Existentially complete lattice-ordered groups

We investigate existentially complete lattice-ordered groups in this paper. In particular, we list some of their algebraic properties and show that there are continuum many countable pairwise non-elementarily equivalent such latticeordered groups. In particular, existentially complete lattice-ordered groups give rise to a new class of simple groups. This paper is dedicated to the memory of Abraham Robinson. Without his pioneer work in model-theoretic forcing, none of this research would have been possible. Research supported in part by a grant from Bowling Green State University Faculty Research Committee. Research conducted in part while on sabbatical leave from the University of Missouri.     

Direct observation of spin dependent electronic structure of GaAs using spin polarized photoemission

The spectrum of spin plarization P(hv) of electrons photoemitted from negative electron affinity GaAs using circularly polarized light, 1.5 eV < hv < 3.6 eV, was measured by Mott scattering; it exhibits structure derived from the spin orbit split energy bands near Γ and L.     

Chapter 9: miscellaneous preserver problems

This chapter consists of three sections of miscellaneous results. Each is self contained with its own abstract, but the references are in one group at the very end of the chapter. The first section considers matrices over semirings. The second concerns a function on a matrix space M which commutes with a linear operator on M. The third considers linear operators preserving certain properties associated with positive semidefinite matrices.     

Realizable posets

Certain p-local orders in n-dimensional division algebras over the rational numbers occur as endomorphism rings of torsion-free abelian groups of rank n if and only if an associated finite poset P has a strict faithful representation of dimension less than |P| over the field with p elements. In this note we obtain a simple characterization of those finite posets which do not admit such a representation.Research supported in part by NSF grant DMS-8802833.     

Disorder-induced microscopic magnetic memory

Using coherent x-ray speckle metrology, we have measured the influence of disorder on major loop return point memory (RPM) and complementary point memory (CPM) for a series of perpendicular anisotropy Co/Pt multilayer films. In the low disorder limit, the domain structures show no memory with field cycling--no RPM and no CPM. With increasing disorder, we observe the onset and the saturation of both the RPM and the CPM. These results provide the first direct ensemble-sensitive experimental study of the effects of varying disorder on microscopic magnetic memory and are compared against the predictions of existing theories.     

Simultaneous intensity, birefringence, and flow measurements with high-speed fiber-based optical coherence tomography

We demonstrate that tissue structure, birefringence, and blood flow can be imaged simultaneously by use of techniques of polarization-sensitive optical coherence tomography and phase-resolved optical Doppler tomography. An efficient data-acquisition procedure is implemented that optimizes the concurrent processing and display of all three image types. Images of in vivo human skin acquired with a high-speed fiber-based system are presented.