Multivalued memory effects in electronic phase-change manganites controlled by Joule heating

Non-volatile multivalued memory effects caused by magnetic fields, currents, and voltage pulses are studied in Nd_{0.65}Ca_{0.35}MnO_3 and (Nd_{1-y}Sm_{y})_{0.5}Sr_{0.5}MnO_3 (y=0.75) single crystals in the hysteretic region between ferromagnetic metallic and charge-ordered insulating states. The current/voltage effects observed in this study are explained by the self-heating effect, which enable us to control the colossal electroresistance effects. This thermal-cycle induced switching between electronic solid and liquid states can be regarded as electronic version of atomic crystal/amorphous transitions in phase-change chalcogenides.Comment: 5 pages, 4 figures. to appear in Phys. Rev.

Near-Infrared Spectroscopy of Very Low-Luminosity Young Stellar Objects in the Taurus Molecular Cloud

We have carried out near-infrared spectroscopic observations of 23 very low-luminosity young stellar object (YSO) candidates and 5 their companions in Heiles Cloud 2, one of the densest parts of the Taurus molecular cloud. Twelve objects were confirmed as YSOs by Br gamma feature. The effective temperatures of the YSOs and of the companions are estimated from the 2.26 micron feature, the 2.21 micron feature, and the H2O band strengths. Detailed comparisons of our photometric and spectroscopic observations with evolutionary tracks on the HR diagram suggest some objects to be very low-mass YSOs.Comment: 15 pages, 19 figures. PASJ accepte

Spectral components at visual and infrared wavelengths in active galactic nuclei

Aperture-dependent infrared photometry of active galactic nuclei are presented which illustrate the importance of eliminating starlight of the galaxy in order to obtain the intrinsic spectral distribution of the active nuclei. Separate components of emission are required to explain the infrared emission with a spectral index of alpha approx = 2 and the typical visual-ultraviolet continuum with alpha approx = 0.3 (where F(nu) varies as nu(sup-alpha). Present evidence does not allow unique determination of the appropriate mechanisms, but the characteristics of each are discussed

Moderate spectral resolution observations of 3 micron absorption features in highly obscured objects

The 3 micron absorption spectra of sources seen in or behind molecular clouds generally show a variety of absorption features. Three separate absorptions are used to explain these features. The cooled-grating array spectrometer (CGAS) at the NASA Infrared Telescope Facility was used to obtain spectra of the late-type mass-loss star OH 0739-12 and the protostars MonR2 IRS-2 and IRS-3 (solid circles). The differences between the spectra are discussed

The Mauna Kea Observatories Near-Infrared Filter Set. I: Defining Optimal 1-5 μ\mum Bandpasses

A new MKO-NIR infrared filter set is described, including techniques and considerations given to designing a new set of bandpasses that are useful at both mid- and high-altitude sites. These filters offer improved photometric linearity and in many cases reduced background, as well as preserve good throughput within the JHKLM atmospheric windows. MKO-NIR filters have already been deployed with a number of instruments around the world as part of a filter consortium purchase to reduce the unit cost of filters. Through this effort we hope to establish, for the first time, a single standard set of infrared fitlers at as many observatories as possible.Comment: PASP, in press; 32 pages, 11 figures, 3 Table

Vortex-chain phases in layered superconductors

Layered superconductors in tilted magnetic field have a very rich spectrum of vortex lattice configurations. In the presence of in-plane magnetic field, a small c-axis field penetrates in the form of isolated vortex chains. The structure of a single chain is mainly determined by the ratio of the London [$\lambda$] and Josephson [$\lambda_{J}$] lengths, $\alpha= \lambda/\lambda_{J}$. At large $\alpha$ the chain is composed of tilted vortices [tilted chains] and at small $\alpha$ it consists of a crossing array of Josephson vortices and pancake stacks [crossing chains]. We studied the chain structures at intermediate $\alpha$'s and found two types of behavior. (I) In the range $0.4 < \alpha < 0.5$ a c-axis field first penetrates in the form of pancake-stack chains located on Josephson vortices. Due to attractive coupling between deformed stacks, their density jumps from zero to a finite value. With further increase of the c-axis field the chain structure smoothly evolves into modulated tilted vortices and then transforms via a second-order phase transition, into the tilted straight vortices. (II) In the range $0.5 < \alpha < 0.65$ a c-axis field first penetrates in the form of kinks creating kinked tilted vortices. With increasing the c-axis field this structure is replaced via a first-order phase transition by the strongly deformed crossing chain. This transition is accompanied by a large jump of pancake density. Further evolution of the chain structure is similar to the higher anisotropy scenario: it smoothly transforms back into the tilted straight vortices.Comment: Accepted to Phys. Rev. B, 20 pages 12 figures, animation of chain structure is available in http://mti.msd.anl.gov/movies/Chains/Nl8al06Im.gif (gif, 441 KB

Nodal degenerations of plane curves and Galois covers

Globally irreducible nodes (i.e. nodes whose branches belong to the same irreducible component) have mild effects on the most common topological invariants of an algebraic curve. In other words, adding a globally irreducible node (simple nodal degeneration) to a curve should not change them a lot. In this paper we study the effect of nodal degeneration of curves on fundamental groups and show examples where simple nodal degenerations produce non-isomorphic fundamental groups and this can be detected in an algebraic way by means of Galois coverings.Comment: 16 pages, 3 figure