Testing Relativity at High Energies Using Spaceborne Detectors

(ABRIDGED) The Gamma-ray Large Area Space Telescope (GLAST) will measure the spectra of distant extragalactic sources of high energy gamma-rays. GLAST can look for energy dependent propagation effects from such sources as a signal of Lorentz invariance violation (LIV). Such sources should also exhibit high energy spectral cutoffs from pair production interactions with low energy photons. The properties of such cutoffs can also be used to test LIV. Detectors to measure gamma-ray polarization can look for the depolarizing effect of space-time birefingence predicted by loop quantum gravity. A spaceborne detector array looking down on Earth to study extensive air showers produced by ultrahigh energy cosmic rays can study their spectral properties and look for a possible deviation from the predicted GZK effect as another signal of LIV.Comment: 14 pages, Text of invitated talk presented at the "From Quantum to Cosmos: Fundamental Physics Studies from Space" meeting. More references adde

On the magnetism and dynamics of prominence legs hosting tornadoes

Solar tornadoes are dark vertical filamentary structures observed in the extreme ultraviolet associated with prominence legs and filament barbs. Their true nature and relationship to prominences requires understanding their magnetic structure and dynamic properties. Recently, a controversy has arisen: is the magnetic field organized forming vertical, helical structures or is it dominantly horizontal? And concerning their dynamics, are tornadoes really rotating or is it just a visual illusion? Here, we analyze four consecutive spectropolarimetric scans of a prominence hosting tornadoes on its legs which help us shed some light on their magnetic and dynamical properties. We show that the magnetic field is very smooth in all the prominence, probably an intrinsic property of the coronal field. The prominence legs have vertical helical fields that show slow temporal variation probably related to the motion of the fibrils. Concerning the dynamics, we argue that 1) if rotation exists, it is intermittent, lasting no more than one hour, and 2) the observed velocity pattern is also consistent with an oscillatory velocity pattern (waves).Comment: accepted for publication in Ap

The Effect of Disorder in an Orbitally Ordered Jahn-Teller Insulator

We study a two dimensional, two-band double-exchange model for $e_g$ electrons coupled to Jahn-Teller distortions in the presence of quenched disorder using a recently developed Monte-Carlo technique. In the absence of disorder the half-filled system at low temperatures is an orbitally ordered ferromagnetic insulator with a staggered pattern of Jahn-Teller distortions. We examine the finite temperature transition to the orbitally disordered phase and uncover a qualitative difference between the intermediate and strongly coupled systems, including a thermally driven insulator to metal crossover in the former case. Long range orbital order is suppressed in the presence of disorder and the system displays a tendency towards metastable states consisting of orbitally disordered stripe-like structures enclosing orbitally ordered domains.Comment: 10 pages, 9 figure

Efficient design of experiment for exponential regression models

In this paper robust and efficient designs are derived for several exponential decay models. These models are widely used in chemistry, pharmacokinetics or microbiology. We propose a maximin approach, which determines the optimal design such that a minimum of the D-efficiencies (taken over a certain range for the nonlinear parameters) becomes maximal. Analytic solutions are derived if optimization is performed in the class of minimal supported designs. In general the optimal designs with respect to the maximin criterion have to be determined numerically and some properties of these designs are also studied. --exponential regression model,D-optimal design,robust design,maximin design,pharmacokinetics,microbiology

Magnetic transitions in Pr2NiO4 single crystal

The magnetic properties of a stoichiometric Pr2NiO4 single crystal have been examined by means of the temperature dependence of the complex ac susceptibility and the isothermal magnetization in fields up to 200 kOe at T=4.2 K. Three separate phases have been identified and their anisotropic character has been analyzed. A collinear antiferromagnetic phase appears first between TN = 325 K and Tc1 = 115 K, where the Pr ions are polarized by an internal magnetic field. At Tc1 a first modification of the magnetic structure occurs in parallel with a structural phase transition (Bmab to P42/ncm). This magnetic transition has a first‐order character and involves both the out‐of‐plane and the in‐plane spin components (magnetic modes gx and gxcyfz, respectively). A second magnetic transition having also a first‐order character is also clearly identified at Tc2 = 90 K which corresponds to a spin reorientation process (gxcyfz to cxgyaz magnetic modes). It should be noted as well that the out‐of‐phase component of χac shows a peak around 30 K which reflects the coexistence of both magnetic configurations in a wide temperature interval. Finally, two field‐induced transitions have been observed at 4.2 K when the field is directed along the c axis. We propose that the high‐field anomaly arises from a metamagnetic transition of the weak ferromagnetic component, similarly to La2CuO4

Validity of a four-factor modelunderlying the physical fitness in adults with intellectual disabilities a confirmatory factor analysis

Purpose: To use confirmatory factor analysis to test whether a four factor might explain the clustering of the components of the physical fitness in adults with intellectual disabilities (FID). Relevance: Individuals with intellectual disabilities (ID) are significantly weaker than individuals without ID at all stages of life. These subjects might be particularly susceptible to loss of basic function because of poor physical fitness. Participants: We studied 267 adults with intellectual disability of the Spanish Special Olympics Games. Methods: The four-factor model included: the flexibility, the strength, the balance and the cardiorespiratory endurance with 9 variables of the fitness assessment. Analysis: The construct validity of the model was assessed through the factor loadings, interpreted as the correlation between the variables in the model and their underlying factor, which is the FID construct. Results: Factor loading were 0,55 for the passive knee extension, o,52 for Functional shoulder rotation, −0.71 for the timed-stand test, 0.58 for the grip test, 0.75 the single leg stance with eyes open, 0.69 single leg stance with eyes closed, 0.72 for the resting heart rate, 0.56 for the two-minute step test (2MST) 0,97 for 2 minutes after finish 2MST. The four-factor model also showed a good fit to the data, as indicated by a high comparative fit index (CFI=0,93) and a low standardized root mean square residual (SRMR=0,072) Conclusions: A four underlying factor has shown acceptable validity to represent FID Implications: The new model of FID can offer understanding better these construct in this special populationUniversidad de Málaga. Campus de Excelencia Internacional Andalucía Tech