A novel nanostructured composite formed by interaction of copper octa(3-aminopropyl)octasilsesquioxane with azide ligands: Preparation, characterization and a voltammetric application

This study presents the preparation, characterization and application of copper octa(3-aminopropyl)octasilsesquioxane following its subsequent reaction with azide ions (ASCA). The precursor (AC) and the novel compound (ASCA) were characterized by Fourier transform infrared spectra (FTIR), nuclear magnetic resonance (NMR), electron paramagnetic resonance (EPR), scanning electronic microscopy (SEM), X-ray diffraction (XRD), Thermogravimetric analyses and voltammetric technique. The cyclic voltammogram of the modified graphite paste electrode with ASCA (GPE-ASCA), showed one redox couple with formal potential (E(1/2)(ox)) = 0.30 V and an irreversible process at 1.1 V (vs. Ag/AgCl; NaCl 1.0 M; v = 20 mV s(-1)). The material is very sensitive to nitrite concentrations. The modified graphite paste electrode (GPE-ASCA) gives a linear range from 1.0 x 10(-4) to 4.0 x 10(-3) mol L(-1) for the determination of nitrite, with a detection limit of 2.1 x 10(-4) mol L(-1) and the amperometric sensitivity of 8.04 mA/mol L(-1). (C) 2010 Elsevier Ltd. All rights reserved.

Simultaneous Differential Pulse Voltammetric Determination of Ascorbic Acid and Caffeine in Pharmaceutical Formulations Using a Boron-Doped Diamond Electrode

A cathodically pretreated boron-doped diamond electrode was used for the simultaneous anodic determination of ascorbic acid (AA) and caffeine (CAF) by differential pulse voltammetry Linear calibration curves (r = 0 999) were obtained from 1 9 x 10(-5) to 2 I x 10(-4) mol L(-1) for AA and from 9 7 x 10(-6) to 1 1 x 10-4 mol L(-1) for CAF. with detection limits of 19 wool L(-1) and 7 0 mu nol L(-1). respectively This method was successfully applied for the determination of AA and CAF in pharmaceutical formulations. with results equal to those obtained using a HPLC reference method

Unga vuxnas åsikter kring bokomslags formgivning : En enkät- och fokusgruppsundersökning

Bokomslaget är ofta läsarens första möte med en bok och det är därför viktigt att bokomslaget tilltalar och sänder ut rätt signaler till konsumenten. Målgruppen unga vuxna, individer mellan 16 och 27 år, är enligt bokbranschen en grupp som är svår att nå. Svårigheten kan ligga i att det finns en viss okunskap i vad unga vuxna tilltalas av på bokomslag. Det är även en bred målgrupp med många olika sorters individer. Målet med denna studie är att ge en bild av vad målgruppen unga vuxna tilltalas av i ett bokomslag. Vi ville ta reda på hur viktigt bokomslaget är för val av bok, samt hur målgruppen ser på omslagets specifika designfaktorer färg, typografi, illustration, fotografi och efterbehandling. För att ge oss en bild av dagens kunskapsläge har litteraturstudier och intervjuer med formgivare av bokomslag genomförts. Genom en omfattande enkätundersökning och utförda fokusgrupper fick vi fram målgruppens syn och tankar kring bokomslag. Fokusgrupper utfördes för att ge oss en djupare förståelse rörande hur målgruppen ser på bokomslag samt ge oss ett djupare resonemang kring de olika bokomslagen. Resultatet visar att unga vuxna lägger stor vikt vid identitet och ett bokomslag bör således sända tydliga signaler som kan bekräfta läsarens identitet. Typografin ska vara lättläst. Målgruppen ser helst fotografiska bilder på bokomslaget och omslaget ska förmedla en känsla av bokens innehåll. Färger i en dovare färgskala tilltalar unga vuxna, rött och svart tycks vara de populäraste färgerna överlag. Efterbehandlingen (t.ex. lackering och foliering) på ett bokomslag bör vara sparsam och användning av färgen rosa lika så.

