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Resistência à flexão, sorção, solubilidade e estabilidade de cor de compósitos odontológicos reforçados por fibras; Flexural strength, water sorption, solubility and color stability of some fiber reinforced composite

Medeiros, Renata Souza
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 10/08/2012 PT
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36.27%
Os objetivos deste estudo foram: 1) avaliar a resistência à flexão em três pontos de um compósito para uso direto (Filtek Z350 XT, 3M ESPE) e um para uso indireto (Signum, Heraeus, Kulzer) reforçados por uma ou duas camadas de fibras de polietileno (Ribbond -THM, Ribbond®) ou de vidro (Interlig, Ângelus) tratados termicamente (170°C por 10 minutos), comparados com os grupos controle (não reforçados por fibras e/ou não tratados termicamente; 2) avaliar a sorção, a solubilidade e a estabilidade de cor dos compósitos reforçados, após armazenamento em água destilada à 37°C por 14 dias. A estabilidade de cor foi avaliada com auxílio de um espectrofotômetro de contato dental (Vita EasyShade, Vident, CA, USA). Para o ensaio de resistência à flexão, foram confeccionados espécimes retangulares com dimensões de 12 x 2 x 2mm (n=10), com os seguintes fatores de variação: a) compósito (para uso direto ou indireto); b) tipo e número de camadas de fibras (vidro ou polietileno/uma ou duas camadas); c) submetidos ou não a tratamento térmico. O tratamento térmico foi realizado 24 horas após fotoativação em estufa à temperatura de 170°C por 10 minutos. O ensaio foi realizado 24 horas após fotoativação ou tratamento térmico. Para avaliação de sorção/solubilidade e estabilidade de cor...

Partial purification, heat stability and kinetic characterization of the pectinmethylesterase from Brazilian guava, Paluma cultivars

Leite, KMDC; Tadiotti, A. C.; Baldochi, D.; Oliveira, OMMF
Fonte: Elsevier B.V. Publicador: Elsevier B.V.
Tipo: Artigo de Revista Científica Formato: 565-572
ENG
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Pectinmethylesterase (PME) was extracted from guava fruit (Psidium guajava L.), cultivar Paluma, by 70% ammonium sulphate saturation and partially purified by gel filtration on Sephadex G100. Gel filtration showed PME isoenzymes with different values of molecular mass. Two samples were examined: concPME (70% saturation by ammonium sulphate) and Iso4 PME (one of the isoforms from gel filtration with the greatest specific activity). Optimum pH of the enzyme (for both samples) was 8.5 and optimum temperature ranged from 75 and 85 degrees C. The optimum sodium chloride concentration was 0.15 M. The K-M and V-max ranged from 0.32 to 0.23 mg m1(-1) and 244 to 53.2 mu mol/min, respectively, for concPME and Iso4PME. The activation energies (E-a) were 64.5 and 103 kJ/mol, respectively, for concPME and Iso4PME. Guava PME, cv Paluma, is a very thermostable enzyme, showing great heat stability at all temperatures studied. (c) 2005 Elsevier Ltd. All rights reserved.

Peroxidase from peach fruit: Thermal stability

Neves, V. A.; Lourenco, E. J.
Fonte: Inst Tecnologia Parana Publicador: Inst Tecnologia Parana
Tipo: Artigo de Revista Científica Formato: 179-186
ENG
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Peroxidase from peach fruit was purified 28.9-fold by DEAE-cellulose, Sephadex G-100 and hydroxylapatite chromatography. The purified enzyme showed only one peak of activity with an optimum pH of 5.0 and temperature of 40 degreesC. The calculated activation energy (Ea) for the reaction was 7.97 kcal/mol. The enzyme was heat-labile in the temperature range of 60 to 80 degreesC with a fast inactivation at 80 degreesC. PAGE of the inactivation course at 70 degreesC showed only one band of activity. Different sugars increased the heat stability of the activity in the following order: sucrose>lactose>glucose>fructose. Measurement of residual activity showed a stabilizing effect of sucrose at various temperature/sugar concentrations (10 to 40%, w/w) with the Ea for inactivation increasing with sucrose concentration from 0 to 20% (w/w). After inactivation at 70 degreesC and 75 degreesC the enzyme was able to be reactivated by up to 40% of the initial activity when stared at 30 degreesC.

