WMAP extragalactic point sources as potential Space VLBI calibrators

The point source list of the Wilkinson Microwave Anisotropy Probe (WMAP) is a uniform, all-sky catalogue of bright sources with flux density measurements at high (up to 94 GHz) radio frequencies. We investigated the five-year WMAP list to compile a new catalogue of bright and compact extragalactic radio sources to be potentially studied with Very Long Baseline Interferometry at millimeter wavelengths (mm-VLBI) and Space VLBI (SVLBI). After comparing the WMAP data with the existing mm-VLBI catalogues, we sorted out the yet unexplored sources. Using the 41, 61 and 94 GHz WMAP flux densities, we calculated the spectral indices. By collecting optical identifications, lower-frequency radio flux densities and VLBI images from the literature, we created a list of objects which have not been investigated with VLBI at 86 GHz before. With total flux density at least 1 Jy and declination above -40 degree, we found 37 suitable new targets. It is a nearly 25% addition to the known mm-VLBI sources. Such objects are also potentially useful as phase-reference calibrators for the future Japanese SVLBI mission ASTRO-G at its highest observing frequency (43 GHz). The phase-referencing capability of ASTRO-G would allow long integrations and hence better sensitivity for observing faint target sources close to suitable phase calibrators in the sky

The role of neutral hydrogen in the life of galaxies and AGN:A spectral stacking analysis

Neutraal waterstofgas (HI) wordt verondersteld een belangrijke rol te spelen in de evolutie van sterrenstelsels, aangezien HI het eerste gas verschaft waaruit de eerste sterren vormen. Verder wordt HI verondersteld deels verantwoordelijk te zijn voor het in gang zetten van een van de meeste energetische fenomenen in het Universum, het voeden van superzware zwart gaten, d.w.z. actieve galactische kernen (engels: active galactic nuclei, AGN) In dit proefschrift onderzoeken we de eigenschappen van HI van honderden sterrenstelsel om een beter begrip van de rol van HI in de evolutie van sterrenstelsels te krijgen over de afgelopen 1,5 miljard jaar. Ook kijken we naar de gas eigenschappen van aangroeiende superzware zwart gaten om het samenspel te onderzoeken tussen AGN activiteit en het omliggende gas. Met waarnemingen genomen m.b.v. de Westerbork Synthese Radio Telescoop (WSRT), voeren we een spectraal opstapel analyse uit van het HI. Spectraal opstapelen is de procedure van bij elkaar optellen van spectra van individuele sterrenstelsels met het doel om het gemiddelde HI signaal te herkrijgen. Deze methode is bijzonder nuttig om de gevoeligheid van individuele niet-gedetecteerde bronnen te verhogen, niet alleen in het nabije universum, maar ook op grote afstanden waarbij de flux die uitgestraald wordt door individuele bronnen onder gevoeligheid ligt van huidige radio telescopen. We vinden dat het aanwezigheid van HI gecorreleerd is met de stervormingsgeschiedenis. In sterrenstelsels waar koud gas (HI) aanwezig is, zijn condities gunstig om (overgebleven) stervorming waar te kunnen nemen. Bovendien, sterrenstelsels met meer gas hebben een hogere stervormingssnelheid. Jonge AGN's zijn rijk in niet gevestigd HI gas, wat de hypothese ondersteunt dat nucleaire activiteit in radiosterrenstelsels in gang wordt gezet door het voeden met koud gas. Bovendien, het waarnemen van HI in gereactiveerde AGN's, suggereert een verband tussen neutraal waterstofgas en de verjonging van de nucleaire activiteit. Wanneer het de gas aangroei periodiek is in radiosterrenstelsels, vinden we aanwijzingen dat dit een effect een afdruk achterlaat op de AGN activiteit en de stervormingsgeschiedenis

The peculiar radio galaxy 4C 35.06: a case for recurrent AGN activity?

