We present reflectance and polarization phase curve measurements of highly reflective planetary regolith analogues having physical characteristics expected on atmosphereless solar system bodies (ASSBs) such as a eucritic asteroids or icy satellites. We used a goniometric photopolarimeter (GPP) of novel design to study thirteen well-sorted particle size fractions of aluminum oxide (Al2O3). The sample suite included particle sizes larger than, approximately equal to, and smaller than the wavelength of the incident monochromatic radiation (lambda = 635 nm). The observed phase angle, alpha, was 0.056 < alpha < 15 degrees. These Al2O3 particulate samples have very high normal reflectance (> similar to 95%). The incident radiation has a very high probability of being multiply scattered before being backscattered toward the incident direction or ultimately absorbed. The five smallest particle sizes exhibited extremely high void space (> similar to 95%). The reflectance phase curves for all particle size fractions show a pronounced non-linear reflectance increase with decreasing phase angle at alpha similar to <3 degrees. Our earlier studies suggest that the cause of this nonlinear reflectance increase is constructive interference of counter-propagating waves in the medium by coherent backscattering (CB), a photonic analog of Anderson localization of electrons in solid state media. The polarization phase curves for particle size fractions with size parameter (particle radius/wavelength) r/lambda < similar to 1, show that the linear polarization rapidly decreases as a increases from 0; it reaches a minimum near alpha = similar to 2 degrees. Longward of similar to 2 degrees, the negative polarization decreases as phase angle increases, becoming positive between 12 degrees and at least 15 degrees, (probably similar to 20 degrees) depending on particle size. For size parameters r/lambda > similar to 1 we detect no polarization. This polarization behavior is distinct from that observed in low albedo solar system objects such as the Moon and asteroids and for absorbing materials in the laboratory. We suggest this behavior arises because photons that are backscattered have a high probability of having interacted with two or more particles, thus giving rise to the CB process. These results may explain the unusual negative polarization behavior observed near small phase angles reported for several decades on highly reflective ASSBs such as the asteroids 44 Nysa, 64 Angelina and the Galilean satellites lo, Europa and Ganymede. Our results suggest these ASSB regoliths scatter electromagnetic radiation as if they were extremely fine grained with void space > similar to 95%, and grain sizes of the order < = lambda. This portends consequences for efforts to deploy landers on high ASSBs such as Europa. These results are also germane to the field of terrestrial geo-engineering, particularly to suggestions that earth's radiation balance can be modified by injecting Al2O3 particulates into the stratosphere thereby offsetting the effect of anthropogenic greenhouse gas emissions. The GPP used in this study was modified from our previous design so that the sample is presented with light that is alternatingly polarized perpendicular to and parallel to the scattering plane. There are no analyzers before the detector. This optical arrangement, following the Helmholtz Reciprocity Principle (HRP), produces a physically identical result to the traditional laboratory reflectance polarization measurements in which the incident light is unpolarized and the analyzers are placed before the detector. The results are identical in samples measured by both methods. We believe that ours is the first experimental demonstration of the HRP for polarized light, first proposed by Helmholtz in 1856. (C) 2017 Elsevier Inc. All rights reserved.

Biofilms are microbial communities attached to a surface and embedded in a matrix composed of exopolysaccharides and excreted nucleic acids. Bacterial biofilms are responsible for undesirable effects such as disease, prostheses colonization, biofouling, equipment damage, and pipe plugging. Biofilms are also more resilient than free-living cells to regular sterilization methods and therefore it is indispensable to develop better ways to control and remove them. The use of gas discharge plasmas is a good alternative since plasmas contain a mixture of reactive agents well-known for their decontamination potential against free microorganisms. We have previously reported that Pseudomonas aeruginosa biofilms were inactivated after a 1-min plasma exposure. We determined that the adhesiveness and the thickness of Pseudomonas biofilms grown on borosilicate were reduced. We also reported sequential morphological changes and loss of viability upon plasma treatment. However, the studies were carried out in batch cultures. The use of a continuous culture results in a more homogenous environment ensuring reproducible biofilm growth. The aim of this work was to study plasma-mediated inactivation of P. aeruginosa biofilms grown on borosilicate in a continuous culture system. In this paper we show that biofilms grown on glass under continuous culture can be inactivated by using gas discharge plasma. Both biofilm architecture and cell culturabilty are impacted by the plasma treatment. The inactivation kinetics is similar to previously described ones and cells go through sequential changes ranging from minimal modification without loss of viability at short plasma exposure times, to major structure and viability loss at longer exposure times. We report that changes in biofilm structure leading to the loss of culturability and viability are related to a decrease of the biofilm matrix adhesiveness. To our knowledge, there has been no attempt to evaluate the inactivation/sterilization of biofilms grown in a continuous system.

Bacterial biofilms are microbial communities that are less susceptible to standard killing methods than free-living bacteria. Gas-discharge plasmas were used to treat biofilms for various exposure times. After 5-min plasma exposure, 90% of culturable cells were removed. Atomic-force-microscope images that reveal the sequential changes in cell morphology occurring during plasma treatment are presented.

We describe a diffraction grating experiment for visible and microwave optics. The groove spacing for the visible-optics grating is determined through atomic force microscopy, so that an additional feature, the blaze angle, is revealed. From the blaze angle, students calculate the theoretical shift in the diffraction pattern and are then able to visualize this shift through measurements of a microwave diffraction pattern produced using a macroscopic grating. The experiment demonstrates the utility of an atomic force microscope in an engineering application and allows separation of diffraction pattern effects associated with slit width and slit spacing.