Thermal structure, heat content and stability of two lakes in The National Park of Rio Doce Valley (Minas Gerais, Brazil)

Henry, R.; Barbosa, F. A R
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 189-199
ENG
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The thermal structure, heat content and stability were studied in Lakes Dom Helvécio and Carioca during an annual cycle. It was found that the maximum heat content, stability and work of the wind in Lake Dom Helvécio correspond to two, four and four times, respectively, the values for the Lake Carioca. These difference can be attributed to morphometric differences in the lakes. A long-term record of heat content and stability for lake Carioca is also presented. Diel variations were studied in summer and winter. The tropicality of the lakes is discussed and compared with other lacustrine systems. © 1989 Kluwer Academic Publishers.

Improvement of technological quality of eucalypt wood by heat treatment in air at 170-200ºC

Esteves, Bruno
Fonte: Instituto Politécnico de Viseu Publicador: Instituto Politécnico de Viseu
Tipo: Artigo de Revista Científica
Publicado em //2007 ENG
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36.18%
Eucalypt wood is a low value wood considered a non durable species with low dimensional stability, used almost exclusively for pulp and paper or as firewood. The heat treatment was made in an oven in the presence of oxygen during 2 to 24 h and temperatures of 170-200ºC. Mass loss with treatment, equilibrium moisture content, dimensional stability measured as ASE in radial and tangential directions and at 35%, 65% and 85% relative humidity, MOE, bending strength and wettability were determined. Mass loss increased with treatment time and temperature reaching 9.5% for wood treated at 190ºC for 24h. Equilibrium moisture content decreased more than 50% (at 35% relative humidity) reaching a maximum of 61% reduction. At higher air relative humidity the reduction was smaller, 49% and 38% at the most for 65% and 85% relative humidity. Dimensional stability (ASE) increased with maximum values of 88% and 96% in radial and tangential direction, respectively. The improvement was higher for lower relative humidity. There was a reduction on mechanical resistance with heat treatment especially for bending strength that decreased about 20% for 3% mass loss, reaching 60% for mass losses higher than 10%. MOE decreased with heat treatment the reduction was under 10% until 8% mass loss. The contact angle increased until 5% mass loss...

Peroxidase from peach fruit: thermal Stability

Neves,Valdir Augusto; Lourenço,E. J.
Fonte: Instituto de Tecnologia do Paraná - Tecpar Publicador: Instituto de Tecnologia do Paraná - Tecpar
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/1998 EN
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56.05%
Peroxidase from peach fruit was purified 28.9-fold by DEAE-cellulose, Sephadex G-100 and hydroxylapatite chromatography. The purified enzyme showed only one peak of activity with an optimum pH of 5.0 and temperature of 40ºC. The calculated activation energy (Ea) for the reaction was 7.97 kcal/mol. The enzyme was heat-labile in the temperature range of 60 to 80ºC with a fast inactivation at 80ºC. PAGE of the inactivation course at 70ºC showed only one band of activity. Different sugars increased the heat stability of the activity in the following order: sucrose>lactose>glucose>fructose. Measurement of residual activity showed a stabilizing effect of sucrose at various temperature/sugar concentrations (10 to 40%, w/w) with the Ea for inactivation increasing with sucrose concentration from 0 to 20% (w/w). After inactivation at 70ºC and 75ºC the enzyme was able to be reactivated by up to 40% of the initial activity when stored at 30ºC.

Photosynthetic oxygen evolution is stabilized by cytochrome c550 against heat inactivation in Synechococcus sp. PCC 7002.

