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On the activation and physical degradation of boron-doped diamond surfaces brought on by cathodic pretreatments

SALAZAR-BANDA, Giancarlo R.; CARVALHO, Adriana E. de; ANDRADE, Leonardo S.; ROCHA-FILHO, Romeu C.; AVACA, Luis A.
Fonte: SPRINGER Publicador: SPRINGER
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
45.85%
The electrochemical activation and physical degradation of boron-doped diamond (BDD) electrodes with different boron doping levels after repeated cathodic pretreatments are reported. Galvanostatic cathodic pretreatment passing up to -14000 C cm(-2) in steps of -600 C cm(-2) using -1 A cm(-2) caused significant physical degradation of the BDD surface, with film detachment in some areas. Because of this degradation, a great increase in the electrochemically active area was observed in Tafel plots for the hydrogen evolution reaction (HER) in acid media. The minimum cathodic pretreatment needed for the electrochemical activation of the BDD electrodes without producing any observable physical degradation on the BDD surfaces was determined using electrochemical impedance spectroscopy (EIS) measurements and cyclic voltammetry: -9 C cm(-2), passed at -1 A cm(-2). This optimized cathodic pretreatment can be safely used when electrochemical experiments are carried out on BDD electrodes with doping levels in the range between 800 and 8000 ppm.; Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); CNPq; CAPES; Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES); FAPESP; Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Caracterização do padrão da ativação elétrica ventricular de indivíduos portadores de ressincronizador cardíaco através do mapeamento eletrocardiográfico de superfície; Body surface potential mapping characterization of the ventricular electrical activation pattern of individuals with cardiac resynchronization device

Samesima, Nelson
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 13/04/2011 PT
Relevância na Pesquisa
35.91%
INTRODUÇÃO: Os benefícios na morbi-mortalidade obtidos pela terapia de ressincronização cardíaca (TRC) em pacientes com insuficiência cardíaca estão bem estabelecidos. Métodos invasivos e não invasivos têm sido utilizados para identificar aqueles que realmente se beneficiarão da TRC, mas 30% destes pacientes não apresentam melhora clínica/funcional. Poucos estudos avaliaram o comportamento elétrico dos pacientes submetidos à TRC. OBJETIVO: Utilizamos um método não invasivo, o mapeamento eletrocardiográfico de superfície (MES) para caracterizar o padrão da ativação elétrica ventricular em pacientes após a TRC. MÉTODOS: Estudamos 91 pacientes submetidos à TRC, com insuficiência cardíaca e bloqueio de ramo esquerdo (BRE), sendo 36 excluídos devido a FA (20), BRD (3), cardiopatias hipertrófica (3) e congênita (1) ou dependentes de marcapasso antes da TRC (9). Idade média:61±10 anos, FEVE:0,28±0,9, QRS:182±24ms, classe funcional NYHA: III(78%) e IV(22%). Com o ressincronizador ligado e desligado, todos realizaram o MES, o qual fornece 87 derivações simultâneas (58 anteriores e 29 posteriores). Os mapas isócronos obtidos pelo MES forneceram os tempos de ativação ventricular (TAV) global máximo e médio nas 87 derivações. Os TAVs obtidos foram regionalizados...

Uso da microscopia eletroquímica no estudo da dinâmica de processos eletródicos em superfícies funcionalizadas; Scanning electrochemical microscopy studies on the kinetics of electrode processes at modified surfaces

Lima, Alex da Silva
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 18/05/2011 PT
Relevância na Pesquisa
35.91%
No presente trabalho, foi utilizada a microscopia eletroquímica de varredura (SECM) com o intuito de obter informações sobre a topografia, reatividade e possíveis intermediários formados em superfícies eletródicas. Foram estudados, em uma etapa inicial, modelos que proporcionaram a aprendizagem do manuseio e tratamento de dados utilizando a SECM. Em uma segunda etapa, a SECM foi aplicada no estudo da reatividade de substratos de cobre que passaram por um processo de ativação eletroquímica. A ativação foi realizada imergindo uma superfície de cobre em uma solução de Na2SO4 0,1 mol L-1 (pH = 2) e posterior aplicação de pulsos de potencial para oxidação de cobre (500 mV vs. Ag/AgCl(KCl sat.)) e subseqüente redução de íons Cu(II) (-250 mV vs. Ag/AgCl(KCl sat.)). Esse procedimento confere um aumento na sensibilidade na determinação de nitrato e nitrito. Para o estudo foram obtidas curvas de aproximação as quais foram correlacionadas com o tempo empregado na ativação. Também foram obtidas informações sobre a geração de Cu(I), estabilizado na presença de íons cloreto, durante o processo de ativação e sua influência na determinação de nitrato e nitrito. Por fim, a SECM foi utilizada no estudo de um sistema biomimético de cobre que catalisa a redução de oxigênio. Foram obtidas imagens com informações sobre a reatividade da superfície...

