α‐Linolenic acid metabolism in adult humans: the effects of gender and age on conversion to longer‐chain polyunsaturated fatty acids

This review summarises and evaluates current knowledge of α‐linolenic acid (αLNA) metabolism in adult humans. The principal biological role of αLNA appears to be as a precursor for the synthesis of longer‐chain n‐3 polyunsaturated fatty acids (PUFA). Stable isotope tracer studies indicate that conversion of αLNA to eicosapentaenoic acid (EPA) occurs but is limited in men and that further transformation to docosahexaenoic acid (DHA) is very low. A lower proportion of αLNA is used for β‐oxidation in women compared with men, while the fractional conversion to the longer‐chain n‐3 PUFA is greater, possibly due to the regulatory effects of oestrogen. Increasing αLNA intake for a period of weeks results in an increase in the proportion of EPA in plasma lipids, circulating cells and breast milk, but there is no increase in DHA, which may even decline in some pools at high αLNA intakes. Overall, αLNA appears to be a limited source of longer‐chain n‐3 PUFA in man, and so adequate intakes of preformed long‐chain n‐3 PUFA, in particular DHA, may be important for maintaining optimal tissue function. The capacity to up‐regulate αLNA transformation in women may be important for meeting the demands of the foetus and neonate for DHA.     

The formation and properties of single nuclei

The formation and growth of single metallic nuclei of silver, mercury and copper have been studied at microscopically small electrodes of platinum and carbon. Once formed, metallic nuclei act as point sinks, growing under hemispherical mass-transfer control. The rate of growth at low overpotential is a function of the mean surface concentration as determined by the Nernst relation.The rate of formation of isolated nuclei has been determined as the inverse of the delay time attending their birth as indicated by the onset of the growth current. A distribution of delay times is observed in keeping with the statistical nature of the nucleation process.The nuclei or crystallites formed are spherical droplets in the case of mercury or microscopic single crystals in the case of solid metals, their size being accessible from the current—time integral of their growth. They are stable on open circuit and exhibit the residual overpotential of their excess surface free energy, ie their Gibbs—Kelvin potential. This potential is a linear function of their inverse equivalent spherical radius. The surface tensions calculated from the simplest application of the Gibbs—Kelvin equations appear to be higher than the known or estimated bulk values.The microscopic metallic crystallites have been used as reactive electrodes. The high mass-transfer flux to their surface enabled the exchange current to be determined by a simple, steady state small amplitude dc procedure.These studies confirm the considerable promise of microscopically small electrodes in electrochemistry.     

Single-processor scheduling with time restrictions

We consider the following list scheduling problem. We are given a set \(S\) of jobs which are to be scheduled sequentially on a single processor. Each job has an associated processing time which is required for its processing. Given a particular permutation of the jobs in \(S\) , the jobs are processed in that order with each job started as soon as possible, subject only to the following constraint: For a fixed integer \(B \ge 2\) , no unit time interval \([x, x+1)\) is allowed to intersect more than \(B\) jobs for any real \(x\) . It is not surprising that this problem is NP-hard when the value \(B\) is variable (which is typical of many scheduling problems). There are several real world situations for which this restriction is natural. For example, suppose in addition to our jobs being executed sequentially on a single main processor, each job also requires the use of one of \(B\) identical subprocessors during its execution. Each time a job is completed, the subprocessor it was using requires one unit of time in order to reset itself. In this way, it is never possible for more than \(B\) jobs to be worked on during any unit interval. In this paper we carry out a classical worst-case analysis for this situation. In particular, we show that any permutation of the jobs can be processed within a factor of \(2-1/(B-1)\) of the optimum (plus an additional small constant) when \(B \ge 3\) and this factor is best possible. For the case \(B=2\) , the situation is rather different, and in this case the corresponding factor we establish is \(4/3\) (plus an additional small constant), which is also best possible. It is fairly rare that best possible bounds can be obtained for the competitive ratios of list scheduling problems of this general type.     

Incorporation of La3+ into a Pt/CeO2/Al2O3 catalyst

The effects of La³⁺ incorporation into a Pt/CeO₂/Al₂O₃ catalyst were investigated by a combination of activity, temperature-programmed reduction (TPR), oxygen storage capacity (OSC), noble-metal surface area, and X-ray diffraction (XRD) measurements. Incorporation of La³⁺ ions into the Al₂O₃, before CeO₂ is added, promoted higher Pt and CeO₂ dispersions. The oxygen storage capacity was also higher in the presence of La³⁺. This is attributed to a combination of Pt and CeO₂ particle-size effects and possible blockage of the reaction between Al₂O₃ and CeO₂. The XRD data show that La³⁺ forms LaAlO₃ with Al₂O₃ and prevents -Al₂O₃ formation after various heat treatments.     

