A new procedure to derive transmission line parameters: Theoretical considerations

The objective of this paper is to show an alternative methodology to calculate transmission line parameters per unit length. With this methodology the transmission line parameters can be obtained starting from the phase currents and voltages in one terminal of the line. First, the article shows the classical methodology to calculate frequency dependent transmission line parameters by using Carson's and Pollaczeck's equations for representing the ground effect and Bessel's functions to represent the skin effect. After that, it is shown a new procedure to calculate frequency dependent transmission line parameters directly from currents and voltages of the line that is already built. Then, this procedure is applied in a two-phase transmission line whose parameters have been previously calculated by using the classical methodology. Finally, the results obtained by using the new procedure and by using the classical methodology are compared. ©2005 IEEE.

Some considerations about a new procedure to derive transmission line parameters concerning three-phase lines

The paper shows an alternative methodology to calculate transmission line parameters per unit length and to apply it in a three-phase line with a vertical symmetry plane. This procedure is derived from a general procedure where the modal transformation matrix of the line is required. In this paper, the unknown modal transformation matrix requested by general procedure is substituted by Clarke's matrix. With the substitution that is shown in the paper, the transmission line parameters can be obtained starting from impedances measured in one terminal of the line. First, the article shows the classical methodology to calculate frequency dependent transmission line parameters by using Carson and Pollaczeck's equations for representing the ground effect and Bessel's functions to represent the skin effect. After that, a new procedure is shown to calculate frequency dependent transmission line parameters directly from currents and voltages of an existing line. Then, this procedure is applied in a non-transposed three-phase transmission line whose parameters have been previously calculated by using the classical methodology. Finally, the results obtained by using the new procedure and by using the classical methodology are compared. The article shows simulation results for typical frequency spectra of switching transients (10 Hz to 10 kHz). Results have shown that procedure has © 2006 IEEE.

Reducing the spurious oscillations in the lumped parameters model using low-pass filter

Voltages and currents in the transmission line are described by differential equations that are difficult to solve due soil and skin effect that has to be considered for accurate results, but it increases their complexity. Therefore there are some models to study the voltages and currents along in transmission line. The distributed parameters model that transforms the equations in time domain to the frequency domain and once the solutions are obtained, they are converted to time domain using the Inverse Laplace Transform using numerical methods. Another model is named lumped parameters model and it considers the transmission line represented by a pi-circuit cascade and the currents and voltages are described by state equations. In the simulations using the lumped parameters model, it can be observed the presence of spurious oscillations that are independent of the quantity of pi-circuits used and do not represent the real value of the transient. In this work will be projected a passive low-pass filter directly inserted in the lumped parameters model to reduce the spurious oscillations in the simulations, making this model more accurate and reliable for studying the electromagnetic transients in power systems.