Ativação de filme de hexametildisiloxano com o uso de plasma de baixa pressão e radiação UV; Activation of hexamethyldisiloxane films with low pressure plasma and UV radiation

Tsai Garcia Perez
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 21/05/2007 PT
Relevância na Pesquisa
35.9%
o desenvolvimento de tecnologias limpas e eficientes que permitam substituir os métodos tradicionais de tratamento da superficie de materiais poliméricos e metálicos em busca de adesão entre eles é uma importante área de pesquisa na atualidade. As tecnologias de modificação superficial com uso de plasma e radiação ultravioleta apresentam-se como alternativas aos tratamentos convencionais em razão de sua pouca geração de resíduos, à fácil manipulação e à possibilidade de tratar superficies de diferentes geometrias. O presente trabalho estuda os processos de ativação de camadas de Hexametildisiloxano (HMDSO), com o uso de plasma de Argônio, Hidrogênio a baixa pressão e radiação ultravioleta (UV, UV/fotoiniciador e VUV), a fim de aumentar sua energia de superficie e melhorar, conseqüentemente, suas características adesivas. Para isso, realizou-se.~ a deposição de camadas de Hexametildisiloxano sobre placas de alumínio, por deposição química, em fase vapor assistida por plasma (PEVD), a que se seguiu o processo de ativação. Estudou-se ainda a influência dos parâmetros de deposição, processos a plasma de baixa pressão e radiação ultravioleta na funcionalização da superfície. Obteve-se, como resultado...

Silver activation on thin films of Ag-ZrCN coatings for antimicrobial activity

Ferreri, Isabel; Calderon Velasquez, S.; Escobar Galindo, R.; Palacio, C.; Henriques, Mariana; Piedade, Ana Paula; Carvalho, S.
Fonte: Elsevier B.V. Publicador: Elsevier B.V.
Tipo: Artigo de Revista Científica
Publicado em //2015 ENG
Relevância na Pesquisa
35.92%
Nowadays, with the increase of elderly population and related health problems, knee and hip joint prosthesis are being widely used worldwide. However, failure of these invasive devices occurs in a high percentage thus demanding the revision of the chirurgical procedure. Within the reasons of failure, microbial infections, either hospital or subsequently-acquired, contribute in high number to the statistics. Staphylococcus epidermidis (S. epidermidis) has emerged as one of the major nosocomial pathogens associated with these infections. Silver has a historic performance in medicine due to its potent antimicrobial activity, with a broad-spectrum on the activity of different types of microorganisms. Consequently, the main goal of this work was to produce Ag-ZrCN coatings with antimicrobial activity, for the surface modification of hip prostheses. Thin films of ZrCN with several silver concentrations were deposited onto stainless steel 316 L, by DC reactive magnetron sputtering, using two targets, Zr and Zr with silver pellets (Zr + Ag target), in an atmosphere containing Ar, C2H2 and N2. The antimicrobial activity of the modified surfaces was tested against S. epidermidis and the influence of an activation step of silver was assessed by testing samples after immersion in a 5 % (w/v) NaClO solution for 5 minutes. The activation procedure revealed to be essential for the antimicrobial activity...

