1 |
Studies on the crystallinity of poly(tetrafluoroethylene)Lehnert, Ralph Juergen January 1994 (has links)
No description available.
|
2 |
Detector de corrente Compton. / Compton current detector.Campos, João Sinézio de Carvalho 30 May 1984 (has links)
O objetivo do presente trabalho é a descrição do projeto e construção de um detector de corrente Compton, com geometria cilíndrica utilizando o material dielétrico teflon; para radiação eletromagnética numa faixa de energia entre 10 KeV à 2 MeV. Basicamente o detector é composto por um cilindro de teflon, recoberto com uma fina camada de tinta prata (chamado eletrodo externo) e um eletrodo interno de chumbo, colocado axialmente no dielétrico; assim o detector forma um capacitor de placas cilíndricas recheado com teflon. A função de cada parte do detector é descrita neste trabalho, também são relatadas as medidas sobre a corrente Compton provocadas no teflon pela passagem de um fluxo de fótons provenientes as fontes de raios-X (aparelho Muller MG 150) e raios gama de cobalto (60Co), estas medidas foram realizadas com auxílio de um eletrômetro da Keitley. Apresenta-se uma teoria elaborada pelo professor Bernhard Gross a qual se ajusta satisfatoriamente com os resultados experimentais obtidos. Levantaram-se as curvas de calibração de carga e corrente acumulada no detector contra taxas de exposição. O detector é bastante simples de ser construído e para que se possam fazer as medidas de corrente, carga ou mesmo voltagem acumulada neste, bastando para isto um eletrômetro. Outro fato importante de se ressaltar, é que tal detector não necessita de campo elétrico aplicado, como encontrado em muitos detectores de radiação de uso comercial. No presente trabalho procura-se ainda fornecer uma idéia dos conceitos e unidades básicas que envolvem o campo das radiações eletromagnéticas. / In this work it is related building of a radiation detector for range energy between 10 KeV 2 MeV. It´s used Teflon (cylindrical geometry) for scattering of radiation for the production of Compton electrons. Axially to Teflon there is a lead internal electrode, which absorbs the incident radiation. Recovering the Teflon there is a silver external electrode that doesn´t absorb the radiation. In this way, the detector behaves as a cylindrical capacitor which Teflon is a dielectric. The measures are made with an electrometer. The detector shows a linear and reproducible behavior as a function of dose rate.
|
3 |
Detector de corrente Compton. / Compton current detector.João Sinézio de Carvalho Campos 30 May 1984 (has links)
O objetivo do presente trabalho é a descrição do projeto e construção de um detector de corrente Compton, com geometria cilíndrica utilizando o material dielétrico teflon; para radiação eletromagnética numa faixa de energia entre 10 KeV à 2 MeV. Basicamente o detector é composto por um cilindro de teflon, recoberto com uma fina camada de tinta prata (chamado eletrodo externo) e um eletrodo interno de chumbo, colocado axialmente no dielétrico; assim o detector forma um capacitor de placas cilíndricas recheado com teflon. A função de cada parte do detector é descrita neste trabalho, também são relatadas as medidas sobre a corrente Compton provocadas no teflon pela passagem de um fluxo de fótons provenientes as fontes de raios-X (aparelho Muller MG 150) e raios gama de cobalto (60Co), estas medidas foram realizadas com auxílio de um eletrômetro da Keitley. Apresenta-se uma teoria elaborada pelo professor Bernhard Gross a qual se ajusta satisfatoriamente com os resultados experimentais obtidos. Levantaram-se as curvas de calibração de carga e corrente acumulada no detector contra taxas de exposição. O detector é bastante simples de ser construído e para que se possam fazer as medidas de corrente, carga ou mesmo voltagem acumulada neste, bastando para isto um eletrômetro. Outro fato importante de se ressaltar, é que tal detector não necessita de campo elétrico aplicado, como encontrado em muitos detectores de radiação de uso comercial. No presente trabalho procura-se ainda fornecer uma idéia dos conceitos e unidades básicas que envolvem o campo das radiações eletromagnéticas. / In this work it is related building of a radiation detector for range energy between 10 KeV 2 MeV. It´s used Teflon (cylindrical geometry) for scattering of radiation for the production of Compton electrons. Axially to Teflon there is a lead internal electrode, which absorbs the incident radiation. Recovering the Teflon there is a silver external electrode that doesn´t absorb the radiation. In this way, the detector behaves as a cylindrical capacitor which Teflon is a dielectric. The measures are made with an electrometer. The detector shows a linear and reproducible behavior as a function of dose rate.
