Soft Multifunctional Composites and Emulsions with Liquid Metals

Binary mixtures of liquid metal (LM) or low‐melting‐point alloy (LMPA) in an elastomeric or fluidic carrier medium can exhibit unique combinations of electrical, thermal, and mechanical properties. This emerging class of soft multifunctional composites have potential applications in wearable computing, bio‐inspired robotics, and shape‐programmable architectures. The dispersion phase can range from dilute droplets to connected networks that support electrical conductivity. In contrast to deterministically patterned LM microfluidics, LMPA‐ and LM‐embedded elastomer (LMEE) composites are statistically homogenous and exhibit effective bulk properties. Eutectic Ga‐In (EGaIn) and Ga‐In‐Sn (Galinstan) alloys are typically used due to their high conductivity, low viscosity, negligible nontoxicity, and ability to wet to nonmetallic materials. Because they are liquid‐phase, these alloys can alter the electrical and thermal properties of the composite while preserving the mechanics of the surrounding medium. For composites with LMPA inclusions (e.g., Field's metal, Pb‐based solder), mechanical rigidity can be actively tuned with external heating or electrical activation. This progress report, reviews recent experimental and theoretical studies of this emerging class of soft material architectures and identifies current technical challenges and opportunities for further advancement.     

Visually Imperceptible Liquid‐Metal Circuits for Transparent,Stretchable Electronics with Direct Laser Writing

A material architecture and laser‐based microfabrication technique is introduced to produce electrically conductive films (sheet resistance = 2.95 Ω sq^?1; resistivity = 1.77 × 10^?6 Ω m) that are soft, elastic (strain limit >100%), and optically transparent. The films are composed of a grid‐like array of visually imperceptible liquid‐metal (LM) lines on a clear elastomer. Unlike previous efforts in transparent LM circuitry, the current approach enables fully imperceptible electronics that have not only high optical transmittance (>85% at 550 nm) but are also invisible under typical lighting conditions and reading distances. This unique combination of properties is enabled with a laser writing technique that results in LM grid patterns with a line width and pitch as small as 4.5 and 100 µm, respectively—yielding grid‐like wiring that has adequate conductivity for digital functionality but is also well below the threshold for visual perception. The electrical, mechanical, electromechanical, and optomechanical properties of the films are characterized and it is found that high conductivity and transparency are preserved at tensile strains of ≈100%. To demonstrate their effectiveness for emerging applications in transparent displays and sensing electronics, the material architecture is incorporated into a couple of illustrative use cases related to chemical hazard warning.     

Set-structured and cost-sharing heuristics for classical planning

Problem abstractions based on (either completely or partially) ignoring delete effects of the actions provide the basis for some seminal classical planning heuristics. However, the palette of the conceptual tools exploited by these heuristics remains rather limited. We study a framework for approximating the optimal cost solutions for problems with no delete effects that bridges between certain works on heuristic-search classical planning and on probabilistic reasoning. Our analysis results in developing a novel heuristic function that combines “informed” set-structured cost estimates and “conservative” action cost sharing. Our empirical comparative evaluation provides a clear evidence for the attractiveness of this heuristic estimate. In addition, we examine a (suggested before in the context of probabilistic reasoning) admissible heuristic based on a stronger variant of action cost sharing. We show that what is good for “typical” problems of probabilistic reasoning turns out not to be so for “typical” problems of classical planning, and provide a formal account for that difference.     

Graphically structured value-function compilation

Classical work on eliciting and representing preferences over multi-attribute alternatives has attempted to recognize conditions under which value functions take on particularly simple and compact form, making their elicitation much easier. In this paper we consider preferences over discrete domains, and show that for a certain class of simple and intuitive qualitative preference statements, one can always generate compact value functions consistent with these statements. These value functions maintain the independence structure implicit in the original statements. For discrete domains, these representation theorems are much more general than previous results. However, we also show that it is not always possible to maintain this compact structure if we add explicit ordering constraints among the available outcomes.     

Microchemical and microstructural investigations of degradation in asbestos-cement sheet

The physical and chemical transformations occurring in asbestos cement (A/C) sheet following a two-year natural exposure to sulfate rich water in a cooling tower have been investigated using a combination of analytical and microstructural techniques. The investigation was conducted on a reference A/C sheet, specimens of the partially degraded A/C sheet and chrysotile fibers recovered from the latter. The methods employed included X-ray diffraction, scanning electron microscopy and EDXA, thermogravimetry, infrared spectroscopy and evolved gas analysis during thermal decomposition. Analysis of the combined data conclusively show that the primary cause of degradation and delamination of the A/C sheet is the formation of gypsum (CaSO₄)·2H₂O crystals which is accompanied by substantial volume expansion. Apparently, carbonation, yielding calcite and/or vaterite crystals, is a secondary degradation mechanism.     

Aetiologies and outcomes of wounds in an outpatient programme

This study reviewed the records of all new patients seen in an outpatient wound-care programme during a six-month period. Most of the 115 patients were referred by physicians in internal medicine or family practice (48%) or surgeons (39%); 101 had a wound (88%). Of the 92 who had their wound measured at the time of their first clinic visit, 72 (78%) had their largest wound located on a lower extremity and 40% of all lower extremity wounds were on the feet. Wounds were most frequently due to pressure (36%), venous insufficiency (16%), diabetic neuropathy (16%), or arterial insufficiency (13%). Within 12 months of their initial presentation, wound closure was documented in 35 of the 92 patients (38%). Of the four most common aetiologies, the healing rate was highest in wounds attributable to venous insufficiency (67%) (p < 0.02).     

Phencyclidine sedation as a technique for handling rhesus monkeys: effects on LH, GH, and prolactin secretion

Rhesus monkeys, sedated with phencyclidine hydrochloride (Sernylan), were quieted for prolonged periods of time, while maintaining somatic reflexes, muscle tone, and respiration. Brief daily periods of sedation did not interfere with the menstrual cycle. Prolonged sedation, however, interfered with the experimentally estrogen-induced LH surge, but not with the inhibitory action of estrogen on LH tonic secretion. Pulsatile release of LH, GH, and prolactin persisted even under prolonged sedation. The secretion of prolactin in response to the administration of TRH was increased in animals sedated with phencyclidine.     

Adjustable spiral phase plate

A spiral phase retarder phi(r, theta) = mtheta has been constructed with use of a deformed cracked plexiglass plate. By changing the degree of deformation, the retarder can be adjusted for use at any wavelength, and the value of the phase step 2pim at theta = 2pi can be chosen.     

CauStereo: range from light in nature

Underwater, natural illumination typically varies strongly temporally and spatially. The reason is that waves on the water surface refract light into the water in a spatiotemporally varying manner. The resulting underwater illumination field forms a caustic network and is known as flicker. This work shows that caustics can be useful for stereoscopic vision, naturally leading to range mapping of the scene. Range triangulation by stereoscopic vision requires the determination of correspondence between image points in different viewpoints, which is often a difficult problem. We show that the spatiotemporal caustic pattern very effectively establishes stereo correspondences. Thus, we term the use of this effect as CauStereo. The temporal radiance variations due to flicker are unique to each object point, thus disambiguating the correspondence, with very simple calculations. Theoretical limitations of the method are analyzed using ray-tracing simulations. The method is demonstrated by underwater in situ experiments.