Functional hydrogels: ferrogel thin films

Die Kombination magnetischer Nanopartikel (NP) mit temperatursensitiven Polymeren führt zur Bildung neuer Komposit-Materialien mit interessanten Eigenschaften, die auf vielfältige Weise genutzt werden können. Mögliche Anwendungsgebiete liegen in der magnetischen Trennung, der selektiven Freisetzung von Medikamenten, dem Aufbau von Sensoren und Aktuatoren. Als Polymerkomponente können z.B. Hydrogele dienen. Die Geschwindigkeit der Quellgradänderung mittels externer Stimuli kann durch eine Reduzierung des Hydrogelvolumens erhöht werden, da das Quellen ein diffusionskontrollierter Prozess ist. rnIm Rahmen dieser Arbeit wurde ein durch ultraviolettes Licht vernetzbares Hydrogel aus N-isopropylacrylamid, Methacrylsäure und dem Vernetzer 4-Benzoylphenylmethacrylat hergestellt (PNIPAAm-Hydrogel) und mit magnetischen Nanopartikeln aus Magnetit (Fe3O4) kombiniert. Dabei wurde die Temperatur- und die pH-Abhängigkeit des Quellgrades im Hinblick auf die Verwendung als nanomechanische Cantilever Sensoren (NCS) untersucht. Desweiteren erfolgte eine Charakterisierung durch Oberflächenplasmonen- und optischer Wellenleitermoden-Resonanz Spektroskopie (SPR/OWS). Die daraus erhaltenen Werte für den pKa-Wert und die lower critical solution Temperatur (LCST) stimmten mit den bekannten Literaturwerten überein. Es konnte gezeigt werden, dass eine stärkere Vernetzung zu einer geringeren LCST führt. Die Ergebnisse mittels NCS wiesen zudem auf einen skin-effect während des Heizens von höher vernetzten Polymeren hin.rnDie Magnetit Nanopartikel wurden ausgehend von Eisen(II)acetylacetonat über eine Hochtemperaturreaktion synthetisiert. Durch Variation der Reaktionstemperatur konnte die Größe der hergestellten Nanopartikel zwischen 3.5 und 20 nm mit einer Größenverteilung von 0.5-2.5 nm eingestellt werden. Durch geeignete Oberflächenfunktionalisierung konnten diese in Wasser stabilisiert werden. Dazu wurde nach zwei Strategien verfahren: Zum einen wurden die Nanopartikel mittels einer Silika-Schale funktionalisiert und zum anderen Zitronensäure als Tensid eingesetzt. Wasserstabilität ist vor allem für biologische Anwendungen wünschenswert. Die magnetischen Partikel wurden mit Hilfe von Transmissionselektronenmikroskopie (TEM), und superconductive quantum interference device (SQUID) charakterisiert. Dabei wurde eine Größenabhängigkeit der magnetischen Eigenschaften sowie superparamagnetisches Verhalten beobachtet. Außerdem wurde die Wärmeerzeugung der magnetischen Nanopartikel in einem AC Magnetfeld untersucht. rnDie Kombination beider Komponenten in Form eines Ferrogels wurde durch Mischen Benzophenon funktionalisierter magnetischer Nanopartikel mit Polymer erreicht. Durch Aufschleudern (Spin-Coaten) wurden dünne Filme erzeugt und diese im Hinblick auf ihr Verhalten in einem Magnetfeld untersucht. Dabei wurde eine geringes Plastikverhalten beobachtet. Die experimentellen Ergebnisse wurden anschließend mit theoretisch berechneten Erwartungswerten verglichen und mit den unterschiedlichen Werten für dreidimensionale Ferrogele in Zusammenhang gestellt. rn

Microhardness mapping and the hardness-yield strength relationship in high-pressure diecast magnesium alloy AZ91

Microhardness maps of cross-sections of high-pressure diecast test bars of AZ91 have been determined. Specimens with rectangular cross-sections, 1, 2 and 3 mm thick, or with a circular cross-section 6.4 mm in diameter, have been studied. The hardness is generally higher near the edges in all specimens, and more so near the corners of the rectangular specimens. The hardness at the center of the castings is generally lower, due to a coarser solidification microstructure and the concentration of porosity. The evidence confirms that the surface of the castings is harder than the core, but it does not support the concept of a skin with a sharp. and definable boundary. This harder layer is irregular in hardness and depth and is not equally hard on opposite sides of the casting. The mean hardness obtained by integrating the microhardness maps over the entire cross-section increased with decreasing thickness of the bars, and was found to be in good correlation with each bar's yield strength. (c) 2005 Elsevier B.V. All rights reserved.

Contribuição à estabilidade transitória de sistemas elétricos industriais de unidades estacionárias de produção de petróleo

Dissertação (mestrado)—Universidade de Brasília, Faculdade de Tecnologia, Departamento de Engenharia Elétrica, 2015.

