Microengineering Laser Plasma Interactions at Relativistic Intensities.

We report on the first successful proof-of-principle experiment to manipulate laser-matter interactions on microscales using highly ordered Si microwire arrays. The interaction of a high-contrast short-pulse laser with a flat target via periodic Si microwires yields a substantial enhancement in both the total and cutoff energies of the produced electron beam. The self-generated electric and magnetic fields behave as an electromagnetic lens that confines and guides electrons between the microwires as they acquire relativistic energies via direct laser acceleration.

H9N2 avian influenza virus dispersal along Bangladeshi poultry trading networks.

Avian influenza virus subtype H9N2 is endemic in Bangladesh's poultry population. The subtype affects poultry production and poses a potential zoonotic risk. Insufficient understanding of how the poultry trading network shapes the dissemination of avian influenza viruses has hindered the design of targeted interventions to reduce their spread. Here, we use phylodynamic analyses of haemagglutinin sequences to investigate the spatial spread and dispersal patterns of H9N2 viruses in Bangladesh's poultry population, focusing on its two largest cities (Dhaka and Chattogram) and their poultry production and distribution networks. Our analyses suggest that H9N2 subtype avian influenza virus lineage movement occurs relatively less frequently between Bangladesh's two largest cities than within each city. H9N2 viruses detected in single markets are often more closely related to viruses from other markets in the same city than to each other, consistent with close epidemiological connectivity between markets. Our analyses also suggest that H9N2 viruses may spread more frequently between chickens of the three most commonly sold types (sunali-a cross-bred of Fayoumi hen and Rhode Island Red cock, deshi-local indigenous, and exotic broiler) in Dhaka than in Chattogram. Overall, this study improves our understanding of how Bangladesh's poultry trading system impacts avian influenza virus spread and should contribute to the design of tailored surveillance that accommodates local heterogeneity in virus dispersal patterns.

Antigenic and genetic evolution of equine influenza A (H3N8) virus from 1968 to 2007.

Equine influenza virus is a major respiratory pathogen in horses, and outbreaks of disease often lead to substantial disruption to and economic losses for equestrian industries. The hemagglutinin (HA) protein is of key importance in the control of equine influenza because HA is the primary target of the protective immune response and the main component of currently licensed influenza vaccines. However, the influenza virus HA protein changes over time, a process called antigenic drift, and vaccine strains must be updated to remain effective. Antigenic drift is assessed primarily by the hemagglutination inhibition (HI) assay. We have generated HI assay data for equine influenza A (H3N8) viruses isolated between 1968 and 2007 and have used antigenic cartography to quantify antigenic differences among the isolates. The antigenic evolution of equine influenza viruses during this period was clustered: from 1968 to 1988, all isolates formed a single antigenic cluster, which then split into two cocirculating clusters in 1989, and then a third cocirculating cluster appeared in 2003. Viruses from all three clusters were isolated in 2007. In one of the three clusters, we show evidence of antigenic drift away from the vaccine strain over time. We determined that a single amino acid substitution was likely responsible for the antigenic differences among clusters.

Transatlantic spread of highly pathogenic avian influenza H5N1 by wild birds from Europe to North America in 2021.

Highly pathogenic avian influenza (HPAI) viruses of the A/Goose/Guangdong/1/1996 lineage (GsGd), which threaten the health of poultry, wildlife and humans, are spreading across Asia, Europe, Africa and North America but are currently absent from South America and Oceania. In December 2021, H5N1 HPAI viruses were detected in poultry and a free-living gull in St. John's, Newfoundland and Labrador, Canada. Our phylogenetic analysis showed that these viruses were most closely related to HPAI GsGd viruses circulating in northwestern Europe in spring 2021. Our analysis of wild bird migration suggested that these viruses may have been carried across the Atlantic via Iceland, Greenland/Arctic or pelagic routes. The here documented incursion of HPAI GsGd viruses into North America raises concern for further virus spread across the Americas by wild bird migration.

Nanoelectromechanical resonator arrays for ultrafast, gas-phase chromatographic chemical analysis.

