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Spin glass behavior in an interacting gamma-Fe2O3 nanoparticle system

In this paper we investigate the superspin glass behavior of a concentrated assembly of interacting maghemite nanoparticles and compare it to that of canonical atomic spin glass systems. ac versus temperature and frequency measurements show evidence of a superspin glass transition taking place at low temperature. In order to fully characterize the superspin glass phase, the aging behavior of both the thermo-remanent magnetization (TRM) and ac susceptibility has been investigated. It is shown that the scaling laws obeyed by superspin glasses and atomic spin glasses are essentially the same, after subtraction of a superparamagnetic contribution from the superspin glass response functions. Finally, we discuss a possible origin of this superparamagnetic contribution in terms of dilute spin glass models

Host and environmental factors as determinants of equine piroplasmosis seroprevalence in Central Spain

Aim of study: To estimate equine piroplasmosis seroprevalence, identify associated risk factors and assess infection recentness.Area of study: Community of Madrid (Central Spain)Material and methods: Sera from 139 horses and 40 donkeys were examined by cELISA to evaluate Babesia caballi and Theileria equi seroprevalences and examine potential risk factors. They included species, gender, age, breed, colour coat, dedication, external parasite treatments, access to pasture, contact with other species, new introduction, tick infestation, farm altitude, land cover, soil type and climatic zone. A bivariate analysis was performed and significant variables were included in a logistic regression model to examine their independent contribution. In positive samples ELISA inhibition percentiles (EIPs) were used to assess whether infections were old or recent.Main results: True seroprevalence (95% CI), adjusted for test sensitivity and specificity was 19% (13-27) for T. equi and 1% (0-3) for B. caballi. In the bivariate analysis, T. equi seroprevalence varied significantly according to horse and farm-level explanatory variables; high seroprevalence groups generally had high EIPs suggesting recent infection. The multivariable analysis revealed that T. equi seroprevalence increased with age, it was higher in police horses compared to sporting, recreational and breeding animals and in those living in lower altitude where planosol soil type was predominant.Research highlights: T. equi seroprevalence in the area was significantly higher than B. caballi seroprevalence and depends on animal management and environmental factors that affect vector abundance and diversity. Identified risk factors must be considered to improve tick and tick-borne disease control and prevention

Computed tomography angiography, perforator flaps, surgeon and OsiriX

Desde la introducción de la transferencia cutánea basada en perforantes, la angiotomografía computerizada ha emergido como una técnica de gran valor en la planificación preoperatoria de los colgajos de perforante. Sin embargo, parece probable que el aprovechamiento de la técnica sea menor del deseable. Evaluamos, a través de la experiencia en 144 pacientes, la utilidad del visor gratuito de imágenes DICOM OsiriX para Mac en la planificación preoperatoria de los colgajos de perforante con tres objetivos: 1) ampliar los conocimientos actuales relacionados con la aplicación de la angiotomografía computerizada en la planificación preoperatoria de los colgajos de perforante, 2) evaluar la aplicación OsiriX en el post-procesamiento de imágenes en la planificación preoperatoria de colgajos de perforante y 3) evaluar el rendimiento obtenible de la angiotomografía considerando que el postprocesamiento es realizado por un cirujano (no especialista en Radiodiagnóstico). La experiencia permite afirmar que el postprocesamiento de las imágenes DICOM por el cirujano con la aplicación Osirix permite habitualmente evaluar de manera adecuada diversas estructuras y parámetros de gran interés en la cirugía de colgajos de perforante: 1) arteria principal, origen de la perforante, 2) diámetro de arteria y vena/s en el hipotético sitio de anastomosis microquirúrgica, 3) recorrido y patrón de ramificación del pedículo del colgajo, 4) disposición de la perforante en la grasa subcutánea (teórico eje de diseño del colgajo), 5) medición del grosor cutáneo en el punto de perforación de la fascia profunda por la rama perforante (teórico grosor de colgajo), 6) medición de la distancia entre el punto de perforación de la fascia profunda por la rama perforante y el origen de la arteria principal (teórica longitud máxima posible de pedículo) y 7) medición del diámetro, en el punto de perforación de la fascia profunda, de la perforante. En consecuencia, parece aconsejable que el cirujano plástico relacionado con los colgajos de perforante se involucre decididamente en el postprocesamiento de las imágenes de angiotomografía computerizada. El visor de imágenes DICOM gratuito OsiriX es una alternativa eficiente, comparable a aplicaciones más profesionales sólo disponibles en servicios de Radiología.With the advent of perforator-based skin transfer, computed tomography angiography has emerged as an invaluable tool in the preoperative planning of perforator flaps. But most likely, the exploitation of the technique is less than desirable. Through our experience with 144 patients, we evaluate the use of the free DICOM viewer OsiriX for Mac in the preoperative planning of perforator flaps with three objectives: 1) increase the present knowledge related with the preoperative planning of perforator flaps with computed tomography angiography, 2) evaluate the OsiriX application in the image post-processing of perforator flaps and 3) evaluate the performance of the procedure when performed by a surgeon (not specialized in Radiology). The experience has shown that the image post-processing performed by the surgeon with the OsiriX application usually allows an adequate evaluation of different structures and parameters of great preoperative interest in perforator flap surgery: 1) source artery, 2) diameter of artery and vein/s at the hypothetical site of microsurgical anastomoses, 3) course and branching pattern of the flap pedicle, 4) perforator course in the subcutaneous fat (theoretical flap axis), 5) measurement of the skin and fat where the perforator pierces the deep fascia (theoretical flap thickness ), 6) measurement of the distance between the point of entrance of the perforator in the subcutaneous fat to the source artery (theoretical maximal pedicle length) and 7) measurement of the perforator diameter where it pierces the deep fascia. Ultimately, in the authors’ opinion, those plastic surgeons involved in perforator flap surgery would largely benefit from incorporating the image post-processing into their routine practice. The free DICOM viewer OsiriX is an efficient alternative, comparable to the more professional software only available in Radiology service

