Purpose built teaching equipment for a laboratory based course in three phase machines and drives

The hazards associated with high voltage three phase inverters and the rotating shafts of large electrical machines have resulted in most of the engineering courses covering these topics to be predominantly theoretical. This paper describes a set of purpose built, low voltage and low cost teaching equipment which allows the "hands on" instruction of three phase inverters and rotating machines. By using low voltages, the student can experiment freely with the motors and inverter and can access all of the current and voltage waveforms, which until now could only be studied in text books or observed as part of laboratory demonstrations. Both the motor and the inverter designs are optimized for teaching purposes cost around $25 and can be made with minimal effort.

Three-phase machines and drives - equipment for a laboratory-based course

The hazards associated with high-voltage three-phase inverters and high-powered large electrical machines have resulted in most of the engineering courses covering three-phase machines and drives theoretically. This paper describes a set of purpose-built, low-voltage, and low-cost teaching equipment that allows the hands-on instruction of three-phase inverters and rotating machines. The motivation for moving towards a system running at low voltages is that the students can safely experiment freely with the motors and inverter. The students can also access all of the current and voltage waveforms, which until now could only be studied in textbooks or observed as part of laboratory demonstrations. Both the motor and the inverter designs are for teaching purposes and require minimal effort and cost

The genus Borassus (Arecaceae) in West Africa, with a description of a new species from Burkina Faso

Borassus akeassii Bayton, Ouedraogo & Guinko sp. nov. (Arecaceae) is described as a new species from western Burkina Faso in West Africa. It has been confused with the widely distributed African species B. aethiopum and more recently with the Asian B. flabellifer. However, it is distinguished by its glaucous, green leaves with weakly armed petioles and a characteristic pattern of lamina venation. The fruits have a pointed apex and are greenish when ripe, and the flowers of the pistillate inflorescence are arranged in three spirals. The pollen has a reticulate tectum and distinctive ornamentation. The distribution of B. akeassii is discussed and the status of the varieties of Borassus aethiopum (var. bagamojensis and var. senegalensis) is examined. (c) 2006 The Linnean Society of London.

Time course of gag protein assembly in HIV-1-infected cells: a study by immunoelectron microscopy

Recent biochemical studies have identified high molecular complexes of the HIV Gag precursor in the cytosol of infected cells. Using immunoelectron microscopy we studied the time course of the synthesis and assembly of a HIV Gag precursor protein (pr55gag) in Sf9 cells infected with recombinant baculovirus expressing the HIV gag gene. We also immunolabeled for pr55gag human T4 cells acutely or chronically infected with HIV-1. In Sf9 cells, the time course study showed that the first Gag protein appeared in the cytoplasm at 28-30 h p.i. and that budding started 6-8 h later. Colloidal gold particles, used to visualize the Gag protein, were first scattered randomly throughout the cytoplasm, but soon clusters representing 100 to 1000 copies of pr55gag were also observed. By contrast, in cells with budding or released virus-like particles the cytoplasm was virtually free of gold particles while the released virus-like particles were heavily labeled. Statistical analysis showed that between 80 and 90% of the gold particles in the cytoplasm were seen as singles, as doublets, or in small groups of up to five particles probably representing small oligomers. Clusters of gold particles were also observed in acutely infected lymphocytes as well as in multinuclear cells of chronically infected cultures of T4 cells. In a few cases small aggregates of gold particles were found in the nuclei of T4 lymphocytes. These observations suggest that the Gag polyprotein forms small oligomers in the cytoplasm of expressing cells but that assembly into multimeric complexes takes place predominantly at the plasma membrane. Large accumulations of Gag protein in the cytoplasm may represent misfolded molecules destined for degradation.

Synthesis, spectroscopic and redox properties of some ruthenium(II) thiosemicarbazone complexes: structural description of four of these complexes

Sixteen neutral mixed ligand thiosemicarbazone complexes of ruthenium having general formula [Ru(PPh3)(2)L-2], where LH = 1-(arylidine)4-aryl thiosemicarbazones, have been synthesized and characterized. All complexes are diamagnetic and hence ruthenium is in the +2 oxidation state (low-spin d(6), S = 0). The complexes show several intense peaks in the visible region due to allowed metal to ligand charge transfer transitions. The structures of four of the complexes have been determined by single-crystal X-ray diffraction and they show that thiosemicarbazone ligands coordinate to the ruthenium center through the hydrazinic nitrogen and sulfur forming four-membered chelate rings with ruthenium in N2S2P2 coordination environment. In dichloromethane solution, the complexes show two quasi-reversible oxidative responses corresponding to loss of electron from HOMO and HOMO - 1. The E-0 values of the above two oxidations shows good linear relationship with Hammett substituents constant (sigma) as well as with the HOMO energy of the molecules calculated by the EHMO method. A DFT calculation on one representative complex suggests that there is appreciable contribution of the sulfur p-orbitals to the HOMO and HOMO - 1. Thus, assignment of the oxidation state of the metal in such complexes must be made with caution. (c) 2005 Elsevier B.V. All rights reserved.

Purpose built teaching equipment for a laboratory based course in three phase machines and drives

The hazards associated with high voltage three phase inverters ond the rotating sha@s of large electrical machines have resulted in most of the engineering courses covering these topics to be predominantly theoretical. This paper describes a set of purpose built, low voltage and low cost teaching equipment which allows the “hands on I’ instruction of three phase inverters and rotating machines. By using low voltages, the student can experiment freely with the motors and inverter and can access all of the current and voltage waveforms, which until now could only be studied in text books or observed as part of laboratory demonstrations. Both the motor and the inverter designs are optimized for teaching purposes, cost around $25 and can be made with minimal effort.

Three-phase machines and drives - Equipment for a laboratory-based course

The hazards associated with high-voltage three-phase inverters and high-powered large electrical machines have resulted in most of the engineering courses covering three-phase machines and drives theoretically. This paper describes a set of purpose-built, low-voltage, and low-cost teaching equipment that allows the hands-on instruction of three-phase inverters and rotating machines. The motivation for moving towards a system running at low voltages is that the students can safely experiment freely with the motors and inverter. The students can also access all of the current and voltage waveforms, which until now could only be studied in textbooks or observed as part of laboratory demonstrations. Both the motor and the inverter designs are for teaching purposes and require minimal effort and cost.

Formate-dependent growth and homoacetogenic fermentation by a bacterium from human feces: Description of Bryantella formatexigens gen. nov., sp nov.

Formate stimulates growth of a new bacterium from human feces. With high formate, it ferments glucose to acetate via the Wood-Ljungdahl pathway. The original isolate fermented vegetable cellulose and carboxymethylcellulose, but it lost this ability after storage at -76degreesC. 16S rRNA gene sequencing identifies it as a distinct line within the Clostridium coccoides supra-generic rRNA grouping. We propose naming it Bryantella formatexigens gen. nov., sp. nov.