Nishiyama, Y; Hayashi, H; Watanabe, T; Murata, N
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /08/1994 EN
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36.2%
We investigated the factors responsible for the heat stability of photosynthetic oxygen evolution by examining thylakoid membranes from the cyanobacterium Synechococcus sp. PCC 7002. We found that treatment of the thylakoid membranes with 0.1% Triton X-100 resulted in a remarkable decrease in the heat stability of oxygen evolution, and that the heat stability could be restored by reconstituting the membranes with the components that had been extracted by Triton X-100. The protein responsible for the restoration of heat stability was purified from the Triton X-100 extract by two successive steps of chromatography. The purified protein had a molecular mass of 16 kD and exhibited the spectrophotometric properties of a c-type Cyt with a low redox potential. The dithionite-minus-ascorbate difference spectrum revealed an alpha band maximum at 551 nm. We were able to clone and sequence the gene encoding this Cyt from Synechococcus sp. PCC 7002, based on the partial amino-terminal amino acid sequence. The deduced amino acid sequence revealed a gene product consisting of a 34-residue transit peptide and a mature protein of 136 residues. The mature protein is homologous to Cyt c550, a Cyt with a low redox potential. Thus, our results indicate that Cyt c550 greatly affects the heat stability of oxygen evolution.

Heat stability of protective antigen of Leptospira interrogans serovar lai.

Masuzawa, T; Nakamura, R; Shimizu, T; Yanagihara, Y
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /04/1990 EN
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46.09%
Protective antigen (PAg; glycolipid antigen; molecular size, 23 to 30 kilodaltons), the serogroup-specific antigen partially purified from leptospiral cells, is one of the most important protective antigens. The heat stability of PAg was compared with that of whole-cell (WC) antigen by using sodium dodecyl sulfate-polyacrylamide gel electrophoresis, immunoblotting, protective activity, opsonin-inducing activity, agglutinating antibody-inducing activity, and an inhibition test in an enzyme-linked immunosorbent assay. A band of 23 to 30 kilodaltons of PAg, which was seen in untreated PAg and WC, shifted to a position with a molecular size of ca. 20 kilodaltons after heat treatment of PAg at 80 degrees C for 30 min and WC at 100 degrees C for 30 min. In the enzyme-linked immunosorbent assay inhibition test with monoclonal antibody LW2 and a sonicated antigen of WC, the inhibition rate of PAg and WC to sonicated WC was reduced by heat treatment at 80 degrees C for 30 min and at 100 degrees C for 30 min, respectively. Agglutinating antibody-inducing activities and opsonin-inducing activities of PAg and WC in mice were reduced by heat treatment under the same conditions; these activities were assayed by a microscopic agglutination test and by chemical luminescence response in serum from immunized mice...

Heat Stability and Species Range of Purified Staphylococcal α-Toxin

Cooper, Louis Z.; Madoff, Morton A.; Weinstein, Louis
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /05/1966 EN
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46.06%
Cooper, Louis Z. (New England Medical Center Hospital, Boston, Mass.), Morton A. Madoff, and Louis Weinstein. Heat stability and species range of purified staphylococcal α-toxin. J. Bacteriol. 91:1686–1692. 1966.—Heating of high-titer purified staphylococcal α-toxin at 60 and 80 C resulted in a double-sloped curve of inactivation of the hemolytic effect on rabbit erythrocytes. Early inactivation was less at the lower temperature, but activity persisted for a longer time at 80 C. Toxin inactivated at 60 C showed renewed activity when heated briefly at 80 C. A precipitate which formed during heating of α-toxin at 60 or 80 C yielded hemolytic activity when resuspended and heated at 80 but not at 60 C. Supernatant fluid of heat-precipitated toxin was heat-labile and did not regain activity when heated at 80 C. The results indicate that the “paradoxical effect” of heating of staphylococcal α-toxin is not due to a thermolabile inhibitor, but results from alteration of the toxin molecule to a heat-stable active form. Demonstration of renewed activity by 80 C heating of purified toxin requires potent toxin preparations and brief heating periods. Hemolysis of erythrocytes of several animal species by purified α-toxin was generally similar to that produced by impure toxin. Rabbit cells were most susceptible. Human and horse erythrocytes hemolyzed to less than 0.1% of the extent of rabbit cells. Blood cells of other species were intermediate in their response to the lytic effect of α-toxin.

