Multiple scattering of gamma rays in water,concrete and sand

The transmitted photon spectra of¹³³Ba,²²Na,¹³⁷Cs,⁵⁴Mn and⁶⁰Co point sources are measured through different thicknesses of water, concrete and sand. The multiple-scatter peaks observed in these materials at 60, 90 and 100 keV energies respectively are found to be independent of incident photon energy and thickness of the medium.     

Critical temperature of an anisotropic ferromagnet in the presence of biquadratic exchange

A formulation, using the double time Green's function method, is presented for the anisotropic spin-one ferromagnetic system in the presence of biquadratic exchange and an expression is given for the critical temperature T_c in terms of parameters associated with the uniaxial anisotropy (treated exactly) and the biquadratic interaction (only the longitudinal part, treated in RPA). The prediction that T_c increases with the biquadratic exchange is found to be consistent with the recent calculation.     

Engaging the pyridine-DMAD zwitterion in a novel strategy for the selective synthesis of highly substituted benzene and cyclopentenedione derivatives

[reaction: see text] The pyridine-mediated reaction of dimethyl acetylenedicarboxylate and cyclobutene-1,2-diones affords selective access to either hexasubstituted benzene derivatives or cyclopentenedione derivatives depending on the concentration of pyridine.     

Pyridine-catalyzed addition of diaryl-1,2-diones to dimethyl butynedioate leading to the formation of 1,2-diaroyl dimethyl maleates via an unprecedented rearrangement

[reaction: see text] Pyridine catalyzes the reaction of 1,2-diaryl diones with dimethyl butynedioate to afford diaroyl maleates. This unprecedented rearrangement involves a unique benzoyl migration and proceeds with complete stereoselectivity.     

Practical synthesis of triaryl- and triheteroarylmethanes by reaction of aldehydes and activated arenes promoted by gold(III) chloride

[reaction: see text] Electron-rich arenes condense efficiently with various aldehydes under the influence of AuCl3, thus opening up a practical route to triarylmethanes, which have important applications. The mild conditions employed are especially noteworthy.     

RF-driven Josephson bifurcation amplifier for quantum measurement

We have constructed a new type of amplifier whose primary purpose is the readout of superconducting quantum bits. It is based on the transition of a rf-driven Josephson junction between two distinct oscillation states near a dynamical bifurcation point. The main advantages of this new amplifier are speed, high sensitivity, low backaction, and the absence of on-chip dissipation. Pulsed microwave reflection measurements on nanofabricated Al junctions show that actual devices attain the performance predicted by theory.     

Lewis acid-promoted annulation of O-quinonediimines by allylstannane: a facile synthesis of quinoxaline derivatives

[reaction: see text] Lewis acid-promoted addition of allyltri-n-butylstannane to o-quinonediimines afforded tetrahydroquinoxaline derivatives or allylated amides depending on the nature of the substituent on imine nitrogen.     

Degree of approximation to function of bounded variation by Bézier variant of MKZ operators

Guo (Approx. Theory Appl. 4 (1988) 9-18) introduced the integral modification of Meyer-Konig and Zeller operators and studied the rate of convergence for functions of bounded variation. In this paper we introduce the Bézier variant of these integrated MKZ operators and study the rate of convergence by means of the decomposition technique of functions of bounded variation together with some results of probability theory and the exact bound of MKZ basis functions. Recently, Zeng (J. Math. Anal. Appl. 219 (1998) 364-376) claimed to improve the results of Guo and Gupta (Approx. Theory Appl. 11 (1995) 106-107), but there is a major mistake in the paper of Zeng. For special case our main theorem gives the correct estimate on the rate of convergence, over the result of Zeng.     

Phases of supersymmetric gauge theories with flavors

We explore the phases of supersymmetric U(N) gauge theories with fundamental matter that arise as deformations of SQCD by the addition of a superpotential for the adjoint chiral multiplet. As the parameters in the superpotential are varied, the vacua of this theory sweep out various branches, which in some cases have multiple semiclassical limits. In such limits, we recover the vacua of various product gauge group theories, with flavors charged under some group factors. We describe in detail the structure of the vacua in both classical and quantum regimes, and develop general techniques such as an addition and a multiplication map which relate vacua of different gauge theories. We also consider possible indices characterizing different branches and potential relationships with matrix models.