Ag ion decoration for surface modifications of multi-walled carbon nanotubes

Travessa,Dilermando N.; Silva,Fábio S. da; Cristovan,Fernando H.; Jorge Jr.,Alberto M.; Cardoso,Kátia Regina
Fonte: ABM, ABC, ABPol Publicador: ABM, ABC, ABPol
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/06/2014 EN
Relevância na Pesquisa
45.84%
The production of high performance metal matrix composites depends on a proper design of the surface of the reinforcing phase, ensuring a good contact with a metal phase. In the present work, two Ag decorating procedures to modify the surface of multi-walled carbon nanotubes (MWCNT) were evaluated for further production of aluminum matrix composites. The procedures consisted in a two steps route based on acid oxidation of carbon nanotubes (CNT) followed by suspension in an Ag ion solution; and a single step route, based on the effect of n-dimethylformamide (DMF) as an activation agent of CNT surface, in presence of Ag ions. Transmission and scanning-transmission electron microscopy, Raman and Fourier-transformed infrared spectroscopy were employed in order to characterize the results. The two steps route resulted in Ag nano-particles homogeneously deposited over the CNT surface. The mechanism for the deposition is based on carboxyl and probably hydroxyl functional groups formed in the first step, acting as nucleation sites for Ag precipitation in the second step. The single step route resulted in the formation of sub-micrometric Ag particles heterogeneously mixed to CNT bundles.

Improved relationship between left and right ventricular electrical activation after cardiac resynchronization therapy in heart failure patients can be quantified by body surface potential mapping

Samesima,Nelson; Pastore,Carlos Alberto; Douglas,Roberto Andres; Martinelli Filho,Martino; Pedrosa,Anisio A.
Fonte: Faculdade de Medicina / USP Publicador: Faculdade de Medicina / USP
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/07/2013 EN
Relevância na Pesquisa
35.99%
OBJECTIVES: Few studies have evaluated cardiac electrical activation dynamics after cardiac resynchronization therapy. Although this procedure reduces morbidity and mortality in heart failure patients, many approaches attempting to identify the responders have shown that 30% of patients do not attain clinical or functional improvement. This study sought to quantify and characterize the effect of resynchronization therapy on the ventricular electrical activation of patients using body surface potential mapping, a noninvasive tool. METHODS: This retrospective study included 91 resynchronization patients with a mean age of 61 years, left ventricle ejection fraction of 28%, mean QRS duration of 182 ms, and functional class III/IV (78%/22%); the patients underwent 87-lead body surface mapping with the resynchronization device on and off. Thirty-six patients were excluded. Body surface isochronal maps produced 87 maximal/mean global ventricular activation times with three regions identified. The regional activation times for right and left ventricles and their inter-regional right-to-left ventricle gradients were calculated from these results and analyzed. The Mann-Whitney U-test and Kruskall-Wallis test were used for comparisons...

Role of cytoskeletal elements in expression of monocyte urokinase plasminogen activator receptor, activation-associated antigen Mo3.

Washington, R; Dore-Duffy, P
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /11/1994 EN
Relevância na Pesquisa
35.92%
Peripheral blood monocytes exposed to bacterial products, phorbol esters, cyclic AMP, and cyclic AMP analogs express cell surface activation protein Mo3, which is the human urokinase plasminogen activator receptor (uPA-R). uPA-R is expressed by circulating monocytes from patients with multiple sclerosis (MS). We examined the role of cytoskeletal elements in the surface expression and subcellular distribution of uPA-R in nonactivated and lipopolysaccharide-activated monocytes and in monocytes from patients with MS. By using immunofluorescence techniques and confocal laser microscopy, we found that in unactivated monocytes, cytoplasmic uPA-R is found to one side of the nucleus, colocalizing with the Golgi. Upon activation with lipopolysaccharide, cytoplasmic Mo3-uPA-R becomes dispersed throughout the cytoplasm and projections concomitant with an increase in the monocyte perimeter (spreading). Cytoplasmic dispersion, as well as cell surface deposition, is dependent on microtubule integrity. Cell surface deposition of uPA-R upon activation is reduced by colchicine, which disrupts microtubules; however, once associated at the cell surface, uPA-R becomes associated with microfilaments via vinculin. Disruption of microfilaments with cytochalasin also alters surface expression of immunologically reactive uPA-R...

Active tissue factor pathway inhibitor is expressed on the surface of coated platelets

Maroney, Susan A.; Haberichter, Sandra L.; Friese, Paul; Collins, Maureen L.; Ferrel, Josephine P.; Dale, George L.; Mast, Alan E.
Fonte: American Society of Hematology Publicador: American Society of Hematology
Tipo: Artigo de Revista Científica
Publicado em 01/03/2007 EN
Relevância na Pesquisa
35.89%
The incorporation of blood-borne forms of tissue factor (TF) into a growing blood clot is necessary for normal fibrin generation and stabilization of the blood clot. Tissue factor pathway inhibitor (TFPI) is the primary physiologic inhibitor of tissue factor and is present within platelets. Expression of TFPI on the platelet surface may be the optimal location for it to abrogate blood-borne TF activity that incorporates within the blood clot, balancing the need for adequate hemostasis while preventing development of occlusive thrombosis. TFPI is produced by megakaryocytes but is not expressed on the platelet surface. Activation of platelets with thrombin receptor activation peptide does not cause release or surface expression of TFPI, demonstrating that TFPI is not stored within platelet α granules. TFPI is expressed on the platelet surface following dual-agonist activation with convulxin plus thrombin to produce coated platelets. In association with its expression on the surface of coated platelets TFPI is also released in microvesicles or as a soluble protein.