An investigation of worn work roll materials used in the finishing stands of the hot strip mill for steel rolling

The surface failure characteristics of different work roll materials, i.e. High Speed Steel, High Chromium Iron and Indefinite Chill Iron, used in the finishing stands of a hot strip mill have been investigated using stereo microscopy, 3D optical profilometry, scanning electron microscopy and energy dispersive X-ray spectroscopy. The results show that the surface failure mechanisms of work rolls for hot rolling are very complex, involving plastic deformation, abrasive wear, adhesive wear, mechanical and thermal induced cracking, material transfer and oxidation. Despite the differences in chemical composition and microstructure, the tribological response of the different work roll materials was found to be strongly dependent on the material microstructure and especially the presence and distribution of microstructural constituents, such as the different carbide phases and graphite (in the case of Indefinite Chill Iron). Cracking and chipping of the work roll surfaces, both having a negative impact on work roll wear, are strongly influenced by the presence of carbides, carbide networks and graphite in the work roll surface. Consequently, the amount of carbide forming elements as well as the manufacturing process must be controlled in order to obtain an optimised microstructure and a predictable wear rate.

A study of slag corrosion of oxides and oxide-carbon refractories during steel refining

The use of ceramic material as refractories in the manufacturing industry is a common practice worldwide. During usage, for example in the production of steel, these materials do experience severe working conditions including high temperatures, low pressures and corrosive environments. This results in lowered service lives and high consumptions of these materials. This, in turn, affects the productivity of the whole steel plant and thereby the cost. In order to investigate how the service life can be improved, studies have been carried out for refractories used in the inner lining of the steel ladles. More specifically, from the slag zone, where the corrosion is most severe. By combining thermodynamic simulations, plant trails and post-mortem studies of the refractories after service, vital information about the behaviour of the slagline refractories during steel refining and the causes of the accelerated wear in this ladle area has been achieved. The results from these studies show that the wear of the slagline refractories of the ladle is initiated at the preheating station, through reduction-oxidation reactions. The degree of the decarburization process is mostly dependent on the preheating fuel or the environment. For refractories without antioxidants, refractory decarburization is slower when coal gas is used in ladle preheating than when a mixture of oil and air is used. In addition, ladle preheating of the refractories without antioxidants leads to direct wear of the slagline refractories. This is due to the total loss of the matrix strength, which results in a sand-like product. Thermal chemical changes that take place in the slagline refractories are due to the MgO-C reaction as well as the formation of liquid phases from impurity oxides. In addition, the decrease in the system pressure during steel refining makes the MgO-C reaction take place at the steel refining temperatures. This reduces the refractory’s resistance to corrosion. This is a serious problem for both the magnesia-carbon and dolomite-carbon refractories. The studies of the reactions between the slagline refractories and the different slag compositions showed that slags rich in iron oxide lead mostly to the oxidation of carbon/graphite in the carbon-containing refractories. This leads to an increased porosity and wettability and therefore an enhanced penetration of slag into the refractory structure. If the slag contains high contents of alumina and or silica (such as the steel refining slag), reactions between the slag components and the dolomite-carbon refractory are promoted. This leads to the formation of low-temperature melting phases such as calcium-aluminates and silicates. The state of these reaction products during steel refining leads to an accelerated wear of the dolomite-carbon refractory. The main products of the reactions between the magnesia-carbon refractory and the steel refining slag are MgAl2O4 spinels, and calcium-aluminates, and silicates. Due to the good refractory properties of MgAl2O4 spinels, the slag corrosion resistance of the magnesiacarbon refractory is promoted.

