Influência do super-resfriamento nas ligas cu-al-ni com efeito de memória de forma

Nesse trabalho foi avaliada a microestrutura da liga 83%Cu – 13%Al – 4%Ni (porcentagem em peso) em 3 condições experimentais: a) estado bruto de fusão, b) estado bruto de fusão temperada e c) solidificada com fluxo. A liga no estado bruto de fusão apresentou grãos contendo partículas precipitadas no interior dos grãos, sem a presença de martensíta e o contorno desses grãos foi definido pelas partículas segregadas, enquanto a liga no estado bruto de fusão temperada apresentou grãos com a presença de martensíta e contornos sem precipitados. A liga solidificada com fluxo apresentou grãos com a presença de martensíta e sem precipitado

Effects of external irradiation of the neck region on intima media thickness of the common carotid artery

<p>Abstract</p> <p>Background</p> <p>Several studies have shown that common carotid intima-media thickness (IMT) is increased after radiotherapy (RT) to the head and neck. However, further studies are needed to define the exact mechanism of radiation-induced injury in large vessels, investigate the relationship between radiation dose and large vessel injury and evaluate the rate of progress of atherosclerosis in irradiated vessels.</p> <p>Objectives</p> <p>To investigate whether external irradiation to the carotid area has any effect on IMT of the common carotid artery in a group of patients who received RT vs control group matched for age, gender and race.</p> <p>Methods</p> <p>We studied 19 patients (10 male; 47.8 ± 17.4 years) during a 5-month period (January 2009-July 2009); they had completed RT with a mean of 2.9 years before (range: 1 month-6 years) The mean radiation dose to the neck in the irradiated patients was 41.2 ± 15.6 Gy (range: 25-70 Gy). Common carotid IMT was measured with echo-color Doppler. Nineteen healthy adult patients (10 male; 47.8 ± 17.6) were recruited as a control group.</p> <p>Results</p> <p>IMT was not significantly higher in patients when compared to the control group (0.59 ± 0.16 vs 0.56 ± 0.16 mm, p = 0.4). There was no significant difference between the two groups in relation to the absence (p = 0.7) or presence (p = 0.6) of vascular risk factors. Although the difference did not reach statistical significance (p = 0.1), the irradiated young patients (age ≤ 52 years) had IMT measurements higher (0.54 ± 0.08 mm) than the non-irradiated young patients (0.49 ± 0.14 mm). The mean carotid IMT increased with increasing doses of radiation to the neck (p = 0.04).</p> <p>Conclusion</p> <p>This study shows that increased IMT of the common carotid artery after RT is radiation-dose-related. Therefore it is important to monitor IMT, which can be used as an imaging biomarker for early diagnosis of cerebrovascular disease in patients who have had radiotherapy for treatment of cancer of the head and neck and who are at increased risk for accelerated atherosclerosis in carotid arteries.</p

An Evaluation of Computer-Based Instruction in Microbiology

There has been a tremendous increase in the availability of computer-based instructional (CBI) materials. Some studies have shown an improvement in learning when CBI is used. However, many researchers believe the current studies are inadequate. While CBI software should be thoroughly tested by developers, as educators, we should be concerned about whether or not the CBI materials we use are improving learning in our classrooms with our students. We present an evaluation of a computer-based hypermedia tutorial that was delivered over our General Microbiology website. We found that CBI was at least as effective as text-based material. However, of all students who used CBI, only those who explored most of the site benefited from using the site. Tracking each student’s use of the CBI was critical for understanding who was learning and why.</jats:p

Copyright © 2000, American Society for Microbiology. All Rights Reserved. An Evaluation of Computer-Based Instruction in Microbiology

There has been a tremendous increase in the availability of computer-based instructional (CBI) materials. Some studies have shown an improvement in learning when CBI is used. However, many researchers believe the current studies are inadequate. While CBI software should be thoroughly tested by developers, as educators, we should be concerned about whether or not the CBI materials we use are improving learning in our classrooms with our students. We present an evaluation of a computer-based hypermedia tutorial that was delivered over our General Microbiology website. We found that CBI was at least as effective as text-based material. However, of all students who used CBI, only those who explored most of the site benefited from using the site. Tracking each student’s use of the CBI was critical for understanding who was learning and why. In the past decade, there has been an explosion in the availability and use of computer-based instruction (CBI) in education (see references 9 and 22). CBI comes in many different types, each with its own educational strengths and weaknesses. For example, computers can be used as tutoring systems that present material and then give users an immediate opportunity to evaluate their knowledge (sometimes referre

Effect of the linear velocity during the melt spinning process on shape memory transformation of Ni-Ti ribbons

AbstractThe usual process to produce NiTi shape memory alloys is vacuum induction melting (VIM). Currently a new alternative process to produce NiTi shape memory alloys by rapid solidification structures called Melt Spinning has been studied. In this work, results of ribbons with a chemical composition Ti-55.2 Ni (wt %) alloy prepared by this method are presented. The ribbons are prepared at two different linear velocities: 30 m/s and 50 m/s. After that, samples are heat treated at 350 °C during 1 hour. The alloys are characterized by Scanning Electron Microscopy (SEM), Differential Scanning Calorimetry (DSC) and X-Ray Diffraction. According to the cycled DSC test, transformation peaks are associated with the B2→R→B19´ transformation during cooling and B19´→R→B2 during heating, showing transformation in multi-peaks. The martensite B19´ start (Ms) is varying from 35 to 39°C and the martensite finish (Mf) from 15 to 21°C, 42-47°C for austenite B2 start (As) and 65-69°C for austenite finish (Af) approximately. All analyzed ribbons show very similar values of transformation hysteresis temperatures at 50% of transformation of around 28°C. In order to change solidification rate, linear velocity is varied during the melt spinning process. Results indicate that linear velocity affects directly the temperature of transformation. When the linear velocity is increasing, crystallographic Ti-rich precipitates are developed, but dendritic growth disappears, changing the microstructure and decreasing these transformation temperatures. Then changes in linear velocity can dramatically affect shape memory properties, and in this case a velocity of 50 m/s produces a more homogenous alloy.</jats:p

Influência do super-resfriamento nas ligas cu-al-ni com efeito de memória de forma.

In this work, 83%Cu - 13%Al - 4%Ni (percentage in weight) alloy was evaluated in 3 experimental conditions: a) as-melted, b) as casting quenched and c) flux solidified. Effects of the undercooling phase structures were investigated. Compared with the The as-melted alloy presented grains containing precipitate particles inside of the grains, without martensite morphology and the contour of those grains were defined by the segregated particle. The alloy in the as-melted quenched presented grains with internal martensite morphology and contours without precipitate. The flux solidified alloy presented grains with martensite morphology and without precipitate.Nesse trabalho foi avaliada a microestrutura da liga 83%Cu � 13%Al � 4%Ni (porcentagem em peso) em 3 condições experimentais: a) estado bruto de fusão, b) estado bruto de fusão temperada e c) solidificada com fluxo. A liga no estado bruto de fusão apresentou grãos contendo partículas precipitadas no interior dos grãos, sem a presença de martensíta e o contorno desses grãos foi definido pelas partículas segregadas, enquanto a liga no estado bruto de fusão temperada apresentou grãos com a presença de martensíta e contornos sem precipitados. A liga solidificada com fluxo apresentou grãos com a presença de martensíta e sem precipitado