Regioselective alkylation reactions of 2,4-diphenyl-3H-1-benzazepine give either 3-alkyl-3H-1-benzazepines or 1-alkyl-1H-1-benzazepines

2,4-Diphenyl-3H-1-benzazepine is deprotonated with either LDA or KHMDS. The resulting anion is alkylated with alkyl halides or MeOTs, giving either products of alkylation at C3, or at N, or a mixture of both. The regioselectivity depends on the base, presence of the complexing agent HMPA, and the leaving group of the alkylating agent. Using MeI as alkylating agent gives exclusively the C3-methylated product, while using MeOTs gives exclusively the N-methylated product. The N-alkylated products show evidence of stereodynamic behavior in their NMR spectra.     

A Boiling‐Water‐Stable,Tunable White‐Emitting Metal–Organic Framework from Soft‐Imprint Synthesis

A new avenue for making porous frameworks has been developed by borrowing an idea from molecularly imprinted polymers (MIPs). In lieu of the small molecules commonly used as templates in MIPs, soft metal components, such as CuI, are used to orient the molecular linker and to leverage the formation of the network. Specifically, a linear dicarboxylate linker with thioether side groups reacted simultaneously with Ln³⁺ ions and CuI, leading to a bimetallic net featuring strong, chemically hard Eu³⁺–carboxylate links, as well as soft, thioether‐bound Cu₂I₂ clusters. The CuI block imparts water stability to the host; with the tunable luminescence from the lanthanide ions, this creates the first white‐emitting MOF that is stable in boiling water. The Cu₂I₂ block also readily reacts with H₂S, and enables sensitive colorimetric detection while the host net remains intact.     

On Arthur Fine's solution to the measurement problem

Arthur Fine has recently proposed a novel solution to the measurement problem. Fine's innovation is to exploit the idea that a measurement is a selective interaction in which the apparatus responds to a probability distribution. I develop Fine's solution in some detail, responding to various potential objections along the way. In the end, however, I suggest that Fine needs to tell us more before we can declare the measurement problem solved.     

Picosecond X-ray diffraction studies of laser-excited acoustic phonons in InSb

We have employed time-resolved X-ray diffraction with picosecond temporal resolution to measure the time-dependent rocking curves of laser-irradiated asymmetrically cut single InSb crystals. Coherent acoustic phonons were excited in the crystals by irradiation with 800-nm, 100-fs laser pulses at irradiances between 0.25 and 12 mJ/cm². The induced time-dependent strain profiles (corresponding to the coherent phonons) were monitored by diffracting collimated, monochromatic pulses of X-rays from the irradiated crystals. Recording of the diffracted radiation with a fast low-jitter X-ray streak camera resulted in an overall temporal resolution of better than 2 ps. The strain associated with the coherent phonons modifies the rocking curve of the crystal in a time-dependent manner, and the rocking curve is recorded by keeping the angle of incidence of the X-rays upon the crystal fixed, but varying the energy of the incident X-rays around a central energy of 8.453 keV (corresponding to the peak of the rocking curve of the unperturbed crystal). The observed time-dependent diffraction from the irradiated crystals is in reasonable agreement with simulations over a wide range of energies from the unperturbed rocking-curve peak. Received: 22 March 2002 / Revised version: 25 March 2002 / Published online: 6 June 2002     

Saturation spectroscopy of electronic states in a magnetic field in InAs/AlxGa1−xSb single quantum wells

We have carried out saturation spectroscopy of cyclotron resonance in a semiconducting InAs/Al_0.5Ga_0.5Sb single quantum well using the UCSB free electron laser and have extracted an effective Landau level lifetime using an n-level rate equation model. The effective lifetime shows strong oscillations (>an order of magnitude) with frequency. Minima are shifted to higher frequencies than those given by the simple parabolic magnetophonon resonance condition due to large nonparabolicity in the InAs conduction band. We have also used this technique to investigate the origins of two lines: the X-line and cyclotron resonance in a “semimetallic” InAs/Al_0.1Ga_0.9Sb single quantum-well structure. Results show that the two lines are of different origin.     

Improved implanted,planar buried heterostructure lasers through enhanced optical confinement

We fabricated and tested implanted, planar-buried heterostructure, graded-index, separate confinement heterostructure (IPBH-GRINSCH) lasers in various waveguide geometries. These devices were also numerically simulated with a two-dimensional waveguide model. We report improved laser performance that results from a reduced overlap of the optical field with the absorbing regions produced by residual implant damage.     

Correlations between electron and positron workfunctions on copper surfaces

We have performed contact potential difference measurements on low-index faces of copper in ultrahigh vacuum using positrons as positive test particles in a retarding field analyzer. For negative positron affinity surfaces bombarded with keV positrons we also measured energy distributions of reemitted slow positrons and found them to sharply peaked in energy about a value which we label ?φ⁺. Both adsorbing sulfur on a Cu(111) sample and raising its temperature cause changes in φ⁺ which are equal and opposite to the contact potential change of the sample, i.e. the electron workfunction change. This result is in complete accordance with φ⁺ being a measure of the negative positron workfunction of the sample and high temperature or adsorbates inducing a change only in the electrostatic surface dipole layer.     

A method for accelerating the iterative solution of a class of Fredholm integral equations

The present paper extends the synthetic method of transport theory to a large class of integral equations. Convergence and divergence properties of the algorithm are studied analytically, and numerical examples are presented which demonstrate the expected theoretical behavior. It is shown that, in some instances, the computational advantage over the familiar Neumann approach is substantial.This authors acknowledge with pleasure conversations with Paul Nelson. Thanks are due also to Janet E. Wing, whose computer program was used in making the calculations reported in Section 8.This work was performed in part under the auspices of USERDA at the Los Alamos Scientific Laboratory of the University of California, Los Alamos, New Mexico.