Low-Level Laser Therapy on the Viability of Skin Flap in Rats Subjected to Deleterious Effect of Nicotine

Objective: The purpose of this study was to evaluate the effect of 830-nm laser in blocking the action of nicotine on the viability of skin flap. Background data: The authors have analyzed the deleterious effect of cigarette smoke or nicotine on the skin flap alone with evidence of increased skin necrosis in the flap. Materials and methods: Twenty-four Wistar-albino rats were divided into three groups of eight animals each: Group 1 (control), subjected to a surgical technique to obtain a flap for cranial base, laser irradiation simulation, and a subcutaneous injection of saline; Group 2, similar to Group 1, with subcutaneous injection of nicotine (2mg/kg/day) for a period of 1 week before and 1 week after surgery; and Group 3, similar to Group 2, with skin flaps subjected to a lambda 830-nm laser irradiation. The laser parameters used were: power 30 mW, beam area 0.07cm(2), irradiance 429 mW/cm(2), irradiation time 84 sec, total energy 2.52J, and energy density 36J/cm(2). The laser was used immediately after surgery and for 4 consecutive days, in one point at 2.5 cm of the flap cranial base. The areas of necrosis were examined by two macroscopic analyses: paper template and Mini-Mop (R). The pervious blood vessels were also counted. Results: The results were statistically analyzed by ANOVA and post-test contrast orthogonal method (multiple comparisons), showing that the laser decreased the area of necrosis in flaps subjected to nicotine, and consequently, increased the number of blood vessels (p < 0.05). Conclusions: The laser proved to be an effective way to decrease the area of necrosis in rats subjected to nicotine, making them similar to the control group.

Evaluation of Protective Effect of a Water-In-Oil Microemulsion Incorporating Quercetin Against UVB-Induced Damage in Hairless Mice Skin

Purpose. Histological aspects were considered in order to evaluate the in vivo photoprotective effect of a w/o microemulsion containing quercetin against UVB irradiation-induced dermal damages. The toxicity in cell culture and the potential skin irritation resulting from topical application of this formulation were investigated. Methods. Mouse dorsal surfaces were treated topically with 300 mg of the unloaded and quercetin-loaded (0.3%, w/w) microemulsions before and after exposure to UVB (2.87 J/cm(2)) irradiation. The untreated control groups irradiated and non-irradiated were also evaluated. UVB-induced histopathological changes as well as the photoprotective effect of this formulation were evaluated considering the parameters of infiltration of inflammatory cells, epidermis thickening (basale and spinosum layers) and collagen and elastic fiber contents. The cytotoxicity of the reported formulation was evaluated in L929 mice fibroblasts by MTT assay and the skin irritation was investigated after topical application of both unloaded and quercetin-loaded microemulsions once a day for 15 days. Results. The results demonstrated that the w/o microemulsion containing quercetin reduced the incidence of histological skin alterations, mainly the connective-tissue damage, induced by exposure to UVB irradiation. This suggests that protective effects of this formulation against UV-induced responses are not secondary to the interference of UV transmission (i.e., blocking the UVB radiation from being absorbed by the skin), as is usually implied with UVB absorbers and sunscreens, but is instead due to different biological effects of this flavonoid. Furthermore, by evaluating the cytotoxic effect on L929 cells and histological aspects such as infiltration of inflammatory cells and epidermis thickness of hairless mice, the present study also demonstrated the lack of toxicity of the proposed system. Conclusion. Based on these mice models, a detailed characterization of the w/o microemulsion incorporating quercetin effects as a photochemoprotective agent on human skin is presented.

