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An integral domain D is called a locally GCD domain if DM is a GCD domain for every maximal ideal M of D. We study some ringtheoretic properties of locally GCD domains. For example, we show that D is a locally GCD domain if and only if aD ∩ bD is locally principal for all 0 ≠ a; b ∈ D, and at overrings of a locally GCD domain are locally GCD.We also show that the t-class group of a locally GCD domain is just its Picard group. We study when a locally GCD domain is Prüfer or a generalized GCD domain. We also characterize locally factorial domains as domains D whose minimal prime ideals of a nonzero principal ideal are locally principal and discuss conditions that make them Krull domains. We use the D + XDS[X] construction to give some interesting ex- amples of locally GCD domains that are not GCD domains. [ABSTRACT FROM AUTHOR]

The effective harmonics estimation for measuring power signals has become an important issue in the power quality assessment. By reviewing those commonly used Kahnan filter-based models, some limitations for harmonics estimation can be observed. In this paper an extended real model of Kalman filter combined with a resetting mechanism for accurately tracking time-varying harmonic components of power signals is presented. The usefulness of the proposed algorithm is demonstrated by a simple laboratory setup with LabVIEW program and the dedicated hardware for harmonics monitoring. Results show that the proposed method can achieve more accurate and robust measurement of harmonic amplitudes and phase angles for the time-varying power signals among compared methods while the uncertainty testing performances required by LEC Standard 61000-4-30 are satisfied. [ABSTRACT FROM AUTHOR]

A series of cells representing normal, non-tumorigenic cell lines, as well as differentiating neoplastic and undifferentiated neoplastic rat tracheal epithelial cell populations were evaluated for their ability to establish homologous and/or heterologous cell-cell gap junction communication in culture. Gap junction communication was evaluated by flow cytometric quantitation of the transfer of the fluorescent dye calcein from a donor to a recipient cell population via gap junctions. The data indicate that normal primary cultures of rat tracheal epithelial cells, as well as non-tumorigenic cell lines and squamous cell carcinomas cell populations, retain the ability to establish both homologous and heterologous gap junction communication. In all cases an average of >48% of recipient cells had acquired calcein label during a 5-h interval of co-culture of donor and recipient cells at confluent densities. Cells harvested directly from squamous cell carcinoma tumors exhibited similar levels of cell-cell communication. In contrast, cells giving rise to undifferentiated carcinomas, as well as cells harvested from undifferentiated carcinomas, exhibited very low levels or no homologous or heterologous cell-cell communication. Cell populations exhibiting distinctly different communication phenotypes were evaluated by Northern blot analysis for expression of connexins (Cx 26, 32 and 43) and E-cadherin. Neither communicating nor non-communicating cells expressed connexin 32. Those cell populations, which established functional gap junctions, expressed E-cadherin as well as connexin 26 and/or 43. In contrast, those cell populations that lacked the ability to communicate universally lacked expression of E-cadherin, and a quarter also lacked expression of detectable levels of connexin. [ABSTRACT FROM PUBLISHER]

This letter proposes a curve-fitting approach for modeling fluorescent lamp voltage--current characteristics based on measured lamp voltage and current. The fluorescent lamp conductance is considered as a series of piecewise cubic polynomials that describes the nonlinear voltage--current characteristic of the lamp. The proposed model has been tested with a 10-W conventional 60-Hz fluorescent lamp and a 20-W high-frequency energy-saving lamp. By comparing the measured and simulated results, it shows that the proposed model can accurately model the lamps for harmonic studies. [ABSTRACT FROM AUTHOR]

This letter presents a new control strategy to determine the reference compensation voltages of a series active power filter (APF) operated under nonideal supply voltages in the steady-state. By employing the proposed control strategy, the load-side voltages can be maintained as being sinusoidal and balanced. The effectiveness of the proposed control strategy is demonstrated through simulations by the use of Pspice. Results show that the expected series APF performances are achieved. [ABSTRACT FROM AUTHOR]

