Creep Effect in Structural Composite Lumber for Bridge Applications

Structural composite lumber (SCL) is a family of newly engineered wood products that are increasing in highway bridge applications. Advantages of SCL are its high strength, flexibility, stiffness, and excellent preservative treatability. A main concern in SCL bridge applications is serviceability performance. The long-term creep behavior of SCL flexural members is not presently determinable. In order to investigate creep effects, deflection monitoring of full-scale SCL T-beam bridge members was performed under ambient conditions and an accelerated aging process. Sixteen beams were monitored under exposed weather conditions with frequent wetting and drying. Variables in the experiment were: lumber type (Douglas fir and southern yellow pine), SCL type (LVL and PSL), preservative type (CCA and penta), and dead load intensity. It was found that creep behavior in SCL bridge members closely follows the Burger theoretical model. LVL, Douglas fir, and CCA treatment causes smaller creep deflections as compared to PSL, Southern Pine, and Penta treatment. NDS type creep multipliers for SCL vary between 2.2 and 2.67 for various subcategories. A single average creep multiplier of 2.3 may be used for treated SCL bridge beams.     

Establishment of a diazepam preference in human volunteers following a differential-conditioning history of placebo versus diazepam choice: Reply to Bouton (2002), Carroll (2002), Kelly (2002), Stewart (2002), and Vuchinich (2002).

The 6 submitted commentaries (see records 2002-12827-003, 2002-12827-004, 2002-12827-005, 2002-12827-006, 2002-12827-007, 2002-12827-008) on the authors' study examining the establishment of diazepam as a conditioned reinforcer were generally supportive of the need to characterize environmental determinants of drug self-administration while emphasizing the need for more research. The comments discuss several important topics, including clarifying the mechanisms responsible for the switch in drug preference the authors reported, comparing the strengths of various procedures used to confer reinforcing efficacy onto a drug, opportunities for collaborative research, and practical applications of differential conditioning to the treatment of drug abuse. The authors suspect that future work on this topic will incorporate the issues discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Perceived academic effects of instant messaging use

College students use information and communication technologies at much higher levels and in different ways than prior generations. They are also more likely to multitask while using information and communication technologies. However, few studies have examined the impacts of multitasking on educational outcomes among students. This study fills a gap in this area by utilizing a large-sample web-based survey of college student technology usage to examine how instant messaging and multitasking affect perceived educational outcomes. Since multitasking can impede the learning process through a form of information overload, we explore possible predictors of academic impairment due to multitasking. Results of this study suggest that college students use instant messaging at high levels, they multitask while using instant messaging, and over half report that instant messaging has had a detrimental effect on their schoolwork. Higher levels of instant messaging and specific types of multitasking activities are associated with students reporting not getting schoolwork done due to instant messaging. We discuss implications of these findings for researchers studying the social impacts of technology and those in higher education administration.     

Positron annihilation lifetime spectroscopy and diffusion studies of large molecule penetrants into alkyd resins

Alkyd resins can be used to create transparent films and their characteristics depend on the method used in their cure. Changing the catalysts can have profound effects on the physical properties of the films formed. Positron annihilation lifetime spectroscopy (PALS) measurements are used to explore how changes in catalyst influence the free volume for an alkyd resin system. Diffusion measurements are reported for large molecule permeants; dioctyl phthalate, 2-ethyl hexylbenzyl phthalate, nonyl phenol ethoxylate, isopropyl myristate and oleic acid into these alkyd resins. The diffusion behaviour changes as the temperature is raised through the glass transition temperature of the resin but is also sensitive to the chemical structure of the permeant. The diffusion deviates from simple Fickian behaviour in a number of cases and is indicative of plasticization influencing diffusion. Comparison of the average molecular size with the available free volume indicates that diffusion involves a complex co-operative motion in which the matrix plays an important role. Increasing the cross link density by post cure of the alkyd resin at elevated temperatures, reduces the free volume and decreases the ability for the large molecules to permeate in to the matrix. Oleic acid exhibits a two stage diffusion process; the second stage being associated with opening up of the resin structure as a result of acid catalysed degradation. The unusual behaviour of isopropyl myristate is attributed to a combination of its ability to adopt favourable conformations and a high degree of compatibility with the matrix. This study highlights the importance of the chemical structure of the permeant on its ability to enter and diffuse through the coating.