Heat stability of human placental alkaline phosphatase

Neale, Frank C.; Clubb, John S.; Hotchkis, Diane; Posen, Solomon
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /05/1965 EN
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45.98%
Alkaline phosphatase prepared from human placentae shows greater resistance to heat inactivation than any other known alkaline phosphatase of human origin. In the presence of magnesium this enzyme may be heated at 70°C. for 30 minutes without loss of activity whereas other human alkaline phosphatases lose most of their activity on being heated at 56°C. for this period of time. This heat stability is seen in freshly prepared enzyme, in alcohol-fractionated and freeze-dried material, and in the sera of individuals into whom placental alkaline phosphatase has been infused. The clinical implications of our observations are briefly indicated.

Studies of Esterase-6 in DROSOPHILA MELANOGASTER. II. the Genetics and Frequency Distributions of Naturally Occurring Variants Studied by Electrophoretic and Heat Stability Criteria

Cochrane, Bruce J.; Richmond, Rollin C.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /10/1979 EN
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45.98%
Measurements of the electrophoretic mobility and thermostability of esterase-6 allozymes have been used to determine the amount of allelic variation at the esterase-6 locus in Drosophila melanogaster. We studied 398 homozygous lines obtained from four natural populations. Use of a spectrophotometric assay for esterase-6 activity has allowed precise quantitation of heat-stability variants. Using these methods, eight putative alleles were detected within the two most common electrophoretic classes. Analyses of F1 and F2 progeny show that the behavior of stability variants is consistent with the hypothesis that this variation is due to allelic variation at the Est-6 locus. Analyses of the gene-frequency distributions within and between populations show (1) that observed allele-frequency distributions do not deviate significantly from those expected for neutral variants, and (2) that there is little evidence for an increase in apparent divergence of the different populations at the genotypic or phenotypic levels when the additional variation detected is considered. These findings suggest that gene-frequency analysis alone is unlikely to resolve the question of the selective significance of allozyme variation.

Heat Stability of Maize Endosperm ADP-Glucose Pyrophosphorylase Is Enhanced by Insertion of a Cysteine in the N Terminus of the Small Subunit1

Lyerly Linebarger, Carla R.; Boehlein, Susan K.; Sewell, Aileen K.; Shaw, Janine; Hannah, L. Curtis
Fonte: American Society of Plant Biologists Publicador: American Society of Plant Biologists
Tipo: Artigo de Revista Científica
Publicado em /12/2005 EN
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46.17%
ADP-glucose pyrophosphorylase (AGPase) is a key regulatory enzyme in starch biosynthesis. However, plant AGPases differ in several parameters, including spatial and temporal expression, allosteric regulation, and heat stability. AGPases of cereal endosperms are heat labile, while those in other tissues, such as the potato (Solanum tuberosum) tuber, are heat stable. Sequence comparisons of heat-stable and heat-labile AGPases identified an N-terminal motif unique to heat-stable enzymes. Insertion of this motif into recombinant maize (Zea mays) endosperm AGPase increased the half-life at 58°C more than 70-fold. Km values for physiological substrates were unaffected, although Kcat was doubled. A cysteine within the inserted motif gives rise to small subunit homodimers not found in the wild-type maize enzyme. Placement of this N-terminal motif into a mosaic small subunit containing the N terminus from maize endosperm and the C terminus from potato tuber AGPase increases heat stability more than 300-fold.

Enhanced thermal stability of lysosomal beta-D-galactosidase in parenchymal cells of tumour bearing mice.

