Isotachophoresis-Based Surface Immunoassay.

PubMed

Paratore, Federico; Zeidman Kalman, Tal; Rosenfeld, Tally; Kaigala, Govind V; Bercovici, Moran

2017-07-18

In the absence of amplification methods for proteins, the immune-detection of low-abundance proteins using antibodies is fundamentally limited by binding kinetic rates. Here, we present a new class of surface-based immunoassays in which protein-antibody reaction is accelerated by isotachophoresis (ITP). We demonstrate the use of ITP to preconcentrate and deliver target proteins to a surface decorated with specific antibodies, where effective utilization of the focused sample is achieved by modulating the driving electric field (stop-and-diffuse ITP mode) or applying a counter flow that opposes the ITP motion (counterflow ITP mode). Using enhanced green fluorescent protein (EGFP) as a model protein, we carry out an experimental optimization of the ITP-based immunoassay and demonstrate a 1300-fold improvement in limit of detection compared to a standard immunoassay, in a 6 min protein-antibody reaction. We discuss the design of buffer chemistries for other protein systems and, in concert with experiments, provide full analytical solutions for the two operation modes, elucidating the interplay between reaction, diffusion, and accumulation time scales and enabling the prediction and design of future immunoassays.

The development of soil organic matter in restored biodiverse Jarrah forests of South-Western Australia as determined by ASE and GCMS.

PubMed

Lin, Deborah S; Greenwood, Paul F; George, Suman; Somerfield, Paul J; Tibbett, Mark

2011-08-01

Soil organic matter (SOM) is known to increase with time as landscapes recover after a major disturbance; however, little is known about the evolution of the chemistry of SOM in reconstructed ecosystems. In this study, we assessed the development of SOM chemistry in a chronosequence (space for time substitution) of restored Jarrah forest sites in Western Australia. Replicated samples were taken at the surface of the mineral soil as well as deeper in the profile at sites of 1, 3, 6, 9, 12, and 17 years of age. A molecular approach was developed to distinguish and quantify numerous individual compounds in SOM. This used accelerated solvent extraction in conjunction with gas chromatography mass spectrometry. A novel multivariate statistical approach was used to assess changes in accelerated solvent extraction (ASE)-gas chromatography-mass spectrometry (GCMS) spectra. This enabled us to track SOM developmental trajectories with restoration time. Results showed total carbon concentrations approached that of native forests soils by 17 years of restoration. Using the relate protocol in PRIMER, we demonstrated an overall linear relationship with site age at both depths, indicating that changes in SOM chemistry were occurring. The surface soils were seen to approach native molecular compositions while the deeper soil retained a more stable chemical signature, suggesting litter from the developing diverse plant community has altered SOM near the surface. Our new approach for assessing SOM development, combining ASE-GCMS with illuminating multivariate statistical analysis, holds great promise to more fully develop ASE for the characterisation of SOM.

Surface and Interface Chemistry for Gate Stacks on Silicon

NASA Astrophysics Data System (ADS)

Frank, M. M.; Chabal, Y. J.

This chapter addresses the fundamental silicon surface science associated with the continued progress of nanoelectronics along the path prescribed by Moore's law. Focus is on hydrogen passivation layers and on ultrathin oxide films encountered during silicon cleaning and gate stack formation in the fabrication of metal-oxide-semiconductor field-effect transistors (MOSFETs). Three main topics are addressed. (i) First, the current practices and understanding of silicon cleaning in aqueous solutions are reviewed, including oxidizing chemistries and cleans leading to a hydrogen passivation layer. The dependence of the final surface termination and morphology/roughness on reactant choice and pH and the influence of impurities such as dissolved oxygen or metal ions are discussed. (ii) Next, the stability of hydrogen-terminated silicon in oxidizing liquid and gas phase environments is considered. In particular, the remarkable stability of hydrogen-terminated silicon surface in pure water vapor is discussed in the context of atomic layer deposition (ALD) of high-permittivity (high-k) gate dielectrics where water is often used as an oxygen precursor. Evidence is also provided for co-operative action between oxygen and water vapor that accelerates surface oxidation in humid air. (iii) Finally, the fabrication of hafnium-, zirconium- and aluminum-based high-k gate stacks is described, focusing on the continued importance of the silicon/silicon oxide interface. This includes a review of silicon surface preparation by wet or gas phase processing and its impact on high-k nucleation during ALD growth, and the consideration of gate stack capacitance and carrier mobility. In conclusion, two issues are highlighted: the impact of oxygen vacancies on the electrical characteristics of high-k MOS devices, and the way alloyed metal ions (such as Al in Hf-based gate stacks) in contact with the interfacial silicon oxide layer can be used to control flatband and threshold voltages.

Timescale Correlation between Marine Atmospheric Exposure and Accelerated Corrosion Testing

NASA Technical Reports Server (NTRS)

Montgomery, Eliza L.; Calle, Luz Marina; Curran, Jerone C.; Kolody, Mark R.

2011-01-01

Evaluation of metal-based structures has long relied on atmospheric exposure test sites to determine corrosion resistance in marine environments. Traditional accelerated corrosion testing relies on mimicking the exposure conditions, often incorporating salt spray and ultraviolet (UV) radiation, and exposing the metal to continuous or cyclic conditions of the corrosive environment. Their success for correlation to atmospheric exposure is often a concern when determining the timescale to which the accelerated tests can be related. Accelerated laboratory testing, which often focuses on the electrochemical reactions that occur during corrosion conditions, has yet to be universally accepted as a useful tool in predicting the long term service life of a metal despite its ability to rapidly induce corrosion. Although visual and mass loss methods of evaluating corrosion are the standard and their use is imperative, a method that correlates timescales from atmospheric exposure to accelerated testing would be very valuable. This work uses surface chemistry to interpret the chemical changes occurring on low carbon steel during atmospheric and accelerated corrosion conditions with the objective of finding a correlation between its accelerated and long-term corrosion performance. The current results of correlating data from marine atmospheric exposure conditions at the Kennedy Space Center beachside corrosion test site, alternating seawater spray, and immersion in typical electrochemical laboratory conditions, will be presented. Key words: atmospheric exposure, accelerated corrosion testing, alternating seawater spray, marine, correlation, seawater, carbon steel, long-term corrosion performance prediction, X-ray photoelectron spectroscopy.

Timescale Correlation between Marine Atmospheric Exposure and Accelerated Corrosion Testing - Part 2

NASA Technical Reports Server (NTRS)

Montgomery, Eliza L.; Calle, Luz Marina; Curran, Jerome C.; Kolody, Mark R.

2012-01-01

Evaluation of metals to predict service life of metal-based structures in corrosive environments has long relied on atmospheric exposure test sites. Traditional accelerated corrosion testing relies on mimicking the exposure conditions, often incorporating salt spray and ultraviolet (UV) radiation, and exposing the metal to continuous or cyclic conditions similar to those of the corrosive environment. Their reliability to correlate to atmospheric exposure test results is often a concern when determining the timescale to which the accelerated tests can be related. Accelerated corrosion testing has yet to be universally accepted as a useful tool in predicting the long-term service life of a metal, despite its ability to rapidly induce corrosion. Although visual and mass loss methods of evaluating corrosion are the standard, and their use is crucial, a method that correlates timescales from accelerated testing to atmospheric exposure would be very valuable. This paper presents work that began with the characterization of the atmospheric environment at the Kennedy Space Center (KSC) Beachside Corrosion Test Site. The chemical changes that occur on low carbon steel, during atmospheric and accelerated corrosion conditions, were investigated using surface chemistry analytical methods. The corrosion rates and behaviors of panels subjected to long-term and accelerated corrosion conditions, involving neutral salt fog and alternating seawater spray, were compared to identify possible timescale correlations between accelerated and long-term corrosion performance. The results, as well as preliminary findings on the correlation investigation, are presented.

Improving density functional tight binding predictions of free energy surfaces for peptide condensation reactions in solution

NASA Astrophysics Data System (ADS)

Kroonblawd, Matthew; Goldman, Nir

First principles molecular dynamics using highly accurate density functional theory (DFT) is a common tool for predicting chemistry, but the accessible time and space scales are often orders of magnitude beyond the resolution of experiments. Semi-empirical methods such as density functional tight binding (DFTB) offer up to a thousand-fold reduction in required CPU hours and can approach experimental scales. However, standard DFTB parameter sets lack good transferability and calibration for a particular system is usually necessary. Force matching the pairwise repulsive energy term in DFTB to short DFT trajectories can improve the former's accuracy for chemistry that is fast relative to DFT simulation times (<10 ps), but the effects on slow chemistry and the free energy surface are not well-known. We present a force matching approach to increase the accuracy of DFTB predictions for free energy surfaces. Accelerated sampling techniques are combined with path collective variables to generate the reference DFT data set and validate fitted DFTB potentials without a priori knowledge of transition states. Accuracy of force-matched DFTB free energy surfaces is assessed for slow peptide-forming reactions by direct comparison to DFT results for particular paths. Extensions to model prebiotic chemistry under shock conditions are discussed. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

Design of Ultrathin Pt-Based Multimetallic Nanostructures for Efficient Oxygen Reduction Electrocatalysis.

PubMed

Lai, Jianping; Guo, Shaojun

2017-12-01

Nanocatalysts with high platinum (Pt) utilization efficiency are attracting extensive attention for oxygen reduction reactions (ORR) conducted at the cathode of fuel cells. Ultrathin Pt-based multimetallic nanostructures show obvious advantages in accelerating the sluggish cathodic ORR due to their ultrahigh Pt utilization efficiency. A focus on recent important developments is provided in using wet chemistry techniques for making/tuning the multimetallic nanostructures with high Pt utilization efficiency for boosting ORR activity and durability. First, new synthetic methods for multimetallic core/shell nanoparticles with ultrathin shell sizes for achieving highly efficient ORR catalysts are reviewed. To obtain better ORR activity and stability, multimetallic nanowires or nanosheets with well-defined structure and surface are further highlighted. Furthermore, ultrathin Pt-based multimetallic nanoframes that feature 3D molecularly accessible surfaces for achieving more efficient ORR catalysis are discussed. Finally, the remaining challenges and outlooks for the future will be provided for this promising research field. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Impact of surface chemistry

PubMed Central

Somorjai, Gabor A.; Li, Yimin

2011-01-01

The applications of molecular surface chemistry in heterogeneous catalyst technology, semiconductor-based technology, medical technology, anticorrosion and lubricant technology, and nanotechnology are highlighted in this perspective. The evolution of surface chemistry at the molecular level is reviewed, and the key roles of surface instrumentation developments for in situ studies of the gas–solid, liquid–solid, and solid–solid interfaces under reaction conditions are emphasized. PMID:20880833

A functionalized poly(ethylene glycol)-based bioassay surface chemistry that facilitates bio-immobilization and inhibits non-specific protein, bacterial, and mammalian cell adhesion

PubMed Central

Harbers, Gregory M.; Emoto, Kazunori; Greef, Charles; Metzger, Steven W.; Woodward, Heather N.; Mascali, James J.; Grainger, David W.; Lochhead, Michael J.

2008-01-01

This paper describes a new bioassay surface chemistry that effectively inhibits non-specific biomolecular and cell binding interactions, while providing a capacity for specific immobilization of desired biomolecules. Poly(ethylene glycol) (PEG) as the primary component in nonfouling film chemistry is well-established, but the multicomponent formulation described here is unique in that it (1) is applied in a single, reproducible, solution-based coating step; (2) can be applied to diverse substrate materials without the use of special primers; and (3) is readily functionalized to provide specific attachment chemistries. Surface analysis data are presented, detailing surface roughness, polymer film thickness, and film chemistry. Protein non-specific binding assays demonstrate significant inhibition of serum, fibrinogen, and lysozyme adsorption to coated glass, indium tin oxide, and tissue culture polystyrene dishes. Inhibition of S. aureus and K. pneumoniae microbial adhesion in a microfluidic flow cell, and inhibition of fibroblast cell adhesion from serum-based cell culture is shown. Effective functionalization of the coating is demonstrated by directing fibroblast adhesion to polymer surfaces activated with an RGD peptide. Batch-to-batch reproducibility data are included. The in situ cross-linked PEG-based coating chemistry is unique in its formulation, and its surface properties are attractive for a broad range of in vitro bioassay applications. PMID:18815622

A Smart Superwetting Surface with Responsivity in Both Surface Chemistry and Microstructure.

PubMed

Zhang, Dongjie; Cheng, Zhongjun; Kang, Hongjun; Yu, Jianxin; Liu, Yuyan; Jiang, Lei

2018-03-26

Recently, smart surfaces with switchable wettability have aroused much attention. However, only single surface chemistry or the microstructure can be changed on these surfaces, which significantly limits their wetting performances, controllability, and applications. A new surface with both tunable surface microstructure and chemistry was prepared by grafting poly(N-isopropylacrylamide) onto the pillar-structured shape memory polymer on which multiple wetting states from superhydrophilicity to superhydrophobicity can be reversibly and precisely controlled by synergistically regulating the surface microstructure and chemistry. Meanwhile, based on the excellent controllability, we also showed the application of the surface as a rewritable platform, and various gradient wettings can be obtained. This work presents for the first time a surface with controllability in both surface chemistry and microstructure, which starts some new ideas for the design of novel superwetting materials. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Deconvoluting the effects of surface chemistry and nanoscale topography: Pseudomonas aeruginosa biofilm nucleation on Si-based substrates.

PubMed

Zhang, Jing; Huang, Jinglin; Say, Carmen; Dorit, Robert L; Queeney, K T

2018-06-01

The nucleation of biofilms is known to be affected by both the chemistry and topography of the underlying substrate, particularly when topography includes nanoscale (<100 nm) features. However, determining the role of topography vs. chemistry is complicated by concomitant variation in both as a result of typical surface modification techniques. Analyzing the behavior of biofilm-forming bacteria exposed to surfaces with systematic, independent variation of both topography and surface chemistry should allow differentiation of the two effects. Silicon surfaces with reproducible nanotopography were created by anisotropic etching in deoxygenated water. Surface chemistry was varied independently to create hydrophilic (OH-terminated) and hydrophobic (alkyl-terminated) surfaces. The attachment and proliferation of Psuedomonas aeruginosa to these surfaces was characterized over a period of 12 h using fluorescence and confocal microscopy. The number of attached bacteria as well as the structural characteristics of the nucleating biofilm were influenced by both surface nanotopography and surface chemistry. In general terms, the presence of both nanoscale features and hydrophobic surface chemistry enhance bacterial attachment and colonization. However, the structural details of the resulting biofilms suggest that surface chemistry and topography interact differently on each of the four surface types we studied. Copyright © 2018 Elsevier Inc. All rights reserved.

Influence of changing water sources and mineral chemistry on the everglades ecosystem

USGS Publications Warehouse

McCormick, P.V.; Harvey, J.W.; Crawford, E.S.

2011-01-01

Human influences during the previous century increased mineral inputs to the Florida Everglades by changing the sources and chemistry of surface inflows. Biogeochemical responses to this enrichment include changes in the availability of key limiting nutrients such as P, the potential for increased turnover of nutrient pools due to accelerated plant decomposition, and increased rates of mercury methylation associated with sulfate enrichment. Mineral enrichment has also been linked to the loss of sensitive macrophyte species, although dominant Everglades species appear tolerant of a broad range of mineral chemistry. Shifts in periphyton community composition and function provide an especially sensitive indicator of mineral enrichment. Understanding the influence of mineral chemistry on Everglades processes and biota may improve predictions of ecosystem responses to ongoing hydrologic restoration efforts and provide guidelines for protecting remaining mineral-poor areas of this peatland. Copyright ?? 2011 Taylor & Francis Group, LLC.

Ab Initio-Based Predictions of Hydrocarbon Combustion Chemistry

DTIC Science & Technology

2015-07-15

There are two prime objectives of the research. One is to develop and apply efficient methods for using ab initio potential energy surfaces (PESs...31-Mar-2015 Approved for Public Release; Distribution Unlimited Final Report: Ab Initio -Based Predictions of Hydrocarbon Combustion Chemistry The...Office P.O. Box 12211 Research Triangle Park, NC 27709-2211 hydrocarbon combustion, ab initio quantum chemistry, potential energy surfaces, chemical

Synchronized chaotic targeting and acceleration of surface chemistry in prebiotic hydrothermal microenvironments

PubMed Central

Priye, Aashish; Yu, Yuncheng; Hassan, Yassin A.; Ugaz, Victor M.

2017-01-01

Porous mineral formations near subsea alkaline hydrothermal vents embed microenvironments that make them potential hot spots for prebiotic biochemistry. But, synthesis of long-chain macromolecules needed to support higher-order functions in living systems (e.g., polypeptides, proteins, and nucleic acids) cannot occur without enrichment of chemical precursors before initiating polymerization, and identifying a suitable mechanism has become a key unanswered question in the origin of life. Here, we apply simulations and in situ experiments to show how 3D chaotic thermal convection—flows that naturally permeate hydrothermal pore networks—supplies a robust mechanism for focused accumulation at discrete targeted surface sites. This interfacial enrichment is synchronized with bulk homogenization of chemical species, yielding two distinct processes that are seemingly opposed yet synergistically combine to accelerate surface reaction kinetics by several orders of magnitude. Our results suggest that chaotic thermal convection may play a previously unappreciated role in mediating surface-catalyzed synthesis in the prebiotic milieu. PMID:28119504

A new AMS facility at Inter University Accelerator Centre, New Delhi

NASA Astrophysics Data System (ADS)

Kumar, Pankaj; Chopra, S.; Pattanaik, J. K.; Ojha, S.; Gargari, S.; Joshi, R.; Kanjilal, D.

2015-10-01

Inter University Accelerator Centre (IUAC), a national facility of government of India, is having a 15UD Pelletron accelerator for multidisciplinary ion beam based research programs. Recently, a new accelerator mass spectrometry (AMS) facility has been developed after incorporating many changes in the existing 15UD Pelletron accelerator. A clean chemistry laboratory for 10Be and 26Al with all the modern facilities has also been developed for the chemical processing of samples. 10Be measurements on sediment samples, inter laboratory comparison results and 26Al measurements on standard samples are presented in this paper. In addition to the 10Be and 26Al AMS facilities, a new 14C AMS facility based on a dedicated 500 kV tandem ion accelerator with two cesium sputter ion sources, is also being setup at IUAC.

Modeling of thermalization phenomena in coaxial plasma accelerators

NASA Astrophysics Data System (ADS)

Subramaniam, Vivek; Panneerchelvam, Premkumar; Raja, Laxminarayan L.

2018-05-01

Coaxial plasma accelerators are electromagnetic acceleration devices that employ a self-induced Lorentz force to produce collimated plasma jets with velocities ~50 km s‑1. The accelerator operation is characterized by the formation of an ionization/thermalization zone near gas inlet of the device that continually processes the incoming neutral gas into a highly ionized thermal plasma. In this paper, we present a 1D non-equilibrium plasma model to resolve the plasma formation and the electron-heavy species thermalization phenomena that take place in the thermalization zone. The non-equilibrium model is based on a self-consistent multi-species continuum description of the plasma with finite-rate chemistry. The thermalization zone is modelled by tracking a 1D gas-bit as it convects down the device with an initial gas pressure of 1 atm. The thermalization process occurs in two stages. The first is a plasma production stage, associated with a rapid increase in the charged species number densities facilitated by cathode surface electron emission and volumetric production processes. The production stage results in the formation of a two-temperature plasma with electron energies of ~2.5 eV in a low temperature background gas of ~300 K. The second, a temperature equilibration stage, is characterized by the energy transfer between the electrons and heavy species. The characteristic length scale for thermalization is found to be comparable to axial length of the accelerator thus putting into question the equilibrium magnetohydrodynamics assumption used in modeling coaxial accelerators.

Can we accelerate medicinal chemistry by augmenting the chemist with Big Data and artificial intelligence?

PubMed

Griffen, Edward J; Dossetter, Alexander G; Leach, Andrew G; Montague, Shane

2018-03-22

AI comes to lead optimization: medicinal chemistry in all disease areas can be accelerated by exploiting our pre-competitive knowledge in an unbiased way. Copyright © 2018 Elsevier Ltd. All rights reserved.

Observation of the controlled assembly of preclick components in the in situ click chemistry generation of a chitinase inhibitor

PubMed Central

Hirose, Tomoyasu; Maita, Nobuo; Gouda, Hiroaki; Koseki, Jun; Yamamoto, Tsuyoshi; Sugawara, Akihiro; Nakano, Hirofumi; Hirono, Shuichi; Shiomi, Kazuro; Watanabe, Takeshi; Taniguchi, Hisaaki; Sharpless, K. Barry; Ōmura, Satoshi; Sunazuka, Toshiaki

2013-01-01

The Huisgen cycloaddition of azides and alkynes, accelerated by target biomolecules, termed “in situ click chemistry,” has been successfully exploited to discover highly potent enzyme inhibitors. We have previously reported a specific Serratia marcescens chitinase B (SmChiB)-templated syn-triazole inhibitor generated in situ from an azide-bearing inhibitor and an alkyne fragment. Several in situ click chemistry studies have been reported. Although some mechanistic evidence has been obtained, such as X-ray analysis of [protein]–[“click ligand”] complexes, indicating that proteins act as both mold and template between unique pairs of azide and alkyne fragments, to date, observations have been based solely on “postclick” structural information. Here, we describe crystal structures of SmChiB complexed with an azide ligand and an O-allyl oxime fragment as a mimic of a click partner, revealing a mechanism for accelerating syn-triazole formation, which allows generation of its own distinct inhibitor. We have also performed density functional theory calculations based on the X-ray structure to explore the acceleration of the Huisgen cycloaddition by SmChiB. The density functional theory calculations reasonably support that SmChiB plays a role by the cage effect during the pretranslation and posttranslation states of selective syn-triazole click formation. PMID:24043811

Turbulent Mixing Chemistry in Disks

NASA Astrophysics Data System (ADS)

Semenov, D.; Wiebe, D.

2006-11-01

A gas-grain chemical model with surface reaction and 1D/2D turbulent mixing is available for protoplanetary disks and molecular clouds. Current version is based on the updated UMIST'95 database with gas-grain interactions (accretion, desorption, photoevaporation, etc.) and modified rate equation approach to surface chemistry (see also abstract for the static chemistry code).

Micromotors for "Chemistry-on-the-Fly".

PubMed

Karshalev, Emil; Esteban-Fernández de Ávila, Berta; Wang, Joseph

2018-03-21

This perspective reviews mobile micro/nanomotor scaffolds for performing "chemistry-on-the-fly". Synthetic nano/micromotors offer great versatility and distinct advantages in diverse chemical applications owing to their efficient propulsion and facile surface functionalization that allow these mobile platforms to move and disperse reactive materials across the solution. Such dynamic microreactors have led to accelerated chemical processes, including organic pollutant degradation, metal chelation, biorecognition, redox chemistry, chemical "writing", and a variety of other chemical transformations. Representative examples of such micromotor-enhanced chemical reactions are discussed, focusing on the specific chemical role of these mobile microreactors. The advantages, gaps and limitations of using micromotors as mobile chemical platforms are discussed, concluding with the future prospects of this emerging field. We envision that artificial nano/micromotors will become attractive dynamic tools for speeding up and enhancing "on-the-fly" chemical reactions.

Loch Vale Watershed Project quality assurance report, 1995-1998

USGS Publications Warehouse

Allstott, E.J.; Bashkin, Michael A.; Baron, Jill S.

1999-01-01

The Loch Vale Watershed (LVWS) project was initiated in 1980 by the National Park Service with funding from the Aquatic Effects Research Program of the National Acid Precipitation Assessment Program. Initial research objectives were to understand the processes that would either mitigate or accelerate the effects of pollution on soil and surface water chemistry, and to build a record in which long-term trends could be identified and examined.It is important for all data collected in Loch Vale to meet the high standards of quality set forth in previous LVWS QA/QC reports and LVWS Methods Manuals. Given the ever-widening usage of data collected in Loch Vale, it is equally important to provide users of that data with a report assuring that all data are sound. Parameters covered in this report are the quality of meteorological measurements, hydrological measurements, surface water chemistry, and similarities in catch efficiency of two raingage types in Loch Vale for the period of 1995-1998.Routine sampling of weather conditions, precipitation chemistry, and stream/lake water chemistry began in 1982. Since then, all samples and data have been analyzed according to widely accepted and published methods. Weather data have been collected, analyzed, and stored by LVWS project personnel. Methods for the handling of meteorological data are well documented (Denning 1988, Edwards 1991, Newkirk 1995,and Allstott 1995). Precipitation chemistry has always been collected according to National Atmospheric Deposition Program protocol (Bigelow 1988), and analyzed at the Central Analytical Laboratory of the Illinois State Water Survey in Champaign, IL. QA/QC procedures of the National Atmospheric Deposition Program are well documented (Aubertin 1990). Protocols for sampling surface waters are also well documented (Newkirk 1995). Analysis of surface water chemistry has been performed using standard EPA protocol at the US Forest Service's Rocky Mt. Station Biogeochemistry Laboratory since 1993.

Measuring restoration progress using pore- and surface-water chemistry across a chronosequence of formerly afforested blanket bogs.

PubMed

Gaffney, Paul P J; Hancock, Mark H; Taggart, Mark A; Andersen, Roxane

2018-08-01

During the restoration of degraded bogs and other peatlands, both habitat and functional recovery can be closely linked with nutrient cycling, which is reflected in pore- and surface-water chemistry. Several peatland restoration studies have shown that the time required for recovery of target conditions is slow (>10 years); for heavily-impacted, drained and afforested peatlands of northern Scotland, recovery time is unknown. We monitored pore- and surface-water chemistry across a chronosequence of formerly drained, afforested bog restoration sites spanning 0-17 years, using a space-for-time substitution, and compared them with open blanket bog control sites. Our aims were to measure rate of recovery towards bog conditions and to identify the best suite of water chemistry variables to indicate recovery. Our results show progress in recovery towards bog conditions over a 0-17 year period post-restoration. Elements scavenged by trees (Mg, Na, S) completely recovered within that period. Many water chemistry variables were affected by the restoration process itself, but recovered within 11 years, except ammonium (NH 4 + ), Zn and dissolved organic carbon (DOC) which remained elevated (when compared to control bogs) 17 years post restoration. Other variables did not completely recover (water table depth (WTD), pH), exhibiting what we term "legacy" effects of drainage and afforestation. Excess N and a lowered WTD are likely to slow the recovery of bog vegetation including key bog plants such as Sphagnum mosses. Over 17 years, we measured near-complete recovery in the chemistry of surface-water and deep pore-water but limited progress in shallow pore-water. Our results suggest that at least >17 years are required for complete recovery of water chemistry to bog conditions. However, we expect that newer restoration methods including conifer harvesting (stem plus brash) and the blocking of plough furrows (to increase the WTD) are likely to accelerate the restoration process (albeit at greater cost); this should be evaluated in future studies. We conclude that monitoring pore- and surface-water chemistry is useful in terms of indicating recovery towards bog conditions and we recommend monitoring WTD, pH, conductivity, Ca, NH 4 + , phosphate (PO 4 3- ), K, DOC, Al and Zn as key variables. Copyright © 2018 Elsevier Ltd. All rights reserved.

A facile route to steady redox-modulated nitroxide spin-labeled surfaces based on diazonium chemistry.

PubMed

Cougnon, Charles; Boisard, Séverine; Cador, Olivier; Dias, Marylène; Levillain, Eric; Breton, Tony

2013-05-18

A TEMPO derivative was covalently grafted onto carbon and gold surfaces via the diazonium chemistry. The acid-dependent redox properties of the nitroxyl group were exploited to elaborate electro-switchable magnetic surfaces. ESR characterization demonstrated the reversible and permanent magnetic character of the material.

Multiscale Simulations of ALD in Cross Flow Reactors

DOE PAGES

Yanguas-Gil, Angel; Libera, Joseph A.; Elam, Jeffrey W.

2014-08-13

In this study, we have developed a multiscale simulation code that allows us to study the impact of surface chemistry on the coating of large area substrates with high surface area/high aspect-ratio features. Our code, based on open-source libraries, takes advantage of the ALD surface chemistry to achieve an extremely efficient two-way coupling between reactor and feature length scales, and it can provide simulated quartz crystal microbalance and mass spectrometry data at any point of the reactor. By combining experimental surface characterization with simple analysis of growth profiles in a tubular cross flow reactor, we are able to extract amore » minimal set of reactions to effectively model the surface chemistry, including the presence of spurious CVD, to evaluate the impact of surface chemistry on the coating of large, high surface area substrates.« less

Tuning Wettability and Adhesion of Structured Surfaces

NASA Astrophysics Data System (ADS)

Badge, Ila

Structured surfaces with feature size ranging from a few micrometers down to nanometers are of great interest in the applications such as design of anti-wetting surfaces, tissue engineering, microfluidics, filtration, microelectronic devices, anti-reflective coatings and reversible adhesives. A specific surface property demands particular roughness geometry along with suitable surface chemistry. Plasma Enhanced Chemical Vapor Deposition (PECVD) is a technique that offers control over surface chemistry without significantly affecting the roughness and thus, provides a flexibility to alter surface chemistry selectively for a given structured surface. In this study, we have used PECVD to fine tune wetting and adhesion properties. The research presented focuses on material design aspects as well as the fundamental understanding of wetting and adhesion phenomena of structured surfaces. In order to study the effect of surface roughness and surface chemistry on the surface wettability independently, we developed a model surface by combination of colloidal lithography and PECVD. A systematically controlled hierarchical roughness using spherical colloidal particles and surface chemistry allowed for quantitative prediction of contact angles corresponding to metastable and stable wetting states. A well-defined roughness and chemical composition of the surface enabled establishing a correlation between theory predictions and experimental measurements. We developed an extremely robust superhydrophobic surface based on Carbon-Nanotubes (CNT) mats. The surface of CNTs forming a nano-porous mesh was modified using PECVD to deposit a layer of hydrophobic coating (PCNT). The PCNT surface thus formed is superhydrophobic with almost zero contact angle hysteresis. We demonstrated that the PCNT surface is not wetted under steam condensation even after prolonged exposure and also continues to retain its superhydrophobicity after multiple frosting-defrosting cycles. The anti-wetting behavior of PCNT surface is consistent with our model predictions, derived based on thermodynamic theory of wetting. The surface of gecko feet is a very unique natural structured surface. The hierarchical surface structure of a Gecko toe pad is responsible for its reversible adhesive properties and superhydrophobicity. van der Waals interactions is known to be the key mechanism behind Gecko adhesion. However, we found that the wettability, thus the surface chemistry plays a significant role in Gecko adhesion mechanism, especially in the case of underwater adhesion. We used PECVD process to deposit a layer of coating with known chemistry on the surface of sheds of gecko toes to study the effect that wettability of the toe surface has on its adhesion. In summary, we demonstrated that PECVD can be effectively used as means of surface chemistry control for tunable structure-property relationship of three types of structured surfaces; each having unique surface features.

Collaborative routes to clarifying the murky waters of aqueous supramolecular chemistry.

PubMed

Cremer, Paul S; Flood, Amar H; Gibb, Bruce C; Mobley, David L

2017-12-19

On planet Earth, water is everywhere: the majority of the surface is covered with it; it is a key component of all life; its vapour and droplets fill the lower atmosphere; and even rocks contain it and undergo geomorphological changes because of it. A community of physical scientists largely drives studies of the chemistry of water and aqueous solutions, with expertise in biochemistry, spectroscopy and computer modelling. More recently, however, supramolecular chemists - with their expertise in macrocyclic synthesis and measuring supramolecular interactions - have renewed their interest in water-mediated non-covalent interactions. These two groups offer complementary expertise that, if harnessed, offer to accelerate our understanding of aqueous supramolecular chemistry and water writ large. This Review summarizes the state-of-the-art of the two fields, and highlights where there is latent chemical space for collaborative exploration by the two groups.

Collaborative routes to clarifying the murky waters of aqueous supramolecular chemistry

NASA Astrophysics Data System (ADS)

Cremer, Paul S.; Flood, Amar H.; Gibb, Bruce C.; Mobley, David L.

2018-01-01

On planet Earth, water is everywhere: the majority of the surface is covered with it; it is a key component of all life; its vapour and droplets fill the lower atmosphere; and even rocks contain it and undergo geomorphological changes because of it. A community of physical scientists largely drives studies of the chemistry of water and aqueous solutions, with expertise in biochemistry, spectroscopy and computer modelling. More recently, however, supramolecular chemists -- with their expertise in macrocyclic synthesis and measuring supramolecular interactions -- have renewed their interest in water-mediated non-covalent interactions. These two groups offer complementary expertise that, if harnessed, offer to accelerate our understanding of aqueous supramolecular chemistry and water writ large. This Review summarizes the state-of-the-art of the two fields, and highlights where there is latent chemical space for collaborative exploration by the two groups.

Baseline Monitoring of the Western Arctic Ocean Estimates 20% of Canadian Basin Surface Waters Are Undersaturated with Respect to Aragonite

PubMed Central

Robbins, Lisa L.; Wynn, Jonathan G.; Lisle, John T.; Yates, Kimberly K.; Knorr, Paul O.; Byrne, Robert H.; Liu, Xuewu; Patsavas, Mark C.; Azetsu-Scott, Kumiko; Takahashi, Taro

2013-01-01

Marine surface waters are being acidified due to uptake of anthropogenic carbon dioxide, resulting in surface ocean areas of undersaturation with respect to carbonate minerals, including aragonite. In the Arctic Ocean, acidification is expected to occur at an accelerated rate with respect to the global oceans, but a paucity of baseline data has limited our understanding of the extent of Arctic undersaturation and of regional variations in rates and causes. The lack of data has also hindered refinement of models aimed at projecting future trends of ocean acidification. Here, based on more than 34,000 data records collected in 2010 and 2011, we establish a baseline of inorganic carbon data (pH, total alkalinity, dissolved inorganic carbon, partial pressure of carbon dioxide, and aragonite saturation index) for the western Arctic Ocean. This data set documents aragonite undersaturation in ∼20% of the surface waters of the combined Canada and Makarov basins, an area characterized by recent acceleration of sea ice loss. Conservative tracer studies using stable oxygen isotopic data from 307 sites show that while the entire surface of this area receives abundant freshwater from meteoric sources, freshwater from sea ice melt is most closely linked to the areas of carbonate mineral undersaturation. These data link the Arctic Ocean’s largest area of aragonite undersaturation to sea ice melt and atmospheric CO2 absorption in areas of low buffering capacity. Some relatively supersaturated areas can be linked to localized biological activity. Collectively, these observations can be used to project trends of ocean acidification in higher latitude marine surface waters where inorganic carbon chemistry is largely influenced by sea ice meltwater. PMID:24040074

Baseline monitoring of the western Arctic Ocean estimates 20% of the Canadian Basin surface waters are undersaturated with respect to aragonite

USGS Publications Warehouse

Robbins, Lisa L.; Wynn, Jonathan G.; Lisle, John T.; Yates, Kimberly K.; Knorr, Paul O.; Byrne, Robert H.; Liu, Xuewu; Patsavas, Mark C.; Azetsu-Scott, Kumiko; Takahashi, Taro

2013-01-01

Marine surface waters are being acidified due to uptake of anthropogenic carbon dioxide, resulting in surface ocean areas of undersaturation with respect to carbonate minerals, including aragonite. In the Arctic Ocean, acidification is expected to occur at an accelerated rate with respect to the global oceans, but a paucity of baseline data has limited our understanding of the extent of Arctic undersaturation and of regional variations in rates and causes. The lack of data has also hindered refinement of models aimed at projecting future trends of ocean acidification. Here, based on more than 34,000 data records collected in 2010 and 2011, we establish a baseline of inorganic carbon data (pH, total alkalinity, dissolved inorganic carbon, partial pressure of carbon dioxide, and aragonite saturation index) for the western Arctic Ocean. This data set documents aragonite undersaturation in ~20% of the surface waters of the combined Canada and Makarov basins, an area characterized by recent acceleration of sea ice loss. Conservative tracer studies using stable oxygen isotopic data from 307 sites show that while the entire surface of this area receives abundant freshwater from meteoric sources, freshwater from sea ice melt is most closely linked to the areas of carbonate mineral undersaturation. These data link the Arctic Ocean’s largest area of aragonite undersaturation to sea ice melt and atmospheric CO2 absorption in areas of low buffering capacity. Some relatively supersaturated areas can be linked to localized biological activity. Collectively, these observations can be used to project trends of ocean acidification in higher latitude marine surface waters where inorganic carbon chemistry is largely influenced by sea ice meltwater.

Acceleration of the chemistry solver for modeling DI engine combustion using dynamic adaptive chemistry (DAC) schemes

NASA Astrophysics Data System (ADS)

Shi, Yu; Liang, Long; Ge, Hai-Wen; Reitz, Rolf D.

2010-03-01

Acceleration of the chemistry solver for engine combustion is of much interest due to the fact that in practical engine simulations extensive computational time is spent solving the fuel oxidation and emission formation chemistry. A dynamic adaptive chemistry (DAC) scheme based on a directed relation graph error propagation (DRGEP) method has been applied to study homogeneous charge compression ignition (HCCI) engine combustion with detailed chemistry (over 500 species) previously using an R-value-based breadth-first search (RBFS) algorithm, which significantly reduced computational times (by as much as 30-fold). The present paper extends the use of this on-the-fly kinetic mechanism reduction scheme to model combustion in direct-injection (DI) engines. It was found that the DAC scheme becomes less efficient when applied to DI engine simulations using a kinetic mechanism of relatively small size and the accuracy of the original DAC scheme decreases for conventional non-premixed combustion engine. The present study also focuses on determination of search-initiating species, involvement of the NOx chemistry, selection of a proper error tolerance, as well as treatment of the interaction of chemical heat release and the fuel spray. Both the DAC schemes were integrated into the ERC KIVA-3v2 code, and simulations were conducted to compare the two schemes. In general, the present DAC scheme has better efficiency and similar accuracy compared to the previous DAC scheme. The efficiency depends on the size of the chemical kinetics mechanism used and the engine operating conditions. For cases using a small n-heptane kinetic mechanism of 34 species, 30% of the computational time is saved, and 50% for a larger n-heptane kinetic mechanism of 61 species. The paper also demonstrates that by combining the present DAC scheme with an adaptive multi-grid chemistry (AMC) solver, it is feasible to simulate a direct-injection engine using a detailed n-heptane mechanism with 543 species with practical computer time.

High-Temperature, Dual-Atmosphere Corrosion of Solid-Oxide Fuel Cell Interconnects

NASA Astrophysics Data System (ADS)

Gannon, Paul; Amendola, Roberta

2012-12-01

High-temperature corrosion of ferritic stainless steel (FSS) surfaces can be accelerated and anomalous when it is simultaneously subjected to different gaseous environments, e.g., when separating fuel (hydrogen) and oxidant (air) streams, in comparison with single-atmosphere exposures, e.g., air only. This so-called "dual-atmosphere" exposure is realized in many energy-conversion systems including turbines, boilers, gasifiers, heat exchangers, and particularly in intermediate temperature (600-800°C) planar solid-oxide fuel cell (SOFC) stacks. It is generally accepted that hydrogen transport through the FSS (plate or tube) and its subsequent integration into the growing air-side surface oxide layer can promote accelerated and anomalous corrosion—relative to single-atmosphere exposure—via defect chemistry changes, such as increased cation vacancy concentrations, decreased oxygen activity, and steam formation within the growing surface oxide layers. Establishment of a continuous and dense surface oxide layer on the fuel side of the FSS can inhibit hydrogen transport and the associated effects on the air side. Minor differences in FSS composition, microstructure, and surface conditions can all have dramatic influences on dual-atmosphere corrosion behaviors. This article reviews high-temperature, dual-atmosphere corrosion phenomena and discusses implications for SOFC stacks, related applications, and future research.

The cell-in-series method: A technique for accelerated electrode degradation in redox flow batteries

DOE PAGES

Pezeshki, Alan M.; Sacci, Robert L.; Veith, Gabriel M.; ...

2015-11-21

Here, we demonstrate a novel method to accelerate electrode degradation in redox flow batteries and apply this method to the all-vanadium chemistry. Electrode performance degradation occurred seven times faster than in a typical cycling experiment, enabling rapid evaluation of materials. This method also enables the steady-state study of electrodes. In this manner, it is possible to delineate whether specific operating conditions induce performance degradation; we found that both aggressively charging and discharging result in performance loss. Post-mortem x-ray photoelectron spectroscopy of the degraded electrodes was used to resolve the effects of state of charge (SoC) and current on the electrodemore » surface chemistry. For the electrode material tested in this work, we found evidence that a loss of oxygen content on the negative electrode cannot explain decreased cell performance. Furthermore, the effects of decreased electrode and membrane performance on capacity fade in a typical cycling battery were decoupled from crossover; electrode and membrane performance decay were responsible for a 22% fade in capacity, while crossover caused a 12% fade.« less

Seventh BES (Basic Energy Sciences) catalysis and surface chemistry research conference

DOE Office of Scientific and Technical Information (OSTI.GOV)

Not Available

1990-03-01

Research programs on catalysis and surface chemistry are presented. A total of fifty-seven topics are included. Areas of research include heterogeneous catalysis; catalysis in hydrogenation, desulfurization, gasification, and redox reactions; studies of surface properties and surface active sites; catalyst supports; chemical activation, deactivation; selectivity, chemical preparation; molecular structure studies; sorption and dissociation. Individual projects are processed separately for the data bases. (CBS)

Microgravity: Teacher's guide with activities for physical science

NASA Technical Reports Server (NTRS)

Vogt, Gregory L.; Wargo, Michael J.; Rosenberg, Carla B. (Editor)

1995-01-01

This guide is an educational tool for teachers of grades 5 through 12. It is an introduction to microgravity and its application to spaceborne laboratory experiments. Specific payloads and missions are mentioned with limited detail, including Spacelab, the International Microgravity Laboratory, and the United States Microgravity Laboratory. Activities for students demonstrate chemistry, mathematics, and physics applications of microgravity. Activity objectives include: modeling how satellites orbit Earth; demonstrating that free fall eliminates the local effects of gravity; measuring the acceleration environments created by different motions; using a plasma sheet to observe acceleration forces that are experienced on board a space vehicle; demonstrating how mass can be measured in microgravity; feeling how inertia affects acceleration; observing the gravity-driven fluid flow that is caused by differences in solution density; studying surface tension and the fluid flows caused by differences in surface tension; illustrating the effects of gravity on the burning rate of candles; observing candle flame properties in free fall; measuring the contact angle of a fluid; illustrating the effects of gravity and surface tension on fiber pulling; observing crystal growth phenomena in a 1-g environment; investigating temperature effects on crystal growth; and observing crystal nucleation and growth rate during directional solidification. Each activity includes a background section, procedure, and follow-up questions.

Estimating the Analytical and Surface Enhancement Factors in Surface-Enhanced Raman Scattering (SERS): A Novel Physical Chemistry and Nanotechnology Laboratory Experiment

ERIC Educational Resources Information Center

Pavel, Ioana E.; Alnajjar, Khadijeh S.; Monahan, Jennifer L.; Stahler, Adam; Hunter, Nora E.; Weaver, Kent M.; Baker, Joshua D.; Meyerhoefer, Allie J.; Dolson, David A.

2012-01-01

A novel laboratory experiment was successfully implemented for undergraduate and graduate students in physical chemistry and nanotechnology. The main goal of the experiment was to rigorously determine the surface-enhanced Raman scattering (SERS)-based sensing capabilities of colloidal silver nanoparticles (AgNPs). These were quantified by…

Determination of bulk and surface superconducting properties of N 2-doped cold worked, heat treated and electro-polished SRF grade niobium

DOE PAGES

Chetri, Santosh; Larbalestier, David C.; Lee, Peter J.; ...

2015-12-01

In this study, nitrogen-doped cavities show significant performance improvement in the medium accelerating field regime due to a lowered RF surface resistivity. However, the mechanism of enhancement has not been clearly explained. Our experiments explore how N 2-doping influences Nb bulk and surface superconducting properties, and compare the N 2-doped properties with those obtained previously with conventionally treated samples. High purity Nb-rod was mechanically deformed and post treated based on a typical SRF cavity treatment recipe. The onset of flux penetration at H c1, and the upper and the surface critical fields, H c2 and H c3, were characterized bymore » magnetic hysteresis and AC susceptibility techniques. The surface depth profile responsible for superconductivity was examined by changing AC amplitude in AC susceptibility, and the microstructure was directly observed with EBSD-OIM. We are also investigating surface chemistry for detailed composition using XPS. We have found that N 2-doping at 800 °C significantly reduces the H c3/H c2 ratio towards the ideal value of ~1.7, and conclude that AC susceptibility is capable of following changes to the surface properties induced by N 2-doping.« less

REGIONAL RELATIONSHIPS BETWEEN GEOMORPHIC/HYDROLOGIC PARAMETERS AND SURFACE WATER CHEMISTRY RELATIVE TO ACIDIC DEPOSITION

EPA Science Inventory

We determined geomorphic and hydrologic parameters for 144 forested, lake watersheds in the Northeast (NE) of the United States based primarily on measurements from topographic maps. hese parameters were used to test for relationships with selected surface water chemistry relevan...

Microbially-accelerated consolidation of oil sands tailings. Pathway I: changes in porewater chemistry

PubMed Central

Siddique, Tariq; Kuznetsov, Petr; Kuznetsova, Alsu; Arkell, Nicholas; Young, Rozlyn; Li, Carmen; Guigard, Selma; Underwood, Eleisha; Foght, Julia M.

2014-01-01

Dispersed clay particles in mine tailings and soft sediments remain suspended for decades, hindering consolidation and challenging effective management of these aqueous slurries. Current geotechnical engineering models of self-weight consolidation of tailings do not consider microbial contribution to sediment behavior, however, here we show that microorganisms indigenous to oil sands tailings change the porewater chemistry and accelerate consolidation of oil sands tailings. A companion paper describes the role of microbes in alteration of clay chemistry in tailings. Microbial metabolism in mature fine tailings (MFT) amended with an organic substrate (hydrolyzed canola meal) produced methane (CH4) and carbon dioxide (CO2). Dissolution of biogenic CO2 lowered the pH of amended MFT to pH 6.4 vs. unamended MFT (pH 7.7). About 12% more porewater was recovered from amended than unamended MFT during 2 months of active microbial metabolism, concomitant with consolidation of tailings. The lower pH in amended MFT dissolved carbonate minerals, thereby releasing divalent cations including calcium (Ca2+) and magnesium (Mg2+) and increasing bicarbonate (HCO−3) in porewater. The higher concentrations increased the ionic strength of the porewater, in turn reducing the thickness of the diffuse double layer (DDL) of clay particles by reducing the surface charge potential (repulsive forces) of the clay particles. The combination of these processes accelerated consolidation of oil sands tailings. In addition, ebullition of biogenic gases created transient physical channels for release of porewater. In contrast, saturating the MFT with non-biogenic CO2 had little effect on consolidation. These results have significant implications for management and reclamation of oil sands tailings ponds and broad importance in anaerobic environments such as contaminated harbors and estuaries containing soft sediments rich in clays and organics. PMID:24711805

Microbially-accelerated consolidation of oil sands tailings. Pathway I: changes in porewater chemistry.

PubMed

Siddique, Tariq; Kuznetsov, Petr; Kuznetsova, Alsu; Arkell, Nicholas; Young, Rozlyn; Li, Carmen; Guigard, Selma; Underwood, Eleisha; Foght, Julia M

2014-01-01

Dispersed clay particles in mine tailings and soft sediments remain suspended for decades, hindering consolidation and challenging effective management of these aqueous slurries. Current geotechnical engineering models of self-weight consolidation of tailings do not consider microbial contribution to sediment behavior, however, here we show that microorganisms indigenous to oil sands tailings change the porewater chemistry and accelerate consolidation of oil sands tailings. A companion paper describes the role of microbes in alteration of clay chemistry in tailings. Microbial metabolism in mature fine tailings (MFT) amended with an organic substrate (hydrolyzed canola meal) produced methane (CH4) and carbon dioxide (CO2). Dissolution of biogenic CO2 lowered the pH of amended MFT to pH 6.4 vs. unamended MFT (pH 7.7). About 12% more porewater was recovered from amended than unamended MFT during 2 months of active microbial metabolism, concomitant with consolidation of tailings. The lower pH in amended MFT dissolved carbonate minerals, thereby releasing divalent cations including calcium (Ca(2+)) and magnesium (Mg(2+)) and increasing bicarbonate (HCO(-) 3) in porewater. The higher concentrations increased the ionic strength of the porewater, in turn reducing the thickness of the diffuse double layer (DDL) of clay particles by reducing the surface charge potential (repulsive forces) of the clay particles. The combination of these processes accelerated consolidation of oil sands tailings. In addition, ebullition of biogenic gases created transient physical channels for release of porewater. In contrast, saturating the MFT with non-biogenic CO2 had little effect on consolidation. These results have significant implications for management and reclamation of oil sands tailings ponds and broad importance in anaerobic environments such as contaminated harbors and estuaries containing soft sediments rich in clays and organics.

The Role of Surface Chemistry in Adhesion and Wetting of Gecko Toe Pads

PubMed Central

Badge, Ila; Stark, Alyssa Y.; Paoloni, Eva L.; Niewiarowski, Peter H.; Dhinojwala, Ali

2014-01-01

An array of micron-sized setal hairs offers geckos a unique ability to walk on vertical surfaces using van der Waals interactions. Although many studies have focused on the role of surface morphology of the hairs, very little is known about the role of surface chemistry on wetting and adhesion. We expect that both surface chemistry and morphology are important, not only to achieve optimum dry adhesion but also for increased efficiency in self-cleaning of water and adhesion under wet conditions. Here, we used a plasma-based vapor deposition process to coat the hairy patterns on gecko toe pad sheds with polar and non-polar coatings without significantly perturbing the setal morphology. By a comparison of wetting across treatments, we show that the intrinsic surface of gecko setae has a water contact angle between 70–90°. As expected, under wet conditions, adhesion on a hydrophilic surface (glass) was lower than that on a hydrophobic surface (alkyl-silane monolayer on glass). Surprisingly under wet and dry conditions the adhesion was comparable on the hydrophobic surface, independent of the surface chemistry of the setal hairs. This work highlights the need to utilize morphology and surface chemistry in developing successful synthetic adhesives with desirable adhesion and self-cleaning properties. PMID:25323067

The Role of Surface Chemistry in Adhesion and Wetting of Gecko Toe Pads

NASA Astrophysics Data System (ADS)

Badge, Ila; Stark, Alyssa Y.; Paoloni, Eva L.; Niewiarowski, Peter H.; Dhinojwala, Ali

2014-10-01

An array of micron-sized setal hairs offers geckos a unique ability to walk on vertical surfaces using van der Waals interactions. Although many studies have focused on the role of surface morphology of the hairs, very little is known about the role of surface chemistry on wetting and adhesion. We expect that both surface chemistry and morphology are important, not only to achieve optimum dry adhesion but also for increased efficiency in self-cleaning of water and adhesion under wet conditions. Here, we used a plasma-based vapor deposition process to coat the hairy patterns on gecko toe pad sheds with polar and non-polar coatings without significantly perturbing the setal morphology. By a comparison of wetting across treatments, we show that the intrinsic surface of gecko setae has a water contact angle between 70-90°. As expected, under wet conditions, adhesion on a hydrophilic surface (glass) was lower than that on a hydrophobic surface (alkyl-silane monolayer on glass). Surprisingly under wet and dry conditions the adhesion was comparable on the hydrophobic surface, independent of the surface chemistry of the setal hairs. This work highlights the need to utilize morphology and surface chemistry in developing successful synthetic adhesives with desirable adhesion and self-cleaning properties.

Processing of ammonia-containing ices by heavy ions and its relevance to outer Solar System surfaces

NASA Astrophysics Data System (ADS)

Pilling, Sergio; Seperuelo Duarte, Eduardo; da Silveira, Enio F.; Domaracka, Alicja; Balanzat, Emmanuel; Rothard, Hermann; Boduch, Philippe

Ammonia-containing ices have been detected or postulated as important components of the icy surfaces of planetary satellites (e.g. Enceladus, Miranda), in the outer Solar System objects (e.g. Charon, Quaoar) and in Oort cloud comets. We present experimental studies of the interaction of heavy, highly-charged, and energetic ions with ammonia-containing ices (pure NH3 ; NH3 :CO; NH3 :H2 O and NH3 :H2 O:CO) in an attempt to simulate the physical chemistry induced by heavy-ion cosmic rays and heavy-ion solar wind particles at outer Solar System surfaces. The measurements were performed inside a high vacuum chamber at the heavy-ion accelerator GANIL (Grand Accelerateur National d'Ions Lourds) in Caen, France. The gas samples were deposited onto a polished CsI substrate previously cooled to 13 K. In-situ analysis was performed by a Fourier transform infrared spectrometer (FTIR) at different ion fluences. The dissociation cross-section and sputtering yield of ammonia and other ice compounds have been determined. Half-life of frozen ammonia due to heavy ion bombardment at different Solar System surfaces has been estimated. Radiolysis products have been identified and their implications for the chemistry on outer Solar System surfaces are discussed.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tao, Franklin

Two main categories of heterogeneous catalysts are metal and metal oxide which catalyze 80% chemical reactions at solid-gas and solid-liquid interfaces. Metal oxide catalysts are much more complicated than metal catalysts. The reason is that the cations of the metal atoms could exhibit a few different oxidation states on surface of the same catalyst particle such as Co 3O 4 or change of their oxidation states under different reactive environments. For a metal catalyst, there is only one oxidation state typically. In addition, surface of a metal oxide can be terminated with multiple surface functionalities including O atoms with differentmore » binding configurations and OH group. For metal, only metal atoms are exposed typically. Obviously, the complication of surface chemistry and structure of a metal oxide makes studies of surface of an oxide catalyst very challenging. Due to the complication of surface of a meal oxide, the electronic and geometric structures of surface of a metal oxide and the exposed species have received enormous attention since oxide catalysts catalyze at least 1/3 chemical reactions in chemical and energy industries. Understanding of catalytic reactions on early transition metal oxide-based catalysts is fundamentally intriguing and of great practical interest in energy- and environment-related catalysis. Exploration of surface chemistry of oxide-based catalysts at molecular level during catalysis has remained challenging though it is critical in deeply understanding catalysis on oxide-based catalysts and developing oxide-based catalysts with high activity and selectivity. Thus, the overall objective of this project is to explore surface chemistry and structure of early transition metal oxide-based catalysts through in-situ characterization of surface of catalysts, measurements of catalytic performances, and then build an intrinsic correlation of surface chemistry and structure with their catalytic performances in a few important catalytic reactions, and essentially fundamentally understand catalytic mechanism. Furthermore, this correlation will guide the design of catalysts with high activity and selectivity.« less

Carbohydrate CuAAC click chemistry for therapy and diagnosis.

PubMed

He, Xiao-Peng; Zeng, Ya-Li; Zang, Yi; Li, Jia; Field, Robert A; Chen, Guo-Rong

2016-06-24

Carbohydrates are important as signaling molecules and for cellular recognition events, therefore offering scope for the development of carbohydrate-mimetic diagnostics and drug candidates. As a consequence, the construction of carbohydrate-based bioactive compounds and sensors has become an active research area. While the advent of click chemistry has greatly accelerated the progress of medicinal chemistry and chemical biology, recent literature has seen an extensive use of such approaches to construct functionally diverse carbohydrate derivatives. Here we summarize some of the progress, covering the period 2010 to mid-2015, in Cu(I)-catalyzed azide-alkyne 1,3-dipolar cycloaddition CuAAC "click chemistry" of carbohydrate derivatives, in the context of potential therapeutic and diagnostic tool development. Copyright © 2016 The Authors. Published by Elsevier Ltd.. All rights reserved.

Land-use and fire drive temporal patterns of soil solution chemistry and nutrient fluxes.

PubMed

Potthast, Karin; Meyer, Stefanie; Crecelius, Anna C; Schubert, Ulrich S; Tischer, Alexander; Michalzik, Beate

2017-12-15

Land-use type and ecosystem disturbances are important drivers for element cycling and bear the potential to modulate soil processes and hence ecosystem functions. To better understand the effect of such drivers on the magnitude and temporal patterns of organic matter (OM) and associated nutrient fluxes in soils, continuous flux monitoring is indispensable but insufficiently studied yet. We conducted a field study to elucidate the impact of land-use and surface fires on OM and nutrient fluxes with soil solution regarding seasonal and temporal patterns analyzing short (<3months) and medium-term (3-12months) effects. Control and prescribed fire-treated topsoil horizons in beech forests and pastures were monitored biweekly for dissolved and particulate OM (DOM, POM) and solution chemistry (pH value, elements: Ca, Mg, Na, K, Al, Fe, Mn, P, S, Si) over one post-fire year. Linear mixed model analyses exhibited that mean annual DOM and POM fluxes did not differ between the two land-use types, but were subjected to strong seasonal patterns. Fire disturbance significantly lowered the annual soil solution pH in both land-uses and increased water fluxes, while DOC fluxes remained unaffected. A positive response of POC and S to fire was limited to short-term effects, while amplified particulate and dissolved nitrogen fluxes were observed in the longer run and co-ocurred with accelerated Ca and Mg fluxes. In summary, surface fires generated stronger effects on element fluxes than the land-use. Fire-induced increases in POM fluxes suggest that the particulate fraction represent a major pathway of OM translocation into the subsoil and beyond. With regard to ecosystem functions, pasture ecosystems were less prone to the risk of nutrient losses following fire events than the forest. In pastures, fire-induced base cation export may accelerate soil acidification, consequently exhausting soil buffer systems and thus may reduce the resilience to acidic depositions and disturbances. Copyright © 2017 Elsevier B.V. All rights reserved.

Surface science analysis of GaAs photocathodes following sustained electron beam delivery

DOE Office of Scientific and Technical Information (OSTI.GOV)

Carlos Hernandez-Garcia, Fay Hannon, Marcy Stutzman, V. Shutthanandan, Z. Zhu, M. Nandasri, S. V. Kuchibhatla, S. Thevuthasan, W. P. Hess

2012-06-01

Degradation of the photocathode materials employed in photoinjectors represents a challenge for sustained operation of nuclear physics accelerators and high power Free Electron Lasers (FEL). Photocathode quantum efficiency (QE) degradation is due to residual gasses in the electron source vacuum system being ionized and accelerated back to the photocathode. These investigations are a first attempt to characterize the nature of the photocathode degradation, and employ multiple surface and bulk analysis techniques to investigate damage mechanisms including sputtering of the Cs-oxidant surface monolayer, other surface chemistry effects, and ion implantation. Surface and bulk analysis studies were conducted on two GaAs photocathodes,more » which were removed from the JLab FEL DC photoemission gun after delivering electron beam, and two control samples. The analysis techniques include Helium Ion Microscopy (HIM), Rutherford Backscattering Spectrometry (RBS), Atomic Force Microscopy (AFM) and Secondary Ion Mass Spectrometry (SIMS). In addition, two high-polarization strained superlattice GaAs photocathode samples, one removed from the Continuous Electron Beam Accelerator Facility (CEBAF) photoinjector and one unused, were also analyzed using Transmission Electron Microscopy (TEM) and SIMS. It was found that heat cleaning the FEL GaAs wafer introduces surface roughness, which seems to be reduced by prolonged use. The bulk GaAs samples retained a fairly well organized crystalline structure after delivering beam but shows evidence of Cs depletion on the surface. Within the precision of the SIMS and RBS measurements the data showed no indication of hydrogen implantation or lattice damage from ion back bombardment in the bulk GaAs wafers. In contrast, SIMS and TEM measurements of the strained superlattice photocathode show clear crystal damage in the wafer from ion back bombardment.« less

Radiation curing progress in Hungary

NASA Astrophysics Data System (ADS)

Czvikovszky, T.

Radiation chemistry and radiation processing is an actively cultivated field of chemical technology and of applied research in several Central/Eastern European countries. Hungary, with his synthetic polymer production over 50 kg/capita/year, with his strong commitment in nuclear power production /almost 40 % of total electric power/, with his pioneering activity in food irradiation, radiation sterilization as well as EB processing of polymer — performs an iniciating role in this region. Actually four industrial EB machines are working in Hungary on plastics converting. Two of these accelerators, manufactured in SU are producing heat-shrinkable products. Two other, low-energy EB machines from FRG are working on industrial-scale surface-coating. An ELECTROCURTAIN /USA/ is serving R/D. Some actual problems of the applied radiation chemistry of EB-curing will be discussed.

Gas-to-Particle Conversion in Surface Discharge Nonthermal Plasmas and Its Implications for Atmospheric Chemistry

PubMed Central

Kim, Hyun-Ha; Ogata, Atsushi

2011-01-01

This paper presents some experimental data on gas-to-particle conversion of benzene using nonthermal plasma (NTP) technology and discusses the possibility of its technical application in atmospheric chemistry. Aerosol measurement using a differential mobility analyzer (DMA) revealed that the parts of benzene molecules were converted into a nanometer-sized aerosol. Aerosol formation was found to be highly related with the missing part in carbon balance. Scanning electron microscopy analysis showed that the aerosols formed in synthetic humid air are the collection of nanoparticles. The carbonyl band (C=O) was found to be an important chemical constituent in the aerosol. The potential of the NTP as an accelerated test tool in studying secondary organic aerosol (SOA) formation from VOCs will be also addressed. PMID:22163781

Laboratory study of hyper-elocity impact-driven chemical reactions and surface evolution in icy targets.

NASA Astrophysics Data System (ADS)

Ulibarri, Z.; Munsat, T.; Dee, R.; Horanyi, M.; James, D.; Kempf, S.; Nagle, M.; Sternovsky, Z.

2017-12-01

Although ice is prevalent in the solar system and the long-term evolution of many airless icy bodies is affected by hypervelocity micrometeoroid bombardment, there has been little experimental investigation into these impact phenomena, especially at the impact speeds encountered in space. For example, there is little direct information about how dust impacts alter the local chemistry, and dust impacts may be an important mechanism for creating complex organic molecules necessary for life. Laser ablation and light-gas gun experiments simulating dust impacts have successfully created amino acid precursors from base components in ice surfaces. Additionally, the Cassini mission revealed CO2 deposits in icy satellites of Saturn, which may have been created by dust impacts. With the creation of a cryogenically cooled ice target for the dust accelerator facility at the NASA SSERVI-funded Institute for Modeling Plasma, Atmospheres, and Cosmic Dust (IMPACT), it is now possible to study the effects of micrometeoroid impacts in a controlled environment under conditions and at energies typically encountered in nature. Complex ice-target mixtures are created with a flash-freezing target which allows for homogeneous mixtures to be frozen in place even with salt mixtures that otherwise would form inhomogeneous ice surfaces. Coupled with the distinctive capabilities of the IMPACT dust facility, highly valuable data concerning the evolution of icy bodies under hypervelocity bombardment and the genesis of complex organic chemistry on these icy bodies can be gathered in unique and tightly controlled experiments. Results from recent and ongoing investigations will be presented.

Multifunctional ultra-high vacuum apparatus for studies of the interactions of chemical warfare agents on complex surfaces

NASA Astrophysics Data System (ADS)

Wilmsmeyer, Amanda R.; Gordon, Wesley O.; Davis, Erin Durke; Mantooth, Brent A.; Lalain, Teri A.; Morris, John R.

2014-01-01

A fundamental understanding of the surface chemistry of chemical warfare agents is needed to fully predict the interaction of these toxic molecules with militarily relevant materials, catalysts, and environmental surfaces. For example, rules for predicting the surface chemistry of agents can be applied to the creation of next generation decontaminants, reactive coatings, and protective materials for the warfighter. Here, we describe a multifunctional ultra-high vacuum instrument for conducting comprehensive studies of the adsorption, desorption, and surface chemistry of chemical warfare agents on model and militarily relevant surfaces. The system applies reflection-absorption infrared spectroscopy, x-ray photoelectron spectroscopy, and mass spectrometry to study adsorption and surface reactions of chemical warfare agents. Several novel components have been developed to address the unique safety and sample exposure challenges that accompany the research of these toxic, often very low vapor pressure, compounds. While results of vacuum-based surface science techniques may not necessarily translate directly to environmental processes, learning about the fundamental chemistry will begin to inform scientists about the critical aspects that impact real-world applications.

Multifunctional ultra-high vacuum apparatus for studies of the interactions of chemical warfare agents on complex surfaces.

PubMed

Wilmsmeyer, Amanda R; Gordon, Wesley O; Davis, Erin Durke; Mantooth, Brent A; Lalain, Teri A; Morris, John R

2014-01-01

A fundamental understanding of the surface chemistry of chemical warfare agents is needed to fully predict the interaction of these toxic molecules with militarily relevant materials, catalysts, and environmental surfaces. For example, rules for predicting the surface chemistry of agents can be applied to the creation of next generation decontaminants, reactive coatings, and protective materials for the warfighter. Here, we describe a multifunctional ultra-high vacuum instrument for conducting comprehensive studies of the adsorption, desorption, and surface chemistry of chemical warfare agents on model and militarily relevant surfaces. The system applies reflection-absorption infrared spectroscopy, x-ray photoelectron spectroscopy, and mass spectrometry to study adsorption and surface reactions of chemical warfare agents. Several novel components have been developed to address the unique safety and sample exposure challenges that accompany the research of these toxic, often very low vapor pressure, compounds. While results of vacuum-based surface science techniques may not necessarily translate directly to environmental processes, learning about the fundamental chemistry will begin to inform scientists about the critical aspects that impact real-world applications.

Multifunctional ultra-high vacuum apparatus for studies of the interactions of chemical warfare agents on complex surfaces

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wilmsmeyer, Amanda R.; Morris, John R.; Gordon, Wesley O.

2014-01-15

A fundamental understanding of the surface chemistry of chemical warfare agents is needed to fully predict the interaction of these toxic molecules with militarily relevant materials, catalysts, and environmental surfaces. For example, rules for predicting the surface chemistry of agents can be applied to the creation of next generation decontaminants, reactive coatings, and protective materials for the warfighter. Here, we describe a multifunctional ultra-high vacuum instrument for conducting comprehensive studies of the adsorption, desorption, and surface chemistry of chemical warfare agents on model and militarily relevant surfaces. The system applies reflection-absorption infrared spectroscopy, x-ray photoelectron spectroscopy, and mass spectrometry tomore » study adsorption and surface reactions of chemical warfare agents. Several novel components have been developed to address the unique safety and sample exposure challenges that accompany the research of these toxic, often very low vapor pressure, compounds. While results of vacuum-based surface science techniques may not necessarily translate directly to environmental processes, learning about the fundamental chemistry will begin to inform scientists about the critical aspects that impact real-world applications.« less

Development and Implementation of a Two-Semester Introductory Organic-Bioorganic Chemistry Sequence: Conclusions from the First Six Years

ERIC Educational Resources Information Center

Goess, Brian C.

2014-01-01

A two-semester second-year introductory organic chemistry sequence featuring one semester of accelerated organic chemistry followed by one semester of bioorganic chemistry is described. Assessment data collected over a six-year period reveal that such a course sequence can facilitate student mastery of fundamental organic chemistry in the first…

Immobilization methods for the rapid total chemical synthesis of proteins on microtiter plates.

PubMed

Zitterbart, Robert; Krumrey, Michael; Seitz, Oliver

2017-07-01

The chemical synthesis of proteins typically involves the solid-phase peptide synthesis of unprotected peptide fragments that are stitched together in solution by native chemical ligation (NCL). The process is slow, and throughput is limited because of the need for repeated high performance liquid chromatography purification steps after both solid-phase peptide synthesis and NCL. With an aim to provide faster access to functional proteins and to accelerate the functional analysis of synthetic proteins by parallelization, we developed a method for the high performance liquid chromatography-free synthesis of proteins on the surface of microtiter plates. The method relies on solid-phase synthesis of unprotected peptide fragments, immobilization of the C-terminal fragment and on-surface NCL with an unprotected peptide thioester in crude form. Herein, we describe the development of a suitable immobilization chemistry. We compared (i) formation of nickel(II)-oligohistidine complexes, (ii) Cu-based [2 + 3] alkine-azide cycloaddition and (iii) hydrazone ligation. The comparative study identified the hydrazone ligation as most suitable. The sequence of immobilization via hydrazone ligation, on-surface NCL and radical desulfurization furnished the targeted SH3 domains in near quantitative yield. The synthetic proteins were functional as demonstrated by an on-surface fluorescence-based saturation binding analysis. Copyright © 2017 European Peptide Society and John Wiley & Sons, Ltd. Copyright © 2017 European Peptide Society and John Wiley & Sons, Ltd.

Anisotropic surface chemistry properties and adsorption behavior of silicate mineral crystals.

PubMed

Xu, Longhua; Tian, Jia; Wu, Houqin; Fang, Shuai; Lu, Zhongyuan; Ma, Caifeng; Sun, Wei; Hu, Yuehua

2018-03-07

Anisotropic surface properties of minerals play an important role in a variety of fields. With a focus on the two most intensively investigated silicate minerals (i.e., phyllosilicate minerals and pegmatite aluminosilicate minerals), this review highlights the research on their anisotropic surface properties based on their crystal structures. Four surface features comprise the anisotropic surface chemistry of minerals: broken bonds, energy, wettability, and charge. Analysis of surface broken bond and energy anisotropy helps to explain the cleavage and growth properties of mineral crystals, and understanding surface wettability and charge anisotropy is critical to the analysis of minerals' solution behavior, such as their flotation performance and rheological properties. In a specific reaction, the anisotropic surface properties of minerals are reflected in the adsorption strengths of reagents on different mineral surfaces. Combined with the knowledge of mineral crushing and grinding, a thorough understanding of the anisotropic surface chemistry properties and the anisotropic adsorption behavior of minerals will lead to the development of effective relational models comprising their crystal structure, surface chemistry properties, and targeted reagent adsorption. Overall, such a comprehensive approach is expected to firmly establish the connection between selective cleavage of mineral crystals for desired surfaces and designing novel reagents selectively adsorbed on the mineral surfaces. As tools to characterize the anisotropic surface chemistry properties of minerals, DLVO theory, atomic force microscopy (AFM), and molecular dynamics (MD) simulations are also reviewed. Copyright © 2017 Elsevier B.V. All rights reserved.

Joint Center for Satellite Data Assimilation Overview and Research Activities

NASA Astrophysics Data System (ADS)

Auligne, T.

2017-12-01

In 2001 NOAA/NESDIS, NOAA/NWS, NOAA/OAR, and NASA, subsequently joined by the US Navy and Air Force, came together to form the Joint Center for Satellite Data Assimilation (JCSDA) for the common purpose of accelerating the use of satellite data in environmental numerical prediction modeling by developing, using, and anticipating advances in numerical modeling, satellite-based remote sensing, and data assimilation methods. The primary focus was to bring these advances together to improve operational numerical model-based forecasting, under the premise that these partners have common technical and logistical challenges assimilating satellite observations into their modeling enterprises that could be better addressed through cooperative action and/or common solutions. Over the last 15 years, the JCSDA has made and continues to make major contributions to operational assimilation of satellite data. The JCSDA is a multi-agency U.S. government-owned-and-operated organization that was conceived as a venue for the several agencies NOAA, NASA, USAF and USN to collaborate on advancing the development and operational use of satellite observations into numerical model-based environmental analysis and forecasting. The primary mission of the JCSDA is to "accelerate and improve the quantitative use of research and operational satellite data in weather, ocean, climate and environmental analysis and prediction systems." This mission is fulfilled through directed research targeting the following key science objectives: Improved radiative transfer modeling; new instrument assimilation; assimilation of humidity, clouds, and precipitation observations; assimilation of land surface observations; assimilation of ocean surface observations; atmospheric composition; and chemistry and aerosols. The goal of this presentation is to briefly introduce the JCSDA's mission and vision, and to describe recent research activities across various JCSDA partners.

Enhanced PM2.5 pollution in China due to aerosol-cloud interactions.

PubMed

Zhao, Bin; Liou, Kuo-Nan; Gu, Yu; Li, Qinbin; Jiang, Jonathan H; Su, Hui; He, Cenlin; Tseng, Hsien-Liang R; Wang, Shuxiao; Liu, Run; Qi, Ling; Lee, Wei-Liang; Hao, Jiming

2017-06-30

Aerosol-cloud interactions (aerosol indirect effects) play an important role in regional meteorological variations, which could further induce feedback on regional air quality. While the impact of aerosol-cloud interactions on meteorology and climate has been extensively studied, their feedback on air quality remains unclear. Using a fully coupled meteorology-chemistry model, we find that increased aerosol loading due to anthropogenic activities in China substantially increases column cloud droplet number concentration and liquid water path (LWP), which further leads to a reduction in the downward shortwave radiation at surface, surface air temperature and planetary boundary layer (PBL) height. The shallower PBL and accelerated cloud chemistry due to larger LWP in turn enhance the concentrations of particulate matter with diameter less than 2.5 μm (PM 2.5 ) by up to 33.2 μg m -3 (25.1%) and 11.0 μg m -3 (12.5%) in January and July, respectively. Such a positive feedback amplifies the changes in PM 2.5 concentrations, indicating an additional air quality benefit under effective pollution control policies but a penalty for a region with a deterioration in PM 2.5 pollution. Additionally, we show that the cloud processing of aerosols, including wet scavenging and cloud chemistry, could also have substantial effects on PM 2.5 concentrations.