Redistribution of the fibrinogen receptor of human platelets after surface activation

Fonte: The Rockefeller University Press Publicador: The Rockefeller University Press
Tipo: Artigo de Revista Científica
Publicado em 01/09/1984 EN
Relevância na Pesquisa
45.89%
We investigated the whole cell distribution of the platelet membrane receptor for fibrinogen in surface-activated human platelets. Fibrinogen-labeled colloidal gold was used in conjunction with platelet whole mount preparations to visualize directly the fibrinogen receptor. Unstimulated platelets fail to bind fibrinogen, and binding was minimal in the stages of activation immediately following adhesion. The amount of fibrinogen bound per platelet increased rapidly during the shape changes associated with surface activation until 7,600 +/- 500 labels were present at saturation. Maximal binding of fibrinogen was followed by receptor redistribution. During the early stages of spreading, fibrinogen labels were uniformly distributed over the entire platelet surface, including pseudopodia, but the labels become progressively centralized as the spreading process continued. In well spread platelets, labels were found over the central regions, whereas peripheral areas were cleared of receptors. Receptor redistribution during spreading was accompanied by cytoskeletal reorganization such that a direct correlation was seen between the development of specific ultrastructural zones and the distribution of surface receptor sites suggesting a link between the surface receptors and the cytoskeleton. The association of fibrinogen receptors with contractile elements of the cytoskeleton...

Contact Activation of Blood Plasma Coagulation: A Contribution from the Hematology at Biomaterial Interfaces Research Group The Pennsylvania State University

Vogler, Erwin A.; Siedlecki, Christopher A.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
35.91%
This opinion identifies inconsistencies in the generally-accepted surface biophysics involved in contact activation of blood-plasma coagulation, reviews recent experimental work aimed at resolving inconsistencies, and concludes that this standard paradigm requires substantial revision to accommodate new experimental observations. Foremost among these new findings is that surface-catalyzed conversion of the blood zymogen factor XII (FXII, Hageman factor) to the enzyme FXIIa ( FXII→surfaceFXIIa, a.k.a. autoactivation) is not specific for anionic surfaces, as proposed by the standard paradigm. Furthermore, it is found that surface activation is moderated by the protein composition of the fluid phase in which FXII autoactivation occurs by what appears to be a protein adsorption-competition effect. Both of these findings argue against the standard view that contact activation of plasma coagulation is potentiated by assembly of activation-complex proteins (FXII, FXI, prekallikrein, and high-molecular-weight kininogen) directly onto activating surfaces (procoagulants) through specific protein/surface interactions. These new findings supplement the observation that adsorption behavior of FXII and FXIIa is not remarkably different from a wide variety of other blood proteins surveyed. Similarity in adsorption properties further undermines the idea that FXII and/or FXIIa are distinguished from other blood proteins by unusual adsorption properties resulting in chemically-specific interactions with activating anionic surfaces.

Moderation of Prekallikrein-Factor XII Interactions in Surface Activation of Coagulation by Protein-Adsorption Competition

Chatterjee, Kaushik; Thornton, Jennifer L.; Bauer, James W.; Vogler, Erwin A.; Siedlecki, Christopher A.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
35.96%
Traditional biochemistry of contact activation of blood coagulation suggesting that anionic hydrophilic surfaces are specific activators of the cascade is inconsistent with known trends in protein adsorption. To investigate contact activation reactions, a chromogenic assay was used to measure prekallikrein (PK) hydrolysis to kallikrein (Kal) by activated factor XII (FXIIa) at test hydrophilic (clean glass) and hydrophobic (silanized glass) surfaces in the presence of bovine serum albumin (BSA). Hydrolysis of PK by FXIIa is detected after contact of the zymogen FXII with a test hydrophobic surface only if putatively-adsorbed FXIIa is competitively displaced by BSA. By contrast, FXIIa activity is detected spontaneously following FXII activation by a hydrophilic surface and requires no adsorption displacement. These results (i) show that an anionic hydrophilic surface is not a necessary cofactor for FXIIa-mediated hydrolysis of PK, (ii) indicate that PK hydrolysis does not need to occur by an activation complex assembled directly on an anionic, activating surface, (iii) confirms that contact activation of FXII (autoactivation) is not specific to anionic hydrophilic surfaces, and (iv) demonstrates that protein-adsorption competition is an essential feature that must be included in any comprehensive mechanism of surface-induced blood coagulation.

