394 research outputs found
Remotely Piloted Aircraft Systems and a Wireless Sensors Network for Radiological Accidents
In critical radiological situations, the real time information that we could get from the disaster area becomes of great importance. However, communication systems could be affected after a radiological accident. The proposed network in this research consists of distributed sensors in charge of collecting radiological data and ground vehicles that are sent to the nuclear plant at the moment of the accident to sense environmental and radiological information. Afterwards, data would be analyzed in the control center. Collected data by sensors and ground vehicles would be delivered to a control center using Remotely Piloted Aircraft Systems (RPAS) as a message carrier. We analyze the pairwise contacts, as well as visiting times, data collection, capacity of the links, size of the transmission window of the sensors, and so forth. All this calculus was made analytically and compared via network simulations
New N-pyrazole, P-phosphine hybrid ligands and their reactivity towards Pd(II): X-ray crystal structures of complexes with [PdCl2(N,P)] core
Two new N-pyrazole, P-phosphine hybrids ligands: 1-[2-(diphenylphosphanyl)methyl]-3,5-dimethylpyrazole (LP1) and 1-[2-(diphenylphosphanyl)propyl]-3,5-dimethylpyrazole (LP3) are presented. The reaction of these two ligands and two other ligands reported in the literature: 1-[2-(diphenylphosphanyl)ethyl]-3,5-dimethylpyrazole (LP2) and 1-[2-(diphenylphosphanyl)ethyl]-3,5-diphenylpyrazole (LP4) with [PdCl2(CH3CN)2] yield [PdCl2(LP)] (LP = LP1 (1), LP2 (2), LP3 (3) and LP4 (4)) complexes. All complexes are fully characterised by analytical and spectroscopic methods and the resolution of the crystal structure of complexes 2 and 3 by single crystal X-ray diffraction is also presented. In these complexes the ligands are coordinated to Pd(II) via Îş2(N,P) forming metallocycles of six (2) and seven (3) members and finish their coordination with two cis-chlorine atoms. Finally, complex 2 is studied in the palladium-catalysed C-C coupling reaction, being active even for aryl chlorides substrates
Astronomical site selection: On the use of satellite data for aerosol content monitoring
The main goal of this work is the analysis of new approaches to the study of
the properties of astronomical sites. In particular, satellite data measuring
aerosols have recently been proposed as a useful technique for site
characterization and searching for new sites to host future very large
telescopes. Nevertheless, these data need to be critically considered and
interpreted in accordance with the spatial resolution and spectroscopic
channels used. In this paper we have explored and retrieved measurements from
satellites with high spatial and temporal resolutions and concentrated on
channels of astronomical interest. The selected datasets are OMI on board the
NASA Aura satellite and MODIS on board the NASA Terra and Aqua satellites. A
comparison of remote sensing and in situ techniques is discussed. As a result,
we find that aerosol data provided by satellites up to now are not reliable
enough for aerosol site characterization, and in situ data are required.Comment: LaTeX2e MN v2.2, 16 pages with 13 figures. Accepted for Mon. Not. R.
Astron. Soc.(2008
Tailoring Organic-Organic Poly(vinylpyrrolidone) Microparticles and Fibers with Multiwalled Carbon Nanotubes for Reinforced Composites
Polymeric-based microparticles and fibers are tailorable for a wide range of common industrial and biomedical applications, while multiwalled carbon nanotubes (MWCNTs) are among the most useful macromolecules based on their outstanding electronic, mechanical, and optical properties at the nanoscale. If one combines these nanostructures with various polymeric precursors, their range of potential applications becomes even greater. One of the simplest and most affordable methods for fabricating micro- and nanostructures is electrospinning. Herein we demonstrate how MWCNTs may be used to produce tailor-made organic-organic poly(vinylpyrrolidone) (PVP) microparticles and fibers via electrospinning by studying their structural, vibrational, rheological, and mechanical properties' dependence on their solvent (ethanol (EtOH) or dimethylformamide (DMF)) and resulting morphology. Specifically, we find clear differences in morphologies from perfectly spherical and isolated microparticles to fibers mats, or a combination of fibers with entangled beads, with solvent type and concentration. On the basis of our findings, we propose that the mechanism governing the shape and size of the particles is a competition between the solvent's surface tension, dielectric constant, and viscoelastic properties. We show, based on both our experimental results and density functional theory (DFT) calculations, that OH functionalization of the MWCNTs is essential for achieving high PVP coverages and promoting the stability of the resulting PVP/MWCNT nanocomposite. Finally, by fabricating PVP/MWCNT fiber mats, we demonstrate that low concentrations (0.01-0.1 wt %) of MWCNTs led to a qualitative improvement (â250%) in the resulting mechanical properties, i.e., a reinforced composite. These results show how by controlling the solvent's dielectric constant, surface tension, and polymer concentration, one may produce tailor-made polymeric nanomaterials in combination with other organic/inorganic nanoparticles, i.e., silver, gold, or carbon allotropes, for next-generation applications
Matching microscopic and macroscopic responses in glasses
We first reproduce on the Janus and Janus II computers a milestone experiment
that measures the spin-glass coherence length through the lowering of
free-energy barriers induced by the Zeeman effect. Secondly we determine the
scaling behavior that allows a quantitative analysis of a new experiment
reported in the companion Letter [S. Guchhait and R. Orbach, Phys. Rev. Lett.
118, 157203 (2017)]. The value of the coherence length estimated through the
analysis of microscopic correlation functions turns out to be quantitatively
consistent with its measurement through macroscopic response functions.
Further, non-linear susceptibilities, recently measured in glass-forming
liquids, scale as powers of the same microscopic length.Comment: 6 pages, 4 figure
An in-depth view of the microscopic dynamics of Ising spin glasses at fixed temperature
Using the dedicated computer Janus, we follow the nonequilibrium dynamics of
the Ising spin glass in three dimensions for eleven orders of magnitude. The
use of integral estimators for the coherence and correlation lengths allows us
to study dynamic heterogeneities and the presence of a replicon mode and to
obtain safe bounds on the Edwards-Anderson order parameter below the critical
temperature. We obtain good agreement with experimental determinations of the
temperature-dependent decay exponents for the thermoremanent magnetization.
This magnitude is observed to scale with the much harder to measure coherence
length, a potentially useful result for experimentalists. The exponents for
energy relaxation display a linear dependence on temperature and reasonable
extrapolations to the critical point. We conclude examining the time growth of
the coherence length, with a comparison of critical and activated dynamics.Comment: 38 pages, 26 figure
The Mpemba effect in spin glasses is a persistent memory effect
The Mpemba effect occurs when a hot system cools faster than an initially
colder one, when both are refrigerated in the same thermal reservoir. Using the
custom built supercomputer Janus II, we study the Mpemba effect in spin glasses
and show that it is a non-equilibrium process, governed by the coherence length
\xi of the system. The effect occurs when the bath temperature lies in the
glassy phase, but it is not necessary for the thermal protocol to cross the
critical temperature. In fact, the Mpemba effect follows from a strong
relationship between the internal energy and \xi that turns out to be a
sure-tell sign of being in the glassy phase. Thus, the Mpemba effect presents
itself as an intriguing new avenue for the experimental study of the coherence
length in supercooled liquids and other glass formers.Comment: Version accepted for publication in PNAS. 6 pages, 7 figure
- …