Lenti, L.; Lipari, M.; Lombardi, D.; Zicari, A.; Dotta, A.; Pontieri, G. M.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /12/1986 EN
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36.2%
The thermal stability of the enzyme beta-D-galactosidase varies among different organs in normal C57Bl/6 mice, and increases in the same organs in mice with Lewis Lung carcinoma. Thermal stability of this enzyme is also increased by treatment of the mice with cell-free extracts of tumour cells or with inflammatory compounds such as carrageenan or orosomucoid. After desialylation, orosomucoid more effectively increases the heat stability of the enzyme. By contrast talc, which has no galactosyl groups, is without effect on the stability of the enzyme in vivo. Macrophages of tumour bearing mice release into the culture medium a more heat resistant enzyme than macrophages from control mice. In both cases the heat resistance of the secreted enzyme is higher when fetal calf serum is present in the culture medium. Bovine serum does not modify the thermal stability of beta-D-galactosidase in this system. Incubation of lysosomal fractions of various organs with the synthetic beta-D-galactosidase substrate, p-nitrophenyl-galactopyranoside, also strongly increases the heat resistance of the enzyme. The results suggest that one factor influencing the heat resistance of this enzyme may be complex formation between the enzyme and its substrates...

Calcium promotes activity and confers heat stability on plant peroxidases

Plieth, Christoph; Vollbehr, Sonja
Fonte: Landes Bioscience Publicador: Landes Bioscience
Tipo: Artigo de Revista Científica
Publicado em 01/06/2012 EN
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46.26%
In this paper we demonstrate how peroxidase (PO) activities and their heat stability correlate with the availability of free Ca2+ ions. Calcium ions work as a molecular switch for PO activity and exert a protective function, rendering POs heat stable. The concentration ranges of these two activities differ markedly. POs are activated by µM Ca2+ concentration ranges, whereas heat stabilization is observed in the nM range. This suggests the existence of different Ca2+ binding sites. The heat stability of POs depends on the source plant species. Terrestrial plants have POs that exhibit higher temperature stability than those POs from limnic and marine plants. Different POs from a single species can differ in terms of heat stability. The abundance of different POs within a plant is dependent on age and developmental stage. The heat stability of a PO does not necessarily correlate with the maximum temperature the source species is usually exposed to in its natural habitat. This raises questions on the role of POs in the heat tolerance of plants. Consequently, detailed investigations are needed to identify and characterize individual POs, with regard to their genetic origin, subcellular expression, tissue abundance, developmental emergence and their functions in innate and acquired heat tolerance.

Efeitos de combinações de hidrocloreto de guanidina, etanol, calor e hipotonicidade na estabilidade de membrana de eritrócitos humanos; Effects of combinations of guanidine hydrochloride, ethanol, heat and hypotonicity on membrane stability of human erythrocytes

Arvelos, Leticia Ramos de
Fonte: Universidade Federal de Uberlândia Publicador: Universidade Federal de Uberlândia
Tipo: Dissertação
POR
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A estabilidade de membrana do eritrócito pode ser monitorada pela quantidade de lise por agentes caotrópicos como calor, hipotonicidade, hidrocloreto de guanidina e etanol. O presente trabalho estuda os efeitos de combinações desses caotrópicos, dois a dois, na estabilidade de eritrócitos humanos. Foram utilizados eritrócitos de amostras de sangue humano colhidos de 10 voluntárias sadias (26 ± 4 anos de idade). A estabilidade de eritrócitos foi avaliada pelas constantes de meia-transição das curvas de lise por hidrocloreto de guanidina, etanol e estresse hipotônico, obtidas por análises de regressão sigmoidal das dependências da absorvância em 540 nm com a concentração de cada caotrópico, após incubação por tempo fixo de 30 minutos. Os resultados foram comparados entre si por análise de variância, utilizando o teste de Tukey. As combinações de hidrocloreto de guanidina com calor e etanol produziram sempre efeitos caotrópicos sinérgicos sobre a lise de eritrócitos e sobre a desnaturação da hemoglobina. Mas a utilização de 0,1 a 0,6 M de hidrocloreto de guanidina causou proteção de eritrócitos contra o estresse hipotônico. Esse efeito protetor deve ser decorrente da natureza salina do hidrocloreto de guanidina. Proteção contra lise também foi parcialmente observada na presença de 0...

