AC Adjustable-Speed Drives with Electronic Power Converters?the Early Days

Some of the early electronic power converters utilized mercury-arc rectifiers such as thyratrons and ignitrons. Their use in an-ac adjustable-speed drive began about 50 years ago. The first commercial application in the United States was made to an induced draft fan at the Logan station. This drive was in service for about 25 years. The early history of ac adjustable-speed drives which employed electronic power conversion is reviewed.     

Reflection-through-performance: personal implications of documenting health behaviors for the collective

Previous work has examined how technology can support health behavior monitoring in social contexts. These tools incentivize behavior documentation through the promise of virtual rewards, rich visualizations, and improved co-management of disease. Social influence is leveraged to motivate improved behaviors through friendly competition and the sharing of emotional and informational support. Prior work has described how by documenting and sharing behaviors in these tools, people engage in performances of the self. This performance happens as users selectively determine what information to share and hide, crafting a particular portrayal of their identity. Much of the prior work in this area has examined the implications of systems that encourage people to share their behaviors with friends, family, and geographically distributed strangers. In this paper, we report upon the performative nature of behavior sharing in a system created for a different social group: the local neighborhood. We designed Community Mosaic (CM), a system with a collectivistic focus: this tool asks users to document their behaviors using photographs and text, but not for their own benefit—for the benefit of others in their community. Through a 6-week deployment of CM, we evaluated the nature of behavior sharing in this system, including participants’ motivations for sharing, the way in which this sharing happened, and the reflexive impact of sharing. Our findings highlight the performative aspects of photograph staging and textual narration and how sharing this content led participants to become more aware and evaluative of their behaviors, and led them to try to eat more healthfully. We conclude with recommendations for behavior monitoring tools, specifically examining the implications of users’ perceived audience and automated behavioral tracking on opportunities for reflection-through-performance.     

Improving Password Cybersecurity Through Inexpensive and Minimally Invasive Means: Detecting and Deterring Password Reuse Through Keystroke-Dynamics Monitoring and Just-in-Time Fear Appeals

Password reuse – using the same password for multiple accounts – is a prevalent phenomenon that can make even the most secure systems vulnerable. When passwords are reused across multiple systems, hackers may compromise accounts by stealing passwords from low-security sites to access sites with higher security. Password reuse can be particularly threatening to users in developing countries in which cybersecurity training is limited, law enforcement of cybersecurity is non-existent, or in which programs to secure cyberspace are limited. This article proposes a two-pronged solution for reducing password reuse through detection and mitigation. First, based on the theories of routine, cognitive load and motor movement, we hypothesize that password reuse can be detected by monitoring characteristics of users' typing behavior (i.e. keystroke dynamics). Second, based on protection motivation theory, we hypothesize that providing just-in-time fear appeals when a violation is detected will decrease password reuse. We tested our hypotheses in an experiment and found that users' keystroke dynamics are diagnostic of password reuse. By analyzing changes in typing patterns, we were able to detect password reuse with 81.71% accuracy. We also found that just-in-time fear appeals decrease password reuse; 88.41% of users who received a fear appeal subsequently created unique passwords, whereas only 4.45% of users who did not receive a fear appeal created unique passwords. Our results suggest that future research should continue to examine keystroke dynamics as an indicator of cybersecurity behaviors and use just-in-time fear appeals as a method for reducing non-secure behavior. The findings of our research provide a practical and cost-effective solution to bolster cybersecurity through discouraging password reuse.     

Numerical simulation of light propagation through highly-ordered titania nanotube arrays: dimension optimization for improved photoabsorption

Propagation of electromagnetic waves in the ultraviolet-visible range (300 to 600 nm) through a unique highly-ordered titania nanotube array structure is studied using the computational technique of Finite Difference Time Domain (FDTD). Through numerical simulation the transmittance, reflectance and absorbance of the nanotube-arrays are obtained as a function of tube length and diameter. The nanotube-arrays are found to completely absorb light having wavelengths less than approximately 330 nm. For wavelengths above 380 nm absorption increases as a function of nanotube length, while above 435 nm absorption increases with decreasing pore size. Computational simulations closely match experimental measurements, indicating the suitability of the computational technique for guiding material optimization.     

