70 research outputs found
A Multi-Analytical study of Rock Paintings from Leandro 5 Megalithic Barrow, North-Weastern Portugal
The colourant composition of a northern Portugal megalithic barrow decorated with âsolarâ motifs was studied using a multi-analytical approach, allowing the characterisa- tion of the painting techniques, pigments and binders. The red pigment was prepared with iron oxide minerals, using vegetal oils as organic additives, while the black pigment was char- coal without any organic additives or binders. The solar motif was first drawn with charcoal and subsequently painted with a red pigment.The work was supported by UID/QUI/50006/2019 with
funding from FCT/MCTES through national funds. CĂ©sar
Oliveira acknowledges Instituto de CiĂȘncias e Tecnologias
AgrĂĄrias e Agro-Alimentares, Porto (ICETA), for his contract
under project NORTE-01-0145-FEDER-000011. This work
was also developed under the project âFunerary and ceremonial practices between the Neolithic and the Bronze Age approached by archaeometryâ (ARQUEOM/Project-Sept2014)
Interferometric inverse synthetic aperture radar experiment using an interferometric linear frequency modulated continuous wave millimetre-wave radar
D. Felguera-MartĂn,1 J.-T. GonzĂĄlez-Partida,1 P. Almorox-GonzĂĄlez,1 M. Burgos-GarcĂa,1 and B.-P. Dorta-Naranjo2
1Universidad Politécnica de Madrid, Ciudad Universitaria s/n, Grupo de Microondas y Radar. Departamento de Señales, Sistemas y Radiocomunicaciones, Madrid, Spain
2Universidad de Las Palmas de Gran Canaria, Departamento de Señales y Comunicaciones, Las Palmas de Gran Canaria, Spain
An interferometric linear frequency modulated continuous wave (LFMCW) millimetre-wave radar is presented, along with the results of an experiment conducted to study the feasibility of using it in a future millimetre-wave interferometric inverse synthetic aperture radar (InISAR) system. First, a description of the radar is given. Then, the signal processing chain is described, with special attention to the phase unwrapping technique. The interferometric phase is obtained by unwrapping the prominent target's phase in each antenna using a sliding frame processing technique. Cell migration issues in this method are also addressed. Simulations were carried out to illustrate and assess the processing chain and to show the effects of multipath echoes on the height measurement. In the real experiment, the range, speed and height of a moving target were tracked over consecutive inverse synthetic aperture radar (ISAR) image frames, verifying the performance of the whole system
Decay of solutions to the Maxwell equation on the Schwarzschild background
A new Morawetz or integrated local energy decay estimate for Maxwell test
fields on the exterior of a Schwarzschild black hole spacetime is proved. The
proof makes use of a new superenergy tensor defined in terms of the
Maxwell field and its first derivatives. The superenergy tensor, although not
conserved, yields a conserved higher order energy current . The tensor vanishes for the static Coulomb field, and
the Morawetz estimate proved here therefore yields integrated decay for the
Maxwell field to the Coulomb solution on the Schwarzschild exterior.Comment: 15 pages, updated reference
Planck intermediate results. VIII. Filaments between interacting clusters
About half of the baryons of the Universe are expected to be in the form of
filaments of hot and low density intergalactic medium. Most of these baryons
remain undetected even by the most advanced X-ray observatories which are
limited in sensitivity to the diffuse low density medium. The Planck satellite
has provided hundreds of detections of the hot gas in clusters of galaxies via
the thermal Sunyaev-Zel'dovich (tSZ) effect and is an ideal instrument for
studying extended low density media through the tSZ effect. In this paper we
use the Planck data to search for signatures of a fraction of these missing
baryons between pairs of galaxy clusters. Cluster pairs are good candidates for
searching for the hotter and denser phase of the intergalactic medium (which is
more easily observed through the SZ effect). Using an X-ray catalogue of
clusters and the Planck data, we select physical pairs of clusters as
candidates. Using the Planck data we construct a local map of the tSZ effect
centered on each pair of galaxy clusters. ROSAT data is used to construct X-ray
maps of these pairs. After having modelled and subtracted the tSZ effect and
X-ray emission for each cluster in the pair we study the residuals on both the
SZ and X-ray maps. For the merging cluster pair A399-A401 we observe a
significant tSZ effect signal in the intercluster region beyond the virial
radii of the clusters. A joint X-ray SZ analysis allows us to constrain the
temperature and density of this intercluster medium. We obtain a temperature of
kT = 7.1 +- 0.9, keV (consistent with previous estimates) and a baryon density
of (3.7 +- 0.2)x10^-4, cm^-3. The Planck satellite mission has provided the
first SZ detection of the hot and diffuse intercluster gas.Comment: Accepted by A&
Mechanisms and Kinetics for Sorption of CO2 on Bicontinuous Mesoporous Silica Modified with n-Propylamine
We studied equilibrium adsorption and uptake kinetics and identified molecular species that formed during sorption of carbon dioxide on amine-modified silica. Bicontinuous silicas (AMS-6 and MCM-48) were postsynthetically modified with (3-aminopropyl)triethoxysilane or (3-aminopropyl)methyldiethoxysilane, and amine-modified AMS-6 adsorbed more CO(2) than did amine-modified MCM-48. By in situ FTIR spectroscopy, we showed that the amine groups reacted with CO(2) and formed ammonium carbamate ion pairs as well as carbamic acids under both dry and moist conditions. The carbamic acid was stabilized by hydrogen bonds, and ammonium carbamate ion pairs formed preferably on sorbents with high densities of amine groups. Under dry conditions, silylpropylcarbamate formed, slowly, by condensing carbamic acid and silanol groups. The ratio of ammonium carbamate ion pairs to silylpropylcarbamate was higher for samples with high amine contents than samples with low amine contents. Bicarbonates or carbonates did not form under dry or moist conditions. The uptake of CO(2) was enhanced in the presence of water, which was rationalized by the observed release of additional amine groups under these conditions and related formation of ammonium carbamate ion pairs. Distinct evidence for a fourth and irreversibly formed moiety was observed under sorption of CO(2) under dry conditions. Significant amounts of physisorbed, linear CO(2) were detected at relatively high partial pressures of CO(2), such that they could adsorb only after the reactive amine groups were consumed.authorCount :7</p
Planck early results III : First assessment of the Low Frequency Instrument in-flight performance
Peer reviewe
Planck early results XVII : Origin of the submillimetre excess dust emission in the Magellanic Clouds
Peer reviewe
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