|
4 |
Producao de politetrafluoroetileno mediante a polimerizacao induzida por radiacao gamaLUGAO, ADEMAR B. 09 October 2014 (has links)
Made available in DSpace on 2014-10-09T12:32:13Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:10:37Z (GMT). No. of bitstreams: 1
02645.pdf: 1691710 bytes, checksum: 39067301c2a53e7ec89ab2f222ef287b (MD5) / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP
|
5 |
Producao de politetrafluoroetileno mediante a polimerizacao induzida por radiacao gamaLUGAO, ADEMAR B. 09 October 2014 (has links)
Made available in DSpace on 2014-10-09T12:32:13Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:10:37Z (GMT). No. of bitstreams: 1
02645.pdf: 1691710 bytes, checksum: 39067301c2a53e7ec89ab2f222ef287b (MD5) / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP
|
6 |
Construction Of A Choline Oxidase BiosensorYucel, Deniz 01 January 2003 (has links) (PDF)
Choline is indispensable for a number of fundamental processes in the body.
Besides being the precursor of the acetylcholine, an important neurotransmitter,
choline is found in the cell membrane structure combining with fatty acids,
phosphate and glycerol. Its deficiency may result in nervous system disorders, fatty
acid build up in the liver, along with increased cholesterol levels, high blood pressure
and memory loss. Thus, rapid detection methods are required for the determination
of choline in biological fluids. In this study a choline oxidase biosensor was constructed for the determination
of choline. During construction of the biosensor, glucose oxidase was used as a
model enzyme, before choline oxidase used. The Teflon (PTFE) membrane of the
oxygen electrode was grafted with 2-hydroxyethyl methacrylate (HEMA, 15%, v/v)
in the presence of ferrous ammonium sulphate (FAS, 0.1%, w/v) by gamma
irradiation and ethyleneglycol dimethacrylate (EGDMA, 0.15 %, v/v) was used as a
crosslinker in a series of membranes. HEMA-grafted membranes were activated with
epichlorohydrin or glutaraldehyde to maintain covalent immobilization of enzyme.
The enzyme activity was measured with an oxygen electrode unit based on oxygen
consumption upon substrate addition.
Membranes were characterized in terms of grafting conditions and mechanical
properties. Membranes, gamma irradiated in a solution of HEMA (15%) and FAS
(0.1%) for 24 h, were found to be suitable for use in the further studies. Mechanical
test results revealed that HEMA grafting made Teflon membrane more flexible and
the presence of EGDMA made the grafted membrane stiffer. During optimization
stage, it was found that the immobilized enzyme amount was not sufficient to obtain
enzyme activity. Thus, the membrane preparation stage was modified to obtain
thinner membranes. The immobilized glucose oxidase and choline oxidase contents
on thin HEMA grafted membranes were determined by Bradford and Lowry
methods. The influence of EGDMA presence and the epichlorohydrin activation
duration on enzyme activity studies revealed that the membrane should be prepared
in the absence of EGDMA and 30 min activation duration is appropriate for
epichlorohydrin coupling. The study on the influence of membrane activation
procedures revealed that the membranes activated with glutaraldehyde had a higher specific activity than the membranes activated with epichlorohydrin. Upon stretching
membrane on the electrode directly rather than placing in the sample unit, the
response of the enzyme immobilized sensor improved with high specific activity.
