Experimental comparison of serpentine and parallel-tubes flat plate collectors for different flow rates

Comparación experimental del comportamiento térmico de dos captadores solares térmicos, uno serpentín y otro parrilla. In the paper, two flat plate solar collectors were simultaneously tested in a side-by-side facility at the UMA, following the steady-state procedure proposed by the EN12975-2:2006 standard. Both collectors have been manufactured at the same date by the same company and belong to the same product range. To demonstrate the relationship between the thermal performance of each collector and the mass flow rate, both collectors were tested for a total of seven flows, which covered all the technically possible flows in a real SDHW installation. Next, the measurement uncertainties were propagated and the different performance curves for each test were obtained, which allowed to have the three characteristic curve coefficients that are usually used to compare different collectors in terms of their operation (collector efficiency and linear and quadratic heat losses coefficients). The paper analyses the suitability of each type of absorber plate configuration and the influence of the mass flow rate. The paper recommends a type of collector depending on their working conditions.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Discovery of a Faint Companion to Alcor Using MMT/AO 5 μ\mum Imaging

We report the detection of a faint stellar companion to the famous nearby A5V star Alcor (80 UMa). The companion has M-band ($\lambda$ = 4.8 $\mu$m) magnitude 8.8 and projected separation 1".11 (28 AU) from Alcor. The companion is most likely a low-mass ($\sim$0.3 \msun) active star which is responsible for Alcor's X-ray emission detected by ROSAT (L$_{\rm X}$ $\simeq$ 10$^{28.3}$ erg/s). Alcor is a nuclear member of the Ursa Major star cluster (UMa; d $\simeq$ 25 pc, age $\simeq$ 0.5 Gyr), and has been occasionally mentioned as a possible distant (709") companion of the stellar quadruple Mizar ($\zeta$ UMa). Comparing the revised Hipparcos proper motion for Alcor with the mean motion for other UMa nuclear members shows that Alcor has a peculiar velocity of 1.1 km/s, which is comparable to the predicted velocity amplitude induced by the newly-discovered companion ($\sim$1 km/s). Using a precise dynamical parallax for Mizar and the revised Hipparcos parallax for Alcor, we find that Mizar and Alcor are physically separated by 0.36 $\pm$ 0.19 pc (74 $\pm$ 39 kAU; minimum 18 kAU), and their velocity vectors are marginally consistent ($\chi^2$ probability 6%). Given their close proximity and concordant motions we suggest that the Mizar quadruple and the Alcor binary be together considered the 2nd closest stellar sextuplet. The addition of Mizar-Alcor to the census of stellar multiples with six or more components effectively doubles the local density of such systems within the local volume (d $<$ 40 pc).Comment: 28 pages, 2 figures, AJ, in press; emulateapj short version at http://www.pas.rochester.edu/~emamajek/alcor.pd

What health care for undocumented migrants in Belgium?

n/

Novas tendências em marketing por causa do auge da Internet

The use of Internet has changed considerably the marketing practice. In this article the authors carry on a literature review to analyse the factors involved in the process and also the advantages, challenges and opportunities of this technology from a marketing perspective.El uso de Internet ha traído cambios considerables para la práctica del Marketing. Este artículo lleva a cabo una revisión bibliográfica donde se analizan los factores que están relacionados con el proceso de cambio así como las ventajas, desafíos y oportunidades que ofrece esta nueva tecnología desde una perspectiva del Marketing.O uso da Internet trouxe mudanças consideráveis para a prática do Marketing. Este artigo realiza uma revisão bibliográfica onde se analisam os fatores que estão relacionados com o processo de mudança assim como as vantagens, desafios e oportunidades oferecidas por esta nova tecnologia a partir de uma perspectiva de Marketing

Power to the people: end-user building of digital library collections

Naturally, digital library systems focus principally on the reader: th e consumer of the material that constitutes the library. In contrast, this paper describes an interface that makes it easy for people to build their own library collections. Collections may be built and served locally from the user's own web server, or (given appropriate permissions) remotely on a shared digital library host. End users can easily build new collections styled after existing ones from material on the Web or from their local files-or both, and collections can be updated and new ones brought on-line at any time. The interface, which is intended for non-professional end users, is modeled after widely used commercial software installation packages. Lest one quail at the prospect of end users building their own collections on a shared system, we also describe an interface for the administrative user who is responsible for maintaining a digital library installation