Gamma-ray optics using57Co-doped iron single crystals

We have begun a search for anomalous emission and anomalous temporal decay of nuclear resonant radiation using internal sources located inside thick single crystals. Our samples are two iron single crystals of thicknesses 0.5 and 1.0 mm that have been doped on one side with⁵⁷Co. From ordinary considerations, these samples are much too thick to allow any 14.4-keV radiation to pass through the crystal and out the other side. However, our results suggest that 14.4-keV radiation is able to be transmitted through the crystals. Furthermore, using coincidence techniques we examined the temporal decay of the 14.4-keV nuclear level under these circumstances.     

Colour dipoles and virtual Compton scattering

An analysis of Deeply Virtual Compton Scattering (DVCS) is made within the colour dipole model. We compare and contrast two models for the dipole cross-section which have been successful in describing structure function data. Both models agree with the available cross section data on DVCS from HERA. We give predictions for various azimuthal angle asymmetries in HERA kinematics and for the DVCS cross section in the THERA region. Received: 22 July 2001 / Revised version: 5 November 2001 / Published online: 14 December 2001     

A detailed next-to-leading order QCD analysis of deeply virtual Compton scattering observables

We present a detailed next-to-leading order (NLO) leading twist QCD analysis of deeply virtual Compton scattering (DVCS) observables, for several different input scenarios, in the scheme. We discuss the size of the NLO effects and the behavior of the observables in skewedness , momentum transfer,t, and photon virtuality, . We present results on the amplitude level for unpolarized and longitudinally polarized lepton probes, and unpolarized and longitudinally polarized proton targets. We make predictions for various asymmetries and for the DVCS cross section and compare with the available data. Received: 30 November 2001 / Revised version: 12 February 2002 / Published online: 15 March 2002     

Laser-polarized Xe NMR and MRI at Ultralow Magnetic Fields

Laser-polarized ¹²⁹Xe and a high-T_csuperconducting quantum interference device (SQUID) are used to obtain magnetic resonance images in porous materials at a magnetic field of 2.3 mT, corresponding to a Larmor frequency of 27 kHz. Image resolution of 1 mm is obtained with gradients of only 1 mT/m. The resolution of xenon chemical shifts in different physicochemical environments at ultralow fields is also demonstrated. Details of the circulating flow optical pumping apparatus and the SQUID spectrometer are presented.     

Prebunched high-harmonic gyrotron

A scheme for harmonic wave generation using a prebunched electron beam has been demonstrated. The prebunched electron beam has been used to further increase the efficiency of the authors' axis-encircling high-harmonic gyrotron. The proof-of-principle experiment was performed at the third harmonic with a TE₃₁₂ mode at 27.7 GHz. The conversion power of 6.7 kW was significantly greater than that used in the nonprebunched experiment. Also, mode competition was effectively suppressed. As expected, the unsaturated output power is proportional to the square of the electron beam current and the start of oscillation current is essentially zero. A linear theory, derived by taking into account the spread of the guiding center and the spread of the axial velocity, gives good agreement with the experimental results     

Regular closure

Regular closure is an operation performed on submodules of arbitrary modules over a commutative Noetherian ring. The regular closure contains the tight closure when both are defined, but in general, the regular closure is strictly larger. Regular closure is interesting, in part, because it is defined a priori in all characteristics, including mixed characteristic. We show that one can test regular closure in a Noetherian ring by considering only local maps to regular local rings. In certain cases, it is necessary only to consider maps to certain affine algebras. We also prove the equivalence of two variants of regular closure for a class of rings that includes .