Water chemistry controlled aggregation and photo-transformation of silver nanoparticles in environmental waters.

PubMed

Yin, Yongguang; Yang, Xiaoya; Zhou, Xiaoxia; Wang, Weidong; Yu, Sujuan; Liu, Jingfu; Jiang, Guibin

2015-08-01

The inevitable release of engineered silver nanoparticles (AgNPs) into aquatic environments has drawn great concerns about its environmental toxicity and safety. Although aggregation and transformation play crucial roles in the transport and toxicity of AgNPs, how the water chemistry of environmental waters influences the aggregation and transformation of engineered AgNPs is still not well understood. In this study, the aggregation of polyvinylpyrrolidone (PVP) coated AgNPs was investigated in eight typical environmental water samples (with different ionic strengths, hardness, and dissolved organic matter (DOM) concentrations) by using UV-visible spectroscopy and dynamic light scattering. Raman spectroscopy was applied to probe the interaction of DOM with the surface of AgNPs. Further, the photo-transformation and morphology changes of AgNPs in environmental waters were studied by UV-visible spectroscopy, inductively coupled plasma mass spectrometry, and transmission electron microscopy. The results suggested that both electrolytes (especially Ca(2+) and Mg(2+)) and DOM in the surface waters are key parameters for AgNP aggregation, and sunlight could accelerate the morphology change, aggregation, and further sedimentation of AgNPs. This water chemistry controlled aggregation and photo-transformation should have significant environmental impacts on the transport and toxicity of AgNPs in the aquatic environments. Copyright © 2015. Published by Elsevier B.V.

Introduction

NASA Astrophysics Data System (ADS)

Assmann, R. W.; Ferrario, M.

2016-09-01

Particle accelerators are a field of continuing and growing success. Today about 30,000 accelerators are operated with various types of particles, including electrons, positrons, protons, neutrinos and various kinds of ions. These particles are used for the investigation of fundamental particles and forces in our universe. In parallel a fast growing field of accelerator-based photon science has developed since the 1970"s. Modern particle beams produce unique photon pulses that are used in ground-breaking studies on fast processes in chemistry and biology, on structures of viruses and bacteria, on the phenomenon of multi-resistivity to medication, on the functioning of photo-synthesis at the electronic level and on other important challenges for human mankind. Last not least, numerous particle accelerators are being used every day for industrial and medical applications, including the irradiation of tumors in human patients.

The impact of surface chemistry on the performance of localized solar-driven evaporation system

PubMed Central

Yu, Shengtao; Zhang, Yao; Duan, Haoze; Liu, Yanming; Quan, Xiaojun; Tao, Peng; Shang, Wen; Wu, Jianbo; Song, Chengyi; Deng, Tao

2015-01-01

This report investigates the influence of surface chemistry (or wettability) on the evaporation performance of free-standing double-layered thin film on the surface of water. Such newly developed evaporation system is composed of top plasmonic light-to-heat conversion layer and bottom porous supporting layer. Under solar light illumination, the induced plasmonic heat will be localized within the film. By modulating the wettability of such evaporation system through the control of surface chemistry, the evaporation rates are differentiated between hydrophilized and hydrophobized anodic aluminum oxide membrane-based double layered thin films. Additionally, this work demonstrated that the evaporation rate mainly depends on the wettability of bottom supporting layer rather than that of top light-to-heat conversion layer. The findings in this study not only elucidate the role of surface chemistry of each layer of such double-layered evaporation system, but also provide additional design guidelines for such localized evaporation system in applications including desalination, distillation and power generation. PMID:26337561

The impact of surface chemistry on the performance of localized solar-driven evaporation system.

PubMed

Yu, Shengtao; Zhang, Yao; Duan, Haoze; Liu, Yanming; Quan, Xiaojun; Tao, Peng; Shang, Wen; Wu, Jianbo; Song, Chengyi; Deng, Tao

2015-09-04

This report investigates the influence of surface chemistry (or wettability) on the evaporation performance of free-standing double-layered thin film on the surface of water. Such newly developed evaporation system is composed of top plasmonic light-to-heat conversion layer and bottom porous supporting layer. Under solar light illumination, the induced plasmonic heat will be localized within the film. By modulating the wettability of such evaporation system through the control of surface chemistry, the evaporation rates are differentiated between hydrophilized and hydrophobized anodic aluminum oxide membrane-based double layered thin films. Additionally, this work demonstrated that the evaporation rate mainly depends on the wettability of bottom supporting layer rather than that of top light-to-heat conversion layer. The findings in this study not only elucidate the role of surface chemistry of each layer of such double-layered evaporation system, but also provide additional design guidelines for such localized evaporation system in applications including desalination, distillation and power generation.

Static Chemistry in Disks or Clouds

NASA Astrophysics Data System (ADS)

Semenov, D.; Wiebe, D.

2006-11-01

This FORTRAN77 code can be used to model static, time-dependent chemistry in ISM and circumstellar disks. Current version is based on the OSU'06 gas-grain astrochemical network with all updates to the reaction rates, and includes surface chemistry from Hasegawa & Herbst (1993) and Hasegawa, Herbst, and Leung (1992). Surface chemistry can be modeled either with the standard rate equation approach or modified rate equation approach (useful in disks). Gas-grain interactions include sticking of neutral molecules to grains, dissociative recombination of ions on grains as well as thermal, UV, X-ray, and CRP-induced desorption of frozen species. An advanced X-ray chemistry and 3 grain sizes with power-law size distribution are also included. An deuterium extension to this chemical model is available.

Physics. Student Investigations and Readings. Investigations in Natural Science.

ERIC Educational Resources Information Center

Renner, John W.; And Others

Investigations in Natural Science is a program in secondary school biology, chemistry, and physics based upon the description of science as a quest for knowledge, not the knowledge itself. This student manual contains the 36 physics investigations which focus on concepts related to: movement; vectors; falling objects; force and acceleration; a…

Recycling microcavity optical biosensors.

PubMed

Hunt, Heather K; Armani, Andrea M

2011-04-01

Optical biosensors have tremendous potential for commercial applications in medical diagnostics, environmental monitoring, and food safety evaluation. In these applications, sensor reuse is desirable to reduce costs. To achieve this, harsh, wet chemistry treatments are required to remove surface chemistry from the sensor, typically resulting in reduced sensor performance and increased noise due to recognition moiety and optical transducer degradation. In the present work, we suggest an alternative, dry-chemistry method, based on O₂ plasma treatment. This approach is compatible with typical fabrication of substrate-based optical transducers. This treatment completely removes the recognition moiety, allowing the transducer surface to be refreshed with new recognition elements and thus enabling the sensor to be recycled.

Diagnostic examination of thermally abused high-power lithium-ion cells

NASA Astrophysics Data System (ADS)

Abraham, D. P.; Roth, E. P.; Kostecki, R.; McCarthy, K.; MacLaren, S.; Doughty, D. H.

The inherent thermal instability of lithium-ion cells is a significant impediment to their widespread commercialization for hybrid-electric vehicle applications. Cells containing conventional organic electrolyte-based chemistries are prone to thermal runaway at temperatures around 180 °C. We conducted accelerating rate calorimetry measurements on high-power 18650-type lithium-ion cells in an effort to decipher the sequence of events leading to thermal runaway. In addition, electrode and separator samples harvested from a cell that was heated to 150 °C then air-quenched to room temperature were examined by microscopy, spectroscopy, and diffraction techniques. Self-heating of the cell began at 84 °C. The gases generated in the cell included CO 2 and CO, and smaller quantities of H 2, C 2H 4, CH 4, and C 2H 6. The main changes on cell heating to 150 °C were observed on the anode surface, which was covered by a thick layer of surface deposits that included LiF and inorganic and organo-phosphate compounds. The sources of gas generation and the mechanisms leading to the formation of compounds observed on the electrode surfaces are discussed.

Organic reactions for the electrochemical and photochemical production of chemical fuels from CO2--The reduction chemistry of carboxylic acids and derivatives as bent CO2 surrogates.

PubMed

Luca, Oana R; Fenwick, Aidan Q

2015-11-01

The present review covers organic transformations involved in the reduction of CO2 to chemical fuels. In particular, we focus on reactions of CO2 with organic molecules to yield carboxylic acid derivatives as a first step in CO2 reduction reaction sequences. These biomimetic initial steps create opportunities for tandem electrochemical/chemical reductions. We draw parallels between long-standing knowledge of CO2 reactivity from organic chemistry, organocatalysis, surface science and electrocatalysis. We point out some possible non-faradaic chemical reactions that may contribute to product distributions in the production of solar fuels from CO2. These reactions may be accelerated by thermal effects such as resistive heating and illumination. Copyright © 2015 Elsevier B.V. All rights reserved.

Effect of Metallic Li on the Behavior of Metals in Molten Salts

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chidambaram, Dev; Phillips, William; Merwin, Augustus

The deleterious effect of Li0 on the reactor container materials has not been studied. Exposure to liquid Li 0 results in material degradation primarily through lithium intercalation, leaching of specific alloying elements, and decarburization. The objective of this research is to understand how the presence of Li 0 in molten LiCl-Li 2O affects the degradation of two classes of alloys by correlating their accelerated and long term electrochemical behavior to the surface chemistry of the alloys and the chemistry of the electrolyte. This study has completed all the proposed tasks. The project led to the design and development of uniquemore » experimental setups and protocols. Several groundbreaking findings resulted from this study. The project had several products in terms of student education, thesis and dissertation, publications and presentations.« less

The behavior of MC3T3-E1 cells on chitosan/poly-L-lysine composite films: effect of nanotopography, surface chemistry, and wettability.

PubMed

Zheng, Zhenhuan; Zhang, Ling; Kong, Lijun; Wang, Aijun; Gong, Yandao; Zhang, Xiufang

2009-05-01

In the present work, a series of composite films were produced from chitosan/poly-L-lysine blend solutions. The surface topography, chemistry, and wettability of composite films were characterized by atomic force microscopy (AFM), attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy, and contact angle assay, respectively. For all composite films, blending with poly-L-lysine induced changes in surface chemistry and wettability. Interestingly, it was also found that increasing poly-L-lysine weight fraction in blend solutions could result in different nanoscaled surface topographic features, which displayed particle-, granule-, or fiber-dominant morphologies. MC3T3-E1 osteoblast-like cells were cultured on all composite films to evaluate the effects of surface nanotopography, chemistry, and wettability on cell behavior. The observations indicated that MC3T3-E1 cell behavior was affected by surface topography, chemistry, and wettability simultaneously and that cells showed strong responses to surface topography. On fiber-dominant surface, cells fully spread with obvious cytoskeleton organization and exhibited significantly higher level of adhesion and proliferation compared with particle- or granule-dominant surfaces. Furthermore, fiber-dominant surface also induced greater expression of mature osteogenic marker osteocalcin and higher mineralization based on RT-PCR and von Kossa staining. The results suggest that topographic modification of chitosan substratum at the nanoscale may be exploited in regulating cell behavior for its applications in tissue engineering.

Adhesion of epoxy primer to hydrotalcite conversion coated AA2024

NASA Astrophysics Data System (ADS)

Leggat, Robert Benton, III

Hydrotalcite-based (HT) conversion coatings are being developed as an environmentally benign alternative to chromate conversion coatings (CCC). Accelerated exposure tests were conducted on epoxy primed, HT-modified AA2024 to gauge service performance. HT-based conversion coatings did not perform as well as the CCC when used with an epoxy primer. The current HT chemistries are optimized for stand-alone corrosion protection, however additional research into the primer/HT interactions is necessary before they can be implemented within a coating scheme. The relative contribution of mechanical and physico-chemical interactions in controlling adhesion has been investigated in this study. Practical adhesion tests were used to assess the dry and wet bond strength of epoxy primer on HT coatings using the pull-off tensile strength (POTS) as the figure of merit. The practical adhesion of HT coated samples generally fell between that observed for the CCC and bare AA2024. Laboratory testing was done to assess the physical and chemical properties of HT coatings. Contact angle measurements were performed using powders representative of different HT chemistries to evaluate the dispersive and acid-base character of the surface. The wet POTS correlated with the electrodynamic (dipole + dispersive) parameter of the surface tension. The HT surfaces were found to be predominantly basic. Given the basicity of epoxy, these results indicate that increasing the acidic character of HT coatings may increase the adhesion performance. This was supported by electrokinetic measurements in which the dry POTS was found to increase with decreasing conversion coating iso-electric point. The correlations with the dry and wet state adhesion are interpreted as indicating that dry state adhesion is optimized by minimizing unfavorable polar interactions between the basic epoxy and HT interfaces. Wet state adhesion, where polar interactions are disrupted, is dictated by non-polar bonding. FTIR spectroscopy suggested that covalent between HT coatings and epoxy primers may occur, but could not definitively indicate so. Present results suggest that the limited chemical interactions, as governed by substrate wetting and acid-base interactions between the epoxy and HT, have minimized the possible mechanical interactions between the resin and the conversion coating.

Designing durable icephobic surfaces

PubMed Central

Golovin, Kevin; Kobaku, Sai P. R.; Lee, Duck Hyun; DiLoreto, Edward T.; Mabry, Joseph M.; Tuteja, Anish

2016-01-01

Ice accretion has a negative impact on critical infrastructure, as well as a range of commercial and residential activities. Icephobic surfaces are defined by an ice adhesion strength τice < 100 kPa. However, the passive removal of ice requires much lower values of τice, such as on airplane wings or power lines (τice < 20 kPa). Such low τice values are scarcely reported, and robust coatings that maintain these low values have not been reported previously. We show that, irrespective of material chemistry, by tailoring the cross-link density of different elastomeric coatings and by enabling interfacial slippage, it is possible to systematically design coatings with extremely low ice adhesion (τice < 0.2 kPa). These newfound mechanisms allow for the rational design of icephobic coatings with virtually any desired ice adhesion strength. By using these mechanisms, we fabricate extremely durable coatings that maintain τice < 10 kPa after severe mechanical abrasion, acid/base exposure, 100 icing/deicing cycles, thermal cycling, accelerated corrosion, and exposure to Michigan wintery conditions over several months. PMID:26998520

Molecular-level chemistry of model single-crystal oxide surfaces with model halogenated compounds

NASA Astrophysics Data System (ADS)

Adib, Kaveh

Synchrotron-based X-ray photoelectron spectroscopy (XPS), temperature-programmed desorption (TPD) and low energy electron diffraction (LEED) have been used to investigate, at a molecular level, the chemistry of different terminations of single crystal iron-oxide surfaces with probe molecules (CCl4 and D2O). Comparisons of the reactivity of these surfaces towards CCl4, indicate that the presence of an uncapped surface Fe cation (strong Lewis acid site) and an adjacent oxygen site capped by that cation can effect the C-Cl bond cleavage in CCl4, resulting in dissociatively adsorbed Cl-adatoms and carbon-containing fragments. If in addition to these sites, an uncapped surface oxygen (Lewis base) site is also available, the carbon-containing moiety can then move that site, coordinate itself with that uncapped oxygen, and stabilize itself. At a later step, the carbon-containing fragment may form a strong covalent bond with the uncapped oxygen and may even abstract that surface oxygen. On the other hand, if an uncapped oxygen is not available to stabilize the carbon-containing fragment, the surface coordination will not occur and upon the subsequent thermal annealing of the surface the Cl-adatoms and the carbon-containing fragments will recombine and desorb as CCl4. Finally, the presence of surface deuteroxyls blocking the strong Lewis acid and base sites of the reactive surface, passivates this surface. Such a deuteroxylated surface will be unreactive towards CCl 4. Such a molecular level understanding of the surface chemistry of metal-oxides will have applications in the areas of selective catalysis, including environmental catalysis, and chemical sensor technology.

Conducting water chemistry of the secondary coolant circuit of VVER-based nuclear power plant units constructed without using copper containing alloys

NASA Astrophysics Data System (ADS)

Tyapkov, V. F.

2014-07-01

The secondary coolant circuit water chemistry with metering amines began to be put in use in Russia in 2005, and all nuclear power plant units equipped with VVER-1000 reactors have been shifted to operate with this water chemistry for the past seven years. Owing to the use of water chemistry with metering amines, the amount of products from corrosion of structural materials entering into the volume of steam generators has been reduced, and the flow-accelerated corrosion rate of pipelines and equipment has been slowed down. The article presents data on conducting water chemistry in nuclear power plant units with VVER-1000 reactors for the secondary coolant system equipment made without using copper-containing alloys. Statistical data are presented on conducting ammonia-morpholine and ammonia-ethanolamine water chemistries in new-generation operating power units with VVER-1000 reactors with an increased level of pH. The values of cooling water leaks in turbine condensers the tube system of which is made of stainless steel or titanium alloy are given.

Impact of harvesting and atmospheric pollution on nutrient depletion of eastern US hardwood forests

Treesearch

M.B. Adams; J.A. Burger; A.B. Jenkins; L. Zelazny

2000-01-01

The eastern hardwood forests of the US may be threatened by the changing atmospheric chemistry and by changes in harvesting levels. Many studies have documented accelerated base cation losses with intensive forest harvesting. Acidic deposition can also alter nutrient cycling in these forests. The combination of increased harvesting, shorter rotations, and more...

Explaining the Spatial Variability in Stream Acid Buffering Chemistry and Aquatic Biota in the Neversink River Watershed, Catskill Mountains, New York State

NASA Astrophysics Data System (ADS)

Harpold, A. A.; Walter, M. T.

2009-12-01

The Neversink River Watershed (NRW) originates at the highest point in the Catskill Mountains and is sensitive to changing patterns in acidic deposition, precipitation, and air temperature. Despite reductions in fossil fuel emission since the Clean Air Act, past acidic deposition has accelerated the leaching of cations from the soil and reduced the stores of base cations necessary for buffering stream acidity. The goal of this study was to investigate connections between different watershed ‘features’ and the apparently complex spatial patterns of stream buffering chemistry (specifically, acid neutralizing capacity ANC and Ca concentrations) and aquatic biota (macroinvertebrate and fish populations). The ten nested NRW watersheds (2.0 km^2 to 176.0 km^2) have relatively homogeneous bedrock geology, forested cover, and soil series; therefore, we hypothesized that differing distributions of hydrological flowpaths between the watersheds control the variability in stream buffering chemistry and aquatic biota. However because the flowpath distributions are not directly measurable, this study used step-wise linear regression to develop relationships between watershed ‘features’ and buffering chemistry. The regression results showed that the mean ratio of precipitation to stream runoff (or runoff ratio) from twenty non-winter storm events explained more than 81% of the variability in mean summer ANC and Ca concentrations. The results also suggested that steeper (higher mean slope) more channelized watersheds (larger drainage density) are more susceptible to stream acidity and negative impacts on biota. A simple linear relationship (using no discharge or water chemistry measurements) was able to explain buffering chemistry and aquatic biota populations in 17 additional NRW watersheds (0.3 km^2 to 160.0 km^2), including 60-80% of the variability in macroinvertebrate populations (EPT richness and BAP) and 50-60% of the variability in fish density and species richness. These results have several important implications for understanding the effects of climate change on buffering chemistry and aquatic biota in this well-studied watershed. First, the results demonstrate that geomorphological and hydrogeological ‘features’ control the spatial variability of stream buffering chemistry, suggesting that acidification ‘hot-spots’ could be predicted a priori. Second, the connection between event-scale processes (runoff ratio) and average stream chemistry imply that changing precipitation patterns in the Catskills may have uneven effects on long-term buffering chemistry between ‘flashy’ and ‘damped’ watersheds. Specifically, an increasing trend in precipitation in the last 25 years in the Catskill Mountains makes it difficult to compare base cation recovery across NRW streams, even if the concentrations are normalized by discharge. The results of this study could improve the modeling of base cation recovery in surface waters in other mountainous Northeastern U.S. watersheds with future reductions in acidic deposition and differing climate scenarios.

Modification of heterogeneous chemistry by complex substrate morphology

DOE Office of Scientific and Technical Information (OSTI.GOV)

Henson, B.F.; Buelow, S.J.; Robinson, J.M.

1998-12-31

This is the final report of a one-year, Laboratory Directed Research and Development (LDRD) project at Los Alamos National Laboratory (LANL). Chemistry in many environmental systems is determined at some stage by heterogeneous reaction with a surface. Typically the surface exists as a dispersion or matrix of particulate matter or pores, and a determination of the heterogeneous chemistry of the system must address the extent to which the complexity of the environmental surface affects the reaction rates. Reactions that are of current interest are the series of chlorine nitrate reactions important in polar ozone depletion. The authors have applied surfacemore » spectroscopic techniques developed at LANL to address the chemistry of chlorine nitrate reactions on porous nitric and sulfuric acid ice surfaces as a model study of the measurement of complex, heterogeneous reaction rates. The result of the study is an experimental determination of the surface coverage of one adsorbed reagent and a mechanism of reactivity based on the dependence of this coverage on temperature and vapor pressure. The resulting mechanism allows the first comprehensive modeling of chlorine nitrate reaction probability data from several laboratories.« less

Indirect photopatterning of functionalized organic monolayers via copper-catalyzed "click chemistry"

NASA Astrophysics Data System (ADS)

Williams, Mackenzie G.; Teplyakov, Andrew V.

2018-07-01

Solution-based lithographic surface modification of an organic monolayer on a solid substrate is attained based on selective area photo-reduction of copper (II) to copper (I) to catalyze the azide-alkyne dipolar cycloaddition "click" reaction. X-ray photoelectron spectroscopy is used to confirm patterning, and spectroscopic results are analyzed and supplemented with computational models to confirm the surface chemistry. It is determined that this surface modification approach requires irradiation of the solid substrate with all necessary components present in solution. This method requires only minutes of irradiation to result in spatial and temporal control of the covalent surface functionalization of a monolayer and offers the potential for wavelength tunability that may be desirable in many applications utilizing organic monolayers.

Constitutional Dynamics of Metal-Organic Motifs on a Au(111) Surface.

PubMed

Kong, Huihui; Zhang, Chi; Xie, Lei; Wang, Likun; Xu, Wei

2016-06-13

Constitutional dynamic chemistry (CDC), including both dynamic covalent chemistry and dynamic noncovalent chemistry, relies on reversible formation and breakage of bonds to achieve continuous changes in constitution by reorganization of components. In this regard, CDC is considered to be an efficient and appealing strategy for selective fabrication of surface nanostructures by virtue of dynamic diversity. Although constitutional dynamics of monolayered structures has been recently demonstrated at liquid/solid interfaces, most of molecular reorganization/reaction processes were thought to be irreversible under ultrahigh vacuum (UHV) conditions where CDC is therefore a challenge to be achieved. Here, we have successfully constructed a system that presents constitutional dynamics on a solid surface based on dynamic coordination chemistry, in which selective formation of metal-organic motifs is achieved under UHV conditions. The key to making this reversible switching successful is the molecule-substrate interaction as revealed by DFT calculations. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Ab initio study of perovskite type oxide materials for solid oxide fuel cells

NASA Astrophysics Data System (ADS)

Lee, Yueh-Lin

2011-12-01

Perovskite type oxides form a family of materials of significant interest for cathodes and electrolytes of solid oxide fuel cells (SOFCs). These perovskites not only are active catalysts for surface oxygen reduction (OR) reactions but also allow incorporating the spilt oxygen monomers into their bulk, an unusual and poorly understood catalytic mechanism that couples surface and bulk properties. The OR mechanisms can be influenced strongly by defects in perovskite oxides, composition, and surface defect structures. This thesis work initiates a first step in developing a general strategy based on first-principles calculations for detailed control of oxygen vacancy content, transport rates of surface and bulk oxygen species, and surface/interfacial reaction kinetics. Ab initio density functional theory methods are used to model properties relevant for the OR reactions on SOFC cathodes. Three main research thrusts, which focus on bulk defect chemistry, surface defect structures and surface energetics, and surface catalytic properties, are carried to investigate different level of material chemistry for improved understanding of key physics/factors that govern SOFC cathode OR activity. In the study of bulk defect chemistry, an ab initio based defect model is developed for modeling defect chemistry of LaMnO 3 under SOFC conditions. The model suggests an important role for defect interactions, which are typically excluded in previous defect models. In the study of surface defect structures and surface energetics, it is shown that defect energies change dramatically (1˜2 eV lower) from bulk values near surfaces. Based on the existing bulk defect model with the calculated ab initio surface defect energetics, we predict the (001) MnO 2 surface oxygen vacancy concentration of (La0.9Sr0.1 )MnO3 is about 5˜6 order magnitude higher than that of the bulk under typical SOFC conditions. Finally, for surface catalytic properties, we show that area specific resistance, oxygen exchange rates, and key OR energetics of the SOFC cathode perovskites, can be described by a single descriptor, either the bulk O p-band or the bulk oxygen vacancy formation energy. These simple descriptors will further enable first-principles optimization/design of new SOFC cathodes.

Corrosion performance of alternative steam generator materials and designs. Volume 3. Posttest examination of a freshwater-faulted alternative materials model steam generator. Final report. [PWR

DOE Office of Scientific and Technical Information (OSTI.GOV)

Krupowicz, J.J.; Scott, D.B.; Rentler, R.M.

Corrosion results obtained from the post-test non-destructive and destructive examinations of an alternative materials model steam generator are described in this final report. The model operated under representative thermal and hydraulic and accelerated (high fresh water contaminant concentration) steam generator secondary water chemistry conditions. Total exposure consisted of 114 steaming days under all volatile treatment (AVT) chemistry conditions followed by 358 fault steaming days at a 40 ppM sulfate concentration in the secondary bulk water. Various support plate and lattice strip support designs incorporated Types 347, 405, 409 and SCR-3 stainless steels; Alloys 600 and 690; and carbon steel. Heatmore » transfer tube materials included Alloy 600 in various heat treated conditions, Alloy 690, and Alloy 800. All tubing materials in this test exhibited significant general corrosion beneath thick surface deposits.« less

The challenges of sequencing by synthesis.

PubMed

Fuller, Carl W; Middendorf, Lyle R; Benner, Steven A; Church, George M; Harris, Timothy; Huang, Xiaohua; Jovanovich, Stevan B; Nelson, John R; Schloss, Jeffery A; Schwartz, David C; Vezenov, Dmitri V

2009-11-01

DNA sequencing-by-synthesis (SBS) technology, using a polymerase or ligase enzyme as its core biochemistry, has already been incorporated in several second-generation DNA sequencing systems with significant performance. Notwithstanding the substantial success of these SBS platforms, challenges continue to limit the ability to reduce the cost of sequencing a human genome to $100,000 or less. Achieving dramatically reduced cost with enhanced throughput and quality will require the seamless integration of scientific and technological effort across disciplines within biochemistry, chemistry, physics and engineering. The challenges include sample preparation, surface chemistry, fluorescent labels, optimizing the enzyme-substrate system, optics, instrumentation, understanding tradeoffs of throughput versus accuracy, and read-length/phasing limitations. By framing these challenges in a manner accessible to a broad community of scientists and engineers, we hope to solicit input from the broader research community on means of accelerating the advancement of genome sequencing technology.

Visual Identification of Light-Driven Breakage of the Silver-Dithiocarbamate Bond by Single Plasmonic Nanoprobes

PubMed Central

Gao, Peng Fei; Yuan, Bin Fang; Gao, Ming Xuan; Li, Rong Sheng; Ma, Jun; Zou, Hong Yan; Li, Yuan Fang; Li, Ming; Huang, Cheng Zhi

2015-01-01

Insight into the nature of metal-sulfur bond, a meaningful one in life science, interface chemistry and organometallic chemistry, is interesting but challenging. By utilizing the localized surface plasmon resonance properties of silver nanoparticles, herein we visually identified the photosensitivity of silver-dithiocarbamate (Ag-DTC) bond by using dark field microscopic imaging (iDFM) technique at single nanoparticle level. It was found that the breakage of Ag-DTC bond could be accelerated effectively by light irradiation, followed by a pH-dependent horizontal or vertical degradation of the DTC molecules, in which an indispensable preoxidation process of the silver was at first disclosed. These findings suggest a visualization strategy at single plasmonic nanoparticle level which can be excellently applied to explore new stimulus-triggered reactions, and might also open a new way to understand traditional organic reaction mechanisms. PMID:26493773

Aromatic, Alphatic, Enigmatic: The Chemistry of Titan

NASA Astrophysics Data System (ADS)

Horst, Sarah

2017-10-01

The extraordinary complexity of Titan’s atmospheric chemistry far surpasses that of any other solar system atmosphere. With its thick N2 atmosphere and stable bodies of liquid on its surface, Titan also possesses many physical processes that are similar to those that occur on Earth. The connection between Titan’s surface and atmosphere is unique in our solar system; atmospheric chemistry produces materials that are deposited on the surface and subsequently altered by surface-atmosphere interactions such as aeolian and fluvial processes resulting in the formation of extensive dune fields and expansive lakes and seas. Titan’s atmosphere is favorable for organic haze formation, which combined with the presence of some oxygen-bearing molecules indicates that Titan’s atmosphere may produce molecules of prebiotic interest. The combination of organics and liquid, in the form of water in a subsurface ocean and methane/ethane in the surface lakes and seas, means that Titan may be the ideal place in the solar system to test ideas about habitability, prebiotic chemistry, and the ubiquity and diversity of life in the universe. I will review our current understanding of chemistry on Titan forged from the powerful combination of Earth-based observations, remote sensing and in situ spacecraft measurements, laboratory experiments, and models. I will conclude with some of the questions that remain after Cassini-Huygens.

Laboratory Activity Worksheet to Train High Order Thinking Skill of Student on Surface Chemistry Lecture

NASA Astrophysics Data System (ADS)

Yonata, B.; Nasrudin, H.

2018-01-01

A worksheet has to be a set with activity which is help students to arrange their own experiments. For this reason, this research is focused on how to train students’ higher order thinking skills in laboratory activity by developing laboratory activity worksheet on surface chemistry lecture. To ensure that the laboratory activity worksheet already contains aspects of the higher order thinking skill, it requires theoretical and empirical validation. From the data analysis results, it shows that the developed worksheet worth to use. The worksheet is worthy of theoretical and empirical feasibility. This conclusion is based on the findings: 1) Assessment from the validators about the theoretical feasibility aspects in the category is very feasible with an assessment range of 95.24% to 97.92%. 2) students’ higher thinking skill from N Gain values ranges from 0.50 (enough) to 1.00 (high) so it can be concluded that the laboratory activity worksheet on surface chemistry lecture is empirical in terms of worth. The empirical feasibility is supported by the responses of the students in very reasonable categories. It is expected that the laboratory activity worksheet on surface chemistry lecture can train students’ high order thinking skills for students who program surface chemistry lecture.

Generating strain signals under consideration of road surface profiles

NASA Astrophysics Data System (ADS)

Putra, T. E.; Abdullah, S.; Schramm, D.; Nuawi, M. Z.; Bruckmann, T.

2015-08-01

The current study aimed to develop the mechanism for generating strain signal utilising computer-based simulation. The strain data, caused by the acceleration, were undertaken from a fatigue data acquisition involving car movements. Using a mathematical model, the measured strain signals yielded to acceleration data used to describe the bumpiness of road surfaces. The acceleration signals were considered as an external disturbance on generating strain signals. Based on this comparison, both the actual and simulated strain data have similar pattern. The results are expected to provide new knowledge to generate a strain signal via a simulation.

Why surface chemistry matters for QD–QD resonance energy transfer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hoffman, Jacob B.; Alam, Rabeka; Kamat, Prashant V.

Resonance energy transfer (RET) has been shown to occur in films of semiconductor quantum dots (QDs) with variation in QD composition and size. When coupled with charge carrier transfer, RET could provide a complementary strategy for light harvesting in QD based solid state photovoltaic devices. Due to a direct dependence on the optical properties of the donor and acceptor, QD surface chemistry plays a drastic role in determining the efficiency of RET. Here, the impact of QD surface chemistry on RET in QD films was investigated using a pair of different sized CdSe QDs spin-cast onto a glass substrate. Themore » effects of QD surface passivation on RET were studied by removing surface ligands through QD washing and adding an insulating ZnS shell. In addition, QD films were subjected to solid state ligand exchanges with thiolated ligands in order to mimic a layer-by-layer deposition method commonly used in the construction of QD photovoltaics. These solid state ligand exchanges exhibit drastic quenching of RET in the films. As a result, these experiments highlight the importance of understanding surface chemistry when designing photovoltaics that utilize RET.« less

Why surface chemistry matters for QD–QD resonance energy transfer

DOE PAGES

Hoffman, Jacob B.; Alam, Rabeka; Kamat, Prashant V.

2017-01-12

Resonance energy transfer (RET) has been shown to occur in films of semiconductor quantum dots (QDs) with variation in QD composition and size. When coupled with charge carrier transfer, RET could provide a complementary strategy for light harvesting in QD based solid state photovoltaic devices. Due to a direct dependence on the optical properties of the donor and acceptor, QD surface chemistry plays a drastic role in determining the efficiency of RET. Here, the impact of QD surface chemistry on RET in QD films was investigated using a pair of different sized CdSe QDs spin-cast onto a glass substrate. Themore » effects of QD surface passivation on RET were studied by removing surface ligands through QD washing and adding an insulating ZnS shell. In addition, QD films were subjected to solid state ligand exchanges with thiolated ligands in order to mimic a layer-by-layer deposition method commonly used in the construction of QD photovoltaics. These solid state ligand exchanges exhibit drastic quenching of RET in the films. As a result, these experiments highlight the importance of understanding surface chemistry when designing photovoltaics that utilize RET.« less

Managing oils pumplessly on open surfaces

NASA Astrophysics Data System (ADS)

Ghosh, Aritra; Morrissette, Jared; Mates, Joseph; Megaridis, Constantine

2017-11-01

Passive management of low-surface-tension liquids (e.g. oils) can be achieved by tuning curvature of liquid volumes (Laplace pressure) on juxtaposed oleophobic/oleophilic domains. Recent advancements in material chemistry in repelling low-surface-tension liquids has enabled researchers to fabricate surfaces and transport oils without the aid of gravity or using a pump. Liquid transport on such surfaces harnesses the force arising from the spatial contrast of surface energy on the substrate, providing rapid fluid actuation. In this work, we demonstrate and study the liquid transport dynamics (velocity, acceleration) in open air for several oils of interest (Jet A, hexadecane, mineral oil) with varying surface tension and viscosity. High-speed image analysis of the motion of the bulk liquid is performed using a droplet-shape tracking algorithm; dominant forces are identified and model predictions are compared with experimental data. Experimental and analytical tools offer new insight on a problem that is relevant to open-surface passive oil transport devices like propellant management devices, oil tankers and many more. Office of Naval Research, Air Force Research Laboratory.

Unsupervised data mining in nanoscale x-ray spectro-microscopic study of NdFeB magnet

DOE Office of Scientific and Technical Information (OSTI.GOV)

Duan, Xiaoyue; Yang, Feifei; Antono, Erin

Novel developments in X-ray based spectro-microscopic characterization techniques have increased the rate of acquisition of spatially resolved spectroscopic data by several orders of magnitude over what was possible a few years ago. This accelerated data acquisition, with high spatial resolution at nanoscale and sensitivity to subtle differences in chemistry and atomic structure, provides a unique opportunity to investigate hierarchically complex and structurally heterogeneous systems found in functional devices and materials systems. However, handling and analyzing the large volume data generated poses significant challenges. Here we apply an unsupervised data-mining algorithm known as DBSCAN to study a rare-earth element based permanentmore » magnet material, Nd 2Fe 14B. We are able to reduce a large spectro-microscopic dataset of over 300,000 spectra to 3, preserving much of the underlying information. Scientists can easily and quickly analyze in detail three characteristic spectra. Our approach can rapidly provide a concise representation of a large and complex dataset to materials scientists and chemists. For instance, it shows that the surface of common Nd 2Fe 14B magnet is chemically and structurally very different from the bulk, suggesting a possible surface alteration effect possibly due to the corrosion, which could affect the material’s overall properties.« less

Unsupervised data mining in nanoscale x-ray spectro-microscopic study of NdFeB magnet

DOE PAGES

Duan, Xiaoyue; Yang, Feifei; Antono, Erin; ...

2016-09-29

Novel developments in X-ray based spectro-microscopic characterization techniques have increased the rate of acquisition of spatially resolved spectroscopic data by several orders of magnitude over what was possible a few years ago. This accelerated data acquisition, with high spatial resolution at nanoscale and sensitivity to subtle differences in chemistry and atomic structure, provides a unique opportunity to investigate hierarchically complex and structurally heterogeneous systems found in functional devices and materials systems. However, handling and analyzing the large volume data generated poses significant challenges. Here we apply an unsupervised data-mining algorithm known as DBSCAN to study a rare-earth element based permanentmore » magnet material, Nd 2Fe 14B. We are able to reduce a large spectro-microscopic dataset of over 300,000 spectra to 3, preserving much of the underlying information. Scientists can easily and quickly analyze in detail three characteristic spectra. Our approach can rapidly provide a concise representation of a large and complex dataset to materials scientists and chemists. For instance, it shows that the surface of common Nd 2Fe 14B magnet is chemically and structurally very different from the bulk, suggesting a possible surface alteration effect possibly due to the corrosion, which could affect the material’s overall properties.« less

Brookhaven highlights, October 1978-September 1979. [October 1978 to September 1979

DOE Office of Scientific and Technical Information (OSTI.GOV)

Not Available

1979-01-01

These highlights present an overview of the major research and development achievements at Brookhaven National Laboratory from October 1978 to September 1979. Specific areas covered include: accelerator and high energy physics programs; high energy physics research; the AGS and improvements to the AGS; neutral beam development; heavy ion fusion; superconducting power cables; ISABELLE storage rings; the BNL Tandem accelerator; heavy ion experiments at the Tandem; the High Flux Beam Reactor; medium energy physics; nuclear theory; atomic and applied physics; solid state physics; neutron scattering studies; x-ray scattering studies; solid state theory; defects and disorder in solids; surface physics; the Nationalmore » Synchrotron Light Source ; Chemistry Department; Biology Department; Medical Department; energy sciences; environmental sciences; energy technology programs; National Center for Analysis of Energy Systems; advanced reactor systems; nuclear safety; National Nuclear Data Center; nuclear materials safeguards; Applied Mathematics Department; and support activities. (GHT)« less

Dragonfly: In Situ Exploration of Titan's Organic Chemistry and Habitability

NASA Astrophysics Data System (ADS)

Turtle, E. P.; Barnes, J. W.; Trainer, M. G.; Lorenz, R. D.

2017-12-01

Titan's abundant complex carbon-rich chemistry, interior ocean, and past presence of liquid water on the surface make it an ideal destination to study prebiotic chemical processes and document the habitability of an extraterrestrial environment. Titan exploration is a high science priority due to the level of organic synthesis that it supports. Moreover, opportunities for organics to have interacted with liquid water at the surface (e.g., in impact melt sheets) increase the potential for chemical processes to progress further, providing an unparalleled opportunity to investigate prebiotic chemistry, as well as to search for signatures of potential water-based or even hydrocarbon-based life. The diversity of Titan's surface materials and environments drives the scientific need to be able to sample a variety of locations, thus mobility is key for in situ measurements. Titan's atmosphere is 4 times denser than Earth's reducing the wing/rotor area required to generate a given amount of lift, and the low gravity reduces the required magnitude of lift, making heavier-than-air mobility highly efficient. Dragonfly is a rotorcraft lander mission proposed to NASA's New Frontiers Program to take advantage of Titan's unique natural laboratory to understand how far chemistry can progress in environments that provide key ingredients for life. Measuring the compositions of materials in different environments will reveal how far organic chemistry has progressed. Surface material can be sampled into a mass spectrometer to identify the chemical components available and processes at work to produce biologically relevant compounds. Bulk elemental surface composition can be determined by a neutron-activated gamma-ray spectrometer. Meteorology measurements can characterize Titan's atmosphere and diurnal and spatial variations therein. Geologic features can be characterized via remote-sensing observations, which also provide context for samples. Seismic sensing can probe subsurface structure and activity. In addition to surface investigations, Dragonfly can perform measurements during flight, including atmospheric profiles and aerial observations of surface geology, which also provide sampling context and scouting for landing sites.

Particle self-assembly at ionic liquid-based interfaces.

PubMed

Frost, Denzil S; Nofen, Elizabeth M; Dai, Lenore L

2014-04-01

This review presents an overview of the nature of ionic liquid (IL)-based interfaces and self-assembled particle morphologies of IL-in-water, oil- and water-in-IL, and novel IL-in-IL Pickering emulsions with emphasis on their unique phenomena, by means of experimental and computational studies. In IL-in-water Pickering emulsions, particles formed monolayers at ionic liquid-water interfaces and were close-packed on fully covered emulsion droplets or aggregated on partially covered droplets. Interestingly, other than equilibrating at the ionic liquid-water interfaces, microparticles with certain surface chemistries were extracted into the ionic liquid phase with a high efficiency. These experimental findings were supported by potential of mean force calculations, which showed large energy drops as hydrophobic particles crossed the interface into the IL phase. In the oil- and water-in-IL Pickering emulsions, microparticles with acidic surface chemistries formed monolayer bridges between the internal phase droplets rather than residing at the oil/water-ionic liquid interfaces, a significant deviation from traditional Pickering emulsion morphology. Molecular dynamics simulations revealed aspects of the mechanism behind this bridging phenomenon, including the role of the droplet phase, surface chemistry, and inter-particle film. Novel IL-in-IL Pickering emulsions exhibited an array of self-assembled morphologies including the previously observed particle absorption and bridging phenomena. The appearance of these morphologies depended on the particle surface chemistry as well as the ILs used. The incorporation of particle self-assembly with ionic liquid science allows for new applications at the intersection of these two fields, and have the potential to be numerous due to the tunability of the ionic liquids and particles incorporated, as well as the particle morphology by combining certain groups of particle surface chemistry, IL type (protic or aprotic), and whether oil or water is incorporated. © 2013.

Protecting High Energy Barriers: A New Equation to Regulate Boost Energy in Accelerated Molecular Dynamics Simulations.

PubMed

Sinko, William; de Oliveira, César Augusto F; Pierce, Levi C T; McCammon, J Andrew

2012-01-10

Molecular dynamics (MD) is one of the most common tools in computational chemistry. Recently, our group has employed accelerated molecular dynamics (aMD) to improve the conformational sampling over conventional molecular dynamics techniques. In the original aMD implementation, sampling is greatly improved by raising energy wells below a predefined energy level. Recently, our group presented an alternative aMD implementation where simulations are accelerated by lowering energy barriers of the potential energy surface. When coupled with thermodynamic integration simulations, this implementation showed very promising results. However, when applied to large systems, such as proteins, the simulation tends to be biased to high energy regions of the potential landscape. The reason for this behavior lies in the boost equation used since the highest energy barriers are dramatically more affected than the lower ones. To address this issue, in this work, we present a new boost equation that prevents oversampling of unfavorable high energy conformational states. The new boost potential provides not only better recovery of statistics throughout the simulation but also enhanced sampling of statistically relevant regions in explicit solvent MD simulations.

Acceleration of Binding Site Comparisons by Graph Partitioning.

PubMed

Krotzky, Timo; Klebe, Gerhard

2015-08-01

The comparison of protein binding sites is a prominent task in computational chemistry and has been studied in many different ways. For the automatic detection and comparison of putative binding cavities the Cavbase system has been developed which uses a coarse-grained set of pseudocenters to represent the physicochemical properties of a binding site and employs a graph-based procedure to calculate similarities between two binding sites. However, the comparison of two graphs is computationally quite demanding which makes large-scale studies such as the rapid screening of entire databases hardly feasible. In a recent work, we proposed the method Local Cliques (LC) for the efficient comparison of Cavbase binding sites. It employs a clique heuristic to detect the maximum common subgraph of two binding sites and an extended graph model to additionally compare the shape of individual surface patches. In this study, we present an alternative to further accelerate the LC method by partitioning the binding-site graphs into disjoint components prior to their comparisons. The pseudocenter sets are split with regard to their assigned phyiscochemical type, which leads to seven much smaller graphs than the original one. Applying this approach on the same test scenarios as in the former comprehensive way results in a significant speed-up without sacrificing accuracy. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Superhydrophobicity enhancement through substrate flexibility

NASA Astrophysics Data System (ADS)

Vasileiou, Thomas; Gerber, Julia; Prautzsch, Jana; Schutzius, Thomas; Poulikakos, Dimos

2017-11-01

Inspired by manifestations in nature, micro/nanoengineering superhydrophobic surfaces has been the focus of much work. Generally, hydrophobicity is increased through the combined effects of surface texturing and chemistry; being durable, rigid substrate materials are the norm. However, many natural and technical materials are flexible, and the resulting effect on hydrophobicity has been largely unexplored. Here, we show that the rational tuning of flexibility can work collaboratively with the surface micro/nanotexture to enhance liquid repellency performance, defined by impalement and breakup resistance, contact time reduction, and restitution coefficient increase. Reduction in substrate stiffness and areal density imparts immediate acceleration and intrinsic responsiveness to impacting droplets, mitigating the collision and lowering the impalement probability by 60 % without the need for active actuation. We demonstrate the above discoveries with materials ranging from thin steel or polymer sheets to butterfly wings. Partial support of the Swiss National Science Foundation under Grant 162565 and the European Research Council under Advanced Grant 669908 (INTICE) is acknowledged.

Superhydrophobicity enhancement through substrate flexibility.

PubMed

Vasileiou, Thomas; Gerber, Julia; Prautzsch, Jana; Schutzius, Thomas M; Poulikakos, Dimos

2016-11-22

Inspired by manifestations in nature, microengineering and nanoengineering of synthetic materials to achieve superhydrophobicity has been the focus of much work. Generally, hydrophobicity is enhanced through the combined effects of surface texturing and chemistry; being durable, rigid materials are the norm. However, many natural and technical surfaces are flexible, and the resulting effect on hydrophobicity has been largely ignored. Here, we show that the rational tuning of flexibility can work synergistically with the surface microtexture or nanotexture to enhance liquid repellency performance, characterized by impalement and breakup resistance, contact time reduction, and restitution coefficient increase. Reduction in substrate areal density and stiffness imparts immediate acceleration and intrinsic responsiveness to impacting droplets (∼350 × g), mitigating the collision and lowering the impalement probability by ∼60% without the need for active actuation. Furthermore, we exemplify the above discoveries with materials ranging from man-made (thin steel or polymer sheets) to nature-made (butterfly wings).

Modulation of terrestrial ion escape flux composition /by low-altitude acceleration and charge exchange chemistry/

NASA Technical Reports Server (NTRS)

Moore, T. E.

1980-01-01

Motivated by recent observations of highly variable hot plasma composition in the magnetosphere, control of the ionospheric escape flux composition by low-altitude particle dynamics and ion chemistry has been investigated for an e(-), H(+), O(+) ionosphere. It is found that the fraction of the steady state escape flux which is O(+) can be controlled very sensitively by the occurrence of parallel or transverse ion acceleration at altitudes below the altitude where the neutral oxygen density falls rapidly below the neutral hydrogen density and the ionospheric source of O(+) tends to be rapidly converted by charge exchange to H(+). The acceleration is required both to overcome the gravitational confinement of O(+) and to violate charge exchange equilibrium so that the neutral hydrogen atmosphere appears 'optically' thin to escaping O(+). Constraints are placed on the acceleration processes, and it is shown that O(+) escape is facilitated by observed ionospheric responses to magnetic activity.

Unprecedented quality factors at accelerating gradients up to 45 MVm -1 in niobium superconducting resonators via low temperature nitrogen infusion

DOE Office of Scientific and Technical Information (OSTI.GOV)

Grassellino, A.; Romanenko, A.; Trenikhina, Y.

We report the finding of new surface treatments that permit to manipulate the niobium resonator nitrogen content in the first few nanometers in a controlled way, and the resonator fundamental Mattis-Bardeen surface resistance and residual resistance accordingly. In particular, we find surface infusion conditions that systematically a) increase the quality factor of these 1.3 GHz superconducting radio frequency (SRF) bulk niobium resonators, up to very high gradients; b) increase the achievable accelerating gradient of the cavity compared to its own baseline with state-of-the-art surface processing. Cavities subject to the new surface process have larger than two times the state ofmore » the art Q at 2K for accelerating fields > 35 MV/m. Moreover, very high accelerating gradients ~ 45 MV/m are repeatedly reached, which correspond to peak magnetic surface fields of 190 mT, among the highest measured for bulk niobium cavities. These findings open the opportunity to tailor the surface impurity content distribution to maximize performance in Q and gradients, and have therefore very important implications on future performance and cost of SRF based accelerators. They also help deepen the understanding of the physics of the RF niobium cavity surface.« less

Unprecedented quality factors at accelerating gradients up to 45 MVm-1 in niobium superconducting resonators via low temperature nitrogen infusion

NASA Astrophysics Data System (ADS)

Grassellino, A.; Romanenko, A.; Trenikhina, Y.; Checchin, M.; Martinello, M.; Melnychuk, O. S.; Chandrasekaran, S.; Sergatskov, D. A.; Posen, S.; Crawford, A. C.; Aderhold, S.; Bice, D.

2017-09-01

We report the finding of new surface treatments that permits one to manipulate the niobium resonator nitrogen content in the first few nanometers in a controlled way, and the resonator fundamental Mattis-Bardeen surface resistance and residual resistance accordingly. In particular, we find surface ‘infusion’ conditions that systematically (a) increase the quality factor of these 1.3 GHz superconducting radio frequency (SRF) bulk niobium resonators, up to very high gradients; (b) increase the achievable accelerating gradient of the cavity compared to its own baseline with state-of-the-art surface processing. Cavities subject to the new surface process have more than two times the state-of-the-art Q at 2 K for accelerating fields >35 MVm-1. Moreover, very high accelerating gradients ˜45 MVm-1 are repeatedly reached, which correspond to peak magnetic surface fields of 190 mT, among the highest measured for bulk niobium cavities. These findings open the opportunity to tailor the surface impurity content distribution to maximize performance in Q and gradients, and have therefore very important implications on future performance and cost of SRF based accelerators. They also help deepen the understanding of the physics of the RF niobium cavity surface.

One-pot reaction for the preparation of biofunctionalized self-assembled monolayers on gold surfaces

NASA Astrophysics Data System (ADS)

Raigoza, Annette F.; Fies, Whitney; Lim, Amber; Onyirioha, Kristeen; Webb, Lauren J.

2017-02-01

The Huisgen cycloaddition reaction (;click; chemistry) has been used extensively to functionalize surfaces with macromolecules in a straightforward manner. We have previously developed a procedure using the copper(I)-catalyzed click reaction to tether synthetic α-helical peptides carrying two alkyne groups to a well-ordered azide-terminated alkanethiol self-assembled monolayer (SAM) on a Au(111) surface. While convenient, click-based strategies potentially pose significant problems from reagents, solvents, and reaction temperatures that may irreversibly damage some molecules or substrates. Tuning click chemistry conditions would allow individual optimization of reaction conditions for a wide variety of biomolecules and substrate materials. Here, we explore the utility of simultaneous SAM formation and peptide-attachment chemistry in a one-pot reaction. We demonstrate that a formerly multistep reaction can be successfully carried out concurrently by mixing azide-terminated alkanethiols, CuCl, and a propargylglycine-containing peptide over a bare gold surface in ethanol and reacting at 70 °C. X-ray photoelectron spectroscopy (XPS), surface infrared spectroscopy, surface circular dichroic (CD) spectroscopy, and scanning tunneling microscopy (STM) were used to determine that this one-pot reaction strategy resulted in a high density of surface-bound α-helices without aggregation. This work demonstrates the simplicity and versatility of a SAM-plus-click chemistry strategy for functionalizing Au surfaces with structured biomolecules.

Selectivity in analytical chemistry: two interpretations for univariate methods.

PubMed

Dorkó, Zsanett; Verbić, Tatjana; Horvai, George

2015-01-01

Selectivity is extremely important in analytical chemistry but its definition is elusive despite continued efforts by professional organizations and individual scientists. This paper shows that the existing selectivity concepts for univariate analytical methods broadly fall in two classes: selectivity concepts based on measurement error and concepts based on response surfaces (the response surface being the 3D plot of the univariate signal as a function of analyte and interferent concentration, respectively). The strengths and weaknesses of the different definitions are analyzed and contradictions between them unveiled. The error based selectivity is very general and very safe but its application to a range of samples (as opposed to a single sample) requires the knowledge of some constraint about the possible sample compositions. The selectivity concepts based on the response surface are easily applied to linear response surfaces but may lead to difficulties and counterintuitive results when applied to nonlinear response surfaces. A particular advantage of this class of selectivity is that with linear response surfaces it can provide a concentration independent measure of selectivity. In contrast, the error based selectivity concept allows only yes/no type decision about selectivity. Copyright © 2014 Elsevier B.V. All rights reserved.

Employing OpenCL to Accelerate Ab Initio Calculations on Graphics Processing Units.

PubMed

Kussmann, Jörg; Ochsenfeld, Christian

2017-06-13

We present an extension of our graphics processing units (GPU)-accelerated quantum chemistry package to employ OpenCL compute kernels, which can be executed on a wide range of computing devices like CPUs, Intel Xeon Phi, and AMD GPUs. Here, we focus on the use of AMD GPUs and discuss differences as compared to CUDA-based calculations on NVIDIA GPUs. First illustrative timings are presented for hybrid density functional theory calculations using serial as well as parallel compute environments. The results show that AMD GPUs are as fast or faster than comparable NVIDIA GPUs and provide a viable alternative for quantum chemical applications.

Dragonfly: Exploring Titan's Surface with a New Frontiers Relocatable Lander

NASA Astrophysics Data System (ADS)

Barnes, Jason W.; Turtle, Elizabeth P.; Trainer, Melissa G.; Lorenz, Ralph

2017-10-01

We proposed to the NASA New Frontiers 4 mission call a lander to assess Titan's prebiotic chemistry, evaluate its habitability, and search for biosignatures on its surface. Titan as an Ocean World is ideal for the study of prebiotic chemical processes and the habitability of an extraterrestrial environment due to its abundant complex carbon-rich chemistry and because both liquid water and liquid hydrocarbons can occur on its surface. Transient liquid water surface environments can be created by both impacts and cryovolcanic processes. In both cases, the water could mix with surface organics to form a primordial soup. The mission would sample both organic sediments and water ice to measure surface composition, achieving surface mobility by using rotors to take off, fly, and land at new sites. The Dragonfly rotorcraft lander can thus convey a single capable instrument suite to multiple locations providing the capability to explore diverse locations 10s to 100s of kilometers apart to characterize the habitability of Titan's environment, investigate how far prebiotic chemistry has progressed, and search for chemical signatures indicative of water- and/or hydrocarbon-based life.

Aryl Diazonium Chemistry for the Surface Functionalization of Glassy Biosensors.

PubMed

Zheng, Wei; van den Hurk, Remko; Cao, Yong; Du, Rongbing; Sun, Xuejun; Wang, Yiyu; McDermott, Mark T; Evoy, Stephane

2016-03-14

Nanostring resonator and fiber-optics-based biosensors are of interest as they offer high sensitivity, real-time measurements and the ability to integrate with electronics. However, these devices are somewhat impaired by issues related to surface modification. Both nanostring resonators and photonic sensors employ glassy materials, which are incompatible with electrochemistry. A surface chemistry approach providing strong and stable adhesion to glassy surfaces is thus required. In this work, a diazonium salt induced aryl film grafting process is employed to modify a novel SiCN glassy material. Sandwich rabbit IgG binding assays are performed on the diazonium treated SiCN surfaces. Fluorescently labelled anti-rabbit IgG and anti-rabbit IgG conjugated gold nanoparticles were used as markers to demonstrate the absorption of anti-rabbit IgG and therefore verify the successful grafting of the aryl film. The results of the experiments support the effectiveness of diazonium chemistry for the surface functionalization of SiCN surfaces. This method is applicable to other types of glassy materials and potentially can be expanded to various nanomechanical and optical biosensors.

Aryl Diazonium Chemistry for the Surface Functionalization of Glassy Biosensors

PubMed Central

Zheng, Wei; van den Hurk, Remko; Cao, Yong; Du, Rongbing; Sun, Xuejun; Wang, Yiyu; McDermott, Mark T.; Evoy, Stephane

2016-01-01

Nanostring resonator and fiber-optics-based biosensors are of interest as they offer high sensitivity, real-time measurements and the ability to integrate with electronics. However, these devices are somewhat impaired by issues related to surface modification. Both nanostring resonators and photonic sensors employ glassy materials, which are incompatible with electrochemistry. A surface chemistry approach providing strong and stable adhesion to glassy surfaces is thus required. In this work, a diazonium salt induced aryl film grafting process is employed to modify a novel SiCN glassy material. Sandwich rabbit IgG binding assays are performed on the diazonium treated SiCN surfaces. Fluorescently labelled anti-rabbit IgG and anti-rabbit IgG conjugated gold nanoparticles were used as markers to demonstrate the absorption of anti-rabbit IgG and therefore verify the successful grafting of the aryl film. The results of the experiments support the effectiveness of diazonium chemistry for the surface functionalization of SiCN surfaces. This method is applicable to other types of glassy materials and potentially can be expanded to various nanomechanical and optical biosensors. PMID:26985910

Surveys of research in the Chemistry Division, Argonne National Laboratory

DOE Office of Scientific and Technical Information (OSTI.GOV)

Grazis, B.M.

1992-01-01

Research reports are presented on reactive intermediates in condensed phase (radiation chemistry, photochemistry), electron transfer and energy conversion, photosynthesis and solar energy conversion, metal cluster chemistry, chemical dynamics in gas phase, photoionization-photoelectrons, characterization and reactivity of coal and coal macerals, premium coal sample program, chemical separations, heavy elements coordination chemistry, heavy elements photophysics/photochemistry, f-electron interactions, radiation chemistry of high-level wastes (gas generation in waste tanks), ultrafast molecular electronic devices, and nuclear medicine. Separate abstracts have been prepared. Accelerator activites and computer system/network services are also reported.

Surveys of research in the Chemistry Division, Argonne National Laboratory

DOE Office of Scientific and Technical Information (OSTI.GOV)

Grazis, B.M.

1992-11-01

Research reports are presented on reactive intermediates in condensed phase (radiation chemistry, photochemistry), electron transfer and energy conversion, photosynthesis and solar energy conversion, metal cluster chemistry, chemical dynamics in gas phase, photoionization-photoelectrons, characterization and reactivity of coal and coal macerals, premium coal sample program, chemical separations, heavy elements coordination chemistry, heavy elements photophysics/photochemistry, f-electron interactions, radiation chemistry of high-level wastes (gas generation in waste tanks), ultrafast molecular electronic devices, and nuclear medicine. Separate abstracts have been prepared. Accelerator activites and computer system/network services are also reported.

Design, development and applications of novel techniques for studying surface mechanical properties

NASA Technical Reports Server (NTRS)

Miyoshi, Kazuhisa

1989-01-01

Research is reviewed for the adhesion, friction, and micromechanical properties of materials and examples of the results presented. The ceramic and metallic materials studied include silicon carbide, aluminum oxide, and iron-base amorphous alloys. The design and operation of a torsion balance adapted for study of adhesion from the Cavendish balance are discussed first. The pull-off force (adhesion) and shear force (friction) required to break the interfacial junctions between contacting surfaces of the materials were examined at various temperatures in a vacuum. The surface chemistry of the materials was analyzed by X-ray photoelectron spectroscopy. Properties and environmental conditions of the surface regions which affect adhesion and friction-such as surface segregation, composition, crystal structure, surface chemistry, and temperature were also studied.

Transport of oxidized multi-walled carbon nanotubes through silica based porous media: influences of aquatic chemistry, surface chemistry, and natural organic matter.

PubMed

Yang, Jin; Bitter, Julie L; Smith, Billy A; Fairbrother, D Howard; Ball, William P

2013-12-17

This paper provides results from studies of the transport of oxidized multi-walled carbon nanotubes (O-MWCNTs) of varying surface oxygen concentrations under a range of aquatic conditions and through uniform silica glass bead media. In the presence of Na(+), the required ionic strength (IS) for maximum particle attachment efficiency (i.e., the critical deposition concentration, or CDC) increased as the surface oxygen concentration of the O-MWCNTs or pH increased, following qualitative tenets of theories based on electrostatic interactions. In the presence of Ca(2+), CDC values were lower than those with Na(+) present, but were no longer sensitive to surface oxygen content, suggesting that Ca(2+) impacts the interactions between O-MWCNTs and glass beads by mechanisms other than electrostatic alone. The presence of Suwannee River natural organic matter (SRNOM) decreased the attachment efficiency of O-MWCNTs in the presence of either Na(+) or Ca(2+), but with more pronounced effects when Na(+) was present. Nevertheless, low concentrations of SRNOM (<4 mg/L of dissolved organic carbon) were sufficient to mobilize all O-MWCNTs studied at CaCl2 concentrations as high as 10 mM. Overall, this study reveals that NOM content, pH, and cation type show more importance than surface chemistry in affecting O-MWCNTs deposition during transport through silica-based porous media.

ADVANCES IN GREEN CHEMISTRY: CHEMICAL SYNTHESES USING MICROWAVE IRRADIATION, ISBN 81-901238-5-8

EPA Science Inventory

16. Abstract Advances in Green Chemistry: Chemical Syntheses Using Microwave Irradiation
Microwave-accelerated chemical syntheses in solvents as well as under solvent-free conditions have witnessed an explosive growth. The technique has found widespread application predomi...

Surface modification of pitch-based spherical activated carbon by CVD of NH 3 to improve its adsorption to uric acid

NASA Astrophysics Data System (ADS)

Liu, Chaojun; Liang, Xiaoyi; Liu, Xiaojun; Wang, Qin; Zhan, Liang; Zhang, Rui; Qiao, Wenming; Ling, Licheng

2008-08-01

Surface chemistry of pitch-based spherical activated carbon (PSAC) was modified by chemical vapor deposition of NH 3 (NH 3-CVD) to improve the adsorption properties of uric acid. The texture and surface chemistry of PSAC were studied by N 2 adsorption, pH PZC (point of zero charge), acid-base titration and X-ray photoelectron spectroscopy (XPS). NH 3-CVD has a limited effect on carbon textural characteristics but it significantly changed the surface chemical properties, resulting in positive effects on uric acid adsorption. After modification by NH 3-CVD, large numbers of nitrogen-containing groups (especially valley-N and center-N) are introduced on the surface of PSAC, which is responsible for the increase of pH PZC, surface basicity and uric acid adsorption capacity. Pseudo-second-order kinetic model can be used to describe the dynamic adsorption of uric acid on PSAC, and the thermodynamic parameters show that the adsorption of uric acid on PSAC is spontaneous, endothermic and irreversible process in nature.

The tunable wettability in multistimuli-responsive smart graphene surfaces

NASA Astrophysics Data System (ADS)

Wan, Shanhong; Pu, Jibin; Zhang, Xiaoqian; Wang, Liping; Xue, Qunji

2013-01-01

The tunable wettability of smart graphene films onto stainless steel substrates with a multi-response to different environmental stimuli has been investigated including light irradiation, pH, electric field, and annealing temperature. Conductive graphene film exhibited the controllable transition from water-repellent to water-loving characteristic in response to different environment fields, which primarily resulted from the morpho-chemically synergistic effect as well as the restoration of electronic stucture. Based on the fundamental theories of wettability, mechanisms in switching from hydrophobicity to hydrophilicity for smart graphene surface including thermal chemistry, electrostatic, photo-induced surface chemistry, solvent, and pH methods were presented.

DNA-Mediated Electrochemistry

PubMed Central

Gorodetsky, Alon A.; Buzzeo, Marisa C.

2009-01-01

The base pair stack of DNA has been demonstrated as a medium for long range charge transport chemistry both in solution and at DNA-modified surfaces. This chemistry is exquisitely sensitive to structural perturbations in the base pair stack as occur with lesions, single base mismatches, and protein binding. We have exploited this sensitivity for the development of reliable electrochemical assays based on DNA charge transport at self-assembled DNA monolayers. Here we discuss the characteristic features, applications, and advantages of DNA-mediated electrochemistry. PMID:18980370

An in situ accelerator-based diagnostic for plasma-material interactions science on magnetic fusion devices.

PubMed

Hartwig, Zachary S; Barnard, Harold S; Lanza, Richard C; Sorbom, Brandon N; Stahle, Peter W; Whyte, Dennis G

2013-12-01

This paper presents a novel particle accelerator-based diagnostic that nondestructively measures the evolution of material surface compositions inside magnetic fusion devices. The diagnostic's purpose is to contribute to an integrated understanding of plasma-material interactions in magnetic fusion, which is severely hindered by a dearth of in situ material surface diagnosis. The diagnostic aims to remotely generate isotopic concentration maps on a plasma shot-to-shot timescale that cover a large fraction of the plasma-facing surface inside of a magnetic fusion device without the need for vacuum breaks or physical access to the material surfaces. Our instrument uses a compact (~1 m), high-current (~1 milliamp) radio-frequency quadrupole accelerator to inject 0.9 MeV deuterons into the Alcator C-Mod tokamak at MIT. We control the tokamak magnetic fields--in between plasma shots--to steer the deuterons to material surfaces where the deuterons cause high-Q nuclear reactions with low-Z isotopes ~5 μm into the material. The induced neutrons and gamma rays are measured with scintillation detectors; energy spectra analysis provides quantitative reconstruction of surface compositions. An overview of the diagnostic technique, known as accelerator-based in situ materials surveillance (AIMS), and the first AIMS diagnostic on the Alcator C-Mod tokamak is given. Experimental validation is shown to demonstrate that an optimized deuteron beam is injected into the tokamak, that low-Z isotopes such as deuterium and boron can be quantified on the material surfaces, and that magnetic steering provides access to different measurement locations. The first AIMS analysis, which measures the relative change in deuterium at a single surface location at the end of the Alcator C-Mod FY2012 plasma campaign, is also presented.

Rapid Covalent Modification of Silicon Oxide Surfaces through Microwave-Assisted Reactions with Alcohols.

PubMed

Lee, Austin W H; Gates, Byron D

2016-07-26

We demonstrate the method of a rapid covalent modification of silicon oxide surfaces with alcohol-containing compounds with assistance by microwave reactions. Alcohol-containing compounds are prevalent reagents in the laboratory, which are also relatively easy to handle because of their stability against exposure to atmospheric moisture. The condensation of these alcohols with the surfaces of silicon oxides is often hindered by slow reaction kinetics. Microwave radiation effectively accelerates this condensation reaction by heating the substrates and/or solvents. A variety of substrates were modified in this demonstration, such as silicon oxide films of various thicknesses, glass substrates such as microscope slides (soda lime), and quartz. The monolayers prepared through this strategy demonstrated the successful formation of covalent surface modifications of silicon oxides with water contact angles of up to 110° and typical hysteresis values of 2° or less. An evaluation of the hydrolytic stability of these monolayers demonstrated their excellent stability under acidic conditions. The techniques introduced in this article were successfully applied to tune the surface chemistry of silicon oxides to achieve hydrophobic, oleophobic, and/or charged surfaces.

Development of a Detailed Surface Chemistry Framework in DSMC

NASA Technical Reports Server (NTRS)

Swaminathan-Gopalan, K.; Borner, A.; Stephani, K. A.

2017-01-01

Many of the current direct simulation Monte Carlo (DSMC) codes still employ only simple surface catalysis models. These include only basic mechanisms such as dissociation, recombination, and exchange reactions, without any provision for adsorption and finite rate kinetics. Incorporating finite rate chemistry at the surface is increasingly becoming a necessity for various applications such as high speed re-entry flows over thermal protection systems (TPS), micro-electro-mechanical systems (MEMS), surface catalysis, etc. In the recent years, relatively few works have examined finite-rate surface reaction modeling using the DSMC method.In this work, a generalized finite-rate surface chemistry framework incorporating a comprehensive list of reaction mechanisms is developed and implemented into the DSMC solver SPARTA. The various mechanisms include adsorption, desorption, Langmuir-Hinshelwood (LH), Eley-Rideal (ER), Collision Induced (CI), condensation, sublimation, etc. The approach is to stochastically model the various competing reactions occurring on a set of active sites. Both gas-surface (e.g., ER, CI) and pure-surface (e.g., LH, desorption) reaction mechanisms are incorporated. The reaction mechanisms could also be catalytic or surface altering based on the participation of the bulk-phase species (e.g., bulk carbon atoms). Marschall and MacLean developed a general formulation in which multiple phases and surface sites are used and we adopt a similar convention in the current work. Microscopic parameters of reaction probabilities (for gas-surface reactions) and frequencies (for pure-surface reactions) that are require for DSMC are computed from the surface properties and macroscopic parameters such as rate constants, sticking coefficients, etc. The energy and angular distributions of the products are decided based on the reaction type and input parameters. Thus, the user has the capability to model various surface reactions via user-specified reaction rate constants, surface properties and parameters.

Accelerators for Discovery Science and Security applications

NASA Astrophysics Data System (ADS)

Todd, A. M. M.; Bluem, H. P.; Jarvis, J. D.; Park, J. H.; Rathke, J. W.; Schultheiss, T. J.

2015-05-01

Several Advanced Energy Systems (AES) accelerator projects that span applications in Discovery Science and Security are described. The design and performance of the IR and THz free electron laser (FEL) at the Fritz-Haber-Institut der Max-Planck-Gesellschaft in Berlin that is now an operating user facility for physical chemistry research in molecular and cluster spectroscopy as well as surface science, is highlighted. The device was designed to meet challenging specifications, including a final energy adjustable in the range of 15-50 MeV, low longitudinal emittance (<50 keV-psec) and transverse emittance (<20 π mm-mrad), at more than 200 pC bunch charge with a micropulse repetition rate of 1 GHz and a macropulse length of up to 15 μs. Secondly, we will describe an ongoing effort to develop an ultrafast electron diffraction (UED) source that is scheduled for completion in 2015 with prototype testing taking place at the Brookhaven National Laboratory (BNL) Accelerator Test Facility (ATF). This tabletop X-band system will find application in time-resolved chemical imaging and as a resource for drug-cell interaction analysis. A third active area at AES is accelerators for security applications where we will cover some top-level aspects of THz and X-ray systems that are under development and in testing for stand-off and portal detection.

Investigation of aluminosilicate as a solid oxide fuel cell refractory

NASA Astrophysics Data System (ADS)

Gentile, Paul S.; Sofie, Stephen W.

2011-05-01

Aluminosilicate represents a potential low cost alternative to alumina for solid oxide fuel cell (SOFC) refractory applications. The objectives of this investigation are to study: (1) changes of aluminosilicate chemistry and morphology under SOFC conditions, (2) deposition of aluminosilicate vapors on yttria stabilized zirconia (YSZ) and nickel, and (3) effects of aluminosilicate vapors on SOFC electrochemical performance. Thermal treatment of aluminosilicate under high temperature SOFC conditions is shown to result in increased mullite concentrations at the surface due to diffusion of silicon from the bulk. Water vapor accelerates the rate of surface diffusion resulting in a more uniform distribution of silicon. The high temperature condensation of volatile gases released from aluminosilicate preferentially deposit on YSZ rather than nickel. Silicon vapor deposited on YSZ consists primarily of aluminum rich clusters enclosed in an amorphous siliceous layer. Increased concentrations of silicon are observed in enlarged grain boundaries indicating separation of YSZ grains by insulating glassy phase. The presence of aluminosilicate powder in the hot zone of a fuel line supplying humidified hydrogen to an SOFC anode impeded peak performance and accelerated degradation. Energy dispersive X-ray spectroscopy detected concentrations of silicon at the interface between the electrolyte and anode interlayer above impurity levels.

Chemistry of the surface and lower atmosphere of Venus

NASA Technical Reports Server (NTRS)

Fegley, B., Jr.; Treiman, A.

1992-01-01

A comprehensive overview of the chemical interactions between the atmosphere and surface of Venus is presented. Earth-based, earth-orbital, and spacecraft data on the composition of the atmosphere and surface of Venus are presented and applied to quantitative evaluations of the chemical interactions between carbon, hydrogen, sulfur, chlorine, fluorine, and nitrogen-containing gases and possible minerals on the Venus surface. The calculation results are used to predict stable minerals and mineral assemblages on the Venus surface to determine which, if any, atmospheric gases are buffered by mineral assemblages on the surface, and to critically review and assess prior work on atmosphere-surface chemistry on Venus. It is concluded that the CO2 pressure on Venus is comparable to the CO2 equilibrium partial pressure developed by the calcite + wollastonite + quartz assemblage at the mean Venus surface temperature of 740 K.