Miniaturized gas chromatography (GC) systems can provide fast, quantitative analysis of chemical vapors in an ultrasmall package. We describe a chemical sensor technology based on resonant nanoelectromechanical systems (NEMS) mass detectors that provides the speed, sensitivity, specificity, and size required by the microscale GC paradigm. Such NEMS sensors have demonstrated detection of subparts per billion (ppb) concentrations of a phosphonate analyte. By combining two channels of NEMS detection with an ultrafast GC front-end, chromatographic analysis of 13 chemicals was performed within a 5 s time window.

Electrochemical reduction of horse heart ferricytochrome c at chemically derivatized electrodes.

Platinum or gold electrodes derivatized with an N,N'-dialkyl-4,4'-bipyridinium reagent can be used to reduce horse heart ferricytochrome c, whereas reduction doses does not occur at the "naked" electrodes. From 3 to 17.7 millimoles per liter, the reduction of ferricytochrome c is mass transport-limited at electrode potentials more negative than about -0.6 volt against a saturated calomel reference electrode. Data for the photoreduction of ferricytochrome c at derivatized p-type silicon photocathodes show directly that the rate of reduction is mass transport-limited. Use of derivatized electrodes may allow convenient manipulation and analysis of biological molecules that do not ordinarily respond at conventional electrodes.

Fabrication and use of nanometer-sized electrodes in electrochemistry.

Electrodes with electrochemical dimensions as small as 10 angstroms have been fabricated and used for electrochemical studies. These nanometer-scale electrodes have enabled the measurement of electron-transfer rate constants, k(het), that are two orders of magnitude faster than k(het) values accessible with any other electrochemical method.

Thin Films of n-Si/Poly-(CH3)3Si-Cyclooctatetraene: Conducting-Polymer Solar Cells and Layered Structures.

The optical and electronic properties of thin films of the solution-processible polymer poly-(CH(3))(3)Si-cyclooctatetraene are presented. This conjugated polymer is based on a polyacetylene backbone with (CH(3))(3)Si side groups. Thin transparent films have been cast onto n-doped silicon (n-Si) substrates and doped with iodine to form surfacebarrier solar cells. The devices produce photovoltages that are at the theoretical limit and that are much greater than can be obtained from n-Si contacts with conventional metals. Two methods for forming layered polymeric materials, one involving the spincoating of preformed polymers and the other comprising the sequential polymerization of different monomers, are also described. An organic polymer analog of a metal/insulator/metal capacitor has been constructed with the latter method.

Analysis of the published calorimetric evidence for electrochemical fusion of deuterium in palladium.

Estimates are given of the raw data that are the basis for the claims of excess power production by the electrochemical charging of palladium in deuterium oxide (D(2)O). Calorimetric results are also presented that show no anomalous power production in either 0.1M LiOD/D(2)O or 0.1M LiOH/H(2)O (LiOH is lithium hydroxide). Several possible sources of error in open-system calorimetry are discussed that can confound interpretation of temperature changes in terms of anomalous power production.

A chemically diverse conducting polymer-based "electronic nose".

We describe a method for generating a variety of chemically diverse broadly responsive low-power vapor sensors. The chemical polymerization of pyrrole in the presence of plasticizers has yielded conducting organic polymer films whose resistivities are sensitive to the identity and concentration of various vapors in air. An array of such sensing elements produced a chemically reversible diagnostic pattern of electrical resistance changes upon exposure to different odorants. Principal component analysis has demonstrated that such sensors can identify and quantify different airborne organic solvents and can yield information on the components of gas mixtures.

The use of 'electronic nose' sensor responses to predict the inhibition activity of alcohols on the cytochrome P-450 catalyzed p-hydroxylation of aniline.

