Showing papers by "Universidade Federal de Santa Catarina published in 1996"
TL;DR: Comparisons between some pro- and antioxidant parameters in erythrocyte, gill, liver and kidney of Nile tilapia, O. niloticus and from a polluted site in the Billings Reservoir provide useful data for future investigations of polluted aquatic sites to provide a data base relating the presence of pollutants to biological effects at a molecular level.
287 citations
Journal Article•
TL;DR: The relatively high antioxidant defense levels that typify fishes, even when compared to endotherms such as birds and mammals, may protect aquatic organisms against the consequences of temperature oscillations.
Abstract: There are few comparative studies of vertebrate antioxidant defenses (AD) in the literature Enzymatic (superoxide dismutase, SOD, and catalase, CAT) and non-enzymatic (alpha-tocopherol, beta-carotene, ubiquinol 10 and blood glutathione) antioxidant defenses were investigated in the liver and blood of 37 fish species, 15 marine species of the southeastern Brazilian coast and 22 freshwater species from the Central Amazon basin More active marine species displayed in general higher concentrations of SOD and CAT in the liver and blood, compared to those of sedentary or bottom-dwelling species AD status in marine fish m ay be related to the oxygen consumption of the tissues and of the whole organism, while in freshwater AD may be related to physical and chemical characteristics of the environment rather than to activity level As thermoconformer organisms, most fish must routinely cope with environmental temperature changes and, consequently, with changes in their metabolic rates The relatively high antioxidant defense levels that typify fishes, even when compared to endotherms such as birds and mammals, may protect aquatic organisms against the consequences of temperature oscillations
208 citations
TL;DR: The results suggest that centrally administered NK1 and NK2 receptor agonists and antagonists can modulate anxiety, as evaluated in the elevated plus-maze test in mice.
174 citations
Journal Article•
TL;DR: Its antinociceptive effect was insensitive to naloxone, suggesting the lack of involvement of endogenous opioid, was not modulated by adrenal glands and does not involve interaction with the L-arginine-nitric oxide pathway, activation of alpha-1 adrenoceptors or tau-aminobutyric acidB receptors, but requires, at least in part, the serotoninergic pathway.
Abstract: The antinociceptive effect of the novel xanthoxyline derivative 2-(4-bromobenzoyl)-3-methyl-4-6-dimethoxy benzofuran) (BMDB), given i.p., p.o., s.c., subplantarly, intrathecally or by i.c.v. routes was assessed in five models of chemical and thermal nociception in mice, namely acetic acid-induced abdominal constriction, formalin and capsaicin-induced licking, hot-plate and tail-flick tests. BMDB given by i.p., s.c., subplantarly or by i.c.v. routes elicited dose-related and long-lasting (4 hr) antinociception, but had no significant effect by p.o. route. At the ID50 level, this compound was about 15- to 100-fold more potent than aspirin and acetaminophen, but it was about 2- to 50-fold less potent than morphine. Its analgesic action was not influenced by naloxone, L-arginine, antagonist of alpha-1 adrenoceptor, prazosin, tau -aminobutyric acid (B) antagonist, phaclofen, after adrenalectomy, but was reversed in part by p-chlorophenylalanine methyl ester. Its analgesic action was not secondary to an anti-inflammatory effect, or was it associated with nonspecific effect such as muscle relaxant or sedative actions of animals. We conclude that BMDB produces dose-dependent spinal and supraspinal antinociception as evaluated in several algesic models in mice, including the neurogenic nociception responses induced by formalin and capsaicin. Its antinociceptive effect was insensitive to naloxone, suggesting the lack of involvement of endogenous opioid, was not modulated by adrenal glands and does not involve interaction with the L-arginine-nitric oxide pathway, activation of alpha-1 adrenoceptors or tau-aminobutyric acidB receptors, but requires, at least in part, the serotoninergic pathway.
