A Front end Switched Rectifier DC Source for Neutral Point Balancing of A NPC Three-Level Inverter for The Full Modulation Range

A switched DC voltage three level NPC is proposed in this paper to eliminate capacitor balancing problems in conventional three-level Neutral Point Clamped (NPC) inverter. The proposed configuration requires only one DC link with a voltage V-dc/2, where V-dc is the DC link voltage in a onventional NPC inverter. To get rated DC link voltage (V-dc), the voltage source is alternately onnected in parallel to one of the two series capacitors using two switches and two diodes with device voltage rating of V-dc/2. The frequency at which the voltage source is switched is independent and will not affect the operation of NPC inverter. The switched voltage source in this configuration balances the capacitors automatically. The proposed configuration can also be used as a conventional two level inverter in lower modulation range, thereby increases the reliability of the drive system. A space vector based PWM scheme is used to verify this proposed topology.

Comment on “path integration of a quadratic action with a generalized memory

Using the promeasure technique, we give an alternative evaluation of a path integral corresponding to a quadratic action with a generalized memory.

A Hierarchical System of Learning Automata

A learning automaton operating in a random environment updates its action probabilities on the basis of the reactions of the environment, so that asymptotically it chooses the optimal action. When the number of actions is large the automaton becomes slow because there are too many updatings to be made at each instant. A hierarchical system of such automata with assured c-optimality is suggested to overcome that problem.The learning algorithm for the hierarchical system turns out to be a simple modification of the absolutely expedient algorithm known in the literature. The parameters of the algorithm at each level in the hierarchy depend only on the parameters and the action probabilities of the previous level. It follows that to minimize the number of updatings per cycle each automaton in the hierarchy need have only two or three actions.

3d and 4d core level X-ray photoelectron spectroscopy of mixed-valence CePd3

3d and 4d core-level XPS spectra for CePd3, a mixed-valence system, have been measured. Each spectrum exhibits two sets of structures, each corresponding to one of the valence states of cerium. Thus the usefulness of XPS, which has so far not been used extensively to investigate the mixed-valence cerium systems, is pointed out.

Mechanistic studies on the action of ammonium phosphate on polymer fire retardancy

The mechanism of fire retardant action of mono- and diammonium phosphates on polystyrene has been investigated. Ignition delay and mass burning rate studies reveal that the phosphates bring down both parameters considerably though to different extents. This has been adequately explained on the basis of the existing combustion models and physicochemical behavior of the material. Similar to their action on cellulosic materials, phosphates bring about fire retardancy in polystyrene via char formation. This is suggested to occur through a series of processes consisting of initial peroxide formation, decomposition to alcohols and aldehydes, formation of alkyl-phosphate esters, dehydration and subsequent char formation. Infrared and mass spectral studies support this mechanism.

Properties of the gold related acceptor level in silicon

The apparent thermal activation energy of 0.56 eV and the electron thermal capture cross section of 2.0 × 10-16 cm2 are measured for the gold related acceptor level in p+ nn+ silicon diodes by isothermal current transient and DLTS techniques. Using the emission and capture rate data and a degeneracy ratio of 2, the energy separation of the trap level from the conduction band is calculated and found to have the same temperature dependence as the band gap indicating that the acceptor level is pinned with respect to the valence band a t Ev + 0.637 eV.

Studies on the Mechanism of Action of Miconazole: Effect of Miconazole on Respiration and Cell Permeability of Candida albicans

The antifungal drug, miconazole nitrate, inhibits the growth of several species of Candida. Candida albicans, one of the pathogenic species, was totally inhibited at a concentration of approximately 10 μg/ml. Endogenous respiration was unaffected by the drug at a concentration as high as 100 μg/ml, whereas exogenous respiration was markedly sensitive and inhibited to an extent of 85%. The permeability of the cell membrane was changed as evidenced by the leakage of 260-nm absorbing materials, amino acids, proteins, and inorganic cations. The results we present clearly show that the drug alters the cellular permeability, and thus the exogenous respiration becomes sensitive to the drug.

Studies on the Mechanism of Action of Miconazole: Effect of Miconazole on Respiration and Cell Permeability of Candida albicans

The antifungal drug, miconazole nitrate, inhibits the growth of several species of Candida. Candida albicans, one of the pathogenic species, was totally inhibited at a concentration of approximately 10 µg/ml. Endogenous respiration was unaffected by the drug at a concentration as high as 100 µg/ml, whereas exogenous respiration was markedly sensitive and inhibited to an extent of 85%. The permeability of the cell membrane was changed as evidenced by the leakage of 260-nm absorbing materials, amino acids, proteins, and inorganic cations. The results we present clearly show that the drug alters the cellular permeability, and thus the exogenous respiration becomes sensitive to the drug.