Effect of the iontophoresis of a chitosan gel on doxorubicin skin penetration and cytotoxicity

The aim of this work was to investigate doxorubicin (DOX) percutaneous absorption and retention in the skin following iontophoresis. The convective flow contribution to the overall electrotransport of DOX was also elucidated for a non-ionic hyd roxyethylcellulose gel and a cationic chitosan gel. Moreover, the cytotoxicity of DOX and its formulations, with and without low electrical current, was verified. It was observed that iontophoresis of DOX significantly increased the skin permeation and retention of the drug. In addition, the electroosmotic flow was dramatically reduced when DOX was added to the non-ionic gel, thereby indicating that the drug interacted with negative charges in the skin. Interestingly, electroosmosis was also significantly reduced when the iontophoresis was performed in the presence of the chitosan gel, but in the absence of DOX. Consequently, the transport of an electroosmotic marker from this gel almost disappeared when the positively charged drug was added to the cationic gel. These results indicated that chitosan appeared to interact with negative charges in the skin. Hence, this carrier not only reduced electroosmotic flow, but also released DOX from ionic interactions with these sites and improved its diffusion to deeper skin layers. The application of the low electrical current directly to melanoma cells increased DOX cytotoxicity by nearly three-fold, which was probably due to membrane permeation. (c) 2008 Elsevier B.V. All rights reserved.

Assessment of the percutaneous penetration of cisplatin: The effect of monoolein and the drug skin penetration pathway

It was intended to examine the in vitro penetration of cisplatin (CIS) through porcine skin in the presence of different concentrations of monoolein (MO) as well as to verify the main barrier for CIS skin penetration. In vitro skin penetration of CIS was studied from propylene glycol (PG) solutions containing 0%, 5%, 10%, and 20% of MO using Franz-type diffusion cell and porcine ear skin. Pretreatment experiments with MO and experiments with skin without stratum corneum (SC) were also carried out. Skin penetration studies of CIS showed that the presence of MO doubled the drug permeation through the intact skin. However, permeation studies through the skin without SC caused only a small enhancement of CIS permeation compared to intact skin. Moreover, pretreatment of skin with MO formulations did not show any significant increase in the flux of the drug. In conclusion, MO did not act as a real penetration enhancer for CIS, but it increased the drug partition to the receptor solution improving CIS transdermal permeation. The absence of improvement in drug permeation by MO pretreatment and by the removal of SC indicates that the SC is not the main barrier for the permeation of the metal coordination compound. (c) 2009 Elsevier B.V. All rights reserved.

Protective effect of Calendula officinalis extract against UVB-induced oxidative stress in skin: Evaluation of reduced glutathione levels and matrix metalloproteinase secretion

Background and purpose: Calendula officinalis flowers have long been employed time in folk therapy, and more than 35 properties have been attributed to decoctions and tinctures from the flowers. The main uses are as remedies for burns (including sunburns), bruises and cutaneous and internal inflammatory diseases of several origins. The recommended doses are a function both of the type and severity of the condition to be treated and the individual condition of each patient. Therefore, the present study investigated the potential use of Calendula officinalis extract to prevent UV irradiation-induced oxidative stress in skin. Methods: Firstly, the physico-chemical composition of marigold extract(ME) (hydroalcoholic extract)was assessed and the in vitro antioxidant efficacy was determined using different methodologies. Secondly, the cytotoxicity was evaluated in L929 and HepG2 cells with the MTT assay. Finally, the in vivo protective effect of ME against UVB-induced oxidative stress in the skin of hairless mice was evaluated by determining reduced glutathione (GSH) levels and monitoring the secretion/activity of metalloproteinases. Results and conclusions: The polyphenol, flavonoid, rutin and narcissin contents found in ME were 28.6 mg/g, 18.8 mg/g, 1.6 mg/g and 12.2 mg/g, respectively and evaluation of the in vitro antioxidant activity demonstrated a dose-dependent effect of ME against different radicals. Cytoxicity experiments demonstrated that ME was not cytotoxic for L929 and HepG2 cells at concentrations less than or equal to of 15 mg/mL However, concentrations greater than or equal to 30 mg/mL, toxic effects were observed. Finally, oral treatment of hairless mice with 150 and 300 mg/kg of ME maintained GSH levels close to non-irradiated control mice. In addition, this extract affects the activity/secretion of matrix metalloproteinases 2 and 9 (MMP-2 and -9) stimulated by exposure to UVB irradiation. However, additional studies are required to have a complete understanding of the protective effects of ME for skin. (C) 2009 Elsevier Ireland Ltd. All rights reserved.