Improving Density Functional Tight Binding Predictions of Free Energy Surfaces for Slow Chemical Reactions in Solution

NASA Astrophysics Data System (ADS)

Kroonblawd, Matthew; Goldman, Nir

2017-06-01

First principles molecular dynamics using highly accurate density functional theory (DFT) is a common tool for predicting chemistry, but the accessible time and space scales are often orders of magnitude beyond the resolution of experiments. Semi-empirical methods such as density functional tight binding (DFTB) offer up to a thousand-fold reduction in required CPU hours and can approach experimental scales. However, standard DFTB parameter sets lack good transferability and calibration for a particular system is usually necessary. Force matching the pairwise repulsive energy term in DFTB to short DFT trajectories can improve the former's accuracy for reactions that are fast relative to DFT simulation times (<10 ps), but the effects on slow reactions and the free energy surface are not well-known. We present a force matching approach to improve the chemical accuracy of DFTB. Accelerated sampling techniques are combined with path collective variables to generate the reference DFT data set and validate fitted DFTB potentials. Accuracy of force-matched DFTB free energy surfaces is assessed for slow peptide-forming reactions by direct comparison to DFT for particular paths. Extensions to model prebiotic chemistry under shock conditions are discussed. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

Chemical state evolution in ferroelectric films during tip-induced polarization and electroresistive switching

DOE PAGES

Ievlev, Anton V.; Maksymovych, Petro; Trassin, Morgan; ...

2016-10-11

Domain formation and ferroelectric switching is fundamentally inseparable from polarization screening, which on free surfaces can be realized via band bending and ionic adsorption. In the latter case, polarization switching is intrinsically coupled to the surface electrochemical phenomena, and the electrochemical stage can control kinetics and induce long-range interactions. However, despite extensive evidence towards the critical role of surface electrochemistry, little is known about the nature of the associated processes. Here we combine SPM tip induce polarization switching and secondary ion mass spectrometry to explore the evolution of chemical state of ferroelectric during switching. Surprisingly, we find that even pristinemore » surfaces contain ions (e.g. Cl -) that are not anticipated based on chemistry of the system and processing. In the ferroelectric switching regime, we find surprising changes in surface chemistry, including redistribution of base cations. Finally, at higher voltages in the electroforming regime significant surface deformation was observed and associated with a strong ion intermixing.« less

Got a Match? Ion Extraction GC-MS Characterization of Accelerants Adsorbed in Charcoal Using Negative Pressure Dynamic Headspace Concentration

ERIC Educational Resources Information Center

Anzivino, Barbara; Tilley, Leon J.; Ingalls, Laura R.; Hall, Adam B.; Drugan, John E.

2009-01-01

An undergraduate organic chemistry experiment demonstrating real-life application of GC-MS to arson accelerant identification is described. Students are given the task of comparing a sample recovered from a "crime scene" to that from a "suspect's clothing". Accelerants subjected to different conditions are recovered using a quick and simple…

Laser Surface Preparation of Epoxy Composites for Secondary Bonding: Optimization of Ablation Depth

NASA Technical Reports Server (NTRS)

Palmieri, Frank L.; Hopkins, John; Wohl, Christopher J.; Lin, Yi; Connell, John W.; Belcher, Marcus A.; Blohowiak, Kay Y.

2015-01-01

Surface preparation has been identified as one of the most critical aspects of attaining predictable and reliable adhesive bonds. Energetic processes such as laser ablation or plasma treatment are amenable to automation and are easily monitored and adjusted for controlled surface preparation. A laser ablation process was developed to accurately remove a targeted depth of resin, approximately 0.1 to 20 micrometers, from a carbon fiber reinforced epoxy composite surface while simultaneously changing surface chemistry and creating micro-roughness. This work demonstrates the application of this process to prepare composite surfaces for bonding without exposing or damaging fibers on the surface. Composite panels were prepared in an autoclave and had a resin layer approximately 10 micrometers thick above the fiber reinforcement. These composite panels were laser surface treated using several conditions, fabricated into bonded panels and hygrothermally aged. Bond performance of aged, experimental specimens was compared with grit blast surface treated specimens using a modified double cantilever beam test that enabled accelerated saturation of the specimen with water. Comparison of bonded specimens will be used to determine how ablation depth may affect average fracture energies and failure modes.

Temporal and diurnal analysis of trace elements in the Cryospheric water at remote Laohugou basin in northeast Tibetan Plateau.

PubMed

Dong, Zhiwen; Kang, Shichang; Qin, Dahe; Qin, Xiang; Yan, Fangping; Du, Wentao; Wei, Ting

2017-03-01

An evaluation of glacial meltwater chemistry is needed under recent dramatic glacier melting when water resources might be significantly impacted. This study investigated trace elements variation in the meltwater stream, and its related aquatic environmental information, at the Laohugou (LHG) glacier basin (4260 m a.s.l.) at a remote location in northeast Tibetan Plateau. We focused on the spatial, temporal and diurnal change of trace elements during the glacier ablation period. Results showed evident elements spatial difference on the glacier surface meltwater, as most of the elements showed increased concentration at the terminus compared to higher elevations sites. Dominant elements in the meltwater were Ba, Sr and Cr, whereas elements with high enrichment factors (EFs) were Sb, Ni, Mo and Zn. Temporal change of some trace elements concentration (e.g. Sc, Cu, and Rb) indicated increasing trend with accelerated snow-ice melting, whereas others (e.g. Ni, Zn, and Pb) showed decreasing trend. We find that, trace elements showed evident diurnal change and a peak value of concentration was observed each day at about 15:00-17:00, and the diurnal change was influenced by runoff level and pH. Moreover, EFs calculations revealed that heavy metals were partially originated from regional anthropogenic sources. Overall, the accelerated diurnal and temporal snow-ice melting (with high runoff level) were correlated to increased elemental concentration, pH, EC and elemental change mode, and thus this work is of great importance for evaluating the impacts of accelerated glacier melting to meltwater chemistry and downstream ecosystem in the northeast Tibetan Plateau. Copyright © 2016 Elsevier Ltd. All rights reserved.

Relationship of wood surface energy to surface composition

Treesearch

Feipeng P. Liu; Timothy G. Rials; John Simonsen

1998-01-01

The wood cell wall is composed of cellulose, lignin, hemicelluloses, and extractives. Thus, the surface energy of the wood material must be some combination of the surface energies of these components. The influence of extractives on wood surface chemistry can be important in diverse industrial applications, such as coating, pulping, and wood-based composites. In this...

Spectroscopic and electrochemical characterization of interfacial biomimetic assemblies on electrochemically generated gold oxide surfaces.

PubMed

Krysiński, Paweł; Blanchard, G J

2005-04-01

We report on the formation of a gold oxide layer and the reaction of this oxide with an acid chloride to form a stable, relatively complete monolayer bound through an ester-like bond to the gold oxide surface. We have used cyclic voltammetry, FTIR and optical ellipsometry to characterize this novel monolayer structure. The exposed functional groups of this monolayer can participate in subsequent surface reactions, opening the door to the use of oxide-based surface attachment chemistry on metallic substrates. This chemistry will allow for the formation of films tailored to contain both hydrophobic and hydrophilic regions, stacked at predetermined distances from the substrate that may serve as biomembrane mimetic assemblies.

Role of Surface Chemistry on Catalyst/Ionomer Interactions for Transition Metal–Nitrogen–Carbon Electrocatalysts

DOE Office of Scientific and Technical Information (OSTI.GOV)

Artyushkova, Kateryna; Workman, Michael J.; Matanovic, Ivana

The role of the interaction between doped carbon-based materials and ionic conductors is essential in multiple technologies, from fuel cells and energy storage devices to conductive polymer composites. In this paper, we report how the surface chemistry of transition metal–nitrogen–carbon (MNC) electrocatalysts affects catalyst–ionomer interaction and the resulting structure of cathodes. The cathode structure resulting from these interactions is directly related to the performance in membrane electrode assembly (MEA) fuel cells. To advance the development of platinum group metal (PGM)-free electrodes for the oxygen reduction reaction it is necessary to understand the structure of the catalyst layers with focus onmore » chemistry and distribution of active sites and ionomer morphology. To assess catalyst interaction with an ionomer, X-ray photoelectron spectroscopy is applied to study the chemistry of catalyst layers while density functional theory (DFT) is used to calculate adsorption energies of the ionomer side chain on different nitrogen species. We report that a high surface concentration of hydrogenated nitrogen at the surface of MNC catalysts causes inefficient ionomer morphology, while an abundance of surface oxides promotes both an efficient distribution of active sites and an optimal ionomer–catalyst interface. The critical role of protonation of nitrogen within catalytic layers in inhibiting proton transport during fuel cell operation is also suggested. As a result, this is the first report of the effect the surface chemistry of MNC catalysts, in the presence of the ionomer, has on the structure and performance of MEA electrodes.« less

Role of Surface Chemistry on Catalyst/Ionomer Interactions for Transition Metal–Nitrogen–Carbon Electrocatalysts

DOE PAGES

Artyushkova, Kateryna; Workman, Michael J.; Matanovic, Ivana; ...

2017-12-18

The role of the interaction between doped carbon-based materials and ionic conductors is essential in multiple technologies, from fuel cells and energy storage devices to conductive polymer composites. In this paper, we report how the surface chemistry of transition metal–nitrogen–carbon (MNC) electrocatalysts affects catalyst–ionomer interaction and the resulting structure of cathodes. The cathode structure resulting from these interactions is directly related to the performance in membrane electrode assembly (MEA) fuel cells. To advance the development of platinum group metal (PGM)-free electrodes for the oxygen reduction reaction it is necessary to understand the structure of the catalyst layers with focus onmore » chemistry and distribution of active sites and ionomer morphology. To assess catalyst interaction with an ionomer, X-ray photoelectron spectroscopy is applied to study the chemistry of catalyst layers while density functional theory (DFT) is used to calculate adsorption energies of the ionomer side chain on different nitrogen species. We report that a high surface concentration of hydrogenated nitrogen at the surface of MNC catalysts causes inefficient ionomer morphology, while an abundance of surface oxides promotes both an efficient distribution of active sites and an optimal ionomer–catalyst interface. The critical role of protonation of nitrogen within catalytic layers in inhibiting proton transport during fuel cell operation is also suggested. As a result, this is the first report of the effect the surface chemistry of MNC catalysts, in the presence of the ionomer, has on the structure and performance of MEA electrodes.« less

Biocompatible, smooth, plasma-treated nickel-titanium surface--an adequate platform for cell growth.

PubMed

Chrzanowski, W; Szade, J; Hart, A D; Knowles, J C; Dalby, M J

2012-02-01

High nickel content is believed to reduce the number of biomedical applications of nickel-titanium alloy due to the reported toxicity of nickel. The reduction in nickel release and minimized exposure of the cell to nickel can optimize the biocompatibility of the alloy and increase its use in the application where its shape memory effects and pseudoelasticity are particularly useful, e.g., spinal implants. Many treatments have been tried to improve the biocompatibility of Ni-Ti, and results suggest that a native, smooth surface could provide sufficient tolerance, biologically. We hypothesized that the native surface of nickel-titanium supports cell differentiation and insures good biocompatibility. Three types of surface modifications were investigated: thermal oxidation, alkali treatment, and plasma sputtering, and compared with smooth, ground surface. Thermal oxidation caused a drop in surface nickel content, while negligible chemistry changes were observed for plasma-modified samples when compared with control ground samples. In contrast, alkali treatment caused significant increase in surface nickel concentration and accelerated nickel release. Nickel release was also accelerated in thermally oxidized samples at 600 °C, while in other samples it remained at low level. Both thermal oxidation and alkali treatment increased the roughness of the surface, but mean roughness R(a) was significantly greater for the alkali-treated ones. Ground and plasma-modified samples had 'smooth' surfaces with R(a)=4 nm. Deformability tests showed that the adhesion of the surface layers on samples oxidized at 600 °C and alkali treatment samples was not sufficient; the layer delaminated upon deformation. It was observed that the cell cytoskeletons on the samples with a high nickel content or release were less developed, suggesting some negative effects of nickel on cell growth. These effects were observed primarily during initial cell contact with the surface. The most favorable cell responses were observed for ground and plasma-sputtered surfaces. These studies indicated that smooth, plasma-modified surfaces provide sufficient properties for cells to grow. © The Author(s), 2011.

Defining an optimal surface chemistry for pluripotent stem cell culture in 2D and 3D

NASA Astrophysics Data System (ADS)

Zonca, Michael R., Jr.

Surface chemistry is critical for growing pluripotent stem cells in an undifferentiated state. There is great potential to engineer the surface chemistry at the nanoscale level to regulate stem cell adhesion. However, the challenge is to identify the optimal surface chemistry of the substrata for ES cell attachment and maintenance. Using a high-throughput polymerization and screening platform, a chemically defined, synthetic polymer grafted coating that supports strong attachment and high expansion capacity of pluripotent stem cells has been discovered using mouse embryonic stem (ES) cells as a model system. This optimal substrate, N-[3-(Dimethylamino)propyl] methacrylamide (DMAPMA) that is grafted on 2D synthetic poly(ether sulfone) (PES) membrane, sustains the self-renewal of ES cells (up to 7 passages). DMAPMA supports cell attachment of ES cells through integrin beta1 in a RGD-independent manner and is similar to another recently reported polymer surface. Next, DMAPMA has been able to be transferred to 3D by grafting to synthetic, polymeric, PES fibrous matrices through both photo-induced and plasma-induced polymerization. These 3D modified fibers exhibited higher cell proliferation and greater expression of pluripotency markers of mouse ES cells than 2D PES membranes. Our results indicated that desirable surfaces in 2D can be scaled to 3D and that both surface chemistry and structural dimension strongly influence the growth and differentiation of pluripotent stem cells. Lastly, the feasibility of incorporating DMAPMA into a widely used natural polymer, alginate, has been tested. Novel adhesive alginate hydrogels have been successfully synthesized by either direct polymerization of DMAPMA and methacrylic acid blended with alginate, or photo-induced DMAPMA polymerization on alginate nanofibrous hydrogels. In particular, DMAPMA-coated alginate hydrogels support strong ES cell attachment, exhibiting a concentration dependency of DMAPMA. This research provides a new avenue for stem cell culture and maintenance using an optimal organic-based chemistry.

Monthly Progress Report No. 60 for April 1948

DOE Office of Scientific and Technical Information (OSTI.GOV)

Various

This report gives a short summary of each of the following programs: (1) 184-inch Cyclotron Program; (2) 60-inch Cyclotron Program; (3) Synchrotron Program; (4) Linear Accelerator Program; (5) Experimental Physics; (6) Theoretical Physics; (7) Chemistry; (8) Medical Physics; and (9) Health Physics and Chemistry.

Nonlinear friction dynamics on polymer surface under accelerated movement

NASA Astrophysics Data System (ADS)

Aita, Yuuki; Asanuma, Natsumi; Takahashi, Akira; Mayama, Hiroyuki; Nonomura, Yoshimune

2017-04-01

Nonlinear phenomena on the soft material surface are one of the most exciting topics of chemical physics. However, only a few reports exist on the friction phenomena under accelerated movement, because friction between two solid surfaces is considered a linear phenomenon in many cases. We aim to investigate how nonlinear accelerated motion affects friction on solid surfaces. In the present study, we evaluate the frictional forces between two polytetrafluoroethylene (PTFE) resins using an advanced friction evaluation system. On PTFE surfaces, the normalized delay time δ, which is the time lag in the response of the friction force to the accelerated movement, is observed in the pre-sliding friction process. Under high-velocity conditions, kinetic friction increases with velocity. Based on these experimental results, we propose a two-phase nonlinear model including a pre-sliding process (from the beginning of sliding of a contact probe to the establishment of static friction) and a kinetic friction process. The present model consists of several factors including velocity, acceleration, stiffness, viscosity, and vertical force. The findings reflecting the viscoelastic properties of soft material is useful for various fields such as in the fabrication of clothes, cosmetics, automotive materials, and virtual reality systems as well as for understanding friction phenomena on soft material surfaces.

Surface chemistry, microstructure and friction properties of some ferrous-base metallic glasses at temperatures to 750 C

NASA Technical Reports Server (NTRS)

Miyoshi, K.; Buckley, D. H.

1982-01-01

X-ray photoelectron spectroscopy analysis, transmission electron microscopy, diffraction studies, and sliding friction experiments were conducted with ferrous-base metallic glasses in sliding contact with aluminum oxide at temperatures from room to 750 C in a vacuum of 30 nPa. The results indicate that there is a significant temperature influence on the friction properties, surface chemistry, and microstructure of metallic glasses. The relative concentrations of the various constituents at the surface of the sputtered specimens were very different from the normal bulk compositions. Contaminants can come from the bulk of the material to the surface upon heating and impart boric oxide and silicon oxide at 350 C and boron nitride above 500 C. The coefficient of friction increased with increasing temperature to 350 C. Above 500 C the coefficient of friction decreased rapidly. The segregation of contaminants may be responsible for the friction behavior.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pezeshki, Alan M.; Sacci, Robert L.; Veith, Gabriel M.

Here, we demonstrate a novel method to accelerate electrode degradation in redox flow batteries and apply this method to the all-vanadium chemistry. Electrode performance degradation occurred seven times faster than in a typical cycling experiment, enabling rapid evaluation of materials. This method also enables the steady-state study of electrodes. In this manner, it is possible to delineate whether specific operating conditions induce performance degradation; we found that both aggressively charging and discharging result in performance loss. Post-mortem x-ray photoelectron spectroscopy of the degraded electrodes was used to resolve the effects of state of charge (SoC) and current on the electrodemore » surface chemistry. For the electrode material tested in this work, we found evidence that a loss of oxygen content on the negative electrode cannot explain decreased cell performance. Furthermore, the effects of decreased electrode and membrane performance on capacity fade in a typical cycling battery were decoupled from crossover; electrode and membrane performance decay were responsible for a 22% fade in capacity, while crossover caused a 12% fade.« less

Water Dimer Concentrations in The Atmosphere

NASA Astrophysics Data System (ADS)

Saykally, R. J.

2000-03-01

The water dimer concentration present in water vapor under equilibrium conditions is rigorously determined as a function of temperature, pressure, and relative humidity via explicit calculations of partition functions on the VRT (ASP-W) potential surface using the SWPS method. Dimer vapor fractions as large as 4.6x10*3 are calculated under tropospheric conditions, and should have observable consequences on chemistry and physical properties of the atmosphere. There has been much recent interest and speculation regarding possible effects of water clusters on the chemistry and radiation balance of the atmosphere. For example, it has been proposed that vibrational overtones of the water dimer absorb solar radiation and account for a significant part of the *anomalous absorption* of the atmosphere, although recent measurements do not support this claim. Similarly, the presence of water dimers has been predicted to accelerate the formation of acid rain, and homogeneous nucleation of raindrops. In all of these contexts, the crucial unknown is the concentration of water dimers present under the specified conditions of temperature, pressure, and relative humidity.

Massive Thermal Acceleration of the Emergence of Primordial Chemistry, the Incidence of Spontaneous Mutation, and the Evolution of Enzymes*

PubMed Central

Wolfenden, Richard

2014-01-01

Kelvin considered it unlikely that sufficient time had elapsed on the earth for life to have reached its present level of complexity. In the warm surroundings in which life first appeared, however, elevated temperatures would have reduced the kinetic barriers to reaction. Recent experiments disclose the profound extent to which very slow reactions are accelerated by elevated temperatures, collapsing the time that would have been required for early events in primordial chemistry before the advent of enzymes. If a primitive enzyme, like model catalysts and most modern enzymes, accelerated a reaction by lowering its enthalpy of activation, then the rate enhancement that it produced would have increased automatically as the environment cooled, quite apart from any improvements in catalytic activity that arose from mutation and natural selection. The chemical events responsible for spontaneous mutation are also highly sensitive to temperature, furnishing an independent mechanism for accelerating evolution. PMID:25210030

Direct conversion of hydride- to siloxane-terminated silicon quantum dots

DOE PAGES

Anderson, Ryan T.; Zang, Xiaoning; Fernando, Roshan; ...

2016-10-20

Here, peripheral surface functionalization of hydride-terminated silicon quantum dots (SiQD) is necessary in order to minimize their oxidation/aggregation and allow for solution processability. Historically thermal hydrosilylation addition of alkenes and alkynes across the Si-H surface to form Si-C bonds has been the primary method to achieve this. Here we demonstrate a mild alternative approach to functionalize hydride-terminated SiQDs using bulky silanols in the presence of free-radical initiators to form stable siloxane (~Si-O-SiR 3) surfaces with hydrogen gas as a byproduct. This offers an alternative to existing methods of forming siloxane surfaces that require corrosive Si-Cl based chemistry with HCl byproducts.more » A 52 nm blue shift in the photoluminescent spectra of siloxane versus alkyl-functionalized SiQDs is observed that we explain using computational theory. Model compound synthesis of silane and silsesquioxane analogues is used to optimize surface chemistry and elucidate reaction mechanisms. Thorough characterization on the extent of siloxane surface coverage is provided using FTIR and XPS. As a result, TEM is used to demonstrate SiQD size and integrity after surface chemistry and product isolation.« less

Interaction between carbon fibers and polymer sizing: Influence of fiber surface chemistry and sizing reactivity

NASA Astrophysics Data System (ADS)

Moosburger-Will, Judith; Bauer, Matthias; Laukmanis, Eva; Horny, Robert; Wetjen, Denise; Manske, Tamara; Schmidt-Stein, Felix; Töpker, Jochen; Horn, Siegfried

2018-05-01

Different aspects of the interaction of carbon fibers and epoxy-based polymer sizings are investigated, e.g. the wetting behavior, the strength of adhesion between fiber and sizing, and the thermal stability of the sizing layer. The influence of carbon fiber surface chemistry and sizing reactivity is investigated using fibers of different degree of anodic oxidation and sizings with different number of reactive epoxy groups per molecule. Wetting of the carbon fibers by the sizing dispersion is found to be specified by both, the degree of fiber activation and the sizing reactivity. In contrast, adhesion strength between fibers and sizing is dominated by the surface chemistry of the carbon fibers. Here, the number of surface oxygen groups seems to be the limiting factor. We also find that the sizing and the additional functionalities induced by anodic oxidation are removed by thermal treatment at 600 °C, leaving the carbon fiber in its original state after carbonization.

Performance of Zinc Anodes for Cathodic Protection of Reinforced Concrete Bridges

DOE Office of Scientific and Technical Information (OSTI.GOV)

Covino, Bernard S. Jr.; Cramer, Stephen D.; Bullard, Sophie J.

2002-03-01

Operation of thermal spray zinc (Zn) anodes for cathodic protection (CP) of reinforced concrete structures was investigated in laboratory and field studies conducted by the Albany Research Center (ARC) in collaboration with the Oregon Department of Transportation. The purposes of the research presented in this report were: evaluate the need for preheating concrete to improve the adhesion of the anode; estimate the service life of thermal spray Zn CP anodes; determine the optimum thickness for Zn CP anodes; characterize the anode-concrete interfacial chemistry; and correlate field and laboratory results. Laboratory studies involved accelerated electrochemical aging of thermal sprayed Zn anodesmore » on concrete slabs, some of which were periodically wetted while others were unwetted. Concrete used in the slabs contained either 1.2 or 3 kg NaCl /m3 (2 or 5 lbs NaCl /yd3) as part of the concrete mix design. The Zn anodes were applied to the slabs using the twin wire arc-spray technique. Half of the slabs were preheated to 120-160 C (250-320 F) to improve the initial Zn anode bond strength and the other half were not. Accelerated aging was done at a current density of 0.032 A/m2 (3 mA/ft2), 15 times that used on Oregon DOT Coastal bridges, i.e, . 0.0022 A/m2 (0.2 mA/ft2) Cores from the Cape Creek Bridge (OR), the Richmond San Rafael Bridge (CA), and the East Camino Underpass (CA) were used to study the anode-concrete interfacial chemistry, to relate the chemistry to electrochemical age at the time of sampling, and to compare the chemistry of the field anodes to the chemistry of anodes from the laboratory studies. Cores from a CALTRANS study of a silane sealant used prior to the application of the Zn anodes and cores with galvanized rebar from the Longbird Bridge (Bermuda) were also studied. Aged laboratory and field anodes were characterized by measuring some or all of the following parameters: thickness, bond strength, anode-concrete interfacial chemistry, bulk chemistry, anode resistance, circuit resistance, electrochemical age, and air and water permeability. Models are presented for the operation of periodically-wetted and unwetted thermal spray Zn anodes from the initial energizing of the anode to the end of its service life. The models were developed in terms of bond strength, circuit resistance, anode-concrete interfacial chemistry, electrochemical age, and anode condition. The most significant results of the research are: (1) preheating concrete surfaces prior to coating with Zn is unnecessary; (2) anodes generally fail due to loss of bond strength rather than Zn consumption; (3) Unwetted anodes fail more quickly than periodically-wetted anodes; (4) 0.47-0.60 mm (12-15 mil) anode thickness is adequate for most Oregon DOT coastal impressed current CP (ICCP) installations; (5) based on bond strength, thermal spray Zn ICCP anode service life is approximately 27 years at 0.0022 A/m2 (0.2 mA/ft2); (6) anode reaction products alter the anode-concrete interface by rejecting Ca from the cement paste, by replacing it with Zn, and by the accumulation of a Zn mineral layer that includes chloride and sulfur compounds; (7) CP system circuit resistance provides an effective means for monitoring the condition of Zn ICCP anodes as they age.« less

EDITORIAL: Laser and Plasma Accelerators Workshop, Kardamyli, Greece, 2009 Laser and Plasma Accelerators Workshop, Kardamyli, Greece, 2009

NASA Astrophysics Data System (ADS)

Bingham, Bob; Muggli, Patric

2011-01-01

The Laser and Plasma Accelerators Workshop 2009 was part of a very successful series of international workshops which were conceived at the 1985 Laser Acceleration of Particles Workshop in Malibu, California. Since its inception, the workshop has been held in Asia and in Europe (Kardamyli, Kyoto, Presqu'ile de Giens, Portovenere, Taipei and the Azores). The purpose of the workshops is to bring together the most recent results in laser wakefield acceleration, plasma wakefield acceleration, laser-driven ion acceleration, and radiation generation produced by plasma-based accelerator beams. The 2009 workshop was held on 22-26 June in Kardamyli, Greece, and brought together over 80 participants. (http://cfp.ist.utl.pt/lpaw09/). The workshop involved five main themes: • Laser plasma electron acceleration (experiment/theory/simulation) • Computational methods • Plasma wakefield acceleration (experiment/theory/simulation) • Laser-driven ion acceleration • Radiation generation and application. All of these themes are covered in this special issue of Plasma Physics and Controlled Fusion. The topic and application of plasma accelerators is one of the success stories in plasma physics, with laser wakefield acceleration of mono-energetic electrons to GeV energies, of ions to hundreds of MeV, and electron-beam-driven wakefield acceleration to 85 GeV. The accelerating electric field in the wake is of the order 1 GeV cm-1, or an accelerating gradient 1000 times greater than in conventional accelerators, possibly leading to an accelerator 1000 times smaller (and much more affordable) for the same energy. At the same time, the electron beams generated by laser wakefield accelerators have very good emittance with a correspondingly good energy spread of about a few percent. They also have the unique feature in being ultra-short in the femtosecond scale. This makes them attractive for a variety of applications, ranging from material science to ultra-fast time-resolved radiobiology or chemistry. Such laser-generated beams will form the basis of the fifth generation light sources and will be compact versions of the much more expensive fourth generation XFEL, such as LCLS light sources. Laser-driven ion acceleration is also making rapid headway; one of the goals in these experiments is to produce protons and carbon ions of hundreds of MeV for oncology. These experiments are carried out using solid-target-laser interactions. There is still a number of issues to be resolved in these experiments including the origin of light ions. The paper by Willingale et al addresses this issue and demonstrates that deuteron ions originating from the front surface can gain comparable energies as those from the rear surface. Furthermore, from two-dimensional simulations they show that a proton-rich contamination layer over the surface is detrimental to deuteron ion acceleration from the rear surface but not detrimental to the front surface acceleration mechanism. Studies of different laser polarizations on ion acceleration at the rear surface were reported by Antici et al. It was shown that no real enhancement using a particular polarization was found. At higher radiation intensities, especially with the multi-petawatt lasers being planned, radiation reaction becomes important. This was reported by Chen et al who found that radiation reaction effects on ion acceleration in laser-foil interactions impeded the backward moving electrons, which enhanced the ion acceleration. An interesting new development is the use of ultra-relativistic proton beams to drive plasma wakefields. This is similar to the SLAC electron-beam-driven wakefields. However, unlike the SLAC electron beam, which is of the order of 30 fs long and matches the period of the plasma wave necessary to create the blowout or bubble regime, the ion beam is very much longer. To create shorter ion beams a magnetic compression scheme is investigated in the paper by Caldwell et al, and results for proton beam self-modulation are presented, showing encouraging results for a first experiment using a compressed 24 GeV CERN PS beam. One of the main challenges with laser wakefields is the control of electron injection. In some experiments involving the bubble regime self-injection occurs naturally. Kneip et al show that the stability of the electron beam with energies close to 1 GeV is correlated with the pointing stability of the laser focal spot and depends on the target alignment. Theory and simulations of self-injection reported by Yi et al demonstrate that there is a minimal expansion rate for efficient self-injection. In contrast to solid target ion acceleration, the electron profile in the bubble regime was shown to be manipulated by rotating the laser polarization. Simulations of self-injection into an expanding bubble are reported by Kalmykov et al with the expanding bubble effectively trapping quiescent electrons. To increase the energy of electrons in the laser wakefield scheme, guiding and injection into plasma channels is important. Andreev et al have studied supershort electron bunches in channels with the view of understanding bunch injection. Modelling of electron acceleration in centimetre long capillary tubes is also necessary for future accelerators and is the main part of the paper by Ferrari et al. One of the applications of short-pulse electron beams is in radiation generation as reported by Karagodsky et al. This is an analogue of a technique pioneered in microwave physics where inverse Compton scattering from an optical Bragg structure generates x-rays with high efficiency. The next workshop will be held on 20-24 June 2011 in Wuzhen, Zhejiang Province of China and the scientific programme will be follow the same model as in 2009.

Acceleration ramps along high operating speed roadways.

DOT National Transportation Integrated Search

2010-11-01

Until recently, guidelines for the geometric design of acceleration lanes used for the : successful merge of an entering vehicle into a high-speed surface transportation system : through-traffic lane have been based upon concepts and vehicle characte...

Cirrus cloud mimic surfaces in the laboratory: organic acids, bases and NOx heterogeneous reactions

NASA Astrophysics Data System (ADS)

Sodeau, J.; Oriordan, B.

2003-04-01

CIRRUS CLOUD MIMIC SURFACES IN THE LABORATORY:ORGANIC ACIDS, BASES AND NOX HETEROGENEOUS REACTIONS. B. ORiordan, J. Sodeau Department of Chemistry and Environment Research Institute, University College Cork, Ireland j.sodeau@ucc.ie /Fax: +353-21-4902680 There are a variety of biogenic and anthropogenic sources for the simple carboxylic acids to be found in the troposphere giving rise to levels as high as 45 ppb in certain urban areas. In this regard it is of note that ants of genus Formica produce some 10Tg of formic acid each year; some ten times that produced by industry. The expected sinks are those generally associated with tropospheric chemistry: the major routes studied, to date, being wet and dry deposition. No studies have been carried out hitherto on the role of water-ice surfaces in the atmospheric chemistry of carboxylic acids and the purpose of this paper is to indicate their potential function in the heterogeneous release of atmospheric species such as HONO. The deposition of formic acid on a water-ice surface was studied using FT-RAIR spectroscopy over a range of temperatures between 100 and 165K. In all cases ionization to the formate (and oxonium) ions was observed. The results were confirmed by TPD (Temperature Programmed Desorption) measurements, which indicated that two distinct surface species adsorb to the ice. Potential reactions between the formic acid/formate ion surface and nitrogen dioxide were subsequently investigated by FT-RAIRS. Co-deposition experiments showed that N2O3 and the NO+ ion (associated with water) were formed as products. A mechanism is proposed to explain these results, which involves direct reaction between the organic acid and nitrogen dioxide. Similar experiments involving acetic acid also indicate ionization on a water-ice surface. The results are put into the context of atmospheric chemistry potentially occuring on cirrus cloud surfaces.

Controlling Surface Plasmons Through Covariant Transformation of the Spin-Dependent Geometric Phase Between Curved Metamaterials

NASA Astrophysics Data System (ADS)

Zhong, Fan; Li, Jensen; Liu, Hui; Zhu, Shining

2018-06-01

General relativity uses curved space-time to describe accelerating frames. The movement of particles in different curved space-times can be regarded as equivalent physical processes based on the covariant transformation between different frames. In this Letter, we use one-dimensional curved metamaterials to mimic accelerating particles in curved space-times. The different curved shapes of structures are used to mimic different accelerating frames. The different geometric phases along the structure are used to mimic different movements in the frame. Using the covariant principle of general relativity, we can obtain equivalent nanostructures based on space-time transformations, such as the Lorentz transformation and conformal transformation. In this way, many covariant structures can be found that produce the same surface plasmon fields when excited by spin photons. A new kind of accelerating beam, the Rindler beam, is obtained based on the Rindler metric in gravity. Very large effective indices can be obtained in such systems based on geometric-phase gradient. This general covariant design method can be extended to many other optical media.

Quantitative analysis of osteoblast behavior on microgrooved hydroxyapatite and titanium substrata.

PubMed

Lu, Xiong; Leng, Yang

2003-09-01

The effects of implant surface topography and chemistry on osteoblast behavior have been a research focus because of their potential importance in orthopedic and dental applications. This work focused on the topographic effects of hydroxyapatite (HA) and titanium (Ti) surface that had identical micropatterns to determine whether there was synergistic interaction between surface chemistry and surface topography. Surface microgrooves with six different groove widths (4, 8, 16, 24, 30, and 38 microm) and three different groove depths (2, 4, and 10 microm) were made on single crystalline silicon wafers using microfabrication techniques. Ti and HA thin films were coated on the microgrooves by radio-frequency magnetron sputtering. After that, human osteoblast-like cells were seeded and cultured on the microgrooved surfaces for up to 7 days. The cells' behavior was examined using scanning electron microscopy after cells were fixed and dehydrated. Statistical analysis was based on quantitative data of orientation angle, evaluating the contact guidance, and form index, describing cell shape or cell morphology changes. The contact guidance and cell shape changes were observed on the HA and Ti microgrooves. No difference in orientation angle between HA and Ti microgrooves was found. This might suggest that surface chemistry was not a significant influence on cell guidance. However, the form index analysis indicated an interaction between topographic effects and surface chemistry. Thus, conclusions about surface topographic effects on cell behavior drawn from one type of material cannot simply be applied to another type of material. Copyright 2003 Wiley Periodicals, Inc. J Biomed Mater Res 66A: 677-687, 2003

Supramolecular chemistry at interfaces: host-guest interactions for fabricating multifunctional biointerfaces.

PubMed

Yang, Hui; Yuan, Bin; Zhang, Xi; Scherman, Oren A

2014-07-15

CONSPECTUS: Host-guest chemistry can greatly improve the selectivity of biomolecule-ligand binding on account of recognition-directed interactions. In addition, functional structures and the actuation of supramolecular assemblies in molecular systems can be controlled efficiently through various host-guest chemistry. Together, these highly selective, strong yet dynamic interactions can be exploited as an alternative methodology for applications in the field of programmable and controllable engineering of supramolecular soft materials through the reversible binding between complementary components. Many processes in living systems such as biotransformation, transportation of matter, and energy transduction begin with interfacial molecular recognition, which is greatly influenced by various external stimuli at biointerfaces. Detailed investigations about the molecular recognition at interfaces can result in a better understanding of life science, and further guide us in developing new biomaterials and medicines. In order to mimic complicated molecular-recognition systems observed in nature that adapt to changes in their environment, combining host-guest chemistry and surface science is critical for fabricating the next generation of multifunctional biointerfaces with efficient stimuli-responsiveness and good biocompatibility. In this Account, we will summarize some recent progress on multifunctional stimuli-responsive biointerfaces and biosurfaces fabricated by cyclodextrin- or cucurbituril-based host-guest chemistry and highlight their potential applications including drug delivery, bioelectrocatalysis, and reversible adsorption and resistance of peptides, proteins, and cells. In addition, these biointerfaces and biosurfaces demonstrate efficient response toward various external stimuli, such as UV light, pH, redox chemistry, and competitive guests. All of these external stimuli can aid in mimicking the biological stimuli evident in complex biological environments. We begin by reviewing the current state of stimuli-responsive supramolecular assemblies formed by host-guest interactions, discussing how to transfer host-guest chemistry from solution onto surfaces required for fabricating multifunctional biosurfaces and biointerfaces. Then, we present different stimuli-responsive biosurfaces and biointerfaces, which have been prepared through a combination of cyclodextrin- or cucurbituril-based host-guest chemistry and various surface technologies such as self-assembled monolayers or layer-by-layer assembly. Moreover, we discuss the applications of these biointerfaces and biosurfaces in the fields of drug release, reversible adsorption and release of some organic molecules, peptides, proteins, and cells, and photoswitchable bioelectrocatalysis. In addition, we summarize the merits and current limitations of these methods for fabricating multifunctional stimuli-responsive biointerfaces in a dynamic noncovalent manner. Finally, we present possible strategies for future designs of stimuli-responsive multifunctional biointerfaces and biosurfaces by combining host-guest chemistry with surface science, which will lead to further critical development of supramolecular chemistry at interfaces.

Modeling, Measurements, and Fundamental Database Development for Nonequilibrium Hypersonic Aerothermodynamics

NASA Technical Reports Server (NTRS)

Bose, Deepak

2012-01-01

The design of entry vehicles requires predictions of aerothermal environment during the hypersonic phase of their flight trajectories. These predictions are made using computational fluid dynamics (CFD) codes that often rely on physics and chemistry models of nonequilibrium processes. The primary processes of interest are gas phase chemistry, internal energy relaxation, electronic excitation, nonequilibrium emission and absorption of radiation, and gas-surface interaction leading to surface recession and catalytic recombination. NASAs Hypersonics Project is advancing the state-of-the-art in modeling of nonequilibrium phenomena by making detailed spectroscopic measurements in shock tube and arcjets, using ab-initio quantum mechanical techniques develop fundamental chemistry and spectroscopic databases, making fundamental measurements of finite-rate gas surface interactions, implementing of detailed mechanisms in the state-of-the-art CFD codes, The development of new models is based on validation with relevant experiments. We will present the latest developments and a roadmap for the technical areas mentioned above

Nanoporous Gold as a Neural Interface Coating: Effects of Topography, Surface Chemistry, and Feature Size

DOE PAGES

Chapman, Christopher A. R.; Chen, Hao; Stamou, Marianna; ...

2015-02-23

We report that designing neural interfaces that maintain close physical coupling of neurons to an electrode surface remains a major challenge for both implantable and in vitro neural recording electrode arrays. Typically, low-impedance nanostructured electrode coatings rely on chemical cues from pharmaceuticals or surface-immobilized peptides to suppress glial scar tissue formation over the electrode surface (astrogliosis), which is an obstacle to reliable neuron–electrode coupling. Nanoporous gold (np-Au), produced by an alloy corrosion process, is a promising candidate to reduce astrogliosis solely through topography by taking advantage of its tunable length scale. In the present in vitro study on np-Au’s interactionmore » with cortical neuron–glia co-cultures, we demonstrate that the nanostructure of np-Au achieves close physical coupling of neurons by maintaining a high neuron-to-astrocyte surface coverage ratio. Atomic layer deposition-based surface modification was employed to decouple the effect of morphology from surface chemistry. Additionally, length scale effects were systematically studied by controlling the characteristic feature size of np-Au through variations in the dealloying conditions. In conclusion, our results show that np-Au nanotopography, not surface chemistry, reduces astrocyte surface coverage while maintaining high neuronal coverage and may enhance neuron–electrode coupling through nanostructure-mediated suppression of scar tissue formation.« less

Effects of Chemistry on Blunt-Body Wake Structure

NASA Technical Reports Server (NTRS)

Dogra, Virendra K.; Moss, James N.; Wilmoth, Richard G.; Taylor, Jeff C.; Hassan, H. A.

1995-01-01

Results of a numerical study are presented for hypersonic low-density flow about a 70-deg blunt cone using direct simulation Monte Carlo (DSMC) and Navier-Stokes calculations. Particular emphasis is given to the effects of chemistry on the near-wake structure and on the surface quantities and the comparison of the DSMC results with the Navier-Stokes calculations. The flow conditions simulated are those experienced by a space vehicle at an altitude of 85 km and a velocity of 7 km/s during Earth entry. A steady vortex forms in the near wake for these freestream conditions for both chemically reactive and nonreactive air gas models. The size (axial length) of the vortex for the reactive air calculations is 25% larger than that of the nonreactive air calculations. The forebody surface quantities are less sensitive to the chemistry than the base surface quantities. The presence of the afterbody has no effect on the forebody flow structure or the surface quantities. The comparisons of DSMC and Navier-Stokes calculations show good agreement for the wake structure and the forebody surface quantities.

Effect of fullerenol surface chemistry on nanoparticle binding-induced protein misfolding

NASA Astrophysics Data System (ADS)

Radic, Slaven; Nedumpully-Govindan, Praveen; Chen, Ran; Salonen, Emppu; Brown, Jared M.; Ke, Pu Chun; Ding, Feng

2014-06-01

Fullerene and its derivatives with different surface chemistry have great potential in biomedical applications. Accordingly, it is important to delineate the impact of these carbon-based nanoparticles on protein structure, dynamics, and subsequently function. Here, we focused on the effect of hydroxylation -- a common strategy for solubilizing and functionalizing fullerene -- on protein-nanoparticle interactions using a model protein, ubiquitin. We applied a set of complementary computational modeling methods, including docking and molecular dynamics simulations with both explicit and implicit solvent, to illustrate the impact of hydroxylated fullerenes on the structure and dynamics of ubiquitin. We found that all derivatives bound to the model protein. Specifically, the more hydrophilic nanoparticles with a higher number of hydroxyl groups bound to the surface of the protein via hydrogen bonds, which stabilized the protein without inducing large conformational changes in the protein structure. In contrast, fullerene derivatives with a smaller number of hydroxyl groups buried their hydrophobic surface inside the protein, thereby causing protein denaturation. Overall, our results revealed a distinct role of surface chemistry on nanoparticle-protein binding and binding-induced protein misfolding.Fullerene and its derivatives with different surface chemistry have great potential in biomedical applications. Accordingly, it is important to delineate the impact of these carbon-based nanoparticles on protein structure, dynamics, and subsequently function. Here, we focused on the effect of hydroxylation -- a common strategy for solubilizing and functionalizing fullerene -- on protein-nanoparticle interactions using a model protein, ubiquitin. We applied a set of complementary computational modeling methods, including docking and molecular dynamics simulations with both explicit and implicit solvent, to illustrate the impact of hydroxylated fullerenes on the structure and dynamics of ubiquitin. We found that all derivatives bound to the model protein. Specifically, the more hydrophilic nanoparticles with a higher number of hydroxyl groups bound to the surface of the protein via hydrogen bonds, which stabilized the protein without inducing large conformational changes in the protein structure. In contrast, fullerene derivatives with a smaller number of hydroxyl groups buried their hydrophobic surface inside the protein, thereby causing protein denaturation. Overall, our results revealed a distinct role of surface chemistry on nanoparticle-protein binding and binding-induced protein misfolding. Electronic supplementary information (ESI) is available: Fluorescence spectra, ITC, CD spectra and other data as described in the text. See DOI: 10.1039/c4nr01544d

Optimization of batteries for plug-in hybrid electric vehicles

NASA Astrophysics Data System (ADS)

English, Jeffrey Robb

This thesis presents a method to quickly determine the optimal battery for an electric vehicle given a set of vehicle characteristics and desired performance metrics. The model is based on four independent design variables: cell count, cell capacity, state-of-charge window, and battery chemistry. Performance is measured in seven categories: cost, all-electric range, maximum speed, acceleration, battery lifetime, lifetime greenhouse gas emissions, and charging time. The performance of each battery is weighted according to a user-defined objective function to determine its overall fitness. The model is informed by a series of battery tests performed on scaled-down battery samples. Seven battery chemistries were tested for capacity at different discharge rates, maximum output power at different charge levels, and performance in a real-world automotive duty cycle. The results of these tests enable a prediction of the performance of the battery in an automobile. Testing was performed at both room temperature and low temperature to investigate the effects of battery temperature on operation. The testing highlighted differences in behavior between lithium, nickel, and lead based batteries. Battery performance decreased with temperature across all samples with the largest effect on nickel-based chemistries. Output power also decreased with lead acid batteries being the least affected by temperature. Lithium-ion batteries were found to be highly efficient (>95%) under a vehicular duty cycle; nickel and lead batteries have greater losses. Low temperatures hindered battery performance and resulted in accelerated failure in several samples. Lead acid, lead tin, and lithium nickel alloy batteries were unable to complete the low temperature testing regime without losing significant capacity and power capability. This is a concern for their applicability in electric vehicles intended for cold climates which have to maintain battery temperature during long periods of inactivity. Three sample optimizations were performed: a compact car, a, truck, and a sports car. The compact car benefits from increased battery capacity despite the associated higher cost. The truck returned the smallest possible battery of each chemistry, indicating that electrification is not advisable. The sports car optimization resulted in the largest possible battery, indicating large performance from increased electrification. These results mirror the current state of the electric vehicle market.

The interactions of atmospheric cosmogenic radionuclides with spacecraft surfaces

NASA Technical Reports Server (NTRS)

Gregory, John C.; Fishman, G. J.; Harmon, A.; Parnell, T. A.; Herzog, G.; Klein, J.; Jull, A. J. T.

1991-01-01

The discovery of the cosmogenic radionuclide Be-7 on the front surface of the Long Duration Exposure Facility (LDEF) has opened new opportunities to study several unexplored regions of space science. The experiments have shown that the Be-7 found was concentrated in a thin surface layer of spacecraft material. The only reasonable source of the isotope is the atmosphere through which the spacecraft passed. It is expected that the uptake of Be in such circumstances will depend on the chemical form of the Be and the chemical nature of the substrate. It was found that the observed concentration of Be-7 does differ between metal surfaces and organic surfaces such as PTFE (Teflon). It is noted however, that (1) organic surfaces are etched by the atomic oxygen found under these orbital conditions, and (2) the relative velocity of the species is 8 km/s relative to the surface and the interaction chemistry and physics may differ from the norm. Be-7 is formed by disintegration of O and N nuclei under cosmic ray proton bombardment. Many other isotopes are produced by cosmic ray reactions, and some of these are suited to measurement by the extremely sensitive methods of accelerator mass spectrometry.

How High Pressure Unifies Solvation Processes in Liquid Chromatography.

PubMed

Bocian, Szymon; Škrinjar, Tea; Bolanca, Tomislav; Buszewski, Bogusław

2017-11-01

A series of core-shell-based stationary phases of varying surface chemistry were subjected to solvent adsorption investigation under ultra-HPLC conditions. Acetonitrile and water excess isotherms were measured using a minor disturbance method. It was observed that adsorption of organic solvent is unified under high pressure. Preferential solvation due to specific interactions between the stationary phases and solvent molecules was limited. The obtained results showed that the solvation process is almost independent of surface chemistry, in contrast to HPLC conditions in which specific interactions differentiate solvation processes.

Biodegradable polyester-based microcarriers with modified surface tailored for tissue engineering.

PubMed

Privalova, A; Markvicheva, E; Sevrin, Ch; Drozdova, M; Kottgen, C; Gilbert, B; Ortiz, M; Grandfils, Ch

2015-03-01

Microcarriers have been proposed in tissue engineering, namely for bone, cartilage, skin, vascular, and central nervous system. Although polyester-based microcarriers have been already used for this purpose, their surface properties should be improved to provide better cell growth. The goal of this study was to prepare microbeads based on poly(D,L-lactide) acid, poly(L-lactide) acid, and to study cell behavior (adhesion, spreading, growth, and proliferation) in function of microbead topography and surface chemistry. To improve L-929 fibroblasts adhesion, microbead surface has been modified with three polycations: chitosan, poly(2-dimethylamino ethylmethacrylate) (PDMAEMA), or chitosan-g-oligolactide copolymer (chit-g-OLA). Although modification of the microbead surface with chitosan and PDMAEMA was performed through physical adsorption on the previously prepared microbeads, chit-g-OLA copolymer was introduced directly during microbead processing. This simple approach (1) bypass the use of an emulsifier (polyvinyl alcohol, PVA); (2) avoid surface "contamination" with PVA molecules limiting a control of the surface characteristics. In vitro study of the growth of mouse fibroblasts on the microbeads showed that both surface topography and chemistry affected cell attachment, spreading, and proliferation. Cultivation of L-929 fibroblasts for 7 days resulted in the formation of a 3D cell-scaffold network. © 2014 Wiley Periodicals, Inc.

Final Report: Rational Design of Anode Surface Chemistry in Microbial Fuel Cells for Improved Exoelectrogen Attachment and Electron Transfer

DTIC Science & Technology

2015-12-21

SECURITY CLASSIFICATION OF: The overall goal of this project is to determine how electrode surface chemistry can be rationally designed to decrease...2015 Approved for Public Release; Distribution Unlimited Final Report: Rational Design of Anode Surface Chemistry in Microbial Fuel Cells for...ABSTRACT Final Report: Rational Design of Anode Surface Chemistry in Microbial Fuel Cells for Improved Exoelectrogen Attachment and Electron Transfer

Probing the chemistry, structure, and dynamics of the water-silica interface

NASA Astrophysics Data System (ADS)

Lockwood, Glenn K.

Despite its natural abundance and wide-ranging technological relevance, much remains unknown or unclear about water-silica interfaces. Computer simulation stands to bridge the gaps of knowledge left by experiment, and a recently developed Dissociative Water Potential has enabled the simulation of large amorphous silica surfaces in contact with water without having to impose a model of surface chemistry a priori. Earlier work with this model has revealed the existence of several protonated surface sites such as SiOH2 + and Si-(OH+)-Si that have yet to be extensively characterized. However, both experiment and quantum mechanical simulation have provided an increasing body of evidence that suggests these sites exist, and these sites may play key roles in some of the unexplained phenomena observed in water-silica systems. To this end, this Dissociative Water Potential has been applied to develop a comprehensive picture of the chemistry, structure, and dynamics of the water-silica interface that is unbiased by any expectation of what sites should form. The bridging OH site, Si-(OH+)-Si, does form and is characterized as a highly acidic site that occurs predominantly on strained Si-O-Si bridges near the interface. Similarly, the transient formation of SiOH2 + is observed, and this site is found to be more acidic than Si-(OH +)-Si. In addition to H3O+ that forms near the interface, all of these sites readily deprotonate and are expected to play a role in the enhanced proton conductivity experimentally observed in hydrated mesoporous silica. The reactions between water and silica are particularly relevant to the engineering of nuclear waste forms, and the role of water-silica interactions are also explored within the context of the degradation of silica-based waste forms exposed to radiation. Despite the significant simulation effort employed in glassy waste form research, no molecular models of radiation damage in silica include the effects of moisture. This deficiency is addressed, and water is found to play a significant role in accelerating the degradation of amorphous silica under irradiation. Water inhibits healing of the network and promotes the formation of voids into which more water can penetrate, giving way to new damage accumulation mechanisms not seen in any past simulations.

Versatile multi-functionalization of protein nanofibrils for biosensor applications

NASA Astrophysics Data System (ADS)

Sasso, L.; Suei, S.; Domigan, L.; Healy, J.; Nock, V.; Williams, M. A. K.; Gerrard, J. A.

2014-01-01

Protein nanofibrils offer advantages over other nanostructures due to the ease in their self-assembly and the versatility of surface chemistry available. Yet, an efficient and general methodology for their post-assembly functionalization remains a significant challenge. We introduce a generic approach, based on biotinylation and thiolation, for the multi-functionalization of protein nanofibrils self-assembled from whey proteins. Biochemical characterization shows the effects of the functionalization onto the nanofibrils' surface, giving insights into the changes in surface chemistry of the nanostructures. We show how these methods can be used to decorate whey protein nanofibrils with several components such as fluorescent quantum dots, enzymes, and metal nanoparticles. A multi-functionalization approach is used, as a proof of principle, for the development of a glucose biosensor platform, where the protein nanofibrils act as nanoscaffolds for glucose oxidase. Biotinylation is used for enzyme attachment and thiolation for nanoscaffold anchoring onto a gold electrode surface. Characterization via cyclic voltammetry shows an increase in glucose-oxidase mediated current response due to thiol-metal interactions with the gold electrode. The presented approach for protein nanofibril multi-functionalization is novel and has the potential of being applied to other protein nanostructures with similar surface chemistry.Protein nanofibrils offer advantages over other nanostructures due to the ease in their self-assembly and the versatility of surface chemistry available. Yet, an efficient and general methodology for their post-assembly functionalization remains a significant challenge. We introduce a generic approach, based on biotinylation and thiolation, for the multi-functionalization of protein nanofibrils self-assembled from whey proteins. Biochemical characterization shows the effects of the functionalization onto the nanofibrils' surface, giving insights into the changes in surface chemistry of the nanostructures. We show how these methods can be used to decorate whey protein nanofibrils with several components such as fluorescent quantum dots, enzymes, and metal nanoparticles. A multi-functionalization approach is used, as a proof of principle, for the development of a glucose biosensor platform, where the protein nanofibrils act as nanoscaffolds for glucose oxidase. Biotinylation is used for enzyme attachment and thiolation for nanoscaffold anchoring onto a gold electrode surface. Characterization via cyclic voltammetry shows an increase in glucose-oxidase mediated current response due to thiol-metal interactions with the gold electrode. The presented approach for protein nanofibril multi-functionalization is novel and has the potential of being applied to other protein nanostructures with similar surface chemistry. Electronic supplementary information (ESI) available: Cyclic voltammetry characterization of biosensor platforms including bare Au electrodes (Fig. S1), biosensor response to various glucose concentrations (Fig. S2), and AFM roughness measurements due to WPNF modifications (Fig. S3). See DOI: 10.1039/c3nr05752f

Engineering of Surface Chemistry for Enhanced Sensitivity in Nanoporous Interferometric Sensing Platforms.

PubMed

Law, Cheryl Suwen; Sylvia, Georgina M; Nemati, Madieh; Yu, Jingxian; Losic, Dusan; Abell, Andrew D; Santos, Abel

2017-03-15

We explore new approaches to engineering the surface chemistry of interferometric sensing platforms based on nanoporous anodic alumina (NAA) and reflectometric interference spectroscopy (RIfS). Two surface engineering strategies are presented, namely (i) selective chemical functionalization of the inner surface of NAA pores with amine-terminated thiol molecules and (ii) selective chemical functionalization of the top surface of NAA with dithiol molecules. The strong molecular interaction of Au 3+ ions with thiol-containing functional molecules of alkane chain or peptide character provides a model sensing system with which to assess the sensitivity of these NAA platforms by both molecular feature and surface engineering. Changes in the effective optical thickness of the functionalized NAA photonic films (i.e., sensing principle), in response to gold ions, are monitored in real-time by RIfS. 6-Amino-1-hexanethiol (inner surface) and 1,6-hexanedithiol (top surface), the most sensitive functional molecules from approaches i and ii, respectively, were combined into a third sensing strategy whereby the NAA platforms are functionalized on both the top and inner surfaces concurrently. Engineering of the surface according to this approach resulted in an additive enhancement in sensitivity of up to 5-fold compared to previously reported systems. This study advances the rational engineering of surface chemistry for interferometric sensing on nanoporous platforms with potential applications for real-time monitoring of multiple analytes in dynamic environments.

Gel nanostructure in alkali-activated binders based on slag and fly ash, and effects of accelerated carbonation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bernal, Susan A., E-mail: s.bernal@sheffield.ac.uk; Department of Materials Science and Engineering, The University of Sheffield, Sheffield S1 3JD; Provis, John L., E-mail: j.provis@sheffield.ac.uk

2013-11-15

Binders formed through alkali-activation of slags and fly ashes, including ‘fly ash geopolymers’, provide appealing properties as binders for low-emissions concrete production. However, the changes in pH and pore solution chemistry induced during accelerated carbonation testing provide unrealistically low predictions of in-service carbonation resistance. The aluminosilicate gel remaining in an alkali-activated slag system after accelerated carbonation is highly polymerised, consistent with a decalcification mechanism, while fly ash-based binders mainly carbonate through precipitation of alkali salts (bicarbonates at elevated CO{sub 2} concentrations, or carbonates under natural exposure) from the pore solution, with little change in the binder gel identifiable by nuclearmore » magnetic resonance spectroscopy. In activated fly ash/slag blends, two distinct gels (C–A–S–H and N–A–S–H) are formed; under accelerated carbonation, the N–A–S–H gel behaves comparably to fly ash-based systems, while the C–A–S–H gel is decalcified similarly to alkali-activated slag. This provides new scope for durability optimisation, and for developing appropriate testing methodologies. -- Highlights: •C-A-S-H gel in alkali-activated slag decalcifies during accelerated carbonation. •Alkali-activated fly ash gel changes much less under CO{sub 2} exposure. •Blended slag-fly ash binder contains two coexisting gel types. •These two gels respond differently to carbonation. •Understanding of carbonation mechanisms is essential in developing test methods.« less

The spectroscopy and chemical dynamics of microparticles explored using an ultrasonic trap.

PubMed

Mason, N J; Drage, E A; Webb, S M; Dawes, A; McPheat, R; Hayes, G

2008-01-01

Microsized particles play an important role in many diverse areas of science and technology, for example, surface reactions of micron-sized particles play a key role in astrochemistry, plasma reactors and atmospheric chemistry. To date much of our knowledge of such surface chemistry is derived from 'traditional' surface science-based research. However, the large surface area and morphology of surface material commonly used in such surface science techniques may not necessarily mimic that on the surface of micron/nano scale particles. Hence, a new generation of experiments in which the spectroscopy (e.g., albedo) and chemical reactivity of micron-sized particles can be studied directly must be developed. One, as yet underexploited, non-invasive technique is the use of ultrasonic levitation. In this article, we describe the operation of an 'ultrasonic trap' to store and study the physical and chemical properties of microparticles.

Operando chemistry of catalyst surfaces during catalysis.

PubMed

Dou, Jian; Sun, Zaicheng; Opalade, Adedamola A; Wang, Nan; Fu, Wensheng; Tao, Franklin Feng

2017-04-03

Chemistry of a catalyst surface during catalysis is crucial for a fundamental understanding of mechanism of a catalytic reaction performed on the catalyst in the gas or liquid phase. Due to the pressure- or molecular density-dependent entropy contribution of gas or liquid phase of the reactants and the potential formation of a catalyst surface during catalysis different from that observed in an ex situ condition, the characterization of the surface of a catalyst under reaction conditions and during catalysis can be significant and even necessary for understanding the catalytic mechanism at a molecular level. Electron-based analytical techniques are challenging for studying catalyst nanoparticles in the gas or liquid phase although they are necessary techniques to employ. Instrumentation and further development of these electron-based techniques have now made in situ/operando studies of catalysts possible. New insights into the chemistry and structure of catalyst nanoparticles have been uncovered over the last decades. Herein, the origin of the differences between ex situ and in situ/operando studies of catalysts, and the technical challenges faced as well as the corresponding instrumentation and innovations utilized for characterizing catalysts under reaction conditions and during catalysis, are discussed. The restructuring of catalyst surfaces driven by the pressure of reactant(s) around a catalyst, restructuring in reactant(s) driven by reaction temperature and restructuring during catalysis are also reviewed herein. The remaining challenges and possible solutions are briefly discussed.

Advances on Aryldiazonium Salt Chemistry Based Interfacial Fabrication for Sensing Applications.

PubMed

Cao, Chaomin; Zhang, Yin; Jiang, Cheng; Qi, Meng; Liu, Guozhen

2017-02-15

Aryldiazonium salts as coupling agents for surface chemistry have evidenced their wide applications for the development of sensors. Combined with advances in nanomaterials, current trends in sensor science and a variety of particular advantages of aryldiazonium salt chemistry in sensing have driven the aryldiazonium salt-based sensing strategies to grow at an astonishing pace. This review focuses on the advances in the use of aryldiazonium salts for modifying interfaces in sensors and biosensors during the past decade. It will first summarize the current methods for modification of interfaces with aryldiazonium salts, and then discuss the sensing applications of aryldiazonium salts modified on different transducers (bulky solid electrodes, nanomaterials modified bulky solid electrodes, and nanoparticles). Finally, the challenges and perspectives that aryldiazonium salt chemistry is facing in sensing applications are critically discussed.

Mechanisms of Hydrocarbon Based Polymer Etch

NASA Astrophysics Data System (ADS)

Lane, Barton; Ventzek, Peter; Matsukuma, Masaaki; Suzuki, Ayuta; Koshiishi, Akira

2015-09-01

Dry etch of hydrocarbon based polymers is important for semiconductor device manufacturing. The etch mechanisms for oxygen rich plasma etch of hydrocarbon based polymers has been studied but the mechanism for lean chemistries has received little attention. We report on an experimental and analytic study of the mechanism for etching of a hydrocarbon based polymer using an Ar/O2 chemistry in a single frequency 13.56 MHz test bed. The experimental study employs an analysis of transients from sequential oxidation and Ar sputtering steps using OES and surface analytics to constrain conceptual models for the etch mechanism. The conceptual model is consistent with observations from MD studies and surface analysis performed by Vegh et al. and Oehrlein et al. and other similar studies. Parameters of the model are fit using published data and the experimentally observed time scales.

Composites Based on Polytetrafluoroethylene and Detonation Nanodiamonds: Filler-Matrix Chemical Interaction and Its Effect on a Composite's Properties

NASA Astrophysics Data System (ADS)

Koshcheev, A. P.; Perov, A. A.; Gorokhov, P. V.; Zaripov, N. V.; Tereshenkov, A. V.; Khatipov, S. A.

2018-06-01

Specific properties of PTFE composites filled with ultradisperse detonation diamonds (UDDs) with different surface chemistries are studied. It is found for the first time that filler in the form of UDDs affects not only the rate of PTFE thermal decomposition in vacuum pyrolysis, but also the chemical composition of the products of degradation. The wear resistance of UDD/PTFE composites is shown to depend strongly on the UDD surface chemistry. The presence of UDDs in a PTFE composite is found to result in perfluorocarbon telomeres, released as a readily condensable fraction upon composite pyrolysis. The chemical interaction between PTFE and UDDs, characterized by an increase in the rate of gas evolution and a change in the desorbed gas's composition, is found to occur at temperature as low as 380°C. It is shown that the intensity of this interaction depends on the concentration of oxygen-containing surface groups, the efficiency of UDDs in terms of the composite's wear resistance being reduced due to the presence of these groups. Based on the experimental data, a conclusion is reached about the chemical interaction between UDDs and a PTFE matrix, its dependence on the nanodiamond surface chemistry, and its effect on a composite's tribology.

Surface-Accelerated Decomposition of δ-HMX.

PubMed

Sharia, Onise; Tsyshevsky, Roman; Kuklja, Maija M

2013-03-07

Despite extensive efforts to study the explosive decomposition of HMX, a cyclic nitramine widely used as a solid fuel, explosive, and propellant, an understanding of the physicochemical processes, governing the sensitivity of condensed HMX to detonation initiation is not yet achieved. Experimental and theoretical explorations of the initiation of chemistry are equally challenging because of many complex parallel processes, including the β-δ phase transition and the decomposition from both phases. Among four known polymorphs, HMX is produced in the most stable β-phase, which transforms into the most reactive δ-phase under heat or pressure. In this study, the homolytic NO2 loss and HONO elimination precursor reactions of the gas-phase, ideal crystal, and the (100) surface of δ-HMX are explored by first principles modeling. Our calculations revealed that the high sensitivity of δ-HMX is attributed to interactions of surfaces and molecular dipole moments. While both decomposition reactions coexist, the exothermic HONO-isomer formation catalyzes the N-NO2 homolysis, leading to fast violent explosions.

Submicron Surface-Patterned Fibers and Textiles

DTIC Science & Technology

2016-11-04

These authors contributed equally Keywords: grating, fiber, polymer , patterning, textile Distribution A: approved for public release...requirements. Second, textile materials are primarily polymer -based, while most surface-patterning techniques have been developed for silicon...Alternative substrates, especially flexible polymers , remain challenging to pattern [25,26] due to the highly specific surface chemistry of different

Finding the chemistry in biomass pyrolysis: Millisecond chemical kinetics and visualization

NASA Astrophysics Data System (ADS)

Krumm, Christoph

Biomass pyrolysis is a promising thermochemical method for producing fuels and chemicals from renewable sources. Development of a fundamental understanding of biomass pyrolysis chemistry is difficult due to the multi-scale and multi-phase nature of the process; biomass length scales span 11 orders of magnitude and pyrolysis phenomena include solid, liquid, and gas phase chemistry in addition to heat and mass transfer. These complexities have a significant effect on chemical product distributions and lead to variability between reactor technologies. A major challenge in the study of biomass pyrolysis is the development of kinetic models capable of describing hundreds of millisecond-scale reactions of biomass into lower molecular weight products. In this work, a novel technique for studying biomass pyrolysis provides the first- ever experimental determination of kinetics and rates of formation of the primary products from cellulose pyrolysis, providing insight into the millisecond-scale chemical reaction mechanisms. These findings highlight the importance of heat and mass transport limitations for cellulose pyrolysis chemistry and are used to identify the length scales at which transport limitations become relevant during pyrolysis. Through this technique, a transition is identified, known as the reactive melting point, between low and high temperature depolymerization. The transition between two mechanisms of cellulose decompositions unifies the mechanisms that govern low temperature char formation, intermediate pyrolysis conditions, and high temperature gas formation. The conditions under which biomass undergoes pyrolysis, including modes of heat transfer, have been shown to significantly affect the distribution of biorenewable chemical and fuel products. High-speed photography is used to observe the liftoff of initially crystalline cellulose particles when impinged on a heated surface, known as the Leidenfrost effect for room-temperature liquids. Order-of-magnitude changes in the lifetime of cellulose particles are observed as a result of changing modes in heat transfer as cellulose intermediate liquid droplets wet and de-wet polished ceramic surfaces. Introduction of surface macroporosity is shown to completely inhibit the cellulose Leidenfrost effect, providing avenues for surface modification and reactor design to control particle heat transfer in industrial pyrolysis applications. Cellulosic particles on surfaces consisting of microstructured, asymmetric ratchets were observed to spontaneously move orthogonal to ratchet wells above the cellulose reactive Leidenfrost temperature (>750 °C). Evaluation of the accelerating particles supported the mechanism of propelling viscous forces (50-200 nN) from rectified pyrolysis vapors, thus providing the first example of biomass conveyors with no moving parts driven by high temperature for biofuel reactors. Combined knowledge of pyrolysis chemistry, kinetics, and heat and mass transport effects direct the design of the next generation pyrolysis reactors for tuning bio- oil quality and design of improved catalytic upgrading technology.

Toxicity Evaluation of Engineered Nanomaterials (Phase 1 Studies)

DTIC Science & Technology

2012-01-01

Surface Chemistry on Cellular Response ...................................................................................................... 48...Gold Nanomaterial Solution Purity and Surface Chemistry Toxicity ................................................................. 18 Figure 7...Solution Purity and Surface Chemistry Control Although several studies have shown that both MPS and PEG are biocompatible, in order to ensure that

Characterization of low thermal conductivity PAN-based carbon fibers

NASA Technical Reports Server (NTRS)

Katzman, Howard A.; Adams, P. M.; Le, T. D.; Hemminger, Carl S.

1992-01-01

The microstructure and surface chemistry of eight low thermal conductivity (LTC) PAN-based carbon fibers were determined and compared with PAN-based fibers heat treated to higher temperatures. Based on wide-angle x ray diffraction, the LTC PAN fibers all appear to have a similar turbostratic structure with large 002 d-spacings, small crystallite sizes, and moderate preferred orientation. Limited small-angle x ray scattering (SAXS) results indicate that, with the exception of LTC fibers made by BASF, the LTC fibers do not have well developed pores. Transmission electron microscopy shows that the texture of the two LTC PAN-based fibers studied (Amoco T350/23X and /25X) consists of multiple sets of parallel, wavy, bent layers that interweave with each other forming a complex three dimensional network oriented randomly around the fiber axis. X ray photoelectron spectroscopy (XPS) analysis finds correlations between heat treated temperatures and the surface composition chemistry of the carbon fiber samples.

Toward 4D Nanoprinting with Tip-Induced Organic Surface Reactions.

PubMed

Carbonell, Carlos; Braunschweig, Adam B

2017-02-21

Future nanomanufacturing tools will prepare organic materials with complex four-dimensional (4D) structure, where the position (x, y, z) and chemical composition within a volume is controlled with sub-1 μm spatial resolution. Such tools could produce substrates that mimic biological interfaces, like the cell surface or the extracellular matrix, whose topology and chemical complexity combine to direct some of the most sophisticated biological events. The control of organic materials at the nanoscale-level of spatial resolution could revolutionize the assembly of next generation optical and electronic devices or substrates for tissue engineering or enable fundamental biological or material science investigations. Organic chemistry provides the requisite control over the orientation and position of matter within a nanoscale reference frame through the formation of new covalent bonds. Several challenges however preclude the integration of organic chemistry with conventional nanomanufacturing approaches, namely most nanolithography platforms would denature or destroy delicate organic and biologically active matter, confirming covalent bond formation at interfaces remains difficult, and finally, only a small handful of the reactions used to transform molecules in solution have been validated on surfaces. Thus, entirely new approaches, where organic transformations and spatial control are considered equally important contributors, are needed to create 4D organic nanoprinting platforms. This Account describes efforts from our group to reconcile nanolithography, and specifically massively parallel scanning probe lithography (SPL), with organic chemistry to further the goal of 4D organic nanoprinting. Massively parallel SPL involves arrays of elastomeric pyramids mounted onto piezoelectric actuators, and creates patterns with feature diameters below 50 nm by using the pyramidal tips for either the direct deposition of ink or the localized delivery of energy to a surface. While other groups have focused on tip and array architetctures, our efforts have been on exploring their use for localizing organic chemistry on surfaces with nanoscale spatial resolution in 3D. Herein we describe the use of massively parallel SPL to create covalently immobilized patterns of organic materials using thermal, catalytic, photochemical, and force-accelerated reactions. In doing so, we have developed a high-throughput protocol for confirming interfacial bond formation. These efforts have resulted in new opportunities for the preparation of glycan arrays, novel approaches for covalently patterning graphene, and a 3D nanoprinter by combining photochemical brush polymerizations with SPL. Achieving true 4D nanoprinting involves advances in surface chemistry and instrumentation development, and to this end 4D micropatterns were produced in a microfluidic photoreactor that can position polymers composed of different monomers within micrometer proximity. A substantial gap remains, however, between these current technologies and the future's 4D nanomanufacturing tools, but the marriage of SPL with organic chemistry is an important step toward this goal. As this field continues to mature we can expect bottom-up 4D nanomanufacturing to begin supplanting conventional top-down strategies for preparing electronics, bioarrays, and functional substrates. In addition, these new printing technologies may enable the preparation of synthetic targets, such as artificial biological interfaces, with a level of organic sophistication that is entirely unachievable using existing technologies.

Pretreatment-dependent surface chemistry of wood nanocellulose for pH-sensitive hydrogels.

PubMed

Chinga-Carrasco, Gary; Syverud, Kristin

2014-09-01

Nanocellulose from wood is a promising material with potential in various technological areas. Within biomedical applications, nanocellulose has been proposed as a suitable nano-material for wound dressings. This is based on the capability of the material to self-assemble into 3D micro-porous structures, which among others have an excellent capacity of maintaining a moist environment. In addition, the surface chemistry of nanocellulose is suitable for various applications. First, OH-groups are abundant in nanocellulose materials, making the material strongly hydrophilic. Second, the surface chemistry can be modified, introducing aldehyde and carboxyl groups, which have major potential for surface functionalization. In this study, we demonstrate the production of nanocellulose with tailor-made surface chemistry, by pre-treating the raw cellulose fibres with carboxymethylation and periodate oxidation. The pre-treatments yielded a highly nanofibrillated material, with significant amounts of aldehyde and carboxyl groups. Importantly, the poly-anionic surface of the oxidized nanocellulose opens up for novel applications, i.e. micro-porous materials with pH-responsive characteristics. This is due to the swelling capacity of the 3D micro-porous structures, which have ionisable functional groups. In this study, we demonstrated that nanocellulose gels have a significantly higher swelling degree in neutral and alkaline conditions, compared to an acid environment (pH 3). Such a capability can potentially be applied in chronic wounds for controlled and intelligent release of antibacterial components into biofilms. © The Author(s) 2014 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav.

