The Determination of Local Government Electoral Boundaries

For British local government elections, it is necessary to divide the total voting population into sub-groups (wards) such that each sub-group elects one or more representatives. At present there are remarkably few legal requirements governing the way in which this division is done. This study emphasizes the difficulties of formulating the problem of division, puts forward criteria which (hopefully) would look respectable and acceptable if embodied in legislation, and develops a linear programming-plus-heuristics approach which is applied to Bristol County Borough data to enable comparisons with current ward boundaries.     

Ground state of magnetic dimers on metal surfaces

We present model studies of the ground state for magnetic dimers on metal surfaces. We find it can be neither ferromagnetic nor antiferromagnetic, but is often canted for nearest neighbors. Thus, the system cannot be described using bilinear exchange. We give a criterion which can be used quite generally to interrogate the local stability of ferromagnetically or antiferromagnetically aligned dimers, and which also may be used to infer the canting angle when canted states are stable.     

Strongly enhanced hole-phonon coupling in the metallic state of the dilute two-dimensional hole gas

We have studied the temperature dependent phonon emission rate P(T) of a strongly interacting (r(s) > or =22) dilute 2D GaAs hole system using a standard carrier heating technique. In the still poorly understood metallic state, we observe that P(T) changes from P(T) approximately T5 to P(T) approximately T7 above 100 mK, indicating a crossover from screened piezoelectric (PZ) coupling to screened deformation potential (DP) coupling for hole-phonon scattering. Quantitative comparison with theory shows that the long range PZ coupling between holes and phonons has the expected magnitude; however, in the metallic state, the short range DP coupling between holes and phonons is almost 20 times stronger than expected from theory. The density dependence of P(T) shows that it is easier to cool low-density 2D holes in GaAs than higher density 2D hole systems.     

3D ultrasound guided breast biopsy system

Stereotactic X-ray mammography (SM) and ultrasound (US) guidance are commonly used techniques for breast biopsy. While SM provides 3D targeting information and US provides real-time guidance, both techniques have limitations. SM is a long and uncomfortable procedure and the US guided procedure is inherently 2D, requiring a skilled physician for both safety and accuracy. We have developed a 3D US-guided biopsy system to integrate with SM. The dual modality breast biopsy system combines the advantages of both approaches with 3D US and SM targeting, near real-time 3D and real-time 2D US guidance, breast stabilisation and a confined needle trajectory. Our goal is to be able to biopsy a larger percentage of suspicious masses using ultrasound, by clarifying ambiguous structures with mammographic imaging. Using breast phantoms, we have shown that our ultrasound guided biopsy system was capable of targeting artificial lesions that were 3.2 mm in diameter, with a 96% success rate. Through this study, we also demonstrated that our system was equivalent to current clinical practice, for an in vitro biopsy task. Metal beads in known relative positions allowed us to determine the geometry of the SM system, so that stereotactic mammography could be registered to 3D US images. The target registration error was found to be 1.6 mm. This error was dominated by positioning error in the vertical direction (perpendicular to the film surface). As an adjunct to SM, we propose that 3D US could provide more complete imaging information for target identification and real-time monitoring of needle insertion, as well as providing a means for rapid confirmation of biopsy success.     

A definitive synthesis of D-myo-inositol 1,4,5,6-tetrakisphosphate and its enantiomer D-myo-inositol 3,4,5,6-tetrakisphosphate from a novel butane-2,3-diacetal-protected inositol

New and rapid syntheses of the enantiomeric intracellular signalling molecules d-myo-inositol 1,4,5,6-tetrakisphosphate (1 a) and D-myo-inositol 3,4,5,6-tetrakisphosphate (1 b) are described. The synthetic strategy employs the novel butane-2,3-diacetal-protected (BDA-protected) myo-inositol (+/-)-3 ab, directly accessible from myo-inositol on a large scale, and an optical resolution with diastereoisomeric (R)-(-)-acetylmandelate esters. The X-ray crystal structure of (+/-)-4, an unusual side product of acid-catalysed reaction of myo-inositol with butanedione is also presented, and the absolute configurations of 1 a and 1 b are definitively assigned by conversion of key precursors into (+)-bornesitol and L-iditol hexaacetate, respectively. Biological activity of synthetic 1 b was confirmed in comparison with the natural polyphosphate.     

Preparation of Enantiomerically Pure β-Silylcarboxyl Derivatives by Asymmetric 1,4-Addition to N-Enoyl-sultams. Preliminary Communication

EtAlCl₂-promoted additions of organocopper reagents to camphor-derived, conjugated N-enoyl-sultams gave saturated and olefinic β-silylcarboxyl derivatives with high diastereodifferentiation. Nondestructive removal of the chiral auxiliary followed by oxidative Si-C bond cleavage furnished enantiomerically pure acetate-derived aldols and propionate-derived ‘anti’ -aldols (via silyl-directed α-methylation).     

On the potentialities of nuclear gamma resonance (Mössbauer effect) spectroscopy as a new,low dose approach to cancer radiation therapy

The extension of a new, low dose, Mössbauer spectroscopy approach to cancer radiation therapy to “easy” isotopes other than Iron-57 is outlined. New in vitro studies using a number of cancer cell lines are reported.     

Cavity induced shift and narrowing of the positronium Lyman-α transition

We report experiments in which the line shape of the Lyman-alpha (1S-2P) transition was measured for positronium (Ps) atoms both inside and outside a porous silica target. The energy interval ΔE for confined atoms was observed to be larger than that of free Ps by 1.26±0.06 meV. A configuration interaction calculation yields results that are consistent with our ～5 nm sample, and suggests that ΔE decreases dramatically for larger cavity diameters. The linewidth of the transition, (0.066±0.004) nm (FWHM), is about half of what one would expect for free Ps at room temperature due to the Dicke line narrowing effect of confinement. Such measurements can be used to determine void sizes in porous films and Ps dynamics therein, and elimination of the Doppler spread of atoms in a porous film could be useful for the efficient excitation of a Ps gas.     

Laser excitation of positronium in the Paschen-Back regime

Zeeman mixing of singlet and triplet 2P states of positronium (Ps) atoms, followed by decay back to the ground state, can effectively turn a long-lived triplet atom into a short-lived singlet state, which would seem to preclude laser cooling of Ps in a magnetic field. Here we report experiments which show that, in fact, because of the large splitting of the n=2 states in a high magnetic field (the Paschen-Back regime), the amount of such mixing diminishes approximately exponentially with an increasing magnetic field >0.01 T and is essentially eliminated above ～2 T. Thus, laser cooling of Ps should be feasible at high fields, which will facilitate the production of a Ps Bose-Einstein condensate.     

Three-dimensional hydrogen-bond geometry and probability information from a crystal survey

Summary An extensive crystal survey of the Cambridge Structural Database has been carried out to provide hydrogen-bond data for use in drug-design strategies. Previous crystal surveys have generated 1D frequency distributions of hydrogen-bond distances and angles, which are not sufficient to model the hydrogen bond as a ligand-receptor interaction. For each hydrogen-bonding group of interest to the drug designer, geometric hydrogen-bond criteria have been derived. The 3D distribution of complementary atoms about each hydrogen-bonding group has been ascertained by dividing the space about each group into bins of equal volume and counting the number of observed hydrogen-bonding contacts in each bin. Finally, the propensity of each group to form a hydrogen bond has been calculated. Together, these data can be used to predict the potential site points with which a ligand could interact and there-fore could be used in molecular-similarity studies, pharmacophore query searching of databases, or de novo design algorithms.