Positioning with stationary emitters in a two-dimensional space-time

The basic elements of the relativistic positioning systems in a two-dimensional space-time have been introduced in a previous work [Phys. Rev. D {\bf 73}, 084017 (2006)] where geodesic positioning systems, constituted by two geodesic emitters, have been considered in a flat space-time. Here, we want to show in what precise senses positioning systems allow to make {\em relativistic gravimetry}. For this purpose, we consider stationary positioning systems, constituted by two uniformly accelerated emitters separated by a constant distance, in two different situations: absence of gravitational field (Minkowski plane) and presence of a gravitational mass (Schwarzschild plane). The physical coordinate system constituted by the electromagnetic signals broadcasting the proper time of the emitters are the so called {\em emission coordinates}, and we show that, in such emission coordinates, the trajectories of the emitters in both situations, absence and presence of a gravitational field, are identical. The interesting point is that, in spite of this fact, particular additional information on the system or on the user allows not only to distinguish both space-times, but also to complete the dynamical description of emitters and user and even to measure the mass of the gravitational field. The precise information under which these dynamical and gravimetric results may be obtained is carefully pointed out.Comment: 14 pages; 5 figure

Analysis of thermal resistance evolution of ash deposits during co-firing of coal with biomass and coal mine waste residues

Co-firing biomass or waste fuels with coal in conventional thermal plants is a promising way to reduce environmental impact of human activities with an acceptable economic investment. One of the main issues to be addressed is the worsening in ash fouling and the reduction of heat transfer rate. In the present paper, the deposits thermal resistance during direct combustion of different blends of coal and various native fuels is investigated by using a deposition probe, kept at 550 °C in order to emulate the conditions of superheaters of conventional power units. Two energy crops (Cynara cardunculus L. and Populus spp.), a forest residue (Pinus pinaster) and a waste coal (coal mine waste residues) were successfully tested in a semi-industrial scale pilot plant. A thermal model of the probe is presented to estimate heat transfer rate and thermal resistance of ash deposits. After the validation with experimental data, a sensitivity analysis allows to identify the deposit surface emissivity and the flue gas temperature as the most influential parameters. The heat uptake in air flow decreases with time for all the experimental tests in spite of the increase in flue gas and walls temperatures. Except for poplar blends, under similar operation conditions, a rise in the substitution percentage means faster decreasing rates in heat transfer and higher thermal resistance due to the ash deposits, especially for cynara and coal mine waste residues. The present work demonstrates the usefulness of thermal models to estimate the thermal resistance of ash deposits without the need of sophisticated instrumentation. Dedicated thermal models, similar to the developed one, could serve to design smart cleaning sequences to improve efficiency in power generation processes

Two-dimensional approach to relativistic positioning systems

A relativistic positioning system is a physical realization of a coordinate system consisting in four clocks in arbitrary motion broadcasting their proper times. The basic elements of the relativistic positioning systems are presented in the two-dimensional case. This simplified approach allows to explain and to analyze the properties and interest of these new systems. The positioning system defined by geodesic emitters in flat metric is developed in detail. The information that the data generated by a relativistic positioning system give on the space-time metric interval is analyzed, and the interest of these results in gravimetry is pointed out.Comment: 11 pages, 5 figures. v2: a brief description of the principal bibliography has been adde

Positioning systems in Minkowski space-time: Bifurcation problem and observational data

In the framework of relativistic positioning systems in Minkowski space-time, the determination of the inertial coordinates of a user involves the {\em bifurcation problem} (which is the indeterminate location of a pair of different events receiving the same emission coordinates). To solve it, in addition to the user emission coordinates and the emitter positions in inertial coordinates, it may happen that the user needs to know {\em independently} the orientation of its emission coordinates. Assuming that the user may observe the relative positions of the four emitters on its celestial sphere, an observational rule to determine this orientation is presented. The bifurcation problem is thus solved by applying this observational rule, and consequently, {\em all} of the parameters in the general expression of the coordinate transformation from emission coordinates to inertial ones may be computed from the data received by the user of the relativistic positioning system.Comment: 10 pages, 7 figures. The version published in PRD contains a misprint in the caption of Figure 3, which is here amende

Magnetic anisotropy of maghemite nanoparticles probed by RF transverse susceptibility

