\textrm{orb} = 55.0802 \pm 0.0003 min. We constrain the binary parameters by modeling the high-speed photometry and radial velocity curves and find Mdonor=0.044±0.024MM_\textrm{donor} = 0.044 \pm0.024 M_{\odot} and Rdonor=0.078±0.012RR_\textrm{donor}=0.078 \pm 0.012 R_{\odot}. The X-ray spectrum is approximated by a power-law model with an unusually flat photon index of Γ1\Gamma\sim 1 previously seen in magnetic CVs with SRG/eROSITA, but verifying the magnetic nature of SRGeJ0453 requires further investigation. Optical spectroscopy suggests that the donor star of SRGeJ0453 could have initially been a He star or a He white dwarf. SRGeJ0453 is the ninth eclipsing AM CVn system published to date, and its lack of optical outbursts have made it elusive in previous surveys. The discovery of SRGeJ0453 using joint X-ray and optical surveys highlights the potential for discovering similar systems in the near future.Comment: Submitted to Ap

    Around the Clock Observations of the Q0957+561 A,B Gravitationally Lensed Quasar II: Results for the second observing season

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    We report on an observing campaign in March 2001 to monitor the brightness of the later arriving Q0957+561 B image in order to compare with the previously published brightness observations of the (first arriving) A image. The 12 participating observatories provided 3543 image frames which we have analyzed for brightness fluctuations. From our classical methods for time delay determination, we find a 417.09 +/- 0.07 day time delay which should be free of effects due to incomplete sampling. During the campaign period, the quasar brightness was relatively constant and only small fluctuations were found; we compare the structure function for the new data with structure function estimates for the 1995--6 epoch, and show that the structure function is statistically non-stationary. We also examine the data for any evidence of correlated fluctuations at zero lag. We discuss the limits to our ability to measure the cosmological time delay if the quasar's emitting surface is time resolved, as seems likely.Comment: AAS LaTeX, 5 PostScript figure

    Platinum Nanoscale Lattice on a Graphite Surface Using Cetyltrimethylammonium Bromide Hemi- and Precylindrical Micelle Templates

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    One-dimentional (1-D) thin-layer (2–5 nm) parallel strips of Pt on a graphite surface have been synthesized via a template-directed chemical deposition of Pt. The templates are a surface micellar strip of cetyltrimethylammonium bromide (CTAB) at highly ordered pyrolytic graphite (HOPG). The concentration- and temperature-dependent morphology of surface micellar strips of CTAB at the graphite/aqueous solution is elucidated by using the atomic force microscopy (AFM) soft-contacting techniques. The dimentions and repeat period of the Pt strips can be widely controlled by the temperature: the width is from 47 to 169 nm and the period from 134 to 233 nm in the temperature range 25–33 °C. The morphological characteristics of the Pt strips depend on those of the original surface micellar strips. The fact that the strips are composed of metallic platinum was confirmed by testing the membrane electrode assembly with the strips in a special fuel cell. This approach could be extended to fabricate a wide range of 1-D self-assembling metallic nanostructures on surfaces using micelle-like self-assemblies carrying metal ions at interfaces
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