Rational approaches to the design of cationic gemini surfactants for gene delivery.

We report a new class of amphiphilic gemini surfactants as vehicles for gene delivery into cells, and the beginnings of a systematic structure-activity study. Preliminary results suggest that combining gemini surfactants with dioleoylphosphatidylethanolamine (DOPE) should allow the preparation of liposomes of various sizes and lipid compositions. Control of such colloidal changes could be as significant as the changes in the molecular composition of the gemini surfactants in delivering optimum gene expression in animal models.     

The factorisation of chemical graphs and their polynomials: A systematic study of certain trees

Characteristic polynomials of the set of 284 trees which have 1 – 12 vertices of valency 1 – 3 have been examined for possible factors (divisors) using polynomial division. Twenty of these trees are prime in the sense that they contain no other trees in the set as factors. The remaining 264 trees can all be constructed from a subset of 5 trees and a at of 152 non-graphical polynomials. Some of these polynomials exhibit iso- or sub-spectral relationships with acyclic (matching) polynomials of certain cyclic structures. A few cyclic factors of trees are noted briefly. Twenty pairs and one triad of the trees examined are isospectral.     

Delta doping of ferromagnetism in antiferromagnetic manganite superlattices

We demonstrate that delta doping can be used to create a dimensionally confined region of metallic ferromagnetism in an antiferromagnetic (AFM) manganite host, without introducing any explicit disorder due to dopants or frustration of spins. Theoretical consideration of these additional carriers shows that they cause a local enhancement of ferromagnetic double exchange with respect to AFM superexchange, resulting in local canting of the AFM spins. This leads to a highly modulated magnetization, as measured by polarized neutron reflectometry. The spatial modulation of the canting is related to the spreading of charge from the doped layer and establishes a fundamental length scale for charge transfer, transformation of orbital occupancy, and magnetic order in these manganites. Furthermore, we confirm the existence of the canted, AFM state as was predicted by de Gennes [Phys. Rev. 118, 141 (1960)] but had remained elusive.     

Laser transfer of sol-gel ferroelectric thin films using an ITO release layer

A new laser transfer process is reported which allows damage-free transfer of ferroelectric thin films from a growth substrate directly to a target substrate. The thin film ferroelectric material is deposited on a fused silica growth substrate with a sacrificial release layer of ITO (indium tin oxide). Regions of the film that are to be transferred are then selectively metallised, and bonded to the target substrate. Separation from the growth substrate is achieved by laser ablation of the ITO release layer by a single pulse from a KrF excimer laser, with the laser light being incident through the growth substrate. The residual ITO on the transferred ferroelectric layer is electrically conducting, and may be suitable for incorporation into the final device, depending on the application. The new process has been demonstrated for 500 nm-thick layers of sol-gel PZT which were thermosonically bonded to a silicon target substrate prior to laser release. The transferred films show ferroelectric behaviour and have a slightly reduced permittivity compared to the as-deposited material.     

Programmable splice-free quasi-monolithic 2 Gbit/s optical fibre pulse code generator

A mechanically programmable optical fibre lattice pulse code generator, implemented in a quasi-monolithic, splice-free polished coupler technology, has been designed, constructed and characterised. The prototype system permits the generation of reconfigurable four bit pulse sequences with a pulse repetition rate of 2 GHz, i.e. 500 ps interval within the pulses in the output train.<>