Simplicity, Scale, and Surprise: Evaluating Structural Form

Aesthetic and ethical issues of building design are presented here to encourage meaningful discussion among today’s architectural engineering students and practitioners. The evaluative aesthetic ideas of scale, simplicity, and surprise are applied to two important structures designed by Fazlur R. Khan. Khan’s profound understanding of load flow in his buildings influenced his aesthetic ideas. Furthermore, his aesthetic ideas were intimately intertwined with his ethical ideas about structural logic and the role of structure in architecture. We explore these ideas and present new insights as well. Our goal is to encourage a public discourse within our profession on the topic of evaluating structural form.     

High voltage floating gate array transistors

A new high voltage field-effect transistor is described. It features an array of uncontacted gate elements between the main gate and the drain which float so as to inhibit avalanche breakdown. Good agreement is obtained between model predictions and the performance of experimental devices fabricated in Si-TaSi/sub 2/ semiconductor-metal eutectic material. Transistors are demonstrated which hold off up to 1000 V, compared with the avalanche breakdown potential of 300 V or less expected for conventional devices made with similarly doped silicon.<>     

Multilevel resistive switching and synaptic plasticity of nanoparticulated cobaltite oxide memristive device

Multilevel resistive switching(RS)is a key property to embrace the full potential of memristive devices for non-volatile memory and neuromorphic computing applications.In this study,we employed nanopar-ticulated cobaltite oxide(Co3O4)as a model material to demonstrate the multilevel RS and synaptic learning capabilities because of its multiple and stable redox state properties.The Pt/Co3O4/Pt memris-tive device exhibited tunable RS properties with respect to different voltages and compliance currents(CC)without the electroforming process.That is,the device showed voltage-dependent RS at a higher CC whereas CC-dependent RS was observed at lower CC.The device showed four different resistance states during endurance and retention measurements and non-volatile memory results indicated that the CC-based measurement had less variation.Besides,we investigated the basic and complex synap-tic plasticity properties using the analog current-voltage characteristics of the Pt/Co3O4/Pt device.In particular,we mimicked the potentiation-depression and four-spike time-dependent plasticity(STDP)rules such as asymmetric Hebbian,asymmetric anti-Hebbian,symmetric Hebbian,and symmetric anti-Hebbian learning rules.The results of the present work indicate that the cobaltite oxide is an excellent nanomaterial for both multilevel RS and neuromorphic computing applications.     

Pull-in-based μg-resolution accelerometer: Characterization and noise analysis

The pull-in time (t_pi) of electrostatically actuated parallel-plate microstructures enables the realization of a high-sensitivity accelerometer that uses time measurement as the transduction mechanism. The key feature is the existence of a metastable region that dominates pull-in behavior, thus making pull-in time very sensitive to external accelerations. Parallel-plate MEMS structures have been designed and fabricated using a SOI micromachining process (SOIMUMPS) for the implementation of the accelerometer. This paper presents the experimental characterization of the microdevices, validating the concept and the analytical models used. The accelerometer has a measured sensitivity of 0.25 μs/μg and a bandwidth that is directly related to the pull-in time, BW = 1/2t_pi ≈ 50 Hz. These specifications place this sensor between the state of the art accelerometers found both in the literature and commercially. More importantly, the resolution of the measurement method used is very high, making the mechanical-thermal noise the only factor limiting the resolution. The in-depth noise analysis to the system supports these conclusions. The total measured noise floor of 400 μg (100 μs) is mainly due to the contribution of the environmental noise, due to lack of isolation of the experimental setup from the building vibrations (estimated mechanical thermal noise of 2.8 μg/√Hz). The low requirements of the electronic readout circuit makes this an interesting approach for high-resolution accelerometers.     

Smoking prevention: implications of study design, research setting, and goals.

Collaborations among various disciplines concerned with smoking prevention are gaining in currency. Such collaborations are predicated, in part, on recognizing both the implicit assumptions in different fields and the consequences of these assumptions. These issues, however, are often ignored in transdisciplinary research. In this article, we demonstrate how simple indices, such as the risk ratio, attributable fraction, or R(2), may have different implications for causal inference and interventions, depending on study setting and research goals.     

The origin of palmitic acid in brain of the developing rat

A rat milk substitute containing lower amounts of palmitic and oleic acid in the triacylglycerols in comparison to natural rat milk was fed to artificially reared rat pups from day 7 after birth to day 14. Pups reared by their mother served as controls. Free trideuterated (D₃) palmitic acid [(C²H₃)(CH₂)₁₄COOH, 98 atom % D] and free perdeuterated (D₃₁) palmitic acid [C₁₅ ²H₃₁COOH, 99 atom % D] in equal quantity were mixed into the triacylglycerols of the milk substitute in an amount equal to 100% of the palmitic acid in the triacylglycerols. A control milk substitute contained unlabeled free palmitic acid in an amount equal to 100% of the palmitic acid in the triacylglycerols of the milk substitute. The objective was to determine if palmitic acid in the diet contributed significantly to the palmitic acid content of developing brain and other organs. The methyl esters of the fatty acids were analyzed by gas chromatography and the palmitic acid methyl ester was examined by fast atom bombardment mass spectrometry. The proportion of deuterated methyl palmitate as a percentage of total palmitate was determined; 32% of the palmitic acid in liver and 12% of the palmitic acid in lung were trideuterated and perdeuterated palmitic acid in approximately equal amounts. The brain, by contrast, did not contain the deuterated palmitic acid moiety. Quantitation of palmitic acid and total fatty acids revealed a significant accumulation in organs in the interval from 7 to 14 days of age. Under our experimental conditions, labeled palmitic acid does not enter the brain. Consequently, we conclude that the developing brain produces all required palmitic acid byde novo synthesis.