161 citations
TL;DR: In this paper, the authors investigated behavior in the open field and shuttle avoidance, for as well as tissue lead burdens of pre- and postnatally lead-exposed rats and found that lead exposure associated with behavioural alterations.
Abstract: In view of conflicting results in literature concerning lead exposure associated with behavioural alterations, this study investigated behaviour in the open-field and shuttle avoidance, for as well as tissue lead burdens of pre- and postnatally lead-exposed rats. Rats were exposed to the metal from conception to weaning by giving the dams 0.5, 2.0 or 4.0 mM lead acetate in drinking water. This regimen did not affect body weight gain of dams or offspring development and had no effect on cerebral weights nor on haematological parameters of 23-day-old rats. In 1-day-old rats, lead accumulated in the blood but not in the brain, whereas both in 23-day-old rats and in dams lead accumulated in blood, kidney and cerebral cortex. In the open-field, lead-exposed groups showed higher locomotor activity in the test session as compared to controls and did not show any decrease in rearing responses in the test, indicating less habituation. Lead-treated rats subjected to a shuttle avoidance task showed no significant increase in avoidance responses between sessions as compared to control, indicating less retention. Moreover, only the control group presented a significant reduction of the footshock escape latency along testing session, suggesting a lead effect on footshock escape acquisition. In the shuttle box, intertrial crossing responses were not affected by lead treatment. The behavioural alterations occurred in animals with blood lead levels in the range 11-50.6 micrograms/dl.
138 citations
TL;DR: In this paper, the salt effect of NaCl on solutions of poly(ethylene oxide) (PEO) and sodium dodecyl sulfate (SDS) was investigated conductimetrically.
134 citations
TL;DR: The two species can be differentiated by differences in the spermathecae, common ducts and number of cibarial horizontal teeth of the females and in the size and proportions of several structures of both sexes.
Abstract: Lutzomyia (Nyssomyia) intermedia (Lutz & Neiva) is redescribed, a neotype is designated, and a very similar species, L. (N.) neivai (Pinto, 1926), is resurrected; the male and the female are redescribed. The two species can be differentiated by differences in the spermathecae, common ducts and number of cibarial horizontal teeth of the females and in the size and proportions of several structures of both sexes. The known geographical distribution of both species is given.
120 citations
TL;DR: The action of NPC 18688 was quite selective for the B2 receptor, and like Hoe 140, it caused graded inhibition of bradykinin (BK, 3 mol/paw)‐induced increase in mouse paw volume, with mean ID50S and MI of 6 and 9 nmol kg−1 and 56±7 and 62±6%, respectively.
Abstract: 1. The purpose of this study was to investigate the topical and systemic anti-hyperalgesic effect of the newly-developed pseudopeptide B2 receptor antagonist, NPC 18688, in different models of nociception in mice. 2. Given systemically 30 min beforehand, NPC 18688 (10-300 nmol kg-1, i.p.) caused no agonist effect, but produced a dose-related and significant inhibition of abdominal constrictions caused by intraperitoneal injection of acetic acid (0.6%), acetylcholine (ACh, 4.5 mg kg-1) or kaolin (50 mg kg-1). The calculated mean ID50s and the percentages of maximal inhibitions (MI) for these effects were: 77, 34 and > 300 nmol kg-1 and 65 +/- 6, 70 +/- 5 and 40 +/- 3%, respectively. The anti-hyperalgesic effect of NPC 18688 (100 nmol kg-1, i.p.) occurred rapidly (30 min) and lasted for at least 150 min. Hoe 140 (3-30 nmol kg-1, i.p.) given 30 min beforehand also inhibited, in a graded manner, acetic acid and ACh-induced writhing, with mean ID50s and MI of 6 and 9 nmol kg-1 and 56 +/- 7 and 62 +/- 6%, respectively. 