Decreased heat stability and increased chaperone requirement of modified human βB1-crystallins; Decreased heat stability and increased chaperone requirement of modified human betaB1-crystallins

Lampi, K.; Kim, Y.; Bachinger, H.; Boswell, B.; Lindner, R.; Carver, J.; Shearer, T.; David, L.; Kapfer, D.
Fonte: Molecular Vision Publicador: Molecular Vision
Tipo: Artigo de Revista Científica
Publicado em //2002 EN
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46.24%
Purpose: To determine how deamidation and partial loss of the N- and C-terminal extensions alter the heat stability of βB1-crystallin. Methods: Human lens βB1, a deamidated βB1, Q204E, and αA-crystallins were expressed. Truncated βB1 was generated by proteolytic removal of part of its terminal extensions. The aggregation and precipitation of these proteins due to heating was monitored by circular dichroism and light scattering. The effect of heat on the stability of both monomers and oligomers was investigated. The flexibility of the extensions in wild type and deamidated βB1 was assessed by 1H NMR spectroscopy. Results: With heat, deamidated βB1 precipitated more readily than wild type βB1. Similar effects were obtained for either monomers or oligomers. Flexibility of the N-terminal extension in deamidated βB1 was significantly reduced compared to the wild type protein. Truncation of the extensions further increased the rate of heat-induced precipitation of deamidated βB1. The presence of the molecular chaperone, αA-crystallin, prevented precipitation of modified βB1s. More αA was needed to chaperone the truncated and deamidated βB1 than deamidated βB1 or truncated βB1. Conclusions: Deamidation and truncation of βB1 led to destabilization of the protein and decreased stability to heat. Decreased stability of lens crystallins may contribute to their insolubilization and cataract formation.; Kirsten J. Lampi...

Further studies on the heat-stability of freeze-dried glutamate BCG vaccine: Effect of storage at 30°-50°C on allergenic potency in humans

Geser, Anton; Azuma, Yoshikuni
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em //1960 EN
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45.98%
In order to avoid the necessity for continuous refrigeration of liquid BCG vaccine during storage and transport in hot climates, various attempts have been made to develop more stable preparations. Several studies have indicated that freeze-dried BCG vaccines, and in particular the Japanese glutamate vaccine, are more resistant to high temperatures than liquid BCG vaccines. The present paper reports the results of three studies in schoolchildren designed to compare the heat-stability of three dried vaccines (Japanese glutamate vaccine, Japanese sucrose vaccine, and French glucose vaccine) and Danish liquid vaccine. The results showed that the allergenic potency of the Japanese glutamate vaccine was not much reduced even after storage at 42°C for one month whereas the liquid vaccine was already seriously damaged after one month's storage at 30°C. Exposure to a temperature of 50°C for one month was found to reduce the allergenic capacity of all three freeze-dried vaccines. As exposure to such high temperatures hardly ever occurs under field conditions, it seems probable that the dried glutamate vaccine can be used without refrigeration even in tropical countries. However, the duration of the allergy induced by the heat-treated glutamate vaccine has not yet been definitely established. This question is under further study.

Microtubule-associated proteins of HeLa cells: heat stability of the 200,000 mol wt HeLa MAPs and detection of the presence of MAP-2 in HeLa cell extracts and cycled microtubules