The optimum choline oxidase concentration was found to be 2 mg/mL considering
the effect of immobilization concentration on enzyme activity. With the choline
oxidase biosensor, the linear working range was determined as 0.052-0.348 mM,
with a 40 ± / 5 µ / M minimum detection limit. The response of the sensor decreased
linearly upon successive measurements.
|
7 |
Static and dynamic wetting of porous Teflon® surfacesWal, Bouwe Pieter van der. January 2006 (has links)
Proefschrift Rijksuniversiteit Groningen. / Met lit. opg. - Met samenvatting in het Nederlands.
|
8 |
O deslocamento do segundo ponto de cruzamento na curva de emissão eletrônica de polímeros com a dose de irradiação absorvida e suas implicações. / The second cross over in the electronic emission curve shift with the absorbed radiation dose and its implication.Chinaglia, Dante Luis 04 December 1992 (has links)
Amostras de Teflón® FEP e Mylar C foram submetidas a um bombardeio eletrônico por longos períodos a fim de se verificar a existência de uma possível corrente de condução na fase final de um carregamento por feixe eletrônico. Em vez disso, descobriu-se que a energia associada ao segundo ponto de cruzamento da curva de emissão eletrônica do material bombardeado varia lentamente com o tempo de exposição à irradiação. Por outro lado foram descobertos também fortes indícios de que o centróide de carga sofre um deslocamento enquanto a amostra está sendo irradiada. A componente da corrente através da amostra, associada a qualquer um desses efeitos se superpõe à corrente de condução (se existir) e acaba tornando inviável a sua observação, enquanto um ou ambos os efeitos persistirem. Na realidade não é só a energia do segundo ponto de cruzamento que varia; toda a curva de emissão característica do material, que é fundamental para se entender os processos e carga e descarga de amostras, sofre modificação com a irradiação prolongada. Além disto, dois novos métodos para se carregar uma amostra de polímero estão sendo propostos. Um deles permite carregar uma amostra positivamente, por etapas, a tensões mais elevadas que o método convencional. O outro possibilita carregar negativamente uma amostra, lançando mão do mecanismo de auto-regulação para interrupção do processo de carga, o que só havia sido feito até o momento para um carregamento positivo. Um novo método para se descarregar uma amostra usando o próprio feixe eletrônico também é apresentado. / Teflon® FEP and Mylar C samples were submitted to an electron beam during long periods of time in order to examine the possible existence of conduction current in the final stages of the charging process. It was found that the energy associated with the second crossover point in the electronic emission curve of the irradiated material varied slightly with the time of irradiation. On the other hand, strong evidence emerged that the charge centroid is shifted while the sample is being irradiated. The component of the current through the sample which is associated with any of these effects is superimposed to the conduction current (if present), hampering the identification of a conduction current. In fact, it is not only the energy of the second crossover point that varies, for the whole emission curve is modified upon prolonged irradiation. This emission curve is fundamental for understanding the charging and discharging processes in the samples. In addition, two new methods for charging a sample are being proposed. The first allows one to charge the sample positively to surface potentials that are higher than those obtained in the conventional method. The other method permits the sample to be charged negatively using the auto-regulation mechanism for interrupting the charging process; this had previously been done only for charging samples positively. A new method for discharging a sample using the electron beam is also presented.