Pretreatment-dependent surface chemistry of wood nanocellulose for pH-sensitive hydrogels

PubMed Central

Syverud, Kristin

2014-01-01

Nanocellulose from wood is a promising material with potential in various technological areas. Within biomedical applications, nanocellulose has been proposed as a suitable nano-material for wound dressings. This is based on the capability of the material to self-assemble into 3D micro-porous structures, which among others have an excellent capacity of maintaining a moist environment. In addition, the surface chemistry of nanocellulose is suitable for various applications. First, OH-groups are abundant in nanocellulose materials, making the material strongly hydrophilic. Second, the surface chemistry can be modified, introducing aldehyde and carboxyl groups, which have major potential for surface functionalization. In this study, we demonstrate the production of nanocellulose with tailor-made surface chemistry, by pre-treating the raw cellulose fibres with carboxymethylation and periodate oxidation. The pre-treatments yielded a highly nanofibrillated material, with significant amounts of aldehyde and carboxyl groups. Importantly, the poly-anionic surface of the oxidized nanocellulose opens up for novel applications, i.e. micro-porous materials with pH-responsive characteristics. This is due to the swelling capacity of the 3D micro-porous structures, which have ionisable functional groups. In this study, we demonstrated that nanocellulose gels have a significantly higher swelling degree in neutral and alkaline conditions, compared to an acid environment (pH 3). Such a capability can potentially be applied in chronic wounds for controlled and intelligent release of antibacterial components into biofilms. PMID:24713295

Regulating Biocompatibility of Carbon Spheres via Defined Nanoscale Chemistry and a Careful Selection of Surface Functionalities

NASA Astrophysics Data System (ADS)

Misra, Santosh K.; Chang, Huei-Huei; Mukherjee, Prabuddha; Tiwari, Saumya; Ohoka, Ayako; Pan, Dipanjan

2015-10-01

A plethora of nanoarchitectures have been evaluated preclincially for applications in early detection and treatment of diseases at molecular and cellular levels resulted in limited success of their clinical translation. It is important to identify the factors that directly or indirectly affect their use in human. We bring a fundamental understanding of how to adjust the biocompatibility of carbon based spherical nanoparticles (CNPs) through defined chemistry and a vigilant choice of surface functionalities. CNPs of various size are designed by tweaking size (2-250 nm), surface chemistries (positive, or negatively charged), molecular chemistries (linear, dendritic, hyperbranched) and the molecular weight of the coating agents (MW 400-20 kDa). A combination of in vitro assays as tools were performed to determine the critical parameters that may trigger toxicity. Results indicated that hydrodynamic sizes are potentially not a risk factor for triggering cellular and systemic toxicity, whereas the presence of a highly positive surface charge and increasing molecular weight enhance the chance of inducing complement activation. Bare and carboxyl-terminated CNPs did present some toxicity at the cellular level which, however, is not comparable to those caused by positively charged CNPs. Similarly, negatively charged CNPs with hydroxyl and carboxylic functionalities did not cause any hemolysis.

Acetonitrile cluster solvation in a cryogenic ethane-methane-propane liquid: Implications for Titan lake chemistry.

PubMed

Corrales, L René; Yi, Thomas D; Trumbo, Samantha K; Shalloway, David; Lunine, Jonathan I; Usher, David A

2017-03-14

The atmosphere of Titan, Saturn's largest moon, exhibits interesting UV- and radiation-driven chemistry between nitrogen and methane, resulting in dipolar, nitrile-containing molecules. The assembly and subsequent solvation of such molecules in the alkane lakes and seas found on the moon's surface are of particular interest for investigating the possibility of prebiotic chemistry in Titan's hydrophobic seas. Here we characterize the solvation of acetonitrile, a product of Titan's atmospheric radiation chemistry tentatively detected on Titan's surface [H. B. Niemann et al., Nature 438, 779-784 (2005)], in an alkane mixture estimated to match a postulated composition of the smaller lakes during cycles of active drying and rewetting. Molecular dynamics simulations are employed to determine the potential of mean force of acetonitrile (CH 3 CN) clusters moving from the alkane vapor into the bulk liquid. We find that the clusters prefer the alkane liquid to the vapor and do not dissociate in the bulk liquid. This opens up the possibility that acetonitrile-based microscopic polar chemistry may be possible in the otherwise nonpolar Titan lakes.

Rail accelerator research at Lewis Research Center

NASA Technical Reports Server (NTRS)

Kerslake, W. R.; Cybyk, B. Z.

1982-01-01

A rail accelerator was chosen for study as an electromagnetic space propulsion device because of its simplicity and existing technology base. The results of a mission feasibility study using a large rail accelerator for direct launch of ton-size payloads from the Earth's surface to space, and the results of initial tests with a small, laboratory rail accelerator are presented. The laboratory rail accelerator has a bore of 3 by 3 mm and has accelerated 60 mg projectiles to velocities of 300 to 1000 m/s. Rail materials of Cu, W, and Mo were tested for efficiency and erosion rate.

Nano interface potential influences in CdTe quantum dots and biolabeling

NASA Astrophysics Data System (ADS)

Kanagasubbulakshmi, S.; Kadirvelu, K.

2018-05-01

Nano interface influences in physiochemical properties of quantum dots (QDs) are the challenging approach to tailor its surface functionalities. In this study, a set of polar and non-polar solvents were selected to analyze the influences in solvent-based dynamic radius and surface potential of QDs. From the nano interface chemistry of polar and non-polar solvents, an appropriate mechanism of precipitation and hydrophobic ligand exchange strategy were elucidated by correlating Henry's equation. Further, the in vitro cytotoxic potential and antimicrobial activity of QDs were assessed to perform biolabeling. From the observations, an appropriate dosage of QDs was fixed to label the animal ((RAW 264.7 cell lines) and bacterial cells (Escherichia coli) for effective cell attachment. Biolabeling was achieved by tailoring nano interface chemistry of QDs without additional support of biomolecules. Bacterial cell wall-based interaction of QDs was evaluated using SEM and EDAX analysis. Thus, provided clear insights into the nano interface chemistry in the development of highly photostable QDs will be helpful in biomedical applications.

Alternative modeling methods for plasma-based Rf ion sources

DOE Office of Scientific and Technical Information (OSTI.GOV)

Veitzer, Seth A., E-mail: veitzer@txcorp.com; Kundrapu, Madhusudhan, E-mail: madhusnk@txcorp.com; Stoltz, Peter H., E-mail: phstoltz@txcorp.com

Rf-driven ion sources for accelerators and many industrial applications benefit from detailed numerical modeling and simulation of plasma characteristics. For instance, modeling of the Spallation Neutron Source (SNS) internal antenna H{sup −} source has indicated that a large plasma velocity is induced near bends in the antenna where structural failures are often observed. This could lead to improved designs and ion source performance based on simulation and modeling. However, there are significant separations of time and spatial scales inherent to Rf-driven plasma ion sources, which makes it difficult to model ion sources with explicit, kinetic Particle-In-Cell (PIC) simulation codes. Inmore » particular, if both electron and ion motions are to be explicitly modeled, then the simulation time step must be very small, and total simulation times must be large enough to capture the evolution of the plasma ions, as well as extending over many Rf periods. Additional physics processes such as plasma chemistry and surface effects such as secondary electron emission increase the computational requirements in such a way that even fully parallel explicit PIC models cannot be used. One alternative method is to develop fluid-based codes coupled with electromagnetics in order to model ion sources. Time-domain fluid models can simulate plasma evolution, plasma chemistry, and surface physics models with reasonable computational resources by not explicitly resolving electron motions, which thereby leads to an increase in the time step. This is achieved by solving fluid motions coupled with electromagnetics using reduced-physics models, such as single-temperature magnetohydrodynamics (MHD), extended, gas dynamic, and Hall MHD, and two-fluid MHD models. We show recent results on modeling the internal antenna H{sup −} ion source for the SNS at Oak Ridge National Laboratory using the fluid plasma modeling code USim. We compare demonstrate plasma temperature equilibration in two-temperature MHD models for the SNS source and present simulation results demonstrating plasma evolution over many Rf periods for different plasma temperatures. We perform the calculations in parallel, on unstructured meshes, using finite-volume solvers in order to obtain results in reasonable time.« less

Alternative modeling methods for plasma-based Rf ion sources.

PubMed

Veitzer, Seth A; Kundrapu, Madhusudhan; Stoltz, Peter H; Beckwith, Kristian R C

2016-02-01

Rf-driven ion sources for accelerators and many industrial applications benefit from detailed numerical modeling and simulation of plasma characteristics. For instance, modeling of the Spallation Neutron Source (SNS) internal antenna H(-) source has indicated that a large plasma velocity is induced near bends in the antenna where structural failures are often observed. This could lead to improved designs and ion source performance based on simulation and modeling. However, there are significant separations of time and spatial scales inherent to Rf-driven plasma ion sources, which makes it difficult to model ion sources with explicit, kinetic Particle-In-Cell (PIC) simulation codes. In particular, if both electron and ion motions are to be explicitly modeled, then the simulation time step must be very small, and total simulation times must be large enough to capture the evolution of the plasma ions, as well as extending over many Rf periods. Additional physics processes such as plasma chemistry and surface effects such as secondary electron emission increase the computational requirements in such a way that even fully parallel explicit PIC models cannot be used. One alternative method is to develop fluid-based codes coupled with electromagnetics in order to model ion sources. Time-domain fluid models can simulate plasma evolution, plasma chemistry, and surface physics models with reasonable computational resources by not explicitly resolving electron motions, which thereby leads to an increase in the time step. This is achieved by solving fluid motions coupled with electromagnetics using reduced-physics models, such as single-temperature magnetohydrodynamics (MHD), extended, gas dynamic, and Hall MHD, and two-fluid MHD models. We show recent results on modeling the internal antenna H(-) ion source for the SNS at Oak Ridge National Laboratory using the fluid plasma modeling code USim. We compare demonstrate plasma temperature equilibration in two-temperature MHD models for the SNS source and present simulation results demonstrating plasma evolution over many Rf periods for different plasma temperatures. We perform the calculations in parallel, on unstructured meshes, using finite-volume solvers in order to obtain results in reasonable time.

Ethanol surface chemistry on MBE-grown GaN(0001), GaOx/GaN(0001), and Ga2O3(2 \\xAF 01 )

NASA Astrophysics Data System (ADS)

Kollmannsberger, Sebastian L.; Walenta, Constantin A.; Winnerl, Andrea; Knoller, Fabian; Pereira, Rui N.; Tschurl, Martin; Stutzmann, Martin; Heiz, Ueli

2017-09-01

In this work, ethanol is used as a chemical probe to study the passivation of molecular beam epitaxy-grown GaN(0001) by surface oxidation. With a high degree of oxidation, no reaction from ethanol to acetaldehyde in temperature-programmed desorption experiments is observed. The acetaldehyde formation is attributed to a mechanism based on α -H abstraction from the dissociatively bound alcohol molecule. The reactivity is related to negatively charged surface states, which are removed upon oxidation of the GaN(0001) surface. This is compared with the Ga2O3(2 ¯ 01 ) single crystal surface, which is found to be inert for the acetaldehyde production. These results offer a toolbox to explore the surface chemistry of nitrides and oxynitrides on an atomic scale and relate their intrinsic activity to systems under ambient atmosphere.

Specific and selective target detection of supra-genome 21 Mers Salmonella via silicon nanowires biosensor

NASA Astrophysics Data System (ADS)

Mustafa, Mohammad Razif Bin; Dhahi, Th S.; Ehfaed, Nuri. A. K. H.; Adam, Tijjani; Hashim, U.; Azizah, N.; Mohammed, Mohammed; Noriman, N. Z.

2017-09-01

The nano structure based on silicon can be surface modified to be used as label-free biosensors that allow real-time measurements. The silicon nanowire surface was functionalized using 3-aminopropyltrimethoxysilane (APTES), which functions as a facilitator to immobilize biomolecules on the silicon nanowire surface. The process is simple, economical; this will pave the way for point-of-care applications. However, the surface modification and subsequent detection mechanism still not clear. Thus, study proposed step by step process of silicon nano surface modification and its possible in specific and selective target detection of Supra-genome 21 Mers Salmonella. The device captured the molecule with precisely; the approach took the advantages of strong binding chemistry created between APTES and biomolecule. The results indicated how modifications of the nanowires provide sensing capability with strong surface chemistries that can lead to specific and selective target detection.

Ethanol surface chemistry on MBE-grown GaN(0001), GaOx/GaN(0001), and Ga2O3(2¯01).

PubMed

Kollmannsberger, Sebastian L; Walenta, Constantin A; Winnerl, Andrea; Knoller, Fabian; Pereira, Rui N; Tschurl, Martin; Stutzmann, Martin; Heiz, Ueli

2017-09-28

In this work, ethanol is used as a chemical probe to study the passivation of molecular beam epitaxy-grown GaN(0001) by surface oxidation. With a high degree of oxidation, no reaction from ethanol to acetaldehyde in temperature-programmed desorption experiments is observed. The acetaldehyde formation is attributed to a mechanism based on α-H abstraction from the dissociatively bound alcohol molecule. The reactivity is related to negatively charged surface states, which are removed upon oxidation of the GaN(0001) surface. This is compared with the Ga 2 O 3 (2¯01) single crystal surface, which is found to be inert for the acetaldehyde production. These results offer a toolbox to explore the surface chemistry of nitrides and oxynitrides on an atomic scale and relate their intrinsic activity to systems under ambient atmosphere.

Biopolymer coated gold nanocrystals prepared using the green chemistry approach and their shape-dependent catalytic and surface-enhanced Raman scattering properties.

PubMed

Chou, Chih-Wei; Hsieh, Hui-Hsuan; Hseu, You-Cheng; Chen, Ko-Shao; Wang, Gou-Jen; Chang, Hsien-Chang; Pan, Yong-Li; Wei, Yi-Syuan; Chang, Ko Hsin; Harn, Yeu-Wei

2013-07-21

This study deals with the preparation of multi-shaped nanoscale gold crystals under synthetically simple, green, and efficient conditions using a seed-mediated growth approach in the presence of hyaluronic acid (HA). These highly biocompatible multi-shaped gold nanocrystals were examined to evaluate their catalytic and surface enhanced Raman scattering (SERS) properties. The results show that the size and shape of the nanocrystals are mainly correlated to the amount of seed, seed size, HA concentration, and reaction temperature. Gold seeds accelerate the reduction of the gold precursor to form gold nanocrystals using HA. The HA serves as a reducing agent and a growth template for the reduction of Au(III) and nanocrystal stabilization. The multi-shaped gold nanocrystals showed superior catalytic properties and higher SERS performance. The simple, green approach efficiently controls the nanocrystals and creates many opportunities for future applications.

Organic Chemistry in Two Dimensions: Surface-Functionalized Polymers and Self-Assembled Monolayer Films

DTIC Science & Technology

1988-09-01

surfaces as components of materials . In particular, we hope to develop the ability to rationalize and predict the macroscooic properties of surfaces...of much of the current research in areas such as materials science, condensed matter and device physics, and polymer physical chemistry. Surface...6 Underlying our program in surface chemistry is a broad interest in the prop- erties of organic surfaces as components of materials . In particular

Click chemistry approach to conventional vegetable tanning process: accelerated method with improved organoleptic properties.

PubMed

Krishnamoorthy, Ganesan; Ramamurthy, Govindaswamy; Sadulla, Sayeed; Sastry, Thotapalli Parvathaleswara; Mandal, Asit Baran

2014-09-01

Click chemistry approaches are tailored to generate molecular building blocks quickly and reliably by joining small units together selectively and covalently, stably and irreversibly. The vegetable tannins such as hydrolyzable and condensed tannins are capable to produce rather stable radicals or inhibit the progress of radicals and are prone to oxidations such as photo and auto-oxidation, and their anti-oxidant nature is well known. A lot remains to be done to understand the extent of the variation of leather stability, color variation (lightening and darkening reaction of leather), and poor resistance to water uptake for prolonged periods. In the present study, we have reported click chemistry approaches to accelerated vegetable tanning processes based on periodates catalyzed formation of oxidized hydrolysable and condensed tannins for high exhaustion with improved properties. The distribution of oxidized vegetable tannin, the thermal stability such as shrinkage temperature (T s) and denaturation temperature (T d), resistance to collagenolytic activities, and organoleptic properties of tanned leather as well as the evaluations of eco-friendly characteristics were investigated. Scanning electron microscopic analysis indicates the cross section of tightness of the leather. Differential scanning calorimetric analysis shows that the T d of leather is more than that of vegetable tanned or equal to aldehyde tanned one. The leathers exhibited fullness, softness, good color, and general appearance when compared to non-oxidized vegetable tannin. The developed process benefits from significant reduction in total solids and better biodegradability in the effluent, compared to non-oxidized vegetable tannins.

Computational Materials Science and Chemistry: Accelerating Discovery and Innovation through Simulation-Based Engineering and Science

DOE Office of Scientific and Technical Information (OSTI.GOV)

Crabtree, George; Glotzer, Sharon; McCurdy, Bill

This report is based on a SC Workshop on Computational Materials Science and Chemistry for Innovation on July 26-27, 2010, to assess the potential of state-of-the-art computer simulations to accelerate understanding and discovery in materials science and chemistry, with a focus on potential impacts in energy technologies and innovation. The urgent demand for new energy technologies has greatly exceeded the capabilities of today's materials and chemical processes. To convert sunlight to fuel, efficiently store energy, or enable a new generation of energy production and utilization technologies requires the development of new materials and processes of unprecedented functionality and performance. Newmore » materials and processes are critical pacing elements for progress in advanced energy systems and virtually all industrial technologies. Over the past two decades, the United States has developed and deployed the world's most powerful collection of tools for the synthesis, processing, characterization, and simulation and modeling of materials and chemical systems at the nanoscale, dimensions of a few atoms to a few hundred atoms across. These tools, which include world-leading x-ray and neutron sources, nanoscale science facilities, and high-performance computers, provide an unprecedented view of the atomic-scale structure and dynamics of materials and the molecular-scale basis of chemical processes. For the first time in history, we are able to synthesize, characterize, and model materials and chemical behavior at the length scale where this behavior is controlled. This ability is transformational for the discovery process and, as a result, confers a significant competitive advantage. Perhaps the most spectacular increase in capability has been demonstrated in high performance computing. Over the past decade, computational power has increased by a factor of a million due to advances in hardware and software. This rate of improvement, which shows no sign of abating, has enabled the development of computer simulations and models of unprecedented fidelity. We are at the threshold of a new era where the integrated synthesis, characterization, and modeling of complex materials and chemical processes will transform our ability to understand and design new materials and chemistries with predictive power. In turn, this predictive capability will transform technological innovation by accelerating the development and deployment of new materials and processes in products and manufacturing. Harnessing the potential of computational science and engineering for the discovery and development of materials and chemical processes is essential to maintaining leadership in these foundational fields that underpin energy technologies and industrial competitiveness. Capitalizing on the opportunities presented by simulation-based engineering and science in materials and chemistry will require an integration of experimental capabilities with theoretical and computational modeling; the development of a robust and sustainable infrastructure to support the development and deployment of advanced computational models; and the assembly of a community of scientists and engineers to implement this integration and infrastructure. This community must extend to industry, where incorporating predictive materials science and chemistry into design tools can accelerate the product development cycle and drive economic competitiveness. The confluence of new theories, new materials synthesis capabilities, and new computer platforms has created an unprecedented opportunity to implement a "materials-by-design" paradigm with wide-ranging benefits in technological innovation and scientific discovery. The Workshop on Computational Materials Science and Chemistry for Innovation was convened in Bethesda, Maryland, on July 26-27, 2010. Sponsored by the Department of Energy (DOE) Offices of Advanced Scientific Computing Research and Basic Energy Sciences, the workshop brought together 160 experts in materials science, chemistry, and computational science representing more than 65 universities, laboratories, and industries, and four agencies. The workshop examined seven foundational challenge areas in materials science and chemistry: materials for extreme conditions, self-assembly, light harvesting, chemical reactions, designer fluids, thin films and interfaces, and electronic structure. Each of these challenge areas is critical to the development of advanced energy systems, and each can be accelerated by the integrated application of predictive capability with theory and experiment. The workshop concluded that emerging capabilities in predictive modeling and simulation have the potential to revolutionize the development of new materials and chemical processes. Coupled with world-leading materials characterization and nanoscale science facilities, this predictive capability provides the foundation for an innovation ecosystem that can accelerate the discovery, development, and deployment of new technologies, including advanced energy systems. Delivering on the promise of this innovation ecosystem requires the following: Integration of synthesis, processing, characterization, theory, and simulation and modeling. Many of the newly established Energy Frontier Research Centers and Energy Hubs are exploiting this integration. Achieving/strengthening predictive capability in foundational challenge areas. Predictive capability in the seven foundational challenge areas described in this report is critical to the development of advanced energy technologies. Developing validated computational approaches that span vast differences in time and length scales. This fundamental computational challenge crosscuts all of the foundational challenge areas. Similarly challenging is coupling of analytical data from multiple instruments and techniques that are required to link these length and time scales. Experimental validation and quantification of uncertainty in simulation and modeling. Uncertainty quantification becomes increasingly challenging as simulations become more complex. Robust and sustainable computational infrastructure, including software and applications. For modeling and simulation, software equals infrastructure. To validate the computational tools, software is critical infrastructure that effectively translates huge arrays of experimental data into useful scientific understanding. An integrated approach for managing this infrastructure is essential. Efficient transfer and incorporation of simulation-based engineering and science in industry. Strategies for bridging the gap between research and industrial applications and for widespread industry adoption of integrated computational materials engineering are needed.« less

CONTROL OF CHELATOR-BASED UPSETS IN SURFACE FINISHING SHOP WASTE WATER TREATMENT SYSTEMS

EPA Science Inventory

Actual surface finishing shop examples are used to illustrate the use of process chemistry understanding and analyses to identify immediate, interim and permanent response options for industrial waste water treatment plant (IWTP) upset problems caused by chelating agents. There i...

Low earth orbit durability evaluation of Haynes 188 solar receiver material

NASA Technical Reports Server (NTRS)

De Groh, Kim K.; Rutledge, Sharon K.; Burke, Christopher A.; Dever, Therese M.; Olle, Raymond M.; Terlep, Judith A.

1992-01-01

The effects of elevated-temperature vacuum and elevated-temperature atomic oxygen exposure on the mass, surface chemistry, surface morphology, and optical properties of Haynes 188, a possible heat receiver material for space-based solar dynamic power systems, have been studied. Pristine and surface modified Haynes 188 were exposed to vacuum less than or equal to 10 exp -6 torr at 820 C for 5215.5 h, and to atomic oxygen in an air plasma asher at 34 and 827 C for fluences up to 5.6 x 10 exp 21 atoms/sq cm. Results obtained indicate that vacuum heat treatment caused surface morphology and chemistry changes with corresponding optical property changes. Atomic oxygen exposure caused optical property changes which diminished with time. Mass changes are considered to be negligible for both exposures.

A new method of measuring gravitational acceleration in an undergraduate laboratory program

NASA Astrophysics Data System (ADS)

Wang, Qiaochu; Wang, Chang; Xiao, Yunhuan; Schulte, Jurgen; Shi, Qingfan

2018-01-01

This paper presents a high accuracy method to measure gravitational acceleration in an undergraduate laboratory program. The experiment is based on water in a cylindrical vessel rotating about its vertical axis at a constant speed. The water surface forms a paraboloid whose focal length is related to rotational period and gravitational acceleration. This experimental setup avoids classical source errors in determining the local value of gravitational acceleration, so prevalent in the common simple pendulum and inclined plane experiments. The presented method combines multiple physics concepts such as kinematics, classical mechanics and geometric optics, offering the opportunity for lateral as well as project-based learning.

Fabrication of a platform to isolate the influences of surface nanotopography from chemistry on bacterial attachment and growth.

PubMed

Pegalajar-Jurado, Adoracion; Easton, Christopher D; Crawford, Russell J; McArthur, Sally L

2015-03-26

Billions of dollars are spent annually worldwide to combat the adverse effects of bacterial attachment and biofilm formation in industries as varied as maritime, food, and health. While advances in the fabrication of antifouling surfaces have been reported recently, a number of the essential aspects responsible for the formation of biofilms remain unresolved, including the important initial stages of bacterial attachment to a substrate surface. The reduction of bacterial attachment to surfaces is a key concept in the prevention or minimization of biofilm formation. The chemical and physical characteristics of both the substrate and bacteria are important in understanding the attachment process, but substrate modification is likely the most practical route to enable the extent of bacterial attachment taking place to be effectively controlled. The microtopography and chemistry of the surface are known to influence bacterial attachment. The role of surface chemistry versus nanotopography and their interplay, however, remain unclear. Most methods used for imparting nanotopographical patterns onto a surface also induce changes in the surface chemistry and vice versa. In this study, the authors combine colloidal lithography and plasma polymerization to fabricate homogeneous, reproducible, and periodic nanotopographies with a controllable surface chemistry. The attachment of Escherichia coli bacteria onto carboxyl (plasma polymerized acrylic acid, ppAAc) and hydrocarbon (plasma polymerized octadiene, ppOct) rich plasma polymer films on either flat or colloidal array surfaces revealed that the surface chemistry plays a critical role in bacterial attachment, whereas the effect of surface nanotopography on the bacterial attachment appears to be more difficult to define. This platform represents a promising approach to allow a greater understanding of the role that surface chemistry and nanotopography play on bacterial attachment and the subsequent biofouling of the surface.

Investigation of molybdenum-crosslinker interfaces for affinity based electrochemical biosensing applications

NASA Astrophysics Data System (ADS)

Kamakoti, Vikramshankar; Shanmugam, Nandhinee Radha; Tanak, Ambalika Sanjeev; Jagannath, Badrinath; Prasad, Shalini

2018-04-01

Molybdenum (Mo) has been investigated for implementation as an electrode material for affinity based biosensing towards devloping flexibe electronic biosensors. Treatment of the native oxide of molybdenum was investigated through two surface treatment strategies namely thiol and carbodiimide crosslinking methods. The binding interaction between cross-linker molecules and Mo electrode surface has been characterized using Fourier Transform Infrared Spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and optical microscopy. The efficacy of treatment of Mo with its native oxide using carbodiimide cross linking methodology was established. The carbodiimide cross-linking chemistry was found to possess better surface coverage and binding affinity with Molybdenum electrode surface when compared to thiol cross-linking chemistry.Electrochemical characterization of Mo electrode using Electrochemical Impedance Spectroscopy (EIS) and Cyclic Voltametry (CV) techniques was performed to evaluate the effect of ionic properties of solution buffer on the Mo electrode's performance. Affinity based biosensing of C-Reactive Protein (CRP) has been demonstrated on a flexible nanoporous polymeric substrate with detection threshold of 100 pg/ml in synthetic urine buffer medium. The biosensor has been evaluated to be developed as a dipstick based point of care device for detection of biomarkers in urine.

Accelerated Integrated Science Sequence (AISS): An Introductory Biology, Chemistry, and Physics Course

ERIC Educational Resources Information Center

Purvis-Roberts, Kathleen L.; Edwalds-Gilbert, Gretchen; Landsberg, Adam S.; Copp, Newton; Ulsh, Lisa; Drew, David E.

2009-01-01

A new interdisciplinary, introductory science course was offered for the first time during the 2007-2008 school year. The purpose of the course is to introduce students to the idea of working at the intersections of biology, chemistry, and physics and to recognize interconnections between the disciplines. Interdisciplinary laboratories are a key…

Bioorthogonal chemistry: strategies and recent development

PubMed Central

Ramil, Carlo P.; Lin, Qing

2013-01-01

The use of covalent chemistry to track biomolecules in their native environment—a focus of bioorthogonal chemistry—has received considerable interests recently among chemical biologists and organic chemists alike. To facilitate wider adoption of bioorthogonal chemistry in biomedical research, a central effort in the last few years has been focused on the optimization of a few known bioorthogonal reactions, particularly with respective to reaction kinetics improvement, novel genetic encoding systems, and fluorogenic reactions for bioimaging. During these optimizations, three strategies have emerged, including the use of ring strain for substrate activation in the cycloaddition reactions, the discovery of new ligands and privileged substrates for accelerated metal-catalysed reactions, and the design of substrates with pre-fluorophore structures for rapid “turn-on” fluorescence after selective bioorthogonal reactions. In addition, new bioorthogonal reactions based on either modified or completely unprecedented reactant pairs have been reported. Finally, increasing attention has been directed toward the development of mutually exclusive bioorthogonal reactions and their applications in multiple labeling of a biomolecule in cell culture. In this feature article, we wish to present the recent progress in bioorthogonal reactions through the selected examples that highlight the above-mentioned strategies. Considering increasing sophistication in bioorthogonal chemistry development, we strive to project several exciting opportunities where bioorthogonal chemistry can make a unique contribution to biology in near future. PMID:24145483

Modulation of Protein Fouling and Interfacial Properties at Carbon Surfaces via Immobilization of Glycans Using Aryldiazonium Chemistry

PubMed Central

Zen, Federico; Angione, M. Daniela; Behan, James A.; Cullen, Ronan J.; Duff, Thomas; Vasconcelos, Joana M.; Scanlan, Eoin M.; Colavita, Paula E.

2016-01-01

Carbon materials and nanomaterials are of great interest for biological applications such as implantable devices and nanoparticle vectors, however, to realize their potential it is critical to control formation and composition of the protein corona in biological media. In this work, protein adsorption studies were carried out at carbon surfaces functionalized with aryldiazonium layers bearing mono- and di-saccharide glycosides. Surface IR reflectance absorption spectroscopy and quartz crystal microbalance were used to study adsorption of albumin, lysozyme and fibrinogen. Protein adsorption was found to decrease by 30–90% with respect to bare carbon surfaces; notably, enhanced rejection was observed in the case of the tested di-saccharide vs. simple mono-saccharides for near-physiological protein concentration values. ζ-potential measurements revealed that aryldiazonium chemistry results in the immobilization of phenylglycosides without a change in surface charge density, which is known to be important for protein adsorption. Multisolvent contact angle measurements were used to calculate surface free energy and acid-base polar components of bare and modified surfaces based on the van Oss-Chaudhury-Good model: results indicate that protein resistance in these phenylglycoside layers correlates positively with wetting behavior and Lewis basicity. PMID:27108562

Modulation of Protein Fouling and Interfacial Properties at Carbon Surfaces via Immobilization of Glycans Using Aryldiazonium Chemistry

NASA Astrophysics Data System (ADS)

Zen, Federico; Angione, M. Daniela; Behan, James A.; Cullen, Ronan J.; Duff, Thomas; Vasconcelos, Joana M.; Scanlan, Eoin M.; Colavita, Paula E.

2016-04-01

Carbon materials and nanomaterials are of great interest for biological applications such as implantable devices and nanoparticle vectors, however, to realize their potential it is critical to control formation and composition of the protein corona in biological media. In this work, protein adsorption studies were carried out at carbon surfaces functionalized with aryldiazonium layers bearing mono- and di-saccharide glycosides. Surface IR reflectance absorption spectroscopy and quartz crystal microbalance were used to study adsorption of albumin, lysozyme and fibrinogen. Protein adsorption was found to decrease by 30-90% with respect to bare carbon surfaces; notably, enhanced rejection was observed in the case of the tested di-saccharide vs. simple mono-saccharides for near-physiological protein concentration values. ζ-potential measurements revealed that aryldiazonium chemistry results in the immobilization of phenylglycosides without a change in surface charge density, which is known to be important for protein adsorption. Multisolvent contact angle measurements were used to calculate surface free energy and acid-base polar components of bare and modified surfaces based on the van Oss-Chaudhury-Good model: results indicate that protein resistance in these phenylglycoside layers correlates positively with wetting behavior and Lewis basicity.

OSCAR4: a flexible architecture for chemical text-mining.

PubMed

Jessop, David M; Adams, Sam E; Willighagen, Egon L; Hawizy, Lezan; Murray-Rust, Peter

2011-10-14

The Open-Source Chemistry Analysis Routines (OSCAR) software, a toolkit for the recognition of named entities and data in chemistry publications, has been developed since 2002. Recent work has resulted in the separation of the core OSCAR functionality and its release as the OSCAR4 library. This library features a modular API (based on reduction of surface coupling) that permits client programmers to easily incorporate it into external applications. OSCAR4 offers a domain-independent architecture upon which chemistry specific text-mining tools can be built, and its development and usage are discussed.

Response of surface water chemistry to reduced levels of acid precipitation: Comparison of trends in two regions of New York, USA

USGS Publications Warehouse

Burns, Douglas A.; McHale, M.R.; Driscoll, C.T.; Roy, K.M.

2006-01-01

In light of recent reductions in sulphur (S) and nitrogen (N) emissions mandated by Title IV of the Clean Air Act Amendments of 1990, temporal trends and trend coherence in precipitation (1984-2001 and 1992-2001) and surface water chemistry (1992-2001) were determined in two of the most acid-sensitive regions of North America, i.e. the Catskill and Adirondack Mountains of New York. Precipitation chemistry data from six sites located near these regions showed decreasing sulphate (SO42-), nitrate (NO3-), and base cation (CB) concentrations and increasing pH during 1984-2001, but few significant trends during 1992-2001. Data from five Catskill streams and 12 Adirondack lakes showed decreasing trends in SO42- concentrations at all sites, and decreasing trends in NO3-, CB, and H+ concentrations and increasing trends in dissolved organic carbon at most sites. In contrast, acid-neutralizing capacity (ANC increased significantly at only about half the Adirondack lakes and in one of the Catskill streams. Flow correction prior to trend analysis did not change any trend directions and had little effect on SO42- trends, but it caused several significant non-flow-corrected trends in NO3- and ANC to become non-significant, suggesting that trend results for flow-sensitive constituents are affected by flow-related climate variation. SO42- concentrations showed high temporal coherence in precipitation, surface waters, and in precipitation-surface water comparisons, reflecting a strong link between S emissions, precipitation SO42- concentrations, and the processes that affect S cycling within these regions. NO3- and H+ concentrations and ANC generally showed weak coherence, especially in surface waters and in precipitation-surface water comparisons, indicating that variation in local-scale processes driven by factors such as climate are affecting trends in acid-base chemistry in these two regions. Copyright ?? 2005 John Wiley & Sons, Ltd.

Aqueous aerosol SOA formation: impact on aerosol physical properties.

PubMed

Woo, Joseph L; Kim, Derek D; Schwier, Allison N; Li, Ruizhi; McNeill, V Faye

2013-01-01

Organic chemistry in aerosol water has recently been recognized as a potentially important source of secondary organic aerosol (SOA) material. This SOA material may be surface-active, therefore potentially affecting aerosol heterogeneous activity, ice nucleation, and CCN activity. Aqueous aerosol chemistry has also been shown to be a potential source of light-absorbing products ("brown carbon"). We present results on the formation of secondary organic aerosol material in aerosol water and the associated changes in aerosol physical properties from GAMMA (Gas-Aerosol Model for Mechanism Analysis), a photochemical box model with coupled gas and detailed aqueous aerosol chemistry. The detailed aerosol composition output from GAMMA was coupled with two recently developed modules for predicting a) aerosol surface tension and b) the UV-Vis absorption spectrum of the aerosol, based on our previous laboratory observations. The simulation results suggest that the formation of oligomers and organic acids in bulk aerosol water is unlikely to perturb aerosol surface tension significantly. Isoprene-derived organosulfates are formed in high concentrations in acidic aerosols under low-NO(x) conditions, but more experimental data are needed before the potential impact of these species on aerosol surface tension may be evaluated. Adsorption of surfactants from the gas phase may further suppress aerosol surface tension. Light absorption by aqueous aerosol SOA material is driven by dark glyoxal chemistry and is highest under high-NO(x) conditions, at high relative humidity, in the early morning hours. The wavelength dependence of the predicted absorption spectra is comparable to field observations and the predicted mass absorption efficiencies suggest that aqueous aerosol chemistry can be a significant source of aerosol brown carbon under urban conditions.

Advances in understanding the surface chemistry of lignocellulosic biomass via time-of-flight secondary ion mass spectrometry

DOE PAGES

Tolbert, Allison K.; Ragauskas, Arthur J.

2016-12-12

Overcoming the natural recalcitrance of lignocellulosic biomass is necessary in order to efficiently convert biomass into biofuels or biomaterials and many times this requires some type of chemical pretreatment and/or biological treatment. While bulk chemical analysis is the traditional method of determining the impact a treatment has on biomass, the chemistry on the surface of the sample can differ from the bulk chemistry. Specifically, enzymes and microorganisms bind to the surface of the biomass and their efficiency could be greatly impacted by the chemistry of the surface. Therefore, it is important to study and understand the chemistry of the biomassmore » at the surface. Time-of- flight secondary ion mass spectrometry (ToF-SIMS) is a powerful tool that can spectrally and spatially analyze the surface chemistry of a sample. This review discusses the advances in understanding lignocellulosic biomass surface chemistry using the ToF-SIMS by addressing the instrument parameters, biomass sample preparation, and characteristic lignocellulosic ion fragmentation peaks along with their typical location in the plant cell wall. Furthermore, the use of the ToF-SIMS in detecting chemical changes due to chemical pretreatments, microbial treatments, and physical or genetic modifications is discussed along with possible future applications of the instrument in lignocellulosic biomass studies.« less

Advances in understanding the surface chemistry of lignocellulosic biomass via time-of-flight secondary ion mass spectrometry

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tolbert, Allison K.; Ragauskas, Arthur J.

Overcoming the natural recalcitrance of lignocellulosic biomass is necessary in order to efficiently convert biomass into biofuels or biomaterials and many times this requires some type of chemical pretreatment and/or biological treatment. While bulk chemical analysis is the traditional method of determining the impact a treatment has on biomass, the chemistry on the surface of the sample can differ from the bulk chemistry. Specifically, enzymes and microorganisms bind to the surface of the biomass and their efficiency could be greatly impacted by the chemistry of the surface. Therefore, it is important to study and understand the chemistry of the biomassmore » at the surface. Time-of- flight secondary ion mass spectrometry (ToF-SIMS) is a powerful tool that can spectrally and spatially analyze the surface chemistry of a sample. This review discusses the advances in understanding lignocellulosic biomass surface chemistry using the ToF-SIMS by addressing the instrument parameters, biomass sample preparation, and characteristic lignocellulosic ion fragmentation peaks along with their typical location in the plant cell wall. Furthermore, the use of the ToF-SIMS in detecting chemical changes due to chemical pretreatments, microbial treatments, and physical or genetic modifications is discussed along with possible future applications of the instrument in lignocellulosic biomass studies.« less

Losses of leaf area owing to herbivory and early senescence in three tree species along a winter temperature gradient

NASA Astrophysics Data System (ADS)

González-Zurdo, P.; Escudero, A.; Nuñez, R.; Mediavilla, S.

2016-11-01

In temperate climates, evergreen leaves have to survive throughout low temperature winter periods. Freezing and chilling injuries can lead to accelerated senescence of part of the leaf surface, which contributes to a reduction of the lifespan of the photosynthetic machinery and of leaf lifetime carbon gain. Low temperatures are also associated with changes in foliar chemistry and morphology that affect consumption by herbivores. Therefore, the severity of foliar area losses caused by accelerated senescence and herbivory can change along winter temperature gradients. The aim of this study is to analyse such responses in the leaves of three evergreen species ( Quercus ilex, Q. suber and Pinus pinaster) along a climatic gradient. The leaves of all three species presented increased leaf mass per area (LMA) and higher concentrations of structural carbohydrates in cooler areas. Only the two oak species showed visible symptoms of damage caused by herbivory, this being less intense at the coldest sites. The leaves of all three species presented chlorotic and necrotic spots that increased in size with leaf age. The foliar surface affected by chlorosis and necrosis was larger at the sites with the coldest winters. Therefore, the effects of the winter cold on the lifespan of the photosynthetic machinery were contradictory: losses of leaf area due to accelerated senescence increased, but there was a decrease in losses caused by herbivory. The final consequences for carbon assimilation strongly depend on the exact timing of the appearance of the damage resulting from low temperature and grazing by herbivores.

Modeling the acid-base surface chemistry of montmorillonite.

PubMed

Bourg, Ian C; Sposito, Garrison; Bourg, Alain C M

2007-08-15

Proton uptake on montmorillonite edge surfaces can control pore water pH, solute adsorption, dissolution kinetics and clay colloid behavior in engineered clay barriers and natural weathering environments. Knowledge of proton uptake reactions, however, is currently limited by strong discrepancies between reported montmorillonite titration data sets and by conflicting estimates of edge structure, reactivity and electrostatics. In the present study, we show that the apparent discrepancy between titration data sets results in large part from the widespread use of an erroneous assumption of zero specific net proton surface charge at the onset of titration. Using a novel simulation scheme involving a surface chemistry model to simulate both pretreatment and titration, we find that montmorillonite edge surface chemistry models that account for the "spillover" of electrostatic potential from basal onto edge surfaces and for the stabilization of deprotonated Al-Si bridging sites through bond-length relaxation at the edge surface can reproduce key features of the best available experimental titration data (the influence of pretreatment conditions on experimental results, the absence of a point of zero salt effect, buffer capacity in the acidic pH range). However, no combination of current models of edge surface structure, reactivity and electrostatics can quantitatively predict, without fitted parameters, the experimental titration data over the entire range of pH (4.5 to 9) and ionic strength (0.001 to 0.5 mol dm(-3)) covered by available data.

Basic and Applied Studies of the RAM Accelerator as a Hypervelocity Projectile Launcher

DTIC Science & Technology

1993-12-10

The quasi-steady, one-dimensional "blackbox" model of thermally choked ram accelerator performance 18 that has been widely used by the authors and...the thermal choke point is assumed to be in equilibrium, the conditions can be determined by an equilibrium chemistry combustion routine. This model ...to operation, the details of the flow field must be examined. I The simplest model of the thermally choked ram accelerator flow field treats the flow

Electrostatic accelerators with high energy resolution

NASA Astrophysics Data System (ADS)

Uchiyama, T.; Agawa, Y.; Nishihashi, T.; Takagi, K.; Yamakawa, H.; Isoya, A.; Takai, M.; Namba, S.

1991-05-01

Several models of electrostatic accelerators based on rotating disks (Disktron) have been manufactured for various ion beam applications like surface analyses and implantation. The high voltage terminal of the Disktron with a terminal voltage of up to 500 kV is open in air, while the generator part is enclosed in FRP (fiber reinforced plastics) or a ceramic vessel filled with sf 6 gas. The 1 MV model is completely enclosed in a steel vessel. A compact tandem accelerator of the pellet chain type with a terminal voltage of 1.5 MV has also been manufactured. The good energy stability of these accelerators, typically in the range of 10 -4, has proved to be quite favorable for applications in precise studies of material surfaces, including the use of microbeam techniques.

Microbially-accelerated consolidation of oil sands tailings. Pathway II: solid phase biogeochemistry.

PubMed

Siddique, Tariq; Kuznetsov, Petr; Kuznetsova, Alsu; Li, Carmen; Young, Rozlyn; Arocena, Joselito M; Foght, Julia M

2014-01-01

Consolidation of clay particles in aqueous tailings suspensions is a major obstacle to effective management of oil sands tailings ponds in northern Alberta, Canada. We have observed that microorganisms indigenous to the tailings ponds accelerate consolidation of mature fine tailings (MFT) during active metabolism by using two biogeochemical pathways. In Pathway I, microbes alter porewater chemistry to indirectly increase consolidation of MFT. Here, we describe Pathway II comprising significant, direct and complementary biogeochemical reactions with MFT mineral surfaces. An anaerobic microbial community comprising Bacteria (predominantly Clostridiales, Synergistaceae, and Desulfobulbaceae) and Archaea (Methanolinea/Methanoregula and Methanosaeta) transformed Fe(III) minerals in MFT to amorphous Fe(II) minerals during methanogenic metabolism of an added organic substrate. Synchrotron analyses suggested that ferrihydrite (5Fe2O3. 9H2O) and goethite (α-FeOOH) were the dominant Fe(III) minerals in MFT. The formation of amorphous iron sulfide (FeS) and possibly green rust entrapped and masked electronegative clay surfaces in amended MFT. Both Pathways I and II reduced the surface charge potential (repulsive forces) of the clay particles in MFT, which aided aggregation of clays and formation of networks of pores, as visualized using cryo-scanning electron microscopy (SEM). These reactions facilitated the egress of porewater from MFT and increased consolidation of tailings solids. These results have large-scale implications for management and reclamation of oil sands tailings ponds, a burgeoning environmental issue for the public and government regulators.

Adsorption of sodium dodecylbenzenesulfonate on activated carbons: effects of solution chemistry and presence of bacteria.

PubMed

Bautista-Toledo, M I; Méndez-Díaz, J D; Sánchez-Polo, M; Rivera-Utrilla, J; Ferro-García, M A

2008-01-01

The objective of the present investigation was to determine the effectiveness of activated carbon in removing sodium dodecylbenzenesulfonate (SDBS) and to analyze the chemical and textural characteristics of the activated carbons that are involved in the adsorption process. Studies were also performed on the influence of operational variables (pH, ionic strength, and presence of microorganisms) and on the kinetics and interactions involved in the adsorption of this pollutant on activated carbon. The kinetics study of SDBS adsorption revealed no problems in its diffusion on any of the activated carbons studied, and Weisz-Prater coefficient (C WP) values were considerably lower than unity for all activated carbons studied. SDBS adsorption isotherms on these activated carbons showed that: (i) adsorption capacity of activated carbons was very high (260-470 mg/g) and increased with larger surface area; and (ii) dispersive interactions between SDBS and carbon surface were largely responsible for the adsorption of this pollutant. SDBS adsorption was not significantly affected by the solution pH, indicating that electrostatic adsorbent-adsorbate interactions do not play an important role in this process. The presence of electrolytes (NaCl) in the medium favors SDBS adsorption, accelerating the process and increasing adsorption capacity. Under the working conditions used, SDBS is not degraded by bacteria; however, the presence of bacteria during the process accelerates and increases SDBS adsorption on the activated carbon. Microorganism adsorption on the activated carbon surface increases its hydrophobicity, explaining the results observed.

Microbially-accelerated consolidation of oil sands tailings. Pathway II: solid phase biogeochemistry

PubMed Central

Siddique, Tariq; Kuznetsov, Petr; Kuznetsova, Alsu; Li, Carmen; Young, Rozlyn; Arocena, Joselito M.; Foght, Julia M.

2014-01-01

Consolidation of clay particles in aqueous tailings suspensions is a major obstacle to effective management of oil sands tailings ponds in northern Alberta, Canada. We have observed that microorganisms indigenous to the tailings ponds accelerate consolidation of mature fine tailings (MFT) during active metabolism by using two biogeochemical pathways. In Pathway I, microbes alter porewater chemistry to indirectly increase consolidation of MFT. Here, we describe Pathway II comprising significant, direct and complementary biogeochemical reactions with MFT mineral surfaces. An anaerobic microbial community comprising Bacteria (predominantly Clostridiales, Synergistaceae, and Desulfobulbaceae) and Archaea (Methanolinea/Methanoregula and Methanosaeta) transformed FeIII minerals in MFT to amorphous FeII minerals during methanogenic metabolism of an added organic substrate. Synchrotron analyses suggested that ferrihydrite (5Fe2O3. 9H2O) and goethite (α-FeOOH) were the dominant FeIII minerals in MFT. The formation of amorphous iron sulfide (FeS) and possibly green rust entrapped and masked electronegative clay surfaces in amended MFT. Both Pathways I and II reduced the surface charge potential (repulsive forces) of the clay particles in MFT, which aided aggregation of clays and formation of networks of pores, as visualized using cryo-scanning electron microscopy (SEM). These reactions facilitated the egress of porewater from MFT and increased consolidation of tailings solids. These results have large-scale implications for management and reclamation of oil sands tailings ponds, a burgeoning environmental issue for the public and government regulators. PMID:24711806

Reality of Dental Implant Surface Modification: A Short Literature Review

PubMed Central

Yeo, In-Sung

2014-01-01

Screw-shaped endosseous implants that have a turned surface of commercially pure titanium have a disadvantage of requiring a long time for osseointegration while those implants have shown long-term clinical success in single and multiple restorations. Titanium implant surfaces have been modified in various ways to improve biocompatibility and accelerate osseointegration, which results in a shorter edentulous period for a patient. This article reviewed some important modified titanium surfaces, exploring the in vitro, in vivo and clinical results that numerous comparison studies reported. Several methods are widely used to modify the topography or chemistry of titanium surface, including blasting, acid etching, anodic oxidation, fluoride treatment, and calcium phosphate coating. Such modified surfaces demonstrate faster and stronger osseointegration than the turned commercially pure titanium surface. However, there have been many studies finding no significant differences in in vivo bone responses among the modified surfaces. Considering those in vivo results, physical properties like roughening by sandblasting and acid etching may be major contributors to favorable bone response in biological environments over chemical properties obtained from various modifications including fluoride treatment and calcium phosphate application. Recently, hydrophilic properties added to the roughened surfaces or some osteogenic peptides coated on the surfaces have shown higher biocompatibility and have induced faster osseointegration, compared to the existing modified surfaces. However, the long-term clinical studies about those innovative surfaces are still lacking. PMID:25400716

Unravelling the surface chemistry of metal oxide nanocrystals, the role of acids and bases.

PubMed

De Roo, Jonathan; Van den Broeck, Freya; De Keukeleere, Katrien; Martins, José C; Van Driessche, Isabel; Hens, Zeger

2014-07-09

We synthesized HfO2 nanocrystals from HfCl4 using a surfactant-free solvothermal process in benzyl alcohol and found that the resulting nanocrystals could be transferred to nonpolar media using a mixture of carboxylic acids and amines. Using solution (1)H NMR, FTIR, and elemental analysis, we studied the details of the transfer reaction and the surface chemistry of the resulting sterically stabilized nanocrystals. As-synthesized nanocrystals are charge-stabilized by protons, with chloride acting as the counterion. Treatment with only carboxylic acids does not lead to any binding of ligands to the HfO2 surface. On the other hand, we find that the addition of amines provides the basic environment in which carboxylic acids can dissociate and replace chloride. This results in stable, aggregate-free dispersions of HfO2 nanocrystals, sterically stabilized by carboxylate ligands. Moreover, titrations with deuterated carboxylic acid show that the charge on the carboxylate ligands is balanced by coadsorbed protons. Hence, opposite from the X-type/nonstoichiometric nanocrystals picture prevailing in literature, one should look at HfO2/carboxylate nanocrystals as systems where carboxylic acids are dissociatively adsorbed to bind to the nanocrystals. Similar results were obtained with ZrO2 NCs. Since proton accommodation on the surface is most likely due to the high Brønsted basicity of oxygen, our model could be a more general picture for the surface chemistry of metal oxide nanocrystals with important consequences on the chemistry of ligand exchange reactions.

Adsorption of benzene and toluene from aqueous solutions onto activated carbon and its acid and heat treated forms: influence of surface chemistry on adsorption.

PubMed

Wibowo, N; Setyadhi, L; Wibowo, D; Setiawan, J; Ismadji, S

2007-07-19

The influence of surface chemistry and solution pH on the adsorption of benzene and toluene on activated carbon and its acid and heat treated forms were studied. A commercial coal-based activated carbon F-400 was chosen as carbon parent. The carbon samples were obtained by modification of F-400 by means of chemical treatment with HNO3 and thermal treatment under nitrogen flow. The treatment with nitric acid caused the introduction of a significant number of oxygenated acidic surface groups onto the carbon surface, while the heat treatment increases the basicity of carbon. The pore characteristics were not significantly changed after these modifications. The dispersive interactions are the most important factor in this adsorption process. Activated carbon with low oxygenated acidic surface groups (F-400Tox) has the best adsorption capacity.

Role of Integrin Subunits in Mesenchymal Stem Cell Differentiation and Osteoblast Maturation on Graphitic Carbon-coated Microstructured Surfaces

PubMed Central

Olivares-Navarrete, Rene; Rodil, Sandra E.; Hyzy, Sharon L.; Dunn, Ginger R.; Almaguer-Flores, Argelia; Schwartz, Zvi; Boyan, Barbara D.

2015-01-01

Surface roughness, topography, chemistry, and energy promote osteoblast differentiation and increase osteogenic local factor production in vitro and bone-to-implant contact in vivo, but the mechanisms involved are not well understood. Knockdown of integrin heterodimer alpha2beta1 (α2β1) blocks the osteogenic effects of the surface, suggesting signaling by this integrin homodimer is required. The purpose of the present study was to separate effects of surface chemistry and surface structure on integrin expression by coating smooth or rough titanium (Ti) substrates with graphitic carbon, retaining surface morphology but altering surface chemistry. Ti surfaces (smooth [Ra<0.4μm], rough [Ra≥3.4μm]) were sputter-coated using a magnetron sputtering system with an ultrapure graphite target, producing a graphitic carbon thin film. Human mesenchymal stem cells and MG63 osteoblast-like cells had higher mRNA for integrin subunits α1, α2, αv, and β1 on rough surfaces in comparison to smooth, and integrin αv on graphitic-carbon-coated rough surfaces in comparison to Ti. Osteogenic differentiation was greater on rough surfaces in comparison to smooth, regardless of chemistry. Silencing integrins β1, α1, or α2 decreased osteoblast maturation on rough surfaces independent of surface chemistry. Silencing integrin αv decreased maturation only on graphitic carbon-coated surfaces, not on Ti. These results suggest a major role of the integrin β1 subunit in roughness recognition, and that integrin alpha subunits play a major role in surface chemistry recognition. PMID:25770999

DOE Office of Scientific and Technical Information (OSTI.GOV)

Choi, Hyekyoung; Kim, Sungwoo; Luther, Joseph M.

Silver dimetal chalcogenide (Ag-V-VI 2) ternary quantum dots (QDs) are emerging lead-free materials for optoelectronic devices due to their NIR band gaps, large absorption coefficients, and superior electronic properties. However, thin film-based devices of the ternary QDs still lag behind due to the lack of understanding of the surface chemistry, compared to that of lead chalcogenide QDs even with the same crystal structure. Here in this paper, the surface ligand interactions of AgSbS 2 QDs, synthesized with 1-dodecanethiol used as a stabilizer, are studied. For nonpolar (1 0 0) surfaces, it is suggested that the thiolate ligands are associated withmore » the crystal lattices, thus preventing surface oxidation by protecting sulfur after air-exposure, as confirmed through optical and surface chemical analysis. Otherwise, silver rich (1 1 1) surfaces are passivated by thiolate ligands, allowing ligand exchange processes for the conductive films. This in-depth investigation of the surface chemistry of ternary QDs will prompt the performance enhancement of their optoelectronic devices.« less

Effects of surface chemistry on the optical properties and cellular interaction of lanthanide-based nanoparticles

NASA Astrophysics Data System (ADS)

Pedraza, Francisco J.; Avalos, Julio C.; Mimun, Lawrence C.; Yust, Brian G.; Tsin, Andrew; Sardar, Dhiraj K.

2015-03-01

Fluorescent nanoparticles (NPs) such as KYb2F7:Tm3+ potential in biomedical applications due to their ability to absorb and emit within the biological window, where near infrared light is less attenuated by soft tissue. This results in less tissue damage and deeper tissue penetration making it a viable candidate in biological imaging. Another big factor in determining their ability to perform in a biological setting is the surface chemistry. Biocompatible coatings, including polyethylene glycol (PEG), polyvinylpyrrolidone (PVP), pluronic and folic acid are commonly used because they pose several advantages such as ease of functionalization, better dispersion, and higher cellular uptake. To study the effects of the NP surface chemistry, KYb2F7:Tm3+ a solvothermal method using PEG, PVP, pluronic acid, and folic acid as a capping agent, followed by thorough optical characterizations. Optical changes were thoroughly studied and compared using absorption, emission, and quantum yield data. Cell viability was obtained by treating Rhesus Monkey Retinal Endothelial cells (RhREC) with KYb2F7:Tm3+ and counting viable cells following a 24 hour uptake period. The work presented will compare the optical properties and toxicity dependency on the surface chemistry on KYb2F7:Tm3+. The results will also indicate that KYb2F7:Tm3+ nanoparticles are viable candidates for various biomedical applications.

JPRS Report, Science & Technology, USSR: Chemistry

DTIC Science & Technology

1990-11-08

desorption cycle. The photochemical activity of the oxides was determined by irradiating them with UV light at 353 K during the oxidation reactions of...No 1, Jan 90] 8 Acid-Base Properties Photochemically Active Titanium Oxide Surfaces [N D. Konovalova, V. I. Stepanenko, etal; UKRAINSKIY...Figures 4; references 13: 10 Russian, 3 Western. UDC 541.183 Acid-Base Properties Photochemically Active Titanium Oxide Surfaces 907M0149B Kiev

Schottky-barrier-free contacts with two-dimensional semiconductors by surface-engineered MXenes

DOE PAGES

Liu, Yuanyue; Xiao, Hai; Goddard, III, William A.

2016-11-22

Two-dimensional (2D) metal carbides and nitrides, called MXenes, have attracted great interest for applications such as energy storage. Here we demonstrate their potential as Schottky-barrier-free metal contacts to 2D semiconductors, providing a solution to the contact-resistance problem in 2D electronics. Based on first principles calculations, we find that the surface chemistry strongly affects the Fermi level of MXenes: O termination always increases the work function with respect to that of bare surface, OH always decreases it, while F exhibits either trend depending on the specific material. This phenomenon originates from the effect of surface dipoles, which together with the weakmore » Fermi level pinning, enable Schottky-barrier-free hole (or electron) injection into 2D semiconductors through van der Waals junctions with some of the O-terminated (or all the OH-terminated) MXenes. Furthermore, we suggest synthetic routes to control the surface terminations based on the calculated formation energies. Finally, this study enhances the understanding of the correlation between surface chemistry and electronic/transport properties of 2D materials, and also gives practical predictions for improving 2D electronics.« less

Nanoporous Anodic Alumina Platforms: Engineered Surface Chemistry and Structure for Optical Sensing Applications

PubMed Central

Kumeria, Tushar; Santos, Abel; Losic, Dusan

2014-01-01

Electrochemical anodization of pure aluminum enables the growth of highly ordered nanoporous anodic alumina (NAA) structures. This has made NAA one of the most popular nanomaterials with applications including molecular separation, catalysis, photonics, optoelectronics, sensing, drug delivery, and template synthesis. Over the past decades, the ability to engineer the structure and surface chemistry of NAA and its optical properties has led to the establishment of distinctive photonic structures that can be explored for developing low-cost, portable, rapid-response and highly sensitive sensing devices in combination with surface plasmon resonance (SPR) and reflective interference spectroscopy (RIfS) techniques. This review article highlights the recent advances on fabrication, surface modification and structural engineering of NAA and its application and performance as a platform for SPR- and RIfS-based sensing and biosensing devices. PMID:25004150

The effect of 17-4PH stainless steel on the lifetime of a Pennzane lubricated Microwave Limb Sounder Antenna Actuator Assembly ball screw for the AURA spacecraft

NASA Astrophysics Data System (ADS)

Jones, William R., Jr.; Jansen, Mark J.; Chen, Gun-Shing; Lam, Jonathan; Balzer, Mark; Lo, John; Anderson, Mark; Schepis, Joseph P.

2005-07-01

During ground based life testing of a Microwave Limb Sounder (MLS) Antenna Actuator Assembly (AAA) ball-screw assembly, lubricant darkening and loss were noted when approximately 10% of required lifetime was completed. The MLS-AAA ball screw and nut are made from 17-4 PH steel, the nut has 440C stainless steel balls, and the assembly is lubricated with a Pennzane formulation containing a three weight percent lead naphthenate additive. Life tests were done in dry nitrogen at 50°C. To investigate the MLS-AAA life test anomaly, Spiral Orbit Tribometer (SOT) accelerated tests were performed. SOT results indicated greatly reduced relative lifetimes of Pennzane formulations in contact with 17-4 PH steel compared to 440C stainless steel. Also, dry nitrogen tests yielded longer relative lifetimes than comparable ultrahigh vacuum tests. Generally, oxidized Pennzane formulations yielded shorter lifetimes than non-oxidized lubricant. This study emphasizes surface chemistry effects on the lubricated lifetime of moving mechanical assemblies.

Palliative effects of H2 on SOFCs operating with carbon containing fuels

NASA Astrophysics Data System (ADS)

Reeping, Kyle W.; Bohn, Jessie M.; Walker, Robert A.

2017-12-01

Chlorine can accelerate degradation of solid oxide fuel cell (SOFC) Ni-based anodes operating on carbon containing fuels through several different mechanisms. However, supplementing the fuel with a small percentage of excess molecular hydrogen effectively masks the degradation to the catalytic activity of the Ni and carbon fuel cracking reaction reactions. Experiments described in this work explore the chemistry behind the "palliative" effect of hydrogen on SOFCs operating with chlorine-contaminated, carbon-containing fuels using a suite of independent, complementary techniques. Operando Raman spectroscopy is used to monitor carbon accumulation and, by inference, Ni catalytic activity while electrochemical techniques including electrochemical impedance spectroscopy and voltammetry are used to monitor overall cell performance. Briefly, hydrogen not only completely hides degradation observed with chlorine-contaminated carbon-containing fuels, but also actively removes adsorbed chlorine from the surface of the Ni, allowing for the methane cracking reaction to continue, albeit at a slower rate. When hydrogen is removed from the fuel stream the cell fails immediately due to chlorine occupation of methane/biogas reaction sites.

The Effect of 17-4 PH Stainless Steel on the Lifetime of a Pennzane(Trademark) Lubricated Microwave Limb Sounder Antenna Actuator Assembly Ball Screw for the AURA Spacecraft

NASA Technical Reports Server (NTRS)

Jones, William R., Jr.; Jansen, Mark J.; Chen, Gun-Shing; Lam, Jonathan; Balzer, Mark; Anderson, Mark; Lo, John; Schepis, Joseph P.

2005-01-01

During ground based life testing of a Microwave Limb Sounder (MLS) Antenna Actuator Assembly (AAA) ball-screw assembly, lubricant darkening and loss were noted when approximately 10 percent of required lifetime was completed. The MLS-AAA ball screw and nut are made from 17-4 PH steel, the nut has 440C stainless steel balls, and the assembly is lubricated with a Pennzane formulation containing a three weight percent lead naphthenate additive. Life tests were done in dry nitrogen at 50 C. To investigate the MLS-AAA life test anomaly, Spiral Orbit Tribometer (SOT) accelerated tests were performed. SOT results indicated greatly reduced relative lifetimes of Pennzane formulations in contact with 17-4 PH steel compared to 440C stainless steel. Also, dry nitrogen tests yielded longer relative lifetimes than comparable ultrahigh vacuum tests. Generally, oxidized Pennzane formulations yielded shorter lifetimes than non-oxidized lubricant. This study emphasizes surface chemistry effects on the lubricated lifetime of moving mechanical assemblies.

Surface functionalization of thin-film diamond for highly stable and selective biological interfaces

PubMed Central

Stavis, Courtney; Clare, Tami Lasseter; Butler, James E.; Radadia, Adarsh D.; Carr, Rogan; Zeng, Hongjun; King, William P.; Carlisle, John A.; Aksimentiev, Aleksei; Bashir, Rashid; Hamers, Robert J.

2011-01-01

Carbon is an extremely versatile family of materials with a wide range of mechanical, optical, and mechanical properties, but many similarities in surface chemistry. As one of the most chemically stable materials known, carbon provides an outstanding platform for the development of highly tunable molecular and biomolecular interfaces. Photochemical grafting of alkenes has emerged as an attractive method for functionalizing surfaces of diamond, but many aspects of the surface chemistry and impact on biological recognition processes remain unexplored. Here we report investigations of the interaction of functionalized diamond surfaces with proteins and biological cells using X-ray photoelectron spectroscopy (XPS), atomic force microscopy, and fluorescence methods. XPS data show that functionalization of diamond with short ethylene glycol oligomers reduces the nonspecific binding of fibrinogen below the detection limit of XPS, estimated as > 97% reduction over H-terminated diamond. Measurements of different forms of diamond with different roughness are used to explore the influence of roughness on nonspecific binding onto H-terminated and ethylene glycol (EG)-terminated surfaces. Finally, we use XPS to characterize the chemical stability of Escherichia coli K12 antibodies on the surfaces of diamond and amine-functionalized glass. Our results show that antibody-modified diamond surfaces exhibit increased stability in XPS and that this is accompanied by retention of biological activity in cell-capture measurements. Our results demonstrate that surface chemistry on diamond and other carbon-based materials provides an excellent platform for biomolecular interfaces with high stability and high selectivity. PMID:20884854

Accelerated sampling by infinite swapping of path integral molecular dynamics with surface hopping

NASA Astrophysics Data System (ADS)

Lu, Jianfeng; Zhou, Zhennan

2018-02-01

To accelerate the thermal equilibrium sampling of multi-level quantum systems, the infinite swapping limit of a recently proposed multi-level ring polymer representation is investigated. In the infinite swapping limit, the ring polymer evolves according to an averaged Hamiltonian with respect to all possible surface index configurations of the ring polymer and thus connects the surface hopping approach to the mean-field path-integral molecular dynamics. A multiscale integrator for the infinite swapping limit is also proposed to enable efficient sampling based on the limiting dynamics. Numerical results demonstrate the huge improvement of sampling efficiency of the infinite swapping compared with the direct simulation of path-integral molecular dynamics with surface hopping.

General Dialdehyde Click Chemistry for Amine Bioconjugation.

PubMed

Elahipanah, Sina; O'Brien, Paul J; Rogozhnikov, Dmitry; Yousaf, Muhammad N

2017-05-17

The development of methods for conjugating a range of molecules to primary amine functional groups has revolutionized the fields of chemistry, biology, and material science. The primary amine is a key functional group and one of the most important nucleophiles and bases used in all of synthetic chemistry. Therefore, tremendous interest in the synthesis of molecules containing primary amines and strategies to devise chemical reactions to react with primary amines has been at the core of chemical research. In particular, primary amines are a ubiquitous functional group found in biological systems as free amino acids, as key side chain lysines in proteins, and in signaling molecules and metabolites and are also present in many natural product classes. Due to its abundance, the primary amine is the most convenient functional group handle in molecules for ligation to other molecules for a broad range of applications that impact all scientific fields. Because of the primary amine's central importance in synthetic chemistry, acid-base chemistry, redox chemistry, and biology, many methods have been developed to efficiently react with primary amines, including activated carboxylic acids, isothiocyanates, Michael addition type systems, and reaction with ketones or aldehydes followed by in situ reductive amination. Herein, we introduce a new traceless, high-yield, fast click-chemistry method based on the rapid and efficient trapping of amine groups via a functionalized dialdehyde group. The click reaction occurs in mild conditions in organic solvents or aqueous media and proceeds in high yield, and the starting dialdehyde reagent and resulting dialdehyde click conjugates are stable. Moreover, no catalyst or dialdehyde-activating group is required, and the only byproduct is water. The initial dialdehyde and the resulting conjugate are both straightforward to characterize, and the reaction proceeds with high atom economy. To demonstrate the broad scope of this new click-conjugation strategy, we designed a straightforward scheme to synthesize a suite of dialdehyde reagents. The dialdehyde molecules were used for applications in cell-surface engineering and for tailoring surfaces for material science applications. We anticipate the broad utility of the general dialdehyde click chemistry to primary amines in all areas of chemical research, ranging from polymers and bioconjugation to material science and nanoscience.

Design of the Next Generation Target at the Lujan Neutron Scattering Center, LANSCE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ferres, Laurent

Los Alamos National Laboratory (LANL) supports scientific research in many diverse fields such as biology, chemistry, and nuclear science. The Laboratory was established in 1943 during the Second World War to develop nuclear weapons. Today, LANL is one of the largest laboratories dedicated to nuclear defense and operates an 800 MeV proton linear accelerator for basic and applied research including: production of high- and low-energy neutrons beams, isotope production for medical applications and proton radiography. This accelerator is located at the Los Alamos Neutron Science Center (LANSCE). The work performed involved the redesign of the target for the low-energy neutronmore » source at the Lujan Neutron Scattering Center, which is one of the facilities built around the accelerator. The redesign of the target involves modeling various arrangements of the moderator-reflector-shield for the next generation neutron production target. This is done using Monte Carlo N-Particle eXtended (MCNPX), and ROOT analysis framework, a C++ based-software, to analyze the results.« less

Impact of managed moorland burning on peat nutrient and base cation status

NASA Astrophysics Data System (ADS)

Palmer, Sheila; Gilpin, Martin; Wearing, Catherine; Johnston, Kerrylyn; Holden, Joseph; Brown, Lee

2013-04-01

Controlled 'patch' burning of moorland vegetation has been used for decades in the UK to stimulate growth of heather (Calluna vulgaris) for game bird habitat and livestock grazing. Typically small patches (300-900 m2) are burned in rotations of 8-25 years. However, our understanding of the short-to-medium term environmental impacts of the practice on these sensitive upland areas has so far been limited by a lack of scientific data. In particular the effect of burning on concentrations of base cations and acid-base status of these highly organic soils has implications both for ecosystem nutrient status and for buffering of acidic waters. As part of the EMBER project peat chemistry data were collected in ten upland blanket peat catchments in the UK. Five catchments were subject to a history of prescribed rotational patch burning. The other five catchments acted as controls which were not subject to burning, nor confounded by other detrimental activities such as drainage or forestry. Soil solution chemistry was also monitored at two intensively studied sites (one regularly burned and one control). Fifty-centimetre soil cores, sectioned into 5-cm intervals, were collected from triplicate patches of four burn ages at each burned site, and from twelve locations at similar hillslope positions at each control site. At the two intensively monitored sites, soil solution chemistry was monitored at four depths in each patch. Across all sites, burned plots had significantly smaller cation exchange capacities, lower concentrations of exchangeable base cations and increased concentrations of exchangeable H+ and Al3+ in near-surface soil. C/N ratios were also lower in burned compared to unburned surface soils. There was no consistent trend between burn age and peat chemistry across all burned sites, possibly reflecting local controls on post-burn recovery rates or external influences on burn management decisions. At the intensively monitored site, plots burned less than two years prior to sampling had significantly smaller exchange capacities and lower concentrations of soil base cations in surface soils relative to plots burned 15-25 years previously. In contrast, surface soil solutions in recently burned plots were enriched in base cations relative to older plots and relative to the control site, possibly due to enhanced leaching at bare soil surfaces. The results offer evidence for an impact of burning on peat nutrient and acid-base status, but suggest that soils recover given time with no further burning.

Molten salt considerations for accelerator-driven subcritical fission to close the nuclear fuel cycle

NASA Astrophysics Data System (ADS)

Sooby, Elizabeth; Adams, Marvin; Baty, Austin; Gerity, James; McIntyre, Peter; Melconian, Karie; Phongikaroon, Supathorn; Pogue, Nathaniel; Sattarov, Akhdiyor; Simpson, Michael; Tripathy, Prabhat; Tsevkov, Pavel

2013-04-01

The host salt selection, molecular modeling, physical chemistry, and processing chemistry are presented here for an accelerator-driven subcritical fission in a molten salt core (ADSMS). The core is fueled solely with the transuranics (TRU) and long-lived fission products (LFP) from used nuclear fuel. The neutronics and salt composition are optimized to destroy the transuranics by fission and the long-lived fission products by transmutation. The cores are driven by proton beams from a strong-focusing cyclotron stack. One such ADSMS system can destroy the transuranics in the used nuclear fuel produced by a 1GWe conventional reactor. It uniquely provides a method to close the nuclear fuel cycle for green nuclear energy.

Anion Solvation in Carbonate-Based Electrolytes

DOE PAGES

von Wald Cresce, Arthur; Gobet, Mallory; Borodin, Oleg; ...

2015-11-16

The correlation between Li + solvation and interphasial chemistry on anodes firmly established in Li-ion batteries, the effect of cation–solvent interaction has gone beyond bulk thermodynamic and transport properties and become an essential element that determines the reversibility of electrochemistry and kinetics of Li-ion intercalation chemistries. Now, most studies are dedicated to the solvation of Li +, and the solvation of anions in carbonate-based electrolytes and its possible effect on the electrochemical stability of such electrolytes remains little understood. Moreover, as a mirror effort to prior Li + solvation studies, this work focuses on the interactions between carbonate-based solvents andmore » two anions (hexafluorophosphate, PF 6–, and tetrafluoroborate, BF 4–) that are most frequently used in Li-ion batteries. The possible correlation between such interaction and the interphasial chemistry on cathode surface is also explored.« less

Investigation of Test Methods, Material Properties and Processes for Solar Cell Encapsulants

NASA Technical Reports Server (NTRS)

Willis, P.; Baum, B.