An Experimental Study of Submerged Entry Nozzles (SEN) Focusing on Decarburization and Clogging

The submerged entry nozzle (SEN) is used to transport the molten steel from a tundish to a mould. The main purpose of its usage is to prevent oxygen and nitrogen pick-up by molten steel from the gas. Furthermore, to achieve the desired flow conditions in the mould. Therefore, the SEN can be considered as a vital factor for a stable casting process and the steel quality. In addition, the steelmaking processes occur at high temperatures around 1873 K, so the interaction between the refractory materials of the SEN and molten steel is unavoidable. Therefore, the knowledge of the SEN behaviors during preheating and casting processes is necessary for the design of the steelmaking processes  The internal surfaces of modern SENs are coated with a glass/silicon powder layer to prevent the SEN graphite oxidation during preheating. The effects of the interaction between the coating layer and the SEN base refractory materials on clogging were studied. A large number of accretion samples formed inside alumina-graphite clogged SENs were examined using FEG-SEM-EDS and Feature analysis. The internal coated SENs were used for continuous casting of stainless steel grades alloyed with Rare Earth Metals (REM). The post-mortem study results clearly revealed the formation of a multi-layer accretion. A harmful effect of the SENs decarburization on the accretion thickness was also indicated. In addition, the results indicated a penetration of the formed alkaline-rich glaze into the alumina-graphite base refractory. More specifically, the alkaline-rich glaze reacts with graphite to form a carbon monoxide gas. Thereafter, dissociation of CO at the interface between SEN and molten metal takes place. This leads to reoxidation of dissolved alloying elements such as REM (Rare Earth Metal). This reoxidation forms the “In Situ” REM oxides at the interface between the SEN and the REM alloyed molten steel. Also, the interaction of the penetrated glaze with alumina in the SEN base refractory materials leads to the formation of a high-viscous alumina-rich glaze during the SEN preheating process. This, in turn, creates a very uneven surface at the SEN internal surface. Furthermore, these uneven areas react with dissolved REM in molten steel to form REM aluminates, REM silicates and REM alumina-silicates. The formation of the large “in-situ” REM oxides and the reaction of the REM alloying elements with the previously mentioned SEN´s uneven areas may provide a large REM-rich surface in contact with the primary inclusions in molten steel. This may facilitate the attraction and agglomeration of the primary REM oxide inclusions on the SEN internal surface and thereafter the clogging. The study revealed the disadvantages of the glass/silicon powder coating applications and the SEN decarburization. The decarburization behaviors of Al2O3-C, ZrO2-C and MgO-C refractory materials from a commercial Submerged Entry Nozzle (SEN), were also investigated for different gas atmospheres consisting of CO2, O2 and Ar. The gas ratio values were kept the same as it is in a propane combustion flue gas at different Air-Fuel-Ratio (AFR) values for both Air-Fuel and Oxygen-Fuel combustion systems. Laboratory experiments were carried out under nonisothermal conditions followed by isothermal heating. The decarburization ratio (α) values of all three refractory types were determined by measuring the real time weight losses of the samples. The results showed the higher decarburization ratio (α) values increasing for MgO-C refractory when changing the Air-Fuel combustion to Oxygen-Fuel combustion at the same AFR value. It substantiates the SEN preheating advantage at higher temperatures for shorter holding times compared to heating at lower temperatures during longer holding times for Al2O3-C samples. Diffusion models were proposed for estimation of the decarburization rate of an Al2O3-C refractory in the SEN. Two different methods were studied to prevent the SEN decarburization during preheating: The effect of an ZrSi2 antioxidant and the coexistence of an antioxidant additive and a (4B2O3 ·BaO) glass powder on carbon oxidation for non-isothermal and isothermal heating conditions in a controlled atmosphere. The coexistence of 8 wt% ZrSi2 and 15 wt% (4B2O3 ·BaO) glass powder of the total alumina-graphite refractory base materials, presented the most effective resistance to carbon oxidation. The 121% volume expansion due to the Zircon formation during heating and filling up the open pores by a (4B2O3 ·BaO) glaze during the green body sintering led to an excellent carbon oxidation resistance. The effects of the plasma spray-PVD coating of the Yttria Stabilized Zirconia (YSZ) powder on the carbon oxidation of the Al2O3-C coated samples were investigated. Trials were performed at non-isothermal heating conditions in a controlled atmosphere. Also, the applied temperature profile for the laboratory trials were defined based on the industrial preheating trials. The controlled atmospheres consisted of CO2, O2 and Ar. The thicknesses of the decarburized layers were measured and examined using light optic microscopy, FEG-SEM and EDS. A 250-290 μm YSZ coating is suggested to be an appropriate coating, as it provides both an even surface as well as prevention of the decarburization even during heating in air. In addition, the interactions between the YSZ coated alumina-graphite refractory base materials in contact with a cerium alloyed molten stainless steel were surveyed. The YSZ coating provided a total prevention of the alumina reduction by cerium. Therefore, the prevention of the first clogging product formed on the surface of the SEN refractory base materials. Therefore, the YSZ plasma-PVD coating can be recommended for coating of the hot surface of the commercial SENs.