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

Zero-temperature spin-glass freezing in self-organized arrays of Co nanoparticles

We study, by means of magnetic susceptibility and magnetic aging experiments, the nature of the glassy magnetic dynamics in arrays of Co nanoparticles, self-organized in N layers from N=1 (two-dimensional limit) up to N=20 (three-dimensional limit). We find no qualitative differences between the magnetic responses measured in these two limits, in spite of the fact that no spin-glass phase is expected above T=0 in two dimensions. More specifically, all the phenomena (critical slowing down, flattening of the field-cooled magnetization below the blocking temperature and the magnetic memory induced by aging) that are usually associated with this phase look qualitatively the same for two-dimensional and three-dimensional arrays. The activated scaling law that is typical of systems undergoing a phase transition at zero temperature accounts well for the critical slowing down of the dc and ac susceptibilities of all samples. Our data show also that dynamical magnetic correlations achieved by aging a nanoparticle array below its superparamagnetic blocking temperature extend mainly to nearest neighbors. Our experiments suggest that the glassy magnetic dynamics of these nanoparticle arrays is associated with a zero-temperature spin-glass transition.Comment: 6 pages 6 figure

Targeted DNA demethylation of the Arabidopsis genome using the human TET1 catalytic domain.

DNA methylation is an important epigenetic modification involved in gene regulation and transposable element silencing. Changes in DNA methylation can be heritable and, thus, can lead to the formation of stable epialleles. A well-characterized example of a stable epiallele in plants is fwa, which consists of the loss of DNA cytosine methylation (5mC) in the promoter of the FLOWERING WAGENINGEN (FWA) gene, causing up-regulation of FWA and a heritable late-flowering phenotype. Here we demonstrate that a fusion between the catalytic domain of the human demethylase TEN-ELEVEN TRANSLOCATION1 (TET1cd) and an artificial zinc finger (ZF) designed to target the FWA promoter can cause highly efficient targeted demethylation, FWA up-regulation, and a heritable late-flowering phenotype. Additional ZF-TET1cd fusions designed to target methylated regions of the CACTA1 transposon also caused targeted demethylation and changes in expression. Finally, we have developed a CRISPR/dCas9-based targeted demethylation system using the TET1cd and a modified SunTag system. Similar to the ZF-TET1cd fusions, the SunTag-TET1cd system is able to target demethylation and activate gene expression when directed to the FWA or CACTA1 loci. Our study provides tools for targeted removal of 5mC at specific loci in the genome with high specificity and minimal off-target effects. These tools provide the opportunity to develop new epialleles for traits of interest, and to reactivate expression of previously silenced genes, transgenes, or transposons

Critical fields for vortex expulsion from narrow superconducting strips

We calculate the critical magnetic fields for vortex expulsion for an infinitely long superconducting strip, using the Ginzburg-Landau formalism. Two critical fields can be defined associated with the disappearance of either the energetic stability or metastability of vortices in the center of the strip for decreasing magnetic fields. We compare the theoretical predictions for the critical fields in the London formalism with ours and with recently published experimental results. As expected, for narrow strips our results reproduce better the experimental findings.Comment: 5 pages, 5 figure