A quantitative structure activity relationship (QSAR) has been formulated to describe the inhibitory action of a series of alcohols on the cytochrome P-450 catalyzed p-hydroxylation of aniline. The descriptors used in the QSAR are the responses of individual sensors in a polymer-based electronic nose, and are all easily generated experimental values. If the various electronic nose sensor response patterns for the family of test alcohols reflect differences in the chemical properties that are involved in the cytochrome P-450 inhibition process, it ought to be possible to correlate the differences in the electronic nose signals of these analytes with the differences in the cytochrome P-450 inhibition by these species. To evaluate this possibility, multiple linear regression was performed on data obtained from exposure of a series of test alcohols to 19 sensors of a conducting polymer composite electronic nose array. A genetic algorithm was then used to select the optimal set of sensors that best described the inhibitory activity of these alcohols within a linear regression model. The regression equation fit the inhibition data of 20 of the alcohols with an R of 0.995. This fit compares favorably with previously published QSARs on this system that have used log P (P triple bond octanol-water partition coefficient) along with steric parameters of the alcohols, and also compares favorably to QSARs formulated using theoretically calculated parameters.

Low power, lightweight vapor sensing using arrays of conducting polymer composite chemically-sensitive resistors.

Arrays of broadly responsive vapor detectors can be used to detect, identify, and quantify vapors and vapor mixtures. One implementation of this strategy involves the use of arrays of chemically-sensitive resistors made from conducting polymer composites. Sorption of an analyte into the polymer composite detector leads to swelling of the film material. The swelling is in turn transduced into a change in electrical resistance because the detector films consist of polymers filled with conducting particles such as carbon black. The differential sorption, and thus differential swelling, of an analyte into each polymer composite in the array produces a unique pattern for each different analyte of interest, Pattern recognition algorithms are then used to analyze the multivariate data arising from the responses of such a detector array. Chiral detector films can provide differential detection of the presence of certain chiral organic vapor analytes. Aspects of the spaceflight qualification and deployment of such a detector array, along with its performance for certain analytes of interest in manned life support applications, are reviewed and summarized in this article.

Detection and classification characteristics of arrays of carbon black/organic polymer composite chemiresistive vapor detectors for the nerve agent simulants dimethylmethylphosphonate and diisopropylmethylphosponate.

Arrays of conducting polymer composite vapor detectors have been evaluated for performance in the presence of the nerve agent simulants dimethylmethylphosphonate (DMMP) and diisopropylmethylphosponate (DIMP). Limits of detection for DMMP on unoptimized carbon black/ organic polymer composite vapor detectors in laboratory air were estimated to be 0.047-0.24 mg m(-3). These values are lower than the EC50 value (where EC50 is the airborne concentration sufficient to induce severe effects in 50% of those exposed for 30 min) for the nerve agents sarin (methylphosphonofluoridic acid, 1-methylethyl ester) and soman (methylphosphonofluoridic acid, 1,2,2-trimethylpropyl ester), which has been established as approximately 0.8 mg m(-3). Arrays of these vapor detectors were easily able to resolve signatures due to exposures to DMMP from those due to DIMP or due to a variety of other test analytes (including water, methanol, benzene, toluene, diesel fuel, lighter fluid, vinegar, and tetrahydrofuran) in a laboratory air background. In addition, DMMP at 27 mg m(-3) could be detected and differentiated from the signatures of the other test analytes in the presence of backgrounds of potential interferences, including water, methanol, benzene, toluene, diesel fuel, lighter fluid, vinegar, and tetrahydrofuran, even when these interferents were present in much higher concentrations than that of the DMMP or DIMP being detected.

Comparison of the performance of different discriminant algorithms in analyte discrimination tasks using an array of carbon black--polymer composite vapor detectors.

An array of 20 compositionally different carbon black--polymer composite chemiresistor vapor detectors was challenged under laboratory conditions to discriminate between a pair of extremely similar pure analytes (H2O and D2O), compositionally similar mixtures of pairs of compounds, and low concentrations of vapors of similar chemicals. Several discriminant algorithms were utilized, including k nearest neighbors (kNN, with k = 1), linear discriminant analysis (LDA, or Fisher's linear discriminant), quadratic discriminant analysis (QDA), regularized discriminant analysis (RDA, a hybrid of LDA and QDA), partial least squares, and soft independent modeling of class analogy (SIMCA). H2O and D2O were perfectly classified by most of the discriminants when a separate training and test set was used. As expected, discrimination performance decreased as the analyte concentration decreased, and performance decreased as the composition of the analyte mixtures became more similar. RDA was the overall best-performing discriminant, and LDA was the best-performing discriminant that did not require several cross-validations for optimization.

