Temperature uniformity in cross-flow double-layered microchannel heat sinks

An in-house finite element method (FEM) procedure is used to carry out a numerical study on the thermal behavior of cross-flow double-layered microchannel heat sinks with an unequal number of microchannels in the two layers. The thermal performance is compared with those yielded by other more conventional flow configurations. It is shown that if properly designed, i.e., with several microchannels in the top layer smaller than that in the bottom layer, cross-flow double-layered microchannel heat sinks can provide an acceptable thermal resistance and a reasonably good temperature uniformity of the heated base with a header design that is much simpler than that required by the counter-flow arrangement

Numerical analysis of the thermal energy storage in cellular structures filled with phase-change material

This paper reports the results of a numerical study on the thermal performance of metal cellular structures that can be obtained by additive manufacturing (selective laser melting) when they are impregnated with phase change material (PCM) for possible applications in electronic cooling. Two body-centered cubic (BCC) periodic structures with cell sizes of 5 mm and 10 mm and a porosity of 87%, made of two solid materials (aluminum alloy and copper), and two paraffins with characteristic melting temperatures of 55 and 64 °C were considered. The numerical simulations are carried out using the commercial code ANSYS Fluent and are based on a previously validated purely conductive heat transfer model. The computational domains include just small repetitive portions of the considered composite structures, thus allowing substantial savings of computational time. Computed results show that, with both paraffins, the copper made finer BCC structure (5 mm) yields the best thermal performances, i.e, the shortest PCM melting time and the highest rate of thermal energy storage during transients

A framework to evaluate the effects of organizational resilience on service quality

Disruptions and unexpected turbulences characterize the contemporary service industry and pose greater criticalities to organizations that have concerns about both their survival and their business sustainability. The answer to this challenge is to design an organizational system aimed at enhancing so-called organizational resilience. The aim of this work is to present and test an assessment methodology based on a framework that links key static and dynamic characteristics of firms as resilient systems and relates these characteristics with service quality preservation after disruptions. The framework adopts a set of indicators, namely resilience dimensions, to comprehend the real effects of resilience characteristics with service quality dimensions. Through the analysis of a real case, we provided evidence of how the model can be applied in a backward perspective to understand fault modes of specific events. Results show how inadequacies in terms of resilience characteristics determine losses of service quality, and also how the model can be used as a predictive tool to determine in which area companies should intervene in order to improve resilience and service quality

Experimental and numerical analysis of the thermal performance of PCM-impregnated reticular structures obtained by additive manufacturing

This paper proposes a combined experimental and numerical analysis of the melting of three different paraffin waxes embedded in reticular structures fabricated by additive manufacturing. The parent material of the reticular structures is AlSi10Mg. Metal structures, having a 100 mm square base and a thickness of 20 mm, were printed between two 10 mm thick plates. Samples were positioned in an upright position and laterally heated applying different heat fluxes. Three different paraffins were tested, with different characteristic melting temperatures (42 °C, 55 °C, and 64 °C), which are suitable for electronics cooling applications. Four different structures were tested, having a cell length of 5 mm and 10 mm, and porosities of 0.87 and 0.93. Besides the experimental tests, numerical simulations of the melting phenomenon were carried out using a purely conductive model implemented in ANSYS Fluent. The discretized numerical domains represented just small repetitive portions of the test modules, thus allowing substantial computational time savings. This simplified method has been proven to yield results that are in good agreement with the experimental data. The main outcome of this work is the setup of the simplified numerical procedure, which was then validated and used to investigate the effectiveness of the considered structures in diffusing heat into the low thermal conductivity phase change materials. It was concluded that the best overall thermal performance can be obtained with low porosity and low cell size since this enables faster melting processes and better surface temperature control

CLASH-VLT: Strangulation of cluster galaxies in MACSJ0416.1-2403 as seen from their chemical enrichment

