Spectral isometries on non-simple C*-algebras

We prove that unital surjective spectral isometries on certain non-simple unital C*-algebras are Jordan isomorphisms. Along the way, we establish several general facts in the setting of semisimple Banach algebras.Comment: 7 pages; paper available since July 201

On the nature of space-time, cosmological inflation, and expansion of the universe

In this article, we propose to investigate the mechanism of cosmological inflation and expansion through the physical properties of space-time. By taking the bulk modulus $K=1.64 \times 10^{109}\text{N}\cdot\text{m}^{-2}$, we show that the dark energy density is decreased by a factor of $\sim 10^{122}$ while the scaling factor expands from $\sim 10^{-60}$ to $\sim 10^{-32}$ during a time of the order of $10^{-42}\text{s}$ during inflation. At the end of this paper, we discuss a microscopic interpretation of the inflation mechanism and future investigations on longitudinal waves.Comment: New paradigms, new figure

X rays from old open clusters: M 67 and NGC 188

We have observed the old open clusters M 67 and NGC 188 with the ROSAT PSPC. In M 67 we detect a variety of X-ray sources. The X-ray emission by a cataclysmic variable, a single hot white dwarf, two contact binaries, and some RS CVn systems is as expected. The X-ray emission by two binaries located below the subgiant branch in the Hertzsprung Russell diagram of the cluster, by a circular binary with a cool white dwarf, and by two eccentric binaries with orbital period > 700 d is puzzling. Two members of NGC 188 are detected, including the FK Com type star D719. Another possible FK Com type star, probably not a member of NGC 188, is also detected.Comment: 10 pages, 5 figures. Accepted for publication on Astronomy & Astrophysic

The nanoscale phase separation in hole-doped manganites

A macroscopic phase separation, in which ferromagnetic clusters are observed in an insulating matrix, is sometimes observed, and believed to be essential to the colossal magnetoresistive (CMR) properties of manganese oxides. The application of a magnetic field may indeed trigger large magnetoresistance effects due to the percolation between clusters allowing the movement of the charge carriers. However, this macroscopic phase separation is mainly related to extrinsic defects or impurities, which hinder the long-ranged charge-orbital order of the system. We show in the present article that rather than the macroscopic phase separation, an homogeneous short-ranged charge-orbital order accompanied by a spin glass state occurs, as an intrinsic result of the uniformity of the random potential perturbation induced by the solid solution of the cations on the $A$-sites of the structure of these materials. Hence the phase separation does occur, but in a more subtle and interesting nanoscopic form, here referred as ``homogeneous''. Remarkably, this ``nanoscale phase separation'' alone is able to bring forth the colossal magnetoresistance in the perovskite manganites, and is potentially relevant to a wide variety of other magnetic and/or electrical properties of manganites, as well as many other transition metal oxides, in bulk or thin film form as we exemplify throughout the article.Comment: jpsj2 TeX style (J. Phys. Soc. Jpn); 18 pages, 7 figure

From RE-211 to RE-123. How to control the final microstructure of superconducting single-domains

This paper reviews the usual techniques for producing YBCO-type single-domains and the microstructure of the as-obtained samples. The problems of seed dissolution and parasite nucleations are discussed in details. Formation of microstructural defects, such as pores and cracks, are examined. An important part of this review is devoted to the study of the influence of RE-211 particles [RE2BaCuO5 where RE denotes Y, Yb, Nd, Sm, Dy, Gd, Eu or a mixture of them. Generally Nd4Ba2Cu2O10 is preferred to Nd2BaCuO5] on the microstructure and properties of RE-Ba-Cu-O single-domains. Trapping/Pushing theory is described in order to explain the spatial distribution of RE-211 particles in the RE-123 [(RE)Ba2Cu3O7-d] monoliths. Formation of RE-211-free regions is discussed. Different ways to limit the RE-211 coarsening are reviewed. Microstructural defects in the RE-123 matrix caused by the RE-211 particles are presented. It is also shown that RE-211 particles play a significant role on the mechanical properties of single-domain samples. We finish this review by discussing the Infiltration and Growth process as a good technique to control the microstructure.Comment: review paper to be published in Supercond. Sci. Technol.; 19 figures; 137 references; 37 page

Fast Mixing of Parallel Glauber Dynamics and Low-Delay CSMA Scheduling

Glauber dynamics is a powerful tool to generate randomized, approximate solutions to combinatorially difficult problems. It has been used to analyze and design distributed CSMA (Carrier Sense Multiple Access) scheduling algorithms for multi-hop wireless networks. In this paper we derive bounds on the mixing time of a generalization of Glauber dynamics where multiple links are allowed to update their states in parallel and the fugacity of each link can be different. The results can be used to prove that the average queue length (and hence, the delay) under the parallel Glauber dynamics based CSMA grows polynomially in the number of links for wireless networks with bounded-degree interference graphs when the arrival rate lies in a fraction of the capacity region. We also show that in specific network topologies, the low-delay capacity region can be further improved.Comment: 12 page