Magnetic polarons in Ca_(1-x)Y_xMnO_3

Experimental evidence show that in the magnetoresistive manganite Ca_(1-x) Y_xMnO_3, ferromagnetic (FM) polarons arises in an antiferromagnetic (AF) background, as a result of the doping with Yttrium. This hypothesis is supported in this work by classical Monte Carlo (MC) calculations performed on a model where FM Double Exchange (DE) and AF Superexhange (SE) compite.Comment: 3 pages, 3 figs, submitted to LAW3M conferenc

Precipitation in the Mediterranean basin as seen from the 2000-2010 TRMM-3B42-v6 database

Sarrand, B. et al.Trabajo presentado en la EGU General Assemby 2012, celebrada del 22 al 27 de septiembre de 2012 en Viena (Austria)This work presents a detailed analysis of 11 yrs of the version 6 of the TRMM-3B42 multi-sensor precipitation product (3-h and 0.25° resolution) from March 2000 to February 2011 over the whole Mediterranean basin and surrounding areas including the Black Sea (25°N-50°N, 10°W-43°E). We first discuss some issues in the data set regarding spatial and temporal discontinuities in coastal areas, and further illustrate a critical underestimation of light rains at latitudes higher than 36-37° that somewhat improves from 2007 on and is associated to the absence of coverage by the Precipitation Radar. North of the radar field of view, it seems that the marine coastal band is subject to a significant under detection of precipitation, whereas, on the opposite, the terrestrial coastal band south of 35°N in North Africa and the Near East shows unrealistic over detection of precipitation. We then evaluate the product against rain gauges with a focus on the western Mediterranean basin and the Adriatic. Our reference rain gauge data set includes about 1 million daily rain reports from more than 260 Mediterranean surface stations from Croatia, France, Italy, Malta, Spain (including 2 stations on the northern coast of Africa) and Tunisia, and from 9 additional non-Mediterranean stations from a flat region in France. It includes stations from almost 20 small Mediterranean islands. The comparison shows a significant correlation between TRMM-3B42v6 and rain gauges but with an overall tendency to underestimation. The average ratio of daily rates between surface stations and TRMM product is ~0.63 with significant regional variations, Corsica showing the poorest results and Spain the best. Over the Mediterranean stations considered, the average rate of success on the occurrence of precipitation (~0.75) is enhanced by the high proportion of dry days in the Mediterranean climate (~4 over 5 on average in the rain gauge data set) and drops off when only days with precipitation recorded at surface stations are considered. Averaging fallout at monthly and annual time scales somewhat improves the comparison to rain gauges. We find that results are better in summer and likely more generally in unstable conditions, as illustrated by a subset of data composed of days with high African dust load over the basin. Using a few TRMM pixels that cover 3 or even 5 surface stations, we further illustrate how the small scale heterogeneity of precipitation is a limitation in the comparison between the integrated view of precipitation from space and the local surface measurements. Finally we integrate the variability of the rainfall geographical distribution at seasonal and annual scales over 5 sub-basins (western and eastern Mediterranean, Adriatic, Aegean, and Black Sea). An increasing trend in annual precipitation in the Mediterranean basin is observed over the decade that is also found at the global scale and appears related to the improving performance of the product with time regarding the detection of light rains, especially over Europe and the Mediterranean. Finally we compare the TRMM-3B42v6 precipitation budget over the basin with comparable budgets from ERA-Interim, HOAPS and CMAP data setsPeer Reviewe

Competing Jahn Teller distortions and ferrimagnetic ordering in the geometrically frustrated system Ni1 xCuxCr2O4

Competing Jahn Teller distortions combined with geometrical frustration give rise to a rich phase diagram as a function of x Cu and temperature in the spinel system Ni1 xCuxCr2O4. The Jahn Teller distortion of the end members acts in opposite ways, with an elongation of the NiO4 tetrahedra resulting in a structural transition at TS1 317K in NiCr2O4, but a flattening in the CuO4 tetrahedra at TS1 846K in CuCr2O4. In both cases the symmetry is lowered from cubic Fd 3m to tetragonal I41 amd on cooling. In order to follow the influence of Jahn Teller active Ni2 and Cu2 ions on the structural and magnetic properties of chromium spinels, we have investigated a series of samples of Ni1 xCuxCr2O4 by x ray and neutron powder diffraction. In the critical range 0.10 lt; x Cu lt; 0.20, strong orthorhombic distortions were observed, where competing Jahn Teller activities between the Cu2 and Ni2 ions result in distortions along both the a and c axes. For Ni0.85Cu0.15Cr2O4, the orthorhombic structure Fddd is stabilized up to TS2 368 2 K, close to the first structural phase transition at TS1 374 2 K. A ferrimagnetic spin alignment of the Ni Cu and chromium atoms sets in at much lower temperature TC 95K in this compound. The end members NiCr2O4 and CuCr2O4 undergo this ferrimagnetic transition at TC 74 and 135 K, respectively. These transitions are accompanied by the structural change to the orthorhombic symmetry which relieves the frustration. NiCr2O4 and Ni0.85Cu0.15Cr2O4 undergo a second magnetic transition at TM2 24 and 67K due to a superimposed antiferromagnetic ordering of the Cr moments resulting in a noncollinear magnetic structure. In the system Ni1 xCuxCr2O4, the magnetic transitions TC and TM2 merge with increasing copper content up to x Cu similar to 0.5. For the Ni rich chromites, geometrical frustration causes a strong reduction of the chromium moments, where magnetic long range order coexists with a disordered spin liquid like or a reentrant spin glass like state. This paper provides insight into the interplay between the Jahn Teller effect, geometrical frustration, and long range magnetic order in these complex system