Purificação de aluminio por fusão zonal horizontal

Durante este trabalho foi construido um sistema experimental de fusão zonal horizontal com a finalidade de purificar metais com ponto de fusão entre 400° e 1200°C. A fonte de aquecimento escolhida foi o aquecimento indutivo, e o metal o alumínio. Uma barra de alumínio foi colocada dentro de um cadinho de grafite alojada dentro de um tubo de quartzo. Para deslocar a zona de fusão o cadinho foi puxado por meio de fios, polias e pesos acoplados a um motor-redutor. As experiências de purificação foram feitas com atmosfera de argônio. Foram produzidas oito barras usando diferentes números de passadas da zona de fusão e velocidade de deslocamento. Os resultados obtidos pelos métdos de análise empregados mostraram-se satisfatoriamente concordantes com a teoria e com os resultados registrados na literatura.

Novas fases amorfas de carbono produzidas por irradiação iônica de filmes de C/sub 60/, [alfa]-C e [alfa]-C:H

Neste trabalho estuda-se a formação de novas fases de carbono amorfo através da irradiação iônica de filmes de fulereno, a-C e a-C:H polimérico. Os efeitos da irradiação iônica na modificação das propriedades ópticas e mecânicas dos filmes de carbono irradiados são analisados de forma correlacionada com as alterações estruturais a nivel atômico. O estudo envolve tanto a análise dos danos induzidos no fulereno pela irradiação iônica a baixas fluências, correspondendo a baixas densidades de energia depositada, quanto a investigação das propriedades físico-químicas das fases amorfas obtidas após irradiações dos filmes de fulereno, a-C e a-C:H com altas densidades de energia depositada. As propriedades ópticas, mecânicas e estruturais das amostras são analisadas através de técnicas de espectroscopia Raman e infravermelho, espectrofotometria UV-VIS-NIR, microscopias ópticas e de força atômica, nanoindentação e técnicas de análise por feixe de íons, tais como retroespalhamento Rutherford e análises por reação nuclear. As irradiações produzem profundas modificações nas amostras de fulereno, a-C e a-C:H, e por conseqüência significativas alterações em suas propriedades ópticas e mecânicas. Após máximas fluências de irradiação fases amorfas rígidas (com dureza de 14 e 17 GPa) e com baixos gaps ópticos (0,2 e 0,5 eV) são formadas. Estas estruturas não usuais correspondem a arranjos atômicos com 90 a 100% de estados sp2. Em geral fases sp2 são planares e apresentam baixa dureza, como predito pelo modelo de “cluster”. Entretanto, os resultados experimentais mostram que as propriedades elásticas das novas fases formadas são alcançadas através da criação de uma estrutura sp2 tridimensional. A indução de altas distorções angulares, através da irradiação iônica, possibilita a formação de anéis de carbono não hexagonais, tais como pentágonos e heptágonos, permitindo assim a curvatura da estrutura. Utilizando um modelo de contagem de vínculos é feita uma análise comparativa entre a topologia (estrutura geométrica) de ligações C-sp2 e as propriedades nanomecânicas. São comparados os efeitos de estruturas sp2 planares e tridimensionais (aleatórias) no processo de contagem de vínculos e, conseqüentemente, nas propriedades elásticas de cada sistema. Os resultados mostram que as boas propriedades mecânicas das novas fases de carbono formadas seguem as predições do modelo de vínculos para uma rede atômica sp2 tridimensional. A formação de uma fase amorfa dura e 100% sp2 representa uma importante conquista na procura de novas estruturas rígidas de carbono. A síntese da estrutura desordenada sp2 tridimensional e vinculada aqui apresentada é bastante incomum na literatura. O presente trabalho mostra que o processo de não-equilíbrio de deposição de energia durante a irradiação iônica permite a formação de distorções angulares nas ligações sp2-C, possibilitando a criação de estruturas grafíticas tridimensionais.