Supramolecular gels `in action'

n recent years, self-assembly has emerged as a powerful tool for the construction of functional nanostructures. Myriad applications of these nanoscale architectures, especially the supramolecular gels derived from low molecular mass compounds, in fields such as optoelectronics, light harvesting, organic–inorganic hybrid materials, tissue engineering and regenerative medicine are being envisaged. This review attempts to present a succinct overview of the current state of research on functional nano-scale systems—the design, synthesis and applications of self-assembled nanomaterials engineered to carry out precise functions, with an emphasis on supramolecular gel phase materials.

Preparation of 1-acyl-2-succinyl glycero-3-phosphorylcholine and evidence against its involvement in succinate dehydrogenase action

1-Acyl-2-succinyl glycero-3-phosphorylcholine (GPC) was synthesized and its properties described. Although 1-acyl-2-succinyl GPC is a good substrate for succinate dehydrogenase, experiments on the incorporation of [2,3-14C]succinate into mitochondrial lipids gave no evidence to indicate that it is an intermediate in the enzymic oxidation of succinate to fumarate, as has been suggested earlier.

Mode of action of antitumour antibiotics: Spectrophotometric studies on the interaction of chromomycin A3 with DNA and chromatin of normal and neoplastic tissue

The binding of chromomycin A3, an antitumour antibiotic, to various DNA and chromatin isolated from mouse and rat liver, mouse fibrosarcoma and Yoshida ascites sarcoma cells was studied spectrophotometrically at 29°C in 10−2 M Tris-HCl buffer, pH 8.0, containing small amounts of MgCl2 (4.5 · 10−5−25 · 10−5 M). An isobestic point at 415 nm was observed when chromomycin A3 was gradually titrated with Image and its spectrum shifted towards higher wavelength. The rates and extent of these spectral changes were found to be dependent on the concentration of Mg2+. The change in absorbance at 440 nm was used to calculate apparent binding constant (Ka p M−1) and sites per nucleotide (n) from Scatchard plots for various DNA and chromatins. As expected, values of n for chromatin (0.06–0.10) were found to be lower than that found for corresponding DNA (0.10–0.15). Apparently no such correlation exists between binding constants (Ka p M−1 · 10−4) of DNA (6.4–11.2) and of chromatin (3.1–8.3), but Ka p M−1 of chromatin isolated from mouse fibrosarcoma and Yoshida ascites sarcoma are 1.5–3 times higher than that found for mouse and rat liver chromatin. These differences may be taken to indicate structural difference in nucleoprotein complexes caused by neoplasia. The relevance of this finding to tumour suppressive action of chromomycin A3 is discussed.

The purification and properties of peroxidase in Mycobacterium tuberculosis H37Rv and its possible role in the mechanism of action of isonicotinic acid hydrazide

Peroxidase from Mycobacterium tuberculosis H37Rv was purified to homogeneity. The homogeneous protein exhibits catalase and Y (Youatt's)-enzyme activities in addition to peroxidase activity. Further confirmation that the three activities are due to a single enzyme was accomplished by other criteria, such as differential thermal inactivation, sensitivity to different inhibitors, and co-purification. The Y enzyme (peroxidase) was separated from NADase (NAD+ glycohydrolase) inhibitor by gel filtration on Sephadex G-200. The molecular weights of peroxidase and NADase inhibitor, as determined by gel filtration, are 240000 and 98000 respectively. The Y enzyme shows two Km values for both isoniazid (isonicotinic acid hydrazide) and NAD at low and high concentrations. Analysis of the data by Hill plots revealed that the enzyme has one binding site at lower substrate concentrations and more than one at higher substrate concentration. The enzyme contains 6g-atoms of iron/mol. Highly purified preparations of peroxidases from different sources catalyse the Y-enzyme reaction, suggesting that the nature of the reaction may be a peroxidatic oxidation of isoniazid. Moreover, the Y-enzyme reaction is enhanced by O2. Isoniazid-resistant mutants do not exhibit Y-enzyme, peroxidase or catalase activities, and do not take up isoniazid. The Y-enzyme reaction is therefore implicated in the uptake of the drug.