This paper presents an efficient approach for tracking the location of the electric utility shunt capacitor bank that generates switching transients by a limited number of power quality (PQ) meters. The approach is based on measuring the voltage-disturbance energy variations at the meter buses and phase angle changes at the connected branch current due to the reactive power supplied by the switched-on utility capacitor. Both measured energy and phase angle variations are used to identify the location of the switched capacitor through a rule-based tracking algorithm. The proposed method is then tested with the IEEE 30-bus transmission system to show its usefulness. [ABSTRACT FROM AUTHOR]

The von Hippel-Lindau tumor suppressor protein (pVHL) has emerged as a key factor in cellular responses to oxygen availability, being required for the oxygen-dependent proteolysis of alpha subunits of hypoxia inducible factor-1 (HIF). Mutations in VHL cause a hereditary cancer syndrome associated with dysregulated angiogenesis, and up-regulation of hypoxia inducible genes. Here we investigate the mechanisms underlying these processes and show that extracts from VHL-deficient renal carcinoma cells have a defect in HIF-alpha ubiquitylation activity which is complemented by exogenous pVHL. This defect was specific for HIF-alpha among a range of substrates tested. Furthermore, HIF-alpha subunits were the only pVHL-associated proteasomal substrates identified by comparison of metabolically labeled anti-pVHL immunoprecipitates from proteosomally inhibited cells and normal cells. Analysis of pVHL/HIF-alpha interactions defined short sequences of conserved residues within the internal transactivation domains of HIF-alpha molecules sufficient for recognition by pVHL. In contrast, while full-length pVHL and the p19 variant interact with HIF-alpha, the association was abrogated by further N-terminal and C-terminal truncations. The interaction was also disrupted by tumor-associated mutations in the beta-domain of pVHL and loss of interaction was associated with defective HIF-alpha ubiquitylation and regulation, defining a mechanism by which these mutations generate a constitutively hypoxic pattern of gene expression promoting angiogenesis. The findings indicate that pVHL regulates HIF-alpha proteolysis by acting as the recognition component of a ubiquitin ligase complex, and support a model in which its beta domain interacts with short recognition sequences in HIF-alpha subunits.

Hypoxia-inducible factor-1 (HIF-1) has a key role in cellular responses to hypoxia, including the regulation of genes involved in energy metabolism, angiogenesis and apoptosis. The alpha subunits of HIF are rapidly degraded by the proteasome under normal conditions, but are stabilized by hypoxia. Cobaltous ions or iron chelators mimic hypoxia, indicating that the stimuli may interact through effects on a ferroprotein oxygen sensor. Here we demonstrate a critical role for the von Hippel-Lindau (VHL) tumour suppressor gene product pVHL in HIF-1 regulation. In VHL-defective cells, HIF alpha-subunits are constitutively stabilized and HIF-1 is activated. Re-expression of pVHL restored oxygen-dependent instability. pVHL and HIF alpha-subunits co-immunoprecipitate, and pVHL is present in the hypoxic HIF-1 DNA-binding complex. In cells exposed to iron chelation or cobaltous ions, HIF-1 is dissociated from pVHL. These findings indicate that the interaction between HIF-1 and pVHL is iron dependent, and that it is necessary for the oxygen-dependent degradation of HIF alpha-subunits. Thus, constitutive HIF-1 activation may underlie the angiogenic phenotype of VHL-associated tumours. The pVHL/HIF-1 interaction provides a new focus for understanding cellular oxygen sensing.