(abridged) We explore the Frontier Fields cluster MACS J0416.1-2403 at z=0.3972 with VIMOS/VLT spectroscopy from the CLASH-VLT survey covering a region which corresponds to almost three virial radii. We measure fluxes of 5 emission lines of 76 cluster members enabling us to unambiguously derive O/H gas metallicities, and also SFRs from Halpha. For intermediate massses we find a similar distribution of cluster and field galaxies in the MZR and mass vs. sSFR diagrams. Bulge-dominated cluster galaxies have on average lower sSFRs and higher O/Hs compared to their disk-dominated counterparts. We use the location of galaxies in the projected velocity vs. position phase-space to separate our cluster sample into a region of objects accreted longer time ago and a region of recently accreted and infalling galaxies. We find a higher fraction of accreted metal-rich galaxies (63%) compared to the fraction of 28% of metal-rich galaxies in the infalling regions. Intermediate mass galaxies falling into the cluster for the first time are found to be in agreement with predictions of the fundamental metallicity relation. In contrast, for already accreted star-forming galaxies of similar masses, we find on average metallicities higher than predicted by the models. This trend is intensified for accreted cluster galaxies of the lowest mass bin, that display metallicities 2-3 times higher than predicted by models with primordial gas inflow. Environmental effects therefore strongly influence gas regulations and control gas metallicities of log(M/Msun)<10.2 (Salpeter IMF) cluster galaxies. We also investigate chemical evolutionary paths of model galaxies with and without inflow of gas showing that strangulation is needed to explain the higher metallicities of accreted cluster galaxies. Our results favor a strangulation scenario in which gas inflow stops for log(M/Msun)<10.2 galaxies when accreted by the cluster.Comment: Version better matched to the published version, including table with observed and derived quantities for the 76 cluster galaxie

Water resource management through systemic approach: The case of Lake Bracciano

Today natural water resources are becoming scarce, both due to global climate change but also due to irresponsible behaviour of human beings. Lakes are among the most delicate aquatic systems due to their limited size. The objective of this paper is to propose a System Dynamics model, employed in a real case study regarding the city of Rome and one of its water reserves, the Bracciano Lake, for the evaluation of different strategies and policies to reduce environmental impacts, considering different climatic and context scenarios. The results indicate that, as the system is currently exposed to a high risk of ecological disaster, the situation might worsen, and the disaster effectively happen. Simulation models may help agencies and administrations to explore policies and find solutions to address this fundamental problem, that may become even worst over the next years, given the potential severe consequences deriving from the current global warming trends

ESO Imaging Survey VII. Distant Cluster Candidates over 12 square degrees

In this paper the list of candidate clusters identified from the I-band data of the ESO Imaging Survey (EIS) is completed using the images obtained over a total area of about 12 square degrees. Together with the data reported earlier the total I-band coverage of EIS is 17 square degrees, which has yielded a sample of 252 cluster candidates in the redshift range 0.2 \lsim z \lsim 1.3. This is the largest optically-selected sample currently available in the Southern Hemisphere. It is also well distributed in the sky thus providing targets for a variety of VLT programs nearly year round.Comment: 5 pages, 3 figures, submitted to Astronomy & Astrophysic

Discovery of a faint, star-forming, multiply lensed, Lyman-alpha blob

We report the discovery of a multiply lensed Lyman-$\alpha$ blob (LAB) behind the galaxy cluster AS1063 using the Multi Unit Spectroscopic Explorer (MUSE) on the Very Large Telescope (VLT). The background source is at $z=$ 3.117 and is intrinsically faint compared to almost all previously reported LABs. We used our highly precise strong lensing model to reconstruct the source properties, and we find an intrinsic luminosity of $L_{\rm Ly\alpha}$=$1.9\times10^{42}$ erg s$^{-1}$, extending to 33 kpc. We find that the LAB is associated with a group of galaxies, and possibly a protocluster, in agreement with previous studies that find LABs in overdensities. In addition to Lyman-$\alpha$ (Ly$\alpha$) emission, we find \ion{C}{IV}, \ion{He}{II}, and \ion{O}{III}] ultraviolet (UV) emission lines arising from the centre of the nebula. We used the compactness of these lines in combination with the line ratios to conclude that the \Lya nebula is likely powered by embedded star formation. Resonant scattering of the \Lya photons then produces the extended shape of the emission. Thanks to the combined power of MUSE and strong gravitational lensing, we are now able to probe the circumgalatic medium of sub-$L_{*}$ galaxies at $z\approx 3$.Comment: 7 pages, 7 figures; moderate changes to match the accepted A&A versoi