Blueprinting Photothermal Shape-Morphing of Liquid Crystal Elastomers

Liquid crystal elastomers (LCEs) are an attractive platform for dynamic shape-morphing due to their ability to rapidly undergo large deformations. While recent work has focused on patterning the director orientation field to achieve desired target shapes, this strategy cannot be generalized to material systems where high-resolution surface alignment is impractical. Instead of programming the local orientation of anisotropic deformation, an alternative strategy for prescribed shape-morphing by programming the magnitude of stretch ratio in a thin LCE sheet with constant director orientation is developed here. By spatially patterning the concentration of gold nanoparticles, uniform illumination leads to gradients in photothermal heat generation and therefore spatially nonuniform deformation profiles that drive out-of-plane buckling of planar films into predictable 3D shapes. Experimentally realized shapes are shown to agree closely with both finite element simulations and geometric predictions for systems with unidirectional variation in deformation magnitude. Finally, the possibility to achieve complex oscillatory motion driven by uniform illumination of a free-standing patterned sheet is demonstrated.     

Bacterial and fungal ecology on air conditioning cooling coils is influenced by climate and building factors

The presence of biofilms on the cooling coils of commercial air conditioning (AC) units can significantly reduce the heat transfer efficiency of the coils and may lead to the aerosolization of microbes into occupied spaces of a building. We investigated how climate and AC operation influence the ecology of microbial communities on AC coils. Forty large-scale commercial ACs were considered with representation from warm-humid and hot-dry climates. Both bacterial and fungal ecologies, including richness and taxa, on the cooling coil surfaces were significantly impacted by outdoor climate, through differences in dew point that result in increased moisture (condensate) on coils, and by the minimum efficiency reporting value (MERV 8 vs MERV 14) of building air filters. Based on targeted qPCR and sequence analysis, low efficiency upstream filters (MERV 8) were associated with a greater abundance of pathogenic bacteria and medically relevant fungi. As the implementation of air conditioning continues to grow worldwide, better understanding of the factors impacting microbial growth and ecology on cooling coils should enable more rational approaches for biofilm control and ultimately result in reduced energy consumption and healthier buildings.     

Scheduling with bus access optimization for distributed embeddedsystems

In this paper, we concentrate on aspects related to the synthesis of distributed embedded systems consisting of programmable processors and application-specific hardware components. The approach is based on an abstract graph representation that captures, at process level, both dataflow and the flow of control. Our goal is to derive a worst case delay by which the system completes execution, such that this delay is as small as possible; to generate a logically and temporally deterministic schedule; and to optimize parameters of the communication protocol such that this delay is guaranteed. We have further investigated the impact of particular communication infrastructures and protocols on the overall performance and, specially, how the requirements of such an infrastructure have to be considered for process and communication scheduling. Not only do particularities of the underlying architecture have to be considered during scheduling but also the parameters of the communication protocol should be adapted to fit the particular embedded application. The optimization algorithm, which implies both process scheduling and optimization of the parameters related to the communication protocol, generates an efficient bus access scheme as well as the schedule tables for activation of processes and communications     

Optimization of PWM technique with partially constant modulating waves

Contents In this paper the waveform quality and overmodulation region voltage-gain characteristic of pulsewidth-modulation (PWM) method with partially constant modulating waves are investigated. Thus the number of switchings in the three-phase inverter decreases by 33 as compared to the classical methods. A PWM version is proposed, in which during an interval of π/3 intervals only two switchings of the inverter semiconductor devices are performed. This method is different to those known in literature because it assure the necessary corrections of PWM-voltage in order to decrease the inverter output low order harmonics amplitudes voltages. These corrections eliminate the undesirable effects of the modulation wave discontinuities.

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übersicht Im vorliegenden Aufsatz wird die Qualit?t der Wellenformen sowie die Charakteristik des Gewinns an Spannung für den Bereich der Supramodulation in Falle der Pulsbreitenmodulationstechnik (PWM) mit partiell konstanten Modulationssignalen studiert. Auf diese Weise wird die Kommutationsanzahl in einem Dreiphasen-Wechselrichter um 33 verringert im Vergleich zur klassischen PWM-Methode. Vorgeschlagen wird eine PWM-Variante, bei der im Winkelbereich von π/3 nur zwei Kommutationen der Halbleitervorrichtungen im Wechselricher durchgeführt werden. Diese Methods unterscheidet sich von den in der bisherigen Literatur beschriebenen Methoden, da diese die notwendigen Korrekturen der Ausgangsspannung zur Verringerung der Amplituden der im Ausgangsspannungspektrum auftretenden kleinen Harmonischen absichern. Diese Korrekturen eliminieren die durch die Diskontinuit?ten der Modulationswelle erzeugten unerwünschten Effekte.

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Received: 25 February 2000     

Single-phase inverter with Z.V.S. capacitors connected on the D.C. side and the load in parallel with the resonance inductance

Contents The paper presents one new version of single-phase inverters having the capacitors for the Z.V.S. connected in the D.C. side and the load in parallel with the resonance inductance. The output frequency of this inverter can be changed in certain ranges, from a maximum frequencyf _max to a minimum frequencyf _min, without imposing a constant load impedanceL–R. The power losses due to the commutation process of the switching devices comprising the inverter are drastically reduced and the resonant pulses have small dv/dt-values, allowing a high electromagnetic compatibility of the proposed inverter.