Population based Local Search for university course timetabling problems

Population based algorithms are generally better at exploring a search space than local search algorithms (i.e. searches based on a single heuristic). However, the limitation of many population based algorithms is in exploiting the search space. We propose a population based Local Search (PB-LS) heuristic that is embedded within a local search algorithm (as a mechanism to exploit the search space). PB-LS employs two operators. The first is applied to a single solution to determine the force between the incumbent solution and the trial current solution (i.e. a single direction force), whilst the second operator is applied to all solutions to determine the force in all directions. The progress of the search is governed by these forces, either in a single direction or in all directions. Our proposed algorithm is able to both diversify and intensify the search more effectively, when compared to other local search and population based algorithms. We use university course timetabling (Socha benchmark datasets) as a test domain. In order to evaluate the effectiveness of PB-LS, we perform a comparison between the performances of PB-LS with other approaches drawn from the scientific literature. Results demonstrate that PB-LS is able to produce statistically significantly higher quality solutions, outperforming many other approaches on the Socha dataset.     

Morphological distribution of injection-moulded isotactic polypropylene: a study of synchrotron small angle X-ray scattering

Synchrotron small-angle X-ray scattering (SAXS) studies were carried out to investigate effects of thickness of injection-moulded isotactic polypropylene (iPP) plates on shear-induced morphology and morphological distribution through the depth direction of the plates. Different levels of effective shear flow are imposed on the iPP melt by changing the thickness of the plates although the injection moulding is performed with the same injection ram speed and the same melt and mould temperatures. Shish-kebab-like morphology is found roughly 100 μm from the surface of plates, regardless of the thickness of plates. However, the type of shish-kebab-like morphology is very sensitive to the thickness. The shish-kebab structure at the surface region can be changed into the kebab-structure only or random crystalline lamellae as the thickness of the plate increases. The preferential orientation of crystalline lamellae along the flow direction strongly depends on the thickness of the plate, although the melt-shear does not significantly enhance the degree of linear crystallinity. It is also found that in the core region, the slow relaxation of polymer chains in the thick plate results in a higher degree of linear crystallinity. The results indicate that the shear-induced morphology is strongly dependent on effective shear flow and should be described individually.     

“Red Tweezers”: Fast,customisable hologram generation for optical tweezers

Holographic Optical Tweezers (HOT) are a versatile way of manipulating microscopic particles in 3D. However, their ease of use has been hampered by the computational load of calculating the holograms, resulting in an unresponsive system. We present a program for generating these holograms on a consumer Graphics Processing Unit (GPU), coupled to an easy-to-use interface in LabVIEW (National Instruments). This enables a HOT system to be set up without writing any additional code, as well as providing a platform enabling the fast generation of other holograms. The GPU engine calculates holograms over 300 times faster than the same algorithm running on a quad core CPU. The hologram algorithm can be altered on-the-fly without recompiling the program, allowing it to be used to control Spatial Light Modulators in any situation where the hologram can be calculated in a single pass. The interface has also been rewritten to take advantage of new features in LabVIEW 2010. It is designed to be easily modified and extended to integrate with hardware other than our own.     

A unifying framework for ℓ 0-sampling algorithms

The problem of building an ? ₀-sampler is to sample near-uniformly from the support set of a dynamic multiset. This problem has a variety of applications within data analysis, computational geometry and graph algorithms. In this paper, we abstract a set of steps for building an ? ₀-sampler, based on sampling, recovery and selection. We analyze the implementation of an ? ₀-sampler within this framework, and show how prior constructions of ? ₀-samplers can all be expressed in terms of these steps. Our experimental contribution is to provide a first detailed study of the accuracy and computational cost of ? ₀-samplers.     

Interaction between a Fab fragment against gp41 of human immunodeficiency virus 1 and its peptide epitope: characterization using a peptide epitope library and molecular modeling

The molecular interaction of the Fab fragment of the human monoclonalantibody 3D6, directed against the transmembrane protein gp41of human immunodeficiency virus (HTV) 1, with its peptide epitopeis characterized by a panel of overlapping peptides, a peptideepitope library and molecular modeling techniques. The sequenceCSGKLICTTAVPW, corresponding to amino acids 605–617 ofgp41, was identified as the best binding peptide (K_D = 1x10^-8mol/1). This peptide served as a starting point to prepare acellulose-bound peptide epitope library in which each residueof the epitope is substituted by all L- and D-amino acids, resultingin 494 epitope peptide variants which were subsequently analyzedfor binding 3D6. The library was synthesized to identify residuescritical for binding and to obtain information about the molecularenvironment of the epitope peptide bound to 3D6. Both cysteineresidues, as well as isoleucine 6, threonine 8 and proline 12,of the epitope were highly sensitive to substitution. Usingthe data obtained from the epitope characterization, as wellas a low-resolution electron density map of a 3D6 Fab-peptidecomplex, a 3-D model of the Fab-peptide complex was generatedby molecular modeling. The modeling experiments predict bindingof the peptide, which is cyclized via the two cysteine residues,to a pocket formed dominantly by the hypervariable loops complementaritydetermining regions CDR3L, CDR2H and CDR3H.     

How other process equipment influences centrifuge performance

When problems occur in industrial processes the centrifuge is often blamed, but this is not necessarily where the problems lie. Nigel Day, NCD Separation Solutions Ltd, UK, discusses how upstream and downstream equipment can negatively impact on centrifuge performance, using a batch basket filtering centrifuge type as an example. He also presents details of a recent process optimization project.