|
9 |
Descargas termo-estimuladas no teflon fep-a em circuito aberto. / Open-circuit TSD method in Teflon fep-AGuimarães Neto, João Mariz 21 January 1983 (has links)
Foram construídas duas montagens experimentais: Com a primeira, mediu-se o decaimento do potencial de superfície em circuito aberto, em função da temperatura; com a segunda mediu-se diretamente a corrente termo-estimulada (derivada do potencial de superfície em circuito aberto) aquecendo-se a amostra a uma taxa constante. Usando essas técnicas estudamos as propriedades de transporte e armazenamento de cargas no Teflon FEP-A, carregado com corona. Usando a segunda técnica, verificou-se que amostras descarregadas, do citado material, podem liberar portadores de cargas positivas que dão origem a uma corrente anômala, que pode interferir nas medidas de corrente termo-estimulada de amostras carregadas positivamente. Estudou-se o comportamento das curvas de corrente em amostras com e sem tratamento térmico, carregadas com corona tanto positiva como negativa. Além disto, é feita uma discussão dos resultados por nós obtidos e os publicados na literatura. / Two experimental systems were constructed: with the first the surface potential could be measured, while with the second, its derivative with respect to the time (the so called open circuit current). In both cases the measurements were performed while heating previously positive or negative corona charged FEP-A Teflon 25μm samples. The results gave information about charge storage and transport properties in this material. During the work it was noticed that positive ions maybe emitted from Teflon surface. This unexpected phenomenon was followed in some detail in order to know how far it influences the usual currents. This study led us to carry measurements in previously annealed samples, whose behavior was found to differ from that of virgin samples. Our results were compared with those found in the literature.
|
10 |
Low Temperature Bonding Techniques for Sealing Teflon Based Microfluidic DevicesLee, Shin-De 05 September 2012 (has links)
Microfluidics emerged during the early 1990s with channel networks in silicon or glass. Microprocessing of these materials is labor-intensive and time-consuming, it requires sophisticated equipment in a clean room, and often involves hazardous chemicals. The subsequent use of polymer greatly simplified the fabrication of microchips and led to the rapid development of the field. Polymer such as poly(dimethylsiloxane) (PDMS), has other attractive properties, such as being elastic (easy to make efficient microvalves), permeable to gases, and compatible with culturing biological cells. Despite these advantages, applications of PDMS chips are severely limited by a few drawbacks that are inherent to this material: (i) strong adsorption of molecules, particularly large biomolecules, onto its surface; (ii) absorption of nonpolar and weakly polar molecules into PDMS bulk; (iii) leaching of
small molecules from PDMS bulk into solutions; and (iv) incompatibility with organic solvents. To overcome all these problems, Teflon plastics seem to be the perfect solution. They are well-known for their superior inertness to almost all chemicals and all solvents; they also show excellent resistance to molecular adsorption and molecule leaching from the polymer bulk to solutions. However, Teflon has a high chemical inertness of the surface, which is restricted the bonding temperature (>260¢XC).It is not conducive to the low-temperature packaging process.
This study presents a simple and rapid process for sealing Teflon-based microfluidic chip at a temperature of 140oC which is lower than typical bonding temperature of 260oC. A simple ammonium plasma treatment is used to enhance the surface energy of Teflon substrates such that the bonding temperature can be greatly reduced. Results indicate that the ammonium plasma treated Teflon substrates can be sealed using hot press bonding at a temperature of 140oC for 20 min. The measured
iv
bonding strength for the Teflon-based microfluidic devices is higher than those bonded at a reported temperature of 260oC for 60 min. It shows the measured contact angle for the Teflon substrates treated with different plasmas. Results indicated that the ammonium hydroxide plasma exhibited the best wettability property and the contact angle reached the minimum value of 45o after 5 min of treatment. The ESCA analysis showed the best Defluorination by ammonium plasma. The fluorine/carbon atomic ratio degraded from 1.96 to 1.10 by 5 minutes. The measured bonding strength for the Teflon substrates bonded with different surface activation protocols. Results showed that the bonding strength was enhanced upto 93% after the plasma treatment. The plasma treatment not only enhanced the bonding strength but also reduced the bonding temperature and time. The measured surface roughness only increased 15¡Ó5 nm (Ra) after the plasma treatment, which is acceptable for most applications in microfluidic systems. Finally, the fluorescence optical architecture and cross-chip successfully detected and isolated £XX-174 fragment of DNA samples confirmed the Teflon substrate for the emerging microfluidic plastic chip. The developed method provides a simple and rapid way to fabricate Teflon-based microfluidic devices.
|
Page generated in 0.0243 seconds