3. NPC 18688 (10-300 nmol kg-1, i.p.) caused a graded inhibition of both phases of formalin (2.5%)-induced pain, its effects being more potent in relation to the second phase of the formalin test. The calculated mean ID50s and the MI were > 300 and 60 nmol kg-1 and 20 +/- 3 and 60 +/- 5% against the first and second phases of formalin-induced nociception, respectively. NPC 18688 at the same doses also inhibited, in a dose-related manner, formalin-induced paw oedema (MI of 35 +/- 3%). 4. When injected locally in the mouse paw, NPC 18688 (2, 10 and 20 nmol/paw) had no agonist activity. However, when co-injected with formalin NPC 18688 (2-20 nmol/paw), it produced significant inhibition of both phases of formalin response, with MI of 40 +/- 3 and 33 +/- 2%, respectively. NPC 18688 at 10 nmol/paw also significantly inhibited formalin-induced paw oedema (25 +/- 2%). 5. Given intraperitoneally, NPC 18688 (30-300 nmol kg-1) determined a graded inhibition of the nociceptive response caused by intraplantar injection of capsaicin (1.6 micrograms/paw) (40 +/- 2%). However, NPC 18688 (up to 300 nmol kg-1, i.p.), given 30 min beforehand, had no significant analgesic effect when analyzed in the tail flick and in the hot plate pain models, nor did it change the performance of animals in the rota rod test. 6. The action of NPC 18688 was quite selective for the B2 receptor, and like Hoe 140, (1 to 100 nmol kg-1, i.p.) it caused graded inhibition of bradykinin (BK, 3 mol/paw)-induced increase in mouse paw volume, with mean ID50s of 61 and 6 nmol kg-1, respectively. In addition, at 100 nmol kg-1, the dose at which NPC 18688 significantly antagonized BK (3 nmol)-mediated rat paw oedema in naive animals, it had no significant effect on des-Arg9-BK (100 nmol/paw)-induced oedema in paws that had been desensitized to BK. NPC 18688 (210 nmol kg-1), like Hoe 140 (230 nmol kg-1) given s.c. 30 min beforehand, completely abolished BK (28 nmol)-induced hypotension, without affecting the fall of mean arterial blood pressure induced by i.v. injection of ACh (2 nmol kg-1). Finally, NPC 18688 (1 microM) did not affect ACh-mediated contraction in the guinea-pig ileum or toad rectus abdominii in vitro. 7. These results demonstrate that the newly-developed and selective pseudopeptide B2 receptor antagonist, NPC 18688, although less potent than the available second generation of B2 peptide BK receptor antagonists, exhibits topical and long-lasting systemic anti-hyperalgesic properties when analysed in several models of nociception in mice, making it a useful tool for investigating the participation of BK and related kinins in physiological and pathological processes. Finally, this new class of selective pseudopeptide B2 receptor antagonist may constitute a new strategy for developing the third generation of potent and long-lasting orally-active non-peptide BK antagonists, which may be useful for the management of clinical disorders involving BK and relate
115 citations
TL;DR: The results indicate that theophylline and cromolyn were able to inhibit the early (4 h) and late (48 h) phases of the inflammatory reaction induced by carrageenin in a murine model of pleurisy.