Fonte: The Rockefeller University Press Publicador: The Rockefeller University Press
Tipo: Artigo de Revista Científica
Publicado em 01/01/1982 EN
Relevância na Pesquisa
46.05%
One of the major groups of microtubule-associated proteins (MAPs) found associated with the microtubules isolated from HeLa cells has a molecular weight of just over 200,000. Previous work has demonstrated that these heLa MAPs are similar in several properties to MAP-2, one of the major MAPs of mammalian neural microtubules, although the two types of proteins are immunologically distinct. The 200,000 mol wt HeLa MAPs have now been found to remain soluble after incubation in a boiling water bath and to retain the ability to promote tubulin polymerization after this treatment, two unusual properties also shown by neural MAP- 2. This property of heat stability has allowed the development of a simplified procedure for purification of the 200,000 HeLa MAPs and has provided a means for detection of these proteins, even in crude cell extracts. These studies have also led to the detection of a protein in crude extracts of HeLa cells and in cycled HeLa microtubules which has been identified as MAP-2 on the basis of (a) comigration with calf brain MAP-2 on SDS PAGE, (b) presence in purified microtubules, (c) heat stability, and (d) reaction with two types of antibodies prepared against neural high molecular weight-MAPs, one of these a monoclonal antibody against hog brain MAP-2...

Antibody binding and functional properties of whey protein hydrolysates obtained under high pressure

Chicón, Rosa; Belloque, Josefina; Alonso, Elena; López-Fandiño, Rosina
Fonte: Elsevier Publicador: Elsevier
Tipo: Artículo Formato: 458108 bytes; application/pdf
ENG
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45.91%
7 pages, 4 figures.-- Available online May 18, 2008.; This paper examines the potential of high hydrostatic pressure to produce whey protein hydrolysates that combine low immunoglobulin (Ig)G- and IgE-binding with acceptable functional properties, with the aim to produce milk-based ingredients with reduced potential allergenicity that could be used in hypoallergenic foods. Treatment with pepsin and chymotrypsin under high pressure produced, in minutes, hydrolysates in which α-lactalbumin and β-lactoglobulin were totally proteolysed, giving rise to large and hydrophobic peptides. Such hydrolysates presented reduced antigenicity and human IgE-binding properties. The hydrolysates obtained with pepsin at 400 MPa showed improved heat stability, particularly at a pH, close to the isoelectric point of the whey proteins, and their emulsion activity indexes at pH 7.0 were superior to those of the untreated whey proteins. These results suggest that the peptides present retained low antigenicity together with sufficient capacity to form emulsions.; This work has been supported by the projects AGL-2004-03322, CONSOLIDER-INGENIO CSD-2007-00063 (Ministerio de Educación y Ciencia, Spain) and S-0505/AGR/0153 (Comunidad Autónoma de Madrid, Spain).; Peer reviewed

Experimental study of flow boiling heat transfer and critical heat flux in microchannels

Kuan, Wai Keat
Fonte: Rochester Instituto de Tecnologia Publicador: Rochester Instituto de Tecnologia
Tipo: Dissertação Formato: 51101274 bytes; application/pdf
EN_US
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36.15%
Advancements in microprocessors and other high power electronics have resulted in increased heat dissipation from those devices. In addition, to reduce cost, the functionality of microprocessor per unit area has been increasing. The increase in functionality accompanied by reduction in chip size has caused its thermal management to be challenging. In order to dissipate the increase in heat generation, the size of conventional fin-type heat sinks has to be increased. As a result, the performance of these high heat flux generating electronics is often limited by the available cooling technology and space to accommodate the larger conventional air-cooled heat sinks. One way to enhance heat transfer from electronics without sacrificing their performance is the use of heat sink with many microchannels and liquid passing through it. The present work is aimed toward understanding the flow boiling stability and critical heat flux (CHF) with water and R-123 in microchannel passages. Experimental data and theoretical model to predict the heat transfer and CHF are the focus of this work. The experimental test section has six parallel microchannels with each having a cross sectional area of 1054 x 157 um2 or 1054 x 197 um2. The effect of flow instabilities in microchannels is investigated using flow restrictors at the inlet of each microchannel to stabilize the flow boiling process and avoid the backflow phenomena. This technique resulted in successfully stabilizing the flow boiling process as seen through a high-speed camera. The present CHF result is found to correlate to mean absolute error (MAE) of 24.1% with a macro-scale empirical equation by Katto et al. [34]. A theoretical analysis of flow boiling phenomena revealed that the ratio of evaporation momentum to surface tension forces is an important parameter. For the first time...