[en] Accurate understanding and forecasting of traffic conditions is a key contemporary problem for local policymakers. Road networks are increasingly congested, yet data on usage patterns is often scarce or expensive to obtain, meaning that informed policy decision-making is difficult. This paper explores the extent to which traffic disruption can be estimated from static features of the volunteer geographic information site OpenStreetMap [OSM]. Kernel Density Estimates of OSM features are used as predictors for a linear regression of counts of traffic incidents at 6,500 separate points within the Oxfordshire road traffic network. For highly granular points of just 10m2 , it is shown that more than half of variation in traffic outcomes can be explained with these static features alone. Furthermore, use of OSM’s granular point of interest data improves considerably on more aggregate categories which are typically used in studies of transportation and land use. Although the estimations are by no means perfect, they offer a good baseline model considering the data is free to obtain and easy to process.

[en] We propose a new kind of transit-time interaction in which the reversal (or any localized transition) in the phase velocity of a wave within a wavelength of an antenna results in a high rate of work done by the wave (1/2 Re(j·E*)) near the antenna for conditions where the wave phase velocity is greater than a few times the thermal speed. This enhanced rate of work near the antenna can significantly exceed the far-field value due to Landau damping. For the conditions of typical low-field (< 0.01 T) and low-density (<10¹⁸m^-3) helicon wave-driven plasma sources, where the phase velocity parallel to the magnetic field can be a few times the thermal speed of electrons, it has been demonstrated that this spatial transient overshoot in the rate of work done by the wave is the dominant kinetic energy coupling process to electrons). In this paper it is demonstrated that, within a half wavelength of the antenna, it is the high-energy electrons that gain energy from both the wave and low velocity electrons as a result of this process. An important practical consequence is that the ionization rate of neutral gas can be significantly enhanced above the Maxwellian rate. The phenomenon is not restricted to helicon sources. This process may also explain the production of high-energy electrons in the near fields of antennas used in fusion plasma heating by radiofrequency waves. (author)

[en] Black hole X-ray binaries in the quiescent state (Eddington ratios typically ≲10⁻⁵) display softer X-ray spectra (photon indices Γ ∼ 2) compared to higher-luminosity black hole X-ray binaries in the hard state (Γ ∼ 1.7). However, the cause of this softening and its implications for the underlying accretion flow are still uncertain. Here, we present quasi-simultaneous X-ray and radio spectral monitoring of the black hole X-ray binary MAXI J1820+070 during the decay of its 2018 outburst and of a subsequent reflare in 2019, providing an opportunity to monitor a black hole X-ray binary as it actively transitions into quiescence. We probe 1–10 keV X-ray luminosities as low as L _X ∼ 4 × 10³² erg s⁻¹, equivalent to Eddington fractions of ∼4 × 10⁻⁷. During its decay toward quiescence, the X-ray spectrum of MAXI J1820+070 softens from Γ ∼ 1.7 to Γ ∼ 2, with the softening taking ∼30 days and completing at L _X ≈ 10³⁴ erg s⁻¹ (≈10⁻⁵ L _Edd). While the X-ray spectrum softens, the radio spectrum generally remains flat or inverted throughout the decay. We also find that MAXI J1820+070 follows a radio (L _R)–X-ray luminosity correlation of the form L _R ∝ L _X ^0.52±0.07, making it the fourth black hole system to follow the so-called “standard track” unbroken over several (in this case, four) decades in L _X. Comparing the radio/X-ray spectral evolution(s) with the L _R–L _X plane, we find that the X-ray softening is consistent with X-rays produced by Comptonization processes in a radiatively inefficient accretion flow. We generally disfavor X-ray emission originating solely from within the jet, with the possible exception of X-rays produced via synchrotron self-Compton processes.

[en] The candidate black hole X-ray binary Swift J1753.5−0127 faded to quiescence in 2016 November after a prolonged outburst that was discovered in 2005. Nearly three months later, the system displayed renewed activity that lasted through 2017 July. Here, we present radio and X-ray monitoring over $\approx <!--\; ???\; -->3$ months of the renewed activity to study the coupling between the jet and the inner regions of the disk/jet system. Our observations cover low X-ray luminosities that have not historically been well-sampled ($L_{\mathrm{X}}\approx <!--\; ???\; -->2\times <!--\; ??\; -->{10}^{33}\text{--}{10}^{36}\mathrm{e}\mathrm{r}\mathrm{g}{\mathrm{s}}^{-<!--\; ???\; -->1};$ 1–10 keV), including time periods when the system was both brightening and fading. At these low luminosities, Swift J1753.5−0127 occupies a parameter space in the radio/X-ray luminosity plane that is comparable to “canonical” systems (e.g., GX 339−4), regardless of whether the system was brightening or fading, even though during its ≳11 year outburst, Swift J1753.5−0127 emitted less radio emission from its jet than expected. We discuss implications for the existence of a single radio/X-ray luminosity correlation for black hole X-ray binaries at the lowest luminosities ($L_{\mathrm{X}}\lesssim <!--\; ???\; -->{10}^{35}\mathrm{e}\mathrm{r}\mathrm{g}{\mathrm{s}}^{-<!--\; ???\; -->1}$), and we compare to supermassive black holes. Our campaign includes the lowest luminosity quasi-simultaneous radio/X-ray detection to date for a black hole X-ray binary during its rise out of quiescence, thanks to early notification from optical monitoring combined with fast responses from sensitive multiwavelength facilities.