Abstract: 1. The aim of this study was to examine the effect of theophylline, cromolyn and salbutamol, three well-known anti-asthmatic drugs, on the early (4 h) and late (48 h) phases of cell migration and fluid leakage induced by carrageenin in the pleural cavity of mice. 2. In the first set of experiments, animals were pretreated (30 min) with different doses of theophylline (0.5-50 mg kg-1, i.p.), cromolyn (0.02-0.2 mg per pleural cavity) or salbutamol (0.05-50 mg kg-1, i.p.); the total and differential cell content, and also the exudate were analysed 4 h after carrageenin (1%) administration. Afterwards, in order to evaluate the time course effects of these drugs on both phases of the inflammatory reaction, one dose employed in the above protocol was chosen, to pretreat (0.5-24 h) different groups of animals. The studied parameters were evaluated 4 and 48 h after pleurisy induction. 3. Acute administration of theophylline (1-50 mg kg-1, i.p.) cromolyn (0.02-0.2 mg per pleural cavity) and salbutamol (0.5-50 mg kg-1, i.p.), 30 min prior to carrageenin, caused significant inhibition of total cell and fluid leakage in the pleural cavity at 4 h (P < 0.01). All drugs exerted a long-lasting inhibitory effect on both exudation and cell migration (P < 0.01) when administered 0.5-8 h before pleurisy induction. However, the temporal profile of the inhibitory effect induced by these drugs on the first phase of the inflammatory reaction was clearly different. Thus, the inhibitory effect induced by theophylline and cromolyn on exudation was significantly longer (up to 24 h) in comparison to their effects on cell migration (only up to 8 h). In contrast, although salbutamol when administered 30 min before pleurisy induction abolished fluid leakage (P < 0.01), this effect was not sustained in the groups pretreated for 4-8 h. In these latter groups, a significant but much smaller reduction of exudation was observed (P < 0.01), whereas the magnitude of cell migration inhibition did not vary. 4. The second phase (48 h) of the inflammatory reaction induced by carrageenin (1%) was significantly inhibited by cromolyn (0.02 mg per pleural cavity) when this drug was administered 0.5-24 h before pleurisy induction (P < 0.01). Similar results were observed when theophylline (50 mg kg-1, i.p.) was administered 0.5-4 h before the injection of the phlogistic agent (P < 0.01). Treatment of the animals with salbutamol (5 mg kg-1, i.p.), 0.5-24 h before pleurisy induction, did not inhibit either cell migration or fluid leakage. In this condition, a significant increase of these parameters was observed in the group pretreated with salbutamol 8-24 h before pleurisy induction (P < 0.01). 5. These results indicate that theophylline and cromolyn were able to inhibit the early (4 h) and late (48 h) phases of the inflammatory reaction induced by carrageenin in a murine model of pleurisy. Salbutamol was effective only against the early phase. The inhibitory effects of theophylline, cromolyn and salbutamol on the early phase of this inflammatory reaction were long-lasting, although a distinct profile of inhibition was observed among them. These findings confirm and extend previous results described in other models of asthma and support both clinical and experimental evidence suggesting that these anti-asthmatic agents exhibit marked anti-inflammatory properties.
109 citations
TL;DR: The results suggest that 60-day-old rats deprived of playfighting experience high basal anxiety levels and also that rearing conditions (isolated or grouped) are able to interact with both anxiolytic and anxiogenic effects of experimental drugs.
88 citations
TL;DR: Data extend previous studies and indicate that the two ellagitannins isolated from P.sellowianus, identified as furosin and geraniin are, at least in part, responsible for the antinociceptive actions reported previously for the hydroalcoholic extract of P. sellowianu and other plants belonging to the genus Phyllanthus.
Abstract: The present study describes the occurrence of two ellagitannins in the ethanolic extract of the leaves and stems of Phyllanthus sellowianus (Euphorbiaceae). Their preliminary antinociceptive properties were also evaluated. The two ellagitannins were identified on the basis of 1H- and 13C-NMR spectra data and by mixed co-TLC and co-HPLC injection with an authentic sample of furosin and geraniin. Preliminary pharmacological analysis revealed that both furosin and geraniin (3 to 30 mg/kg, i.p.), given 30 min before testing, exhibited significant and dose-related antinociceptive properties against acetic acid-induced abdominal constrictions in mice. Geraniin and furosin were about six- to seven-fold more potent at the ID50 level (micromol/kg) as analgesics than aspirin and acetaminophen, respectively, although they were less efficacious when compared with the standard drugs. These data extend our previous studies and indicate that the two ellagitannins isolated from P.sellowianus, identified as furosin and geraniin are, at least in part, responsible for the antinociceptive actions reported previously for the hydroalcoholic extract of P.sellowianus and other plants belonging to the genus Phyllanthus.