Fatigue behavior of SiC reinforced Ti(6AI-4V) at 650 °C

Axial, low cycle fatigue properties of 25 and 44 fiber vol pct SiC/Ti(6Al-4V) composites, measured at 650 °C, were compared with the fatigue properties of unreinforced Ti(6Al-4V) at the same temperature. A prior study of the fatigue behavior of this composite system at room temperature indicated that the SiC fiber reinforcement did not provide the anticipated improvement of fatigue resistance of this alloy. At 650 °C, the composite fatigue properties degraded somewhat from those at room temperature. However, these properties degraded more for the unreinforced matrix at 650 °C with the result that the composite fatigue strength was two to three times the fatigue strength of the matrix alloy. The reasons for this reversal are discussed in terms of crack initiation at broken fibers and residual matrix stresses.     

Physical, Social, and Experiential Knowledge in Pervasive Computing Environments

Pervasive computing designers and researchers often create services and applications to help people record their experiences. At the same time, cheap, small, and easy-to-deploy recording technologies are quickly emerging throughout public spaces. In many ways, these technologies are pervasive computing realized. Understanding how people deal with audio and video recording is therefore a good way to explore how people might adopt, adapt, and react to pervasive computing technologies in general. A long-term deployment of a system for recording experiences in informal spaces demonstrates that people use physical, social, and experiential knowledge to determine new technologies' relative utility and safety. In this paper, we aim to add significantly to the research surrounding security and privacy concerns by focusing on them rather than just noting them as a side effect of testing an application's utility and usability.     

Application of finite-difference time domain to dye-sensitized solar cells: The effect of nanotube-array negative electrode dimensions on light absorption

We examine the light absorbing behavior of dye-sensitized solar cells (DSCs) having cathodes (negative electrodes) comprised of highly ordered TiO₂ nanotube arrays using the electromagnetic computational technique, finite-difference time domain (FDTD). The highly ordered nanotube arrays, grown using anodic oxidation of titanium foils or thin films, feature an open end with the other end fixed on a dense oxide layer (barrier layer). The numerical simulation model is comprised of nanotube arrays on a transparent conducting glass substrate under front-side illumination. In the FDTD analysis, a transverse electromagnetic (TEM) wave is incident onto a N719 dye-coated nanotube array initially passing through the barrier layer; light that emerges from the nanotubes is reflected by a perfectly conducting layer (perfect electric conductor—PEC) boundary that simulates the effect of the DSC platinum counter electrode. An observation plane placed between the electromagnetic source and DSC detects the intensity of both the incident wave and the wave returning back from the DSC structure. The absorbance and transmittance spectra are determined in the wavelength range 300–700 nm as a function of nanotube-array dimensions including length, pore size, barrier layer thickness, and surface roughness while keeping the wall thickness constant at 12 nm. The validity of the computational simulations is experimentally verified. A significant increase in the light absorption by the dye-coated nanotubes was observed for increasing nanotube length; smaller pore sizes, and increased surface roughness. Changes in the barrier layer thickness had a negligible effect on the absorbance spectrum. Our efforts demonstrate FDTD to be a broadly applicable technique capable of guiding design of an optimal DSC architecture.     

Incorporation of Monovalent Ions in ZnO and Their Influence on Varistor Degradation

An atomistic simulation technique has been used to predict the spatial arrangement of the dopant species sodium, lithium, and chlorine within the zinc oxide lattice. The alkaline oxides are preferentially incorporated via a self-compensating mode, forming interstitial cations which hinder the migration of zinc interstitials and hence slow the degradation of the varistor. The addition of chloride ions is shown to negate this effect by forming sodium and chloride substitutional defects rather than any species involving sodium interstitial ions.