1982-01-01

The evaluation of potentially useful low cost encapsulation materials is discussed. The goal is to identify, evaluate, test and recommend encapsulant materials and processes for the production of cost effective, long life solar cell modules. Technical investigations concerned the development of advanced cure chemistries for lamination type pottants; the continued evaluation of soil resistant surface treatment, and the results of an accelerated aging test program for the comparison of material stabilities. New compounds were evaluated for efficiency in curing both ethylene/vinyl acetate and ethylene/methyl acrylate pottants intended for vacuum bag lamination of solar cells. Two component aliphatic urethane casting syrups were evaluated for suitability as solar module pottants on the basis of optical, physical and fabrication characteristics.

Materials Chemistry and Performance of Silicone-Based Replicating Compounds.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brumbach, Michael T.; Mirabal, Alex James; Kalan, Michael

Replicating compounds are used to cast reproductions of surface features on a variety of materials. Replicas allow for quantitative measurements and recordkeeping on parts that may otherwise be difficult to measure or maintain. In this study, the chemistry and replicating capability of several replicating compounds was investigated. Additionally, the residue remaining on material surfaces upon removal of replicas was quantified. Cleaning practices were tested for several different replicating compounds. For all replicating compounds investigated, a thin silicone residue was left by the replica. For some compounds, additional inorganic species could be identified in the residue. Simple solvent cleaning could removemore » some residue.« less

Preparation of water-soluble magnetic nanocrystals using aryl diazonium salt chemistry.

PubMed

Griffete, Nébéwia; Herbst, Frédéric; Pinson, Jean; Ammar, Souad; Mangeney, Claire

2011-02-16

A novel and facile methodology for the in situ surface functionalization of Fe(3)O(4) nanoparticles is proposed, based on the use of aryl diazonium salts chemistry. The grafting reaction involves the formation of diazoates in a basic medium. These species are unstable and dediazonize along a homolytic pathway to give aryl radicals which further react with the Fe(3)O(4) NPs during their formation and stop their growth. Advantages of the present approach rely not only on the simplicity, rapidity, and efficiency of the procedure but also on the formation of strong Fe(3)O(4)-aryl surface bonds, highly suitable for further applications.

Cleaning and passivation of copper surfaces to remove surface radioactivity and prevent oxide formation

NASA Astrophysics Data System (ADS)

Hoppe, E. W.; Seifert, A.; Aalseth, C. E.; Bachelor, P. P.; Day, A. R.; Edwards, D. J.; Hossbach, T. W.; Litke, K. E.; McIntyre, J. I.; Miley, H. S.; Schulte, S. M.; Smart, J. E.; Warren, G. A.

2007-08-01

High-purity copper is an attractive material for constructing ultra-low-background radiation measurement devices. Many low-background experiments using high-purity copper have indicated surface contamination emerges as the dominant background. Radon daughters plate out on exposed surfaces, leaving a residual 210Pb background that is difficult to avoid. Dust is also a problem; even under cleanroom conditions, the amount of U and Th deposited on surfaces can represent the largest remaining background. To control these backgrounds, a copper cleaning chemistry has been developed. Designed to replace an effective, but overly aggressive concentrated nitric acid etch, this peroxide-based solution allows for a more controlled cleaning of surfaces. The acidified hydrogen peroxide solution will generally target the Cu +/Cu 2+ species which are the predominant surface participants, leaving the bulk of copper metal intact. This preserves the critical tolerances of parts and eliminates significant waste disposal issues. Accompanying passivation chemistry has also been developed that protects copper surfaces from oxidation. Using a high-activity polonium surface spike, the most difficult-to-remove daughter isotope of radon, the performance of these methods are quantified.

OSCAR4: a flexible architecture for chemical text-mining

PubMed Central

2011-01-01

The Open-Source Chemistry Analysis Routines (OSCAR) software, a toolkit for the recognition of named entities and data in chemistry publications, has been developed since 2002. Recent work has resulted in the separation of the core OSCAR functionality and its release as the OSCAR4 library. This library features a modular API (based on reduction of surface coupling) that permits client programmers to easily incorporate it into external applications. OSCAR4 offers a domain-independent architecture upon which chemistry specific text-mining tools can be built, and its development and usage are discussed. PMID:21999457

Time-varying changes in the simulated structure of the Brewer-Dobson Circulation

NASA Astrophysics Data System (ADS)

Garfinkel, Chaim I.; Aquila, Valentina; Waugh, Darryn W.; Oman, Luke D.

2017-01-01

A series of simulations using the NASA Goddard Earth Observing System Chemistry Climate Model are analyzed in order to assess changes in the Brewer-Dobson Circulation (BDC) over the past 55 years. When trends are computed over the past 55 years, the BDC accelerates throughout the stratosphere, consistent with previous modeling results. However, over the second half of the simulations (i.e., since the late 1980s), the model simulates structural changes in the BDC as the temporal evolution of the BDC varies between regions in the stratosphere. In the mid-stratosphere in the midlatitude Northern Hemisphere, the BDC does not accelerate in the ensemble mean of our simulations despite increases in greenhouse gas concentrations and warming sea surface temperatures, and it even decelerates in one ensemble member. This deceleration is reminiscent of changes inferred from satellite instruments and in situ measurements. In contrast, the BDC in the lower stratosphere continues to accelerate. The main forcing agents for the recent slowdown in the mid-stratosphere appear to be declining ozone-depleting substance (ODS) concentrations and the timing of volcanic eruptions. Changes in both mean age of air and the tropical upwelling of the residual circulation indicate a lack of recent acceleration. We therefore clarify that the statement that is often made that climate models simulate a decreasing age throughout the stratosphere only applies over long time periods and is not necessarily the case for the past 25 years, when most tracer measurements were taken.

Time-Varying Changes in the Simulated Structure of the Brewer-Dobson Circulation

NASA Technical Reports Server (NTRS)

Garfinkel, Chaim I.; Aquila, Valentina; Waugh, Darryn W.; Oman, Luke D.

2017-01-01

A series of simulations using the NASA Goddard Earth Observing System Chemistry Climate Model are analyzed in order to assess changes in the Brewer-Dobson Circulation (BDC) over the past 55 years. When trends are computed over the past 55 years, the BDC accelerates throughout the stratosphere, consistent with previous modeling results. However, over the second half of the simulations (i.e., since the late 1980s), the model simulates structural changes in the BDC as the temporal evolution of the BDC varies between regions in the stratosphere. In the mid-stratosphere in the midlatitude Northern Hemisphere, the BDC does not accelerate in the ensemble mean of our simulations despite increases in greenhouse gas concentrations and warming sea surface temperatures, and it even decelerates in one ensemble member. This deceleration is reminiscent of changes inferred from satellite instruments and in situ measurements. In contrast, the BDC in the lower stratosphere continues to accelerate. The main forcing agents for the recent slowdown in the mid-stratosphere appear to be declining ozone-depleting substance (ODS) concentrations and the timing of volcanic eruptions. Changes in both mean age of air and the tropical upwelling of the residual circulation indicate a lack of recent acceleration. We therefore clarify that the statement that is often made that climate models simulate a decreasing age throughout the stratosphere only applies over long time periods and is not necessarily the case for the past 25 years, when most tracer measurements were taken.

Modeling the Acceleration of Global Surface Temperture

NASA Astrophysics Data System (ADS)

Jones, B.

2017-12-01

A mathematical projection focusing on the changing rate of acceleration of Global Surface Temperatures. Using historical trajectory and informed expert near-term prediction, it is possible to extend this further forward drawing a reference arc of acceleration. Presented here is an example of this technique based on data found in the Summary of Findings of A New Estimate of the Average Earth Surface Land Temperature Spanning 1753 to 2011 and that same team's stated prediction to 2050. With this, we can project a curve showing future acceleration: Decade (midpoint) Change in Global Land Temp Degrees C Known Slope Projected Trend 1755 0.000 1955 0.600 0.0030 2005 1.500 0.0051 2045 3.000 0.0375 2095 5.485 0.0497 2145 8.895 0.0682 2195 13.488 0.0919 Observations: Slopes are getting steeper and doing so faster in an "acceleration of the acceleration" or an "arc of acceleration". This is consistent with the non-linear accelerating feedback loops of global warming. Such projected temperatures threaten human civilization and human life. This `thumbnail' projection is consistent with the other long term predictions based on anthropogenic greenhouse gases. This projection is low when compared to those whose forecasts include greenhouse gases released from thawing permafrost and clathrate hydrates. A reference line: This curve should be considered a point of reference. In the near term and absent significant drawdown of greenhouse gases, my "bet" for this AGU session is that future temperatures will generally be above this reference curve. For example, the decade ending 2020 - more than 1.9C and the decade ending 2030 - more than 2.3C - again measured from the 1750 start point. *Caveat: The long term curve and prediction assumes that mankind does not move quickly away from high cost fossil fuels and does not invent, mobilize and take actions drawing down greenhouse gases. Those seeking a comprehensive action plan are directed to drawdown.org

Beam by design: Laser manipulation of electrons in modern accelerators

NASA Astrophysics Data System (ADS)

Hemsing, Erik; Stupakov, Gennady; Xiang, Dao; Zholents, Alexander

2014-07-01

Accelerator-based light sources such as storage rings and free-electron lasers use relativistic electron beams to produce intense radiation over a wide spectral range for fundamental research in physics, chemistry, materials science, biology, and medicine. More than a dozen such sources operate worldwide, and new sources are being built to deliver radiation that meets with the ever-increasing sophistication and depth of new research. Even so, conventional accelerator techniques often cannot keep pace with new demands and, thus, new approaches continue to emerge. In this article, a variety of recently developed and promising techniques that rely on lasers to manipulate and rearrange the electron distribution in order to tailor the properties of the radiation are reviewed. Basic theories of electron-laser interactions, techniques to create microstructures and nanostructures in electron beams, and techniques to produce radiation with customizable waveforms are reviewed. An overview of laser-based techniques for the generation of fully coherent x rays, mode-locked x-ray pulse trains, light with orbital angular momentum, and attosecond or even zeptosecond long coherent pulses in free-electron lasers is presented. Several methods to generate femtosecond pulses in storage rings are also discussed. Additionally, various schemes designed to enhance the performance of light sources through precision beam preparation including beam conditioning, laser heating, emittance exchange, and various laser-based diagnostics are described. Together these techniques represent a new emerging concept of "beam by design" in modern accelerators, which is the primary focus of this article.

The selectivity of protein-imprinted gels and its relation to protein properties: A computer simulation study.

PubMed

Yankelov, Rami; Yungerman, Irena; Srebnik, Simcha

2017-07-01

Polymer-based protein recognition systems have enormous potential within clinical and diagnostic fields due to their reusability, biocompatibility, ease of manufacturing, and potential specificity. Imprinted polymer matrices have been extensively studied and applied as a simple technique for creating artificial polymer-based recognition gels for a target molecule. Although this technique has been proven effective when targeting small molecules (such as drugs), imprinting of proteins have so far resulted in materials with limited selectivity due to the large molecular size of the protein and aqueous environment. Using coarse-grained molecular simulation, we investigate the relation between protein makeup, polymer properties, and the selectivity of imprinted gels. Nonspecific binding that results in poor selectivity is shown to be strongly dependent on surface chemistry of the template and competitor proteins as well as on polymer chemistry. Residence time distributions of proteins diffusing within the gels provide a transparent picture of the relation between polymer constitution, protein properties, and the nonspecific interactions with the imprinted gel. The pronounced effect of protein surface chemistry on imprinted gel specificity is demonstrated. Copyright © 2017 John Wiley & Sons, Ltd.

Endothelial cell behaviour on gas-plasma-treated PLA surfaces: the roles of surface chemistry and roughness.

PubMed

Shah, Amita; Shah, Sarita; Mani, Gopinath; Wenke, Joseph; Agrawal, Mauli

2011-04-01

Glow-discharge gas-plasma (GP) treatment has been shown to induce surface modifications such that cell adhesion and growth are enhanced. However, it is not known which gas used in GP treatment is optimal for endothelial cell function. Polylactic acid (PLA) films treated oxygen, argon, or nitrogen GP were characterized using contact angles, scanning electron microscopy, atomic force microscopy, optical profilometry, and x-ray photoelectron spectroscopy. All three GP treatments decreased the carbon atomic concentration and surface roughness and increased the oxygen atomic concentration. Human umbilical vein endothelial cells were cultured on the PLA films for up to 7 days. Based on proliferation and live/dead assays, surface chemistry was shown to have the greatest effect on the attachment, proliferation, and viability of these cells, while roughness did not have a significant influence. Of the different gases, endothelial cell viability, attachment and proliferation were most significantly increased on PLA surfaces treated with oxygen and argon gas plasma. Copyright © 2010 John Wiley & Sons, Ltd.

A Bioanalytical Chemistry Experiment for Undergraduate Students: Biosensors Based on Metal Nanoparticles

ERIC Educational Resources Information Center

Niagi, John; Warner, John; Andreesco, Silvana

2007-01-01

The study describes the development of new biosensors based on metal nanoparticles because of its high surface area and large binding ability. The adopted procedure is extremely simple and versatile and can be used in various applications of electrochemistry.

High capacity Li-ion battery anodes: Impact of crystallite size, surface chemistry and PEG-coating

DOE PAGES

Minnici, Krysten; Kwon, Yo Han; Huie, Matthew M.; ...

2017-12-06

Battery electrodes are complex mesoscale systems comprised of an active material, conductive agent, current collector, and polymeric binder. Previous work showed that introduction of poly [3-(potassium-4-butanoate) thiophene] (PPBT) as a binder component coupled with a polyethylene glycol (PEG) surface coating on magnetite (Fe 3O 4) nanoparticles enhanced electron and ion transport in the high capacity anode system. Here, the impact of Fe 3O 4 crystallite size (10 nm vs. 20 nm) and surface chemistry were explored to evaluate their effects on interfacial interactions within the composite PEG/PPBT based electrodes and resultant battery performance. The Fe 3O 4 synthesis methods inevitablymore » lead to differences in surface chemistry. For instance, the Fe 3O 4 particles synthesized using ammonium hydroxide appeared more dispersed, and afforded improved rate capability performance. Notably, chemical interactions between the active nanoparticles and PPBT binder were only seen with particles synthesized using triethylamine. Capacity retention and cycling performance were unaffected. Thus, this study provides fundamental insights into the significant impact of active material synthesis on the design and fabrication of composite battery electrodes.« less

High capacity Li-ion battery anodes: Impact of crystallite size, surface chemistry and PEG-coating

DOE Office of Scientific and Technical Information (OSTI.GOV)

Minnici, Krysten; Kwon, Yo Han; Huie, Matthew M.

Battery electrodes are complex mesoscale systems comprised of an active material, conductive agent, current collector, and polymeric binder. Previous work showed that introduction of poly [3-(potassium-4-butanoate) thiophene] (PPBT) as a binder component coupled with a polyethylene glycol (PEG) surface coating on magnetite (Fe 3O 4) nanoparticles enhanced electron and ion transport in the high capacity anode system. Here, the impact of Fe 3O 4 crystallite size (10 nm vs. 20 nm) and surface chemistry were explored to evaluate their effects on interfacial interactions within the composite PEG/PPBT based electrodes and resultant battery performance. The Fe 3O 4 synthesis methods inevitablymore » lead to differences in surface chemistry. For instance, the Fe 3O 4 particles synthesized using ammonium hydroxide appeared more dispersed, and afforded improved rate capability performance. Notably, chemical interactions between the active nanoparticles and PPBT binder were only seen with particles synthesized using triethylamine. Capacity retention and cycling performance were unaffected. Thus, this study provides fundamental insights into the significant impact of active material synthesis on the design and fabrication of composite battery electrodes.« less

Tunable Luminescent Carbon Nanospheres with Well-Defined Nanoscale Chemistry for Synchronized Imaging and Therapy.

PubMed

Mukherjee, Prabuddha; Misra, Santosh K; Gryka, Mark C; Chang, Huei-Huei; Tiwari, Saumya; Wilson, William L; Scott, John W; Bhargava, Rohit; Pan, Dipanjan

2015-09-01

In this work, we demonstrate the significance of defined surface chemistry in synthesizing luminescent carbon nanomaterials (LCN) with the capability to perform dual functions (i.e., diagnostic imaging and therapy). The surface chemistry of LCN has been tailored to achieve two different varieties: one that has a thermoresponsive polymer and aids in the controlled delivery of drugs, and the other that has fluorescence emission both in the visible and near-infrared (NIR) region and can be explored for advanced diagnostic modes. Although these particles are synthesized using simple, yet scalable hydrothermal methods, they exhibit remarkable stability, photoluminescence and biocompatibility. The photoluminescence properties of these materials are tunable through careful choice of surface-passivating agents and can be exploited for both visible and NIR imaging. Here the synthetic strategy demonstrates the possibility to incorporate a potent antimetastatic agent for inhibiting melanomas in vitro. Since both particles are Raman active, their dispersion on skin surface is reported with Raman imaging and utilizing photoluminescence, their depth penetration is analysed using fluorescence 3D imaging. Our results indicate a new generation of tunable carbon-based probes for diagnosis, therapy or both. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Characterisation of a PdCl 2/SnCl 2 electroless plating catalyst system adsorbed on barium titanate-based electroactive ceramics

NASA Astrophysics Data System (ADS)

Meenan, B. J.; Brown, N. M. D.; Wilson, J. W.

1994-03-01

A PdCl 2/SnCl 2 metallisation catalyst system, of the type used to activate non-conducting surfaces for electroless metal deposition, has been characterised by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The substrate is a barium titanate (BaTiO 3)-based electroactive ceramic of the type used in the fabrication of multilayer ceramic capacitors (MLCC). The treatment of the substrate surface with the PdCl 2/SnCl 2 "sensitiser" solution leads to the adsorption of catalytically inactive compounds of palladium and tin. Subsequent treatment of this surface with an "accelerator" solution removes excess oxides, hydroxides and salts of tin thereby leaving the active catalyst species, Pd xSn y, on the surface. Such sites, on exposure to the appropriete electroless plating bath, are then responsible for the metal deposition. In this study, the chemical state and relative quantities of the various surface species present after each of the processing stages have been determined by XPS. The surface roughness of the substrate results in less of the tin compounds present thereon being removed on washing the catalysed surface in the accelerator solution than normally reported for such systems, thereby affecting the measured Pd: Sn ratio. SEM studies show that the accelerator solution treatment generates crystalline areas, which may be a result of coagulation of the Pd xSn y particles present, in the otherwise amorphous catalyst coating.

WATER CHEMISTRY ASSESSMENT METHODS

EPA Science Inventory

This section summarizes and evaluates the surfce water column chemistry assessment methods for USEPA/EMAP-SW, USGS-NAQA, USEPA-RBP, Oho EPA, and MDNR-MBSS. The basic objective of surface water column chemistry assessment is to characterize surface water quality by measuring a sui...

Surface chemistry: Key to control and advance myriad technologies

PubMed Central

Yates, John T.; Campbell, Charles T.

2011-01-01

This special issue on surface chemistry is introduced with a brief history of the field, a summary of the importance of surface chemistry in technological applications, a brief overview of some of the most important recent developments in this field, and a look forward to some of its most exciting future directions. This collection of invited articles is intended to provide a snapshot of current developments in the field, exemplify the state of the art in fundamental research in surface chemistry, and highlight some possibilities in the future. Here, we show how those articles fit together in the bigger picture of this field. PMID:21245359

Reaction of methyl formate with VC(1 0 0) and TiC(1 0 0) surfaces

NASA Astrophysics Data System (ADS)

Frantz, Peter; Kim, Hyun I.; Didziulis, Stephen V.; Li, Shuang; Chen, Zhiying; Perry, Scott S.

2005-12-01

The chemistry of the (1 0 0) surface of the tribologically important materials vanadium carbide (VC) and titanium carbide (TiC) with methyl formate (CH 3OCHO) has been studied with X-ray photoelectron spectroscopy (XPS), high resolution electron energy loss spectroscopy (HREELS), and temperature programmed desorption (TPD). The molecule reacts with each surface at temperatures below 150 K, although the extent of reaction is greater on the TiC surface. XPS and HREELS results indicate that the first step in this chemistry is the cleavage of the CH 3O-CHO bond, generating surface methoxy groups (CH 3O-) and either carbon monoxide on VC or a formyl (CHO) group on TiC. The methoxy group reacts further on both surfaces via pathways expected based on previous methanol adsorption studies, primarily decomposing through a formyl intermediate on VC to generate formaldehyde and evolving methanol on TiC. The formyl group formed directly from methyl formate on TiC enables the production and evolution of formaldehyde, and also appears to break down further to the elements. These results indicate a propensity for these carbides to react with esters, leading potentially to the beneficial formation of friction lowering surface films or the deleterious degradation of ester-based lubricants.

Effect of accelerated ageing and surface sealing on the permanent deformation of auto-polymerising soft linings.

PubMed

da Silva, Joaquim; Takahashi, Jessica; Nuňez, Juliana; Consani, Rafael; Mesquita, Marcelo

2012-09-01

To compare the effects of different ageing methods on the permanent deformation of two permanent soft liners. The materials selected were auto-polymerising acrylic resin and silicone-based reliners. Sealer coating was also evaluated. Sixty specimens of each reliner were manufactured (12.7 mm diameter and 19 mm length). Specimens were randomly distributed into 12 groups (n = 10) and submitted to one of the accelerated ageing processes. Permanent deformation tests were conducted with a mechanical device described within the American Dental Association specification number 18 with a compressive load of 750 gf applied for 30 s. All data were submitted for statistical analysis. Mann-Whitney test compared the effect of the surface sealer on each material and the permanent deformation of the materials in the same ageing group (p = 0.05). Kruskal-Wallis and Dunn tests compared all ageing groups of each material (p = 0.05). The silicone-based reliner presented a lower permanent deformation than the acrylic resin-based reliner, regardless of the ageing procedure. The surface sealer coating was effective only for the thermocycled silicone group and the accelerated ageing processes affected only the permanent deformation of the acrylic resin-based material. The silicone-based reliner presented superior elastic properties and the thermocycling was more effective in ageing the materials. © 2010 The Gerodontology Society and John Wiley & Sons A/S.

In the Footsteps of Irving Langmuir: Physical Chemistry in Service of Society

NASA Astrophysics Data System (ADS)

Carter, Emily

The approach that Irving Langmuir took during his scientific career in industry at General Electric exemplifies the best that we chemical physicists/physical chemists can offer the world. His name is associated with very fundamental concepts and phenomena (e.g., the Langmuir isotherm, Langmuir-Blodgett films) along with practical inventions (e.g., the Langmuir probe, Langmuir trough). He worked at the interface of physics, chemistry, and engineering, with much of his important work devoted to understanding surface and interface phenomena. I have - unintentionally - followed in his footsteps, trained as a physical chemist who now leads the engineering school at Princeton. In this talk, I will give examples from my research as to how fundamental physical chemistry techniques and concepts - based largely on quantum mechanics - can be harnessed to help the world transition to a sustainable energy future. In the footsteps of Irving, surface and interfacial phenomena will figure prominently in the examples chosen.

Bioactivating Silicon (100) Surfaces with Novel UV Grafting of Cyclopropylamine for Promotion of Cell Adhesion

PubMed Central

Ching, Jing Yuan

2018-01-01

In this report, utraviolent (UV) photoionization of cyclopropylamine on silicon (100) hydride was employed to examine interfacing with three different epithelial cell types (MDA-MB 231, AGS and HEC1A). The cellular viability using this novel methodology had been quantified to evaluate the bioactivating potential of this ring-opening chemistry when compared to standardized controls (aminopropyltriethoxylamine, collagen and poly-L lysine). X-ray photospectroscopy (XPS) and atomic force microscopy (AFM) were used to characterize surface chemistry composition, while cell viability and confocal microscopy after 24 h of incubation were performed. Based on the results acquired from this novel ring-opening metastasis process, the promotion of cell adhesion and viability was found to be higher using this chemistry when compared to other conventional control groups, even for the collagen coating, without any observable issues of cytotoxicity. PMID:29724039

Tuning the Reversibility of Mg Anodes via Controlled Surface Passivation by H 2O/Cl – in Organic Electrolytes

DOE PAGES

Connell, Justin G.; Genorio, Bostjan; Lopes, Pietro Papa; ...

2016-10-17

Developing a new generation of battery chemistries is a critical challenge to moving beyond current Li-ion technologies. In this work, we introduce a surface-science-based approach for understanding the complex phenomena controlling the reversibility of Mg anodes for Mg-ion batteries. In addition, we identify the profound impact of trace levels of H 2O (≤3 ppm) on the kinetics of Mg deposition and determine that passive films of MgO and Mg(OH) 2 are formed only after Mg deposition ceases, rather than continuously during Mg reduction. We also find that Cl – inhibits passivation through the formation of adsorbed Cl – (Mg–Cl(ad)) and/ormore » MgCl 2 on the surface, as well as through a dynamic competition with H 2O in the double layer. In conclusion, this surface-science-based approach goes well beyond Mg anodes, highlighting the need for more in-depth understanding of electrolyte chemistries before a new generation of efficient and reversible battery technologies can be realized.« less

Nitrous acid chemistry in Los Angeles during the CalNex-LA experiment

NASA Astrophysics Data System (ADS)

Stutz, J.; Tsai, C.; Wong, K.; Pikelnaya, O.; Hurlock, S. C.; Young, C. J.; Veres, P. R.; Washenfelder, R. A.; Brown, S. S.; Flynn, J. H.; Grossberg, N.; Lefer, B. L.

2011-12-01

The role of nitrous acid, HONO, as an OH radical precursor during the early morning and during the day has received considerable attention over the past decade. Several studies have reported that HONO photolysis in the polluted boundary layer is the dominant source of OH in the early morning, and that it contributes up to 30% to the diurnally averaged primary OH formation. Despite the importance of HONO for boundary layer chemistry, our understanding of HONO sources is still incomplete. Laboratory studies suggest that HONO is formed by the conversion of NO2 on humid surfaces at night. As this process is too slow during the day, several photo-enhanced processes have been proposed that either accelerate the NO2 conversion, or involve other nitrogen species, such as HNO3. Field observations of vertical HONO and NO2 concentration profiles, together with accurate measurements of other nitrogen species and actinic flux measurements offer a unique opportunity to constrain the proposed HONO formation mechanisms. Here we present observations of HONO, NO2, and other parameters made by various instruments during the 2010 CalNex experiment on the east side of the Los Angeles basin. We will discuss the vertical profiles of HONO and NO2 measured by LP-DOAS, CEAS, CIMS, and photolytic conversion + CL with regard to the formation of HONO. The observations will be compared to 1D chemistry and transport model calculations to test various proposed formation mechanisms. We will discuss the most likely formation pathway of HONO and the potential impact of HONO on atmospheric chemistry in Los Angeles.

Computational screening of organic polymer dielectrics for novel accelerator technologies

DOE PAGES

Pilania, Ghanshyam; Weis, Eric; Walker, Ethan M.; ...

2018-06-18

The use of infrared lasers to power accelerating dielectric structures is a developing area of research. Within this technology, the choice of the dielectric material forming the accelerating structures, such as the photonic band gap (PBG) structures, is dictated by a range of interrelated factors including their dielectric and optical properties, amenability to photo-polymerization, thermochemical stability and other target performance metrics of the particle accelerator. In this direction, electronic structure theory aided computational screening and design of dielectric materials can play a key role in identifying potential candidate materials with the targeted functionalities to guide experimental synthetic efforts. In anmore » attempt to systematically understand the role of chemistry in controlling the electronic structure and dielectric properties of organic polymeric materials, here we employ empirical screening and density functional theory (DFT) computations, as a part of our multi-step hierarchal screening strategy. Our DFT based analysis focused on the bandgap, dielectric permittivity, and frequency-dependent dielectric losses due to lattice absorption as key properties to down-select promising polymer motifs. In addition to the specific application of dielectric laser acceleration, the general methodology presented here is deemed to be valuable in the design of new insulators with an attractive combination of dielectric properties.« less

Covalent-Bond Formation via On-Surface Chemistry.

PubMed

Held, Philipp Alexander; Fuchs, Harald; Studer, Armido

2017-05-02

In this Review article pioneering work and recent achievements in the emerging research area of on-surface chemistry is discussed. On-surface chemistry, sometimes also called two-dimensional chemistry, shows great potential for bottom-up preparation of defined nanostructures. In contrast to traditional organic synthesis, where reactions are generally conducted in well-defined reaction flasks in solution, on-surface chemistry is performed in the cavity of a scanning probe microscope on a metal crystal under ultrahigh vacuum conditions. The metal first acts as a platform for self-assembly of the organic building blocks and in many cases it also acts as a catalyst for the given chemical transformation. Products and hence success of the reaction are directly analyzed by scanning probe microscopy. This Review provides a general overview of this chemistry highlighting advantages and disadvantages as compared to traditional reaction setups. The second part of the Review then focuses on reactions that have been successfully conducted as on-surface processes. On-surface Ullmann and Glaser couplings are addressed. In addition, cyclodehydrogenation reactions and cycloadditions are discussed and reactions involving the carbonyl functionality are highlighted. Finally, the first examples of sequential on-surface chemistry are considered in which two different functionalities are chemoselectively addressed. The Review gives an overview for experts working in the area but also offers a starting point to non-experts to enter into this exciting new interdisciplinary research field. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Effect of surface chemistries and characteristics of Ti6Al4V on the Ca and P adsorption and ion dissolution in Hank's ethylene diamine tetra-acetic acid solution.

PubMed

Chang, E; Lee, T M

2002-07-01

This study examined the influence of chemistries and surface characteristics of Ti6Al4V on the adsorption of Ca and P species and ion dissolution behavior of the material exposed in Hank's solution with 8.0 mM ethylene diamine tetra-acetic acid at 37 degrees C. The variation of chemistries of the alloy and nano-surface characteristics (chemistries of nano-surface oxides, amphoteric OH group adsorbed on oxides, and oxide thickness) was effected by surface modification and three passivation methods (34% nitric acid passivation. 400 degrees C heated in air, and aged in 100 degrees C water). X-ray photoelectron spectroscopy and Auger electron spectroscopy were used for surface analyses. The chemistries of nano-surface oxides in a range studied should not change the capability of Ca and P adsorption. Nor is the capability affected significantly by amphoteric OH group and oxide thickness. However, passivations influence the surface oxide thickness and the early stage ion dissolution rate of the alloy. The rate-limiting step of the rate can be best explained by metal-ion transport through the oxide film, rather than hydrolysis of the film. Variation of the chemistries of titanium alloy alters the electromotive force potential of the metal, thereby affecting the corrosion and ion dissolution rate.

A Study on Advanced Lithium-Based Battery Cell Chemistries to Enhance Lunar Exploration Missions

NASA Technical Reports Server (NTRS)

Reid, Concha M.; Bennett, William R.

2010-01-01

NASAs Exploration Technology Development Program (ETDP) Energy Storage Project conducted an advanced lithium-based battery chemistry feasibility study to determine the best advanced chemistry to develop for the Altair Lunar Lander and the Extravehicular Activities (EVA) advanced Lunar surface spacesuit. These customers require safe, reliable batteries with extremely high specific energy as compared to state-of-the-art. The specific energy goals for the development project are 220 watt-hours per kilogram (Wh/kg) delivered at the battery-level at 0 degrees Celsius ( C) at a C/10 discharge rate. Continuous discharge rates between C/5 and C/2, operation between 0 and 30 C and 200 cycles are targeted. Electrode materials that were considered include layered metal oxides, spinel oxides, and olivine-type cathode materials, and lithium metal, lithium alloy, and silicon-based composite anode materials. Advanced cell chemistry options were evaluated with respect to multiple quantitative and qualitative attributes while considering their projected performance at the end of the available development timeframe. Following a rigorous ranking process, a chemistry that combines a lithiated nickel manganese cobalt oxide Li(LiNMC)O2 cathode with a silicon-based composite anode was selected as the technology that can potentially offer the best combination of safety, specific energy, energy density, and likelihood of success.

Molecular Studies of Complex Soil Organic Matter Interactions with Metal Ions and Mineral Surfaces using Classical Molecular Dynamics and Quantum Chemistry Methods

NASA Astrophysics Data System (ADS)

Andersen, A.; Govind, N.; Laskin, A.

2017-12-01

Mineral surfaces have been implicated as potential protectors of soil organic matter (SOM) against decomposition and ultimate mineralization to small molecules which can provide nutrients for plants and soil microbes and can also contribute to the Earth's elemental cycles. SOM is a complex mixture of organic molecules of biological origin at varying degrees of decomposition and can, itself, self-assemble in such a way as to expose some biomolecule types to biotic and abiotic attack while protecting other biomolecule types. The organization of SOM and SOM with mineral surfaces and solvated metal ions is driven by an interplay of van der Waals and electrostatic interactions leading to partitioning of hydrophilic (e.g. sugars) and hydrophobic (e.g., lipids) SOM components that can be bridged with amphiphilic molecules (e.g., proteins). Classical molecular dynamics simulations can shed light on assemblies of organic molecules alone or complexation with mineral surfaces. The role of chemical reactions is also an important consideration in potential chemical changes of the organic species such as oxidation/reduction, degradation, chemisorption to mineral surfaces, and complexation with solvated metal ions to form organometallic systems. For the study of chemical reactivity, quantum chemistry methods can be employed and combined with structural insight provided by classical MD simulations. Moreover, quantum chemistry can also simulate spectroscopic signatures based on chemical structure and is a valuable tool in interpreting spectra from, notably, x-ray absorption spectroscopy (XAS). In this presentation, we will discuss our classical MD and quantum chemistry findings on a model SOM system interacting with mineral surfaces and solvated metal ions.

A Chemical Approach to Understanding Oxide Surface Structure and Reactivity

NASA Astrophysics Data System (ADS)

Enterkin, James Andrew

Transmission electron microscopy and diffraction are powerful tools for solving complex structural problems. They complement other analytical techniques, such as x-ray diffraction, elucidating problems which cannot be solved by other techniques. One area where they are of particularly great value is in the determination of surface structures. The research presented herein uses electron microscopy and diffraction as the primary experimental techniques in the development of a chemistry of surface structures. High-resolution electron microscopy revealed that the La4Cu 3MoO12 structure has turbostratic disorder and a lower symmetry space group (Pm) than was previously found. The refinement of the x-ray data was significantly improved by using a disordered model and the Pm space group. A bond valence analysis confirmed that the disordered structure is the superior model. Strontium titanate, SrTiO3, single crystal surfaces were examined principally via transmission electron diffraction. A homologous series with intergrowths was discovered on the (110) surface of strontium titanate, marking the first time that these important concepts of solid state chemistry have been found at the surface. Atmospheric adsorbates, such as H2O and CO2, were found to help to stabilize undercoordinated surface structures on the (100) surface. It was shown that chemical bonding, bond valence, atomic coordination, and stoichiometry greatly influence the development of surface structures. Additionally, such chemistry based analysis was demonstrated to be able to predict surface structure stability and reactivity. Application of a modified Wulff construction to the observed shape of strontium titanate nanocuboids revealed that the surface structure and particle stoichiometry are interlinked, with control over one allowing equally precise control over the other. Platinum nanoparticles on the strontium titanate nanocuboids were shown via high resolution electron microscopy to have cube-on-cube epitaxy, with the shape of the platinum nanoparticles governed by the Winterbottom construction. Precise modification of the support surface will therefore allow engineering of supported metal particles with precise control over which facets are exposed. These results suggest that control over the support surface chemistry can be used to engineer thermodynamically stable, face selective catalysts.

Erosion rate diagnostics in ion thrusters using laser-induced fluorescence

NASA Technical Reports Server (NTRS)

Gaeta, C. J.; Matossian, J. N.; Turley, R. S.; Beattie, J. R.; Williams, J. D.; Williamson, W. S.

1993-01-01

We have used laser-induced fluorescence (LIF) to monitor the charge-exchange ion erosion of the molybdenum accelerator electrode in ion thrusters. This real-time, nonintrusive method was implemented by operating a 30cm-diam ring-cusp thruster using xenon propellant. With the thruster operating at a total power of 5 kW, laser radiation at a wavelength of 390 nm (corresponding to a ground state atomic transition of molybdenum) was directed through the extracted ion beam adjacent to the downstream surface of the molybdenum accelerator electrode. Molybdenum atoms, sputtered from this surface as a result of charge-exchange ion erosion, were excited by the laser radiation. The intensity of the laser-induced fluorescence radiation, which is proportional to the sputter rate of the molybdenum atoms, was measured and correlated with variations in thruster operating conditions such as accelerator electrode voltage, accelerator electrode current, and test facility background pressure. We also demonstrated that the LIF technique has sufficient sensitivity and spatial resolution to evaluate accelerator electrode lifetime in ground-based test facilities.

Clathrin to Lipid Raft-Endocytosis via Controlled Surface Chemistry and Efficient Perinuclear Targeting of Nanoparticle.

PubMed

Chakraborty, Atanu; Jana, Nikhil R

2015-09-17

Nanoparticle interacts with live cells depending on their surface chemistry, enters into cell via endocytosis, and is commonly trafficked to an endosome/lysozome that restricts subcellular targeting options. Here we show that nanoparticle surface chemistry can be tuned to alter their cell uptake mechanism and subcellular trafficking. Quantum dot based nanoprobes of 20-30 nm hydrodynamic diameters have been synthesized with tunable surface charge (between +15 mV to -25 mV) and lipophilicity to influence their cellular uptake processes and subcellular trafficking. It is observed that cationic nanoprobe electrostatically interacts with cell membrane and enters into cell via clathrin-mediated endocytosis. At lower surface charge (between +10 mV to -10 mV), the electrostatic interaction with cell membrane becomes weaker, and additional lipid raft endocytosis is initiated. If a lipophilic functional group is introduced on a weakly anionic nanoparticle surface, the uptake mechanism shifts to predominant lipid raft-mediated endocytosis. In particular, the zwitterionic-lipophilic nanoprobe has the unique advantage as it weakly interacts with anionic cell membrane, migrates toward lipid rafts for interaction through lipophilic functional group, and induces lipid raft-mediated endocytosis. While predominate or partial clathrin-mediated entry traffics most of the nanoprobes to lysozome, predominate lipid raft-mediated entry traffics them to perinuclear region, particularly to the Golgi apparatus. This finding would guide in designing appropriate nanoprobe for subcellular targeting and delivery.

Chemistry of surface nanostructures in lead precursor-rich PbZr0.52Ti0.48O3 sol-gel films

NASA Astrophysics Data System (ADS)

Gueye, I.; Le Rhun, G.; Gergaud, P.; Renault, O.; Defay, E.; Barrett, N.

2016-02-01

We present a study of the chemistry of the nanostructured phase at the surface of lead zirconium titanate PbZr0.52Ti0.48O3 (PZT) films synthesized by sol-gel method. In sol-gel synthesis, excess lead precursor is used to maintain the target stoichiometry. Surface nanostructures appear at 10% excess whereas 30% excess inhibits their formation. Using the surface-sensitive, quantitative X-ray photoelectron spectroscopy and glancing angle X-ray diffraction we have shown that the chemical composition of the nanostructures is ZrO1.82-1.89 rather than pyrochlore often described in the literature. The presence of a possibly discontinuous layer of wide band gap ZrO1.82-1.89 could be of importance in determining the electrical properties of PZT-based metal-insulator-metal heterostructures.

Chemistry and Materials Science, 1990--1991. [Second annual report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sugihara, T.T.; Bruner, J.M.; McElroy, L.A.

1991-12-31

This 2-year (FY 1990-91) contains 49 technical articles in ten sections: research sampler, metals and alloys, energetic materials, chemistry and physics of advanced materials, bonding and reactions at surfaces and interfaces, superconductivity, energy R and D, waste processing and management, characterization and analysis, and facilities and instrumentation. Two more sections list department personnel, their publications etc., consultants, and summary of department budgets. The articles are processed separately for the data base. (DLC)

A Gas-Surface Interaction Model based on Accelerated Reactive Molecular Dynamics for Hypersonic Conditions including Thermal Conduction

DTIC Science & Technology

2012-02-28

Interaction Model based on Accelerated Reactive Molecular Dynamics for Hypersonic conditions including Thermal Conduction FA9550-09-1-0157 Schwartzentruber...Dynamics for Hypersonic Conditions including Thermal Conduction Grant/Contract Number: FA9550-09-1-0157 Program Manager: Dr. John Schmisseur PI...through the boundary layer and may chemically react with the vehicle’s thermal protection system (TPS). Many TPS materials act as a catalyst for the

Macroparticle generation in DC arc discharge from a WC cathode

NASA Astrophysics Data System (ADS)

Zhirkov, Igor; Polcik, Peter; Kolozsvári, Szilard; Rosen, Johanna

2017-03-01

We have studied macroparticle generation from a tungsten carbide cathode used in a dc vacuum arc discharge. Despite a relatively high decomposition/melting point (˜3100 K), there is an intensive generation of visible particles with sizes in the range 20-35 μm. Visual observations during the discharge and scanning electron microscopy of the cathode surface and of collected macroparticles indicate a new mechanism for particle formation and acceleration. Based on the W-C phase diagram, there is an intensive sublimation of carbon from the melt resulting from the cathode spot. The sublimation supports the formation of a sphere, which is accelerated upon an explosion initiated by Joule heating at the critical contact area between the sphere and the cathode body. The explosive nature of the particle acceleration is confirmed by surface features resembling the remains of a splash on the droplet surface.

Organic chemistry on solid surfaces

NASA Astrophysics Data System (ADS)

Ma, Zhen; Zaera, Francisco

2006-07-01

Chemistry on solid surfaces is central to many areas of practical interest such as heterogeneous catalysis, tribology, electrochemistry, and materials processing. With the development of many surface-sensitive analytical techniques in the past decades, great advances have been possible in our understanding of such surface chemistry at the molecular level. Earlier studies with model systems, single crystals in particular, have provided rich information about the adsorption and reaction kinetics of simple inorganic molecules. More recently, the same approach has been expanded to the study of the surface chemistry of relatively complex organic molecules, in large measure in connection with the selective synthesis of fine chemicals and pharmaceuticals. In this report, the chemical reactions of organic molecules and fragments on solid surfaces, mainly on single crystals of metals but also on crystals of metal oxides, carbides, nitrides, phosphides, sulfides and semiconductors as well as on more complex models such as bimetallics, alloys, and supported particles, are reviewed. A scheme borrowed from the organometallic and organic chemistry literature is followed in which key examples of representative reactions are cited first, and general reactivity trends in terms of both the reactants and the nature of the surface are then identified to highlight important mechanistic details. An attempt has been made to emphasize recent advances, but key earlier examples are cited as needed. Finally, correlations between surface and organometallic and organic chemistry, the relevance of surface reactions to applied catalysis and materials functionalization, and some promising future directions in this area are briefly discussed.

The Chemistry of Inorganic Precursors during the Chemical Deposition of Films on Solid Surfaces.

PubMed

Barry, Seán T; Teplyakov, Andrew V; Zaera, Francisco

2018-03-20

The deposition of thin solid films is central to many industrial applications, and chemical vapor deposition (CVD) methods are particularly useful for this task. For one, the isotropic nature of the adsorption of chemical species affords even coverages on surfaces with rough topographies, an increasingly common requirement in microelectronics. Furthermore, by splitting the overall film-depositing reactions into two or more complementary and self-limiting steps, as it is done in atomic layer depositions (ALD), film thicknesses can be controlled down to the sub-monolayer level. Thanks to the availability of a vast array of inorganic and metalorganic precursors, CVD and ALD are quite versatile and can be engineered to deposit virtually any type of solid material. On the negative side, the surface chemistry that takes place in these processes is often complex, and can include undesirable side reactions leading to the incorporation of impurities in the growing films. Appropriate precursors and deposition conditions need to be chosen to minimize these problems, and that requires a proper understanding of the underlying surface chemistry. The precursors for CVD and ALD are often designed and chosen based on their known thermal chemistry from inorganic chemistry studies, taking advantage of the vast knowledge developed in that field over the years. Although a good first approximation, however, this approach can lead to wrong choices, because the reactions of these precursors at gas-solid interfaces can be quite different from what is seen in solution. For one, solvents often aid in the displacement of ligands in metalorganic compounds, providing the right dielectric environment, temporarily coordinating to the metal, or facilitating multiple ligand-complex interactions to increase reaction probabilities; these options are not available in the gas-solid reactions associated with CVD and ALD. Moreover, solid surfaces act as unique "ligands", if these reactions are to be viewed from the point of view of the metalorganic complexes used as precursors: they are bulky and rigid, can provide multiple binding sites for a single reaction, and can promote unique bonding modes, especially on metals, which have delocalized electronic structures. The differences between the molecular and surface chemistry of CVD and ALD precursors can result in significant variations in their reactivity, ultimately leading to unpredictable properties in the newly grown films. In this Account, we discuss some of the main similarities and differences in chemistry that CVD/ALD precursors follow on surfaces when contrasted against their known behavior in solution, with emphasis on our own work but also referencing other key contributions. Our approach is unique in that it combines expertise from the inorganic, surface science, and quantum-mechanics fields to better understand the mechanistic details of the chemistry of CVD and ALD processes and to identify new criteria to consider when designing CVD/ALD precursors.

Study of the Effect of Grafting Method on Surface Polarity of Tempo-Oxidized Nanocellulose Using Polycaprolactone as the Modifying Compound: Esterification versus Click-Chemistry

PubMed Central

Benkaddour, Abdelhaq; Jradi, Khalil; Robert, Sylvain; Daneault, Claude

2013-01-01

Esterification and click-chemistry were evaluated as surface modification treatments for TEMPO-oxidized nanocelluloses (TONC) using Polycaprolactone-diol (PCL) as modifying compound in order to improve the dispersion of nanofibers in organic media. These two grafting strategies were analyzed and compared. The first consists of grafting directly the PCL onto TONC, and was carried out by esterification between hydroxyl groups of PCL and carboxyl groups of TONC. The second strategy known as click-chemistry is based on the 1,3-dipolar cycloaddition reaction between azides and alkyne terminated moieties to form the triazole ring between PCL and TONC. The grafted samples were characterized by transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and Thermogravimetry analysis (TGA). Further, the effects of the two treatments on the surface hydrophobization of TONC were investigated by contact angle measurements. The results show that both methods confirm the success of such a modification and the click reaction was significantly more effective than esterification. PMID:28348357

GPU Linear Algebra Libraries and GPGPU Programming for Accelerating MOPAC Semiempirical Quantum Chemistry Calculations.

PubMed

Maia, Julio Daniel Carvalho; Urquiza Carvalho, Gabriel Aires; Mangueira, Carlos Peixoto; Santana, Sidney Ramos; Cabral, Lucidio Anjos Formiga; Rocha, Gerd B

2012-09-11

In this study, we present some modifications in the semiempirical quantum chemistry MOPAC2009 code that accelerate single-point energy calculations (1SCF) of medium-size (up to 2500 atoms) molecular systems using GPU coprocessors and multithreaded shared-memory CPUs. Our modifications consisted of using a combination of highly optimized linear algebra libraries for both CPU (LAPACK and BLAS from Intel MKL) and GPU (MAGMA and CUBLAS) to hasten time-consuming parts of MOPAC such as the pseudodiagonalization, full diagonalization, and density matrix assembling. We have shown that it is possible to obtain large speedups just by using CPU serial linear algebra libraries in the MOPAC code. As a special case, we show a speedup of up to 14 times for a methanol simulation box containing 2400 atoms and 4800 basis functions, with even greater gains in performance when using multithreaded CPUs (2.1 times in relation to the single-threaded CPU code using linear algebra libraries) and GPUs (3.8 times). This degree of acceleration opens new perspectives for modeling larger structures which appear in inorganic chemistry (such as zeolites and MOFs), biochemistry (such as polysaccharides, small proteins, and DNA fragments), and materials science (such as nanotubes and fullerenes). In addition, we believe that this parallel (GPU-GPU) MOPAC code will make it feasible to use semiempirical methods in lengthy molecular simulations using both hybrid QM/MM and QM/QM potentials.

Role of surfaces and interfaces in controlling the mechanical properties of metallic alloys.

PubMed

Lee, Won-Jong; Chia, Wen-Jui; Wang, Jinliu; Chen, Yanfeng; Vaynman, Semyon; Fine, Morris E; Chung, Yip-Wah

2010-11-02

This article explores the subtle effects of surfaces and interfaces on the mechanical properties of bulk metallic alloys using three examples: environmental effects on fatigue life, hydrogen embrittlement effects on the ductility of intermetallics, and the role of coherent precipitates in the toughness of steels. It is demonstrated that the marked degradation of the fatigue life of metals is due to the strong chemisorption of adsorbates on exposed slip steps that are formed during fatigue deformation. These adsorbates reduce the reversibility of slip, thus accelerating fatigue damage in a chemically active gas environment. For certain intermetallic alloys such as Ni(3)Al and Ni(3)Fe, the ductility depends on the ambient gas composition and the atomic ordering in these alloys, both of which govern the complex surface chemical reactions taking place in the vicinity of crack tips. Finally, it is shown that local stresses at a coherent precipitate-matrix interface can activate dislocation motion at low temperatures, thus improving the fracture toughness of bulk alloys such as steels at cryogenic temperatures. These examples illustrate the complex interplay between surface chemistry and mechanics, often yielding unexpected results.

Advancing the frontiers in nanocatalysis, biointerfaces, and renewable energy conversion by innovations of surface techniques.

PubMed

Somorjai, Gabor A; Frei, Heinz; Park, Jeong Y

2009-11-25

The challenge of chemistry in the 21st century is to achieve 100% selectivity of the desired product molecule in multipath reactions ("green chemistry") and develop renewable energy based processes. Surface chemistry and catalysis play key roles in this enterprise. Development of in situ surface techniques such as high-pressure scanning tunneling microscopy, sum frequency generation (SFG) vibrational spectroscopy, time-resolved Fourier transform infrared methods, and ambient pressure X-ray photoelectron spectroscopy enabled the rapid advancement of three fields: nanocatalysts, biointerfaces, and renewable energy conversion chemistry. In materials nanoscience, synthetic methods have been developed to produce monodisperse metal and oxide nanoparticles (NPs) in the 0.8-10 nm range with controlled shape, oxidation states, and composition; these NPs can be used as selective catalysts since chemical selectivity appears to be dependent on all of these experimental parameters. New spectroscopic and microscopic techniques have been developed that operate under reaction conditions and reveal the dynamic change of molecular structure of catalysts and adsorbed molecules as the reactions proceed with changes in reaction intermediates, catalyst composition, and oxidation states. SFG vibrational spectroscopy detects amino acids, peptides, and proteins adsorbed at hydrophobic and hydrophilic interfaces and monitors the change of surface structure and interactions with coadsorbed water. Exothermic reactions and photons generate hot electrons in metal NPs that may be utilized in chemical energy conversion. The photosplitting of water and carbon dioxide, an important research direction in renewable energy conversion, is discussed.

Friction and surface chemistry of some ferrous-base metallic glasses

NASA Technical Reports Server (NTRS)

Miyoshi, K.; Buckley, D. H.

1982-01-01

The friction properties of some ferrous-base metallic glasses were measured both in argon and in vacuum to a temperature of 350 C. The alloy surfaces were also analyzed with X-ray photoelectron spectroscopy to identify the compounds and elements present on the surface. The results of the investigation indicate that even when the surfaces of the amorphous alloys, or metallic glasses, are atomically clean, bulk contaminants such as boric oxide and silicon dioxide diffuse to the surfaces. Friction measurements in both argon and vacuum indicate that the alloys exhibit higher coefficients of friction in the crystalline state than they do in the amorphous state.

Marrying the mussel inspired chemistry and Kabachnik-Fields reaction for preparation of SiO2 polymer composites and enhancement removal of methylene blue

NASA Astrophysics Data System (ADS)

Huang, Qiang; Liu, Meiying; Chen, Junyu; Wan, Qing; Tian, Jianwen; Huang, Long; Jiang, Ruming; Deng, Fengjie; Wen, Yuanqing; Zhang, Xiaoyong; Wei, Yen

2017-11-01

The removal of organic dyes using functionalization SiO2 composites (denoted as SiO2-PDA-CSH) were prepared via a facile method that combined with mussel inspired chemistry and Kabachnik-Fields (KF) reaction. The size and surface morphology, chemical structure, thermal stability, surface charging property, and elemental composition were evaluated by means of transmission electron microscope (TEM), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), zeta potential, and X-ray photoelectron spectroscopy (XPS), respectively. The results demonstrated that the organic functional groups can be successfully introduced onto the surface of SiO2 microspheres through the combination of mussel inspired chemistry and KF reaction. The removal of cationic dye methylene blue (MB) by the raw SiO2 and SiO2-PDA-CSH composites was examined and compared using a series of batch adsorption experiments. The results suggested that SiO2-PDA-CSH composites had a 3-fold increase in the adsorption capacity towards MB than that of pure SiO2 microspheres and the adsorption process was dependent on the solution pH. According to the adsorption kinetics, the adsorption of MB onto SiO2-PDA-CSH composites was well described by pseudo-second-order kinetic model. The equilibrium data were fitted with Langmuir and Freundlich isotherm models with R2 = 0.9981 and R2 = 0.9982, respectively. The maximum adsorption capacity from Langmuir isotherm was found to be 688.85 mg/g. The adsorption thermodynamics was also investigated in detailed. The parameters revealed that the adsorption process was spontaneous and endothermic in nature. The adsorption mechanism might be the synergistic action of physical adsorption of SiO2-PDA-CSH particles and electrostatic interaction between the MB and functional groups on the surface of SiO2-PDA-CSH composites, including sulfydryl, amino, aromatic moieties, and phosphate groups. Taken together, we developed a novel and facile strategy for the surface modification of SiO2 to achieve high adsorption towards MB based on the mussel inspired chemistry and multicomponent KF reaction. More importantly, this strategy could be easily extended for fabrication of many other high efficient adsorbents due to the universality of mussel inspired chemistry and various multicomponent reactions based on amino groups. Therefore, this work will open a new avenue and direction for the environmental applications of mussel inspired chemistry.

Droplet Deformation in an Extensional Flow: The Role of Surfactant Physical Chemistry

NASA Technical Reports Server (NTRS)

Stebe, Kathleen J.

1996-01-01

Surfactant-induced Marangoni effects strongly alter the stresses exerted along fluid particle interfaces. In low gravity processes, these stresses can dictate the system behavior. The dependence of Marangoni effects on surfactant physical chemistry is not understood, severely impacting our ability to predict and control fluid particle flows. A droplet in an extensional flow allows the controlled study of stretching and deforming interfaces. The deformations of the drop allow both Marangoni stresses, which resist tangential shear, and Marangoni elasticities, which resist surface dilatation, to develop. This flow presents an ideal model system for studying these effects. Prior surfactant-related work in this flow considered a linear dependence of the surface tension on the surface concentration, valid only at dilute surface concentrations, or a non-linear framework at concentrations sufficiently dilute that the linear approximation was valid. The linear framework becomes inadequate for several reasons. The finite dimensions of surfactant molecules must be taken into account with a model that includes surfaces saturation. Nonideal interactions between adsorbed surfactant molecules alter the partitioning of surfactant between the bulk and the interface, the dynamics of surfactant adsorptive/desorptive exchange, and the sensitivity of the surface tension to adsorbed surfactant. For example, cohesion between hydrocarbon chains favors strong adsorption. Cohesion also slows the rate of desorption from interfaces, and decreases the sensitivity of the surface tension to adsorbed surfactant. Strong cohesive interactions result in first order surface phase changes with a plateau in the surface tension vs surface concentration. Within this surface concentration range, the surface tension is decoupled from surface concentration gradients. We are engaged in the study of the role of surfactant physical chemistry in determining the Marangoni stresses on a drop in an extensional flow in a numerical and experimental program. Using surfactants whose dynamics and equilibrium behavior have been characterized in our laboratory, drop deformation will be studied in ground-based experiment. In an accompanying numerical study, predictive drop deformations will be determined based on the isotherm and equation of state determined in our laboratory. This work will improve our abilities to predict and control all fluid particle flows.

An investigation into the effectiveness of problem-based learning in a physical chemistry laboratory course

NASA Astrophysics Data System (ADS)

Gürses, Ahmet; Açıkyıldız, Metin; Doğar, Çetin; Sözbilir, Mustafa

2007-04-01

The aim of this study was to investigate the effectiveness of a problem-based learning (PBL) approach in a physical chemistry laboratory course. The parameters investigated were students’ attitudes towards a chemistry laboratory course, scientific process skills of students and their academic achievement. The design of the study was one group pre-test post-test. Four experiments, covering the topics adsorption, viscosity, surface tension and conductivity were performed using a PBL approach in the fall semester of the 2003/04 academic year at Kazim Karabekir Education Faculty of Atatürk University. Each experiment was done over a three week period. A total of 40 students, 18 male and 22 female, participated in the study. Students took the Physical Chemistry Laboratory Concept Test (PCLCT), Attitudes towards Chemistry Laboratory (ATCL) questionnaire and Science Process Skills Test (SPST) as pre and post-tests. In addition, the effectiveness of the PBL approach was also determined through four different scales; Scales Specific to Students’ Views of PBL. A statistically significant difference between the students’ academic achievement and scientific process skills at p

Nb3Sn SRF Cavities for Nuclear Physics Applications

NASA Astrophysics Data System (ADS)

Eremeev, Grigory

2017-01-01

Nuclear physics experiments rely increasingly on accelerators, which employ superconducting RF (SRF) technology. CEBAF, SNS, FRIB, ESS, among others exploit the low surface resistance of SRF cavities to efficiently accelerate particle beams towards experimental targets. Niobium is the cavity material of choice for all current or planned SRF accelerators, but it has been long recognized that other superconductors with high superconducting transition temperatures have the potential to surpass niobium for SRF applications. Among the alternatives, Nb3Sn coated cavities are the most advanced on the path to practical applications: Nb3Sn coatings on R&D cavities have Tc consistently close the optimal 18 K, very low RF surface resistances, and very recently were shown to reach above Hc1 without anomalous RF surface resistance increase. In my talk I will discuss the prospects of Nb3Sn SRF cavities, the research efforts to realize Nb3Sn coatings on practical multi-cell accelerating structures, and the path toward possible inclusion in CEBAF. This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics.

Does the climate warming hiatus exist over the Tibetan Plateau?

PubMed

Duan, Anmin; Xiao, Zhixiang

2015-09-02

The surface air temperature change over the Tibetan Plateau is determined based on historical observations from 1980 to 2013. In contrast to the cooling trend in the rest of China, and the global warming hiatus post-1990s, an accelerated warming trend has appeared over the Tibetan Plateau during 1998-2013 (0.25 °C decade(-1)), compared with that during 1980-1997 (0.21 °C decade(-1)). Further results indicate that, to some degree, such an accelerated warming trend might be attributable to cloud-radiation feedback. The increased nocturnal cloud over the northern Tibetan Plateau would warm the nighttime temperature via enhanced atmospheric back-radiation, while the decreased daytime cloud over the southern Tibetan Plateau would induce the daytime sunshine duration to increase, resulting in surface air temperature warming. Meanwhile, the in situ surface wind speed has recovered gradually since 1998, and thus the energy concentration cannot explain the accelerated warming trend over the Tibetan Plateau after the 1990s. It is suggested that cloud-radiation feedback may play an important role in modulating the recent accelerated warming trend over the Tibetan Plateau.

Contributions to Pliocene Arctic warmth from removal of anthropogenic aerosol and enhanced forest fire emissions

NASA Astrophysics Data System (ADS)

Feng, R.; Otto-Bliesner, B. L.; Fletcher, T.; Ballantyne, A.; Brady, E. C.

2016-12-01

Changing atmosphere chemistry in the past has been hypothesized to have altered the earth's radiation budget, and hence the climate. Here, we use an advanced climate model to test whether this hypothesis can help explain the amplified warming in the northern high latitudes during the mid-Pliocene warm period (mPWP, 3.0 - 3.3 Ma). The amplified warming, suggested by terrestrial proxy records of northern high latitudes, is underestimated in previous climate simulations. This mismatch between observations and models may be partially due to proxy uncertainties, but also to insufficient model sensitivity, or incomplete knowledge of mPWP climate forcings. To explore the latter aspect, we conducted three coupled simulations using the same mPWP geography and topography, vegetation and CO2 level according to the PRISM3 reconstructions, but alternating emission scenarios among clean, polluted, and clean plus forest fire case. In the clean and polluted case, year-1850 emission and year-1850 natural plus year-2000 industrial emission are prescribed respectively. For the clean-plus-forest fire simulation, emissions from mPWP forest fire are constrained with a process-based prognostic fire model using fixed proxy SSTs. Preliminary results suggest that mPWP Arctic warmth is largely attributable to the removal of anthropogenic aerosols and enhanced deposition of the black carbon on snow and ice emitted from northern high latitude forest fires. Cloud radiative responses are shown to accelerate the summer sea ice melting from the continental margins, triggering the positive surface albedo and water vapor feedback that maintain a low perennial sea ice state in the Arctic Ocean. These results identify the important role that changes in aerosol chemistry may play in amplifying arctic surface temperatures of mPWP and insights on the role that aerosols may play in amplifying future Arctic temperatures.

Roles of Bulk and Surface Chemistry in the Oxygen Exchange Kinetics and Related Properties of Mixed Conducting Perovskite Oxide Electrodes

PubMed Central

Perry, Nicola H.; Ishihara, Tatsumi

2016-01-01

Mixed conducting perovskite oxides and related structures serving as electrodes for electrochemical oxygen incorporation and evolution in solid oxide fuel and electrolysis cells, respectively, play a significant role in determining the cell efficiency and lifetime. Desired improvements in catalytic activity for rapid surface oxygen exchange, fast bulk transport (electronic and ionic), and thermo-chemo-mechanical stability of oxygen electrodes will require increased understanding of the impact of both bulk and surface chemistry on these properties. This review highlights selected work at the International Institute for Carbon-Neutral Energy Research (I2CNER), Kyushu University, set in the context of work in the broader community, aiming to characterize and understand relationships between bulk and surface composition and oxygen electrode performance. Insights into aspects of bulk point defect chemistry, electronic structure, crystal structure, and cation choice that impact carrier concentrations and mobilities, surface exchange kinetics, and chemical expansion coefficients are emerging. At the same time, an understanding of the relationship between bulk and surface chemistry is being developed that may assist design of electrodes with more robust surface chemistries, e.g., impurity tolerance or limited surface segregation. Ion scattering techniques (e.g., secondary ion mass spectrometry, SIMS, or low energy ion scattering spectroscopy, LEIS) with high surface sensitivity and increasing lateral resolution are proving useful for measuring surface exchange kinetics, diffusivity, and corresponding outer monolayer chemistry of electrodes exposed to typical operating conditions. Beyond consideration of chemical composition, the use of strain and/or a high density of active interfaces also show promise for enhancing performance. PMID:28773978

Enabling Chemistry Technologies and Parallel Synthesis-Accelerators of Drug Discovery Programmes.

PubMed

Vasudevan, A; Bogdan, A R; Koolman, H F; Wang, Y; Djuric, S W

There is a pressing need to improve overall productivity in the pharmaceutical industry. Judicious investments in chemistry technologies can have a significant impact on cycle times, cost of goods and probability of technical success. This perspective describes some of these technologies developed and implemented at AbbVie, and their applications to the synthesis of novel scaffolds and to parallel synthesis. © 2017 Elsevier B.V. All rights reserved.

Spatially controlled immobilisation of biomolecules: A complete approach in green chemistry

NASA Astrophysics Data System (ADS)

Grinenval, Eva; Nonglaton, Guillaume; Vinet, Françoise

2014-01-01

The development of 'green' sensors is a challenging task in the field of biomolecule sensing, for example in the detection of cardiac troponin-I (cTnI). In the present work a complete approach in green chemistry was developed to create chemically active patterns for the immobilisation of biological probes. This key technology is discussed on the basis of the twelve green chemistry principles, and is a combination of surface patterning by spotting and surface chemistries modified by molecular vapour deposition. The (1H,1H,2H,2H)-perfluorodecyltrichlorosilane (FDTS) was used as a novel anti-adsorption layer while the 3,4-epoxybutyltrimethoxysilane (EBTMOS) was used to immobilise probes. Oligonucleotides and the anti-cTnI antibody were studied. The spatially controlled immobilisation of probes was characterised by fluorescence. The demonstrated surface modification has broad applications in areas such as diagnostics and bio-chemical sensing. Moreover, the environmental impacts of surface patterning and surface chemistry were discussed from a 'greenness' point of view.

Hoof accelerations and ground reaction forces of Thoroughbred racehorses measured on dirt, synthetic, and turf track surfaces.

PubMed

Setterbo, Jacob J; Garcia, Tanya C; Campbell, Ian P; Reese, Jennifer L; Morgan, Jessica M; Kim, Sun Y; Hubbard, Mont; Stover, Susan M

2009-10-01

To compare hoof acceleration and ground reaction force (GRF) data among dirt, synthetic, and turf surfaces in Thoroughbred racehorses. 3 healthy Thoroughbred racehorses. Forelimb hoof accelerations and GRFs were measured with an accelerometer and a dynamometric horseshoe during trot and canter on dirt, synthetic, and turf track surfaces at a racecourse. Maxima, minima, temporal components, and a measure of vibration were extracted from the data. Acceleration and GRF variables were compared statistically among surfaces. The synthetic surface often had the lowest peak accelerations, mean vibration, and peak GRFs. Peak acceleration during hoof landing was significantly smaller for the synthetic surface (mean + or - SE, 28.5g + or - 2.9g) than for the turf surface (42.9g + or - 3.8g). Hoof vibrations during hoof landing for the synthetic surface were < 70% of those for the dirt and turf surfaces. Peak GRF for the synthetic surface (11.5 + or - 0.4 N/kg) was 83% and 71% of those for the dirt (13.8 + or - 0.3 N/kg) and turf surfaces (16.1 + or - 0.7 N/kg), respectively. The relatively low hoof accelerations, vibrations, and peak GRFs associated with the synthetic surface evaluated in the present study indicated that synthetic surfaces have potential for injury reduction in Thoroughbred racehorses. However, because of the unique material properties and different nature of individual dirt, synthetic, and turf racetrack surfaces, extending the results of this study to encompass all track surfaces should be done with caution.

Facet-Specific Ligand Interactions on Ternary AgSbS 2 Colloidal Quantum Dots

DOE PAGES

Choi, Hyekyoung; Kim, Sungwoo; Luther, Joseph M.; ...

2017-11-07

Silver dimetal chalcogenide (Ag-V-VI 2) ternary quantum dots (QDs) are emerging lead-free materials for optoelectronic devices due to their NIR band gaps, large absorption coefficients, and superior electronic properties. However, thin film-based devices of the ternary QDs still lag behind due to the lack of understanding of the surface chemistry, compared to that of lead chalcogenide QDs even with the same crystal structure. Here in this paper, the surface ligand interactions of AgSbS 2 QDs, synthesized with 1-dodecanethiol used as a stabilizer, are studied. For nonpolar (1 0 0) surfaces, it is suggested that the thiolate ligands are associated withmore » the crystal lattices, thus preventing surface oxidation by protecting sulfur after air-exposure, as confirmed through optical and surface chemical analysis. Otherwise, silver rich (1 1 1) surfaces are passivated by thiolate ligands, allowing ligand exchange processes for the conductive films. This in-depth investigation of the surface chemistry of ternary QDs will prompt the performance enhancement of their optoelectronic devices.« less

PES Surface Modification Using Green Chemistry: New Generation of Antifouling Membranes.

PubMed

Nady, Norhan

2016-04-18

A major limitation in using membrane-based separation processes is the loss of performance due to membrane fouling. This drawback can be addressed thanks to surface modification treatments. A new and promising surface modification using green chemistry has been recently investigated. This modification is carried out at room temperature and in aqueous medium using green catalyst (enzyme) and nontoxic modifier, which can be safely labelled "green surface modification". This modification can be considered as a nucleus of new generation of antifouling membranes and surfaces. In the current research, ferulic acid modifier and laccase bio-catalyst were used to make poly(ethersulfone) (PES) membrane less vulnerable to protein adsorption. The blank and modified PES membranes are evaluated based on e.g., their flux and protein repellence. Both the blank and the modified PES membranes (or laminated PES on silicon dioxide surface) are characterized using many techniques e.g., SEM, EDX, XPS and SPM, etc. The pure water flux of the most modified membranes was reduced by 10% on average relative to the blank membrane, and around a 94% reduction in protein adsorption was determined. In the conclusions section, a comparison between three modifiers-ferulic acid, and two other previously used modifiers (4-hydroxybenzoic acid and gallic acid)-is presented.

PES Surface Modification Using Green Chemistry: New Generation of Antifouling Membranes

PubMed Central

Nady, Norhan

2016-01-01

A major limitation in using membrane-based separation processes is the loss of performance due to membrane fouling. This drawback can be addressed thanks to surface modification treatments. A new and promising surface modification using green chemistry has been recently investigated. This modification is carried out at room temperature and in aqueous medium using green catalyst (enzyme) and nontoxic modifier, which can be safely labelled “green surface modification”. This modification can be considered as a nucleus of new generation of antifouling membranes and surfaces. In the current research, ferulic acid modifier and laccase bio-catalyst were used to make poly(ethersulfone) (PES) membrane less vulnerable to protein adsorption. The blank and modified PES membranes are evaluated based on e.g., their flux and protein repellence. Both the blank and the modified PES membranes (or laminated PES on silicon dioxide surface) are characterized using many techniques e.g., SEM, EDX, XPS and SPM, etc. The pure water flux of the most modified membranes was reduced by 10% on average relative to the blank membrane, and around a 94% reduction in protein adsorption was determined. In the conclusions section, a comparison between three modifiers—ferulic acid, and two other previously used modifiers (4-hydroxybenzoic acid and gallic acid)—is presented. PMID:27096873

Surface chemistry of Ti6Al4V components fabricated using selective laser melting for biomedical applications.

PubMed

Vaithilingam, Jayasheelan; Prina, Elisabetta; Goodridge, Ruth D; Hague, Richard J M; Edmondson, Steve; Rose, Felicity R A J; Christie, Steven D R

2016-10-01

Selective laser melting (SLM) has previously been shown to be a viable method for fabricating biomedical implants; however, the surface chemistry of SLM fabricated parts is poorly understood. In this study, X-ray photoelectron spectroscopy (XPS) was used to determine the surface chemistries of (a) SLM as-fabricated (SLM-AF) Ti6Al4V and (b) SLM fabricated and mechanically polished (SLM-MP) Ti6Al4V samples and compared with (c) traditionally manufactured (forged) and mechanically polished Ti6Al4V samples. The SLM-AF surface was observed to be porous with an average surface roughness (Ra) of 17.6±3.7μm. The surface chemistry of the SLM-AF was significantly different to the FGD-MP surface with respect to elemental distribution and their existence on the outermost surface. Sintered particles on the SLM-AF surface were observed to affect depth profiling of the sample due to a shadowing effect during argon ion sputtering. Surface heterogeneity was observed for all three surfaces; however, vanadium was witnessed only on the mechanically polished (SLM-MP and FGD-MP) surfaces. The direct and indirect 3T3 cell cytotoxicity studies revealed that the cells were viable on the SLM fabricated Ti6Al4V parts. The varied surface chemistry of the SLM-AF and SLM-MP did not influence the cell behaviour. Copyright © 2016 The Authors. Published by Elsevier B.V. All rights reserved.

