A microfluidic device for thermal particle detection

We demonstrate the use of heat to count microscopic particles. A thermal particle detector (TPD) was fabricated by combining a 500-nm-thick silicon nitride membrane containing a thin-film resistive temperature detector with a silicone elastomer microchannel. Particles with diameters of 90 and 200 μm created relative temperature changes of 0.11 and ?0.44 K, respectively, as they flowed by the sensor. A first-order lumped thermal model was developed to predict the temperature changes. Multiple particles were counted in series to demonstrate the utility of the TPD as a particle counter.     

Use of oxygen isotope exchange in CO2 to characterize active sites

The characterization of carbon surface activity in the absence of gasification was attempted using oxygen isotope exchange in CO₂ over spectroscopically pure natural graphite, the surface activity being characterized by the rate of approach to isotopic equilibrium. The probable mechanism of exchange is via the first step in the carbon-CO₂ reaction, the dissociation of CO₂ over a carbon free site: $\text{CO}{}_2\text{+}\text{C}{}_{\mathrm{f}}\text{?}\text{i}{}_1\text{j}{}_1\text{C(O)}\text{+}\text{CO}$. Assuming this mechanism to hold for isotopic exchange, the theoretical rate equation was derived. The rate constants i₁, and j₁, were obtained from previous studies. Theoretical calculations show that the exchange rate is negligible over natural graphite at temperatures much below gasification conditions. Experimental verification of the theoretical analysis was not possible due to the activity of the quartz boat, holding the graphite, for catalyzing the exchange reaction. The exchange reaction was successfully followed over the Pt and CaO supported on a graphitized carbon black, in which case the activity was much, much greater than that ovgr the empty quartz boat.     

Oxidation of hydrogen sulfide over microporous carbons

Microporous carbon of high purity was produced by the carbonization of Saran at 900° followed by activation in either CO₂ at 900°, O₂ at 300°, or air at 425°. The activated carbons were characterized using N₂ adsorption at ?195° CO₂ adsorption at 25°, and mercury and helium displacements. Hydrogen sulfide oxidation (at H₂S pressures between 0.4–3.8 Torr) by O₂ (in excess of stoichiometric amount) was studied between 100–160° using a microbalance, that is by weighing the build-up of sulfur on the carbon. The predominant reaction, $\text{H}{}_2\text{S +}\text{1}\text{2}\text{O}{}_2\text{→}\text{1}\text{2}\text{S}{}_2\text{+ H}{}_2\text{O}$ was first order in H₂S concentration and independent of O₂ concentration. The rate was only slightly reduced by sulfur build-up to at least 36%, by weight, on the carbon. The oxidation rate was significantly higher over the O₂-activated carbon than over the CO₂-activated carbon. Throughout the studies, oxidation rates could be correlated with area active to O₂ chemisorption. It is concluded that H₂S oxidation proceeds via rapid dissociative chemisorption of oxygen on carbon sites followed by reaction with H₂S. Rates of H₂S oxidation were also studies over commercial, granular activated carbons of significant ash contents.     

How In-Home Technologies Mediate Caregiving Relationships in Later Life

In-home technologies can support older adults' activities of daily living, provide physical safety and security, and connect elders to family and friends. They facilitate aging in place while reducing caregiver burden. One of older adults' primary concerns about in-home technologies is their potential to reduce human contact, particularly from cherished caregivers. In this exploratory in situ study, we provided an ecosystem of networked monitoring technologies to six older adults and their caregivers. We analyzed the amount and content of communication between them. The amount of noncomputer-mediated communication did not decrease through the 6-week study. The content of communication coalesced into four themes: communication about the technologies, communication facilitated by technologies, intrusiveness of technologies, and fun and playfulness with the technologies. Results suggest that in-home technologies, designed with sensitivity to older adults' primary motivations, have the potential to shape and tailor important relationships in later life.     

Parallel evolution using multi-chromosome cartesian genetic programming

Parallel and distributed methods for evolutionary algorithms have concentrated on maintaining multiple populations of genotypes, where each genotype in a population encodes a potential solution to the problem. In this paper, we investigate the parallelisation of the genotype itself into a collection of independent chromosomes which can be evaluated in parallel. We call this multi-chromosomal evolution (MCE). We test this approach using Cartesian Genetic Programming and apply MCE to a series of digital circuit design problems to compare the efficacy of MCE with a conventional single chromosome approach (SCE). MCE can be readily used for many digital circuits because they have multiple outputs. In MCE, an independent chromosome is assigned to each output. When we compare MCE with SCE we find that MCE allows us to evolve solutions much faster. In addition, in some cases we were able to evolve solutions with MCE that we unable to with SCE. In a case-study, we investigate how MCE can be applied to to a single objective problem in the domain of image classification, namely, the classification of breast X-rays for cancer. To apply MCE to this problem, we identify regions of interest (RoI) from the mammograms, divide the RoI into a collection of sub-images and use a chromosome to classify each sub-image. This problem allows us to evaluate various evolutionary mutation operators which can pairwise swap chromosomes either randomly or topographically or reuse chromosomes in place of other chromosomes.     

Homopolymer Nanolithography

Future progress in nanoscience and nanotechnology necessitates further development of versatile, labor‐, and cost‐efficient surface patterning strategies. A new approach to nanopatterning is reported, which utilizes surface segregation of a smooth layer of an end‐grafted homopolymer in a poor solvent. The variation in polymer grafting density yields a range of surface nanostructures, including randomly organized pinned spherical micelles, worm‐like structures, networks, and porous films. The capability to use the polymer patterns for site‐specific deposition of small molecules, polymers, or nanoparticles is shown. This versatile strategy enables patterning of curved surfaces with direct access to the substrate and no need in changing polymer composition to realize different surface patterns.     

Time-of-Flight Optical Ranging System Based on Time-Correlated Single-Photon Counting

The design and implementation of a prototype time-of-flight optical ranging system based on the time-correlated single-photon-counting technique are described. The sensor is characterized in terms of its longitudinal and transverse spatial resolution, single-point measurement time, and long-term stability. The system has been operated at stand-off distances of 0.5-5 m, has a depth repeatability of <30 mum, and has a lateral spatial resolution of <500 mum.     

Photon density waves scattered from cylindrical inhomogeneities: theory and experiments

We present an analytical solution for the scattering of diffuse photon density waves from an infinite circular, cylindrical inhomogeneity embedded in a homogeneous highly scattering turbid medium. The analytical solution, based on the diffusion approximation of the Boltzmann transport equation, represents the contribution of the cylindrical inhomogeneity as a series of modified Bessel functions integrated from zero to infinity and weighted by different angular dependencies. This series is truncated at the desired precision, similar to the Mie theory. We introduce new boundary conditions that account for specular reflections at the interface between the background medium and the cylindrical inhomogeneity. These new boundary conditions allow the separate recovery of the index of refraction of an object from its absorption and reduced scattering coefficients. The analytical solution is compared with data obtained experimentally to evaluate the predictive capability of the model. Optical properties of known cylindrical objects are recovered accurately. However, as the radius of the cylinder decreases, the required measurement signal-to-noise ratiorapidly increases. Because of the new boundary conditions, an upperlimit can be placed on the recovered size of cylindrical objects with radii below 0.3 cm if they have a substantially different index of refraction from that of the background medium.