Invariance of the Glass Transition Temperature of Plant Vitrification Solutions with Cooling Rate

The solutions studied were Plant Vitrification Solutions 1, 2 and 3: (PVS1: Uragami et al. 1989, Plant Cell Rep. 8, 418; PVS2: Sakai et al. 1990, Plant Cell Rep. 9, 30; PVS3: Nishizawa et al. 1993, Plant Sci. 91, 67). Cooling was performed using the calorimeter control (5, 10 and 20°C min-1), or for higher rates, by quenching the closed pan with PVS in LN, either naked (faster - 5580°C min-1) or introduced in cryovials (reduced rate 360°C min-1). Quenched pans were then transferred to the sample chamber, pre-cooled to -196°C. Glass transition temperature was observed by DSC with a TA 2920 instrument, upon warming pans with solution samples from -145°C to room temperature, at standard warming rate10°C min-1.

Web-based education in Spanish Universities. A Comparison of Open Source E-Learning Platforms

Web-based education or „e-learning‟ has become a critical component in higher education for the last decade, replacing other distance learning methods, such as traditional computer training or correspondence learning. The number of university students who take on-line courses is continuously increasing all over the world. In Spain, nearly a 90% of the universities have an institutional e-learning platform and over 60% of the traditional on-site courses use this technology as a supplement to the traditional face-to-face classes. This new form of learning allows the disappearance of geographical barriers and enables students to schedule their own learning process, among some other advantages. On-line education is developed through specific software called „e-learning platform‟ or „virtual learning environment‟ (VLE). A considerable number of web-based tools to deliver distance courses are currently available. Open source software packages such as Moodle, Sakai, dotLRN or Dokeos are the most commonly used in the virtual campuses of Spanish universities. This paper analyzes the possibilities that virtual learning environments provide university teachers and learners and offers a technical comparison among some of the most popular e-learning learning platforms.