Estudo da sinterabilidade de ligas de níquel obtidas por meio dos portadores de liga sic, si3n4 ou si metálico com grafita

Nickel alloys are frequently used in applications that require resistance at high temperatures associated with resistance to corrosion. Alloys of Ni-Si-C can be obtained by means of powder metallurgy in which powder mixtures are made of metallic nickel powders with additions of various alloying carriers for such were used in this study SiC, Si3N4 or Si metal with graphite. Carbonyl Ni powder with mean particle size of 11 mM were mixed with 3 wt% of SiC powders with an average particle size of 15, 30 and 50 μm and further samples were obtained containing 4 to 5% by mass of SiC with average particle size of 15 μm. Samples were also obtained by varying the carrier alloy, these being Si3N4 powder with graphite, with average particle size of 1.5 and 5 μm, respectively. As a metallic Si graphite with average particle size of 12.5 and 5 μm, respectively. The reference material used was nickel carbonyl sintered without adding carriers. Microstructural characterization of the alloys was made by optical microscopy and scanning electron microscopy with semi-quantitative chemical analysis. We determined the densities of the samples and measurement of microhardness. We studied the dissociation of carriers alloy after sintering at 1200 ° C for 60 minutes. Was evaluated also in the same sintering conditions, the influence of the variation of average particle size of the SiC carrier to the proportion of 3% by mass. Finally, we studied the influence of variation of the temperatures of sintering at 950, 1080 and 1200 ° C without landing and also with heights of 30, 60, 120 and 240 minutes for sintering where the temperature was 950 °C. Dilatometry curves showed that the SiC sintered Ni favors more effectively than other carriers alloy analyzed. SiC with average particle size of 15 μm active sintering the alloy more effectively than other SiC used. However, with the chemical and morphological analyzes for all leagues, it was observed that there was dissociation of SiC and Si3N4, as well as diffusion of Si in Ni matrix and carbon cluster and dispersed in the matrix, which also occurred for the alloys with Si carriers and metallic graphite. So the league that was presented better results containing Si Ni with graphite metallic alloy as carriers, since this had dispersed graphite best in the league, reaching the microstructural model proposed, which is necessary for material characteristic of solid lubricant, so how we got the best results when the density and hardness of the alloy

Processamento e caracterização de compósitos Poli(METACRILATO DE METILA)/Sílica (PMMA/SiO2)

Currently the search for new materials with properties suitable for specific applications has increased the number of researches that aim to address market needs. The poly (methyl methacrylate) (PMMA) is one of the most important polymers of the family of polyacrylates and polymethacrylates, especially for its unique optical properties and weathering resistance, and exceptional hardness and gloss. The development of polymer composites by the addition of inorganic fillers to the PMMA matrix increases the potential use of this polymer in various fields of application. The most commonly used inorganic fillers are particles of silica (SiO2), modified clays, graphite and carbon nanotubes. The main objective of this work is the development of PMMA/SiO2 composites at different concentrations of SiO2, for new applications as engineering plastics. The composites were produced by extrusion of tubular film, and obtained via solution for application to commercial PMMA plates, and also by injection molding, for improved the abrasion and scratch resistance of PMMA without compromising transparency. The effects of the addition of silica particles in the polymer matrix properties were evaluated by the maximum tensile strength, hardness, abrasion and scratch resistance, in addition to preliminary characterization by torque rheometry and melt flow rate. The results indicated that it is possible to use silica particles in a PMMA matrix, and a higher silica concentration produced an increase of the abrasion and scratch resistance, hardness, and reduced tensile strength