Industrial multimedia put into practice

Recent developments in the factory floor technologies together with the widespread use of TCP/IP and the Internet are increasing the eagerness to support a new wide class of devices and applications, such as industrial multimedia applications, in factory floor networks. This paper presents how this new field of applications can be put into practice, via a manufacturing cell field trial being implemented. This manufacturing automation field trial involves the use of traditional distributed computer control systems and 'factory-floor-oriented' multimedia (e.g. voice, video) application services

A simulational and theoretical study of the spherical electrical double layer for a size-asymmetric electrolyte: the case of big coions

Monte Carlo simulations of a spherical macroion, surrounded by a size-asymmetric electrolyte in the primitive model, were performed. We considered 1:1 and 2:2 salts with a size ratio of 2 (i.e., with coions twice the size of counterions), for several surface charge densities of the macrosphere. The radial distribution functions, electrostatic potential at the Helmholtz surfaces, and integrated charge are reported. We compare these simulational data with original results obtained from the Ornstein-Zernike integral equation, supplemented by the hypernetted chain/hypernetted chain (HNC/HNC) and hypernetted chain/mean spherical approximation (HNC/MSA) closures, and with the corresponding calculations using the modified Gouy-Chapman and unequal-radius modified Gouy-Chapman theories. The HNC/HNC and HNC/MSA integral equations formalisms show good concordance with Monte Carlo "experiments", whereas the notable limitations of point-ion approaches are evidenced. Most importantly, the simulations confirm our previous theoretical predictions of the non-dominance of the counterions in the size-asymmetric spherical electrical double layer [J. Chem. Phys. 123, 034703 (2005)], the appearance of anomalous curvatures at the outer Helmholtz plane and the enhancement of charge reversal and screening at high colloidal surface charge densities due to the ionic size asymmetry.Comment: 11 pages, 7 figure

Evidence of strong antiferromagnetic coupling between localized and itinerant electrons in ferromagnetic Sr2FeMoO6

Magnetic dc susceptibility ($\chi$) and electron spin resonance (ESR) measurements in the paramagnetic regime, are presented. We found a Curie-Weiss (CW) behavior for $\chi$(T) with a ferromagnetic $\Theta = 446(5)$ K and $\mu_{eff} = 4.72(9) \mu_{B}/f.u.$, this being lower than that expected for either $Fe^{3+}(5.9\mu_{B})$ or $Fe^{2+}(4.9\mu_{B})$ ions. The ESR g-factor $g = 2.01(2)$, is associated with $Fe^{3+}$. We obtained an excellent description of the experiments in terms of two interacting sublattices: the localized $Fe^{3+}$ ($3d^{5}$) cores and the delocalized electrons. The coupled equations were solved in a mean-field approximation, assuming for the itinerant electrons a bare susceptibility independent on $T$. We obtained $\chi_{e}^{0} = 3.7$ $10^{-4}$ emu/mol. We show that the reduction of $\mu_{eff}$ for $Fe^{3+}$ arises from the strong antiferromagnetic (AFM) interaction between the two sublattices. At variance with classical ferrimagnets, we found that $\Theta$ is ferromagnetic. Within the same model, we show that the ESR spectrum can be described by Bloch-Hasegawa type equations. Bottleneck is evidenced by the absence of a $g$-shift. Surprisingly, as observed in CMR manganites, no narrowing effects of the ESR linewidth is detected in spite of the presence of the strong magnetic coupling. These results provide evidence that the magnetic order in $Sr_{2}FeMoO_{6}$ does not originates in superexchange interactions, but from a novel mechanism recently proposed for double perovskites

Spin waves in ultrathin ferromagnetic overlayers

The influence of a non-magnetic metallic substrate on the spin wave excitations in ultrathin ferromagnetic overlayers is investigated for different crystalline orientations. We show that spin wave dumping in these systems occur due to the tunneling of holes from the substrate into the overlayer, and that the spin wave energies may be considerably affected by the exchange coupling mediated by the substrate.Comment: RevTeX 4, 7 pages, 5 figures; submitted to Phys. Rev.

Prototype WSN platform for performing dynamic monitoring of civil engineering structures

Structural Health Monitoring represents the present and future of the civil engineering since, until few years ago, structural diagnosis works had been performed with few resources regarding to experimental techniques. Precisely in the field of monitoring sensors, the progress of new technologies based on wireless communications and Micro-Electro-Mechanical- Systems (MEMS) are of high interest for replacing the handle difficult wired sensors. However, three major limitations of the commercial off-the-shelf technology on WSN (combination of MEMS and wireless technology) for performing dynamic monitoring were identified by means of: (1) not enough sensitivity of the accelerometers; (2) low resolution of the ADC embedded; and (3) lack of synchronization algorithms implemented. This paper presents a new prototype system conceived for performing dynamic monitoring civil engineering structures. This system was jointly conceived by a team of civil, electrical and communication engineers and is a combination of the last technology on high resolution MEMS accelerometers and the state of the art of communication technologies. Despite the fact that the prototype system needs more improvements; the results of several rounds of validation experiences confirm the feasibility for its consideration as an alternative to the conventional wired based sensors.(undefined