An investigation of the concentration dependence and response to analyte mixtures of carbon black/insulating organic polymer composite vapor detectors.

The responses relative to an air background of carbon black/polymer composite vapor detectors have been determined as a function of the concentration of a homologous series of alcohols (n-CnH2n+1OH, 1 < or = n < or = 8), a homologous series of alkanes (n-CnH2n+2, 5 < or = n < or = 10 and n = 12, 14), and a set of diverse solvent vapors. In all cases, the steady-state relative differential resistance responses, delta R/Rb, of the carbon black/polymer composite vapor detectors were well-described by a linear relationship with respect to the analyte partial pressure, at least over the tested concentration range (P/P degree = 0.005-0.03, where P degree is the vapor pressure of the analyte). When two vapors in air were simultaneously presented to the detectors, the delta R/Rb response, relative to an air background, was the sum of the delta R/Rb values obtained when each analyte was exposed separately to the carbon black/polymer composite detectors under study. Similarly, when an analyte was exposed to the detectors on top of a background level of another analyte, the delta R/Rb values of the array of detectors were very close to those obtained when the test analyte was exposed to the detectors only in the presence of background air. The initial training requirements from the array response output data of such detectors are minimized because the delta R/Rb response pattern produced by the analyte of concern can be associated uniquely with that odor, under the conditions explored in this work.

Trends in odor intensity for human and electronic noses: relative roles of odorant vapor pressure vs. molecularly specific odorant binding.

Response data were collected for a carbon black-polymer composite electronic nose array during exposure to homologous series of alkanes and alcohols. The mean response intensity of the electronic nose detectors and the response intensity of the most strongly driven set of electronic nose detectors were essentially constant for members of a chemically homologous odorant series when the concentration of each odorant in the gas phase was maintained at a constant fraction of the odorant's vapor pressure. A similar trend is observed in human odor detection threshold values for these same homologous series of odorants. Because the thermodynamic activity of an odorant at equilibrium in a sorbent phase is equal to the partial pressure of the odorant in the gas phase divided by the vapor pressure of the odorant and because the activity coefficients are similar within these homologous series of odorants for sorption of the vapors into specific polymer films, the data imply that the trends in detector response can be understood based on the thermodynamic tendency to establish a relatively constant concentration of sorbed odorant into each of the polymeric films of the electronic nose at a constant fraction of the odorant's vapor pressure. Similarly, the data are consistent with the hypothesis that the odor detection thresholds observed in human psychophysical experiments for the odorants studied herein are driven predominantly by the similarity in odorant concentrations sorbed into the olfactory epithelium at a constant fraction of the odorant's vapor pressure.

n-Type silicon photoelectrochemistry in methanol: Design of a 10.1% efficient semiconductor/liquid junction solar cell.

n-Type Si electrodes in MeOH solvent with 0.2 M (1-hydroxyethyl)ferrocene, 0.5 mM (1-hydroxyethyl)ferricenium, and 1.0 M LiClO(4) exhibit air mass 2 conversion efficiencies of 10.1% for optical energy into electricity. We observe open-circuit voltages of 0.53 V and short-circuit quantum efficiencies for electron flow of nearly unity. The fill factor of the cell does not decline significantly with increases in light intensity, indicating substantial reduction in efficiency losses in MeOH solvent compared to previous nonaqueous n-Si systems. Matte etch texturing of the Si surface decreases surface reflectivity and increases photocurrent by 50% compared to shiny, polished Si samples. The high values of the open-circuit voltage observed are consistent with the presence of a thin oxide layer, as in a Schottky metal-insulator-semiconductor device, which yields decreased surface recombination and increased values of open-circuit voltage and short-circuit current. The n-Si system was shown to provide sustained photocurrent at air mass 2 levels (20 mA/cm(2)) for charge through the interface of >2,000 C/cm(2). The n-Si/MeOH system represents a liquid junction cell that has exceeded the 10% barrier for conversion of optical energy into electricity.