Divalent cations regulate the folding and activation status of integrins during their intracellular trafficking

Tiwari, Shweta; Askari, Janet A.; Humphries, Martin J.; Bulleid, Neil J.
Fonte: Company of Biologists Publicador: Company of Biologists
Tipo: Artigo de Revista Científica
Publicado em 15/05/2011 EN
Relevância na Pesquisa
35.92%
Integrins are divalent cation-dependent, αβ heterodimeric adhesion receptors that control many fundamental aspects of cell behaviour by bi-directional signalling between the extracellular matrix and intracellular cytoskeleton. The activation state of cell surface integrins is tightly regulated by divalent cation occupancy of the ligand-binding pocket and by interaction with cytoplasmic adaptor proteins, such as talin. These agents elicit gross conformational changes across the entire molecule, which specify the activation state. Much less is known about the activation state of newly synthesised integrins or the role of cations during the early folding and trafficking of integrins. Here we use a number of well-characterised, conformation-specific antibodies to demonstrate that β1-integrins adopt the bent, inactive conformation after assembly with α-integrins in the endoplasmic reticulum. Folding and assembly are totally dependent on the binding of Ca2+ ions. In addition, Ca2+ binding prevents integrin activation before its arrival at the cell surface. Activation at the cell surface occurs only following displacement of Ca2+ with Mg2+ or Mn2+. These results demonstrate the essential roles played by divalent cations to facilitate folding of the β-integrin subunit...

Extracting Surface Activation Time from the Optically Recorded Action Potential in Three-Dimensional Myocardium

Walton, Richard D.; Smith, Rebecca M.; Mitrea, Bogdan G.; White, Edward; Bernus, Olivier; Pertsov, Arkady M.
Fonte: The Biophysical Society Publicador: The Biophysical Society
Tipo: Artigo de Revista Científica
Publicado em 04/01/2012 EN
Relevância na Pesquisa
45.91%
Optical mapping has become an indispensible tool for studying cardiac electrical activity. However, due to the three-dimensional nature of the optical signal, the optical upstroke is significantly longer than the electrical upstroke. This raises the issue of how to accurately determine the activation time on the epicardial surface. The purpose of this study was to establish a link between the optical upstroke and exact surface activation time using computer simulations, with subsequent validation by a combination of microelectrode recordings and optical mapping experiments. To simulate wave propagation and associated optical signals, we used a hybrid electro-optical model. We found that the time of the surface electrical activation (tE) within the accuracy of our simulations coincided with the maximal slope of the optical upstroke (tF∗) for a broad range of optical attenuation lengths. This was not the case when the activation time was determined at 50% amplitude (tF50) of the optical upstroke. The validation experiments were conducted in isolated Langendorff-perfused rat hearts and coronary-perfused pig left ventricles stained with either di-4-ANEPPS or the near-infrared dye di-4-ANBDQBS. We found that tF∗ was a more accurate measure of tE than was tF50 in all experimental settings tested (P = 0.0002). Using tF∗ instead of tF50 produced the most significant improvement in measurements of the conduction anisotropy and the transmural conduction time in pig ventricles.