Engineered microtopographies and surface chemistries direct cell attachment and function

NASA Astrophysics Data System (ADS)

Magin, Chelsea Marie

Harrison, in 1914, first recognized that cells respond to physicochemical cues such as substratum topography when he observed that fibroblasts elongated while cultured on spider silk. Recently, techniques developed in the micro-electronics industry have been used to create molds for producing microscaled topographies with various shapes and spatial arrangements. Although these patterning techniques are well-established, very little is known about the mechanisms underlying cell sensing and response to microtopographies. In this work cellular micro-environments with varying surface topographies and chemistries were evaluated with marine organisms and mammalian cells to investigate cellular sensing and response. Biofouling---the accumulation of micro-organisms, plants, and animals on submerged surfaces---is an environmental and economic concern. Engineered topographies, replicated in polydimethylsiloxane elastomer (PDMSe) and functionalized poly(ethylene glycol)-dimethacrylate (PEGDMA) hydrogels, were evaluated for inhibition of marine fouling organism attachment. Microtopographies replicated in PDMSe inhibited attachment of the marine bacterium, Cobetia marina up to 99% versus smooth. The average normalized attachment densities of cells of C. marina and zoospores of the green algae Ulva on PDMSe topographies scaled inversely with the Engineered Roughness Index (ERIII), a representation of surface energy. Attachment densities of Ulva from four assays and C. marina from two growth phases to PDMSe surfaces scaled inversely with one equation: ERI II multiplied by the Reynolds number of the organism (Re) (R 2 = 0.77). The same microtopographies created in PDMSe reduced the initial attachment density and attachment strength of cells of the diatoms Navicula incerta and Seminavis robusta compared to smooth PDMSe. The average normalized attachment density of Navicula after exposure to shear stress (48 Pa) was correlated with the contact area between the diatom and a topographically modified surface (R2=0.82). Functionalized PEGDMA hydrogels significantly reduced attachment and attachment strength of Navicula and C. marina. These hydrogels also reduced attachment of zoospores of Ulva compared to PDMSe. Attachment of Ulva to microtopographies in PDMSe and PEGDMA-co-HEMA negatively correlated with ERIII*Re (R2 = 0.94 and R2 = 0.99, respectively). Incorporating a surface energy term into this equation created a correlation between the attachment densities of cells from two evolutionarily diverse groups on substrates of two surface chemistries with an equation that describes the various microtopographies and surface chemistries in terms of surface energy (R2 = 0.80). The current Attachment Model can now be used to design engineered antifouling surface microtopographies and chemistries that inhibit the attachment of organisms from three evoluntionarily diverse groups. Hydrogels based on PEGDMA were also chosen as a substratum material for mammalian cell culture. Capturing endothelial progenitor cells (EPCs) and inducing differentiation into the endothelial cell (EC) phenotype is the ideal way to re-endothelialize a small-diameter vascular graft. Substratum elasticity has been reported to direct stem cell differentiation into specific lineages. Functionalized PEGDMA hydrogels provided good compliance, high fidelity of topographic features and sites for surface modification with biomolecules. Fibronectin grafting and topography both increased EC attachment. This combination of adjustable elasticity, surface chemistry and topography has the potential to promote the capture and differentiation of EPCs into a confluent EC monolayer. Engineered microtopographies replicated in PDMSe directed elongation and alignment of human coronary artery endothelial cells (HCAECs) and human coronary artery smooth muscle cells (HCASMCs) compared to smooth surfaces. Engineered cellular micro-environments were created with specific surface energies defined by chemistry and topography to successfully direct cell attachment and function.

Reactions in Droplets in Microfluidic Channels

PubMed Central

Song, Helen; Chen, Delai L.; Ismagilov, Rustem F.

2006-01-01

Fundamental and applied research in chemistry and biology benefits from opportunities provided by droplet-based microfluidic systems. These systems enable the miniaturization of reactions by compartmentalizing reactions in droplets of femoliter to microliter volumes. Compartmentalization in droplets provides rapid mixing of reagents, control of the timing of reactions on timescales from milliseconds to months, control of interfacial properties, and the ability to synthesize and transport solid reagents and products. Droplet-based microfluidics can help to enhance and accelerate chemical and biochemical screening, protein crystallization, enzymatic kinetics, and assays. Moreover, the control provided by droplets in microfluidic devices can lead to new scientific methods and insights. PMID:17086584

Tunnel flexibility effect on the ground surface acceleration response

NASA Astrophysics Data System (ADS)

Baziar, Mohammad Hassan; Moghadam, Masoud Rabeti; Choo, Yun Wook; Kim, Dong-Soo

2016-09-01

Flexibility of underground structures relative to the surrounding medium, referred to as the flexibility ratio, is an important factor that influences their dynamic interaction. This study investigates the flexibility effect of a box-shaped subway tunnel, resting directly on bedrock, on the ground surface acceleration response using a numerical model verified against dynamic centrifuge test results. A comparison of the ground surface acceleration response for tunnel models with different flexibility ratios revealed that the tunnels with different flexibility ratios influence the acceleration response at the ground surface in different ways. Tunnels with lower flexibility ratios have higher acceleration responses at short periods, whereas tunnels with higher flexibility ratios have higher acceleration responses at longer periods. The effect of the flexibility ratio on ground surface acceleration is more prominent in the high range of frequencies. Furthermore, as the flexibility ratio of the tunnel system increases, the acceleration response moves away from the free field response and shifts towards the longer periods. Therefore, the flexibility ratio of the underground tunnels influences the peak ground acceleration (PGA) at the ground surface, and may need to be considered in the seismic zonation of urban areas.

Sol-gel chemistry-based Ucon-coated columns for capillary electrophoresis.

PubMed

Hayes, J D; Malik, A

1997-07-18

A sol-gel chemistry-based novel approach for the preparation of a Ucon-coated fused-silica capillary column in capillary electrophoresis is presented. In this approach the sol-gel process is carried out inside 25 microm I.D. fused-silica capillaries. The sol solution contained appropriate quantities of an alkoxide-based sol-gel precursor, a polymeric coating material (Ucon), a crosslinking reagent, a surface derivatizing reagent, controlled amounts of water and a catalyst dissolved in a suitable solvent system. The coating procedure involves filling a capillary with the sol solution and allowing the sol-gel process to proceed for an optimum period. Hydrolysis of the alkoxide precursor and polycondensation of the hydrolyzed products with the surface silanol groups and the hydroxy-terminated Ucon molecules lead to the formation of a surface-bonded sol-gel coating on the inner walls of the capillary. The thickness of the coated film can be controlled by varying the reaction time, coating solution composition and experimental conditions. Commercial availability of high purity sol-gel precursors (e.g., TEOS 99.999%), the ease of coating, run-to-run and column-to-column reproducibility, and long column lifetimes make sol-gel coating chemistry very much suitable for being applied in analytical microseparations column technology. Test samples of basic proteins and nucleotides were used to evaluate the column performance. These results show that the sol-gel coating scheme has allowed for the generation of bio-compatible surfaces characterized by high separation efficiencies in CE. For different types of solutes, the sol-gel coated Ucon column consistently provided migration time R.S.D. values of the order of 0.5%.

Curvature Forces in Membrane Lipid-Protein Interactions

PubMed Central

Brown, Michael F.

2012-01-01

Membrane biochemists are becoming increasingly aware of the role of lipid-protein interactions in diverse cellular functions. This review describes how conformational changes of membrane proteins—involving folding, stability, and membrane shape transitions—potentially involve elastic remodeling of the lipid bilayer. Evidence suggests that membrane lipids affect proteins through interactions of a relatively long-range nature, extending beyond a single annulus of next-neighbor boundary lipids. It is assumed the distance scale of the forces is large compared to the molecular range of action. Application of the theory of elasticity to flexible soft surfaces derives from classical physics, and explains the polymorphism of both detergents and membrane phospholipids. A flexible surface model (FSM) describes the balance of curvature and hydrophobic forces in lipid-protein interactions. Chemically nonspecific properties of the lipid bilayer modulate the conformational energetics of membrane proteins. The new biomembrane model challenges the standard model (the fluid mosaic model) found in biochemistry texts. The idea of a curvature force field based on data first introduced for rhodopsin gives a bridge between theory and experiment. Influences of bilayer thickness, nonlamellar-forming lipids, detergents, and osmotic stress are all explained by the FSM. An increased awareness of curvature forces suggests that research will accelerate as structural biology becomes more closely entwined with the physical chemistry of lipids in explaining membrane structure and function. PMID:23163284

Microbial synthesis of core/shell gold/palladium nanoparticles for applications in green chemistry

PubMed Central

Deplanche, Kevin; Merroun, Mohamed L.; Casadesus, Merixtell; Tran, Dung T.; Mikheenko, Iryna P.; Bennett, James A.; Zhu, Ju; Jones, Ian P.; Attard, Gary A.; Wood, J.; Selenska-Pobell, Sonja; Macaskie, Lynne E.

2012-01-01

We report a novel biochemical method based on the sacrificial hydrogen strategy to synthesize bimetallic gold (Au)–palladium (Pd) nanoparticles (NPs) with a core/shell configuration. The ability of Escherichia coli cells supplied with H2 as electron donor to rapidly precipitate Pd(II) ions from solution is used to promote the reduction of soluble Au(III). Pre-coating cells with Pd(0) (bioPd) dramatically accelerated Au(III) reduction, with the Au(III) reduction rate being dependent upon the initial Pd loading by mass on the cells. Following Au(III) addition, the bioPd–Au(III) mixture rapidly turned purple, indicating the formation of colloidal gold. Mapping of bio-NPs by energy dispersive X-ray microanalysis suggested Au-dense core regions and peripheral Pd but only Au was detected by X-ray diffraction (XRD) analysis. However, surface analysis of cleaned NPs by cyclic voltammetry revealed large Pd surface sites, suggesting, since XRD shows no crystalline Pd component, that layers of Pd atoms surround Au NPs. Characterization of the bimetallic particles using X-ray absorption spectroscopy confirmed the existence of Au-rich core and Pd-rich shell type bimetallic biogenic NPs. These showed comparable catalytic activity to chemical counterparts with respect to the oxidation of benzyl alcohol, in air, and at a low temperature (90°C). PMID:22399790

Bactericidal effects of plasma-modified surface chemistry of silicon nanograss

NASA Astrophysics Data System (ADS)

Ostrikov, Kola; Macgregor-Ramiasa, Melanie; Cavallaro, Alex; (Ken Ostrikov, Kostya; Vasilev, Krasimir

2016-08-01

The surface chemistry and topography of biomaterials regulate the adhesion and growth of microorganisms in ways that are still poorly understood. Silicon nanograss structures prepared via inductively coupled plasma etching were coated with plasma deposited nanometer-thin polymeric films to produce substrates with controlled topography and defined surface chemistry. The influence of surface properties on Staphylococcus aureus proliferation is demonstrated and explained in terms of nanograss substrate wetting behaviour. With the combination of the nanograss topography; hydrophilic plasma polymer coatings enhanced antimicrobial activity while hydrophobic coatings reduced it. This study advances the understanding of the effects of surface wettability on the bactericidal properties of reactive nano-engineered surfaces.

Method of protecting the surface of a substrate. [by applying aluminide coating

NASA Technical Reports Server (NTRS)

Gedwill, M. A. (Inventor); Grisaffe, S. J.

1974-01-01

The surface of a metallic base system is initially coated with a metallic alloy layer that is ductile and oxidation resistant. An aluminide coating is then applied to the metallic alloy layer. The chemistry of the metallic alloy layer is such that the oxidation resistance of the subsequently aluminized outermost layer is not seriously degraded.

MURI Center for Materials Chemistry in the Space Environment

DTIC Science & Technology

2006-11-30

ionic species in relevant reaction environments, surface photochemistry expertise, synchrotron-based measurement and irradiation, synthesis of structural...and Ne+ ions with dodecanethiolate and semifluorinated dodecanethiolate self-assembled monolayers (SAM), polyhedral oligomeric silsesquioxane (POSS...POSS/Kapton models as gas phase species, and with alkane thiol self assembled monolayers on gold surfaces, and with liquid squalane. We have also

THE INTEGRATED USE OF COMPUTATIONAL CHEMISTRY, SCANNING PROBE MICROSCOPY, AND VIRTUAL REALITY TO PREDICT THE CHEMICAL REACTIVITY OF ENVIRONMENTAL SURFACES

EPA Science Inventory

In the last decade three new techniques scanning probe microscopy (SPM), virtual reality (YR) and computational chemistry ave emerged with the combined capability of a priori predicting the chemically reactivity of environmental surfaces. Computational chemistry provides the cap...

A Self Consistent RF Discharge, Plasma Chemistry and Surface Model for Plasma Enhanced Chemical Vapor Deposition

DTIC Science & Technology

1988-06-30

consists of three submodels for the electron kinetics, plasma chemistry , and surface deposition kinetics for a-Si:H deposited from radio frequency...properties. Plasma enhanced, Chemical vapor deposition, amorphous silicon, Modeling, Electron kinetics, Plasma chemistry , Deposition kinetics, Rf discharge, Silane, Film properties, Silicon.

Acetone Chemistry on Oxidized and Reduced TiO 2(110)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Henderson, Michael A

2004-12-09

The chemistry of acetone on the oxidized and reduced surfaces of TiO 2(110) was examined using temperature programmed desorption (TPD) and high resolution electron energy loss spectroscopy (HREELS). The reduced surface was prepared with about 7% oxygen vacancy sites by annealing in ultrahigh vacuum (UHV) at 850 K, and the oxidized surface was prepared by exposure of the reduced surface to molecular oxygen at 95 K followed by heating the surface to a variety of temperatures between 200 and 500 K. Acetone adsorbs molecularly on the reduced surface with no evidence for either decomposition or preferential binding at vacancy sites.more » Based on HREELS, the majority of acetone molecules adsorbed in an η¹ configuration at Ti⁴⁺ sites through interaction of lone pair electrons on the carbonyl oxygen atom. Repulsive acetone-acetone interactions shift the desorption peak from 345 K at low coverage to 175 K as the first layer saturates with a coverage of ~ 1 ML. In contrast, about 7% of the acetone adlayer decomposes when the surface is pretreated with molecular oxygen. Acetate is among the detected decomposition products, but only comprises about 1/3rd of the amount of acetone decomposed and its yield depends on the temperature at which the O₂ exposed surface was preheated to prior to acetone adsorption. Aside from the small level of irreversible decomposition, about 0.25 ML of acetone is stabilized to 375 K by coadsorbed oxygen. These acetone species exhibit an HREELS spectrum unlike that of η¹-acetone or of any other species proposed to exist from the interaction of acetone with TiO₂ powders. Based on the presence of extensive ¹⁶O/¹⁸O exchange between acetone and coadsorbed oxygen in the 375 K acetone TPD state, it is proposed that a polymeric form of acetone forms on the TiO₂(110) surface through nucleophilic attack of oxygen on the carbonyl carbon atom of acetone, and is propagated to neighboring η¹-acetone molecules. This process is initiated at temperatures as low as 135 K based on HREELS. Although the dominant thermal pathway of this surface species is to liberate acetone in UHV, it may be a key intermediate in acetone thermal and photolytic chemistry on TiO₂ surfaces.« less

Nanoporous membranes with electrochemically switchable, chemically stabilized ionic selectivity

NASA Astrophysics Data System (ADS)

Small, Leo J.; Wheeler, David R.; Spoerke, Erik D.

2015-10-01

Nanopore size, shape, and surface charge all play important roles in regulating ionic transport through nanoporous membranes. The ability to control these parameters in situ provides a means to create ion transport systems tunable in real time. Here, we present a new strategy to address this challenge, utilizing three unique electrochemically switchable chemistries to manipulate the terminal functional group and control the resulting surface charge throughout ensembles of gold plated nanopores in ion-tracked polycarbonate membranes 3 cm2 in area. We demonstrate the diazonium mediated surface functionalization with (1) nitrophenyl chemistry, (2) quinone chemistry, and (3) previously unreported trimethyl lock chemistry. Unlike other works, these chemistries are chemically stabilized, eliminating the need for a continuously applied gate voltage to maintain a given state and retain ionic selectivity. The effect of surface functionalization and nanopore geometry on selective ion transport through these functionalized membranes is characterized in aqueous solutions of sodium chloride at pH = 5.7. The nitrophenyl surface allows for ionic selectivity to be irreversibly switched in situ from cation-selective to anion-selective upon reduction to an aminophenyl surface. The quinone-terminated surface enables reversible changes between no ionic selectivity and a slight cationic selectivity. Alternatively, the trimethyl lock allows ionic selectivity to be reversibly switched by up to a factor of 8, approaching ideal selectivity, as a carboxylic acid group is electrochemically revealed or hidden. By varying the pore shape from cylindrical to conical, it is demonstrated that a controllable directionality can be imparted to the ionic selectivity. Combining control of nanopore geometry with stable, switchable chemistries facilitates superior control of molecular transport across the membrane, enabling tunable ion transport systems.Nanopore size, shape, and surface charge all play important roles in regulating ionic transport through nanoporous membranes. The ability to control these parameters in situ provides a means to create ion transport systems tunable in real time. Here, we present a new strategy to address this challenge, utilizing three unique electrochemically switchable chemistries to manipulate the terminal functional group and control the resulting surface charge throughout ensembles of gold plated nanopores in ion-tracked polycarbonate membranes 3 cm2 in area. We demonstrate the diazonium mediated surface functionalization with (1) nitrophenyl chemistry, (2) quinone chemistry, and (3) previously unreported trimethyl lock chemistry. Unlike other works, these chemistries are chemically stabilized, eliminating the need for a continuously applied gate voltage to maintain a given state and retain ionic selectivity. The effect of surface functionalization and nanopore geometry on selective ion transport through these functionalized membranes is characterized in aqueous solutions of sodium chloride at pH = 5.7. The nitrophenyl surface allows for ionic selectivity to be irreversibly switched in situ from cation-selective to anion-selective upon reduction to an aminophenyl surface. The quinone-terminated surface enables reversible changes between no ionic selectivity and a slight cationic selectivity. Alternatively, the trimethyl lock allows ionic selectivity to be reversibly switched by up to a factor of 8, approaching ideal selectivity, as a carboxylic acid group is electrochemically revealed or hidden. By varying the pore shape from cylindrical to conical, it is demonstrated that a controllable directionality can be imparted to the ionic selectivity. Combining control of nanopore geometry with stable, switchable chemistries facilitates superior control of molecular transport across the membrane, enabling tunable ion transport systems. Electronic supplementary information (ESI) available: Experimental procedures, synthesis, and characterization of molecules 1, 2 and 3. Explanation of the electrochemical method for approximating nanopore diameter. Additional XPS spectra. See DOI: 10.1039/C5NR02939B

Implementing Computer Based Laboratories

NASA Astrophysics Data System (ADS)

Peterson, David

2001-11-01

Physics students at Francis Marion University will complete several required laboratory exercises utilizing computer-based Vernier probes. The simple pendulum, the acceleration due to gravity, simple harmonic motion, radioactive half lives, and radiation inverse square law experiments will be incorporated into calculus-based and algebra-based physics courses. Assessment of student learning and faculty satisfaction will be carried out by surveys and test results. Cost effectiveness and time effectiveness assessments will be presented. Majors in Computational Physics, Health Physics, Engineering, Chemistry, Mathematics and Biology take these courses, and assessments will be categorized by major. To enhance the computer skills of students enrolled in the courses, MAPLE will be used for further analysis of the data acquired during the experiments. Assessment of these enhancement exercises will also be presented.

An experimental study on low-velocity low-gravity collisions into granular surfaces

NASA Astrophysics Data System (ADS)

Sunday, C.; Murdoch, N.; Mimoun, D.

2014-07-01

The Japanese Space Agency (JAXA) is scheduled to launch the asteroid sample-return mission, Hayabusa-2, to target body 1999 JU_3 in December 2014 [1]. The spacecraft will arrive at the C-type near-Earth asteroid in mid-2018 and deploy several science payloads to its surface. Among these payloads is a 10-kg lander, the Mobile Asteroid Surface Scout (MASCOT), provided by the German Space Agency (DLR) with cooperation from the Centre National d'Etudes Spatiales (CNES). MASCOT will reach the asteroid's surface with an anticipated impact speed of 10--20 cm/s. In addition to housing four instruments for in-situ science investigation, MASCOT contains a mobility mechanism that will correct its orientation and enable it to ''hop'' to various measurement sites [2]. Based on thermal infrared observations [3,4,5] and previous space missions [6,7], it is strongly believed that 1999 JU_3 is covered by loose regolith. The asteroid's granular surface, in combination with the low surface gravity, makes it difficult to predict the lander's collision behavior from existing theoretical models. However, to ensure that MASCOT can successfully fulfill its mission, it is vital to understand the rebound dynamics of the lander in the asteroid surface environment. The objective of this work, derived from the needs of current and future asteroid missions, is to present an experiment designed to study low-velocity, low-gravity collisions into granular surfaces. The experiment measures the amount of energy lost during impact via a projectile's coefficient of restitution and also the acceleration profile of the projectile during collision. The key challenge to designing an asteroid collision experiment is finding a way to simulate reduced gravity conditions on the Earth so that the prevailing forces in micro-gravity collisions can be reflected in the experimental results. The proposed way to achieve this goal is to let a free-falling projectile impact a surface with a constant downward acceleration, or an acceleration less than that of gravity, so that the effective surface acceleration felt by the grains at impact is very small. In reducing the effective surface acceleration of the granular material, the medium's inter-grain cohesion forces will become more important compared to its weight force [8], and the properties of the granular material will become more representative of those on an asteroid's surface. The concept of effective acceleration drives the design of this experiment and results in the following key features: First, the granular surface is given a constant downward acceleration using an Atwood machine, or a system of pulleys and counterweights. Next, the projectile and surface are simultaneously released from rest using a magnetic solenoid and hook assembly. The starting height of the surface container and the initial separation distance between the projectile and surface are variable and chosen to accommodate collision velocities of 10--20 cm/s and effective accelerations of 0.3--1.0 m/s^2. Finally, wireless accelerometers, placed on the surface container and in the projectile, provide acceleration data, while high-speed cameras capable of recording 100,000 frames per second capture the collision and act as secondary data sources. The experiment is built into an existing 6-m drop-tower frame and requires the custom design of all components, including the projectile, surface sample container, release mechanism, and deceleration system. This work will present the detailed design of the asteroid-collision experiment as well as a discussion on the planned experimental trials. The experimental results, once obtained, will be used to create a scaling law that will help predict a projectile's rebound and acceleration behavior during a low-velocity collision into a granular surface in micro-gravity conditions.

Biological soil crusts accelerate the nitrogen cycle through large NO and HONO emissions in drylands.

PubMed

Weber, Bettina; Wu, Dianming; Tamm, Alexandra; Ruckteschler, Nina; Rodríguez-Caballero, Emilio; Steinkamp, Jörg; Meusel, Hannah; Elbert, Wolfgang; Behrendt, Thomas; Sörgel, Matthias; Cheng, Yafang; Crutzen, Paul J; Su, Hang; Pöschl, Ulrich

2015-12-15

Reactive nitrogen species have a strong influence on atmospheric chemistry and climate, tightly coupling the Earth's nitrogen cycle with microbial activity in the biosphere. Their sources, however, are not well constrained, especially in dryland regions accounting for a major fraction of the global land surface. Here, we show that biological soil crusts (biocrusts) are emitters of nitric oxide (NO) and nitrous acid (HONO). Largest fluxes are obtained by dark cyanobacteria-dominated biocrusts, being ∼20 times higher than those of neighboring uncrusted soils. Based on laboratory, field, and satellite measurement data, we obtain a best estimate of ∼1.7 Tg per year for the global emission of reactive nitrogen from biocrusts (1.1 Tg a(-1) of NO-N and 0.6 Tg a(-1) of HONO-N), corresponding to ∼20% of global nitrogen oxide emissions from soils under natural vegetation. On continental scales, emissions are highest in Africa and South America and lowest in Europe. Our results suggest that dryland emissions of reactive nitrogen are largely driven by biocrusts rather than the underlying soil. They help to explain enigmatic discrepancies between measurement and modeling approaches of global reactive nitrogen emissions. As the emissions of biocrusts strongly depend on precipitation events, climate change affecting the distribution and frequency of precipitation may have a strong impact on terrestrial emissions of reactive nitrogen and related climate feedback effects. Because biocrusts also account for a large fraction of global terrestrial biological nitrogen fixation, their impacts should be further quantified and included in regional and global models of air chemistry, biogeochemistry, and climate.

Biological soil crusts accelerate the nitrogen cycle through large NO and HONO emissions in drylands

PubMed Central

Wu, Dianming; Tamm, Alexandra; Ruckteschler, Nina; Rodríguez-Caballero, Emilio; Meusel, Hannah; Elbert, Wolfgang; Behrendt, Thomas; Sörgel, Matthias; Cheng, Yafang; Crutzen, Paul J.; Su, Hang; Pöschl, Ulrich

2015-01-01

Reactive nitrogen species have a strong influence on atmospheric chemistry and climate, tightly coupling the Earth’s nitrogen cycle with microbial activity in the biosphere. Their sources, however, are not well constrained, especially in dryland regions accounting for a major fraction of the global land surface. Here, we show that biological soil crusts (biocrusts) are emitters of nitric oxide (NO) and nitrous acid (HONO). Largest fluxes are obtained by dark cyanobacteria-dominated biocrusts, being ∼20 times higher than those of neighboring uncrusted soils. Based on laboratory, field, and satellite measurement data, we obtain a best estimate of ∼1.7 Tg per year for the global emission of reactive nitrogen from biocrusts (1.1 Tg a−1 of NO-N and 0.6 Tg a−1 of HONO-N), corresponding to ∼20% of global nitrogen oxide emissions from soils under natural vegetation. On continental scales, emissions are highest in Africa and South America and lowest in Europe. Our results suggest that dryland emissions of reactive nitrogen are largely driven by biocrusts rather than the underlying soil. They help to explain enigmatic discrepancies between measurement and modeling approaches of global reactive nitrogen emissions. As the emissions of biocrusts strongly depend on precipitation events, climate change affecting the distribution and frequency of precipitation may have a strong impact on terrestrial emissions of reactive nitrogen and related climate feedback effects. Because biocrusts also account for a large fraction of global terrestrial biological nitrogen fixation, their impacts should be further quantified and included in regional and global models of air chemistry, biogeochemistry, and climate. PMID:26621714

Chemical changes in DMP1-null murine bone & silica based pecvd coatings for titanium implant osseoapplications

NASA Astrophysics Data System (ADS)

Maginot, Megen

In order to improve clinical outcomes in bone-implant systems, a thorough understanding of both local bone chemistry and implant surface chemistry is necessary. This study consists, therefore, of two main parts: one focused on determining the nature of the changes in bone chemistry in a DMP1-null transgenic disease model and the other on the development of amorphous silica-based coatings for potential use as titanium bone implant coatings. For the study of bone mineral in the DMP1 transgenic model, which is known to have low serum phosphate levels, transgenic DMP1-null and wild type mice were fed a high phosphate diet, sacrificed, and had their long bone harvested. This bone was characterized using SEM, FTIR, microCT and XANES and compared to DMP1-null and wild type control groups to assess the therapeutic effect of high Pi levels on the phenotype and the role of DMP1 in mineralization in vivo. Findings suggest that though the high phosphate diet results in restoring serum phosphate levels, it does not completely rescue the bone mineral phenotype at an ultrastructural level and implicates DMP1 in phosphate nucleation. Since plasma enhanced chemical vapor deposition (PECVD) silica like coatings have not previously been fabricated for use in oessoapplications, the second part of this study initially focused on the characterization of novel SiOx chemistries fabricated via a chemical vapor deposition process that were designed specifically to act as bioactive coatings with a loose, hydrogenated structure. These coatings were then investigated for their potential initial stage response to bone tissue through immersion in a simulated body fluid and through the culture of MC3T3 cells on the coating surfaces. Coating surfaces were characterized by SEM, FTIR, contact angle measurements, and XANES. Coating dissolution and ionic release were also investigated by ICP-OES. Findings suggest that some SiOx chemistries may form a bioactive coating while more highly substituted chemistries may form a bioresorbable coating, similar to commercially available bioactive glasses.

GPU-accelerated atmospheric chemical kinetics in the ECHAM/MESSy (EMAC) Earth system model (version 2.52)

NASA Astrophysics Data System (ADS)

Alvanos, Michail; Christoudias, Theodoros

2017-10-01

This paper presents an application of GPU accelerators in Earth system modeling. We focus on atmospheric chemical kinetics, one of the most computationally intensive tasks in climate-chemistry model simulations. We developed a software package that automatically generates CUDA kernels to numerically integrate atmospheric chemical kinetics in the global climate model ECHAM/MESSy Atmospheric Chemistry (EMAC), used to study climate change and air quality scenarios. A source-to-source compiler outputs a CUDA-compatible kernel by parsing the FORTRAN code generated by the Kinetic PreProcessor (KPP) general analysis tool. All Rosenbrock methods that are available in the KPP numerical library are supported.Performance evaluation, using Fermi and Pascal CUDA-enabled GPU accelerators, shows achieved speed-ups of 4. 5 × and 20. 4 × , respectively, of the kernel execution time. A node-to-node real-world production performance comparison shows a 1. 75 × speed-up over the non-accelerated application using the KPP three-stage Rosenbrock solver. We provide a detailed description of the code optimizations used to improve the performance including memory optimizations, control code simplification, and reduction of idle time. The accuracy and correctness of the accelerated implementation are evaluated by comparing to the CPU-only code of the application. The median relative difference is found to be less than 0.000000001 % when comparing the output of the accelerated kernel the CPU-only code.The approach followed, including the computational workload division, and the developed GPU solver code can potentially be used as the basis for hardware acceleration of numerous geoscientific models that rely on KPP for atmospheric chemical kinetics applications.

Earth system modelling on system-level heterogeneous architectures: EMAC (version 2.42) on the Dynamical Exascale Entry Platform (DEEP)

NASA Astrophysics Data System (ADS)

Christou, Michalis; Christoudias, Theodoros; Morillo, Julián; Alvarez, Damian; Merx, Hendrik

2016-09-01

We examine an alternative approach to heterogeneous cluster-computing in the many-core era for Earth system models, using the European Centre for Medium-Range Weather Forecasts Hamburg (ECHAM)/Modular Earth Submodel System (MESSy) Atmospheric Chemistry (EMAC) model as a pilot application on the Dynamical Exascale Entry Platform (DEEP). A set of autonomous coprocessors interconnected together, called Booster, complements a conventional HPC Cluster and increases its computing performance, offering extra flexibility to expose multiple levels of parallelism and achieve better scalability. The EMAC model atmospheric chemistry code (Module Efficiently Calculating the Chemistry of the Atmosphere (MECCA)) was taskified with an offload mechanism implemented using OmpSs directives. The model was ported to the MareNostrum 3 supercomputer to allow testing with Intel Xeon Phi accelerators on a production-size machine. The changes proposed in this paper are expected to contribute to the eventual adoption of Cluster-Booster division and Many Integrated Core (MIC) accelerated architectures in presently available implementations of Earth system models, towards exploiting the potential of a fully Exascale-capable platform.

A new and compact system at the AMS laboratory in Bucharest

NASA Astrophysics Data System (ADS)

Stan-Sion, C.; Enachescu, M.; Petre, A. R.; Simion, C. A.; Calinescu, C. I.; Ghita, D. G.

2015-10-01

AMS research started more than 15 years ago at our National Institute for Physics and Nuclear Engineering (IFIN-HH), Bucharest. A first facility was constructed based on our multipurpose 9 MV tandem accelerator and was upgraded several times. In May 2012 a new Cockcroft Walton type 1 MV HVEE tandetron AMS system, was commissioned. Two chemistry laboratories were constructed and are routinely performing the target preparation for carbon dating and for other isotope applications such as for geology, environment physics, medicine and forensic physics. Performance parameters of the new system are shown.

2013 Chemical reactions at surfaces. Surfaces in Energy and the Environment. Gordon Research Conference and Gordon Research Seminar (April 28 - May 3, 2013 - Les Diablerets, Switzerland)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stair, Peter C.

presentations on chemistry at solid and liquid surfaces of relevance to catalysis, synthesis, photochemistry, environmental science, and tribology. Topics include: Fundamental Surface Chemistry; Catalysis; Solid Liquid and Aerosol Interfaces; Surface Photochemistry; Synthesis of Surfaces; Environmental Interfaces; Hot Topics in Surface Chemical Reactions; Tribology; Gas-Surface Scattering and Reactions; Novel Materials and Environments.

Tyre-road friction coefficient estimation based on tyre sensors and lateral tyre deflection: modelling, simulations and experiments

NASA Astrophysics Data System (ADS)

Hong, Sanghyun; Erdogan, Gurkan; Hedrick, Karl; Borrelli, Francesco

2013-05-01

The estimation of the tyre-road friction coefficient is fundamental for vehicle control systems. Tyre sensors enable the friction coefficient estimation based on signals extracted directly from tyres. This paper presents a tyre-road friction coefficient estimation algorithm based on tyre lateral deflection obtained from lateral acceleration. The lateral acceleration is measured by wireless three-dimensional accelerometers embedded inside the tyres. The proposed algorithm first determines the contact patch using a radial acceleration profile. Then, the portion of the lateral acceleration profile, only inside the tyre-road contact patch, is used to estimate the friction coefficient through a tyre brush model and a simple tyre model. The proposed strategy accounts for orientation-variation of accelerometer body frame during tyre rotation. The effectiveness and performance of the algorithm are demonstrated through finite element model simulations and experimental tests with small tyre slip angles on different road surface conditions.

The effects of atmospheric chemistry on radiation budget in the Community Earth Systems Model

NASA Astrophysics Data System (ADS)

Choi, Y.; Czader, B.; Diao, L.; Rodriguez, J.; Jeong, G.

2013-12-01

The Community Earth Systems Model (CESM)-Whole Atmosphere Community Climate Model (WACCM) simulations were performed to study the impact of atmospheric chemistry on the radiation budget over the surface within a weather prediction time scale. The secondary goal is to get a simplified and optimized chemistry module for the short time period. Three different chemistry modules were utilized to represent tropospheric and stratospheric chemistry, which differ in how their reactions and species are represented: (1) simplified tropospheric and stratospheric chemistry (approximately 30 species), (2) simplified tropospheric chemistry and comprehensive stratospheric chemistry from the Model of Ozone and Related Chemical Tracers, version 3 (MOZART-3, approximately 60 species), and (3) comprehensive tropospheric and stratospheric chemistry (MOZART-4, approximately 120 species). Our results indicate the different details in chemistry treatment from these model components affect the surface temperature and impact the radiation budget.

Surface Chemistry in Heterogeneous Catalysis: An Emerging Discipline.

ERIC Educational Resources Information Center

White, J. M.; Campbell, Charles T.

1980-01-01

Provides background data on surface chemistry as an emerging discipline. Highlights the important role which surfaces play in catalysis by focusing on the catalyzed oxidation of carbon monoxide. Provides a demonstration of how surfaces exert their influences in heterogeneous phenomena and illustrates how experimental problems in this field are…

Effect of chitosan and cationic starch on the surface chemistry properties of bagasse paper.

PubMed

Ashori, Alireza; Cordeiro, Nereida; Faria, Marisa; Hamzeh, Yahya

2013-07-01

The use of non-wood fibers in the paper industry has been an economical and environmental necessity. The application of dry-strength agents has been a successful method to enhance the strength properties of paper. The experimental results evidencing the potential of chitosan and cationic starch utilization in bagasse paper subjected to hot water pre-extraction has been presented in this paper. The research analyzes the surface properties alterations due to these dry-strength agents. Inverse gas chromatography was used to evaluate the properties of surface chemistry of the papers namely the surface energy, active sites, surface area as well as the acidic/basic character. The results of the study revealed that the handsheets process causes surface arrangement and orientation of chemical groups, which induce a more hydrophobic and basic surface. The acid-base surface characteristics after the addition of dry-strength agents were the same as the bagasse handsheets with and without hot water pre-extraction. The results showed that the dry-strength agent acts as a protecting film or glaze on the surfaces of bagasse paper handsheets. Copyright © 2013 Elsevier B.V. All rights reserved.

Cleaning and passivation of copper surfaces to remove surface radioactivity and prevent oxide formation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hoppe, Eric W.; Seifert, Allen; Aalseth, Craig E.

High-purity copper is an attractive material for constructing ultra-low-background radiation measurement devices. Many low-background experiments using high-purity copper have indicated surface contamination emerges as the dominant background. Radon daughters plate out on exposed surfaces, leaving a residual 210Pb background that is difficult to avoid. Dust is also a problem; even under cleanroom conditions, the amount of U and Th deposited on surfaces can represent the largest remaining background. To control these backgrounds, a copper cleaning chemistry has been developed. Designed to replace an effective, but overly aggressive concentrated nitric acid etch, this peroxide-based solution allows for a more controlled cleaningmore » of surfaces. The acidified hydrogen peroxide solution will generally target the Cu+/Cu2+ species which are the predominant surface participants, leaving the bulk of copper metal intact. This preserves the critical tolerances of parts and eliminates significant waste disposal issues. Accompanying passivation chemistry has also been developed that protects copper surfaces from oxidation. Using a high-activity polonium surface spike, the most difficult-to-remove daughter isotope of radon, the performance of these methods are quantified. © 2001 Elsevier Science. All rights reserved« less

The effect of freezing on reactions with environmental impact.

PubMed

O'Concubhair, Ruairí; Sodeau, John R

2013-11-19

The knowledge that the freezing process can accelerate certain chemical reactions has been available since the 1960s, particularly in relation to the food industry. However, investigations into such effects on environmentally relevant reactions have only been carried out since the late 1980s. Some 20 years later, the field has matured and scientists have conducted research into various important processes such as the oxidation of nitrite ions to nitrates, sulfites to sulfates, and elemental mercury to inorganic mercury. Field observations mainly carried out in the polar regions have driven this work. For example, researchers have found that both ozone and mercury are removed from the troposphere completely (and almost instantaneously) at the time of Arctic polar sunrise. The monitoring activities suggested that both the phenomena were caused by involvement of bromine (and possibly iodine) chemistry. Scientists investigating the production of interhalide products (bromine and iodine producing interhalides) in frozen aqueous solutions have found that these reactions result in both rate accelerations and unexpected products. Furthermore, these scientists did this research with environmentally relevant concentrations of reagents, thereby suggesting that these reactions could occur in the polar regions. The conversion of elemental mercury to more oxidized forms has also shown that the acceleration of reactions can occur when environmentally relevant concentrations of Hg(0) and oxidants are frozen together in aqueous solutions. These observations, coupled with previous investigations into the effect of freezing on environmental reactions, lead us to conclude that this type of chemistry could potentially play a significant role in the chemical processing of a wide variety of inorganic components in polar regions. More recently, researchers have recognized the implications of these complementary field and laboratory findings toward human health and climate change. In this Account, we focus on the chemical and physical mechanisms that may promote novel chemistry and rate accelerations when water-ice is present. Future prospects will likely concentrate, once again, on the low-temperature chemistry of organic compounds, such as the humic acids, which are known cryospheric contaminants. Furthermore, data on the kinetics and thermodynamics of all types of reaction promoted by the freezing process would provide much assistance in determining their implications to environmental computer models.

High pressure in solid state chemistry: Combined experimental and modeling approaches for assessing and predicting properties

NASA Astrophysics Data System (ADS)

Etourneau, Jean; Matar, Samir F.

2018-06-01

The thermodynamic pressure parameter has been thoroughly used with mastership by Gérard Demazeau throughout his rich career in solid state chemistry and materials sciences and more recently in biosciences. After a review of such works, focus is made in this topical article on his contribution together with his team in the field of hard materials based on light elements B, C, N with a proposition of a new ultra-hard carbon nitride C2N on one hand and on the structural transformations under high pressures of perovskite into postperovskite with a change of dimensionality from 3D to 2D and related oxides, regarding the arrangement of octahedra, on the other hand. Investigation and concepts first arising from experimental observables are shown to be aided and accelerated via first principles calculations of energy and energy-related quantities.

Technique for etching monolayer and multilayer materials

DOEpatents

Bouet, Nathalie C. D.; Conley, Raymond P.; Divan, Ralu; Macrander, Albert

2015-10-06

A process is disclosed for sectioning by etching of monolayers and multilayers using an RIE technique with fluorine-based chemistry. In one embodiment, the process uses Reactive Ion Etching (RIE) alone or in combination with Inductively Coupled Plasma (ICP) using fluorine-based chemistry alone and using sufficient power to provide high ion energy to increase the etching rate and to obtain deeper anisotropic etching. In a second embodiment, a process is provided for sectioning of WSi.sub.2/Si multilayers using RIE in combination with ICP using a combination of fluorine-based and chlorine-based chemistries and using RF power and ICP power. According to the second embodiment, a high level of vertical anisotropy is achieved by a ratio of three gases; namely, CHF.sub.3, Cl.sub.2, and O.sub.2 with RF and ICP. Additionally, in conjunction with the second embodiment, a passivation layer can be formed on the surface of the multilayer which aids in anisotropic profile generation.

Biochip-based instruments development for space exploration: influence of the antibody immobilization process on the biochip resistance to freeze-drying, temperature shifts and cosmic radiations

NASA Astrophysics Data System (ADS)

Coussot, G.; Moreau, T.; Faye, C.; Vigier, F.; Baqué, M.; Le Postollec, A.; Incerti, S.; Dobrijevic, M.; Vandenabeele-Trambouze, O.

2017-04-01

Due to the diversity of antibody (Ab)-based biochips chemistries available and the little knowledge about biochips resistance to space constraints, immobilization of Abs on the surface of the biochips dedicated to Solar System exploration is challenging. In the present paper, we have developed ten different biochip models including covalent or affinity immobilization with full-length Abs or Ab fragments. Ab immobilizations were carried out in oriented/non-oriented manner using commercial activated surfaces with N-hydroxysuccinic ester (NHS-surfaces) or homemade surfaces using three generations of dendrimers (dendrigraft of poly L-lysine (DGL) surfaces). The performances of the Ab -based surfaces were cross-compared on the following criteria: (i) analytical performances (expressed by both the surface density of immobilized Abs and the amount of antigens initially captured by the surface) and (ii) resistance of surfaces to preparation procedure (freeze-drying, storage) or spatial constraints (irradiation and temperature shifts) encountered during a space mission. The latter results have been expressed as percentage of surface binding capacity losses (or percentage of remaining active Abs). The highest amount of captured antigen was achieved with Ab surfaces having full-length Abs and DGL-surfaces that have much higher surface densities than commercial NHS-surface. After freeze-drying process, thermal shift and storage sample exposition, we found that more than 80% of surface binding sites remained active in this case. In addition, the resistance of Ab surfaces to irradiation with particles such as electron, carbon ions or protons depends not only on the chemistries (covalent/affinity linkages) and strategies (oriented/non-oriented) used to construct the biochip, but also on the type, energy and fluence of incident particles. Our results clearly indicate that full-length Ab immobilization on NHS-surfaces and DGL-surfaces should be preferred for potential use in instruments for planetary exploration.

Inorganic Chemistry Solutions to Semiconductor Nanocrystal Problems

DOE Office of Scientific and Technical Information (OSTI.GOV)

Alvarado, Samuel R.; Guo, Yijun; Ruberu, T. Purnima A.

2014-03-15

The optoelectronic and chemical properties of semiconductor nanocrystals heavily depend on their composition, size, shape and internal structure, surface functionality, etc. Available strategies to alter these properties through traditional colloidal syntheses and ligand exchange methods place a premium on specific reaction conditions and surfactant combinations. In this invited review, we apply a molecular-level understanding of chemical precursor reactivity to reliably control the morphology, composition and intimate architecture (core/shell vs. alloyed) of semiconductor nanocrystals. We also describe our work aimed at achieving highly selective, low-temperature photochemical methods for the synthesis of semiconductor–metal and semiconductor–metal oxide photocatalytic nanocomposites. In addition, we describemore » our work on surface modification of semiconductor nanocrystal quantum dots using new approaches and methods that bypass ligand exchange, retaining the nanocrystal's native ligands and original optical properties, as well as on spectroscopic methods of characterization useful in determining surface ligand organization and chemistry. Using recent examples from our group and collaborators, we demonstrate how these efforts have lead to faster, wider and more systematic application of semiconductor nanocrystal-based materials to biological imaging and tracking, and to photocatalysis of unconventional substrates. We believe techniques and methods borrowed from inorganic chemistry (including coordination, organometallic and solid state chemistry) have much to offer in reaching a better understanding of the synthesis, functionalization and real-life application of such exciting materials as semiconductor nanocrystals (quantum dots, rods, tetrapods, etc.).« less

How Reliable Are ATP Bioluminescence Meters in Assessing Decontamination of Environmental Surfaces in Healthcare Settings?

PubMed Central

Omidbakhsh, Navid; Ahmadpour, Faraz; Kenny, Nicole

2014-01-01

Background Meters based on adenosine triphosphate (ATP) bioluminescence measurements in relative light units (RLU) are often used to rapidly assess the level of cleanliness of environmental surfaces in healthcare and other settings. Can such ATP measurements be adversely affected by factors such as soil and cleaner-disinfectant chemistry? Objective This study tested a number of leading ATP meters for their sensitivity, linearity of the measurements, correlation of the readings to the actual microbial contamination, and the potential disinfectant chemicals’ interference in their readings. Methods First, solutions of pure ATP in various concentrations were used to construct a standard curve and determine linearity and sensitivity. Serial dilutions of a broth culture of Staphylococcus aureus, as a representative nosocomial pathogen, were then used to determine if a given meter’s ATP readings correlated with the actual CFUs. Next, various types of disinfectant chemistries were tested for their potential to interfere with the standard ATP readings. Results All four ATP meters tested herein demonstrated acceptable linearity and repeatability in their readings. However, there were significant differences in their sensitivity to detect the levels of viable microorganisms on experimentally contaminated surfaces. Further, most disinfectant chemistries tested here quenched the ATP readings variably in different ATP meters evaluated. Conclusions Apart from their limited sensitivity in detecting low levels of microbial contamination, the ATP meters tested were also prone to interference by different disinfectant chemistries. PMID:24940751

Polymorphism and electronic structure of polyimine and its potential significance for prebiotic chemistry on Titan.

PubMed

Rahm, Martin; Lunine, Jonathan I; Usher, David A; Shalloway, David

2016-07-19

The chemistry of hydrogen cyanide (HCN) is believed to be central to the origin of life question. Contradictions between Cassini-Huygens mission measurements of the atmosphere and the surface of Saturn's moon Titan suggest that HCN-based polymers may have formed on the surface from products of atmospheric chemistry. This makes Titan a valuable "natural laboratory" for exploring potential nonterrestrial forms of prebiotic chemistry. We have used theoretical calculations to investigate the chain conformations of polyimine (pI), a polymer identified as one major component of polymerized HCN in laboratory experiments. Thanks to its flexible backbone, the polymer can exist in several different polymorphs, which are relatively close in energy. The electronic and structural variability among them is extraordinary. The band gap changes over a 3-eV range when moving from a planar sheet-like structure to increasingly coiled conformations. The primary photon absorption is predicted to occur in a window of relative transparency in Titan's atmosphere, indicating that pI could be photochemically active and drive chemistry on the surface. The thermodynamics for adding and removing HCN from pI under Titan conditions suggests that such dynamics is plausible, provided that catalysis or photochemistry is available to sufficiently lower reaction barriers. We speculate that the directionality of pI's intermolecular and intramolecular =N-H(…)N hydrogen bonds may drive the formation of partially ordered structures, some of which may synergize with photon absorption and act catalytically. Future detailed studies on proposed mechanisms and the solubility and density of the polymers will aid in the design of future missions to Titan.

Accelerating proof of concept for small molecule drugs using solid-state chemistry.

PubMed

Byrn, Stephen R; Zografi, George; Chen, Xiaoming Sean

2010-09-01

In this perspective we have shown that the process of "proof of concept" (POC) in the early part of drug development can be greatly accelerated by close attention to the underlying solid-state chemistry (SSC) of a new chemical entity. POC seeks data that provide confidence in the therapeutic activity and safety of a new chemical entity, which can rapidly lead to a key "GO/NO-GO" decision point for further development. Due to the high cost of the development of new chemical entities and the current low overall productivity of obtaining successful candidates, the pharmaceutical industry is being required to develop accelerated POC strategies. The success of accelerated approaches to POC depends on a full understanding of the SSC of drugs in relation to solubility and stability. Dissolution-limited absorption due to poor solubility of drug substances is particularly important because it can lead to low exposure in animals and undesired bioavailability in humans. Choosing a desirable solid form with sufficient solubility and acceptable stability is essential in developing formulations for POC with superior quality. In this perspective we present an approach that utilizes SSC as part of a novel 2-year development strategy for reaching the pivotal clinical trial stage of development.

F 2 excimer laser (157 nm) radiation modification and surface ablation of PHEMA hydrogels and the effects on bioactivity: Surface attachment and proliferation of human corneal epithelial cells

NASA Astrophysics Data System (ADS)

Zainuddin; Chirila, Traian V.; Barnard, Zeke; Watson, Gregory S.; Toh, Chiong; Blakey, Idriss; Whittaker, Andrew K.; Hill, David J. T.

2011-02-01

Physical and chemical changes at the surface of poly(2-hydroxyethyl methacrylate) (PHEMA) hydrogels modified by ablation with an F 2 excimer laser were investigated experimentally. An important observation was that only the outer exposed surface layers of the hydrogel were affected by the exposure to 157 nm radiation. The effect of the surface changes on the tendency of cells to adhere to the PHEMA was also investigated. A 0.5 cm 2 area of the hydrogel surfaces was exposed to laser irradiation at 157 nm to fluences of 0.8 and 4 J cm -2. The changes in surface topography were analysed by light microscopy and atomic force microscopy, while the surface chemistry was characterized by attenuated total reflection infrared and X-ray photoelectron spectroscopies. Cell-interfacial interactions were examined based on the proliferation of human corneal limbal epithelial (HLE) cells cultured on the laser-modified hydrogels, and on the unexposed hydrogels and tissue culture plastic for comparison. It was observed that the surface topography of laser-exposed hydrogels showed rippled patterns with a surface roughness increasing at the higher exposure dose. The changes in surface chemistry were affected not only by an indirect effect of hydrogen and hydroxyl radicals, formed by water photolysis, on the PHEMA, but also by the direct action of laser radiation on PHEMA if the surface layers of the gel become depleted of water. The laser treatment led to a change in the surface characteristics, with a lower concentration of ester side-chains and the formation of new oxygenated species at the surface. The surface also became more hydrophobic. Most importantly, the surface chemistry and the newly created surface topographical features were able to improve the attachment, spreading and growth of HLE cells.

Characterization of the surface properties of epoxy-type models used for multiphase flow studies in fractured media and creation of a new model

NASA Astrophysics Data System (ADS)

Bergslien, Elisa; Fountain, John; Giese, Rossman

2004-05-01

Epoxy models have been used as analogs for fractured rock surfaces in many laboratory investigations of multiphase flow processes. However, there is no agreement on how well or poorly such an analog replicates the surface chemistry of geologic materials, nor is there a satisfactory analysis of the surface properties of epoxy. This paper addresses the issue of accurately characterizing the surface chemistry of a typical epoxy used in laboratory multiphase flow studies and comparing that surface to a polystyrene surface and a radio frequency glow discharge treated polystyrene surface. Surface properties were determined using direct contact angle measurements of polar and apolar liquids on flat test samples. The epoxy was determined to have surface properties as follows: γ = 62.3, γLW = 39, γAB = 23.3, γ⊕ = 0, and γ? = 23.3 mJ/m2, where γ is the total surface tension of the solid, γLW is the Lifshitz-van der Waals (LW) surface tension component, γAB is the Lewis acid base (AB) surface tension component, γ? is the electron-donor (negative) parameter, and γ⊕ is the electron-acceptor (positive) parameter. Values of γ? < 27.9 mJ/m2 indicate a hydrophobic surface, which means that epoxy is not a good analog for most geologic materials. This study also explores the use of radio frequency glow discharge plasma to add hydroxyl functionality to polymer surfaces producing a material with alterable surface properties and the same optical and casting properties as epoxy. Using this method, the degree of alteration of the surface chemistry of polymer fracture models can be controlled, allowing the creation of models with a variety of different wettabilities. The resultant models were found to be durable, long lasting, and a potentially very useful alternative to the more typical epoxy models.

Coupled Sulfur and Chlorine Chemistry in Venus' Upper Cloud Layer

NASA Astrophysics Data System (ADS)

Mills, Franklin P.

2006-09-01

Venus' atmosphere likely contains a rich variety of sulfur and chlorine compounds because HCl, SO2, and OCS have all been observed. Photodissociation of CO2 and SO2 in the upper cloud layer produces oxygen which can react directly or indirectly with SO2 to form SO3 and eventually H2SO4. Photodissociation of HCl within and above the upper cloud layer produces chlorine which can react with CO and O2 to form ClCO and ClC(O)OO. These two species have been identified as potentially critical intermediaries in the production of CO2. Much less work has been done on the potential coupling between sulfur and chlorine chemistry that may occur within the upper cloud layer. Several aspects have been examined in recent modeling: (1) linkage of the CO2 and sulfur oxidation cycles (based on ideas from Yung and DeMore, 1982), (2) reaction of Cl with SO2 to form ClSO2 (based on ideas from DeMore et al., 1985), and (3) the chemistry of SmCln for m,n = 1,2 (based on preliminary work in Mills, 1998). Initial results suggest the chemistry of SmCln may provide a pathway for accelerated production of polysulfur, Sx, if the oxygen abundance in the upper cloud layer is as small as is implied by the observational limit on O2 (Trauger and Lunine, 1983). Initial results also suggest that ClSO2 can act as a buffer which helps increase the scale height of SO2 and decrease the rate of production of H2SO4. This presentation will describe the results from this modeling; discuss their potential implications for the CO2, sulfur oxidation, and polysulfur cycles; and outline key observations from Venus Express that can help resolve existing questions concerning the chemistry of Venus' upper cloud. Partial funding for this research was provided by the Australian Research Council.

Use of soil-streamwater relationships to assess regional patterns of acidic deposition effects in the northeastern USA

USGS Publications Warehouse

Siemion, Jason; Lawrence, Gregory B.; Murdoch, Peter S.

2013-01-01

Declines of acidic deposition levels by as much as 50% since 1990 have led to partial recovery of surface waters in the northeastern USA but continued depletion of soil calcium through this same period suggests a disconnection between soil and surface water chemistry. To investigate the role of soil-surface water interactions in recovery from acidification, the first regional survey to directly relate soil chemistry to stream chemistry during high flow was implemented in a 4144-km2 area of the Catskill region of New York, where acidic deposition levels are among the highest in the East.More than 40% of 95 streams sampled in the southern Catskill Mountains were determined to be acidified and had inorganic monomeric aluminum concentrations that exceeded a threshold that is toxic to aquatic biota. More than 80% likely exceeded this threshold during the highest flows, but less than 10% of more than 100 streams sampled were acidified in the northwestern portion of the region. Median Oa horizon soil base saturation ranged from 50% to 80% at 200 sites across the region, but median base saturation in the upper 10 cm of the B horizon was less than 20% across the region and was only 2% in the southern area. Aluminum is likely to be interfering with root uptake of calcium in the mineral horizon in approximately half the sampled watersheds. Stream chemistry was highly variable over the Catskill region and, therefore, did not always reflect the calcium depletion of the B horizon that our sampling suggested was nearly ubiquitous throughout the region. Published 2013. This article is a U.S. Government work and is in the public domain in the USA.

Iron oxide magnetic nanoparticles with versatile surface functions based on dopamine anchors

NASA Astrophysics Data System (ADS)

Mazur, Mykola; Barras, Alexandre; Kuncser, Victor; Galatanu, Andrei; Zaitzev, Vladimir; Turcheniuk, Kostiantyn V.; Woisel, Patrice; Lyskawa, Joel; Laure, William; Siriwardena, Aloysius; Boukherroub, Rabah; Szunerits, Sabine

2013-03-01

The synthesis of multifunctional magnetic nanoparticles (MF-MPs) is one of the most active research areas in advanced materials as their multifunctional surfaces allow conjugation of biological and chemical molecules, thus making it possible to achieve target-specific diagnostic in parallel to therapeutics. We report here a simple strategy to integrate in a one-step reaction several reactive sites onto the particles. The preparation of MF-MPs is based on their simultaneous modification with differently functionalized dopamine derivatives using simple solution chemistry. The formed MF-MPs show comparable magnetic properties to those of naked nanoparticles with almost unaltered particle size of around 25 nm. The different termini, amine, azide and maleimide functions, enable further functionalization of MF-MPs by the grafting-on approach. Michael addition, Cu(i) catalyzed « click » chemistry and amidation reactions are performed on the MF-MPs integrating subsequently 6-(ferrocenyl)-hexanethiol, horseradish peroxidase (HRP) and mannose.

What's on the Surface? Physics and Chemistry of Delta-Doped Surfaces

NASA Technical Reports Server (NTRS)

Hoenk, Michael

2011-01-01

Outline of presentation: 1. Detector surfaces and the problem of stability 2. Delta-doped detectors 3. Physics of Delta-doped Silicon 4. Chemistry of the Si-SiO2 Interface 5. Physics and Chemistry of Delta-doped Surfaces a. Compensation b. Inversion c. Quantum exclusion. Conclusions: 1. Quantum confinement of electrons and holes dominates the behavior of delta-doped surfaces. 2. Stability of delta-doped detectors: Delta-layer creates an approx 1 eV tunnel barrier between bulk and surface. 3. At high surface charge densities, Tamm-Shockley states form at the surface. 4. Surface passivation by quantum exclusion: Near-surface delta-layer suppresses T-S trapping of minority carriers. 5. The Si-SiO2 interface compensates the surface 6. For delta-layers at intermediate depth, surface inversion layer forms 7. Density of Si-SiO2 interface charge can be extremely high (>10(exp 14)/sq cm)

Nanocellulose-Based Materials for Water Purification

PubMed Central

Voisin, Hugo; Bergström, Lennart; Liu, Peng; Mathew, Aji P.

2017-01-01

Nanocellulose is a renewable material that combines a high surface area with high strength, chemical inertness, and versatile surface chemistry. In this review, we will briefly describe how nanocellulose is produced, and present—in particular, how nanocellulose and its surface modified versions affects the adsorption behavior of important water pollutants, e.g., heavy metal species, dyes, microbes, and organic molecules. The processing of nanocellulose-based membranes and filters for water purification will be described in detail, and the uptake capacity, selectivity, and removal efficiency will also be discussed. The processing and performance of nanocellulose-based membranes, which combine a high removal efficiency with anti-fouling properties, will be highlighted. PMID:28336891

Mass Spectrometric Analysis of the Cell Surface N-Glycoproteome by Combining Metabolic Labeling and Click Chemistry

NASA Astrophysics Data System (ADS)

Smeekens, Johanna M.; Chen, Weixuan; Wu, Ronghu

2015-04-01

Cell surface N-glycoproteins play extraordinarily important roles in cell-cell communication, cell-matrix interactions, and cellular response to environmental cues. Global analysis is exceptionally challenging because many N-glycoproteins are present at low abundances and effective separation is difficult to achieve. Here, we have developed a novel strategy integrating metabolic labeling, copper-free click chemistry, and mass spectrometry (MS)-based proteomics methods to analyze cell surface N-glycoproteins comprehensively and site-specifically. A sugar analog containing an azido group, N-azidoacetylgalactosamine, was fed to cells to label glycoproteins. Glycoproteins with the functional group on the cell surface were then bound to dibenzocyclooctyne-sulfo-biotin via copper-free click chemistry under physiological conditions. After protein extraction and digestion, glycopeptides with the biotin tag were enriched by NeutrAvidin conjugated beads. Enriched glycopeptides were deglycosylated with peptide- N-glycosidase F in heavy-oxygen water, and in the process of glycan removal, asparagine was converted to aspartic acid and tagged with 18O for MS analysis. With this strategy, 144 unique N-glycopeptides containing 152 N-glycosylation sites were identified in 110 proteins in HEK293T cells. As expected, 95% of identified glycoproteins were membrane proteins, which were highly enriched. Many sites were located on important receptors, transporters, and cluster of differentiation proteins. The experimental results demonstrated that the current method is very effective for the comprehensive and site-specific identification of the cell surface N-glycoproteome and can be extensively applied to other cell surface protein studies.

Factors affecting the removal of ammonia from air on carbonaceous materials: Investigation of reactive adsorption mechanism

NASA Astrophysics Data System (ADS)

Petit, Camille

Air pollution related to the release of industrial toxic gases, represents one of the main concerns of our modern world owing to its detrimental effect on the environment. To tackle this growing issue, efficient ways to reduce/control the release of pollutants are required. Adsorption of gases on porous materials appears as a potential solution. However, the physisorption of small molecules of gases such as ammonia is limited at ambient conditions. For their removal, adsorbents providing strong adsorption forces must be used/developed. In this study, new carbon-based materials are prepared and tested for ammonia adsorption at ambient conditions. Characterization of the adsorbents' texture and surface chemistry is performed before and after exposure to ammonia to identify the features responsible for high adsorption capacity and for controlling the mechanisms of retention. The characterization techniques include: nitrogen adsorption, thermal analysis, potentiometric titration, FT-IR spectroscopy, X-ray diffraction, Energy Dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy and Electron Microscopy. The results obtained indicate that ammonia removal is governed by the adsorbent's surface chemistry. On the contrary, porosity (and thus physisorption) plays a secondary role in this process, unless strong dispersive forces are provided by the adsorbent. The surface chemistry features responsible for the enhanced ammonia adsorption include the presence of oxygen-(carboxyl, hydroxyl, epoxy) and sulfur- (sulfonic) containing groups. Metallic species improve the breakthrough capacity as well as they lead to the formation of Lewis acid-base interactions, hydrogen-bonding or complexation. In addition to the latter three mechanisms, ammonia is retained on the adsorbent surface via Bronsted acid-base interactions or via specific reactions with the adsorbent's functionalities leading to the incorporation of ammonia into the adsorbent's matrix. Another mechanism involves dissolution of ammonia in water when moisture is present in the system. Even though this process increases the breakthrough capacity of a material, it provides rather weak retention forces since ammonia dissolved in water is easily desorbed from the adsorbent's surface.

Hydrogeology and Water Quality of the Pepacton Reservoir Watershed in Southeastern New York. Part 3. Responses of Stream Base-Flow Chemistry to Hydrogeologic Factors and Nonpoint-Sources of Contamination

USGS Publications Warehouse

Heisig, Paul M.; Phillips, Patrick J.

2004-01-01

The implications of this study are that seasonal and more frequent base-flow surveys of water chemistry from small stream basins can help refine the understanding of local hydrogeologic systems and define the effects of nonpointsource contamination on base-flow water quality. The concentration of most nonpoint sources in valley-bottom or lower-hillside areas helped indicate the relative contributions of water from hillside and valley-bottom areas at different times of year. The positive correlations between the intensity of nonpoint-source activities and nonpoint-source constituents in base flow underscores the link between land use (nonpoint sources), ground-water quality, and surface-water quality.

International Symposium on Molecular Spectroscopy (70th)

DTIC Science & Technology

2015-06-22

N DAY June 22 8:30 AM TU ESDAY June 23 8:30 AM W EDN ESDAY June 24 8:30 AM THU RSDAY June 25 8:30 AM FRIDAY June 26 8:30 AM Foellinger Auditorium M A...energy surfaces Room 100 N oyes Laboratory TB M ini-sym posium : Accelerator-Based Spectroscopy RB M ini-sym posium : Accelerator-Based...Conform ers, isom ers, chirality, stereochem istry RD Astronom y FD Atm ospheric science Room 217 N oyes Laboratory TE Instrum

Trampoline Effect: Observations and Modeling

NASA Astrophysics Data System (ADS)

Guyer, R.; Larmat, C. S.; Ulrich, T. J.

2009-12-01

The Iwate-Miyagi earthquake at site IWTH25 (14 June 2008) had large, asymmetric at surface vertical accelerations prompting the sobriquet trampoline effect (Aoi et. al. 2008). In addition the surface acceleration record showed long-short waiting time correlations and vertical-horizontal acceleration correlations. A lumped element model, deduced from the equations of continuum elasticity, is employed to describe the behavior at this site in terms of a surface layer and substrate. Important ingredients in the model are the nonlinear vertical coupling between the surface layer and the substrate and the nonlinear horizontal frictional coupling between the surface layer and the substrate. The model produces results in qualitative accord with observations: acceleration asymmetry, Fourier spectrum, waiting time correlations and vertical acceleration-horizontal acceleration correlations. [We gratefully acknowledge the support of the U. S. Department of Energy through the LANL/LDRD Program for this work].

Synergistic Anion-(π) n-π Catalysis on π-Stacked Foldamers.

PubMed

Bornhof, Anna-Bea; Bauzá, Antonio; Aster, Alexander; Pupier, Marion; Frontera, Antonio; Vauthey, Eric; Sakai, Naomi; Matile, Stefan

2018-04-11

In this report, we demonstrate that synergistic effects between π-π stacking and anion-π interactions in π-stacked foldamers provide access to unprecedented catalytic activity. To elaborate on anion-(π) n -π catalysis, we have designed, synthesized and evaluated a series of novel covalent oligomers with up to four face-to-face stacked naphthalenediimides (NDIs). NMR analysis including DOSY confirms folding into π stacks, cyclic voltammetry, steady-state and transient absorption spectroscopy the electronic communication within the π stacks. Catalytic activity, assessed by chemoselective catalysis of the intrinsically disfavored but biologically relevant addition reaction of malonate half thioesters to enolate acceptors, increases linearly with the length of the stacks to reach values that are otherwise beyond reach. This linear increase violates the sublinear power laws of oligomer chemistry. The comparison of catalytic activity with ratiometric changes in absorption and decreasing energy of the LUMO thus results in superlinearity, that is synergistic amplification of anion-π catalysis by remote control over the entire stack. In computational models, increasing length of the π-stacked foldamers correlates sublinearly with changes in surface potentials, chloride binding energies, and the distances between chloride and π surface and within the π stack. Computational evidence is presented that the selective acceleration of disfavored but relevant enolate chemistry by anion-π catalysis indeed originates from the discrimination of planar and bent tautomers with delocalized and localized charges, respectively, on π-acidic surfaces. Computed binding energies of keto and enol intermediates of the addition reaction as well as their difference increase with increasing length of the π stack and thus reflect experimental trends correctly. These results demonstrate that anion-(π) n -π interactions exist and matter, ready for use as a unique new tool in catalysis and beyond.

Gravity Modeling for Variable Fidelity Environments

NASA Technical Reports Server (NTRS)

Madden, Michael M.

2006-01-01

Aerospace simulations can model worlds, such as the Earth, with differing levels of fidelity. The simulation may represent the world as a plane, a sphere, an ellipsoid, or a high-order closed surface. The world may or may not rotate. The user may select lower fidelity models based on computational limits, a need for simplified analysis, or comparison to other data. However, the user will also wish to retain a close semblance of behavior to the real world. The effects of gravity on objects are an important component of modeling real-world behavior. Engineers generally equate the term gravity with the observed free-fall acceleration. However, free-fall acceleration is not equal to all observers. To observers on the sur-face of a rotating world, free-fall acceleration is the sum of gravitational attraction and the centrifugal acceleration due to the world's rotation. On the other hand, free-fall acceleration equals gravitational attraction to an observer in inertial space. Surface-observed simulations (e.g. aircraft), which use non-rotating world models, may choose to model observed free fall acceleration as the gravity term; such a model actually combines gravitational at-traction with centrifugal acceleration due to the Earth s rotation. However, this modeling choice invites confusion as one evolves the simulation to higher fidelity world models or adds inertial observers. Care must be taken to model gravity in concert with the world model to avoid denigrating the fidelity of modeling observed free fall. The paper will go into greater depth on gravity modeling and the physical disparities and synergies that arise when coupling specific gravity models with world models.

Acceleration and sensitivity analysis of lattice kinetic Monte Carlo simulations using parallel processing and rate constant rescaling

NASA Astrophysics Data System (ADS)

Núñez, M.; Robie, T.; Vlachos, D. G.

2017-10-01

Kinetic Monte Carlo (KMC) simulation provides insights into catalytic reactions unobtainable with either experiments or mean-field microkinetic models. Sensitivity analysis of KMC models assesses the robustness of the predictions to parametric perturbations and identifies rate determining steps in a chemical reaction network. Stiffness in the chemical reaction network, a ubiquitous feature, demands lengthy run times for KMC models and renders efficient sensitivity analysis based on the likelihood ratio method unusable. We address the challenge of efficiently conducting KMC simulations and performing accurate sensitivity analysis in systems with unknown time scales by employing two acceleration techniques: rate constant rescaling and parallel processing. We develop statistical criteria that ensure sufficient sampling of non-equilibrium steady state conditions. Our approach provides the twofold benefit of accelerating the simulation itself and enabling likelihood ratio sensitivity analysis, which provides further speedup relative to finite difference sensitivity analysis. As a result, the likelihood ratio method can be applied to real chemistry. We apply our methodology to the water-gas shift reaction on Pt(111).

Manipulating the Surface Chemistry of Quantum Dots for Sensitive Ratiometric Fluorescence Detection of Sulfur Dioxide.

PubMed

Li, Huihui; Zhu, Houjuan; Sun, Mingtai; Yan, Yehan; Zhang, Kui; Huang, Dejian; Wang, Suhua

2015-08-11

Herein, we report a novel approach to the rapid visual detection of gaseous sulfur dioxide (SO2) by manipulating the surface chemistry of 3-aminopropyltriethoxysilane (APTS)-modified quantum dots (QDs) using fluorescent coumarin-3-carboxylic acid (CCA) for specific reaction with SO2. The CCA molecules are attached to the surface amino groups of the QDs through electrostatic attraction, thus the fluorescence of CCA is greatly suppressed because of the formation of an ion-pair complex between the ATPS-modified QDs and CCA. Such an interaction is vulnerable to SO2 because SO2 can readily react with surface amino groups to form strong charge-transfer complexes and subsequently release the strongly fluorescent CCA molecules. The mechanism has been carefully verified through a series of control experiments. Upon exposure to different amounts of SO2, the fluorescent color of the nanoparticle-based sensor displays continuously changes from red to blue. Most importantly, the approach owns high selectivity for SO2 and a tolerance of interference, which enables the sensor to detect SO2 in a practical application. Using this fluorescence-based sensing method, we have achieved a visual detection limit of 6 ppb for gaseous SO2.

Impacts of chemical modification on the toxicity of diverse nanocellulose materials to developing zebrafish

PubMed Central

Harper, Bryan J.; Clendaniel, Alicea; Sinche, Federico; Way, Daniel; Hughes, Michael; Schardt, Jenna; Simonsen, John; Stefaniak, Aleksandr B.

2016-01-01

Cellulose is an abundant and renewable resource currently being investigated for utility in nanomaterial form for various promising applications ranging from medical and pharmaceutical uses to mechanical reinforcement and biofuels. The utility of nanocellulose and wide implementation ensures increasing exposure to humans and the environment as nanocellulose-based technologies advance. Here, we investigate how differences in aspect ratio and changes to surface chemistry, as well as synthesis methods, influence the biocompatibility of nanocellulose materials using the embryonic zebrafish. Investigations into the toxicity of neutral, cationic and anionic surface functionalities revealed that surface chemistry had a minimal influence on the overall toxicity of nanocellulose materials. Higher aspect ratio cellulose nanofibers produced by mechanical homogenization were, in some cases, more toxic than other cellulose-based nanofibers or nanocrystals produced by chemical synthesis methods. Using fluorescently labeled nanocellulose we were able to show that nanocellulose uptake did occur in embryonic zebrafish during development. We conclude that the benign nature of nanocellulose materials makes them an ideal platform to systematically investigate the inherent surface features driving nanomaterial toxicity in order to create safer design principles for engineered nanoparticles. PMID:27468180

The role of surfaces, chemical interfaces, and disorder on plutonium incorporation in pyrochlores

DOE PAGES

Perriot, Romain; Dholabhai, Pratik P.; Uberuaga, Blas P.

2016-07-27

Pyrochlores, a class of complex oxides with formula A 2B 2O 7, are one of the candidates for nuclear waste encapsulation, due to the natural occurrence of actinide-bearing pyrochlore minerals and laboratory observations of high radiation tolerance. In this work, we use atomistic simulations to determine the role of surfaces, chemical interfaces, and cation disorder on the plutonium immobilization properties of pyrochlores as a function of pyrochlore chemistry. We find that both Pu 3+ and Pu 4+ segregate to the surface for the four low-index pyrochlore surfaces considered, and that the segregation energy varies with the chemistry of the compound.more » We also find that pyrochlore/pyrochlore bicrystals A 2B 2O 7/A 2'B 2'O 7 can be used to immobilize Pu 3+ and Pu 4+ either in the same or separate phases of the compound, depending on the chemistry of the material. Finally, we find that Pu 4+ segregates to the disordered phase of an order/disorder bicrystal, driven by the occurrence of local oxygen-rich environments. However, Pu 3+ is weakly sensitive to the oxygen environment, and therefore only slightly favors the disordered phase. This behavior suggests that, at some concentration, Pu incorporation can destabilize the pyrochlore structure. Together, these results provide new insight into the ability of pyrochlore compounds to encapsulate Pu and suggest new considerations in the development of waste forms based on pyrochlores. Particularly, the phase structure of a multi-phase pyrochlore composite can be used to independently getter decay products based on their valence and size.« less

Polar boundary layer bromine explosion and ozone depletion events in the chemistry-climate model EMAC v2.52: implementation and evaluation of AirSnow algorithm

NASA Astrophysics Data System (ADS)

Falk, Stefanie; Sinnhuber, Björn-Martin

2018-03-01

Ozone depletion events (ODEs) in the polar boundary layer have been observed frequently during springtime. They are related to events of boundary layer enhancement of bromine. Consequently, increased amounts of boundary layer volume mixing ratio (VMR) and vertical column densities (VCDs) of BrO have been observed by in situ observation, ground-based as well as airborne remote sensing, and from satellites. These so-called bromine explosion (BE) events have been discussed serving as a source of tropospheric BrO at high latitudes, which has been underestimated in global models so far. We have implemented a treatment of bromine release and recycling on sea-ice- and snow-covered surfaces in the global chemistry-climate model EMAC (ECHAM/MESSy Atmospheric Chemistry) based on the scheme of Toyota et al. (2011). In this scheme, dry deposition fluxes of HBr, HOBr, and BrNO3 over ice- and snow-covered surfaces are recycled into Br2 fluxes. In addition, dry deposition of O3, dependent on temperature and sunlight, triggers a Br2 release from surfaces associated with first-year sea ice. Many aspects of observed bromine enhancements and associated episodes of near-complete depletion of boundary layer ozone, both in the Arctic and in the Antarctic, are reproduced by this relatively simple approach. We present first results from our global model studies extending over a full annual cycle, including comparisons with Global Ozone Monitoring Experiment (GOME) satellite BrO VCDs and surface ozone observations.