TL;DR: The effect of pretreatment with bacterial endotoxin on the bradykinin B1 and B2 receptor‐induced oedema in the rat paw, and the interaction of B1‐mediated responses with other inflammatory mediators, was investigated.
Abstract: 1. The effect of pretreatment with bacterial endotoxin (LPS, 10 micrograms, i.v., 24 h) on the bradykinin B1 and B2 receptor-induced oedema in the rat paw, and the interaction of B1-mediated responses with other inflammatory mediators, was investigated. 2. Intraplantar (i.pl.) injection of the selective B1 agonist, des-Arg9-BK (DABK, 100 nmol) in naive animals pretreated with the angiotensin converting enzyme inhibitor, captopril caused a small increase in paw volume (0.04 +/- 0.003 ml, mean +/- s.e. mean, n = 6), while the B2-selective agonist, tyrosine8-bradykinin (T-BK, 3 nmol) induced marked oedema (0.36 +/- 0.02 ml). However, i.pl. injection of DABK (3-300 nmol) in rats pretreated with LPS (24 h beforehand) resulted in a marked dose- and time-related increase in paw volume, with mean ED50 of 24.1 nmol. In contrast, oedema caused by T-BK (3 nmol) was reduced by 79 +/- 4% in animals treated with LPS when compared with naive animals. 3. Oedema caused by prostaglandin E2 (PGE2, 10 nmol) was unaffected by LPS treatment, while oedema induced by histamine (100 nmol), 5-hydroxytryptamine (5-HT, 10 nmol) and substance P (SP, 3 nmol) was reduced (P < 0.05). 4. The selective B1 antagonist, des-Arg9[Leu8]-BK (100-300 nmol), produced dose-dependent inhibition of DABK (100 nmol)-induced paw oedema in LPS-treated animals with mean IC50 of 134 nmol, while the selective B2 antagonists, Hoe 140 and NPC 17731 (each 10 nmol), had no effect. 5. Treatment of animals with dexamethasone (0.5 mg kg-1, s.c.) 24 or 48 h prior to LPS injection resulted in a graded inhibition of DABK (100 nmol)-induced oedema formation (58 +/- 3 and 82 +/- 2%, respectively), and almost reversed to control value oedema formation induced by T-BK (3 nmol) in LPS-pretreated rats. Cycloheximide (1 mg kg-1, s.c.) or indomethacin (2 mg kg-1, i.p.) pretreatment 24 and 1 h prior to LPS injection, respectively, markedly inhibited DABK (100 nmol)-induced paw oedema (98 +/- 2 and 50 +/- 4%, respectively). 6. Intraplantar injection of submaximal dose of DABK (10 nmol) in LPS-treated rats produced modest paw oedema (0.09 +/- 0.03 ml). However, i.pl. injections of PGE2, prostacyclin (PGI2), calcitonin-gene-related peptide (CGRP), SP, 5-HT, or platelet activating factor (PAF) (each 1 nmol), which alone caused little or no paw oedema, resulted in a potentiation of the DABK-induced oedema. The increases in paw volume (in ml) were: PGE2 + DABK (0.31 +/- 0.03), PGI2 + DABK (0.39 +/- 0.02), CGRP+DABK (0.35 +/- 0.04), DABK+SP (0.33 +/- 0.04), DABK + 5-HT (0.40 +/- 0.02) and DABK+PAF (0.38 +/- 0.016) ml. In contrast, histamine (1 nmol) was ineffective in potentiating the response to DABK. 7. The selective B1 receptor antagonist, DALBK (100-300 nmol), produced dose-dependent inhibition of paw oedema potentiation induced by co-injection of DABK and other mediators with mean ID50S (nmol) of: 180, 160, 139 and 135 in the presence of PGE2, PGI2, SP and 5-HT, respectively. 8. These results demonstrate that DABK-induced increase in paw volume in LPS-treated rats is probably mediated by induction of B1 receptors, associated with downregulation of B2 receptors. The induction of B1 receptors by LPS is sensitive to dexamethasone and cycloheximide treatment and requires activation of cyclo-oxygenase pathway. In addition, B1 receptors, when upregulated following LPS treatment, can interact in a synergistic manner with several inflammatory mediators such as PGI2, PGE2, CGRP, PAF and 5-HT. Such results indicate that induction of the B1 receptor might have a significant pathophysiological role in modulating chronic inflammatory diseases.