The influence of oxygen ordering on the Meissner fraction (the ratio of field cooled to zero field cooled magnetization) on a number of YBa2Cu3O7−δ single crystals over a wide range of oxygen deficient states (15 K≤Tc≤60 K) has been investigated. The Meissner fraction increases in almost all cases with an increase in oxygen ordering. In only a few cases where the change in transition temperature is very small (ΔTc<2 K) following ordering is no discernible increase measured. We attribute these results to both intrinsic parameters that change with the ordering phenomenon, for example the lower critical field, and extrinsic effects such as the redistribution of oxygen vacancies.

Using a scanning tunneling microscope in a large number of approach and retraction experiments, quantized conductance is observed for the first time in gallium. We compare the conductance quantization at temperatures between 300 and 4.2 K, just slightly below and far below the bulk melting point of gallium. We find that the conductance is significantly dependent on temperature and find a moderate conductance peak at 1Go (2e2/h) that increases in intensity with decreasing temperature. At 4.2 K, a second conductance peak at 2Go is observed. We attribute our observations to gallium’s unique orthorhombic crystal structure and a significant increase in atomic disorder at temperatures near the melting point.

Compared to pyrolytic graphite (PG) and pyrolytically coated polycrystalline graphite (PCPG), which are commonly employed substrates for graphite furnace atomic absorption spectrometry (GFAAS), highly oriented pyrolytic graphite (HOPG) is characterized by a high degree ofc-axis alignment with relatively few active sites and imperfections present on the surface. The usefulness of HOPG and commercial PG platforms for the determination of lead, copper, and aluminum by GFAAS was compared. Qualitative comparison of the absorption profiles and temperature optimizations suggest that lead, copper with a chemical modifier (palladium), and aluminum interact similarly with the two graphite substrates, while copper without a modifier interacts less strongly with HOPG than with PG. These results are in agreement with previous studies that have demonstrated that copper interacts strongly with PG and PCPG. HOPG and PG were employed for the determination of a pine needles standard reference material (SRM) and Fraser fir (Abies fraseri) samples. The analyses of the SRM gave good agreement with the certified value using both substrates, and comparable values were obtained for the samples. These results suggest that HOPG may be useful as a model for PG or PCPG when techniques such as scanning tunneling microscopy that require a high degree ofc-axis alignment are employed.

We performed in-situ X-ray reflectivity measurements of gold films during sputter deposition on polished silicon substrates. The measurements were performed at several substrate temperatures and under two argon pressures. The gold surfaces were also examined by scanning tunneling microscopy after deposition to obtain their real-space topographic images. These images were used to complement the X-ray reflectivity measurements in determining the effect of argon pressure on the gold surface and its height-height difference functions. An approximation for height-height difference functions was employed to analyze the X-ray reflectivity data. The measured interface width during growth followed a simple power law, consistent with recent theoretical results of dynamic scaling behavior. The scaling exponents, however, do not agree well with predictions based on some models in 2 + 1 dimensions.

Scanning tunneling microscopy (STM) was used to elucidate monolayer etch pits that form on highly oriented pyrolytic graphite (HOPG) heated in an electrothermal analyzer. Pits form at elevated temperatures due to reactions between oxygen and exposed carbon edge atoms (defects) and additionally with intraplanar carbon atoms (through abstraction). Samples of HOPG without analyte or matrix modifier were placed in the depression of a pure pyrolytic graphite platform and heated by using standard analysis furnace programs. Under argon stop-flow conditions, pits form in less than a second at atomization temperatures equal to and above 1200 °C. With low argon flow rates (40 mL/min), pits formed at atomization temperatures equal to and greater than 1750 °C in less than a second. Quantitative pit formation rates were used to indicate oxygen partial pressure, which may be as high as ∼ 10−3 atm at 1200 °C. Reaction rates were used to predict surface degradation due to oxygen attack and determine that 1-μm depth normal to the surface would be removed by 200 successive 5-second-period furnace firings at 1200 °C. Implications for increases in surface reactivity and analyte intercalation are discussed.

BY VAHID MAJIDI,* JAMES A. HOLCOMBE, KURT G. VANDERVOORT, DAVID J. BUTCHER, AND J. DAVID ROBERTSON CHEMICAL SCIENCE AND TECHNOLOGY DIVISION (CST-9), LOS ALAMOS NATIONAL LABORATORY, LOS ALAMOS, NEW MEXICO 87545 (V. M.); DEPARTMENT OF CHEMISTRY AND BIOCHEMISTRY, UNIVERSITY OF TEXAS, AUSTIN, TEXAS 78712 (J. A. H.); DEPARTMENT OF CHEMISTRY AND PHYSICS, WESTERN CAROLINA UNIVERSITY, CULLOWHEE, NORTH CAROLINA 28723 (K. G. V., D. J. B.); AND DEPARTMENT OF CHEMISTRY, UNIVERSITY OF KENTUCKY, LEXINGTON, KENTUCKY 40506 (J. D. R.)

Proximity effect gaps were observed consistently in Nb/Au, Bi2Sr2CaCu2O8+y/Au, and HgBa2CuO4/Ag bilayers using a low temperature scanning tunneling microscope. The Nb/Au conductance curves [dl(V)/dV vs V] were fit by the Arnold model, using the accepted energy gap value of Nb, 1.55 meV. The application of gold and silver overlayers allowed vacuum tunneling and topographic images of BSCCO single crystals and the HgBa2CuO4 polycrystalline sample. Cleavage steps of varying sizes (up to 1500 Angstrom) in the BSCCO/Au sample were observed, and gaplike features were found on such steps. Consistent, reproducible energy gaps were also found in the Hg-compound sample. (C) 1996 American Institute of Physics.