Effect of Space Radiation Processing on Lunar Soil Surface Chemistry: X-Ray Photoelectron Spectroscopy Studies

NASA Technical Reports Server (NTRS)

Dukes, C.; Loeffler, M.J.; Baragiola, R.; Christoffersen, R.; Keller, J.

2009-01-01

Current understanding of the chemistry and microstructure of the surfaces of lunar soil grains is dominated by a reference frame derived mainly from electron microscopy observations [e.g. 1,2]. These studies have shown that the outermost 10-100 nm of grain surfaces in mature lunar soil finest fractions have been modified by the combined effects of solar wind exposure, surface deposition of vapors and accretion of impact melt products [1,2]. These processes produce surface-correlated nanophase Feo, host grain amorphization, formation of surface patinas and other complex changes [1,2]. What is less well understood is how these changes are reflected directly at the surface, defined as the outermost 1-5 atomic monolayers, a region not easily chemically characterized by TEM. We are currently employing X-ray Photoelectron Spectroscopy (XPS) to study the surface chemistry of lunar soil samples that have been previously studied by TEM. This work includes modification of the grain surfaces by in situ irradiation with ions at solar wind energies to better understand how irradiated surfaces in lunar grains change their chemistry once exposed to ambient conditions on earth.

ANNUAL REPORT ON PHYSICAL SCIENCES, ENGINEERING AND LIFE SCIENCES , JULY 1, 1961

DOE Office of Scientific and Technical Information (OSTI.GOV)

None

1962-10-31

The research program at Brooknaven is described. Current activities in physics, high-energy accelerators, instrumentation, chemistry, nuclear engineering, applied mathematics, biology, and medical research are outlined. (D.L.C.)

Edwin M. McMillan, A Biographical Sketch

DOE R&D Accomplishments Database

Lofgren, E. J.

1994-07-01

Edwin M. McMillan was one of the great scientists of the middle years of this century. He made notable contributions to nuclear and particle physics, the chemistry of transuranium elements, and accelerator physics.

NOx Binding and Dissociation: Enhanced Ferroelectric Surface Chemistry by Catalytic Monolayers

NASA Astrophysics Data System (ADS)

Kakekhani, Arvin; Ismail-Beigi, Sohrab

2013-03-01

NOx molecules are regulated air pollutants produced during automotive combustion. As part of an effort to design viable catalysts for NOx decomposition operating at higher temperatures that would allow for improved fuel efficiency, we examine NOx chemistry on ferroelectric perovskite surfaces. Changing the direction of ferroelectric polarization can modify surface electronic properties and may lead to switchable surface chemistry. Here, we describe our recent work on potentially enhanced surface chemistry using catalytic RuO2 monolayers on perovskite ferroelectric substrates. In addition to thermodynamic stabilization of the RuO2 layer, we present results on the polarization-dependent binding of NO, O2, N2, and atomic O and N. We present results showing that one key problem with current catalysts, involving the difficulty of releasing dissociation products (especially oxygen), can be ameliorated by this method. Primary support from Toyota Motor Engineering and Manufacturing, North America, Inc.

Iterative algorithm for reconstructing rotationally asymmetric surface deviation with pixel-level spatial resolution

NASA Astrophysics Data System (ADS)

Quan, Haiyang; Wu, Fan; Hou, Xi

2015-10-01

New method for reconstructing rotationally asymmetric surface deviation with pixel-level spatial resolution is proposed. It is based on basic iterative scheme and accelerates the Gauss-Seidel method by introducing an acceleration parameter. This modified Successive Over-relaxation (SOR) is effective for solving the rotationally asymmetric components with pixel-level spatial resolution, without the usage of a fitting procedure. Compared to the Jacobi and Gauss-Seidel method, the modified SOR method with an optimal relaxation factor converges much faster and saves more computational costs and memory space without reducing accuracy. It has been proved by real experimental results.

Superconducting Thin Films for the Enhancement of Superconducting Radio Frequency Accelerator Cavities

NASA Astrophysics Data System (ADS)

Burton, Matthew C.

Bulk niobium (Nb) superconducting radio frequency (SRF) cavities are currently the preferred method for acceleration of charged particles at accelerating facilities around the world. However, bulk Nb cavities have poor thermal conductance, impose material and design restrictions on other components of a particle accelerator, have low reproducibility and are approaching the fundamental material-dependent accelerating field limit of approximately 50MV/m. Since the SRF phenomena occurs at surfaces within a shallow depth of ˜1 microm, a proposed solution to this problem has been to utilize thin film technology to deposit superconducting thin films on the interior of cavities to engineer the active SRF surface in order to achieve cavities with enhanced properties and performance. Two proposed thin film applications for SRF cavities are: 1) Nb thin films coated on bulk cavities made of suitable castable metals (such as copper or aluminum) and 2) multilayer films designed to increase the accelerating gradient and performance of SRF cavities. While Nb thin films on copper (Cu) cavities have been attempted in the past using DC magnetron sputtering (DCMS), such cavities have never performed at the bulk Nb level. However, new energetic condensation techniques for film deposition, such as High Power Impulse Magnetron Sputtering (HiPIMS), offer the opportunity to create suitably thick Nb films with improved density, microstructure and adhesion compared to traditional DCMS. Clearly use of such novel technique requires fundamental studies to assess surface evolution and growth modes during deposition and resulting microstructure and surface morphology and the correlation with RF superconducting properties. Here we present detailed structure-property correlative research studies done on Nb/Cu thin films and NbN- and NbTiN-based multilayers made using HiPIMS and DCMS, respectively.

Linking molecular level chemistry to macroscopic combustion behavior for nano-energetic materials with halogen containing oxides.

PubMed

Farley, Cory W; Pantoya, Michelle L; Losada, Martin; Chaudhuri, Santanu

2013-08-21

Coupling molecular scale reaction kinetics with macroscopic combustion behavior is critical to understanding the influences of intermediate chemistry on energy propagation, yet bridging this multi-scale gap is challenging. This study integrates ab initio quantum chemical calculations and condensed phase density functional theory to elucidate factors contributing to experimentally measured high flame speeds (i.e., >900 m∕s) associated with halogen based energetic composites, such as aluminum (Al) and iodine pentoxide (I2O5). Experiments show a direct correlation between apparent activation energy and flame speed suggesting that flame speed is directly influenced by chemical kinetics. Toward this end, the first principle simulations resolve key exothermic surface and intermediate chemistries contributing toward the kinetics that promote high flame speeds. Linking molecular level exothermicity to macroscopic experimental investigations provides insight into the unique role of the alumina oxide shell passivating aluminum particles. In the case of Al reacting with I2O5, the alumina shell promotes exothermic surface chemistries that reduce activation energy and increase flame speed. This finding is in contrast to Al reaction with metal oxides that show the alumina shell does not participate exothermically in the reaction.

Boosting the Supercapacitance of Nitrogen-Doped Carbon by Tuning Surface Functionalities.

PubMed

Biemolt, Jasper; Denekamp, Ilse M; Slot, Thierry K; Rothenberg, Gadi; Eisenberg, David

2017-10-23

The specific capacitance of a highly porous, nitrogen-doped carbon is nearly tripled by orthogonal optimization of the microstructure and surface chemistry. First, the carbons' hierarchical pore structure and specific surface area were tweaked by controlling the temperature and sequence of the thermal treatments. The best process (pyrolysis at 900 °C, washing, and subsequent annealing at 1000 °C) yielded a carbon with a specific capacitance of 117 F g -1 -nearly double that of a carbon made by a typical single-step synthesis at 700 °C. Following the structural optimization, the surface chemistry of the carbons was enriched by applying an oxidation routine based on a mixture of nitric and sulfuric acid in a 1:4 ratio at two different treatment temperatures (0 and 20 °C) and different treatment times. The optimal treatment times were 4 h at 0 °C and only 1 h at 20 °C. Overall, the specific capacitance nearly tripled relative to the original carbon, reaching 168 F g -1 . The inherent nitrogen doping of the carbon comes into interplay with the acid-induced surface functionalization, creating a mixture of oxygen- and nitrogen-oxygen functionalities. The evolution of the surface chemistry was carefully followed by X-ray photoelectron spectroscopy and by N 2 sorption porosimetry, revealing stepwise surface functionalization and simultaneous carbon etching. Overall, these processes are responsible for the peak-shaped capacitance trends in the carbons. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Effects of activated carbon surface chemistry and pore structure on the adsorption of trace organic contaminants from aqueous solution

NASA Astrophysics Data System (ADS)

Li, Lei

The objectives were (1) to identify activated pore structure and surface chemistry characteristics that assure the effective removal of trace organic contaminants from aqueous-solution, and (2) to develop a procedure to predict the adsorption capacity of activated carbons from fundamental adsorbent and adsorbate properties. A matrix of activated carbon fibers (ACFs) (with three activation levels and four surface chemistry levels) and three commercially available granular activated carbons (GACs) served as the adsorbents. BET surface area, pore size distribution, elemental composition, point of zero charge and infrared spectroscopy data were obtained to characterize the adsorbents. The adsorption of relative hydrophilic methyl tertiary-butyl ether (MTBE) and relative hydrophobic trichloroethene (TCE) were conducted in both ultrapure water and Sacramento-San Joaquin Delta water. The results showed that an effective adsorbent for the removal of micropollutants from water requires (1) a large volume of micropores with widths that are about 1.5 times larger than the kinetic diameter of the target adsorbate, (2) a micropore size distribution that extends to widths that are approximately twice the kinetic diameter of the target adsorbate to prevent pore blockage by NOM, and (3) a hydrophobic pore surface chemistry with the sum of oxygen and nitrogen contents less than 2 to 3 mmol/g. A procedure based on the Polanyi Potential Theory (PPT) was developed to predict the adsorption capacities of activated carbons from fundamental adsorbent and adsorbate properties. A correlation between the coalescing factor for water adsorption and adsorbent oxygen content was developed. Based on this correlation, the PPT yielded reasonable estimates of aqueous phase adsorption capacities for both relatively polar and non-polar adsorbates on both relatively hydrophobic and hydrophilic activated carbons. With the developed procedure, the adsorption capacities of organic compounds that are partially miscible in water can be predicted from (1) N2 and CO2 adsorption isotherms of a given adsorbent, (2) the adsorbent oxygen content, and (3) the molar volume and parachor of the target adsorbate.

Does the climate warming hiatus exist over the Tibetan Plateau?

PubMed Central

Duan, Anmin; Xiao, Zhixiang

2015-01-01

The surface air temperature change over the Tibetan Plateau is determined based on historical observations from 1980 to 2013. In contrast to the cooling trend in the rest of China, and the global warming hiatus post-1990s, an accelerated warming trend has appeared over the Tibetan Plateau during 1998–2013 (0.25 °C decade−1), compared with that during 1980–1997 (0.21 °C decade−1). Further results indicate that, to some degree, such an accelerated warming trend might be attributable to cloud–radiation feedback. The increased nocturnal cloud over the northern Tibetan Plateau would warm the nighttime temperature via enhanced atmospheric back-radiation, while the decreased daytime cloud over the southern Tibetan Plateau would induce the daytime sunshine duration to increase, resulting in surface air temperature warming. Meanwhile, the in situ surface wind speed has recovered gradually since 1998, and thus the energy concentration cannot explain the accelerated warming trend over the Tibetan Plateau after the 1990s. It is suggested that cloud–radiation feedback may play an important role in modulating the recent accelerated warming trend over the Tibetan Plateau. PMID:26329678

Deep learning for computational chemistry.

PubMed

Goh, Garrett B; Hodas, Nathan O; Vishnu, Abhinav

2017-06-15

The rise and fall of artificial neural networks is well documented in the scientific literature of both computer science and computational chemistry. Yet almost two decades later, we are now seeing a resurgence of interest in deep learning, a machine learning algorithm based on multilayer neural networks. Within the last few years, we have seen the transformative impact of deep learning in many domains, particularly in speech recognition and computer vision, to the extent that the majority of expert practitioners in those field are now regularly eschewing prior established models in favor of deep learning models. In this review, we provide an introductory overview into the theory of deep neural networks and their unique properties that distinguish them from traditional machine learning algorithms used in cheminformatics. By providing an overview of the variety of emerging applications of deep neural networks, we highlight its ubiquity and broad applicability to a wide range of challenges in the field, including quantitative structure activity relationship, virtual screening, protein structure prediction, quantum chemistry, materials design, and property prediction. In reviewing the performance of deep neural networks, we observed a consistent outperformance against non-neural networks state-of-the-art models across disparate research topics, and deep neural network-based models often exceeded the "glass ceiling" expectations of their respective tasks. Coupled with the maturity of GPU-accelerated computing for training deep neural networks and the exponential growth of chemical data on which to train these networks on, we anticipate that deep learning algorithms will be a valuable tool for computational chemistry. © 2017 Wiley Periodicals, Inc. © 2017 Wiley Periodicals, Inc.

Direct in situ observation of the electron-driven synthesis of Ag filaments on α-Ag2WO4 crystals

PubMed Central

Longo, E.; Cavalcante, L. S.; Volanti, D. P.; Gouveia, A. F.; Longo, V. M.; Varela, J. A.; Orlandi, M. O.; Andrés, J.

2013-01-01

In this letter, we report, for the first time, the real-time in situ nucleation and growth of Ag filaments on α-Ag2WO4 crystals driven by an accelerated electron beam from an electronic microscope under high vacuum. We employed several techniques to characterise the material in depth. By using these techniques combined with first-principles modelling based on density functional theory, a mechanism for the Ag filament formation followed by a subsequent growth process from the nano- to micro-scale was proposed. In general, we have shown that an accelerated electron beam from an electronic microscope under high vacuum enables in situ visualisation of Ag filaments with subnanometer resolution and offers great potential for addressing many fundamental issues in materials science, chemistry, physics and other fields of science. PMID:23591807

Photothermal-enhanced catalysis in core-shell plasmonic hierarchical Cu7S4 microsphere@zeolitic imidazole framework-8.

PubMed

Wang, Feifan; Huang, Yanjie; Chai, Zhigang; Zeng, Min; Li, Qi; Wang, Yuan; Xu, Dongsheng

2016-12-01

Conventional semiconductor photocatalysis based on band-edge absorption remains inefficient due to the limited harvesting of solar irradiation and the complicated surface/interface chemistry. Herein, novel photothermal-enhanced catalysis was achieved in a core-shell hierarchical Cu 7 S 4 nano-heater@ZIF-8 heterostructures via near-infrared localized surface plasmon resonance. Our results demonstrated that both the high surface temperature of the photothermal Cu 7 S 4 core and the close-adjacency of catalytic ZIF-8 shell contributed to the extremely enhanced catalytic activity. Under laser irradiation (1450 nm, 500 mW), the cyclocondensation reaction rate increased 4.5-5.4 fold compared to that of the process at room temperature, in which the 1.6-1.8 fold enhancement was due to the localized heating effect. The simulated sunlight experiments showed a photothermal activation efficiency (PTAE) of 0.07%, further indicating the validity of photothermal catalysis based on the plasmonic semiconductor nanomaterials. More generally, this approach provides a platform to improve reaction activity with efficient utilization of solar energy, which can be readily extended to other green-chemistry processes.

An automated synthesis-purification-sample-management platform for the accelerated generation of pharmaceutical candidates.

PubMed

Sutherland, J David; Tu, Noah P; Nemcek, Thomas A; Searle, Philip A; Hochlowski, Jill E; Djuric, Stevan W; Pan, Jeffrey Y

2014-04-01

A flexible and integrated flow-chemistry-synthesis-purification compound-generation and sample-management platform has been developed to accelerate the production of small-molecule organic-compound drug candidates in pharmaceutical research. Central to the integrated system is a Mitsubishi robot, which hands off samples throughout the process to the next station, including synthesis and purification, sample dispensing for purity and quantification analysis, dry-down, and aliquot generation.

Soil mineralogy and chemistry on Mars - Possible clues from salts and clays in SNC meteorites

NASA Technical Reports Server (NTRS)

Gooding, James L.

1992-01-01

If the shergottite, nakhlite, and chassignite (SNC) meteorites' parent planet is Mars, then the aqueous precipitates found in them imply that oxidizing, water-based solutions may have been chemically active on that planet over the past 200-1300 million yrs. It is suggested that the mixture of aqueous precipitates found in the SNCs furnish a self-consistent model for the bulk elemental composition of surface sediments at the Viking Lander sites. Further mineralogical and stable-isotope studies of the secondary minerals may establish the limits for biological activity over the last 1300 million years of Mars' water-based chemistry.

Effects of topographical and mechanical property alterations induced by oxygen plasma modification on stem cell behavior.

PubMed

Yang, Yong; Kulangara, Karina; Lam, Ruby T S; Dharmawan, Rena; Leong, Kam W

2012-10-23

Polymeric substrates intended for cell culture and tissue engineering are often surface-modified to facilitate cell attachment of most anchorage-dependent cell types. The modification alters the surface chemistry and possibly topography. However, scant attention has been paid to other surface property alterations. In studying oxygen plasma treatment of polydimethylsiloxane (PDMS), we show that oxygen plasma treatment alters the surface chemistry and, consequently, the topography and elasticity of PDMS at the nanoscale level. The elasticity factor has the predominant effect, compared with the chemical and topographical factors, on cell adhesions of human mesenchymal stem cells (hMSCs). The enhanced focal adhesions favor cell spreading and osteogenesis of hMSCs. Given the prevalent use of PDMS in biomedical device construction and cell culture experiments, this study highlights the importance of understanding how oxygen plasma treatment would impact subsequent cell-substrate interactions. It helps explain inconsistency in the literature and guides preparation of PDMS-based biomedical devices in the future.

Probing the Surface of Platinum during the Hydrogen Evolution Reaction in Alkaline Electrolyte

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stoerzinger, Kelsey A.; Favaro, Marco; Ross, Philip N.

Understanding the surface chemistry of electrocatalysts in operando can bring insight into the reaction mechanism, and ultimately the design of more efficient materials for sustainable energy storage and conversion. Recent progress in synchrotron based X-ray spectroscopies for in operando characterization allows us to probe the solid/liquid interface directly while applying an external potential, applied here to the model system of Pt in alkaline electrolyte for the hydrogen evolution reaction (HER). We employ ambient pressure X-ray photoelectron spectroscopy (AP-XPS) to identify the oxidation and reduction of Pt-oxides and hydroxides on the surface as a function of applied potential, and further assessmore » the potential for hydrogen adsorption and absorption (hydride formation) during and after the HER. This new window into the surface chemistry of Pt in alkaline brings insight into the nature of the rate limiting step, the extent of H ad/absorption and it’s persistence at more anodic potentials.« less

Radical Rearrangement Chemistry in Ultraviolet Photodissociation of Iodotyrosine Systems: Insights from Metastable Dissociation, Infrared Ion Spectroscopy, and Reaction Pathway Calculations.

PubMed

Ranka, Karnamohit; Zhao, Ning; Yu, Long; Stanton, John F; Polfer, Nicolas C

2018-05-29

We report on the ultraviolet photodissociation (UVPD) chemistry of protonated tyrosine, iodotyrosine, and diiodotyrosine. Distonic loss of the iodine creates a high-energy radical at the aromatic ring that engages in hydrogen/proton rearrangement chemistry. Based on UVPD kinetics measurements, the appearance of this radical is coincident with the UV irradiation pulse (8 ns). Conversely, sequential UVPD product ions exhibit metastable decay on ca. 100 ns timescales. Infrared ion spectroscopy is capable of confirming putative structures of the rearrangement products as proton transfers from the imine and β-carbon hydrogens. Potential energy surfaces for the various reaction pathways indicate that the rearrangement chemistry is highly complex, compatible with a cascade of rearrangements, and that there is no preferred rearrangement pathway even in small molecular systems like these. Graphical Abstract.

"Turn-on" fluorescence detection of lead ions based on accelerated leaching of gold nanoparticles on the surface of graphene.

PubMed

Fu, Xiuli; Lou, Tingting; Chen, Zhaopeng; Lin, Meng; Feng, Weiwei; Chen, Lingxin

2012-02-01

A novel platform for effective "turn-on" fluorescence sensing of lead ions (Pb(2+)) in aqueous solution was developed based on gold nanoparticle (AuNP)-functionalized graphene. The AuNP-functionalized graphene exhibited minimal background fluorescence because of the extraordinarily high quenching ability of AuNPs. Interestingly, the AuNP-functionalized graphene underwent fluorescence restoration as well as significant enhancement upon adding Pb(2+), which was attributed to the fact that Pb(2+) could accelerate the leaching rate of the AuNPs on graphene surfaces in the presence of both thiosulfate (S(2)O(3)(2-)) and 2-mercaptoethanol (2-ME). Consequently, this could be utilized as the basis for selective detection of Pb(2+). With the optimum conditions chosen, the relative fluorescence intensity showed good linearity versus logarithm concentration of Pb(2+) in the range of 50-1000 nM (R = 0.9982), and a detection limit of 10 nM. High selectivity over common coexistent metal ions was also demonstrated. The practical application had been carried out for determination of Pb(2+) in tap water and mineral water samples. The Pb(2+)-specific "turn-on" fluorescence sensor, based on Pb(2+) accelerated leaching of AuNPs on the surface of graphene, provided new opportunities for highly sensitive and selective Pb(2+) detection in aqueous media.

Kinetic analyses and performance of a colloidal magnetic nanoparticle based immunoassay dedicated to allergy diagnosis.

PubMed

Teste, Bruno; Kanoufi, Frédéric; Descroix, Stéphanie; Poncet, Pascal; Georgelin, Thomas; Siaugue, Jean-Michel; Petr, Jan; Varenne, Anne; Hennion, Marie-Claire

2011-07-01

In this paper, we demonstrate the possibility to use magnetic nanoparticles as immunosupports for allergy diagnosis. Most immunoassays used for immunosupports and clinical diagnosis are based on a heterogeneous solid-phase system and suffer from mass-transfer limitation. The nanoparticles' colloidal behavior and magnetic properties bring the advantages of homogeneous immunoassay, i.e., species diffusion, and of heterogeneous immunoassay, i.e., easy separation of the immunocomplex and free forms, as well as analyte preconcentration. We thus developed a colloidal, non-competitive, indirect immunoassay using magnetic core-shell nanoparticles (MCSNP) as immunosupports. The feasibility of such an immunoassay was first demonstrated with a model antibody and described by comparing the immunocapture kinetics using macro (standard microtiter plate), micro (microparticles) and nanosupports (MCSNP). The influence of the nanosupport properties (surface chemistry, antigen density) and of the medium (ionic strength, counter ion nature) on the immunocapture efficiency and specificity was then investigated. The performances of this original MCSNP-based immunoassay were compared with a gold standard enzyme-linked immunosorbent assay (ELISA) using a microtiter plate. The capture rate of target IgG was accelerated 200-fold and a tenfold lower limit of detection was achieved. Finally, the MCSNP-based immunoassay was successfully applied to the detection of specific IgE from milk-allergic patient's sera with a lower LOD and a good agreement (CV < 6%) with the microtiter plate, confirming the great potential of this analytical platform in the field of immunodiagnosis.

Simulation studies of DNA at the nanoscale: Interactions with proteins, polycations, and surfaces

NASA Astrophysics Data System (ADS)

Elder, Robert M.

Understanding the nanoscale interactions of DNA, a multifunctional biopolymer with sequence-dependent properties, with other biological and synthetic substrates and molecules is essential to advancing these technologies. This doctoral thesis research is aimed at understanding the thermodynamics and molecular-level structure when DNA interacts with proteins, polycations, and functionalized surfaces. First, we investigate the ability of a DNA damage recognition protein (HMGB1a) to bind to anti-cancer drug-induced DNA damage, seeking to explain how HMGB1a differentiates between the drugs in vivo. Using atomistic molecular dynamics simulations, we show that the structure of the drug-DNA molecule exhibits drug- and base sequence-dependence that explains some of the experimentally observed differential recognition of the drugs in various sequence contexts. Then, we show how steric hindrance from the drug decreases the deformability of the drug-DNA molecule, which decreases recognition by the protein, a concept that can be applied to rational drug design. Second, we study how polycation architecture and chemistry affect polycation-DNA binding so as to design optimal polycations for high efficiency gene (DNA) delivery. Using a multiscale computational approach involving atomistic and coarse-grained simulations, we examine how rearranging polylysine from a linear to a grafted architecture, and several aspects of the grafted architecture, affect polycation-DNA binding and the structure of polycation-DNA complexes. Next, going beyond lysine we examine how oligopeptide chemistry and sequence in the grafted architecture affects polycation-DNA binding and find that strategic placement of hydrophobic peptides might be used to tailor binding strength. Third, we study the adsorption and conformations of single-stranded DNA (an amphiphilic biopolymer) on model hydrophilic and hydrophobic surfaces. Short ssDNA oligomers adsorb to both surfaces with similar strength, with the strength of adsorption to the hydrophobic surface depending on the composition of the DNA strands, i.e. purine or pyrimidine bases. Additionally, DNA-surface and DNA-water interactions near the surfaces govern the adsorption. For longer ssDNA oligomers, the effects of surface chemistry and temperature on ssDNA conformations are rather small, but either the hydrophilic surface or increased temperature favor slightly more compact conformations due to energetic and entropic effects, respectively.

Influence of matrix and filler fraction on biofilm formation on the surface of experimental resin-based composites.

PubMed

Ionescu, Andrei; Brambilla, Eugenio; Wastl, Daniel S; Giessibl, Franz J; Cazzaniga, Gloria; Schneider-Feyrer, Sibylle; Hahnel, Sebastian

2015-01-01

The aim of this study was to investigate the impact of resin matrix chemistry and filler fraction on biofilm formation on the surface of experimental resin-based composites (RBCs). Specimens were prepared from eight experimental RBC formulations differing in resin matrix blend (BisGMA/TEGDMA in a 7:3 wt% ratio or UDMA/aliphatic dimethacrylate in a 1:1 wt% ratio) and filler fraction (no fillers; 65 wt% dental glass with an average diameter of 7 or 0.7 µm or 65 wt% SiO2 with an average diameter of 20 nm). Surface roughness, surface free energy, and chemical surface composition were determined; surface topography was visualized using atomic force microscopy. Biofilm formation was simulated under continuous flow conditions for a 48 h period using a monospecies Streptococcus mutans and a multispecies biofilm model. In the monospecies biofilm model, the impact of the filler fraction overruled the influence of the resin matrix, indicating lowest biofilm formation on RBCs with nano-scaled filler particles and those manufactured from the neat resin blends. The multispecies model suggested a more pronounced effect of the resin matrix blend, as significantly higher biofilm formation was identified on RBCs with a UDMA/dimethacrylate matrix blend than on those including a BisGMA/TEGDMA matrix blend but analogous filler fractions. Although significant differences in surface properties between the various materials were identified, correlations between the surface properties and biofilm formation were poor, which highlights the relevance of surface topography and chemistry. These results may help to tailor novel RBC formulations which feature reduced biofilm formation on their surface.

Role of Viscous Dissipative Processes on the Wetting of Textured Surfaces

PubMed Central

Grewal, H. S.; Nam Kim, Hong; Cho, Il-Joo; Yoon, Eui-Sung

2015-01-01

We investigate the role of viscous forces on the wetting of hydrophobic, semi-hydrophobic, and hydrophilic textured surfaces as second-order effects. We show that during the initial contact, the transition from inertia- to viscous-dominant regime occurs regardless of their surface topography and chemistry. Furthermore, we demonstrate the effect of viscosity on the apparent contact angle under quasi-static conditions by modulating the ratio of a water/glycerol mixture and show the effect of viscosity, especially on the semi-hydrophobic and hydrophobic textured substrates. The reason why the viscous force does not affect the apparent contact angle of the hydrophilic surface is explained based on the relationship between the disjoining pressure and surface chemistry. We further propose a wetting model that can predict the apparent contact angle of a liquid drop on a textured substrate by incorporating a viscous force component in the force balance equation. This model can predict apparent contact angles on semi-hydrophobic and hydrophobic textured surfaces exhibiting Wenzel state more accurately than the Wenzel model, indicating the importance of viscous forces in determining the apparent contact angle. The modified model can be applied for estimating the wetting properties of arbitrary engineered surfaces. PMID:26390958

Adsorption of dyes by ACs prepared from waste tyre reinforcing fibre. Effect of texture, surface chemistry and pH.

PubMed

Acevedo, Beatriz; Rocha, Raquel P; Pereira, Manuel F R; Figueiredo, José L; Barriocanal, Carmen

2015-12-01

This paper compares the importance of the texture and surface chemistry of waste tyre activated carbons in the adsorption of commercial dyes. The adsorption of two commercial dyes, Basic Astrazon Yellow 7GLL and Reactive Rifafix Red 3BN on activated carbons made up of reinforcing fibres from tyre waste and low-rank bituminous coal was studied. The surface chemistry of activated carbons was modified by means of HCl-HNO3 treatment in order to increase the number of functional groups. Moreover, the influence of the pH on the process was also studied, this factor being of great importance due to the amphoteric characteristics of activated carbons. The activated carbons made with reinforcing fibre and coal had the highest SBET, but the reinforcing fibre activated carbon samples had the highest mesopore volume. The texture of the activated carbons was not modified upon acid oxidation treatment, unlike their surface chemistry which underwent considerable modification. The activated carbons made with a mixture of reinforcing fibre and coal experienced the largest degree of oxidation, and so had more acid surface groups. The adsorption of reactive dye was governed by the mesoporous volume, whilst surface chemistry played only a secondary role. However, the surface chemistry of the activated carbons and dispersive interactions played a key role in the adsorption of the basic dye. The adsorption of the reactive dye was more favored in a solution of pH 2, whereas the basic dye was adsorbed more easily in a solution of pH 12. Copyright © 2015 Elsevier Inc. All rights reserved.

Influence of EDC/NHS coupling chemistry on stability and cytotoxicity of ZnO nanoparticles modified with proteins

NASA Astrophysics Data System (ADS)

Keleştemur, Seda; Altunbek, Mine; Culha, Mustafa

2017-05-01

The toxicity of ZnO nanoparticles (NPs) is a growing concern due to its increasing use in several products including sunscreens, paints, pigments and ceramics for its antibacterial, antifungal, anti-corrosive and UV filtering properties. The toxicity of ZnO NPs is mostly attributed to the Zn2+ release causing an increase in the intracellular reactive oxygen species (ROS) level. The surface modification with a biocompatible ligand or a polymer can be a good strategy to reduce dissolution based toxicity. In two previous studies, the conflicting results with EDC/NHS coupling chemistry for ZnO NPs were reported. In this study, the same surface modification strategy with an emphasis on the stability of ZnO NPs is clarified. First, the density of -OH groups on the ZnO NPs is increased with hydrogen peroxide (H2O2) treatment, and then a silica coating on the ZnO NPs (Si-ZnO) surface is performed. Finally, a covalent attachment of bovine serum albumin (BSA) on three different concentrations of ZnO-Si is carried out by EDC/NHS coupling chemistry. ZnO NPs have a very high dissolution rate under acidic conditions of EDC/NHS coupling chemistry as determined from the ICP-MS analysis. In addition, the amount of ZnO NPs in coupling reaction has an important effect on the dissolution rate of Zn2+ and dependently BSA attached on the ZnO NP surfaces. Finally, the cytotoxicity of the BSA modified Si-ZnO NPs on human lung cancer (A549) and human skin fibroblast (HSF) is evaluated. Although an increased association of BSA modified ZnO NPs with cells was observed, the modification significantly decreased their cytotoxicity. This can be explained with the decreased active surface area of ZnO NPs with the surface modification. However, an increase in the mitochondrial depolarization and ROS production was observed depending on the amount of BSA coverage.

Phage as a Genetically Modifiable Supramacromolecule in Chemistry, Materials and Medicine.

PubMed

Cao, Binrui; Yang, Mingying; Mao, Chuanbin

2016-06-21

Filamentous bacteriophage (phage) is a genetically modifiable supramacromolecule. It can be pictured as a semiflexible nanofiber (∼900 nm long and ∼8 nm wide) made of a DNA core and a protein shell with the former genetically encoding the latter. Although phage bioengineering and phage display techniques were developed before the 1990s, these techniques have not been widely used for chemistry, materials, and biomedical research from the perspective of supramolecular chemistry until recently. Powered by our expertise in displaying a foreign peptide on its surface through engineering phage DNA, we have employed phage to identify target-specific peptides, construct novel organic-inorganic nanohybrids, develop biomaterials for disease treatment, and generate bioanalytical methods for disease diagnosis. Compared with conventional biomimetic chemistry, phage-based supramolecular chemistry represents a new frontier in chemistry, materials science, and medicine. In this Account, we introduce our recent successful efforts in phage-based supramolecular chemistry, by integrating the unique nanofiber-like phage structure and powerful peptide display techniques into the fields of chemistry, materials science, and medicine: (1) successfully synthesized and assembled silica, hydroxyapatite, and gold nanoparticles using phage templates to form novel functional materials; (2) chemically introduced azo units onto the phage to form photoresponsive functional azo-phage nanofibers via a diazotization reaction between aromatic amino groups and the tyrosine residues genetically displayed on phage surfaces; (3) assembled phage into 2D films for studying the effects of both biochemical (the peptide sequences displayed on the phages) and biophysical (the topographies of the phage films) cues on the proliferation and differentiation of mesenchymal stem cells (MSCs) and induced pluripotent stem cells (iPSCs) and identified peptides and topographies that can induce their osteogenic differentiation; (4) discovered that phage could induce angiogenesis and osteogenesis for MSC-based vascularized bone regeneration; (5) identified novel breast cancer cell-targeting and MSC-targeting peptides and used them to significantly improve the efficiency of targeted cancer therapy and MSC-based gene delivery, respectively; (6) employed engineered phage as a probe to achieve ultrasensitive detection of biomarkers from serum of human patients for disease diagnosis; and (7) constructed centimeter-scale 3D multilayered phage assemblies with the potential application as scaffolds for bone regeneration and functional device fabrication. Our findings demonstrated that phage is indeed a very powerful supramacromolecule suitable for not only developing novel nanostructures and biomaterials but also advancing important fields in biomedicine, including molecular targeting, cancer diagnosis and treatment, drug and gene delivery, stem cell fate direction, and tissue regeneration. Our successes in exploiting phage in chemistry, materials, and medicine suggest that phage itself is nontoxic at the cell level and can be safely used for detecting biomarkers in vitro. Moreover, although we have demonstrated successful in vivo tissue regeneration induced by phage, we believe future studies are needed to evaluate the in vivo biodistribution and potential risks of the phage-based biomaterials.

Phage as a Genetically Modifiable Supramacromolecule in Chemistry, Materials and Medicine

PubMed Central

Cao, Binrui; Yang, Mingying; Mao, Chuanbin

2016-01-01

CONSPECTUS Filamentous bacteriophage (phage) is a genetically modifiable supramacromolecule. It can be pictured as a semiflexible nanofiber (~900 nm long and ~8 nm wide) made of a DNA core and a protein shell with the former genetically encoding the latter. Although phage bioengineering and phage display techniques were developed before the 1990s, these techniques have not been widely used for chemistry, materials, and biomedical research from the perspective of supramolecular chemistry until recently. Powered by our expertise in displaying a foreign peptide on its surface through engineering phage DNA, we have employed phage to identify target-specific peptides, construct novel organic–inorganic nanohybrids, develop biomaterials for disease treatment, and generate bioanalytical methods for disease diagnosis. Compared with conventional biomimetic chemistry, phage-based supramolecular chemistry represents a new frontier in chemistry, materials science, and medicine. In this Account, we introduce our recent successful efforts in phage-based supramolecular chemistry, by integrating the unique nanofiber-like phage structure and powerful peptide display techniques into the fields of chemistry, materials science, and medicine: (1) successfully synthesized and assembled silica, hydroxyapatite, and gold nanoparticles using phage templates to form novel functional materials; (2) chemically introduced azo units onto the phage to form photoresponsive functional azo-phage nanofibers via a diazotization reaction between aromatic amino groups and the tyrosine residues genetically displayed on phage surfaces; (3) assembled phage into 2D films for studying the effects of both biochemical (the peptide sequences displayed on the phages) and biophysical (the topographies of the phage films) cues on the proliferation and differentiation of mesenchymal stem cells (MSCs) and induced pluripotent stem cells (iPSCs) and identified peptides and topographies that can induce their osteogenic differentiation; (4) discovered that phage could induce angiogenesis and osteogenesis for MSC-based vascularized bone regeneration; (5) identified novel breast cancer cell-targeting and MSC-targeting peptides and used them to significantly improve the efficiency of targeted cancer therapy and MSC-based gene delivery, respectively; (6) employed engineered phage as a probe to achieve ultrasensitive detection of biomarkers from serum of human patients for disease diagnosis; and (7) constructed centimeter-scale 3D multilayered phage assemblies with the potential application as scaffolds for bone regeneration and functional device fabrication. Our findings demonstrated that phage is indeed a very powerful supramacromolecule suitable for not only developing novel nanostructures and biomaterials but also advancing important fields in biomedicine, including molecular targeting, cancer diagnosis and treatment, drug and gene delivery, stem cell fate direction, and tissue regeneration. Our successes in exploiting phage in chemistry, materials, and medicine suggest that phage itself is nontoxic at the cell level and can be safely used for detecting biomarkers in vitro. Moreover, although we have demonstrated successful in vivo tissue regeneration induced by phage, we believe future studies are needed to evaluate the in vivo biodistribution and potential risks of the phage-based biomaterials. PMID:27153341

ATR-FTIR Spectroscopy in the Undergraduate Chemistry Laboratory: Part II--A Physical Chemistry Laboratory Experiment on Surface Adsorption

ERIC Educational Resources Information Center

Schuttlefield, Jennifer D.; Larsen, Sarah C.; Grassian, Vicki H.

2008-01-01

Attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy is a useful technique for measuring the infrared spectra of solids and liquids as well as probing adsorption on particle surfaces. The use of FTIR-ATR spectroscopy in organic and inorganic chemistry laboratory courses as well as in undergraduate research was presented…

Catalase coupled gold nanoparticles: Comparison between carbodiimide and biotin-streptavidin methods

PubMed Central

Chirra, Hariharasudhan D.; Sexton, Travis; Biswal, Dipti; Hersh, Louis B.; Hilt, J. Zach

2011-01-01

The use of proteins for therapeutic applications requires the protein to maintain sufficient activity for the period of in vivo treatment. Many proteins exhibit a short half-life in vivo and, thus, require delivery systems for them to be applied as therapeutics. The relative biocompatibility and the ability to form functionalized bioconjugates via simple chemistry make gold nanoparticles excellent candidates as protein delivery systems. Herein, two protocols for coupling proteins to gold nanoparticles were compared. In the first, the strong biomolecular binding between biotin and streptavidin was used to couple catalase to the surface of gold nanoparticles. In the second protocol, the formation of an amide bond between carboxylic acid coated gold nanoparticles and free surface amines of catalase using carbodiimide chemistry was performed. The stability and kinetics of the different steps involved in these protocols were studied using UV-Visible spectroscopy, dynamic light scattering, and transmission electron microscopy. The addition of mercaptoundecanoic acid in conjugation with (N-(6-(biotinamido)hexyl)-3′-(2′-pyridyldithio)-propionamide increased the stability of biotinylated gold nanoparticles. Although the carbodiimide chemistry based bioconjugation approach exhibited a decrease in catalase activity, the carbodiimide chemistry based bioconjugation approach resulted in more active catalase per gold nanoparticle compared to that of mercaptoundecanoic acid stabilized biotinylated gold nanoparticles. Both coupling protocols resulted in gold nanoparticles loaded with active catalase. Thus, these gold nanoparticle systems and coupling protocols represent promising methods for the application of gold nanoparticles for protein delivery. PMID:21232642

Observation of the adsorption and desorption of vibrationally excited molecules on a metal surface

NASA Astrophysics Data System (ADS)

Shirhatti, Pranav R.; Rahinov, Igor; Golibrzuch, Kai; Werdecker, Jörn; Geweke, Jan; Altschäffel, Jan; Kumar, Sumit; Auerbach, Daniel J.; Bartels, Christof; Wodtke, Alec M.

2018-06-01

The most common mechanism of catalytic surface chemistry is that of Langmuir and Hinshelwood (LH). In the LH mechanism, reactants adsorb, become thermalized with the surface, and subsequently react. The measured vibrational (relaxation) lifetimes of molecules adsorbed at metal surfaces are in the range of a few picoseconds. As a consequence, vibrational promotion of LH chemistry is rarely observed, with the exception of LH reactions occurring via a molecular physisorbed intermediate. Here, we directly detect adsorption and subsequent desorption of vibrationally excited CO molecules from a Au(111) surface. Our results show that CO (v = 1) survives on a Au(111) surface for 1 × 10-10 s. Such long vibrational lifetimes for adsorbates on metal surfaces are unexpected and pose an interesting challenge to the current understanding of vibrational energy dissipation on metal surfaces. They also suggest that vibrational promotion of surface chemistry might be more common than is generally believed.

Nitrogen Oxides in the Nocturnal Boundary Layer: Chemistry of Nitrous Acid (HONO) and the Nitrate Radical (N03)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jochen Stutz

Summary Chemical processes occurring at night in the lowest part of the urban atmosphere, the so called nocturnal boundary layer (NBL), can influence the composition of the atmosphere during the night as well as the following day. They may impact the budgets of some of the most important pollutants, such as ozone and nitrogen oxides, as well as influence size and composition of particular matter. Few studies have thus far concentrated on the nocturnal chemistry of the urban NBL, most likely due to the strong influence of vertical transport and mixing, which requires the measurement of trace gas profiles insteadmore » of simple point observations. Motivated by our lack of observations and understanding of nocturnal chemistry, the focus of this project was the study of the vertical distribution of trace gases and the altitude dependence of nocturnal chemistry under polluted conditions through field observations and modeling studies. The analysis of three field experiments (TEXAQS, Houston, 2000; Phoenix Sunrise Ozone Experiment, 2001; NAPOX, Boston, 2002), two of which were performed in this project, showed that ozone concentrations typically increase with height in the lowest 150m, while NO2 typically decreases. NO3, the dominant nocturnal radical species, showed much higher concentrations in the upper part of the NBL, and was often not present at the ground. With the help of a one-dimensional chemical transport model, developed in this project, we found that the interaction of ground emissions of NOx and hydrocarbons, together with their vertical transport, is responsible for the vertical profiles. The dominant chemical reactions influencing ozone, NO2 and NO3 are the reaction of ozone and NO3 with freshly emitted NO. Sensitivity studies with our model showed that the magnitude of the trace gas gradients depend both on the emission rates and the vertical stability of the NBL. Observations and model analysis clearly show that nocturnal chemistry in urban areas is altitude dependent. Measurements at one altitude, for example at the ground, where most air quality monitoring stations are located, are not representative for the rest of the NBL. Our model also revealed that radical chemistry is, in general, altitude dependent at night. We distinguish three regions: an unreactive, NO rich, ground layer; an upper, O3 and NO3 dominated layer, and a reactive mixing layer, where RO2 radicals are mixed from aloft with NO from the ground. In this reactive layer an active radical chemistry and elevated OH radical levels can be found. The downward transport of N2O5 and HO2NO2, followed by their thermal decay, was also identified as a radical source in this layer. Our observations also gave insight into the formation of HONO in the NBL. Based on our field experiments we were able to show that the NO2 to HONO conversion was relative humidity dependent. While this fact was well known, we found that it is most likely the uptake of HONO onto surfaces which is R.H. dependent, rather than the NO2 to HONO conversion. This finding led to the proposal of a new NO2 to HONO conversion mechanism, which is based on solid physical chemical principles. Noteworthy is also the observation of enhanced NO2 to HONO conversion during a dust storm event in Phoenix. The final activity in our project investigated the influence of the urban canopy, i.e. building walls and surfaces, on nocturnal chemistry. For the first time the surface area of a city was determined based on a Geographical Information System database of the city of Santa Monica. The surface to volume areas found in this study showed that, in the 2 lower part of the NBL, buildings provide a much larger surface area than the aerosol. In addition, buildings take up a considerable amount of the volume near the ground. The expansion of our model and sensitivity studies based on the Santa Monica data revealed that the surface area of buildings considerably influences HONO levels in urban areas. The volume reduction leads to a decrease of O3 and an increase of NO2 near the ground due to the stronger impact of NO emissions. Our project shows that the urban canopy should be included in future air quality models to better represent nocturnal chemistry. This project has considerably advanced our understanding of the chemistry of the urban nocturnal boundary layer. The results of this project have implications for air quality studies in the urban nocturnal boundary layer. The study has also identified new questions on nocturnal processes, which we will continue to address through other projects.« less

The effect of autoclave resterilisation on polyester vascular grafts.

PubMed

Riepe, G; Whiteley, M S; Wente, A; Rogge, A; Schröder, A; Galland, R B; Imig, H

1999-11-01

polyester grafts are expensive, single-use items. Some manufacturers of uncoated, woven grafts include instructions for autoclave resterilisation to be performed at the surgeon's own request. Others warn against such manipulation. Theoretically, the glass transition point of polyester at 70-80 degrees C and the possible acceleration of hydrolysis suggest that autoclave resterilisation at 135 degrees C might be a problem. a DeBakey Soft Woven Dacron Vascular Prosthesis (Bard) and a Woven Double Velour Dacron Graft (Meadox) were autoclave-resterilised 0 to 20 times, having been weighed before and after sterilisation. Tactile testing was performed. Mechanical properties were examined by probe puncture and single-filament testing, the surface was examined by scanning electron microscopy and the degree of hydrolysis by infra-red spectroscopy. tactile testing revealed a change of feeling with increasing cycles of resterilisation. Investigation of weight, textile strength, single-filament strength, electron microscopy of the surface and infra-red spectroscopy showed no change of the material. changes felt are presumably a surface phenomenon, not measurably affecting strength or chemistry of material after autoclave resterilisation. We therefore feel that it is safe to use once-autoclave-resterilised surplus uncoated polyester grafts, provided that sterility is guaranteed. Copyright 1999 Harcourt Publishers Ltd.

Computer Series, 115.

ERIC Educational Resources Information Center

Birk, James P., Ed.

1990-01-01

Reviewed are six computer programs which may be useful in teaching college level chemistry. Topics include dynamic data storage in FORTRAN, "KC?DISCOVERER," pH of acids and bases, calculating percent boundary surfaces for orbitals, and laboratory interfacing with PT Nomograph for the Macintosh. (CW)

Effects of surface chemistry on hot corrosion life

NASA Technical Reports Server (NTRS)

Fryxell, R. E.; Gupta, B. K.

1984-01-01

Hot corrosion life prediction methodology based on a combination of laboratory test data and field service turbine components, which show evidence of hot corrosion, were examined. Components were evaluated by optical metallography, scanning electron microscopy (SEM), and electron micropulse (EMP) examination.

[60]Fullerene-based monolayers as neuroprotective biocompatible hybrid materials.

PubMed

Giust, Davide; Albasanz, José Luis; Martín, Mairena; Marega, Riccardo; Delforge, Arnaud; Bonifazi, Davide

2011-10-14

Here we report on the surface immobilization of redox-active [60]fullerene derivatives and the consequent neuroprotective effects toward l-glutamate induced excitotoxicity in human derived undifferentiated neuroblastoma cells. This journal is © The Royal Society of Chemistry 2011

Rapid in situ generation of two patterned chemoselective surface chemistries from a single hydroxy-terminated surface using controlled microfluidic oxidation.

PubMed

Pulsipher, Abigail; Westcott, Nathan P; Luo, Wei; Yousaf, Muhammad N

2009-06-10

In this work, we develop a new, rapid and inexpensive method to generate spatially controlled aldehyde and carboxylic acid surface groups by microfluidic oxidation of 11-hydroxyundecylphosphonic acid self-assembled monolayers (SAMs) on indium tin oxide (ITO) surfaces. SAMs are activated and patterned using a reversibly sealable, elastomeric polydimethylsiloxane cassette, fabricated with preformed micropatterns by soft lithography. By flowing the mild oxidant pyridinium chlorochromate through the microchannels, only selected areas of the SAM are chemically altered. This microfluidic oxidation strategy allows for ligand immobilization by two chemistries originating from a single SAM composition. ITO is robust, conductive, and transparent, making it an ideal platform for studying interfacial interactions. We display spatial control over the immobilization of a variety of ligands on ITO and characterize the resulting oxime and amide linkages by electrochemistry, X-ray photoelectron spectroscopy, contact angle, fluorescence microscopy, and atomic force microscopy. This general method may be used with many other materials to rapidly generate patterned and tailored surfaces for studies ranging from molecular electronics to biospecific cell-based assays and biomolecular microarrays.

Accelerator boom hones China's engineering expertise

NASA Astrophysics Data System (ADS)

Normile, Dennis

2018-02-01

In raising the curtain on the China Spallation Neutron Source, China has joined just four other nations in having mastered the technology of accelerating and controlling beams of protons. The $277 million facility, set to open to users this spring in Dongguan, is expected to yield big dividends in materials science, chemistry, and biology. More world class machines are on the way, as China this year starts construction on four other major accelerator facilities. The building boom is prompting a scramble to find enough engineers and technicians to finish the projects. But if they all come off as planned, the facilities would position China to tackle the next global megaproject: a giant accelerator that would pick up where Europe's Large Hadron Collider leaves off.

Wear and Damage of Articular Cartilage with Friction Against Orthopaedic Implant Materials

PubMed Central

Oungoulian, Sevan R.; Durney, Krista M.; Jones, Brian K.; Ahmad, Christopher S.; Hung, Clark T.; Ateshian, Gerard A.

2015-01-01

The objective of this study was to measure the wear response of immature bovine articular cartilage tested against glass or alloys used in hemiarthroplasties. Two cobalt chromium alloys and a stainless steel alloy were selected for these investigations. The surface roughness of one of the cobalt chromium alloys was also varied within the range considered acceptable by regulatory agencies. Cartilage disks were tested in a configuration that promoted loss of interstitial fluid pressurization to accelerate conditions believed to occur in hemiarthroplasties. Results showed that considerably more damage occurred in cartilage samples tested against stainless steel (10 nm roughness) and low carbon cobalt chromium alloy (27 nm roughness) compared to glass (10 nm) and smoother low or high carbon cobalt chromium (10 nm). The two materials producing the greatest damage also exhibited higher equilibrium friction coefficients. Cartilage damage occurred primarily in the form of delamination at the interface between the superficial tangential zone and the transitional middle zone, with much less evidence of abrasive wear at the articular surface. These results suggest that cartilage damage from frictional loading occurs as a result of subsurface fatigue failure leading to the delamination. Surface chemistry and surface roughness of implant materials can have a significant influence on tissue damage, even when using materials and roughness values that satisfy regulatory requirements. PMID:25912663

Microfluidic Platform for High-throughput Screening of Leach Chemistry.

PubMed

Yang, Die; Priest, Craig

2018-06-20

We demonstrate an optofluidic screening platform for studying thiosulfate leaching of Au in a transparent microchannel. The approach permits in situ (optical) monitoring of Au thickness, reduced reagent use, rapid optimization of reagent chem-istry, screening of temperature, and determination of the activation energy. The results demonstrate the critical importance of the (1) preparation and storage of the leach solution, (2) deposition and annealing of the Au film, and (3) lixiviant chem-istry. The density of sputter deposited Au films decreased with depth resulting in accelerating leach rates during experiments. Atomic leach rates were determined and were constant throughout each experiment. Annealing above 270 °C was found to prevent leaching, which can be attributed to diffusion of the chromium adhesion layer into the Au film. The optofluidic analysis revealed leach rates that are sensitive to the stoichiometric ratio of thiosulphate, ammonia and copper in the leach solution, and optimized for 10 mM CuSO 4 , 1 M Na 2 S 2 O 3 and 1 M NH 4 OH. The temperature dependence of the leach rate gave an apparent activation energy of ~ 40 kJ.mol -1 , based on Arrhenius' relationship.

Sphagnum establishment in alkaline fens: Importance of weather and water chemistry.

PubMed

Vicherová, Eliška; Hájek, Michal; Šmilauer, Petr; Hájek, Tomáš

2017-02-15

Sphagnum expansion to alkaline fens has accelerated during the last decades in Europe, leading to changes in diversity, habitat distributions and carbon storage. The causes are still not clearly understood and involve an interplay between climate change, hydrology, nutrient supply and Sphagnum physiology. We conducted a 4-year field experiment in eight fens in Central European highlands and assessed survival and establishment of individual apical shoot fragments of S. flexuosum, S. warnstorfii and S. squarrosum transplanted along the microtopographical gradient. In a laboratory experiment, we tested combined effects of desiccation and high calcium bicarbonate concentration on Sphagnum survival. We found that in unflooded positions, living shoots of Sphagnum and brown mosses lowered [Ca 2+ ] and pH in their capillary water, in contrast to dead fragments; yet without differences between species. Survival and expansion of Sphagnum fragments, which did not die of acute calcium toxicity during first weeks/months, was negatively affected by dry weather and alkaline water chemistry, reflecting Sphagnum intolerance to desiccation and to combined high [Ca 2+ ] and pH. Shoot fragments expanded to patches only when precipitation was high. Interestingly, non-toxic concentration of calcium bicarbonate reduced desiccation damage in Sphagnum, probably through protection of membranes or other cell components. This mechanism would facilitate Sphagnum survival in elevated, frequently desiccated microhabitats of calcareous fens such as brown-moss hummocks. However, since water-retaining capacity of few Sphagnum shoots is insufficient to change water chemistry in its surroundings, surface acidification may occur only once the environment (e.g. sufficient humidity) enabled expansion to larger mats. Then, the retained rainwater together with hardly decomposable Sphagnum litter would separate mire surface from groundwater, speeding up successional shift towards poor fens. Sphagnum expansion to alkaline fens is therefore more likely in humid regions. Copyright © 2016 Elsevier B.V. All rights reserved.

Dust evolution, a global view: III. Core/mantle grains, organic nano-globules, comets and surface chemistry

NASA Astrophysics Data System (ADS)

Jones, A. P.

2016-12-01

Within the framework of The Heterogeneous dust Evolution Model for Interstellar Solids (THEMIS), this work explores the surface processes and chemistry relating to core/mantle interstellar and cometary grain structures and their influence on the nature of these fascinating particles. It appears that a realistic consideration of the nature and chemical reactivity of interstellar grain surfaces could self-consistently and within a coherent framework explain: the anomalous oxygen depletion, the nature of the CO dark gas, the formation of `polar ice' mantles, the red wing on the 3 μm water ice band, the basis for the O-rich chemistry observed in hot cores, the origin of organic nano-globules and the 3.2 μm `carbonyl' absorption band observed in comet reflectance spectra. It is proposed that the reaction of gas phase species with carbonaceous a-C(:H) grain surfaces in the interstellar medium, in particular the incorporation of atomic oxygen into grain surfaces in epoxide functional groups, is the key to explaining these observations. Thus, the chemistry of cosmic dust is much more intimately related with that of the interstellar gas than has previously been considered. The current models for interstellar gas and dust chemistry will therefore most likely need to be fundamentally modified to include these new grain surface processes.

Polymorphism and electronic structure of polyimine and its potential significance for prebiotic chemistry on Titan

NASA Astrophysics Data System (ADS)

Rahm, Martin; Lunine, Jonathan I.; Usher, David A.; Shalloway, David

2016-07-01

The chemistry of hydrogen cyanide (HCN) is believed to be central to the origin of life question. Contradictions between Cassini-Huygens mission measurements of the atmosphere and the surface of Saturn’s moon Titan suggest that HCN-based polymers may have formed on the surface from products of atmospheric chemistry. This makes Titan a valuable “natural laboratory” for exploring potential nonterrestrial forms of prebiotic chemistry. We have used theoretical calculations to investigate the chain conformations of polyimine (pI), a polymer identified as one major component of polymerized HCN in laboratory experiments. Thanks to its flexible backbone, the polymer can exist in several different polymorphs, which are relatively close in energy. The electronic and structural variability among them is extraordinary. The band gap changes over a 3-eV range when moving from a planar sheet-like structure to increasingly coiled conformations. The primary photon absorption is predicted to occur in a window of relative transparency in Titan’s atmosphere, indicating that pI could be photochemically active and drive chemistry on the surface. The thermodynamics for adding and removing HCN from pI under Titan conditions suggests that such dynamics is plausible, provided that catalysis or photochemistry is available to sufficiently lower reaction barriers. We speculate that the directionality of pI’s intermolecular and intramolecular =N-H…N hydrogen bonds may drive the formation of partially ordered structures, some of which may synergize with photon absorption and act catalytically. Future detailed studies on proposed mechanisms and the solubility and density of the polymers will aid in the design of future missions to Titan.

Polymorphism and electronic structure of polyimine and its potential significance for prebiotic chemistry on Titan

PubMed Central

Rahm, Martin; Lunine, Jonathan I.; Usher, David A.; Shalloway, David

2016-01-01

The chemistry of hydrogen cyanide (HCN) is believed to be central to the origin of life question. Contradictions between Cassini–Huygens mission measurements of the atmosphere and the surface of Saturn’s moon Titan suggest that HCN-based polymers may have formed on the surface from products of atmospheric chemistry. This makes Titan a valuable “natural laboratory” for exploring potential nonterrestrial forms of prebiotic chemistry. We have used theoretical calculations to investigate the chain conformations of polyimine (pI), a polymer identified as one major component of polymerized HCN in laboratory experiments. Thanks to its flexible backbone, the polymer can exist in several different polymorphs, which are relatively close in energy. The electronic and structural variability among them is extraordinary. The band gap changes over a 3-eV range when moving from a planar sheet-like structure to increasingly coiled conformations. The primary photon absorption is predicted to occur in a window of relative transparency in Titan’s atmosphere, indicating that pI could be photochemically active and drive chemistry on the surface. The thermodynamics for adding and removing HCN from pI under Titan conditions suggests that such dynamics is plausible, provided that catalysis or photochemistry is available to sufficiently lower reaction barriers. We speculate that the directionality of pI’s intermolecular and intramolecular =N–H…N hydrogen bonds may drive the formation of partially ordered structures, some of which may synergize with photon absorption and act catalytically. Future detailed studies on proposed mechanisms and the solubility and density of the polymers will aid in the design of future missions to Titan. PMID:27382167

Metal-composite adhesion based on diazonium chemistry.

PubMed

Oweis, Yara; Alageel, Omar; Kozak, Paige; Abdallah, Mohamed-Nur; Retrouvey, Jean-Marc; Cerruti, Marta; Tamimi, Faleh

2017-11-01

Composite resins do not adhere well to dental alloys. This weak bond can result in failure at the composite-metal interface in fixed dental prostheses and orthodontic brackets. The aim of this study was to develop a new adhesive, based on diazonium chemistry, to facilitate chemical bonding between dental alloys and composite resin. Samples of two types of dental alloys, stainless steel and cobalt chromium were primed with a diazonium layer in order to create a surface coating favorable for composite adhesion. Untreated metal samples served as controls. The surface chemical composition of the treated and untreated samples was analyzed by X-ray photoelectron spectroscopy (XPS) and the tensile strength of the bond with composite resin was measured. The diazonium adhesive was also tested for shear bond strength between stainless steel orthodontic brackets and teeth. XPS confirmed the presence of a diazonium coating on the treated metals. The coating significantly increased the tensile and shear bond strengths by three and four folds respectively between the treated alloys and composite resin. diazonium chemistry can be used to develop composite adhesives for dental alloys. Diazonium adhesion can effectively achieve a strong chemical bond between dental alloys and composite resin. This technology can be used for composite repair of fractured crowns, for crown cementation with resin based cements, and for bracket bonding. Copyright © 2017 The Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

Continuous Wavelet Transform Analysis of Acceleration Signals Measured from a Wave Buoy

PubMed Central

Chuang, Laurence Zsu-Hsin; Wu, Li-Chung; Wang, Jong-Hao

2013-01-01

Accelerometers, which can be installed inside a floating platform on the sea, are among the most commonly used sensors for operational ocean wave measurements. To examine the non-stationary features of ocean waves, this study was conducted to derive a wavelet spectrum of ocean waves and to synthesize sea surface elevations from vertical acceleration signals of a wave buoy through the continuous wavelet transform theory. The short-time wave features can be revealed by simultaneously examining the wavelet spectrum and the synthetic sea surface elevations. The in situ wave signals were applied to verify the practicality of the wavelet-based algorithm. We confirm that the spectral leakage and the noise at very-low-frequency bins influenced the accuracies of the estimated wavelet spectrum and the synthetic sea surface elevations. The appropriate thresholds of these two factors were explored. To study the short-time wave features from the wave records, the acceleration signals recorded from an accelerometer inside a discus wave buoy are analysed. The results from the wavelet spectrum show the evidence of short-time nonlinear wave events. Our study also reveals that more surface profiles with higher vertical asymmetry can be found from short-time nonlinear wave with stronger harmonic spectral peak. Finally, we conclude that the algorithms of continuous wavelet transform are practical for revealing the short-time wave features of the buoy acceleration signals. PMID:23966188

Improvements to the WRF-Chem 3.5.1 model for quasi-hemispheric simulations of aerosols and ozone in the Arctic

DOE PAGES

Marelle, Louis; Raut, Jean-Christophe; Law, Kathy S.; ...

2017-01-01

In this study, the WRF-Chem regional model is updated to improve simulated short-lived pollutants (e.g., aerosols, ozone) in the Arctic. Specifically, we include in WRF-Chem 3.5.1 (with SAPRC-99 gas-phase chemistry and MOSAIC aerosols) (1) a correction to the sedimentation of aerosols, (2) dimethyl sulfide (DMS) oceanic emissions and gas-phase chemistry, (3) an improved representation of the dry deposition of trace gases over seasonal snow, and (4) an UV-albedo dependence on snow and ice cover for photolysis calculations. We also (5) correct the representation of surface temperatures over melting ice in the Noah Land Surface Model and (6) couple and further test the recent KF-CuP (Kain–Fritsch +more » Cumulus Potential) cumulus parameterization that includes the effect of cumulus clouds on aerosols and trace gases. The updated model is used to perform quasi-hemispheric simulations of aerosols and ozone, which are evaluated against surface measurements of black carbon (BC), sulfate, and ozone as well as airborne measurements of BC in the Arctic. The updated model shows significant improvements in terms of seasonal aerosol cycles at the surface and root mean square errors (RMSEs) for surface ozone, aerosols, and BC aloft, compared to the base version of the model and to previous large-scale evaluations of WRF-Chem in the Arctic. These improvements are mostly due to the inclusion of cumulus effects on aerosols and trace gases in KF-CuP (improved RMSE for surface BC and BC profiles, surface sulfate, and surface ozone), the improved surface temperatures over sea ice (surface ozone, BC, and sulfate), and the updated trace gas deposition and UV albedo over snow and ice (improved RMSE and correlation for surface ozone). DMS emissions and chemistry improve surface sulfate at all Arctic sites except Zeppelin, and correcting aerosol sedimentation has little influence on aerosols except in the upper troposphere.« less

Improvements to the WRF-Chem 3.5.1 model for quasi-hemispheric simulations of aerosols and ozone in the Arctic

DOE Office of Scientific and Technical Information (OSTI.GOV)

Marelle, Louis; Raut, Jean-Christophe; Law, Kathy S.

In this study, the WRF-Chem regional model is updated to improve simulated short-lived pollutants (e.g., aerosols, ozone) in the Arctic. Specifically, we include in WRF-Chem 3.5.1 (with SAPRC-99 gas-phase chemistry and MOSAIC aerosols) (1) a correction to the sedimentation of aerosols, (2) dimethyl sulfide (DMS) oceanic emissions and gas-phase chemistry, (3) an improved representation of the dry deposition of trace gases over seasonal snow, and (4) an UV-albedo dependence on snow and ice cover for photolysis calculations. We also (5) correct the representation of surface temperatures over melting ice in the Noah Land Surface Model and (6) couple and further test the recent KF-CuP (Kain–Fritsch +more » Cumulus Potential) cumulus parameterization that includes the effect of cumulus clouds on aerosols and trace gases. The updated model is used to perform quasi-hemispheric simulations of aerosols and ozone, which are evaluated against surface measurements of black carbon (BC), sulfate, and ozone as well as airborne measurements of BC in the Arctic. The updated model shows significant improvements in terms of seasonal aerosol cycles at the surface and root mean square errors (RMSEs) for surface ozone, aerosols, and BC aloft, compared to the base version of the model and to previous large-scale evaluations of WRF-Chem in the Arctic. These improvements are mostly due to the inclusion of cumulus effects on aerosols and trace gases in KF-CuP (improved RMSE for surface BC and BC profiles, surface sulfate, and surface ozone), the improved surface temperatures over sea ice (surface ozone, BC, and sulfate), and the updated trace gas deposition and UV albedo over snow and ice (improved RMSE and correlation for surface ozone). DMS emissions and chemistry improve surface sulfate at all Arctic sites except Zeppelin, and correcting aerosol sedimentation has little influence on aerosols except in the upper troposphere.« less

Improvements to the WRF-Chem 3.5.1 model for quasi-hemispheric simulations of aerosols and ozone in the Arctic

NASA Astrophysics Data System (ADS)

Marelle, Louis; Raut, Jean-Christophe; Law, Kathy S.; Berg, Larry K.; Fast, Jerome D.; Easter, Richard C.; Shrivastava, Manish; Thomas, Jennie L.

2017-10-01

In this study, the WRF-Chem regional model is updated to improve simulated short-lived pollutants (e.g., aerosols, ozone) in the Arctic. Specifically, we include in WRF-Chem 3.5.1 (with SAPRC-99 gas-phase chemistry and MOSAIC aerosols) (1) a correction to the sedimentation of aerosols, (2) dimethyl sulfide (DMS) oceanic emissions and gas-phase chemistry, (3) an improved representation of the dry deposition of trace gases over seasonal snow, and (4) an UV-albedo dependence on snow and ice cover for photolysis calculations. We also (5) correct the representation of surface temperatures over melting ice in the Noah Land Surface Model and (6) couple and further test the recent KF-CuP (Kain-Fritsch + Cumulus Potential) cumulus parameterization that includes the effect of cumulus clouds on aerosols and trace gases. The updated model is used to perform quasi-hemispheric simulations of aerosols and ozone, which are evaluated against surface measurements of black carbon (BC), sulfate, and ozone as well as airborne measurements of BC in the Arctic. The updated model shows significant improvements in terms of seasonal aerosol cycles at the surface and root mean square errors (RMSEs) for surface ozone, aerosols, and BC aloft, compared to the base version of the model and to previous large-scale evaluations of WRF-Chem in the Arctic. These improvements are mostly due to the inclusion of cumulus effects on aerosols and trace gases in KF-CuP (improved RMSE for surface BC and BC profiles, surface sulfate, and surface ozone), the improved surface temperatures over sea ice (surface ozone, BC, and sulfate), and the updated trace gas deposition and UV albedo over snow and ice (improved RMSE and correlation for surface ozone). DMS emissions and chemistry improve surface sulfate at all Arctic sites except Zeppelin, and correcting aerosol sedimentation has little influence on aerosols except in the upper troposphere.

Nanoscale silicon substrate patterns from self-assembly of cylinder forming poly(styrene)-block-poly(dimethylsiloxane) block copolymer on silane functionalized surfaces.

PubMed

Borah, Dipu; Cummins, Cian; Rasappa, Sozaraj; Watson, Scott M D; Pike, Andrew R; Horrocks, Benjamin R; Fulton, David A; Houlton, Andrew; Liontos, George; Ntetsikas, Konstantinos; Avgeropoulos, Apostolos; Morris, Michael A

2017-01-27

Poly(styrene)-block-poly(dimethylsiloxane) (PS-b-PDMS) is an excellent block copolymer (BCP) system for self-assembly and inorganic template fabrication because of its high Flory-Huggins parameter (χ ∼ 0.26) at room temperature in comparison to other BCPs, and high selective etch contrast between PS and PDMS block for nanopatterning. In this work, self-assembly in PS-b-PDMS BCP is achieved by combining hydroxyl-terminated poly(dimethylsiloxane) (PDMS-OH) brush surfaces with solvent vapor annealing. As an alternative to standard brush chemistry, we report a simple method based on the use of surfaces functionalized with silane-based self-assembled monolayers (SAMs). A solution-based approach to SAM formation was adopted in this investigation. The influence of the SAM-modified surfaces upon BCP films was compared with polymer brush-based surfaces. The cylinder forming PS-b-PDMS BCP and PDMS-OH polymer brush were synthesized by sequential living anionic polymerization. It was observed that silane SAMs provided the appropriate surface chemistry which, when combined with solvent annealing, led to microphase segregation in the BCP. It was also demonstrated that orientation of the PDMS cylinders may be controlled by judicious choice of the appropriate silane. The PDMS patterns were successfully used as an on-chip etch mask to transfer the BCP pattern to underlying silicon substrate with sub-25 nm silicon nanoscale features. This alternative SAM/BCP approach to nanopattern formation shows promising results, pertinent in the field of nanotechnology, and with much potential for application, such as in the fabrication of nanoimprint lithography stamps, nanofluidic devices or in narrow and multilevel interconnected lines.

Nanoscale silicon substrate patterns from self-assembly of cylinder forming poly(styrene)-block-poly(dimethylsiloxane) block copolymer on silane functionalized surfaces

NASA Astrophysics Data System (ADS)

Borah, Dipu; Cummins, Cian; Rasappa, Sozaraj; Watson, Scott M. D.; Pike, Andrew R.; Horrocks, Benjamin R.; Fulton, David A.; Houlton, Andrew; Liontos, George; Ntetsikas, Konstantinos; Avgeropoulos, Apostolos; Morris, Michael A.

2017-01-01

Poly(styrene)-block-poly(dimethylsiloxane) (PS-b-PDMS) is an excellent block copolymer (BCP) system for self-assembly and inorganic template fabrication because of its high Flory-Huggins parameter (χ ˜ 0.26) at room temperature in comparison to other BCPs, and high selective etch contrast between PS and PDMS block for nanopatterning. In this work, self-assembly in PS-b-PDMS BCP is achieved by combining hydroxyl-terminated poly(dimethylsiloxane) (PDMS-OH) brush surfaces with solvent vapor annealing. As an alternative to standard brush chemistry, we report a simple method based on the use of surfaces functionalized with silane-based self-assembled monolayers (SAMs). A solution-based approach to SAM formation was adopted in this investigation. The influence of the SAM-modified surfaces upon BCP films was compared with polymer brush-based surfaces. The cylinder forming PS-b-PDMS BCP and PDMS-OH polymer brush were synthesized by sequential living anionic polymerization. It was observed that silane SAMs provided the appropriate surface chemistry which, when combined with solvent annealing, led to microphase segregation in the BCP. It was also demonstrated that orientation of the PDMS cylinders may be controlled by judicious choice of the appropriate silane. The PDMS patterns were successfully used as an on-chip etch mask to transfer the BCP pattern to underlying silicon substrate with sub-25 nm silicon nanoscale features. This alternative SAM/BCP approach to nanopattern formation shows promising results, pertinent in the field of nanotechnology, and with much potential for application, such as in the fabrication of nanoimprint lithography stamps, nanofluidic devices or in narrow and multilevel interconnected lines.

Dragonfly: Investigating the Surface Composition of Titan

NASA Technical Reports Server (NTRS)

Brinckerhoff, W. B.; Lawrence, D. J.; Barnes, J. W.; Lorenz, R. D.; Horst, S. M.; Zacny, K.; Freissinet, C.; Parsons, A. M.; Turtle, E. P.; Trainer, M. G.;

Impact of ship emissions on air pollution and AOD over North Atlantic and European Arctic

NASA Astrophysics Data System (ADS)

Kaminski, Jacek W.; Struzewska, Joanna; Jefimow, Maciej; Durka, Pawel

2016-04-01

The iAREA project is combined of experimental and theoretical research in order to contribute to the new knowledge on the impact of absorbing aerosols on the climate system in the European Arctic (http://www.igf.fuw.edu.pl/iAREA). A tropospheric chemistry model GEM-AQ (Global Environmental Multiscale Air Quality) was used as a computational tool. The core of the model is based on a weather prediction model with environmental processes (chemistry and aerosols) implanted on-line and are interactive (i.e. providing feedback of chemistry on radiation and dynamics). The numerical grid covered the Euro-Atlantic region with the resolution of 50 km. Emissions developed by NILU in the ECLIPSE project was used (Klimont et al., 2013). The model was run for two 1-year scenarios. 2014 was chosen as a base year for simulations and analysis. Scenarios include a base run with most up-to-date emissions and a run without maritime emissions. The analysis will focus on the contribution of maritime emissions on levels of particulate matter and gaseous pollutants over the European Arctic, North Atlantic and coastal areas. The annual variability will be assessed based on monthly mean near-surface concentration fields. Analysis of shipping transport on near-surface air pollution over the Euro-Atlantic region will be assessed for ozone, NO2, SO2, CO, PM10, PM2.5. Also, a contribution of ship emissions to AOD will be analysed.

