Perfect crystal grasers

We discuss the advantages obtained in the conditions for γ-ray lasing (grasing) by utilizing a crystalline sample rather than an amorphous needle. We show that, for emitters of multipole M1 or higher, the favored grasing mode will be a Borrmann channel at the largest available Bragg angle. Further, we give necessary conditions on the population inversion density to determine a practical pulsed laser. The same gain factors, and thus the same advantages of crystalline over amorphous samples, occur in the equations describing both steady state and pulsed lasers, as well as superradiators. Finally, we indicate that, for any practical system, the predominant mode of de-excitation will be superradiance, rather than stimulated emission.     

Channelized detection filters

The problem of detecting objects in noisy backgrounds is addressed. We derive detection filters by training a linear classifier, using features obtained from subimages corresponding to circular channels in the Fourier domain. The classifier weights approach the prewhitening matched filter when the classifier is trained for the detection of known objects in stationary noise. A simple form of rotation invariance is attained for considerably less computation than by the direct application of multiple matched filters. The method is demonstrated for the task of detecting simulated tumors in simulated nuclear medical images.     

Geometrical isomerism in divalent-carbon intermediates

Three classes of monosubstituted carbenes (aryl-, vinyl-, carbonyl-) and one class of disubstituted carbenes (dicarbonyl-), all of them ground state triplets, can exist in more than one rotameric form with distinct zero field splitting parameters. Representative examples of these carbenes are discussed and selected aspects of triplet carbenes are evaluated, including their π spin density distribution, intramolecular H-abstraction, and cis-trans isomerization. Lastly, the structures assigned to two triplets generated by photolysis of dibenzoyldiazomethane are re-evaluated.     

β-Selective Glucosylation in the Absence of Neighboring Group Participation: Influence of the 3,4-O-Bisacetal Protecting System

A 3,4-O-bisacetal 2,6-di-O-benzyl protected thioglucoside is converted to the corresponding glucosyl triflate with 1-benzenesulfinyl piperidine and trifluoromethanesulfonic anhydride. The moderate to excellent β-selectivity exhibited with this glucosyl triflate with a range of alcohols is generally higher than that observed with the more electronically disarmed corresponding 3,4-O-carbonate, for which a possible reason is advanced.     

Synthesis, characterization and cytotoxicity of some palladium(II), platinum(II), rhodium(I) and iridium(I) complexes of ferrocenylpyridine and related ligands. Crystal and molecular structure of trans-dichlorobis(3-ferrocenylpyridine)palladium(II)

The preparation of a series of ferrocenyl nitrogen donor ligands including ferrocenylpyridines, ferrocenylphenylpyridines and 1,1^′-di(2-pyridyl)ferrocene is described. Coordination studies of the substituted pyridines (L) were carried out with platinum, palladium, rhodium and iridium. This resulted in the preparation of the following types of complexes: [MCl(CO)₂(L)] and [M(cod)(L)₂]ClO₄ where M=Rh or Ir, cod=1,5-cyclooctadiene; [M^′Cl₂(L)₂] where M^′=Pt or Pd. The X-ray crystal structure of trans-dichlorobis(3-ferrocenylpyridine)palladium was obtained. The complexes were screened for activity against two human cancer cell lines. At least two of the complexes displayed growth inhibition similar to that of the widely used chemotherapeutic agent, cisplatin.     

The Reduction of Prostaglandin Intermediates Using Alumino Hydride Reagents

The assembly of the correct C-15¹ stereochemistry in prostaglandin synthesis has been attained by either generating the desired stereochemistry at C-15¹ through stereoselective reduction of a ketone precursor² or by adding the fully functionalised C₁₂-C₂₀ side chain intact by means of organometallic³, borane⁴ and β-oxidoylid reagents⁵. This paper is concerned with the first of these two approaches. It illustrates how a prostaglandin precursor (1) was reduced using bulky alumino hydride reagents derived from 3-0-benzyl-1,2,0-cyclohexylidene- α -D-glucofuranose to give benefits of yield or moderate stereoselectivity over other methods available at the time the work was carried out.