Pharmakologische Beeinflussung der Monozytenaktivierung bei Hypothermie durch GPIIb/IIIa-Rezeptorantagonisten im modifizierten Chandler Loop Modell; Pharmacologic impact of monocyte activation in hypothermia by glycoprotein IIb/IIIa receptor antagonists in a modified Chandler-loop model

Griesel, Eva
Fonte: Universidade de Tubinga Publicador: Universidade de Tubinga
Tipo: Dissertação
DE_DE
Relevância na Pesquisa
35.94%
Die Monozytenaktivierung ist bei einem entzündlichen Geschehen wie der Arteriosklerose ein wichtiger Fakt. Studien der letzten Jahre konnten eine antiinflammatorische Wirkung der Hypothermie belegen. Aus diesem Grund hat die Hypothermie nach Veröffentlichung von zwei multizentrischen Studien im Jahr 2002 Einzug erhalten in die Leitlinien bezüglich reanimierter Patienten nach Myokardinfarkt. Die Verbesserung des neurologischen Outcomes ist auch in der Neuro- und Kardiochirurgie ein wichtiger Grundstein für den Einsatz einer Hypothermie. Unter milder therapeutischer Hypothermie kam es zu signifikant weniger Reinfarkten, als unter Normothermie. Die durch die Hypothermie reduzierten Enzymausschüttungen und Expressionsminderungen von Oberflächenmarkern bewirken eine antiinflammatorische Situation. Der Einsatz einer Kühlung - sei es über extra- oder intrakorporale Methoden - konfrontiert den Organismus mit einer unphysiologischen Oberfläche. Die Oberfläche der Katheter und Schläuche aktiviert die Gerinnungskaskade und trägt zur Thrombusbildung bei. Oftmals kommt bei Patienten nach Reanimation ein intrakorporales Kühlverfahren (z.B.CoolGard®) zum Einsatz. Neben der Koronarangiografie stellt die kardiopulmonale Bypass- (CPB-) Operation ein weiteres Interventionsverfahren bei Patienten mit koronarer Herzerkrankung dar. Hierbei kommt Blut ebenfalls durch die Herz-Lungen-Maschine mit einer unphysiologischen Oberfläche in Kontakt. Zudem wird die CPB-Operation unter Hypothermie durchgeführt. Viele Studien der letzten Jahre beschäftigten sich mit der Frage der Thrombozytenaktivierung bei Hypothermie. Ziel der hier vorliegenden Studie war es...

THE ROLE OF NEU1 SIALIDASE IN Trk TYROSINE KINASE RECEPTOR ACTIVATION

Jayanth, Preethi
Fonte: Quens University Publicador: Quens University
Tipo: Tese de Doutorado
EN; EN
Relevância na Pesquisa
35.93%
The signaling pathways of tyrosine kinase Trk receptors and their downstream biological effects are well known, but the parameters controlling the interactions between the receptors and their natural ligands still remain to be defined. Recent published reports from our laboratory indicate that nerve growth factor (NGF)-induced TrkA receptor activation is dependent on a membrane cellular sialidase. This sialidase activity specifically targets and hydrolyzes sialyl α-2, 3-linked β-galactosyl residues resulting in the desialylation and activation of the receptor. These findings support a novel hypothesis that places mammalian sialidase(s) in a cycle of activation of these receptors by their natural ligand. Taken together, they also predict a prerequisite desialylation of Trk receptors caused by a sialidase on the cell surface enabling the removal of a steric hindrance to receptor dimerization. Until now, the sialidase associated with neurotrophin-treated live Trk-expressing cells has not been identified. The molecular mechanism(s) of sialidase activation by neurotrophin factors binding to their receptors also remains unknown. In this thesis, the novel role of Neu1 sialidase in the activation of ligand-induced TrkA and TrkB receptors has been identified. It has been reported for the first time that Neu1 is already in complex with naïve and ligand-induced Trk receptors. In addition...

Activation of carbon nanofibres for hydrogen storage

Blackman, James M.; Patrick, John W.; Arenillas de la Puente, Ana; Shi, Wei; Snape, Colin E.
Fonte: Elsevier Publicador: Elsevier
Tipo: Artículo Formato: 918459 bytes; application/pdf
ENG
Relevância na Pesquisa
35.95%
10 pages, 10 figures, 6 tables.-- Printed version published Jul 2006.; The present study was aimed to investigate different methods of activation of carbon nanofibres, CNF, in order to determine the beneficial effect on the hydrogen sorption capacities of increasing the surface area. Two activation systems were used: physical activation with CO2 and chemical activation with KOH. A range of potential adsorbents were thus prepared by varying the temperature and time of activation. The structure of the CNF proved more suitable to activation by KOH than by CO2, with the former yielding higher surface area carbons (up to 1000 m2 g−1). The increased surface area, however, did not correspond directly with a proportional increase in hydrogen adsorption capacity. Although high surface areas are important for hydrogen storage by adsorption on solids, it would appear that it is essential that not only the physical, but also the chemical, properties of the adsorbents have to be considered in the quest for carbon based materials, with high hydrogen storage capacities.; The financial support of the EPSRC (Engineering and Physical Sciences Research Council) and Air Products and Chemicals, Inc. is gratefully acknowledged.; Peer reviewed