TL;DR: In this paper, the major components of these reins are polyisoprenylated benzophenones, a class of biologically active compounds used by pollinating bees for nest construction.
TL;DR: The collected data demonstrated that there was no functional motor or sensory reinnervation after the end-to-side nerve anastomoses of the rat brachial plexus, and the conjunctive layers of the peripheral nerve represented an effective barrier to reinnoration.
Abstract: The repair of large peripheral nerve defects is not always possible, especially when the proximal stump is not available. In these cases, end-to-side nerve anastomosis has been proposed. In the present experiment, using the terminal branches of the rat brachial plexus, the authors studied behavioral responses after end-to-side nerve anastomoses using fibrin glue, 3 and 6 months after surgery. Rats were evaluated by results of a grasping test, a capsaicin test and a hot-plate test. The collected data demonstrated that there was no functional motor or sensory reinnervation after the end-to-side nerve anastomoses. The conjunctive layers of the peripheral nerve thus represented an effective barrier to reinnervation.
TL;DR: The results showed that this extract exert a significant antispasmodic activity which inhibits the action of some neurotransmitters, such as acetylcholine, bradykinin, prostaglandin E(2), histamine and oxytocin, with putative selectivity for cholinergic contractions.
TL;DR: The horizontal linear complementarity problem is studied, and general convergence properties for algorithms based on Newton iterations are derived, which provide a simple and general framework for most existing primal-dual interior point methods.
Abstract: The literature on interior point algorithms shows impressive results related to the speed of convergence of the objective values, but very little is known about the convergence of the iterate sequences.
This paper studies the horizontal linear complementarity problem, and derives general convergence properties for algorithms based on Newton iterations. This problem provides a simple and general framework for most existing primal-dual interior point methods. The conclusion is that most of the published algorithms of this kind generate convergent sequences. In many cases whenever the convergence is not too fast in a certain sense, the sequences converge to the analytic center of the optimal face.
TL;DR: The novel pseudopeptide bradykinin B2 receptor antagonist, NPC 18521, has an effect with rapid onset, and produces potent and relatively long-lasting antioedematogenic and antinociceptive properties.
TL;DR: Studies by light and scanning electron microscopes at the greatest concentration of NH3 have shown that the changes in the cells and branchial tissue were more intense in the alevins.
Abstract: The average lethal concentration of un-ionized ammonia (48-h LC50NH3) has been determined by the static assay for larvae (0.48 mg l−1) and alevins (0.92 mg l−1) of ‘pacama’Lophiosilurus alexandri. Studies by light and scanning electron microscopes at the greatest concentration of NH3 (0.99 mg l−1 for larvae and 1.5 mg l−1 for alevins) have shown that the changes in the cells and branchial tissue were more intense in the alevins.
TL;DR: The use of indigenous microorganisms to degrade hazardous substances within aquifers without engineered stimulation, shows great promise as a cost-effective approach to hydrocarbon plume management.
23 Jun 1996
TL;DR: In this paper, a parallel connection technique is applied to a unity power-factor preregulator based on a boost power converter incontinuous inductor-current mode, which allows an increased output power being processed by two half-rated semiconductor devices.