We present radio frequency magnetic transverse susceptibility measurements on γ-Fe2O3 nanoparticles, which yield an estimation of their effective anisotropy constant, Keff as a function of nanoparticle size. The resulting values range from 4 to 8 × 104 erg/cm3, being on the order of the magnetocrystalline anisotropy in bulk maghemite. Keff values increase as the particle diameter increases. Evidences of anisotropy field distribution given by the size distribution in the samples, and interparticle interactions that increase as the particle size increases, are also observed in the TS measurements. The effects of such interparticle interaction overcome those of thermal fluctuations, in contrast with the behavior of other iron oxide particles.The financial support of the Spanish MINECO MAT2011-23791, MAT2014-53921-R, and MAT2014-54975-R and Aragonese DGA-IMANA E34 and M4 projects is acknowledged.Peer Reviewe

Síndroma Ovo-Ave na Criança:Um Caso Clínico

A síndroma ovo -ave é uma entidade clínica rara, em especial em idade pediátrica. Descreve -se o caso de criança de sexo masculino, 5 anos, que habita zona rural, com clínica sugestiva de alergia ao ovo e à carne de frango desde os 7 meses. Aos 2,5 anos apresenta queixas de asma brônquica, rinite alérgica e eczema atópico. Os testes cutâneos foram positivos para extractos de clara e gema de ovo. Dosearam -se IgE específi cas para clara e gema de ovo (>100 kU/L), carne de frango (1,0 kU/L), α -livetina (0,7 kU/L), penas de frango (15,3 kU/L). O estudo de immunoblotting evidenciou ligação de IgE a bandas com peso molecular entre 30-66 kDa e 32-45 kDa para clara e gema, respectivamente, 38/39/42 kDa para carne de frango e 33-45 kDa para penas de frango. Em doentes com alergia a carne de aves, expostos a factores ambientais de risco e sensibilização elevada a gema de ovo, dever -se -á suspeitar da síndroma ovo-ave

Magnetism of Cr10 wheels on Au(111) and Cu(111) surfaces

Trabajo presentado al X Meeting de GEFES (División de Física de la Materia Condensada de la Real Sociedad Española de Física), celebrado en Valencia del 24 al 26 de enero de 2018We report on the magnetic properties of {Cr10} wheels (Cr10(OMe)20(O2CCMe)10) UHVsublimated on Cu(111) and Au(111) single-crystals investigated by means of by XAS & XMCD, SQUID magnetometry and STM. We discuss the magnetic anisotropy and magnetic moment field-dependence of the grafted {Cr10} molecules, as a function of the metallic substrate and layer thickness, and compare it with bulk material. Our results demonstrate that evaporated molecules show negligible anisotropy and weak dependence with the substrate. A combination of XMCD and SQUID magnetometry show that Mono- and Multilayer {Cr10} samples exhibit a magnetic behavior stemming from a S = 9 ground state, ruling out some previous results. Montecarlo simulations show that the magnetic evolution can be explained by {Cr10} molecules magneticaly consisting of two semi-crowns containing 4 Cr ions interacting ferromagnetically, separated by 2 Cr ions with antiferromagnetic interactions, giving rise to the ground S = 9 state, in agreement with previous EPR data in literature. Evaporation of {Cr10} onto a substrate producing subtle structural changes induce strong changes in the Cr-Cr interactions and distinct magnetic behavior from the bulk.Peer Reviewe

Virtual restitution of the parietal decoration in the Sala del Mosaico de los Amores, Cástulo Archaelogical site (Linares, Spain)

The use of photogrammetry in the field of archaeology is increasingly widespread. In the case of restoration, the use of 3D contributes to facilitating the complex process of an intervention and bringing the artwork closer to the general public. This paper describes the application of 3D modelling techniques in the specific case of the Roman wall paintings from the Sala del Mosaico de los Amores, in Castulo Archaeological Site (Linares, province of Jaén). These paintings were found in 2011, collapsed over the mosaic pavement, and they were moved to the University of Granada for their restoration. After the intervention, the photogrammetric surveys of the different fragments and of the room to which they belong were developed, and the virtual restitution was generated, therefore making it possible for the general public to reliably appreciate how the room would look like with the parietal decoration located in-situ.Ministry of Economy and CompetitivenessEuropean Regional Development Fund (MINECO/FEDER, UE) HAR2015-66139-PResearch project "Chromatic treatments in architecture of Islamic tradition. Techniques and Conservation" by the Andalusian Regional Government, Department of Economy, Innovation, Science and Employment P12 HUM 1941German Research Foundation (DFG