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Einphasenwechselrichter mit Kondensatoren im Gleichstromzwischenkreis zum Kommutieren auf die Nullspannung und Parallelbelastung mit Resonanzinduktanz

Übersicht Die Arbeit stellt eine neue Variante von Einphasenwechselrichtern vor, die Kondensatoren im Gleichstromzwischenkreis zum Kommutieren auf die Nullspannung und Parallelbelastung mit Resonanzinduktanz haben. Die Ausgangsfrequenz dieser Wechselrichter kann in gewissen Grenzen variiert werden, zwischen der maximalen Frequenzf _max und der minimalen Frequenzf _min, ohne daß es notwending ist, die LastimpedanzL–R konstant zu halten. Die Leistungsverluste in den Kommutierungsprozessen der in den Kondensatoren befindlichen Halbleiterelemente werden drastisch reduziert, und die Schwingungspulse haben Anstiegeschwindigkeiten dv/dt von ebenfalls reduzierten Werten, was zu einer erhöhten elektromagnetischen Kompatibilität der vorgeschlagenen Wechselrichter führt.

     

Analog circuit design space description based on ordered clustering of feature uniqueness and similarity

This paper presents a symbolic technique to create ordered feature clustering schemes that express the main similarities and differences between analog circuits. Four separation scores, based on entropy, item characteristics, category characteristics, and Bayesian classifiers, were studied to produce clustering schemes that offer insight about the uniqueness and importance of specific design features in setting AC performance as well as the limiting factors of the designs. The experiments consider a set of 50 state-of-the-art amplifier circuits. The paper offers a detailed discussion on using the insight obtained from circuit feature clustering for topology synthesis and refinement.     

Do two separate speech measures contrain verbal short-term memory in children?

Previous research has indicated that 2 processing rates may constrain verbal short-term memory performance. These have been linked to individual differences in (a) the time taken to articulate spoken words and (b) the duration of pauses that occur between words in the output responses to memory tasks. Two experiments examined whether evidence for these effects on memory can be obtained for measures taken from a single speech sample. Children articulated pairs of words as rapidly as possible. In both experiments, the spoken duration of words and the length of the pauses between them predicted significant variance in verbal short-term memory performance. It is argued that the duration of words is linked to memory performance through the processes underlying time-based forgetting in short-term memory. In contrast, the duration of pauses in speeded articulation may index individual differences in speech planning processes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Parallax Walls: Light fields from occlusion on height fields

We introduce a simple, inexpensively manufacturable, height field surface geometry that, when appropriately painted, can produce diffuse reflections under ambient lighting approximating a target light field. We demonstrate a light field basis analysis of these surfaces which allows us to formulate the problem as a gamut-mapping, and propose a perceptually motivated metric for bringing complex light fields into gamut while preserving their structure. We show resultant surfaces displaying physical light fields, animations, HDR exposure stacks, and scene relighting.     

Influence of NaCl,Na2SO4 and O2 on power generation from microbial fuel cells with non-catalyzed carbon electrodes and natural inocula

Microbial fuel cells (MFCs) are facing several technological challenges before they can be considered as reliable energy sources. Although several feasible inocula, materials and catalysts have been employed to produce energy, the design of a MFC should be done under realistic conditions: abundant and economic feedstock. In this study, two different MFC designs (parallel plate and tank reactors) are tested with non-catalyzed carbon electrodes and natural inocula. In both approaches cathodic oxygen reduction is performed on two different non-catalyzed carbon materials: carbon fabric and reticulate vitreous carbon. This study shows that power and current densities can be boosted by systematically decreasing the catholyte resistance (by additions of NaCl or Na₂SO₄) and dissolved oxygen concentration. In the parallel plate cell configuration, a mixed culture coming from sludge wastewater was used and power outputs up to 73 mW m^?2 (2867 mW m^?3) coupled to 187 mA m^?2 (anode surface area), were achieved. In the Sediment MFC cell configuration, lagoon sediment was used as both organic source of energy and natural supply of bacteria. Under this approach, the concentration of the organic matter is limited but it is demonstrated that bacteria can be adapted to degrade acetate. Power outputs up to 3.9 mW m^?2 normalized to the anodic electrode footprint area, coupled to 13 mA m^?2 were achieved.     

Oxidative stability of water/oil mixtures as influenced by the addition of free Cu or Cu–alginate gel beads

The formation of Cu–alginate complexes and the impact of free or bound copper on the oxidative stability of model water/oil mixtures containing edible sunflower or corn oil were examined. Equilibrium dialysis showed that copper binding capacity of alginate increased proportionally with copper concentration and the binding was rapid. The results indicated that 25 mM CuCl₂ was necessary in obtaining beads of spherical shape and adequate mechanical strength (0.45 N at 80% compression) to avoid rupture during mixing, whereas lower CuCl₂ concentrations resulted in weak gel beads (0.34 N) of irregular shape. When Cu–alginate beads were dispersed in the aqueous phase to give 0.5 mM copper, the peroxide value of water/corn oil mixtures was 3.7 mEq peroxide/kg oil after 7 days. Corn oil-containing mixtures with 0.5 mM free Cu²⁺ in the aqueous phase had a peroxide value ∼3 times higher (P < 0.001) after the same storage time. However, copper binding by alginate did not significantly reduce the peroxide values of the water/sunflower oil mixtures. Results indicated that the binding of pro-oxidant minerals, such as copper, in alginate beads can reduce the levels of oxidation in water/oil mixtures.