Abstract: This paper applies a recently introduced parallel connection technique to a unity power-factor preregulator based on a boost power converter incontinuous inductor-current mode. By means of a small extra inductance, two MOSFET pulsewidth modulation (PWM) cells are safely associated in parallel, which allows an increased output power being processed by two half-rated semiconductor devices. The new technique overcomes the existent alternatives, leading to a reliable switched power converter along with simplified layout requirements. This paper also presents a theoretical analysis accompanied by digital simulation cases. Results from a 3 kW prototype, based on the Unitrdae's UC3854 strategy, show that the present technique is very useful in revealing a natural balance among device currents. The laboratory circuit works at a 70 kHz switching frequency and also employs a soft-commutation network. This feature points to a high-efficiency converter and negligible device stresses, which have been verified in the laboratory.
TL;DR: Deterministic nonlinear recursions are derived for the mean and second moment matrix of the weight vector about the Wiener weight for white Gaussian data models and small algorithm step sizes /spl mu/ to yield a desired transient behavior and cancellation performance.
Abstract: This paper extends conditional moment techniques previously developed for the study of nonlinear versions of the LMS algorithm to the study of the effects of quantizers in the finite precision case. Deterministic nonlinear recursions are derived for the mean and second moment matrix of the weight vector about the Wiener weight for white Gaussian data models and small algorithm step sizes /spl mu/. These recursions are solved numerically and shown to be in very close agreement with the Monte Carlo simulations during all phases of the adaptation process. A design example is presented that demonstrates how the theory can be used to select the number of quantizer bits and the adaptation step size /spl mu/ to yield a desired transient behavior and cancellation performance.
01 Dec 1996
TL;DR: In this paper, a discussion about the need to define a conceito de competitividade mais claro e abrangente, which transcends a tendencia existente no campo da microeconomia de associa-Ia somente a indicadores de desempenho ou de eficiencia tecnica, intensificam-se na literatura especializada.
Abstract: Neste final de seculo, o processo de globalizacao dos mercados e seu efeito sobre os padroes de conduta economica, politica, social e organizacional, vem assumindo importância crescente, compondo um cenario no qual a competitividade emerge como uma questao imperativa. Em decorrencia, intensificam-se na literatura especializada as discussoes em torno da necessidade de elaboracao de um conceito de competitividade mais claro e abrangente, que transcenda a tendencia existente no campo da microeconomia de associa-Ia somente a indicadores de desempenho ou de eficiencia tecnica. Para tanto, economistas menos ortodoxos tem sugerido vinculacoes a fatores como estrategia e padroes de concorrencia setoriais, e estudiosos organizacionais tem enfatizado mecanismos de selecao e de exclusao competitiva, pressupondo a relevância de se considerar a influencia das circunstâncias ambientais. No entanto, na essencia tais abordagens ainda se concentram na avaliacao da eficiencia de aspectos organizacionais. Acredita-se que o problema reside no fato de ambas confinarem o seu tratamento do ambiente aos limites do mercado ou de uma populacao de organizacoes, menosprezando a forca das pressoes que os rodeiam. Esse e o foco de analise da teoria institucional. Portanto, pretende-se apresentar no pre¬sente artigo alguns pressupostos da teoria microeconomica e da teoria institucional, e demonstrar o seu potencial de intersecao e de consequente aplicacao ao exame mais apurado do fenomeno da competitividade.
TL;DR: In this article, the relationship between variability, luminosity and redshift in the South Galactic Pole QSO sample is examined in an effort to disentangle the effects of luminosity, redshift and variability in the amplitude of the optical variations.
Abstract: The relationship between variability, luminosity and redshift in the South Galactic Pole QSO sample is examined in an effort to disentangle the effects of luminosity and redshift in the amplitude of the optical variations. The anticorrelation between variability and luminosity found by other authors is confirmed. Our analysis also supports claims that variability increases with redshift, most likely due to an anticorrelation between variability and wavelength. In particular, our parametric fits show that the QSO variability-wavelength relation is consistent with that observed in low-luminosity nearby active galactic nuclei.
