The enclosed laser ablation of multiple stacks of laminated, metallised polymer

Enclosed laser ablation of single laminated, metallised polymer films (i.e. polymer, metal, adhesive, polymer layers respectively) has been studied in depth previously by the authors. It was found that most of the energy during this process was transmitted by the transparentised films. Therefore, it was proposed that multiple stacks of laminated metallised polymer samples could be transparentised with a single pass. In this paper, such experiments were carried out and stacks of 10 samples could be transparentised successfully with a single laser pass. The pulse energy incident upon each film was calculated from transmissivity measurements of each sample layer in a successfully demetallised stack, and the results were used to explain the behaviour observed from the experiments. Additional physical phenomena that were not present with single layer enclosed ablation have now been observed for the enclosed laser ablation of multiple layered stacks.     

Asymmetric Baeyer-Villiger oxidations of 4-mono- and 4,4-disubstituted cyclohexanones by whole cells of engineered Escherichia coli.

Whole cells of an Escherichia coli strain that overexpresses Acinetobacter sp. NCIB 9871 cyclohexanone monooxygenase have been used for the Baeyer-Villiger oxidations of a variety of 4-mono- and 4,4-disubstituted cyclohexanones. In cases where comparisons were possible, this new biocatalytic reagent provided lactones with chemical yields and optical purities that were comparable to those obtained from the purified enzyme or a strain of bakers' yeast that expresses the same enzyme. The efficient production of cyclohexanone monooxygenase in the E. coli expression system (ca. 30% of total soluble protein) allowed these oxidations to reach completion in approximately half the time required for the engineered bakers' yeast strain. Surprisingly, 4,4-disubstituted cyclohexanones were also accepted by the enzyme, and the enantioselectivities of these oxidations could be rationalized by considering the conformational energies of bound substrates along with the enzyme's intrinsic enantioselectivity. The enzyme expressed in E. coli cells also oxidized several 4-substituted cyclohexanones bearing polar substituents, often with high enantioselectivities. In the case of 4-iodocyclohexanone, the lactone was obtained in > 98% ee and its absolute configuration was assigned by X-ray crystallography. The crystal belongs to the monoclinic P2(1) space group with a = 5.7400(10), b = 6.1650(10), c = 11.377(2) A, b = 99.98(2) degrees, and Z = 2. Taken together, these results demonstrate the utility of an engineered bacterial strain in delivering useful chiral building blocks in an experimentally simple manner.     

On the weighting method for least squares problems with linear equality constraints

The weighting method for solving a least squares problem with linear equality constraints multiplies the constraints by a large number and appends them to the top of the least squares problem, which is then solved by standard techniques. In this paper we give a new analysis of the method, based on the QR decomposition, that exhibits many features of the algorithm. In particular it suggests a natural criterion for chosing the weighting factor. This work was supported in part by the National Science Foundation under grant CCR 95503126.     

Liquid crystals in biology II. Origins and processes of life

Part II of this review elaborates a hypothesis presented in Part I (2003 Liq. Cryst. 30, 541) and earlier publications. This hypothesis proposes that specified naturally occurring substances in the aqueous lyotropic mesophase of the liquid crystalline state of matter possess the ability to replicate, polymerize spontaneously and engage in further transitions to form ordered two- and three-dimensional layered, cubic, helical and spherulitic structures resembling those described geochemically, and observed experimentally in elementary forms of living substance. This ability uses energy originating in the kinetics of particles showing Brownian movements, spin and tensions at liquid-liquid and solid-liquid interfaces. Energy is derived also from chemiosmosis, phosphorylation, negative entropy and bonding by covalent and electro-weak forces to build macromolecules in ordered sequences of lipids, peptides and nucleic acids. These can polymerize to form glyco- and lipo-proteins, polynucleotides, anabolic and catalytic enzymes, plausibly and causally associated with the morphogenesis, metabolism and replication of protista, plankton and other primitive forms of life observed in prebiotic pools and surfaces of the cooling litho-hydrosphere of planet earth.

