Enhancement of weak anti-localization signatures in the magneto-resistance of bismuth anti-dot thin films

Anti-dot array thin films of bismuth were prepared by the e-beam deposition of this semi-metal on nano-porous substrates. The magneto-resistance measurements of bismuth thin films deposited under identical conditions on various substrates displayed signatures from both classical magneto-resistance and weak anti-localization effects. The relative intensity of the two effects could be altered by the choice of the substrate, with the anti-dot array morphology suppressing the classical magneto-resistance, and enhancing the weak anti-localization contribution to the measured magneto-resistance. As a result, the weak anti-localization effect can be traced to higher magnetic field strengths and higher temperatures than is possible in non-patterned films, improving the accuracy of the parameters extracted from the data. PACS 73.20.Fz; 73.23-b; 73.61.At     

The influence of CO on the surface plasmon absorption band of small silver clusters (D≤20 Å)

The surface plasmon absorption band of small Ag particles (diameter≤100 Å) in the gasphase as well as for clusters embedded in noble gas matrices is known to shift to higher energies and to broaden with decreasing diameter. This size effect depends sensitively on the microscopic surface properties of the clusters, which can be influenced by the interaction with the embedding matrix. Previous experiments with silver clusters in the size range 20 Å≤D≤100 Å proved that for SiO₂ and CO the matrix influence is strong enough to supersede the intrinsic size effect as observed in the noble gas matrices. The investigation of the influence of a CO matrix on smaller clusters with D≤20 Å reveals a novel feature: the position as well as the width of the surface plasmon absorption band become independent of the cluster size.     

Fluorescence spectroscopy of silver clusters formed in rare gas droplets

The Pick Up technique allows continuous formation of high density metal cluster beams in the otherwise hardly accessible size range Me₂ to about Me₅₀. With an apparatus based on the use of cryo-condensation pumps, Ar as inert gas for production of the host clusters by adiabatic expansion and silver as metal we demonstrate how the various source parameters influence the composition and mean size of the resulting cluster distributions. The analysis in the gas phase by means fluorescence spectroscopy allows to conclude that an Ar shell encapsulates the metal clusters. Received 30 November 2000     

Supertori are algebraic curves

Super Riemann surfaces of genus 1, with arbitrary spin structures, are shown to be the sets of zeroes of certain polynomial equations in projective superspace. We conjecture that the same is true for arbitrary genus. Properties of superelliptic functions and super theta functions are discussed. The boundary of the genus 1 super moduli space is determined.Research partially supported by the DOE (DE-AC02-82-ER-40073) and NSF (PHY-85-21588)     

Methylphenylphosphinate complexes with tri- and tetra-positive metal ions

Summary A series of methylphenylphosphinate {mpp; [-O-P-Ph(Me)-O-]^–} complexes of the forms M(mpp)₃ (M = Al, Ga, In, Sc, Y, Dy, Ti, V, Cr and Fe) and M(mpp)₄ (M = Th or U) were made from the appropriate metal chloride and a large excess of MeO(Me)PhP(O) at elevated temperatures. Structures involving linear, ligand-bridged polymeric species are suggested on the basis of the i.r. and magnetic data.     

Observation of a four-pion vector-meson state of mass ≈ 1.5 GeV produced by linearly polarized 9.3 GeV photons

From a study of γp → 2π⁺2π⁻p using 9.3 GeV linearly polarized photons, evidence is found for a J^P = 1⁻, I^G = 1⁺ four pion enhancement of mass ∼ 1.5 GeV with a production cross section of 1.6 ± 0.4 μb.     

Double negative: The necessity principle,commognitive conflict,and negative number operations

We use the DNR framework to analyze a classroom episode introducing negative integer exponents, comparing and contrasting our analysis with Sfard's recent commognitive analysis of a similar episode concerning multiplication of signed numbers. Students in both episodes objected to the standard rules for integer products or exponents, and they persisted in preferring their own rules even after the teacher justified the standard ones. We examine how pattern-based justifications may not address students’ intellectual needs, and we suggest other pedagogical strategies that promote student reasoning.     

Micro-electrodeposition techniques for the preparation of small actinide counting sources for ultra-high resolution alpha spectrometry by microcalorimetry

Special considerations and techniques are desired for the preparation of small actinide counting sources. Counting sources have been prepared on metal disk substrates (planchets) with an active area of only 0.079 mm². This represents a 93.75% reduction in deposition area from standard electrodeposition methods. The actinide distribution upon the smaller planchet must remain thin and uniform to allow alpha particle emissions to escape the counting source with a minimal amount of self-attenuation. This work describes the development of micro-electrodeposition methods and optimization of the technique with respect to deposition time and current density for various planchet sizes.     

How different are the supermanifolds of Rogers and DeWitt?

A DeWitt supermanifold always has the structure of a vector bundle over an ordinary spacetime manifold, whereas a Rogers supermanifold is not so restricted. Corresponding to the vector space fibers of the DeWitt supermanifold, a Rogers supermanifold has a foliation by submanifolds, or leaves, parametrized by soul coordinates only. We show that the universal covering space of any leaf always admits a flat metric. If the covering space is complete in this metric, it must in fact be a vector space. We combine this result with known theorems about foliations to give conditions under which a compact Rogers supermanifold with a single even dimension is necessarily a quotient space of flat superspace. We also show that a supermanifold defined by a polynomial equation in flat superspace is always of the DeWitt type. Finally, we exhibit new supermanifold structures forR ² and the 2-torus which show that the foliation of a Rogers supermanifold can be quite exotic.Enrico Fermi Fellow. Research supported by the NSF: PHY 83-01221, and the Department of Energy: DE AC02-82-ER-40073