The results are used to constrain Poissonian-type models. We find that if QSO variability results from a random superposition of pulses, then the individual events must have B-band energies between $\sim 10^{50}$ and a few times $10^{51}$ erg and time-scales of $\sim 2$ yr. Generalized Poissonian models in which the pulse energy and lifetime scale with luminosity are also discussed.
TL;DR: This paper focuses on the applicability of fuzzy Petri net approaches in the field of Discrete Events Dynamic Systems and the elements that are fuzzyfied in Petri nets.
Journal Article•
06 Oct 1996
TL;DR: In this article, a new low cost, high power factor electronic ballast for compact fluorescent lamps is proposed, which integrates power factor correction and half-bridge power converters using self-oscillating technique.
Abstract: This paper introduces a new low cost, high power factor electronic ballast for compact fluorescent lamps. The proposed ballast integrates power factor correction and half-bridge power converters. Another feature of this work is that the self-oscillating technique is used. The MOSFET's gate drive can be implemented with simplicity and low cost. Theoretical analysis is presented and a very simple design methodology is obtained, since the integrated topology can be treated separately as two independent power converters. Simulation and experimental results are provided to verify the principle of operation and the high power factor of the proposed topology.
TL;DR: It is argued that extended fractal sets in parameter space are relatively common characteristics to be expected for models typically used to describe economic processes and by choosing appropriate paths in the parameter space, it is possible to observe several different routes to chaos.
Abstract: This paper studies the dynamics of economic models when two parameters are simultaneously varied and concentrates on the dynamics of the cobweb model with adaptive expectations. The simultaneous variation of several parameters intervening in economic processes is a very realistic situation of interest. Using reliable numerical methods, we argue that extended fractal sets in parameter space are relatively common characteristics to be expected for models typically used to describe economic processes. In addition, by choosing appropriate paths in the parameter space, it is possible to observe several different routes to chaos.
TL;DR: In this article, the IGMK physical model was used to calculate monthly averages from daily mean incident solar radiation over Brazil, using the satellite data for the period 1985-1986.
TL;DR: In this paper, a numerical methodology for thermal analysis of buried power cables in presence of heat and moisture migration in the surrounding soil is presented, and the governing equations are solved via a finite volume methodology and both cable and soil are incorporated in the problem formulation.
Abstract: A numerical methodology for thermal analysis of buried power cables in presence of heat and moisture migration in the surrounding soil is presented. The governing equations are solved via a finite volume methodology and both cable and soil are incorporated in the problem formulation. The developed program is versatile and user-friendly, and was implemented in a personal computer. Results are presented for constant and cyclic loads, stressing the importance of moisture migration in power cable design.
01 Jan 1996
TL;DR: In this paper, the Zeta converter operating in continuous conduction mode for power factor correction by using the average current mode control is presented, and the main characteristics and advantage of this converter in face of the limitations of the boost converter are discussed.
Abstract: Several topologies have been researched in search of a structure which not only is able to fulfil the requirements of the power factor and the amount of harmonics injected in a line foreseen in the norms, but which would also show the best ensemble of characteristics. Although being the most frequently employed and studied structure, the boost converter presents some limitations in its application, for it is not a naturally isolated structure and because it only operates as step up voltage. As an alternative to these limitations the Zeta converter operating in discontinuous mode applied to the power factor correction was proposed (D.C. Martins, 1994). The Zeta converter showed itself as very attractive because it operates as step up as well as step down voltage, beside the fact of being a naturally isolated structure and processing power at one single stage. But in applications which imply high power, the operation of a converter in discontinuous mode is not attractive because it results in high RMS values of the currents causing high levels of stress in the semiconductors. Aiming to extend the alternative by use of the Zeta converter in power factor correction to applications in higher powers, and having in mind the main characteristics and advantage of this converter in face of the limitations of the boost converter, this paper presents the study of the Zeta converter operating in continuous conduction mode for power factor correction by using the average current mode control.