Interactions in these ecological niches would undoubtedly promote biochemical evolution compatible with self-organization of diversified living processes. These phenomena reveal plausible, natural mechanisms for formation of bilayer membranes with ionic channels, and other ordered structures providing spaces in which oxidative reactions and syntheses may proceed. All of this can be linked causally to early steps in animation of matter in accordance with laws governing particle physics and chemistry, templates and the general logic of molecular memories expressed in polynucleotides and proteins. Phenomena indicative of transfer of information, cellular organization, metabolism and transmission of neural signals are identifiable additionally as mechanisms for diversification and evolution. There are, however, credibility gaps in trying to extend this reasoning to sexual reproduction, speciation, competitive survival and ontogeny in the higher plants and metazoa. Various probabilities are discussed in statistical and physico-chemical terms. It is suggested that these could justify the hypothesis in so far as natural processes are sufficient to engender conditions for emergence of primitive life and Darwinian evolution in eco-niches of terrestrial space and measurable time. But there are also, in the unique utilization of energy, exploitation of advantages and adaptive capabilities of organisms at all levels to changing environmental stresses, many indications of teleonomic forces operating in ways for which there is no explanation in accordance with the laws of physical or chemical processes. This might be because understanding of particle physics and wave mechanics is insufficiently deployed in molecular biology, or because the laws of physics are scientifically incomplete in this respect.     

Magnetic size growth in nanocrystalline copper ferrite

When nanocrystalline copper ferrite (average grain size D≈6 nm) is subjected to high-energy-milling in air over different periods up to 12 h, we observe both a progressive enhancement of the ferrite's magnetic response and a shifting of its superparamagnetic limit. These are revealed by the shift to higher values of the Mössbauer blocking temperature, the maximum of the zero-field cooled magnetization and the start of the irreversibility between the zero-field and field-cooled magnetization curves, while the saturation magnetization and the mean magnetic moment per particle increase. The X-ray diffraction data show that the spinel improves its crystallinity with the milling, by increasing the grain size up to ≈13 nm and, also, reducing its micro-strain level. After 10 h of milling the copper ferrite stabilizes in its cubic metastable phase.     

Application of high gradient magnetic separation principles to magnetic drug targeting

A hypothetical magnetic drug targeting system, utilizing high gradient magnetic separation (HGMS) principles, was studied theoretically using FEMLAB simulations. This new approach uses a ferromagnetic wire placed at a bifurcation point inside a blood vessel and an externally applied magnetic field, to magnetically guide magnetic drug carrier particles (MDCP) through the circulatory system and then to magnetically retain them at a target site. Wire collection (CE) and diversion (DE) efficiencies were defined and used to evaluate the system performance. CE and DE both increase as the strength of the applied magnetic field (0.3–2.0 T), the amount of ferromagnetic material (iron) in the MDCP (20–100%) and the size of the MDCP (1–10 μm radius) increase, and as the average inlet velocity (0.1–0.8 m s⁻¹), the size of the wire (50–250 μm radius) and the ratio (4–10) of the parent vessel radius (0.25–1.25 mm radius) to wire radius decrease. The effect of the applied magnetic field direction (0° and 90°) on CE and DE was minimal. Under these plausible conditions, CEs as high as 70% were obtained, with DEs reaching only 30%; however, when the MDCPs were allowed to agglomerate (4–10 μm radius), CEs and DEs of 100% were indeed achieved. These results reveal that this new magnetic drug targeting approach for magnetically collecting MDCPs at a target site, even in arteries with very high velocities, is feasible and very promising; this new approach for magnetically guiding MDCPs through the circulatory system is also feasible but more limited. Overall, this study shows that magnetic drug targeting, based on HGMS principles, has considerable promise as an effective drug targeting tool with many potential applications.     

Economic evaluation of chronic conditions: framework for a quasi-Markov process

This paper presents a general model for economic evaluation of treatments of chronic conditions. The model is applicable in the situation where multiple possible treatments are available none of which is completely satisfactory by virtue of either lack of effect of adverse effects occurring for some patients. Treatments may include any process designed to enable patients to manage their condition. Since none are completely satisfactory, the model cannot determine the ‘best’ treatment, merely help identify an order in which treatments should be tried. This economic model must be used in conjunction with clinical or other relevant information. The model should be used to make comparisons between treatment options within one discrete category. The information provided can thus assist allocative microeconomic decisions, where funds must be allocated between specific competing alternatives. These decisions may apply to either purchasers or providers of health care services.