Tuning of texture and surface chemistry of carbon xerogels

Mahata, N.; Pereira, M. F. R.; Suárez García, Fabián; Martínez Alonso, Amelia; Díez Tascón, Juan Manuel; Figueiredo, José Luís
Fonte: Elsevier Publicador: Elsevier
Tipo: Artículo Formato: 22195 bytes; application/pdf
ENG
Relevância na Pesquisa
45.97%
6 pages, 4 figures, 5 tables.-- PMID: 18533175 [PubMed].-- Printed version published Aug 2008.; The influence of different activation processes on the textural and surface chemical properties of carbon xerogels was studied. Carbon xerogels were prepared by the conventional sol–gel approach using resorcinol and formaldehyde; two different pHs of sol–gel processing led to carbon materials with distinct pore size distributions. The materials were subjected to controlled activation by three different methods: activation by oxygen plasma, activation by HNO3, and activation by diluted air. Treatments with HNO3 and diluted air created oxygen groups on the external surface as well as inside the pore channels, whereas plasma is more suitable for introducing oxygen groups selectively on the external surface. Nevertheless, it was shown that samples with wider pores can be oxidized to some extent on the pore interiors by plasma. Significant changes in total surface area by air activation were observed.; This work was supported by “Fundação para a Ciência e a Tecnologia,” under programme POCTI/FEDER (POCTI 1181) and Project POCI/EQU/57369/2004 “Nanostructured carbon catalysts” and by the GRICES/CSIC cooperation in science and technology program. N.M. thanks FCT for a postdoctoral grant (SFRH/BPD/14804/2003).; Peer reviewed

Cell surface expression of the 300 kDa mannose-6-phosphate receptor by activated T lymphocytes

Hindmarsh, Elizabeth; Staykova, Maria; Willenborg, D; Parish, Christopher
Fonte: Blackwell Publishing Ltd Publicador: Blackwell Publishing Ltd
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
35.92%
Phosphosugars, such as mannose-6-phosphate (M6P), have been shown previously to display anti-inflammatory properties, notably inhibition of experimental autoimmune encephalomyelitis (EAE) and adjuvant-induced arthritis in rats. It has been proposed that M6P exerts its anti-inflammatory effect by displacing lysosomal enzymes, which are involved in T-cell extravasation into inflammatory sites, from the 300 kDa mannose-6-phosphate receptor (MPR-300) on the surface of T cells. If this model is correct MPR-300 should be selectively expressed on the surface of activated T cells, as T cell entry into the central nervous system in EAE depends on the T cells being in an activated state. Thus, the present study examines whether cell surface expression of MPR-300 by T lymphocytes correlates with their state of activation and whether T cells in inflammatory sites express the receptor. Flow cytometric studies showed MPR-300 to be absent from the surface of unstimulated rat T cells isolated from peripheral blood and lymphoid tissues, and T cells resident within the peritoneal cavity. In contrast, MPR-300 was expressed on activated T cells derived from an inflammatory peritoneal exudate. In vitro studies demonstrated transient expression of MPR-300 on the surface of splenic T cells following stimulation with Con A. MPR-300 was also induced on T-cell lines by antigen stimulation. These data demonstrate that T cells in inflammatory sites express MPR-300 on their surface and activation of T lymphocytes induces cell surface expression of MPR-300. Such findings are consistent with the hypothesis that cell surface MPR-300 is required for the entry of T cells into inflammatory sites.

Surface modifications of volcanic glasses (perlites) by water vapor

Abalos,R.; Erdmann,E.; Destefanis,H.A.
Fonte: Latin American applied research Publicador: Latin American applied research
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2003 EN
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Hydrothermal treatments on expanded volcanic glasses (perlites) were studied. The main objective of this paper is to obtain an activated surface able to interact with specific chemical substances. The above mentioned treatment consists on exposing the glass surface to water vapor at temperatures over 250°C at the correspondent vapor pressure during different periods of time and for different size of particles. The glass surface modifications were studied by IR, DTA-TG and adsorption techniques. The grade of surface activation was tested by studying the chemical interaction with polysiloxane polymers.