Determination of the effect of lipophilicity on the in vitro permeability and tissue reservoir characteristics of topically applied solutes in human skin layers

In order to establish the relationship between solute lipophilicity and skin penetration (including flux and concentration behavior), we examined the in vitro penetration and membrane concentration of a series of homologous alcohols (C2-C10) applied topically in aqueous solutions to human epidermal, full-thickness, and dermal membranes. The partitioning/distribution of each alcohol between the donor solution, stratum corneum, viable epidermis, dermis, and receptor phase compartments was determined during the penetration process and separately to isolated samples of each tissue type. Maximum flux and permeability coefficients are compared for each membrane and estimates of alcohol diffusivity are made based on flux/concentration data and also the related tissue resistance (the reciprocal of permeability coefficient) for each membrane type. The permeability coefficient increased with increasing lipophilicity to alcohol C8 (octanol) with no further increase for C10 (decanol). Log vehicle:stratum corneum partition coefficients were related to logP , and the concentration of alcohols in each of the tissue layers appeared to increase with lipophilicity. No difference was measured in the diffusivity of smaller more polar alcohols in the three membranes; however, the larger more lipophilic solutes showed slower diffusivity values. The study showed that the dermis may be a much more lipophilic environment than originally believed and that distribution of smaller nonionized solutes into local tissues below a site of topical application may be estimated based on knowledge of their lipophilicity alone.

Effect of solute lipophilicity on penetration through canine skin

Objective To investigate the effect of lipophilicity on the percutaneous penetration of a homologous series of alcohols through canine skin Design Skin harvested from Greyhound thorax was placed in Franz-type diffusion cells and the in vitro passage of radio-labelled (C-14) alcohols (ethanol, butanol, hexanol and octanol (Log P 0.19 - 3.0)) through separate skin sections was measured in replicates of five. Permeability coefficient (k(P), cm/h), maximum flux (J(max), mol/cm(2)/h) and residue remaining within the skin were determined. Results The k(P) increased with increasing lipophilicity (6.2 x 10(-4) +/- 1.6 x 10(-4) cm/h for ethanol to 1.8 x 10(-2) 3.6 x 10(-3) cm/h for octanol). Alcohol residues remaining within each skin sample followed a similar pattern. An exponential decrease in Jmax with increasing lipophilicity was observed. Conclusion Changes in canine skin permeability occur with increasing alcohol lipophilicity. This finding has practical consequences for the design of topical formulations and optimisation of drug delivery through animal skin.

Effect of skin colour and selected physical characteristics on Schistosoma mansoni dependent morbidity

The effect of the colour group on the morbidity due to Schistosoma mansoni was examined in two endemic areas situated in the State of Minas Gerais, Brazil. Of the 2773 eligible inhabitants, 1971 (71.1%) participated in the study: 545 (27.6%) were classified as white, 719 (36.5%) as intermediate and 707 (35.9%) as black. For each colour group, signs and symptoms of individuals who eliminated S.mansoni eggs (cases) were compared to those who did not present eggs in the faeces (controls). The odds ratios were adjusted by age, gender, previous treatment for schistosomiasis, endemic area and quality of the household. There was no evidence of a modifier effect of colour on diarrhea, bloody faeces or abdominal pain. A modifier effect of colour on hepatomegaly was evident among those heaviest infected (> 400 epg): the adjusted odds ratios for palpable liver at the middle clavicular and the middle sternal lines were smaller among blacks (5.4 and 6.5, respectively) and higher among whites (10.6 and 12.9) and intermediates (10.4 and 10.1, respectively). These results point out the existence of some degree of protection against hepatomegaly among blacks heaviest infected in the studied areas.