Fermionic Casimir stress on a spherical bag

The zero-point energy due to quantum fluctuations in a massless fermionic field inside and outside an ideal spherical bag is computed. The result is a repulsive stress, the Casimir energy being , where a is the bag radius.     

Optical performance models for FDDI links

A loss budget model has been developed to predict optical perjormnce of the fiber distributed-data interjace (FDDI) type of networks in the premises-distribution environment. This model tailors existing statistical loss budget models to the FDDI standard. It is expected that as FDDI becomes popular, fiber-based distribution systems will become common. When designing a fiber-distribution system, it is important to understand the constraints placed on link perjormance by the cable plant. To determine these constraints, the model is examined numerically using a large range of initial conditions. The total link length is used as the dependent variable. This set of initial conditions corresponds to an ensemble ofpossible link configurations, and these link configurations are studied in the context of the premises-distribution environment.

The model is extended to include the use of optical bypass switches. Laboratory measurement data are presented to verify the accuracy of the bypass switch model. The extended model, including the bypass switch, is examined numerically for a similar set of initial conditions. These constraints are applied to the use of bypass switches in wiring closets, between Jlaors, and at the work location. Distance limitations are determined for FDDI links utilizing optical bypass switches.     

Anomalies in PT-Symmetric Quantum Field Theory

It is shown that a version of PT-symmetric electrodynamics based on an axial-vector current coupling massless fermions to the photon possesses anomalies and so is rendered nonrenormalizable. An alternative theory is proposed based on the conventional vector current constructed from massive Dirac fields, but in which the PT transformation properties of electromagnetic fields are reversed. Such a theory seems to possess many attractive features.     

Three-dimensional critical behavior with 2D, 1D, and 0D dimensionality crossover: surface and edge specific heats

The critical behavior at a second order phase transition is characterized by the divergence of the correlation length xi. We have studied the superfluid transition of 4He in a series of experimental cells in which this divergence of xi is modified due to finite-size confinement. In particular, the design of these cells is such that the smallest dimension is kept the same, 1 microm, but the geometry is such that one obtains crossover to dimensionality of 2, 1, and 0. This corresponds to films, channels, and boxes filled with helium. We measure the specific heat and compare these results with theoretical expectations. We identify surface and line specific heat contributions by analyzing the deviation of the specific heat from its behavior in the thermodynamic limit. The design of these cells is made possible by a combination of silicon lithography and direct wafer bonding.     

Magnetic and119Sn Mössbauer studies on a new Heusler alloy Co2ScSn

A new alloy, having the formula, Co₂ScSn, has been prepared. This is found to have the cubic Heusler L2₁ type structure (a = 6.19A). Magnetization measurements reveal a large drop in magnetization around 270K. Low field ac susceptibility also shows a transition at 268K which we take to be the Curie temperature of the alloy. The magnetic moment at 5K is found to be 0.55 _B per cobalt atom.¹¹⁹Sn Mössbauer measurements at 8K show a hyperfine split spectrum with a hyperfine field of about 40 kOe. Attempts to prepare other Co₂RSn alloys particularly with R=Lu, were not successful.     

Deciphering the mechanistic dichotomy in the cyclization of 1-(2-ethynylphenyl)-3,3-dialkyltriazenes: competition between pericyclic and pseudocoarctate pathways

The mechanistic aspects of the cyclization of (2-ethynylphenyl)triazenes under both thermal and copper-mediated conditions are reported. For cyclization to an isoindazole, a carbene mechanistic pathway is proposed. The carbene intermediate can react with oxygen, dimerize to give an alkene, or be trapped either intermolecularly (using 2,3-dimethyl-2-butene to generate a cyclopropane) or intramolecularly (using a biphenyl moiety at the terminus of the acetylene to form a fluorene). Density-functional theory (DFT) calculations support a pseudocoarctate pathway for this type of cyclization. Thermal cyclization to give a cinnoline from (2-ethynylphenyl)triazenes is proposed to occur through a pericyclic pathway. DFT calculations predict a zwitterionic dehydrocinnolinium intermediate that is supported by deuterium trapping studies as well as cyclizations performed using a 2,2,6,6-tetramethylpiperidine moiety at the 3-position of the triazene.     

The relation between repair of radiation damage and mutation induction

Abstract— This essay, written in honor of Alexander Hollaender's seventieth birthday, reviews the development of the concept of repair of premutational damage at both the biological and molecular levels. It stresses the important hut not exclusive role that repair processes play in determining the mutation yield, with emphasis on mutations induced by ultraviolet radiation. It points out that under special circumstances repair may be sufficiently efficient to almost completely eliminate premutational damage.     

Response factor considerations for the quantitative analysis of western redcedar (Thuja plicata) foliar monoterpenes

A method is described for quantitative analysis of monoterpenes in western redcedar (Thuja plicata) foliage by gas chromatography with flame ionization detection. Response factors for monoterpenes identified in redcedar are evaluated to determine similarities among monoterpene responses. Evaluation demonstrates that redcedar monoterpenes yield detector responses that fall into two groups. One monoterpene from each group is used as a standard for quantitative analysis. Redcedar monoterpenes are quantitated by comparing analyte response with the response factor of one of the standards in single-point calibrations. Homogenized foliage samples are extracted with ethyl acetate and the extracts passed through a solid phase extraction column of graphitized carbon to remove plant pigments. Method bias and repeatability are evaluated by fortifying foliage samples with (1S)-(+)-carvone and (1S)-(+)-2-carene and subjecting the samples to the extraction and analysis procedures. Detection limits are also assessed from fortified samples. Excellent recovery (> 95.0%) and precision (< 5%) are obtained from the analysis of 2-carene from fortified samples. Carvone recovery is approximately 80% with excellent precision (< 4%). The method limits of detection obtained from 2-carene and carvone fortified samples are 4.7 and 13.5 microg/g, respectively.     

Chiral N-Acetyl Selone-Promoted Aldol Reactions

The chiral oxazolidineselone functionality was found to be an excellent partner in the stereospecific acetate aldol reaction with aldehydes via the titanium enolates. Good stereocontrol was obtained as determined by NMR spectroscopy. The oxazolidineselone also provided a straightforward way to establish the stereopurity of the coupling reaction through ⁷⁷Se NMR spectroscopy.