Porous electrodes provide high-surface-area supports for the catalysts of many reactions, but the influences of electrode preparation conditions on electrocatalysts are not always well understood. Electrochemical impedance spectroscopy (EIS) can provide extensive information about an electrode, but the models describing the spectra are often too idealized to draw useful conclusions. We describe a new model based on an array of parallel, nonuniform transmission lines for predicting the response of porous electrodes. The model incorporates physically realistic elements, such as discrete particles of variable size and adjustable multilayer stacking geometries. Resistance parameters were derived from experimental data for -coated and Ebonex electrodes prepared under varying degrees of oxidative conditioning. The results, which indicate a high degree of impedance at the support-solution interface and consequently, low catalyst utilization, suggest several strategies for improved electrode design. © 2003 The Electrochemical Society. All rights reserved.
Abstract : The corrosion of carbon steel due to the metabolic activity of bacteria, specifically sulfate-reducing bacteria (SRB), is known as Microbially-Influenced Corrosion (MIC). This type of corrosion usually results in a form of localized corrosion, e.g., crevice corrosion. The present research is intended to explore the effectiveness of cathodic protection in eliminating or limiting the destructive effects of MIC.
This paper presents an in-depth review of the memristor from a rigorous circuit-theoretic perspective, independent of the material the device is made of. From an experimental perspective, a memristor is best defined as any two-terminal device that exhibits a pinched hysteresis loop in the voltage–current plane when driven by any periodic voltage or current signal that elicits a periodic response of the same frequency. This definition greatly broadens the scope of memristive devices to encompass even non-semiconductor devices, both organic and inorganic, from many unrelated disciplines, including biology, botany, brain science, etc. For pedagogical reasons, the broad terrain of memristors is partitioned into three classes of increasing generality, dubbed Ideal Memristors, Generic Memristors, and Extended Memristors. Each class is distinguished from the others via unique fingerprints and signatures. This paper clarifies many confusing issues, such as non-volatility, dc V–I curves, high-frequency v–i curves, local activity, as well as nonlinear dynamical and bifurcation phenomena that are the hallmarks of memristive devices. Above all, this paper addresses several fundamental issues and questions that many memristor researchers do not comprehend but are afraid to ask.
This paper introduces a pipeline to parametrically sample and render static multi-task vision datasets from comprehensive 3D scans from the real-world. In addition to enabling interesting lines of research, we show the tooling and generated data suffice to train robust vision models. Familiar architectures trained on a generated starter dataset reached state-of-the-art performance on multiple common vision tasks and benchmarks, despite having seen no benchmark or non-pipeline data. The depth estimation network outperforms MiDaS and the surface normal estimation network is the first to achieve human-level performance for in-the-wild surface normal estimation-at least according to one metric on the OASIS benchmark.
The quantitative end-capping of polyethylene glycols with bromine-substituted, dendritic, aromatic polyethers 1 produces amphiphilic block copolymers. In solvents in which both blocks are only slightly soluble or in which only one block is soluble, micelles form. Depending on the solvent, they can alter their size and shape.
Theoretical capacity and improved rate capability achieved in LiMn<sub>0.5</sub>Fe<sub>0.4</sub>Mg<sub>0.1</sub>BO<sub>3</sub> by defect engineering to enable channel-to-channel Li migration.
The basic problem of synthesizing a nonlinear resistor, inductor, or capacitor with a prescribed i-v, φ-i, or q-v curve is solved by introducing three new linear two-port network elements, namely the mutator, the reflector, and the scalor. The mutator has the property that a nonlinear resistor is transformed into a nonlinear inductor, or a nonlinear capacitor, upon connecting this resistor across port two of an appropriate mutator. The reflector has the property that a given i-v, φ-i, or q-v curve can be reflected about an arbitrary straight line through the origin. The scalor is characterized by the property that any i-v, φ-i, or q-v curve can be compressed or expanded along a horizontal direction, or along a vertical direction. Using these new elements as building blocks, it is shown that any prescribed single-valued (which need not be monotonic) i-v, φ-i, or q-v curve can be synthesized. Active circuit realizations for each of these new elements are given. Laboratory models of mutators, reflectors, and scalors have been built using discrete components. Oscilloscope tracings of typical mutated, reflected, and scaled i-v, φ-i, and q-v curves are given. The experimental results are in good agreement with theory at relatively low operating frequencies. The practical problems that remain to be solved are the stability and frequency limitation of the present circuits.
Abstract Throughout early development, a child spends more time asleep than in any waking activity. Yet, the specific role of sleep in brain maturation is a complete mystery. In this article, the developmental psychobiology of sleep regulation is conceptualized within the context of close links to the control of arousal, affect, and attention. The interactions among these systems are considered from an ontogenetic and evolutionary biological perspective. A model is proposed for the development of sleep and arousal regulation with the following major tenets: 1. Sleep and vigilance represent opponent processes in a larger system of arousal regulation. 2. The regulation of sleep, arousal, affect, and attention overlap in physiological, neuroanatomical, clinical, and developmental domains. 3. Complex interactions among these regulatory systems are modulated and integrated in regions of the prefrontal cortex (PFC). 4. Changes at the level of PFC underlie maturational shifts in the relative balance across these regulatory systems (such as decreases in the depth/length of sleep and increased capacity for vigilance and attention), which occur with normal development. 5. The effects of sleep deprivation (including alterations in attention, emotions, and goal-directed behaviors) also involve changes at the level of PFC integration across regulatory systems. This model is then discussed in the context of developmental pathology in the control of affect and attention, with an emphasis on sleep changes in depression.