Specific regulatory pathways in neoplastic cells seem to be responsive to control signals provided by the normal cell/tissue environment. The present experiments were designed to define, at the molecular level, the growth-regulatory signals in neoplastic cells that are associated with the modulation of expression of the neoplastic phenotype by normal cell populations. When cultured in the presence of normal cell-conditioned medium, a highly malignant rat tracheal carcinoma-derived cell population (IC-12) undergoes dramatic changes in morphology, and the anchorage-independent growth of these cells is inhibited. This phenomenon is termed normalization. The strategy adopted for elucidating the cellular/molecular changes associated with the induction of these phenotypic alterations was to define the differences in mRNA expression patterns between IC-12 populations exhibiting the neoplastic phenotype (wild-type cells) and those exhibiting the normalized phenotype. For this purpose, the differential display technique and subsequent Northern blot analyses were used. Once specific, differentially expressed genes were identified, the temporal sequence of altered gene expression was determined by monitoring the levels of mRNA expression after the addition of normal cell-conditioned medium. Some of the identified known genes are grouped into three general categories: (a) group I genes are those involved in cellular adhesion processes; (b) group II genes are those involved in signal transduction pathways; and (c) group III genes are those involved in transcriptional and translational processes. Genes that are differentially expressed during the normalization process seemed to exhibit characteristic temporal expression patterns after the addition of normal cell-conditioned medium. Identification of these differentially expressed genes and their associated cellular functions provide insight into some of those regulatory pathways in neoplastic cells that are amenable to regulation by normal cells. An analysis of the temporal sequence of altered gene expression provides further information that allows the identification of those genes that are likely to be critical upstream effectors regulating transcriptional regulatory events that result in the moderation of neoplastic behavior.

Apparent intestinal permeability was determined indirectly by orally administering a poorly absorbed dye, phenol red, to rats and measuring its recovery in feces and in urine. Increased apparent permeability was recognized by increased dye recovery in urine and by an increased ratio of urinary to fecal dye recovery. Guar gum, pectin, carrageenan type I (80% kappa, 20% lambda), carrageenan type II (iota) and cellulose were each fed at levels of 5 and 15% (wt/wt) of the diet for 31 d to male Fischer 344 rats. The average initial weight of rats was 230 g. Rats fed 15% guar gum gained significantly less weight than most of the other rats (P less than 0.05). Phenol red recovery was measured at 2 and 4 wk after the beginning of the experiment. At 2 wk urinary recoveries of phenol red were high in rats fed fiber-free and carrageenan type II diets, indicating increased apparent permeability. By 4 wk, adaptation had apparently taken place. Urinary dye recoveries were lower in every diet group, and most fiber-containing diet groups gave significantly lower recoveries than did the fiber-free group. Fecal recovery of phenol red was high in the cellulose, carrageenan I, and 5% carrageenan II groups, intermediate in the 5% pectin and 15% carrageenan II groups, and low in the fiber-free, guar gum and 15% pectin groups at both 2 and 4 wk. The ratio of phenol red recovery from urine to that from feces, another index of apparent intestinal permeability, was higher in the fiber-free diet group than in all the other groups. Rats fed 15% dietary fiber had higher average ratios than those fed the same fiber at 5%. These data are consistent with the hypothesis that intestinal permeability to foreign substances may be altered considerably by diet.

The ability of dietary fiber to modify the effects of a bile acid on permeability of the cecum and colon was studied. A cecal catheter, which permits administration of test materials to conscious, unrestrained rats over a period of several weeks, was designed. Rats were fed fiber-free diet or diets containing 20% bran or lignin. Permeability of the lower intestine was assessed indirectly by infusing polyethylene glycol (PEG) and measuring excretion of PEG in urine. Under these conditions there was little effect of diet on permeability of PEG. However, when sodium deoxycholate was infused with the PEG, permeability was increased in rats fed fiber-free and lignin diets. In contrast, rats fed the bran diet showed no such response to the bile acid. The interaction among type of dietary fiber, presence of bile acid and intestinal permeability may have important implications for the etiology of intestinal disease.

The hisT gene, one of six genes in which mutation causes derepression of the histidine operon in Salmonella typhimurium, is shown to code for a protein that is not essential for the growth of the bacteria. This is indicated by the characterization of particular classes of mutations in the hisT gene: amber mutations, frame-shift mutations, and temperature-sensitive mutations that affect repression but not growth. In addition, the class of semilethal mutations was selected for but not found.

In the course of selection of bacteria with derepressed levels of histidine biosynthetic enzymes, it was found that when mutagen-treated cells were spread on a selective medium without allowing intervening growth to occur, the frequency of operator mutants obtained was dramatically increased. This may be useful as a general enrichment for operator or other dominant mutations.