Microbial Populations in Tropical Reservoirs Using Flow Cytometry

Flow cytometry was applied in the study of bacteria and phytoplankton populations in five tropical reservoirs. Water quality between different reservoirs was compared and correlation analyses were carried out to investigate how the biomass of bacteria and phytoplankton related to other water quality parameters measured (i.e., temperature, dissolved oxygen, pH, conductivity, water transparency, turbidity, chlorophyll a, and total nitrogen and phosphorus). Average chlorophyll a concentrations were typically greater than 20?μg/L. Bacteria populations detected with flow cytometry were generally small in size (typically <0.08?μm3 or 0.3?μm equivalent spherical diameter) and contributed less than 13% of the total microbial biomass. Subpopulations of pico-, ultra-, and net phytoplankton were discriminated flow cytometrically by their red and orange autofluorescence. Cyanobacteria dominated four out of the five reservoirs in terms of numbers but only contributed more than 50% of the microbial biomass in two of the reservoirs. In general, local reservoirs were found to be phosphorus limited and alkaline conditions favored the growth of phytoplankton and bacteria.     

On a Wavenumber Optimized Streamline Upwinding Method for Solving Steady Incompressible Navier-Stokes Equations

A stabilized upwind finite-element model is developed to solve the three-dimensional incompressible steady Navier-Stokes equations. The test function is constructed to have a larger weight on the upstream side. This has been achieved by adding a stabilized term to the shape function so as to optimize the numerical wavenumber for convection terms. To avoid Lanczos or pivoting breakdown while solving the resulting unsymmetric and indefinite mixed finite-element matrix equations iteratively, the finite-element equation has been modified by pre-multiplying it with its transpose. The resulting normalized matrix equation becomes symmetric and positive-definite. We can therefore apply a computationally efficient conjugate gradient Krylov iterative solver to get an unconditionally convergent solution. However, the condition number of the new system becomes the square of the original unsymmetric indefinite system. To fully exploit excellent convergence nature of the conjugate gradient iterative solver, an element-by-element strategy is adopted to avoid assembling of all the stiffness matrices obtained at element level. We alleviate the drawback of slower convergence of the conjugate gradient method due to the increased condition number by preconditioning the positive-definite matrix. The resulting preconditioned matrix equation is solved in a matrix-free manner using the preconditioned conjugate gradient iterative solver. The developed finite-element code is first verified by solving a problem amenable to analytical solution. The benchmark lid-driven cavity problem is also solved in a cube for assessing the three chosen iterative solvers.     

Fluoroscopic bone fragment tracking for surgical navigation in femur fracture reduction by incorporating optical tracking of hip joint rotation center

A new method for fluoroscopic tracking of a proximal bone fragment in femoral fracture reduction is presented. The proposed method combines 2-D and 3-D image registration from single-view fluoroscopy with tracking of the head center position of the proximal femoral fragment to improve the accuracy of fluoroscopic registration without the need for repeated manual adjustment of the C-arm as required in stereo-view registrations. Kinematic knowledge of the hip joint, which has a positional correspondence with the femoral head center and the pelvis acetabular center, allows the position of the femoral fragment to be determined from pelvis tracking. The stability of the proposed method with respect to fluoroscopic image noise and the desired continuity of the fracture reduction operation is demonstrated, and the accuracy of tracking is shown to be superior to that achievable by single-view image registration, particularly in depth translation.     

A High-Efficiency 100-W GaN Three-Way Doherty Amplifier for Base-Station Applications

A three-way Doherty 100-W GaN base-station power amplifier at 2.14 GHz is presented. Simple, but accurate design equations for the output power combiner of the amplifier are introduced. Mixed-signal techniques are utilized for uncompromised control of the amplifier stages to optimize efficiency, as well as linearity. The combination of the above techniques resulted in an unprecedented high efficiency over a 12-dB power backoff range, facilitating a record high power-added efficiency for a wideband code division multiple access test signal with high crest factor, while meeting all the spectral requirements for Universal Mobile Telecommunications System base stations.      

A Biomimetic Approach to Taxol: Stereoselective Synthesis of a 12-Membered Ring Ene-Epoxide

The stereoselective synthesis of a taxol intermediate via a biomimetic route is described. Aldol condensation of γ-butyrolactone and citral derivatives generated three stereogenic centers at positions C1, C2, and C11 corresponding to taxol. Intramolecular alkylation of the cyanohydrin ether efficiently formed the 12-membered ring system in which stereoselective reduction, followed by directed epoxidation, afforded the key intermediate epoxide.     

Direct determinations of the unperturbed dimensions of linear polyethylene molecules

Light scattering measurements were carried out on three linear polyethylene samples in diphenyl at 127.5°C, i.e., under theta conditions. The unperturbed molecular dimensions and hence the characteristic ratio C_n were directly determined without recourse to theory for the excluded volume effect. It was found that the values of C_n were 8.7 to 10.5 in this theta solvent. These values suggest that the parameters, assigned to agree with the C_n value of 6.7, should be re-examined for the refinement of theory.     

Phenolic acid analysis and antioxidant activity assessment of oil palm (E. guineensis) fruit extracts

Phenolic compounds in oil palm fruit (E. guineensis) were extracted in soluble free (SFP), insoluble-bound (ISBP) and esterified (EFP) forms. The total phenolic content (TPC) of the oil palm fruit extracts was determined using the Folin–Ciocalteu method and found to range from 5.03 to 9.04 g/L per g of dried weight (DW). The antioxidant activities of oil palm phenolic extracts were analysed using free radical scavenging assays and results showed that oil palm phenolic extracts contained antioxidant activities in the order of ISBP > EFP > SFP. Eight different phenolic acids were identified and quantified using a simple reversed-phase high performance liquid chromatography (HPLC) with a diode array detector (DAD) and liquid chromatography/tandem mass spectrometry (LC/MS/MS). Ferulic, p-hydroxybenzoic and p-coumaric acid were the dominant phenolic acids found in oil palm fruit extracts and ranged from 55 to 376 μg/g of DW.     

A bibliometric study of bioinformatics research in South Africa

This paper reports on the practises of bioinformatics research in South Africa using bibliometric techniques. The search strategy was designed to cover the common concepts in biological data organisation, retrieval and analysis; the development and application of tools and methodologies in biological computation; and related subjects in genomics and structural bioinformatics. The South African literature in bioinformatics has grown by 66.5% between 2001 and 2006. However, its share of world production is not on par with comparator countries, Brazil, India and Australia.