Using observations obtained with the LOw Fequency ARray (LOFAR), the Westerbork Synthesis Radio Telescope (WSRT) and archival Very Large Array (VLA) data, we have traced the radio emission to large scales in the complex source 4C 35.06 located in the core of the galaxy cluster Abell 407. At higher spatial resolution (~ 4″), the source was known to have two inner radio lobes spanning 31 kpc and a diffuse, low-brightness extension running parallel to them, offset by about 11 kpc (in projection). At 62 MHz, we detect the radio emission of this structure extending out to 210 kpc. At 1.4 GHz and intermediate spatial resolution (~ 30″), the structure appears to have a helical morphology. We have derived the characteristics of the radio spectral index across the source. We show that the source morphology is most likely the result of at least two episodes of AGN activity separated by a dormant period of around 35 Myr. The outermost regions of radio emission have a steep spectral index (α-1), similar to what is found in other clusters. The derived column density is NHI ~ 4 × 1020 cm-2 for a Tspin = 100 K. This detection supports the connection – already suggested for other restarted radio sources – between the presence of cold gas and restarting activity. The cold gas appears to be dominated by a blue-shifted component although the broad H I profile could also include gas with different kinematics. Understanding the duty cycle of the radio emission as well as the triggering mechanism for starting (or restarting) the radio-loud activity can provide important constraints to quantify the impact of AGN feedback on galaxy evolution. The study of these mechanisms at low frequencies using morphological and spectral information promises to bring new important insights in this field

Attract, promote and retain women in the IT industry : A study on the women's network Geek Girl Meetup

The aim of this study is to examine the conditions for participation in women's networks for the members of the Geek Girl Meetup network, to expose the members' perceptions of the IT industry and to highlight the network's impact on women's situation in the IT industry. The empirical material consists of interviews and a survey. The interviews were carried out with the network leaders for a better understanding of the network structure and why it exists. The survey completed by the members illuminates how the members perceive the networks function in the IT industry and what kind of an impact the network has on the members and if it has any at all. The result of the study shows that participation in networks like Geek Girl Meetup can be a model for promoting gender equality and improving conditions for women in the IT industry. However, the study does not clearly show whether being a member of the Geek Girl Meetup network has any effect on other women to start training or career in IT, or that this would promote a certain influx of women into IT-related occupations. The essay concludes that a direct impact of the women's network Geek Girl Meetup on IT industry can not be verified but it has a positive impact on the member

Private Computations Over the Integers

The subject of this work is the possibility of private distributed computations of n- argument functions defined over the integers. A function f is t-private if there exists a protocol for computing f , so that no coalition of at most t participants can infer any additional information from the execution of the protocol. It is known that over finite domains, every function can be computed b(n \Gamma 1)=2c-privately. Some functions, like addition, are even n-private. We prove that this result cannot be extended to infinite domains. The possibility of privately computing f is shown to be closely related to the communication complexity of f . Using this relation, we show, for example, that n-argument addition is b(n \Gamma 1)=2c-private over the non-negative integers, but not even 1-private over all the integers. Finally, a complete characterization of t-private Boolean functions over countable domains is given. A Boolean function is 1-private if and only if its communication complexit..

HI absorption in flux-selected radio AGNs

VizieR online Data Catalogue associated with article published in journal Astronomy & Astrophysics with title 'The HI absorption "Zoo".' (bibcode: 2015A&A...575A..44G

Towards Integrated Flexible Energy Harvester and Supercapacitor for Self-powered Wearable Sensors

We present the first results of a flexible energy harvester and a foldable supercapacitor to power wearable and flexible sensors. The flexible energy harvester is fabricated by using 38 mu m piezoelectric polyvinylidene difluoride (PVDF) sandwiched between carbon electrodes. Both the design and process excel in simplicity and cost-effectiveness. The flexible harvester demonstrates a power output of 2.6 mu W cm(-3) at a resonant frequency of 50 Hz with a 3dB bandwidth of about 11 Hz, which is higher than devices previously reported and similar to a commercial PZT harvester film of same size. A flexible energy storage supercapacitor (GP-SC) was fabricated using a graphite/VACNTs (vertically aligned carbon nanotubes) material as electrodes. A prototype GP-SCs has an areal capacitance of about 1.2 mF cm(-2). Finally, an integrated scheme is proposed for future work