Efeito da adição de grafite expandido por microondas nas propriedades térmicas, elétricas e mecânicas de nanocompósitos de matriz epóxi

Epoxy based nanocomposites with 1 wt % and 3 wt % of nanographite were processed by high shear mixing. The nanographite was obtained by chemical (acid intercalation), thermal (microwave expansion) and mechanical (ultrasonic exfoliation) treatments. The mechanical, electrical and thermal behavior of the nanocomposites was determined and evaluated as a function of the percentage of reinforcement. According to the experimental results, the electrical conductivity of epoxy was not altered by the addition of nanographite in the contents evaluated. However, based on the mechanical tests, nanocomposites with addition of 1 wt.% and 3 wt.% of nanographite showed increase in tensile strength of 16,62 % and 3,20 %, respectively, compared to the neat polymer. The smaller increase in mechanical strength of the nanocomposite with 3 wt.% of nanographite was related to the formation of agglomerates. The addition of 1 wt.% and 3 wt.% of nanographite also resulted in a decrease of 6,25 % and 17,60 %, respectively, in the relative density of the material. Thus, the specific strength of the nanocomposites was approximately 33,33 % greater when compared to the neat polymer. The addition of 1 wt.% and 3 wt.% of nanographite in the material increased the mean values of thermal conductivity in 28,33 % and 132,62 %, respectively, combined with a reduction of 26,11 % and 49,80 % in volumetric thermal capacity, respectively. In summary, it has been determined that an addition of nanographite of the order of 1 wt.% and 3 wt.% produced notable elevations in specific strength and thermal conductivity of epoxy

Voltammetric determination of L-dopa using an electrode modified with trinuclear ruthenium ammine complex (Ru-red) supported on Y-type zeolite

The L-dopa is the immediate precursor of the neurotransmitter dopamine. Unlike dopamine, L-dopa easily enters the central nervous system and is used in the treatment of Parkinson's disease. A sensitive and selective method is presented for the voltammetric determination of L-dopa in pharmaceutical formulations using a carbon paste electrode modified with trinuclear ruthenium ammine complex [(NH3)(5)Ru-III-O-Ru-IV(NH3)(4)-O-Ru-III(NH3)(5)](6+) (Ru-red) incorporated in NaY zeolite. The parameters which influence on the electrode response (paste composition, potential scan rate, pH and interference) were also investigated. The optimum conditions were found to an electrode composition (m/m) of 25% zeolite containing 6.7% Ru, 50% graphite and 25% mineral oil in acetate buffer at pH 4.8. Voltammetric peak currents showed a linear response for L-dopa concentration in the range between 1.2 x 10(-4) and 1.0 x 10(-2) Mol l(-1) (r = 0.9988) with a detection limit of 8.5 x 10(-5) mol l(-1). The variation coefficient for a 1.0 x 10(-3) mol l(-1) L-dopa (n = 10) was 5.5%. The results obtained for L-dopa in pharmaceutical formulations (tablet) was in agreement with compared official method. In conclusion, this study has illustrated that the proposed electrode modified with Ru-red incorporated zeolite is suitable valuable for selective measurements of L-dopa. (C) 2004 Elsevier B.V. All rights reserved.

Voltammetric determination of isoprenaline in pharmaceutical preparations using a copper(II) hexacyanoferrate(III) modified carbon paste electrode

The electroanalytical determination of isoprenaline in pharmaceutical preparations of a homemade carbon paste electrode modified with copper(II) hexacyanoferrate(III) (CuHCF) was studied by cyclic voltammetry. Several parameters were studied for the optimization of the sensor such as electrode composition, electrolytic solution, pH effect, potential scan rate and interferences in potential. The optimum conditions were found in an electrode composition (in mass) of 15% CuHCF, 60% graphite and 25% mineral oil in 0.5 mol l(-1) acetate buffer solution at pH 6.0. The analytical curve for isoprenaline was linear in the concentration range from 1.96 x 10(-4) to 1.07 x 10(-3) mol l(-1) with a detection limit of 8.0 x 10(-5) mol l(-1). The relative standard deviation was 1.2% for 1.96 x 10(-4) mol l(-1) isoprenaline solution (n=5). The procedure was successfully applied to the determination of isoprenaline in pharmaceutical preparations; the CuHCF modified carbon paste electrode gave comparable results to those results obtained using a UV spectrophotometric method. (C) 2004 Elsevier B.V. All rights reserved.

