Origins of Solar System Dust Beyond Jupiter

The measurements of cosmic interplanetary dust by the instruments on board the Pioneer 10 and 11 spacecraft contain the dynamical signature of dust generated by Edgeworth-Kuiper Belt objects, as well as short period Oort Cloud comets and short period Jupiter family comets. While the dust concentration detected between Jupiter and Saturn is mainly due to the cometary components, the dust outside Saturn's orbit is dominated by grains originating from the Edgeworth-Kuiper Belt. In order to sustain a dust concentration that accounts for the Pioneer measurements, short period external Jupiter family comets, on orbits similar to comet 29P/Schwassmann-Wachmann-1, have to produce $8\times 10^4:{\rm g}:{\rm s}^{-1}$ of dust grains with sizes between 0.01 and $6:{\rm mm}$. A sustained production rate of $3\times 10^5:{\rm g}:{\rm s}^{-1}$ has to be provided by short period Oort cloud comets on 1P/Halley-like orbits. The comets can not, however, account for the dust flux measured outside Saturn's orbit. The measurements there can only be explained by a generation of dust grains in the Edgeworth-Kuiper belt by mutual collisions of the source objects and by impacts of interstellar dust grains onto the objects' surfaces. These processes have to release in total $5\times 10^7:{\rm g}:{\rm s}^{-1}$ of dust from the Edgeworth Kuiper belt objects in order to account for the amount of dust found by Pioneer beyond Saturn, making the Edgeworth-Kuiper disk the brightest extended feature of the Solar System when observed from afar

The Speed and Orientation of the Parsec-Scale Jet in 3C 279

We have calculated inverse-Compton Doppler factors for 3C 279 using the collection of VLBI data recently published by us, and the collection of multiwavelength spectra recently published by Hartman et al. From the Doppler factor and superluminal apparent speed, we then calculate the Lorentz factor and angle to the line-of-sight of the parsec-scale relativistic jet. We model the jet components as homogeneous spheres and the VLBI core as an unresolved inhomogeneous conical jet. The conical-jet model can be made to match both the observed X-ray emission and the VLBI properties of the core with a suitable choice of Doppler factor, implying the core makes a significant contribution to the X-ray emission. The parameters of the conical models indicate the jet is particle dominated at the radii that produce significant emission, and is not in equipartition. At the inner radius of the conical jet the magnetic field is of order 0.1 G and the relativistic-particle number density is of order 10 cm^{-3}. When all components are included in the calculation, then on average the core produces about half of the X-rays, with the other half being split between the long-lived component C4 and the brightest inner-jet component. We calculate an average speed and angle to the line-of-sight for the region of the jet interior to 1 mas of v=0.992c (gamma=8) and 4 degrees, and an average speed and angle to the line-of-sight for C4 (at a distance from the core of 3 mas) of v=0.997c (gamma=13) and 2 degrees. These values imply average Doppler factors of delta=12 for the inner jet, and delta=21 for C4

Kinematics of the Parsec-Scale Relativistic Jet in Quasar 3C 279: 1991-1997

We present results of long-term high-frequency VLBI monitoring of the relativistic jet in 3C 279, consisting of 18 epochs at 22 GHz from 1991 to 1997 and 10 epochs at 43 GHz from 1995 to 1997. Three major results of this study are apparent speeds measured for six superluminal components range from 4.8c to 7.5c (H0=70 km s-1Mpc-1, q0=0.1), variations in the total radio flux are due primarily to changes in the VLBI core flux, and the uniform-sphere brightness temperature of the VLBI core is ~1×1013 K at 22 GHz after 1995, one of the highest direct estimates of a brightness temperature. If the variability brightness temperature measured for 3C 279 by Lähteenmäki & Valtaoja is an actual value and not a lower limit, then the rest-frame brightness temperature of 3C 279 is quite high and limited by inverse Compton effects rather than equipartition. The parsec-scale morphology of 3C 279 consists of a bright, compact VLBI core, a jet component (C4) that moved from ~2 to ~3.5 mas from the core during the course of our monitoring, and an inner jet that extends from the core to a stationary component, C5, at ~1 mas from the core. Component C4 followed a curved path, and we reconstruct its three-dimensional trajectory using polynomial fits to its position versus time. Component C5 faded with time, possibly due to a previous interaction with C4 similar to interactions seen in simulations by Gómez et al. Components in the inner jet are relatively short lived and fade by the time they reach ~1 mas from the core. The components have different speeds and position angles from each other, but these differences do not match the differences predicted by the precession model of Abraham & Carrara. Although VLBI components were born about six months prior to each of the two observed γ-ray high states, the sparseness of the γ-ray data prevents a statistical analysis of possible correlations

Structure of the Edgeworth-Kuiper Belt (EKB) Dust Disk and Implications for Extrasolar Planet(s) epsilon Eridani

Numerical simulations of the orbital evolution of dust particles from Edgeworth-Kuiper Belt (EKB) objects show that the three giant planets, Neptune, Jupiter, and Saturn impose distinct and dramatic signatures on the overall distribution of EKB dust particles. The features are very similar to those observed in the dust disk around the nearby star Eridani. Numerical simulations of dust particles in the epsilon Eridani system show that planetary perturbations may be responsible for the observed feature

