Locative Media and Sociability:Using Location-Based Social Networks to Coordinate Everyday Life

Foursquare was a mobile social networking application that enabled people to share location with friends in the form of “check-ins.” The visualization of surrounding known social connections as well as unknown others has the potential to impact how people coordinate social encounters and forge new social ties. While many studies have explored mobile phones and sociability, there is a lack of empirical research examining location-based social network’s (LSBNs) from a sociability perspective. Drawing on a dataset of original qualitative research with a range of Foursquare users, the paper examines the application in the context of social coordination and sociability in three ways. First, the paper explores if Foursquare is used to organize certain social encounters, and if so, why. Second, the paper examines the visualization of surrounding social connections and whether this leads to “serendipitous encounters.” Lastly, the paper examines whether the use of Foursquare can produce new social relationships

Correlated X-Ray and Millimetre Variability of the Blazar 3C273

The authors present the results of X-ray and millimetre monitoring of the blazar 3C 273 at 1-2 day intervals over the period 12 December 1992 to 24 January 1993. No large flares are seen in this period but variations in both wavebands of ≡30% on few day timescales are apparent. The ROSAT PSPC X-ray spectrum consists of 2 power-law components with the harder component dominating above 0.5 keV. There is very little correlation between the variability of the soft and hard components. The results show that the hard X-ray component cannot be a simple extrapolation of the millimetre/IR synchrotron component but may be explained as a self-Compton component in a shocked jet

Correlated X-ray and millimetre variability of the blazar 3C 273

The authors present the results of X-ray and millimetre monitoring of the blazar 3C 273 at 1-2 day intervals over the period 12 December 1992 to 24 January 1993. No large flares are seen in this period but variations in both wavebands of ≡30% on few day timescales are apparent. The ROSAT PSPC X-ray spectrum consists of 2 power-law components with the harder component dominating above 0.5 keV. There is very little correlation between the variability of the soft and hard components. The results show that the hard X-ray component cannot be a simple extrapolation of the millimetre/IR synchrotron component but may be explained as a self-Compton component in a shocked jet

The spectral shape and variability of the blazar 3C 446

The radio to X-ray spectrum and variability of 3C 446 are discussed, and it is shown that the entire infrared-ultraviolet wavelength region exhibits strongly correlated variations, with the infrared and optical fluxes varying together on a time-scale of weeks or less. The variations in spectral shape which occur in the submillimeter to optical wavelength region are examined; it is proposed that continuous injection or reacceleration of the emitting electrons takes place during the observed flare events, and that the changes in spectral shape reflect the different effects that radiative energy losses have on the energy distribution of the electrons during and after such periods of injection or reacceleration. An overall brightening of the source observed throughout the millimeter to optical wavelength region between late 1968 and late 1983 is attributed to an increase in a slowly varying 'quiescent' emission component

Submillimeter observations of an asymmetric dust disk around Fomalhaut

New submillimeter images of the cold dust emission around the nearby main-sequence star Fomalhaut are presented. Observations at a wavelength of 450 ?m, where the telescope beam size is equivalent to a resolution of 50 AU, reveal that Fomalhaut is encircled by a significantly nonaxisymmetric inclined ring. Smooth axisymmetric models of the ring images suggest the existence of a least one "clump" with an estimated flux of about 5% of the total from the disk, thus implying a clump mass of 0.075 lunar masses. At the resolution of the data, this clump could instead be a ring arc. The most plausible explanation is that this feature is produced by dust trapped in a resonance with a large planet. The observed structures around Fomalhaut and other Vega-excess stars qualitatively resemble features seen in numerical simulations with a gas giant perturber

Millimeter-wave observations of flat spectrum radio sources

Measurements at wavelengths between 0.4 and 2.0 mm of a sample of 26 compact, flat spectrum radio sources are presented. These observations extend the known radio spectra of this class of sources to higher frequencies and show that most of these sources are still flat at short millimeter wavelengths. The spectral shapes are consistent with an inhomogeneous synchrotron model (with some degree of relativistic beaming); however, the lack of concurrent multifrequency data prevents more definite conclusions at this stage

The infrared-millimetre-centimetre flaring behaviour of the quasar 3C 273

Results are presented of an investigation of the IR-cm light curve of 3C 273 for the period 1987-1991, during which several flares were observed. The apparent details of individual flares are shown to be critically dependent on the temporal sampling. Excellent correlation is found between all these wavelengths, but there is a delay between flare onset as sampled in the IR and the emission at longer wavelengths, with a significant difference occurring between 2.0 and 3.3 mm. The emission between IR and 2.0-mm wavelengths is commensurate with a single synchrotron component which is associated with the innermost part of the relativistic jet or the injection region, while the 3.3-13.5-mm wavelength emission probably reflects the evolution of the flaring electron population in the jet and is bound up with optical depth effects. The light curve in shown to be strongly dependent on wavelength, particularly between 3.3 and 8.1 mm for the 1990/1991 events

The relativistic jets of superluminal radio sources at ultra-high resolution [Abstract]

e are engaged in a long-term project to monitor the polarized intensity structure of 15 blazars and blazar-like radio galaxies with the VLBA at 43 GHz and with the JCMT at 230 GHz. The lead author will report on the first phase of this project. In a number of cases, the 230 GHz polarization matches closely that of the 43 GHz core region, although usually with a higher fractional polarization (indicating more localized emission regions), while for others the relationship is not as clear (suggesting physically distinct emission regions). The polarization near the core changes on timescales shorter than our monitoring interval of two months in some of the sources. The cores of the two radio galaxies are not polarized at 43 GHz, but appear to be at 230 GHz, which suggests that Faraday depolarization occurs at the lower frequency. The core of 3C 273 appears not to be significantly polarized at both frequencies. The talk will include movies that show the evolution of the polarized intensity VLBA images alongside the variability of the 230 GHz integrated polarization. This research is supported in part by US National Science Foundation grant AST-9802941

Measurement of Superluminal Motion of Radio-Loud AGNs at 43 GHz with the VLBA [Abstract]

We present the results of bi-monthly VLBA observations at 7mm in 1998-1999 of 15 radio-bright AGNs. These include 5 BL Lac objects (3C~66A, OJ 287, 1803+784, 1823+568, and BL~Lac), 8 quasars (0420-014, 0528+134, 3C~273, 3C~279, PKS~1510-089, 3C~345, CTA~102, and 3C~454.3), and 2 radio galaxies (3C~111 and 3C~120). This is part of a mm-wave polarization monitoring program with the VLBA, JCMT, and (starting in February 1999) Steward Observatory, plus total flux density monitoring at BIMA and OVRO (mm array calibration data). Several of the sources (BL~Lac, 3C~279, PKS~1510-089, and 3C~120) are being monitored weekly or semi-weekly with RXTE. The regular monitoring with high angular resolution allows us to identify components across different epochs with high confidence, and to determine with to high accuracy the extrapolated times of zero separation from the core. We will show the VLBA images and measurements of proper motions. For a number of sources the values of proper motions of components in the jets will be compared with the results of our previous program of VLBA monitoring of \gamma-ray bright blazars at high frequencies in 1994--1997. This research is supported in part by the National Science Foundation through grant AST-9802941. The \gamma-ray blazar VLBA monitoring was supported in part by various NASA guest investigator grants (RXTE and CGRO)