Avaliação da aprendizagem no no contexto dos ciclos: sentidos da prática avaliativa docente

The present paper analyses matters about the assessment in the context of the school organization in cycles. The complexity that involves the assessment turns it into a difficult subject, since the evidence that the model supported by the traditional approach contributes to foil the fulfillment of new continuous and wide-ranging assessment practices, that are coherent with a view of learning as a process established in the student-teacher-knowledge interaction. This paper has as guidance the following questions: How did the introduction of the teaching organization in cycles happen in Fortaleza/ CE? How far are the teachers prepared to the introduction of the cycles system, specially in the way of thinking and practicing the assessment? What are the teacher s involvements with this project and with the continuous assessment in the cycles? What meanings do the teachers give to the assessment in this project? Therefore, were determined as objectives: to comprehend the meanings attributed to the learning assessment by the teachers in contact with the cycles in Fortaleza/CE; to identify assessment practices that are closer to a less qualifying perspective, more related to the students learning and to the educational intervention in order to improve this process. The methodological orientation chosen was based on the presuppositions of the comprehensible interview, with reference to the studies of the French sociologist Jean Claude Kaufmann, developed with 15 (fifteen) teachers of 15 (fifteen) schools of the state teaching system of Fortaleza/CE. It was considered, in the methodology, the word as a central fact in the consolidation of the object of study, what allows to conceive the teachers as active participants of this research and of the discussions about assessment. The analysis about the speeches in the interviews made possible to glimpse the meanings attributed to the learning assessment that are not related to the traditional paragon, in spite of the dilemma in which the participants of the research faced at the time of the introduction of the cycles in Fortaleza/CE. These meanings were created between the presence and the absence of the teachers knowledge that, in their way, interact with the changes caused by the obligation of the teaching organization in cycles, seeking a strategy of self-organization as a consequence of the search for new knowledge connected with the teaching

Electrical conductivity of soybean seeds after storage in several environments

Membrane integrity, as measured by electrical conductivity (EC), is suggested as an indicator of seed vigor in soybean [Glycine max (L.) Merrill] seeds. This study evaluated the effect of storage time and temperature on EC of six soybean seed lots (two lots each of high, medium and low vigor). All seed lots were adjusted to 120 g kg(-1) seed moisture, sealed in aluminum foil packets and placed in storage at 10 and 20 degreesC or stored unsealed in multi-wall paper bags in warehouse (WH) conditions at Lexington, KY, USA for 486 days. Four of the six seed lots were also stored unsealed at 10 degreesC. All seed lots were sampled at 3-month intervals and evaluated for seed moisture (SMC), standard germination (SG) and vigor [accelerated aging (AA) and EC]. After 91 and 204 days in storage, samples initially stored at 20 degreesC and WH were moved to 10 degreesC and sampled at the same intervals. Seed moisture content for unsealed samples equilibrated at 107 g kg(-1) (+/-9 g kg(-1)) in both the WH and 10 degreesC environments. No change in SG occurred for seeds stored sealed (120 g kg(-1)) at 10 degreesC, except for the low vigor seed lots which declined significantly at the last sample date. The AA germination declined significantly for all, seed lots stored sealed at 10 degreesC, however the EC did not change during the same storage period. Seeds stored sealed at 20 degreesC and unsealed in the WH showed rapid declines in AA and SG and significant increases in EC. When these seeds were moved to 10 degreesC, however, the AA continued to decline while the EC remained at the same level (no significant change) for the remainder of the seed storage period. Thus whilst the AA declined in all environments, the EC only increased at higher temperatures (20 degreesC, WH) but showed little change during storage at 10 degreesC. Thus, precautions must be taken if using EC to measure soybean seed vigor following storage at 10 degreesC.