Magnetic and magnetooptical properties of polycrystalline films of La0.7Sr0.3MnO3

Magnetic circular dichroism (MCD) is studied in comparison with the magnetic behavior of polycrystalline films of La_0.7Sr_0.3MnO₃ (LSMO) deposited on a single crystal of zirconium oxide stabilized by yttrium (YSZ). It is found that the bands observed in MCD spectra are characterized by different temperature dependences.     

Synthesis and Characterization of Crosslinked Polymers for Biomedical Composites

Three kinds of low molecular weight unsaturated polyesters containing carbon-carbon double bonds were synthesized by the reaction of poly (ε-caprolactone) diol or D,L-lactide and glycolic acid with maleic anhydride or fumaric acid. These functionalized polymers were thermally crosslinked in the presence of radical initiator to prepare the crosslinked polymers available as a matrix resin for biomedical composites. Hydrolysis of the crosslinked polyesters was investigated in buffer solution at 37°C.     

Density of states of quantum spin systems from isotropic entanglement

We propose a method that we call isotropic entanglement (IE), which predicts the eigenvalue distribution of quantum many body (spin) systems with generic interactions. We interpolate between two known approximations by matching fourth moments. Though such problems can be QMA-complete, our examples show that isotropic entanglement provides an accurate picture of the spectra well beyond what one expects from the first four moments alone. We further show that the interpolation is universal, i.e., independent of the choice of local terms.     

Tuning Phenols with Intra‐Molecular Bond Shifted HYdrogens (IM‐SHY) as diaCEST MRI Contrast Agents

The optimal exchange properties for chemical exchange saturation transfer (CEST) contrast agents on 3 T clinical scanners were characterized using continuous wave saturation transfer, and it was demonstrated that the exchangeable protons in phenols can be tuned to reach these criteria through proper ring substitution. Systematic modification allows the chemical shift of the exchangeable protons to be positioned between 4.8 to 12 ppm from water and enables adjustment of the proton exchange rate to maximize CEST contrast at these shifts. In particular, 44 hydrogen‐bonded phenols are investigated for their potential as CEST MRI contrast agents and the stereoelectronic effects on their CEST properties are summarized. Furthermore, a pair of compounds, 2,5‐dihydroxyterephthalic acid and 4,6‐dihydroxyisophthalic acid, were identified which produce the highest sensitivity through incorporating two exchangeable protons per ring.     

A recurrence for linear extensions

The number e(P) of linear extensions of a finite poset P is expressed in terms of e(Q) for certain smaller posets Q. The proof is based on M. Schützengerger's concept of promotions of linear extensions.Partially supported by NSF Grant #DMS-8700995.Partially supported by NSF Grant #DMS-8401376.     

Hysteresis phenomena in charging of Si Mosfet in quantizing magnetic field

We report the observation of nonequilibrium processes of charging in 2D electron layer in Si MOSFET. There were investigated the hysteresis variations of a 2D-layer charge Q_S with a gate voltage V_g or with a magnetic field H, and the hysteresis of a gate potential U_g vs magnetic field at Q_S = Const. At sufficiently low temperature T < 1K the relaxation time of a nonequilibrium state is much higher than 10³ sec. The observed phenomena may be explained qualitatively in frame of a surface potential randomness conception.     

Convex, Acyclic, and Free Sets of an Oriented Matroid

We study the global and local topology of three objects associated to a simple oriented matroid: the lattice of convex sets, the simplicial complex of acyclic sets, and the simplicial complex of free sets. Special cases of these objects and their homotopy types have appeared in several places in the literature. The global homotopy types of all three are shown to coincide, and are either spherical or contractible depending on whether the oriented matroid is totally cyclic. Analysis of the homotopy type of links of vertices in the complex of free sets yields a generalization and more conceptual proof of a recent result counting the interior points of a point configuration. Received October 23, 2000, and in revised form May 3, 2001. Online publication November 2, 2001.     

Magneto-optical properties of Dy<Superscript>3+</Superscript> in oxide glasses: The origin of the magneto-optical activity of <Emphasis Type="Italic">f-f</Emphasis> transitions and its anomalous temperature dependence

The temperature dependence of the absorption spectra and magnetic circular dichroism due to f-f transitions from the ⁶ H _15/2 to ⁶ F _5/2 and ⁶(F _7/2 + H _5/2) states in the Dy³⁺ ion in (Dy₂O₃-P₂O₅-SiO₂-GeO₂) and (Dy₂O₃-La₂O₃-Al₂O₃-B₂O₃-SiO₂-GeO₂) glasses and the temperature dependence of the Faraday effect were studied. The temperature dependence of the Faraday effect caused by f-d transitions was found to differ from that of the magnetic circular dichroism due to f-f transitions. It was shown that f-f transitions occur preferentially in Dy³⁺ ions associated into clusters. The origin of the paramagnetic magneto-optical activity of f-f transitions was analyzed. It was shown that the contributions to this activity can differ in value and sign and that the ratio between these contributions depends on the transition type. In some cases, this difference results in an anomalous temperature dependence of the magneto-optical activity.     

Error analysis of free probability approximations to the density of States of disordered systems

Theoretical studies of localization, anomalous diffusion and ergodicity breaking require solving the electronic structure of disordered systems. We use free probability to approximate the ensemble-averaged density of states without exact diagonalization. We present an error analysis that quantifies the accuracy using a generalized moment expansion, allowing us to distinguish between different approximations. We identify an approximation that is accurate to the eighth moment across all noise strengths, and contrast this with perturbation theory and isotropic entanglement theory.