Browsing by Author "Allen, Ben"
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- Overview of Aluminum Alloy Mechanical Properties During and After FiresSummers, Patrick T.; Chen, Yanyun; Rippe, Christian; Allen, Ben; Mouritz, Adrian; Case, Scott W.; Lattimer, Brian Y. (Springer, 2015)Aluminum alloys are increasingly being used in a broad spectrum of load-bearing applications such as lightweight structures, light rail, bridge decks, marine crafts, and off-shore platforms. A major concern in the design of land-based and marine aluminum structures is fire safety, at least in part due to mechanical property reduction at temperatures significantly lower than that for steel. A substantial concern also exists regarding the integrity and stability of an aluminum structure following a fire; however, little research has been reported on this topic. This paper provides a broad overview of the mechanical behavior of aluminum alloys both during and following fire. The two aluminum alloys discussed in this work, 5083-H116 and 6061-T651, were selected due to their prevalence as lightweight structural alloys and their differing strengthening mechanisms (5083 – strain hardened, 6061 – precipitation hardened). The high temperature quasi-static mechanical and creep behavior are discussed. A creep model is presented to predict the secondary and tertiary creep strains followed by creep rupture. The residual mechanical behavior following fire (with and without applied stress) is elucidated in terms of the governing kinetically-dependent microstructural mechanisms. A review is provided on modeling techniques for residual mechanical behavior following fire including empirical relations, physically-based constitutive models, and finite element implementations. The principal objective is to provide a comprehensive description of select aluminum alloys, 5083-H116 and 6061-T651, to aid design and analysis of aluminum structures during and after fire.
- Threatening the Heart and Mind of Gender Stereotypes: Can Imagined Contact Influence the Physiology of Stereotype Threat?Allen, Ben (Virginia Tech, 2012-05-07)Research shows that when a gender stereotype is made salient and the target of the stereotype is asked to perform in the stereotyped domain, targets of the stereotype often perform at a lower level compared to situations when the stereotype was not made salient (Spencer, Steele, & Quinn, 1999). Current models of stereotype threat show that increased physiological arousal and reduced working memory capacity partially explain this decrement in performance (Ben-Zeev, Fein, & Inzlicht, 2005; Schmader, Johns, & Forbes, 2008). Furthermore, the noticeable absence of female faculty and students in math and science departments at coed universities throughout the United States may increase the belief in gender stereotypes and discourage women from pursuing careers in these fields (Dasgupta & Asgari, 2004). Contact with counter-stereotypical exemplars, such as female science experts, decreases belief in gender stereotypes and increases women's motivation to pursue careers in science (Stout, Dasgupta, Hunsinger, & McManus, 2011). Thus, the present study examined whether imagining an interpersonal interaction with a counter-stereotypic exemplar removes the physiological and performance effects of stereotype threat. However, the stereotype threat manipulation failed to elicit a strong stereotype threat effect on performance or physiology. Only reaction time and high frequency heart rate variability were sensitive to the stereotype threat induction. The imagination manipulation significantly attenuated the physiological effects of stereotype threat, whereas the reaction time effects were only marginally significant. Limitations and future directions for stereotype threat and imagined contact are discussed.
- What Resonates with you? Methods of Induced Cardiovascular ResonanceAllen, Ben (Virginia Tech, 2010-04-26)Patients with autonomic dysfunction have benefited from balancing of parasympathetic and sympathetic activity through the practice of slow breathing exercises. In preliminary studies, patients with various autonomic dysfunctions used biofeedback of respiratory activity to slow breathing to a cadence of six cycles per minute, a frequency known as the resonant frequency (Vaschillo, Vaschillo, & Lehrer, 2006). Breathing at this rate produces cardiovascular resonance (large oscillations in heart rate and blood pressure), forcing the autonomic nervous system to continuously regulate these changes, thereby exercising, and eventually strengthening autonomic control over hemodynamic events. The present study examined several methodologies, such as slow breathing exercises, which are believed to strengthen autonomic control by inducing cardiovascular resonance. Specifically, the current experiment compared different methods of inducing cardiovascular resonance, such as paced breathing and biofeedback assisted protocols. The utility of positive emotion inductions to attenuate respiratory discomfort during slow breathing exercises was also examined. Accurate estimation of the resonant frequency using respiratory methods was largely unsuccessful. However, all respiratory methods produced profound effects in the cardiovascular system, with some differences in the magnitude of effect. In addition, the utility of an emotion induction during slow paced breathing was also demonstrated. The results of this study also support the notion that slow breathing improves pulmonary gas exchange efficiency, in addition to strengthening the baroreflex, by increasing heart rate variability.