Charge-induced conformational changes of dendrimers

We study the effect of chargeable monomers on the conformation of dendrimers of low generation by computer simulations, employing bare Coulomb interactions. The presence of the latter leads to an increase in size of the dendrimer due to a combined effect of electrostatic repulsion and the presence of counterions within the dendrimer, and also enhances a shell-like structure for the monomers of different generations. In the resulting structures the bond-length between monomers, especially near the center, will increase to facilitate a more effective usage of space in the outer-regions of the dendrimer.Comment: 7 pages, 12 figure

Unusual Flaring Activity in the Blazar PKS 1424-418 during 2008-2011

Context. Blazars are a subset of active galactic nuclei (AGN) with jets that are oriented along our line of sight. Variability and spectral energy distribution (SED) studies are crucial tools for understanding the physical processes responsible for observed AGN emission. Aims. We report peculiar behaviour in the bright gamma-ray blazar PKS 1424-418 and use its strong variability to reveal information about the particle acceleration and interactions in the jet. Methods. Correlation analysis of the extensive optical coverage by the ATOM telescope and nearly continuous gamma-ray coverage by the Fermi Large Area Telescope is combined with broadband, time-dependent modeling of the SED incorporating supplemental information from radio and X-ray observations of this blazar. Results. We analyse in detail four bright phases at optical-GeV energies. These flares of PKS 1424-418 show high correlation between these energy ranges, with the exception of one large optical flare that coincides with relatively low gamma-ray activity. Although the optical/gamma-ray behaviour of PKS 1424-418 shows variety, the multiwavelength modeling indicates that these differences can largely be explained by changes in the flux and energy spectrum of the electrons in the jet that are radiating. We find that for all flares the SED is adequately represented by a leptonic model that includes inverse Compton emission from external radiation fields with similar parameters. Conclusions. Detailed studies of individual blazars like PKS 1424-418 during periods of enhanced activity in different wavebands are helping us identify underlying patterns in the physical parameters in this class of AGN.Comment: accepted for publication in A&

Magnetoconductivity of quantum wires with elastic and inelastic scattering

We use a Boltzmann equation to determine the magnetoconductivity of quantum wires. The presence of a confining potential in addition to the magnetic field removes the degeneracy of the Landau levels and allows one to associate a group velocity with each single-particle state. The distribution function describing the occupation of these single-particle states satisfies a Boltzmann equation, which may be solved exactly in the case of impurity scattering. In the case where the electrons scatter against both phonons and impurities we solve numerically - and in certain limits analytically - the integral equation for the distribution function, and determine the conductivity as a function of temperature and magnetic field. The magnetoconductivity exhibits a maximum at a temperature, which depends on the relative strength of the impurity and electron-phonon scattering, and shows oscillations when the Fermi energy or the magnetic field is varied.Comment: 21 pages (revtex 3.0), 5 postscript figures available upon request at [email protected] or [email protected]

On the Location of the Gamma-ray Emission in the 2008 Outburst in the BL Lacertae Object AO 0235+164 through Observations across the Electromagnetic Spectrum

We present observations of a major outburst at centimeter, millimeter, optical, X-ray, and gamma-ray wavelengths of the BL Lacertae object AO 0235+164. We analyze the timing of multi-waveband variations in the flux and linear polarization, as well as changes in Very Long Baseline Array (VLBA) images at 7mm with 0.15 milliarcsecond resolution. The association of the events at different wavebands is confirmed at high statistical significance by probability arguments and Monte-Carlo simulations. A series of sharp peaks in optical linear polarization, as well as a pronounced maximum in the 7 mm polarization of a superluminal jet knot, indicate rapid fluctuations in the degree of ordering of the magnetic field. These results lead us to conclude that the outburst occurred in the jet both in the quasi-stationary "core" and in the superluminal knot, both parsecs downstream of the supermassive black hole. We interpret the outburst as a consequence of the propagation of a disturbance, elongated along the line of sight by light-travel time delays, that passes through a standing recollimation shock in the core and propagates down the jet to create the superluminal knot. The multi-wavelength light curves vary together on long time-scales (months/years), but the correspondence is poorer on shorter time-scales. This, as well as the variability of the polarization and the dual location of the outburst, agrees with the expectations of a multi-zone emission model in which turbulence plays a major role in modulating the synchrotron and inverse Compton fluxes.Comment: Accepted for Publication in the Astrophysical Journal Letters. 7 pages (including 5 figures). Minor corrections with regard to previous version, as proposed by the refere

Internet of things

Manual of Digital Earth / Editors: Huadong Guo, Michael F. Goodchild, Alessandro Annoni .- Springer, 2020 .- ISBN: 978-981-32-9915-3Digital Earth was born with the aim of replicating the real world within the digital world. Many efforts have been made to observe and sense the Earth, both from space (remote sensing) and by using in situ sensors. Focusing on the latter, advances in Digital Earth have established vital bridges to exploit these sensors and their networks by taking location as a key element. The current era of connectivity envisions that everything is connected to everything. The concept of the Internet of Things(IoT)emergedasaholisticproposaltoenableanecosystemofvaried,heterogeneous networked objects and devices to speak to and interact with each other. To make the IoT ecosystem a reality, it is necessary to understand the electronic components, communication protocols, real-time analysis techniques, and the location of the objects and devices. The IoT ecosystem and the Digital Earth (DE) jointly form interrelated infrastructures for addressing today’s pressing issues and complex challenges. In this chapter, we explore the synergies and frictions in establishing an efficient and permanent collaboration between the two infrastructures, in order to adequately address multidisciplinary and increasingly complex real-world problems. Although there are still some pending issues, the identified synergies generate optimism for a true collaboration between the Internet of Things and the Digital Earth