Titan's atmosphere and climate

NASA Astrophysics Data System (ADS)

Hörst, S. M.

2017-03-01

Titan is the only moon with a substantial atmosphere, the only other thick N2 atmosphere besides Earth's, the site of extraordinarily complex atmospheric chemistry that far surpasses any other solar system atmosphere, and the only other solar system body with stable liquid currently on its surface. The connection between Titan's surface and atmosphere is also unique in our solar system; atmospheric chemistry produces materials that are deposited on the surface and subsequently altered by surface-atmosphere interactions such as aeolian and fluvial processes resulting in the formation of extensive dune fields and expansive lakes and seas. Titan's atmosphere is favorable for organic haze formation, which combined with the presence of some oxygen-bearing molecules indicates that Titan's atmosphere may produce molecules of prebiotic interest. The combination of organics and liquid, in the form of water in a subsurface ocean and methane/ethane in the surface lakes and seas, means that Titan may be the ideal place in the solar system to test ideas about habitability, prebiotic chemistry, and the ubiquity and diversity of life in the universe. The Cassini-Huygens mission to the Saturn system has provided a wealth of new information allowing for study of Titan as a complex system. Here I review our current understanding of Titan's atmosphere and climate forged from the powerful combination of Earth-based observations, remote sensing and in situ spacecraft measurements, laboratory experiments, and models. I conclude with some of our remaining unanswered questions as the incredible era of exploration with Cassini-Huygens comes to an end.

CuAAC click chemistry accelerates the discovery of novel chemical scaffolds as promising protein tyrosine phosphatases inhibitors.

PubMed

He, X-P; Xie, J; Tang, Y; Li, J; Chen, G-R

2012-01-01

Protein tyrosine phosphatases (PTPs) are crucial regulators for numerous biological processes in nature. The dysfunction and overexpression of many PTP members have been demonstrated to cause fatal human diseases such as cancers, diabetes, obesity, neurodegenerative diseases and autoimmune disorders. In the past decade, considerable efforts have been devoted to the production of PTPs inhibitors by both academia and the pharmaceutical industry. However, there are only limited drug candidates in clinical trials and no commercial drugs have been approved, implying that further efficient discovery of novel chemical entities competent for inhibition of the specific PTP target in vivo remains yet a challenge. In light of the click-chemistry paradigm which advocates the utilization of concise and selective carbon-heteroatom ligation reactions for the modular construction of useful compound libraries, the Cu(I)-catalyzed azidealkyne 1,3-dipolar cycloaddition reaction (CuAAC) has fueled enormous energy into the modern drug discovery. Recently, this ingenious chemical ligation tool has also revealed efficacious and expeditious in establishing large combinatorial libraries for the acquisition of novel PTPs inhibitors with promising pharmacological profiles. We thus offer here a comprehensive review highlighting the development of PTPs inhibitors accelerated by the CuAAC click chemistry.

Preparation and measurement methods for studying nanoparticle aggregate surface chemistry.

PubMed

Szakal, Christopher; McCarthy, James A; Ugelow, Melissa S; Konicek, Andrew R; Louis, Kacie; Yezer, Benjamin; Herzing, Andrew A; Hamers, Robert J; Holbrook, R David

2012-07-01

Despite best efforts at controlling nanoparticle (NP) surface chemistries, the environment surrounding nanomaterials is always changing and can impart a permanent chemical memory. We present a set of preparation and measurement methods to be used as the foundation for studying the surface chemical memory of engineered NP aggregates. We attempt to bridge the gap between controlled lab studies and real-world NP samples, specifically TiO(2), by using well-characterized and consistently synthesized NPs, controllably producing NP aggregates with precision drop-on-demand inkjet printing for subsequent chemical measurements, monitoring the physical morphology of the NP aggregate depositions with scanning electron microscopy (SEM), acquiring "surface-to-bulk" mass spectra of the NP aggregate surfaces with time-of-flight secondary ion mass spectrometry (ToF-SIMS), and developing a data analysis scheme to interpret chemical signatures more accurately from thousands of data files. We present differences in mass spectral peak ratios for bare TiO(2) NPs compared to NPs mixed separately with natural organic matter (NOM) or pond water. The results suggest that subtle changes in the local environment can alter the surface chemistry of TiO(2) NPs, as monitored by Ti(+)/TiO(+) and Ti(+)/C(3)H(5)(+) peak ratios. The subtle changes in the absolute surface chemistry of NP aggregates vs. that of the subsurface are explored. It is envisioned that the methods developed herein can be adapted for monitoring the surface chemistries of a variety of engineered NPs obtained from diverse natural environments.

A General Small-Scale Reactor To Enable Standardization and Acceleration of Photocatalytic Reactions.

PubMed

Le, Chi Chip; Wismer, Michael K; Shi, Zhi-Cai; Zhang, Rui; Conway, Donald V; Li, Guoqing; Vachal, Petr; Davies, Ian W; MacMillan, David W C

2017-06-28

Photocatalysis for organic synthesis has experienced an exponential growth in the past 10 years. However, the variety of experimental procedures that have been reported to perform photon-based catalyst excitation has hampered the establishment of general protocols to convert visible light into chemical energy. To address this issue, we have designed an integrated photoreactor for enhanced photon capture and catalyst excitation. Moreover, the evaluation of this new reactor in eight photocatalytic transformations that are widely employed in medicinal chemistry settings has confirmed significant performance advantages of this optimized design while enabling a standardized protocol.

The influence of EI-21 redox ion-exchange resins on the secondary-coolant circuit water chemistry of vehicular nuclear power installations

NASA Astrophysics Data System (ADS)

Moskvin, L. N.; Rakov, V. T.

2015-06-01

The results obtained from testing the secondary-coolant circuit water chemistry of full-scale land-based prototype bench models of vehicular nuclear power installations equipped with water-cooled water-moderated and liquid-metal reactor plants are presented. The influence of copper-containing redox ionexchange resins intended for chemically deoxygenating steam condensate on the working fluid circulation loop's water chemistry is determined. The influence of redox ion-exchange resins on the water chemistry is evaluated by generalizing an array of data obtained in the course of extended monitoring using the methods relating to physicochemical analysis of the quality of condensate-feedwater path media and the methods relating to metallographic analysis of the state of a faulty steam generator's tube system surfaces. The deoxygenating effectiveness of the normal state turbine condensate vacuum deaeration system is experimentally determined. The refusal from applying redox ion-exchange resins in the condensate polishing ion-exchange filters is formulated based on the obtained data on the adverse effect of copper-containing redox ionexchange resins on the condensate-feedwater path water chemistry and based on the data testifying a sufficient effect from using the normal state turbine condensate vacuum deaeration system. Data on long-term operation of the prototype bench model of a vehicular nuclear power installation without subjecting the turbine condensate to chemical deoxygenation are presented.

Purchase of Microwave Reactors for Implementation of Small-scale Microwave-accelerated Organic Chemistry Laboratory Program in Undergraduate Curriculum and Synthetic Chemistry Research at HU

DTIC Science & Technology

2015-05-16

synthesis of iron magnetic nanoparticles is being investigated (Appendix A; Scheme IV). In the first step, precursor iron(III) chloride nanoparticles...and other methods. Currently, we are developing a two-step scheme for the synthesis of esters that will require distillation and/or column...recognize the link between them. We are developing for the above purpose, the microwave-assisted, two-step synthesis of high boiling point esters. The

Concerns of Hydrothermal Degradation in CAD/CAM Zirconia

PubMed Central

Kim, J.-W.; Covel, N.S.; Guess, P.C.; Rekow, E.D.; Zhang, Y.

2010-01-01

Zirconia-based restorations are widely used in prosthetic dentistry; however, their susceptibility to hydrothermal degradation remains elusive. We hypothesized that CAD/CAM machining and subsequent surface treatments, i.e., grinding and/or grit-blasting, have marked effects on the hydrothermal degradation behavior of Y-TZP. CAD/CAM-machined Y-TZP plates (0.5 mm thick), both with and without subsequent grinding with various grit sizes or grit-blasting with airborne alumina particles, were subjected to accelerated aging tests in a steam autoclave. Results showed that the CAD/CAM-machined surfaces initially exhibited superior hydrothermal degradation resistance, but deteriorated at a faster rate upon prolonged autoclave treatment compared with ground and grit-blasted surfaces. The accelerated hydrothermal degradation of CAD/CAM surfaces is attributed to the CAD/CAM machining damage and the absence of surface compressive stresses in the fully sintered material. Clinical relevance for surface treatments of zirconia frameworks in terms of hydrothermal and structural stabilities is addressed. PMID:19966039

Colloidal characterization of ultrafine silicon carbide and silicon nitride powders

NASA Technical Reports Server (NTRS)

Whitman, Pamela K.; Feke, Donald L.

1986-01-01

The effects of various powder treatment strategies on the colloid chemistry of aqueous dispersions of silicon carbide and silicon nitride are examined using a surface titration methodology. Pretreatments are used to differentiate between the true surface chemistry of the powders and artifacts resulting from exposure history. Silicon nitride powders require more extensive pretreatment to reveal consistent surface chemistry than do silicon carbide powders. As measured by titration, the degree of proton adsorption from the suspending fluid by pretreated silicon nitride and silicon carbide powders can both be made similar to that of silica.

On the use of SPM to probe the interplay between polymer surface chemistry and polymer surface mechanics

NASA Astrophysics Data System (ADS)

Brogly, Maurice; Noel, Olivier; Awada, Houssein; Castelein, Gilles

2007-03-01

Adhesive properties of a polymer surface results from the complex contribution of surface chemistry and activation of sliding and dissipating mechanisms within the polymer surface layer. The purpose of this study is to dissociate the different contributions (chemical and mechanical) included in an AFM force-distance curve in order to establish relationships between the surface viscoelastic properties of the polymer, the surface chemistry of functionalized polymer surfaces and the adhesive forces, as determined by C-AFM experiments. Indeed we are interested in the measurements of local attractive or adhesive forces in AFM contact mode, of controlled chemical and mechanical model substrates. In order to investigate the interplay between mechanical or viscoelastic mechanisms and surface chemistry during the tip - polymer contact, we achieved force measurements on model PDMS polymer networks, whose surfaces are chemically controlled with the same functional groups as before (silicon substrates). On the basis of AFM nano-indentation experiments, surface Young moduli have been determined. The results show that the viscoelastic contribution is dominating in the adhesion force measurement. We propose an original model, which express the local adhesion force to the energy dissipated within the contact and the surface properties of the material (thermodynamic work of adhesion). Moreover we show that the dissipation function is related to Mc, the mass between crosslinks of the network.

Space-Based Diagnosis of Surface Ozone Sensitivity to Anthropogenic Emissions

NASA Technical Reports Server (NTRS)

Martin, Randall V.; Fiore, Arlene M.; VanDonkelaar, Aaron

2004-01-01

We present a novel capability in satellite remote sensing with implications for air pollution control strategy. We show that the ratio of formaldehyde columns to tropospheric nitrogen dioxide columns is an indicator of the relative sensitivity of surface ozone to emissions of nitrogen oxides (NO(x) = NO + NO2) and volatile organic compounds (VOCs). The diagnosis from these space-based observations is highly consistent with current understanding of surface ozone chemistry based on in situ observations. The satellite-derived ratios indicate that surface ozone is more sensitive to emissions of NO(x) than of VOCs throughout most continental regions of the Northern Hemisphere during summer. Exceptions include Los Angeles and industrial areas of Germany. A seasonal transition occurs in the fall when surface ozone becomes less sensitive to NOx and more sensitive to VOCs.

Functionalization of graphene for efficient energy conversion and storage.

PubMed

Dai, Liming

2013-01-15

As global energy consumption accelerates at an alarming rate, the development of clean and renewable energy conversion and storage systems has become more important than ever. Although the efficiency of energy conversion and storage devices depends on a variety of factors, their overall performance strongly relies on the structure and properties of the component materials. Nanotechnology has opened up new frontiers in materials science and engineering to meet this challenge by creating new materials, particularly carbon nanomaterials, for efficient energy conversion and storage. As a building block for carbon materials of all other dimensionalities (such as 0D buckyball, 1D nanotube, 3D graphite), the two-dimensional (2D) single atomic carbon sheet of graphene has emerged as an attractive candidate for energy applications due to its unique structure and properties. Like other materials, however, a graphene-based material that possesses desirable bulk properties rarely features the surface characteristics required for certain specific applications. Therefore, surface functionalization is essential, and researchers have devised various covalent and noncovalent chemistries for making graphene materials with the bulk and surface properties needed for efficient energy conversion and storage. In this Account, I summarize some of our new ideas and strategies for the controlled functionalization of graphene for the development of efficient energy conversion and storage devices, such as solar cells, fuel cells, supercapacitors, and batteries. The dangling bonds at the edge of graphene can be used for the covalent attachment of various chemical moieties while the graphene basal plane can be modified via either covalent or noncovalent functionalization. The asymmetric functionalization of the two opposite surfaces of individual graphene sheets with different moieties can lead to the self-assembly of graphene sheets into hierarchically structured materials. Judicious application of these site-selective reactions to graphene sheets has opened up a rich field of graphene-based energy materials with enhanced performance in energy conversion and storage. These results reveal the versatility of surface functionalization for making sophisticated graphene materials for energy applications. Even though many covalent and noncovalent functionalization methods have already been reported, vast opportunities remain for developing novel graphene materials for highly efficient energy conversion and storage systems.

Chemistry of atmosphere-surface interactions on Venus and Mars

NASA Astrophysics Data System (ADS)

Fegley, Bruce, Jr.; Treiman, Allan H.

Earth-based, earth-orbital, and spacecraft observational data are used in the present evaluation of Venus atmosphere-surface interactions to quantitatively characterize the reactions between C, H, S, Cl, F, and N gases and plausible surface minerals. Calculation results are used to predict stable minerals and mineral assemblages on the Venus surface, in order to ascertain which (if any) of the atmospheric gases are buffeted by mineral assemblages. Chemical equilibrium calculations using extant thermodynamic data on scapolite minerals predict that carbonate-bearing scapolite and sulfate meionite are unstable on the surface of Venus, while chloride-bearing scapolite is stable.

Surface characterization of weathered wood-plastic composites produced from modified wood flour

Treesearch

James S. Fabiyi; Armando G. McDonald; Nicole M. Stark

2007-01-01

The effects of weathering on the surface properties of wood-plastic composites (WPC) were examined. High-density polyethylene (HDPE) based WPCs made from modified wood flour (untreated, extractives free, and holocellulose (delignified) fibers) were subjected to accelerated (xenon-arc) weathering. Colorimetry and Fourier-transform infrared spectroscopy were employed to...

ESCA study of oxidation and hot corrosion of nickel-base superalloys. [Electron Spectroscopy for Chemical Analysis

NASA Technical Reports Server (NTRS)

Smith, S. R.; Carter, W. J., III; Mateescu, G. D.; Kohl, F. J.; Fryburg, G. C.; Stearns, C. A.

1980-01-01

A study of the high-temperature oxidation and Na2SO4-induced hot corrosion of nickel-base superalloys has been accomplished by using ESCA to determine the surface composition of the oxidized or corroded samples. Oxidation was carried out at 900 or 1000 C in slowly flowing O2 for samples of B-1900, NASA-TRW VIA, 713C, and IN-738. Hot corrosion of B-1900 was induced by applying a coating of Na2SO4 to preoxidized samples, then heating to 900 C in slowly flowing O2. For oxidized samples, the predominant type of scale formed by each superalloy showed a marked surface enrichment of Ti. For corroded samples, the transfer of significant amounts of material from the oxide layer to the surface of the salt layer was observed before the onset of rapidly accelerating weight gain. Marked changes in surface composition coincided with the beginning of accelerating corrosion, the most striking of which were a tenfold decrease in the sulfur to sodium ratio and an increase in the Cr(VI) to Cr(III) ratio.

Surface chemistry driven actuation in nanoporous gold

DOE Office of Scientific and Technical Information (OSTI.GOV)

Biener, J; Wittstock, A; Zepeda-Ruiz, L

Although actuation in biological systems is exclusively powered by chemical energy, this concept has not been realized in man-made actuator technologies, as these rely on generating heat or electricity first. Here, we demonstrate that surface-chemistry driven actuation can be realized in high surface area materials such as nanoporous gold. For example, we achieve reversible strain amplitudes in the order of a few tenths of a percent by alternating exposure of nanoporous Au to ozone and carbon monoxide. The effect can be explained by adsorbate-induced changes of the surface stress, and can be used to convert chemical energy directly into amore » mechanical response thus opening the door to surface-chemistry driven actuator and sensor technologies.« less

Accelerated Discovery of Large Electrostrains in BaTiO3 -Based Piezoelectrics Using Active Learning.

PubMed

Yuan, Ruihao; Liu, Zhen; Balachandran, Prasanna V; Xue, Deqing; Zhou, Yumei; Ding, Xiangdong; Sun, Jun; Xue, Dezhen; Lookman, Turab

2018-02-01

A key challenge in guiding experiments toward materials with desired properties is to effectively navigate the vast search space comprising the chemistry and structure of allowed compounds. Here, it is shown how the use of machine learning coupled to optimization methods can accelerate the discovery of new Pb-free BaTiO 3 (BTO-) based piezoelectrics with large electrostrains. By experimentally comparing several design strategies, it is shown that the approach balancing the trade-off between exploration (using uncertainties) and exploitation (using only model predictions) gives the optimal criterion leading to the synthesis of the piezoelectric (Ba 0.84 Ca 0.16 )(Ti 0.90 Zr 0.07 Sn 0.03 )O 3 with the largest electrostrain of 0.23% in the BTO family. Using Landau theory and insights from density functional theory, it is uncovered that the observed large electrostrain is due to the presence of Sn, which allows for the ease of switching of tetragonal domains under an electric field. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Molecular Rotors

DTIC Science & Technology

2006-10-31

microwave signal processing components, and micro-fluidic devices. The projected involved the preparation, surface mounting, and characterization of...Guisinger, R. Basu, and M. C. Hersam, “Atomic-level characterization and control of free radical surface chemistry using scanning tunneling microscopy...Basu, and M. C. Hersam, “Atomic level characterization and control of organosilicon surface chemistry using scanning tunneling microscopy,” presented

Surface chemistry and moisture sorption properties of wood coated with multifunctional alkoxysilanes by sol-gel process

Treesearch

Mandla A. Tshabalala; Peter Kingshott; Mark R. VanLandingham; David Plackett

2003-01-01

Sol-gel surface deposition of a hydrophobic polysiloxane coating on wood was accomplished by using a mixture of a low molecular weight multifunctional alkoxysilane, methyltrimethoxysilane (MTMOS), and a high molecular weight multifunctional alkoxysilane, hexadecyltrimethoxysilane (HDTMOS). Investigation of the surface chemistry and morphology of the wood specimens by...

Do sediment type and test durations affect results of laboratory-based, accelerated testing studies of permeable pavement clogging?

PubMed

Nichols, Peter W B; White, Richard; Lucke, Terry

2015-04-01

Previous studies have attempted to quantify the clogging processes of Permeable Interlocking Concrete Pavers (PICPs) using accelerated testing methods. However, the results have been variable. This study investigated the effects that three different sediment types (natural and silica), and different simulated rainfall intensities, and testing durations had on the observed clogging processes (and measured surface infiltration rates) of laboratory-based, accelerated PICP testing studies. Results showed that accelerated simulated laboratory testing results are highly dependent on the type, and size of sediment used in the experiments. For example, when using real stormwater sediment up to 1.18 mm in size, the results showed that neither testing duration, nor stormwater application rate had any significant effect on PICP clogging. However, the study clearly showed that shorter testing durations generally increased clogging and reduced the surface infiltration rates of the models when artificial silica sediment was used. Longer testing durations also generally increased clogging of the models when using fine sediment (<300 μm). Results from this study will help researchers and designers better anticipate when and why PICPs are susceptible to clogging, reduce maintenance and extend the useful life of these increasingly common stormwater best management practices. Copyright © 2015 Elsevier B.V. All rights reserved.

Anticorrelation between Surface and Subsurface Point Defects and the Impact on the Redox Chemistry of TiO2(110)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yoon, Yeohoon; Du, Yingge; Garcia, Juan C.

2015-02-02

Using combination of STM, DFT and SIMS, we explored the interplay and relative impact of surface vs. subsurface defects on the surface chemistry of rutile TiO2. STM results show that surface O vacancies (VO’s) are virtually absent in the vicinity of positively-charged subsurface point-defects. This observation is consistent with DFT calculations of impact of subsurface defect proximity on VO formation energy. To monitor the influence of such lateral anticorrelation on surface redox chemistry, a test reaction of the dissociative adsorption of O2 is employed, which is observed to be suppressed around them. DFT results attribute this to a perceived absencemore » of the intrinsic (Ti) (and likely extrinsic) interstitials in the nearest subsurface layer beneath “inhibited” areas. We also postulate that the entire nearest subsurface region could be voided of any charged point-defects, whereas prevalent VO’s are largely responsible for mediation of the redox chemistry at reduced TiO2(110) surface.« less

Surface-Enhanced Raman Spectroscopy as a Probe of the Surface Chemistry of Nanostructured Materials.

PubMed

Dick, Susan; Konrad, Magdalena P; Lee, Wendy W Y; McCabe, Hannah; McCracken, John N; Rahman, Taifur M D; Stewart, Alan; Xu, Yikai; Bell, Steven E J

2016-07-01

Surface-enhanced Raman spectroscopy (SERS) is now widely used as a rapid and inexpensive tool for chemical/biochemical analysis. The method can give enormous increases in the intensities of the Raman signals of low-concentration molecular targets if they are adsorbed on suitable enhancing substrates, which are typically composed of nanostructured Ag or Au. However, the features of SERS that allow it to be used as a chemical sensor also mean that it can be used as a powerful probe of the surface chemistry of any nanostructured material that can provide SERS enhancement. This is important because it is the surface chemistry that controls how these materials interact with their local environment and, in real applications, this interaction can be more important than more commonly measured properties such as morphology or plasmonic absorption. Here, the opportunity that this approach to SERS provides is illustrated with examples where the surface chemistry is both characterized and controlled in order to create functional nanomaterials. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Effect of Hydrofluoric Acid Etching Time on Titanium Topography, Chemistry, Wettability, and Cell Adhesion

PubMed Central

Zahran, R.; Rosales Leal, J. I.; Rodríguez Valverde, M. A.; Cabrerizo Vílchez, M. A.

2016-01-01

Titanium implant surface etching has proven an effective method to enhance cell attachment. Despite the frequent use of hydrofluoric (HF) acid, many questions remain unresolved, including the optimal etching time and its effect on surface and biological properties. The objective of this study was to investigate the effect of HF acid etching time on Ti topography, surface chemistry, wettability, and cell adhesion. These data are useful to design improved acid treatment and obtain an improved cell response. The surface topography, chemistry, dynamic wetting, and cell adhesiveness of polished Ti surfaces were evaluated after treatment with HF acid solution for 0, 2; 3, 5, 7, or 10 min, revealing a time-dependent effect of HF acid on their topography, chemistry, and wetting. Roughness and wetting increased with longer etching time except at 10 min, when roughness increased but wetness decreased. Skewness became negative after etching and kurtosis tended to 3 with longer etching time. Highest cell adhesion was achieved after 5–7 min of etching time. Wetting and cell adhesion were reduced on the highly rough surfaces obtained after 10-min etching time. PMID:27824875

Controlling nonspecific protein adsorption in a plug-based microfluidic system by controlling interfacial chemistry using fluorous-phase surfactants.

PubMed

Roach, L Spencer; Song, Helen; Ismagilov, Rustem F

2005-02-01

Control of surface chemistry and protein adsorption is important for using microfluidic devices for biochemical analysis and high-throughput screening assays. This paper describes the control of protein adsorption at the liquid-liquid interface in a plug-based microfluidic system. The microfluidic system uses multiphase flows of immiscible fluorous and aqueous fluids to form plugs, which are aqueous droplets that are completely surrounded by fluorocarbon oil and do not come into direct contact with the hydrophobic surface of the microchannel. Protein adsorption at the aqueous-fluorous interface was controlled by using surfactants that were soluble in fluorocarbon oil but insoluble in aqueous solutions. Three perfluorinated alkane surfactants capped with different functional groups were used: a carboxylic acid, an alcohol, and a triethylene glycol group that was synthesized from commercially available materials. Using complementary methods of analysis, adsorption was characterized for several proteins (bovine serum albumin (BSA) and fibrinogen), including enzymes (ribonuclease A (RNase A) and alkaline phosphatase). These complementary methods involved characterizing adsorption in microliter-sized droplets by drop tensiometry and in nanoliter plugs by fluorescence microscopy and kinetic measurements of enzyme catalysis. The oligoethylene glycol-capped surfactant prevented protein adsorption in all cases. Adsorption of proteins to the carboxylic acid-capped surfactant in nanoliter plugs could be described by using the Langmuir model and tensiometry results for microliter drops. The microfluidic system was fabricated using rapid prototyping in poly(dimethylsiloxane) (PDMS). Black PDMS microfluidic devices, fabricated by curing a suspension of charcoal in PDMS, were used to measure the changes in fluorescence intensity more sensitively. This system will be useful for microfluidic bioassays, enzymatic kinetics, and protein crystallization, because it does not require surface modification during fabrication to control surface chemistry and protein adsorption.

Surface Functionalization of Exosomes Using Click Chemistry

PubMed Central

2015-01-01

A method for conjugation of ligands to the surface of exosomes was developed using click chemistry. Copper-catalyzed azide alkyne cycloaddition (click chemistry) is ideal for biocojugation of small molecules and macromolecules to the surface of exosomes, due to fast reaction times, high specificity, and compatibility in aqueous buffers. Exosomes cross-linked with alkyne groups using carbodiimide chemistry were conjugated to a model azide, azide-fluor 545. Conjugation had no effect on the size of exosomes, nor was there any change in the extent of exosome adherence/internalization with recipient cells, suggesting the reaction conditions were mild on exosome structure and function. We further investigated the extent of exosomal protein modification with alkyne groups. Using liposomes with surface alkyne groups of a similar size and concentration to exosomes, we estimated that approximately 1.5 alkyne groups were present for every 150 kDa of exosomal protein. PMID:25220352

The Plasma Wake Downstream of Lunar Topographic Obstacles: Preliminary Results from 2D Particle Simulations

NASA Technical Reports Server (NTRS)

Zimmerman, Michael I.; Farrell, W. M.; Snubbs, T. J.; Halekas, J. S.

2011-01-01

Anticipating the plasma and electrical environments in permanently shadowed regions (PSRs) of the moon is critical in understanding local processes of space weathering, surface charging, surface chemistry, volatile production and trapping, exo-ion sputtering, and charged dust transport. In the present study, we have employed the open-source XOOPIC code [I] to investigate the effects of solar wind conditions and plasma-surface interactions on the electrical environment in PSRs through fully two-dimensional pattic1e-in-cell simulations. By direct analogy with current understanding of the global lunar wake (e.g., references) deep, near-terminator, shadowed craters are expected to produce plasma "mini-wakes" just leeward of the crater wall. The present results (e.g., Figure I) are in agreement with previous claims that hot electrons rush into the crater void ahead of the heavier ions, fanning a negative cloud of charge. Charge separation along the initial plasma-vacuum interface gives rise to an ambipolar electric field that subsequently accelerates ions into the void. However, the situation is complicated by the presence of the dynamic lunar surface, which develops an electric potential in response to local plasma currents (e.g., Figure Ia). In some regimes, wake structure is clearly affected by the presence of the charged crater floor as it seeks to achieve current balance (i.e. zero net current to the surface).

Implementation of an ADME enabling selection and visualization tool for drug discovery.

PubMed

Stoner, Chad L; Gifford, Eric; Stankovic, Charles; Lepsy, Christopher S; Brodfuehrer, Joanne; Prasad, J V N Vara; Surendran, Narayanan

2004-05-01

The pharmaceutical industry has large investments in compound library enrichment, high throughput biological screening, and biopharmaceutical (ADME) screening. As the number of compounds submitted for in vitro ADME screens increases, data analysis, interpretation, and reporting will become rate limiting in providing ADME-structure-activity relationship information to guide the synthetic strategy for chemical series. To meet these challenges, a software tool was developed and implemented that enables scientists to explore in vitro and in silico ADME and chemistry data in a multidimensional framework. The present work integrates physicochemical and ADME data, encompassing results for Caco-2 permeability, human liver microsomal half-life, rat liver microsomal half-life, kinetic solubility, measured log P, rule of 5 descriptors (molecular weight, hydrogen bond acceptors, hydrogen bond donors, calculated log P), polar surface area, chemical stability, and CYP450 3A4 inhibition. To facilitate interpretation of this data, a semicustomized software solution using Spotfire was designed that allows for multidimensional data analysis and visualization. The solution also enables simultaneous viewing and export of chemical structures with the corresponding ADME properties, enabling a more facile analysis of ADME-structure-activity relationship. In vitro and in silico ADME data were generated for 358 compounds from a series of human immunodeficiency virus protease inhibitors, resulting in a data set of 5370 experimental values which were subsequently analyzed and visualized using the customized Spotfire application. Implementation of this analysis and visualization tool has accelerated the selection of molecules for further development based on optimum ADME characteristics, and provided medicinal chemistry with specific, data driven structural recommendations for improvements in the ADME profile. Copyright 2004 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 93: 1131-1141, 2004

Novel neutron sources at the Radiological Research Accelerator Facility

PubMed Central

Xu, Yanping; Garty, Guy; Marino, Stephen A.; Massey, Thomas N.; Randers-Pehrson, Gerhard; Johnson, Gary W.; Brenner, David J.

2012-01-01

Since the 1960s, the Radiological Research Accelerator Facility (RARAF) has been providing researchers in biology, chemistry and physics with advanced irradiation techniques, using charged particles, photons and neutrons. We are currently developing a unique facility at RARAF, to simulate neutron spectra from an improvised nuclear device (IND), based on calculations of the neutron spectrum at 1.5 km from the epicenter of the Hiroshima atom bomb. This is significantly different from a standard fission spectrum, because the spectrum changes as the neutrons are transported through air, and is dominated by neutron energies between 0.05 and 8 MeV. This facility will be based on a mixed proton/deuteron beam impinging on a thick beryllium target. A second, novel facility under development is our new neutron microbeam. The neutron microbeam will, for the first time, provide a kinematically collimated neutron beam, 10–20 micron in diameter. This facility is based on a Proton Microbeam, impinging on a thin lithium target near the threshold of the 7Li(p,n)7Be reaction. This novel neutron microbeam will enable studies of neutron damage to small targets, such as single cells, individual organs within small animals or microelectronic components. PMID:22545061

Novel neutron sources at the Radiological Research Accelerator Facility.

PubMed

Xu, Yanping; Garty, Guy; Marino, Stephen A; Massey, Thomas N; Randers-Pehrson, Gerhard; Johnson, Gary W; Brenner, David J

2012-03-16

Since the 1960s, the Radiological Research Accelerator Facility (RARAF) has been providing researchers in biology, chemistry and physics with advanced irradiation techniques, using charged particles, photons and neutrons.We are currently developing a unique facility at RARAF, to simulate neutron spectra from an improvised nuclear device (IND), based on calculations of the neutron spectrum at 1.5 km from the epicenter of the Hiroshima atom bomb. This is significantly different from a standard fission spectrum, because the spectrum changes as the neutrons are transported through air, and is dominated by neutron energies between 0.05 and 8 MeV. This facility will be based on a mixed proton/deuteron beam impinging on a thick beryllium target.A second, novel facility under development is our new neutron microbeam. The neutron microbeam will, for the first time, provide a kinematically collimated neutron beam, 10-20 micron in diameter. This facility is based on a Proton Microbeam, impinging on a thin lithium target near the threshold of the (7)Li(p,n)(7)Be reaction. This novel neutron microbeam will enable studies of neutron damage to small targets, such as single cells, individual organs within small animals or microelectronic components.

Novel neutron sources at the Radiological Research Accelerator Facility

DOE PAGES

Xu, Yanping; Garty, G.; Marino, S. A.; ...

2012-03-16

Since the 1960s, the Radiological Research Accelerator Facility (RARAF) has been providing researchers in biology, chemistry and physics with advanced irradiation techniques, using charged particles, photons and neutrons. We are currently developing a unique facility at RARAF, to simulate neutron spectra from an improvised nuclear device (IND), based on calculations of the neutron spectrum at 1.5 km from the epicenter of the Hiroshima atom bomb. This is significantly different from a standard fission spectrum, because the spectrum changes as the neutrons are transported through air, and is dominated by neutron energies between 0.05 and 8 MeV. This facility will bemore » based on a mixed proton/deuteron beam impinging on a thick beryllium target. A second, novel facility under development is our new neutron microbeam. The neutron microbeam will, for the first time, provide a kinematically collimated neutron beam, 10-20 micron in diameter. This facility is based on a proton microbeam, impinging on a thin lithium target near the threshold of the Li-7(p,n)Be-7 reaction. Lastly, this novel neutron microbeam will enable studies of neutron damage to small targets, such as single cells, individual organs within small animals or microelectronic components.« less

Novel neutron sources at the Radiological Research Accelerator Facility

NASA Astrophysics Data System (ADS)

Xu, Y.; Garty, G.; Marino, S. A.; Massey, T. N.; Randers-Pehrson, G.; Johnson, G. W.; Brenner, D. J.

2012-03-01

Since the 1960s, the Radiological Research Accelerator Facility (RARAF) has been providing researchers in biology, chemistry and physics with advanced irradiation techniques, using charged particles, photons and neutrons. We are currently developing a unique facility at RARAF, to simulate neutron spectra from an improvised nuclear device (IND), based on calculations of the neutron spectrum at 1.5 km from the epicenter of the Hiroshima atom bomb. This is significantly different from a standard fission spectrum, because the spectrum changes as the neutrons are transported through air, and is dominated by neutron energies between 0.05 and 8 MeV. This facility will be based on a mixed proton/deuteron beam impinging on a thick beryllium target. A second, novel facility under development is our new neutron microbeam. The neutron microbeam will, for the first time, provide a kinematically collimated neutron beam, 10-20 micron in diameter. This facility is based on a proton microbeam, impinging on a thin lithium target near the threshold of the 7Li(p,n)7Be reaction. This novel neutron microbeam will enable studies of neutron damage to small targets, such as single cells, individual organs within small animals or microelectronic components.

Effect of Ionic Strength and Surface Charge Density on the Kinetics of Cellulose Nanocrystal Thin Film Swelling.

PubMed

Reid, Michael S; Kedzior, Stephanie A; Villalobos, Marco; Cranston, Emily D

2017-08-01

This work explores cellulose nanocrystal (CNC) thin films (<50 nm) and particle-particle interactions by investigating film swelling in aqueous solutions with varying ionic strength (1-100 mM). CNC film hydration was monitored in situ via surface plasmon resonance, and the kinetics of liquid uptake were quantified. The contribution of electrostatic double-layer forces to film swelling was elucidated by using CNCs with different surface charges (anionic sulfate half ester groups, high and low surface charge density, and cationic trimethylammonium groups). Total water uptake in the thin films was found to be independent of ionic strength and surface chemistry, suggesting that in the aggregated state van der Waals forces dominate over double-layer forces to hold the films together. However, the rate of swelling varied significantly. The water uptake followed Fickian behavior, and the measured diffusion constants decreased with the ionic strength gradient between the film and the solution. This work highlights that nanoparticle interactions and dispersion are highly dependent on the state of particle aggregation and that the rate of water uptake in aggregates and thin films can be tailored based on surface chemistry and solution ionic strength.

Elementary photocatalytic chemistry on TiO2 surfaces.

PubMed

Guo, Qing; Zhou, Chuanyao; Ma, Zhibo; Ren, Zefeng; Fan, Hongjun; Yang, Xueming

2016-07-07

Photocatalytic hydrogen production and pollutant degradation provided both great opportunities and challenges in the field of sustainable energy and environmental science. Over the past few decades, we have witnessed fast growing interest and efforts in developing new photocatalysts, improving catalytic efficiency and exploring the reaction mechanism at the atomic and molecular levels. Owing to its relatively high efficiency, nontoxicity, low cost and high stability, TiO2 becomes one of the most extensively investigated metal oxides in semiconductor photocatalysis. Fundamental studies on well characterized single crystals using ultrahigh vacuum based surface science techniques could provide key microscopic insight into the underlying mechanism of photocatalysis. In this review, we have summarized recent progress in the photocatalytic chemistry of hydrogen, water, oxygen, carbon monoxide, alcohols, aldehydes, ketones and carboxylic acids on TiO2 surfaces. We focused this review mainly on the rutile TiO2(110) surface, but some results on the rutile TiO2(011), anatase TiO2(101) and (001) surfaces are also discussed. These studies provided fundamental insights into surface photocatalysis as well as stimulated new investigations in this exciting field. At the end of this review, we have discussed how these studies can help us to develop new photocatalysis models.

How accelerated biological aging can affect solar reflective polymeric based building materials

NASA Astrophysics Data System (ADS)

Ferrari, C.; Santunione, G.; Libbra, A.; Muscio, A.; Sgarbi, E.

2017-11-01

Among the main issues concerning building materials, in particular outdoor ones, one can identify the colonization by microorganisms referred to as biological aggression. This can affect not only the aesthetical aspect but also the thermal performance of solar reflective materials. In order to improve the reliability of tests aimed to assess the resistance to biological aggression and contextually reduce the test duration, an accelerated test method has been developed. It is based on a lab reproducible setup where specific and controlled environmental and boundary conditions are imposed to accelerate as much as possible biological growth on building materials. Due to their widespread use, polymeric materials have been selected for the present analysis, in the aim of reaching an advanced bio-aged level in a relatively short time (8 weeks or less) and at the same time comparatively evaluate different materials under a given set of ageing conditions. Surface properties before, during and after ageing have been investigated by surface, microstructural and chemical analyses, as well as by examination of time progressive images to assess bacterial and algal growth rate.

Moderate pressure plasma source of nonthermal electrons

NASA Astrophysics Data System (ADS)

Gershman, S.; Raitses, Y.

2018-06-01

Plasma sources of electrons offer control of gas and surface chemistry without the need for complex vacuum systems. The plasma electron source presented here is based on a cold cathode glow discharge (GD) operating in a dc steady state mode in a moderate pressure range of 2–10 torr. Ion-induced secondary electron emission is the source of electrons accelerated to high energies in the cathode sheath potential. The source geometry is a key to the availability and the extraction of the nonthermal portion of the electron population. The source consists of a flat and a cylindrical electrode, 1 mm apart. Our estimates show that the length of the cathode sheath in the plasma source is commensurate (~0.5–1 mm) with the inter-electrode distance so the GD operates in an obstructed regime without a positive column. Estimations of the electron energy relaxation confirm the non-local nature of this GD, hence the nonthermal portion of the electron population is available for extraction outside of the source. The use of a cylindrical anode presents a simple and promising method of extracting the high energy portion of the electron population. Langmuir probe measurements and optical emission spectroscopy confirm the presence of electrons with energies ~15 eV outside of the source. These electrons become available for surface modification and radical production outside of the source. The extraction of the electrons of specific energies by varying the anode geometry opens exciting opportunities for future exploration.

Low temperature surface chemistry and nanostructures

NASA Astrophysics Data System (ADS)

Sergeev, G. B.; Shabatina, T. I.

2002-03-01

The new scientific field of low temperature surface chemistry, which combines the low temperature chemistry (cryochemistry) and surface chemistry approaches, is reviewed in this paper. One of the most exciting achievements in this field of science is the development of methods to create highly ordered hybrid nanosized structures on different organic and inorganic surfaces and to encapsulate nanosized metal particles in organic and polymer matrices. We consider physical and chemical behaviour for the systems obtained by co-condensation of the components vapours on the surfaces cooled down to 4-10 and 70-100 K. In particular the size effect of both types, the number of atoms in the reactive species structure and the thickness of growing co-condensate film, on the chemical activity of the system is analysed in detail. The effect of the internal mechanical stresses on the growing interfacial co-condensate film formation and on the generation of fast (explosive) spontaneous reactions at low temperatures is discussed. The examples of unusual chemical interactions of metal atoms, clusters and nanosized particles, obtained in co-condensate films on the cooled surfaces under different conditions, are presented. The examples of highly ordered surface and volume hybrid nanostructures formation are analysed.

Emphasizing the role of surface chemistry on hydrophobicity and cell adhesion behavior of polydimethylsiloxane/TiO2 nanocomposite films.

PubMed

Yousefi, Seyedeh Zahra; Tabatabaei-Panah, Pardis-Sadat; Seyfi, Javad

2018-07-01

Improving the bioinertness of materials is of great importance for developing biomedical devices that contact human tissues. The main goal of this study was to establish correlations among surface morphology, roughness and chemistry with hydrophobicity and cell adhesion in polydimethylsiloxane (PDMS) nanocomposites loaded with titanium dioxide (TiO 2 ) nanoparticles. Firstly, wettability results showed that the nanocomposite loaded with 30 wt.% of TiO 2 exhibited a superhydrophobic behavior; however, the morphology and roughness analysis proved that there was no discernible difference between the surface structures of samples loaded with 20 and 30 wt.% of nanoparticles. Both cell culture and MTT assay experiments showed that, despite the similarity between the surface structures, the sample loaded with 30 wt.% nanoparticles exhibits the greatest reduction in the cell viability (80%) as compared with the pure PDMS film. According to the X-ray photoelectron spectroscopy results, the remarkable reduction in cell viability of the superhydrophobic sample could be majorly attributed to the role of surface chemistry. The obtained results emphasize the importance of adjusting the surface properties especially surface chemistry to gain the optimum cell adhesion behavior. Copyright © 2018 Elsevier B.V. All rights reserved.

Process of welding gamma prime-strengthened nickel-base superalloys

DOEpatents

Speigel, Lyle B.; White, Raymond Alan; Murphy, John Thomas; Nowak, Daniel Anthony

2003-11-25

A process for welding superalloys, and particularly articles formed of gamma prime-strengthened nickel-base superalloys whose chemistries and/or microstructures differ. The process entails forming the faying surface of at least one of the articles to have a cladding layer of a filler material. The filler material may have a composition that is different from both of the articles, or the same as one of the articles. The cladding layer is machined to promote mating of the faying surfaces, after which the faying surfaces are mated and the articles welded together. After cooling, the welded assembly is free of thermally-induced cracks.

Complex amine-based reagents

NASA Astrophysics Data System (ADS)

Suslov, S. Yu.; Kirilina, A. V.; Sergeev, I. A.; Zezyulya, T. V.; Sokolova, E. A.; Eremina, E. V.; Timofeev, N. V.

2017-03-01

Amines for a long time have been applied to maintaining water chemistry conditions (WCC) at power plants. However, making use of complex reagents that are the mixture of neutralizing and the filmforming amines, which may also contain other organic components, causes many disputes. This is mainly due to lack of reliable information about these components. The protective properties of any amine with regard to metal surfaces depend on several factors, which are considered in this article. The results of applying complex reagents to the protection of heating surfaces in industrial conditions and estimated behavior forecasts for various reagents under maintaining WCC on heat-recovery boilers with different thermal circuits are presented. The case of a two-drum heat-recovery boiler with in-line drums was used as an example, for which we present the calculated pH values for various brands of reagents under the same conditions. Work with different reagent brands and its analysis enabled us to derive a composition best suitable for the conditions of their practical applications in heat-recovery boilers at different pressures. Testing the new amine reagent performed at a CCPP power unit shows that this reagent is an adequate base for further development of reagents based on amine compounds. An example of testing a complex reagent is shown created with the participation of the authors within the framework the program of import substitution and its possible use is demonstrated for maintaining WCC of power-generating units of combined-cycle power plants (CCPP) and TPP. The compliance of the employed reagents with the standards of water chemistry conditions and protection of heating surfaces were assessed. The application of amine-containing reagents at power-generating units of TPP makes it possible to solve complex problems aimed at ensuring the sparing cleaning of heating surfaces from deposits and the implementation of conservation and management of water chemistry condition on the TPP equipment.

Molecular-level characterization of the structure and the surface chemistry of periodic mesoporous organosilicates using DNP-surface enhanced NMR spectroscopy.

PubMed

Grüning, Wolfram R; Rossini, Aaron J; Zagdoun, Alexandre; Gajan, David; Lesage, Anne; Emsley, Lyndon; Copéret, Christophe

2013-08-28

We present the molecular level characterization of a phenylpyridine-based periodic mesoporous organosilicate and its post-functionalized organometallic derivatives through the fast acquisition of high quality natural isotopic abundance 1D (13)C, (15)N, and (29)Si and 2D (1)H-(13)C and (1)H-(29)Si solid-state NMR spectra enhanced with dynamic nuclear polarization.

High intensity surface plasma waves, theory and PIC simulations

NASA Astrophysics Data System (ADS)

Raynaud, M.; Héron, A.; Adam, J.-C.

2018-01-01

With the development of intense (>1019 W cm-2) short pulses (≤25 fs) laser with very high contrast, surface plasma wave (SPW) can be explored in the relativistic regime. As the SPW propagates with a phase velocity close to the speed of light it may results in a strong acceleration of electron bunches along the surface permitting them to reach relativistic energies. This may be important e.g. for applications in the field of plasma-based accelerators. We investigate in this work the excitation of SPWs on grating preformed over-dense plasmas for laser intensities ranging from 1019 up to 1021 W cm-2. We discuss the nature of the interaction with respect to the solid case in which surface plasmon can be resonantly excited with weak laser intensity. In particular, we show the importance of the pulse duration and focalization of the laser beam on the amplitude of the SPW.

Thermal Reactions of H2O2 on Icy Satellites and Small Bodies: Descent with Modification?

NASA Technical Reports Server (NTRS)

Hudson, Reggie L.; Loeffler, Mark J.

2012-01-01

Magnetospheric radiation drives surface and near-surface chemistry on Europa, but below a few meters Europa's chemistry is hidden from direct observation . As an example, surface radiation chemistry converts H2O and SO2 into H2O2 and (SO4)(sup 2-), respectively, and these species will be transported downward for possible thermally-driven reactions. However, while the infrared spectra and radiation chemistry of H2O2-containing ices are well documented, this molecule's thermally-induced solid-phase chemistry has seldom been studied. Here we report new results on thermal reactions in H2O + H2O2 + SO2 ices at 50 - 130 K. As an example of our results, we find that warming H2O + H2O2 + SO2 ices promotes SO2 oxidation to (SO4)(sup 2-). These results have implications for the survival of H2O2 as it descends, with modification, towards a subsurface ocean on Europa. We suspect that such redox chemistry may explain some of the observations related to the presence and distribution of H2O2 across Europa's surface as well as the lack of H2O2 on Ganymede and Callisto.

In vitro toxicity of carbon nanotubes, nano-graphite and carbon black, similar impacts of acid functionalization.

PubMed

Figarol, Agathe; Pourchez, Jérémie; Boudard, Delphine; Forest, Valérie; Akono, Céline; Tulliani, Jean-Marc; Lecompte, Jean-Pierre; Cottier, Michèle; Bernache-Assollant, Didier; Grosseau, Philippe

2015-12-25

Carbon nanotubes (CNT) and nano-graphite (NG) are graphene-based nanomaterials which share exceptional physicochemical properties, but whose health impacts are unfortunately still not well understood. On the other hand, carbon black (CB) is a conventional and widely studied material. The comparison of these three carbon-based nanomaterials is thus of great interest to improve our understanding of their toxicity. An acid functionalization was carried out on CNT, NG and CB so that, after a thorough characterization, their impacts on RAW 264.7 macrophages could be compared for a similar surface chemistry (15 to 120 μg·mL(-1) nanomaterials, 90-min to 24-h contact). Functionalized nanomaterials triggered a weak cytotoxicity similar to the pristine nanomaterials. Acid functionalization increased the pro-inflammatory response except for CB which did not trigger any TNF-α production before or after functionalization, and seemed to strongly decrease the oxidative stress. The toxicological impact of acid functionalization appeared thus to follow a similar trend whatever the carbon-based nanomaterial. At equivalent dose expressed in surface and equivalent surface chemistry, the toxicological responses from murine macrophages to NG were higher than for CNT and CB. It seemed to correspond to the hypothesis of a platelet and fiber paradigm. Copyright © 2015. Published by Elsevier Ltd.

A plant derived multifunctional tool for nanobiotechnology based on Tomato bushy stunt virus.

PubMed

Grasso, Simone; Lico, Chiara; Imperatori, Francesca; Santi, Luca

2013-06-01

Structure, size, physicochemical properties and production strategies make many plant viruses ideal protein based nanoscaffolds, nanocontainers and nano-building blocks expected to deliver a multitude of applications in different fields such as biomedicine, pharmaceutical chemistry, separation science, catalytic chemistry, crop pest control and biomaterials science. Functionalization of viral nanoparticles through modification by design of their external and internal surfaces is essential to fully exploit the potentiality of these objects. In the present paper we describe the development of a plant derived multifunctional tool for nanobiotechnology based on Tomato bushy stunt virus. We demonstrate the ability of this system to remarkably sustain genetic modifications and in vitro chemical derivatizations of its outer surface, which resulted in the successful display of large chimeric peptides fusions and small chemical molecules, respectively. Moreover, we have defined physicochemical conditions for viral swelling and reversible viral pore gating that we have successfully employed for foreign molecules loading and retention in the inner cavity of this plant virus nanoparticles system. Finally, a production and purification strategy from Nicotiana benthamiana plants has been addressed and optimized.

ELIMED: a new hadron therapy concept based on laser driven ion beams

NASA Astrophysics Data System (ADS)

Cirrone, Giuseppe A. P.; Margarone, Daniele; Maggiore, Mario; Anzalone, Antonello; Borghesi, Marco; Jia, S. Bijan; Bulanov, Stepan S.; Bulanov, Sergei; Carpinelli, Massimo; Cavallaro, Salvatore; Cutroneo, Mariapompea; Cuttone, Giacomo; Favetta, Marco; Gammino, Santo; Klimo, Ondrej; Manti, Lorenzo; Korn, Georg; La Malfa, Giuseppe; Limpouch, Jiri; Musumarra, Agatino; Petrovic, Ivan; Prokupek, Jan; Psikal, Jan; Ristic-Fira, Aleksandra; Renis, Marcella; Romano, Francesco P.; Romano, Francesco; Schettino, Giuseppe; Schillaci, Francesco; Scuderi, Valentina; Stancampiano, Concetta; Tramontana, Antonella; Ter-Avetisyan, Sargis; Tomasello, Barbara; Torrisi, Lorenzo; Tudisco, Salvo; Velyhan, Andriy

2013-05-01

Laser accelerated proton beams have been proposed to be used in different research fields. A great interest has risen for the potential replacement of conventional accelerating machines with laser-based accelerators, and in particular for the development of new concepts of more compact and cheaper hadrontherapy centers. In this context the ELIMED (ELI MEDical applications) research project has been launched by INFN-LNS and ASCR-FZU researchers within the pan-European ELI-Beamlines facility framework. The ELIMED project aims to demonstrate the potential clinical applicability of optically accelerated proton beams and to realize a laser-accelerated ion transport beamline for multi-disciplinary user applications. In this framework the eye melanoma, as for instance the uveal melanoma normally treated with 62 MeV proton beams produced by standard accelerators, will be considered as a model system to demonstrate the potential clinical use of laser-driven protons in hadrontherapy, especially because of the limited constraints in terms of proton energy and irradiation geometry for this particular tumour treatment. Several challenges, starting from laser-target interaction and beam transport development up to dosimetry and radiobiology, need to be overcome in order to reach the ELIMED final goals. A crucial role will be played by the final design and realization of a transport beamline capable to provide ion beams with proper characteristics in terms of energy spectrum and angular distribution which will allow performing dosimetric tests and biological cell irradiation. A first prototype of the transport beamline has been already designed and other transport elements are under construction in order to perform a first experimental test with the TARANIS laser system by the end of 2013. A wide international collaboration among specialists of different disciplines like Physics, Biology, Chemistry, Medicine and medical doctors coming from Europe, Japan, and the US is growing up around the ELIMED project with the aim to work on the conceptual design, technical and experimental realization of this core beamline of the ELI Beamlines facility.

Evanescent field Sensors Based on Tantalum Pentoxide Waveguides – A Review

PubMed Central

Schmitt, Katrin; Oehse, Kerstin; Sulz, Gerd; Hoffmann, Christian

2008-01-01

Evanescent field sensors based on waveguide surfaces play an important role where high sensitivity is required. Particularly tantalum pentoxide (Ta2O5) is a suitable material for thin-film waveguides due to its high refractive index and low attenuation. Many label-free biosensor systems such as grating couplers and interferometric sensors as well as fluorescence-based systems benefit from this waveguide material leading to extremely high sensitivity. Some biosensor systems based on Ta2O5 waveguides already took the step into commercialization. This report reviews the various detection systems in terms of limit of detection, the applications, and the suitable surface chemistry. PMID:27879731

Direct Measurements of 3D Structure, Chemistry and Mass Density During the Induction Period of C3S Hydration

PubMed Central

Hu, Qinang; Aboustait, Mohammed; Kim, Taehwan; Ley, M. Tyler; Bullard, Jeffrey W.; Scherer, George; Hanan, Jay C.; Rose, Volker; Winarski, Robert; Gelb, Jeffrey

2017-01-01

The reasons for the start and end of the induction period of cement hydration remain topic of controversy. One long-standing hypothesis is that a thin metastable hydrate forming on the surface of cement grains significantly reduces the particle dissolution rate; the eventual disappearance of this layer re-establishes higher dissolution rates at the beginning of the acceleration period. However, the importance, or even the existence, of this metastable layer has been questioned because it cannot be directly detected in most experiments. In this work, a combined analysis using nano-tomography and nano-X-ray fluorescence makes the direct imaging of early hydration products possible. These novel X-ray imaging techniques provide quantitative measurements of 3D structure, chemical composition, and mass density of the hydration products during the induction period. This work does not observe a low density product on the surface of the particle, but does provide insights into the formation of etch pits and the subsequent hydration products that fill them. PMID:28919638

Giant magnetoresistive biosensors for molecular diagnosis: surface chemistry and assay development

NASA Astrophysics Data System (ADS)

Yu, Heng; Osterfeld, Sebastian J.; Xu, Liang; White, Robert L.; Pourmand, Nader; Wang, Shan X.

2008-08-01

Giant magnetoresistive (GMR) biochips using magnetic nanoparticle as labels were developed for molecular diagnosis. The sensor arrays consist of GMR sensing strips of 1.5 μm or 0.75 μm in width. GMR sensors are exquisitely sensitive yet very delicate, requiring ultrathin corrosion-resistive passivation and efficient surface chemistry for oligonucleotide probe immobilization. A mild and stable surface chemistry was first developed that is especially suitable for modifying delicate electronic device surfaces, and a practical application of our GMR biosensors was then demonstrated for detecting four most common human papillomavirus (HPV) subtypes in plasmids. We also showed that the DNA hybridization time could potentially be reduced from overnight to about ten minutes using microfluidics.

Dust evolution, a global view: III. Core/mantle grains, organic nano-globules, comets and surface chemistry

PubMed Central

2016-01-01

Within the framework of The Heterogeneous dust Evolution Model for Interstellar Solids (THEMIS), this work explores the surface processes and chemistry relating to core/mantle interstellar and cometary grain structures and their influence on the nature of these fascinating particles. It appears that a realistic consideration of the nature and chemical reactivity of interstellar grain surfaces could self-consistently and within a coherent framework explain: the anomalous oxygen depletion, the nature of the CO dark gas, the formation of ‘polar ice’ mantles, the red wing on the 3 μm water ice band, the basis for the O-rich chemistry observed in hot cores, the origin of organic nano-globules and the 3.2 μm ‘carbonyl’ absorption band observed in comet reflectance spectra. It is proposed that the reaction of gas phase species with carbonaceous a-C(:H) grain surfaces in the interstellar medium, in particular the incorporation of atomic oxygen into grain surfaces in epoxide functional groups, is the key to explaining these observations. Thus, the chemistry of cosmic dust is much more intimately related with that of the interstellar gas than has previously been considered. The current models for interstellar gas and dust chemistry will therefore most likely need to be fundamentally modified to include these new grain surface processes. PMID:28083090

Microbiological Characterization and Concerns of the International Space Station Internal Active Thermal Control System

NASA Technical Reports Server (NTRS)

Roman, Monsi C.; Wieland, Paul O.

2005-01-01

Since January 1999, the chemical the International Space Station Thermal Control System (IATCS) and microbial state of (ISS) Internal Active fluid has been monitored by analysis of samples returned to Earth. Key chemical parameters have changed over time, including a drop in pH from the specified 9.5 +/- 0.5 ta = 58.4, an increase in the level of total inorganic carbon (TIC), total organic carbon (TOC) and dissolved nickel (Ni) in the fluid, and a decrease in the phosphate (PO,) level. In addition, silver (AS) ion levels in the fluid decreased rapidly as Ag deposited on internal metallic surfaces of the system. The lack of available Ag ions coupled with changes in the fluid chemistry has resulted in a favorable environment for microbial growth. Counts of heterotrophic bacteria have increased from less than 10 colony-forming units (CFUs)/l00 mL to l0(exp 6) to l0(exp 7) CFUs/100 mL. The increase of the microbial population is of concern because uncontrolled microbiological growth in the IATCS can contribute to deterioration in the performance of critical components within the system and potentially impact human health if opportunistic pathogens become established and escape into the cabin atmosphere. Micro-organisms can potentially degrade the coolant chemistry; attach to surfaces and form biofilms; lead to biofouling of filters, tubing, and pumps; decrease flow rates; reduce heat transfer; initiate and accelerate corrosion; and enhance mineral scale formation. The micro- biological data from the ISS IATCS fluid, and approaches to addressing the concerns, are summarized in this paper.

Controlling Short-Range Interactions by Tuning Surface Chemistry in HDPE/Graphene Nanoribbon Nanocomposites.

PubMed

Sadeghi, Soheil; Zehtab Yazdi, Alireza; Sundararaj, Uttandaraman

2015-09-03

Unique dispersion states of nanoparticles in polymeric matrices have the potential to create composites with enhanced mechanical, thermal, and electrical properties. The present work aims to determine the state of dispersion from the melt-state rheological behavior of nanocomposites based on carbon nanotube and graphene nanoribbon (GNR) nanomaterials. GNRs were synthesized from nitrogen-doped carbon nanotubes via a chemical route using potassium permanganate and some second acids. High-density polyethylene (HDPE)/GNR nanocomposite samples were then prepared through a solution mixing procedure. Different nanocomposite dispersion states were achieved using different GNR synthesis methods providing different surface chemistry, interparticle interactions, and internal compartments. Prolonged relaxation of flow induced molecular orientation was observed due to the presence of both carbon nanotubes and GNRs. Based on the results of this work, due to relatively weak interactions between the polymer and the nanofillers, it is expected that short-range interactions between nanofillers play the key role in the final dispersion state.

Influence of short chain organic acids and bases on the wetting properties and surface energy of submicrometer ceramic powders.

PubMed

Neirinck, Bram; Soccol, Dimitri; Fransaer, Jan; Van der Biest, Omer; Vleugels, Jef

2010-08-15

The effect of short chained organic acids and bases on the surface energy and wetting properties of submicrometer alumina powder was assessed. The surface chemistry of treated powders was determined by means of Diffuse Reflectance Infrared Fourier Transform spectroscopy and compared to untreated powder. The wetting of powders was measured using a modified Washburn method, based on the use of precompacted powder samples. The geometric factor needed to calculate the contact angle was derived from measurements of the porous properties of the powder compacts. Contact angle measurements with several probe liquids before and after modification allowed a theoretical estimation of the surface energy based on the surface tension component theory. Trends in the surface energy components were linked to observations in infrared spectra. The results showed that the hydrophobic character of the precompacted powder depends on both the chain length and polar group of the modifying agent. Copyright 2010 Elsevier Inc. All rights reserved.

Mechanism of Zn Insertion into Nanostructured δ-MnO 2 : A Nonaqueous Rechargeable Zn Metal Battery

DOE Office of Scientific and Technical Information (OSTI.GOV)

Han, Sang-Don; Kim, Soojeong; Li, Dongguo

2017-05-19

Unlike the more established lithium-ion based energy storage chemistries, the complex intercalation chemistry of multivalent cations in a host lattice is not well understood, especially the relationship between the intercalating species solution chemistry and the prevalence and type of side reactions. Among multivalent metals, a promising model system can be based on nonaqueous Zn2+ ion chemistry. Several examples of these systems support the use of a Zn metal anode, and reversible intercalation cathodes have been reported. This study utilizes a combination of analytical tools to probe the chemistry of a nanostructured delta-MnO2 cathode in association with a nonaqueous acetonitrile-Zn(TFSI)(2) electrolytemore » and a Zn metal anode. As many of the issues related to understanding a multivalent battery relate to the electrolyte electrode interface, the high surface area of a nanostructured cathode provides a significant interface between the electrolyte and cathode host that maximizes the spectroscopic signal of any side reactions or minor mechanistic pathways. Numerous factors affecting capacity fade and issues associated with the second phase formation including Mn dissolution in heavily cycled Zn/delta-MnO2 cells are presented including dramatic mechanistic differences in the storage mechanism of this couple when compared to similar aqueous electrolytes are noted.« less

3D Printed Potential and Free Energy Surfaces for Teaching Fundamental Concepts in Physical Chemistry

ERIC Educational Resources Information Center

Kaliakin, Danil S.; Zaari, Ryan R.; Varganov, Sergey A.

2015-01-01

Teaching fundamental physical chemistry concepts such as the potential energy surface, transition state, and reaction path is a challenging task. The traditionally used oversimplified 2D representation of potential and free energy surfaces makes this task even more difficult and often confuses students. We show how this 2D representation can be…

Synthesis of GEMS from Shock-accelerated Crystalline Dust in Superbubbles: Model and Predictions

NASA Technical Reports Server (NTRS)

Westphal, Andrew J.; Bradley, John P.

2005-01-01

GEMS (Glass Embedded with Metals and Sulfides) are highly enigmatic yet common components of anhydrous IDPs. We have recently proposed a model of GEMS formation from shock-accelerated crystalline dust in superbubbles[1] which explains the three most perplexing properties of GEMS: pseudomorphism[2], their chemistry[3], and their size range. In this Abstract, we briefly review the main points of the model, and suggest tests that will either prove or rule out this hypothesis.

Impact of Surface Functionalization on the Quantum Coherence of Nitrogen-Vacancy Centers in Nanodiamonds.

PubMed

Ryan, Robert G; Stacey, Alastair; O'Donnell, Kane M; Ohshima, Takeshi; Johnson, Brett C; Hollenberg, Lloyd C L; Mulvaney, Paul; Simpson, David A

2018-04-18

Nanoscale quantum probes such as the nitrogen-vacancy (NV) center in diamonds have demonstrated remarkable sensing capabilities over the past decade as control over fabrication and manipulation of these systems has evolved. The biocompatibility and rich surface chemistry of diamonds has added to the utility of these probes but, as the size of these nanoscale systems is reduced, the surface chemistry of diamond begins to impact the quantum properties of the NV center. In this work, we systematically study the effect of the diamond surface chemistry on the quantum coherence of the NV center in nanodiamonds (NDs) 50 nm in size. Our results show that a borane-reduced diamond surface can on average double the spin relaxation time of individual NV centers in nanodiamonds when compared to thermally oxidized surfaces. Using a combination of infrared and X-ray absorption spectroscopy techniques, we correlate the changes in quantum relaxation rates with the conversion of sp 2 carbon to C-O and C-H bonds on the diamond surface. These findings implicate double-bonded carbon species as a dominant source of spin noise for near surface NV centers. The link between the surface chemistry and quantum coherence indicates that through tailored engineering of the surface, the quantum properties and magnetic sensitivity of these nanoscale systems may approach that observed in bulk diamond.

Characterization of a resorbable poly(ester urethane) with biodegradable hard segments.

PubMed

Dempsey, David K; Robinson, Jennifer L; Iyer, Ananth V; Parakka, James P; Bezwada, Rao S; Cosgriff-Hernandez, Elizabeth M

2014-01-01

The rapid growth of regenerative medicine and drug delivery fields has generated a strong need for improved polymeric materials that degrade at a controlled rate into safe, non-cytotoxic by-products. Polyurethane thermoplastic elastomers offer several advantages over other polymeric materials including tunable mechanical properties, excellent fatigue strength, and versatile processing. The variable segmental chemistry in developing resorbable polyurethanes also enables fine control over the degradation profile as well as the mechanical properties. Linear aliphatic isocyanates are most commonly used in biodegradable polyurethane formulations; however, these aliphatic polyurethanes do not match the mechanical properties of their aromatic counterparts. In this study, a novel poly(ester urethane) (PEsU) synthesized with biodegradable aromatic isocyanates based on glycolic acid was characterized for potential use as a new resorbable material in medical devices. Infrared spectral analysis confirmed the aromatic and phase-separated nature of the PEsU. Uniaxial tensile testing displayed stress-strain behavior typical of a semi-crystalline polymer above its Tg, in agreement with calorimetric findings. PEsU outperformed aliphatic PCL-based polyurethanes likely due to the enhanced cohesion of the aromatic hard domains. Accelerated degradation of the PEsU using 0.1 M sodium hydroxide resulted in hydrolysis of the polyester soft segment on the surface, reduced molecular weight, surface cracking, and a 30% mass loss after four weeks. Calorimetric studies indicated a disruption of the soft segment crystallinity after incubation which corresponded with a drop in initial modulus of the PEsU. Finally, cytocompatibility testing with 3T3 mouse fibroblasts exhibited cell viability on PEsU films comparable to a commercial poly(ether urethane urea) after 24 h followed by 85% cell viability at 72 h. Overall, this new resorbable polyurethane shows strong potential for use in wide range of biomedical applications.

Control of Surface Chemistry, Substrate Stiffness, and Cell Function in a Novel Terpolymer Methacrylate Library

PubMed Central

Joy, Abraham; Cohen, Daniel M.; Luk, Arnold; Anim-Danso, Emmanuel; Chen, Christopher; Kohn, Joachim

2011-01-01

A focused library of methacrylate terpolymers was synthesized to explore the effects of varying surface chemistry and adhesive peptide ligands on cell function. The chemical diversity of methacrylate monomers enabled construction of a library of polymers in which one can systematically vary the chemical composition to achieve a wide range of contact angle, Young's modulus, and Tg values. Furthermore, the materials were designed to allow surface immobilization of bioactive peptides. We then examined the effects of these material compositions on protein adsorption and cell attachment, proliferation, and differentiation. We observed that chemical composition of the polymers was an important determinant for NIH 3T3 cell attachment and proliferation, as well as human mesenchymal stem cell differentiation, and correlated directly with the ability of the polymers to adsorb proteins that mediate cell adhesion. Importantly, functionalization of the methacrylate terpolymer library with an adhesive GRGDS peptide normalized cellular responses. RGD-functionalized polymers uniformly exhibited robust attachment, proliferation, and differentiation irrespective of the underlying substrate chemistry. These studies provide a library-based approach to rapidly explore the biological functionality of biomaterials with a wide range of compositions, and highlights the importance of cell and protein cell adhesion in predicting their performance. PMID:21226505

Physico-chemical changes of ZnO nanoparticles with different size and surface chemistry under physiological pH conditions.

PubMed

Gwak, Gyeong-Hyeon; Lee, Won-Jae; Paek, Seung-Min; Oh, Jae-Min

2015-03-01

We studied the physico-chemical properties of ZnO nanoparticles under physiological pH conditions (gastric, intestinal and plasma) as functions of their size (20 and 70 nm) and surface chemistry (pristine, L-serine, or citrate coating). ZnO nanoparticles were dispersed in phosphate buffered saline under physiological pH conditions and aliquots were collected at specific time points (0.5, 1, 4, 10 and 24 h) for further characterization. The pH values of the aqueous ZnO colloids at each condition were in the neutral to slightly basic range and showed different patterns depending on the original size and surface chemistry of the ZnO nanoparticles. The gastric pH condition was found to significantly dissolve ZnO nanoparticles up to 18-30 wt%, while the intestinal or plasma pH conditions resulted in much lower dissolution amounts than expected. Based on the X-ray diffraction patterns and X-ray absorption spectra, we identified partial phase transition of the ZnO nanoparticles from wurtzite to Zn(OH)2 under the intestinal and plasma pH conditions. Using scanning electron microscopy, we verified that the overall particle size and morphology of all ZnO nanoparticles were maintained regardless of the pH. Copyright © 2015 Elsevier B.V. All rights reserved.

PRECP: the Department of Energy's program on the nonlinearity of acid precipitation processes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tanner, R.L.; Tichler, J.; Brown, R.

During the period of 1 April to 3 May 1985, staff from Argonne National Laboratory (ANL), Brookhaven National Laboratory (BNL), and Pacific Northwest Laboratory (PNL), participated in a multifaceted, coordinated set of field studies from an aircraft logistical base in Columbus, OH, and a surface precipitation and air chemistry network in the Philadelphia area. The general goals of these activities, conducted within the DOE-sponsored PRocessing of Emissions by Clouds and Precipitation (PRECP) program were to obtain information concerning scavenging ratios and the vertical distribution of cloud and precipitation chemistry for sulfur and nitrogen oxides and oxyacids, and for oxidant speciesmore » in the vicinity of precipitating and nonprecipitating clouds. Profiling of pollutant concentrations and phase distributions, and studies of scavenging processes were accomplished principally by airborne measurements of aerosol and gaseous species in pre-cloud and below-cloud air and of aqueous-phase species in clouds and precipitation, accompanied by documentation of meteorological and cloud physics parameters in the sampled regimes. Studies in the Midwest utilized only limited surface precipitation collection and chemical measurements, whereas a more extensive ground precipitation network was deployed in the Philadelphia area studies together with surface air chemistry measurements at a single nonurban site.« less

Effect of gaseous ammonia on nicotine sorption

DOE Office of Scientific and Technical Information (OSTI.GOV)

Webb, A.M.; Singer, B.C.; Nazaroff, W.W.

2002-06-01

Nicotine is a major constituent of environmental tobacco smoke. Sorptive interactions of nicotine with indoor surfaces can substantially alter indoor concentrations. The phenomenon is poorly understood, including whether sorption is fully reversible or partially irreversible. They hypothesize that acid-base chemistry on indoor surfaces might contribute to the apparent irreversibility of nicotine sorption under some circumstances. Specifically, they suggest that nicotine may become protonated on surfaces, markedly reducing its vapor pressure. If so, subsequent exposure of the surface to gaseous ammonia, a common base, could raise the surface pH, causing deprotonation and desorption of nicotine from surfaces. A series of experimentsmore » was conducted to explore the effect of ammonia on nicotine sorption to and reemission from surfaces. The results indicate that, under some conditions, exposure to gaseous ammonia can substantially increase the rate of desorption of previously sorbed nicotine from common indoor surface materials.« less

Improving Ionic Conductivity and Lithium-Ion Transference Number in Lithium-Ion Battery Separators.

PubMed

Zahn, Raphael; Lagadec, Marie Francine; Hess, Michael; Wood, Vanessa

2016-12-07

The microstructure of lithium-ion battery separators plays an important role in separator performance; however, here we show that a geometrical analysis falls short in predicting the lithium-ion transport in the electrolyte-filled pore space. By systematically modifying the surface chemistry of a commercial polyethylene separator while keeping its microstructure unchanged, we demonstrate that surface chemistry, which alters separator-electrolyte interactions, influences ionic conductivity and lithium-ion transference number. Changes in separator surface chemistry, particularly those that increase lithium-ion transference numbers can reduce voltage drops across the separator and improve C-rate capability.

Effect of non-equilibrium flow chemistry and surface catalysis on surface heating to AFE

NASA Technical Reports Server (NTRS)

Stewart, David A.; Henline, William D.; Chen, Yih-Kanq

1991-01-01

The effect of nonequilibrium flow chemistry on the surface temperature distribution over the forebody heat shield on the Aeroassisted Flight Experiment (AFE) vehicle was investigated using a reacting boundary-layer code. Computations were performed by using boundary-layer-edge properties determined from global iterations between the boundary-layer code and flow field solutions from a viscous shock layer (VSL) and a full Navier-Stokes solution. Surface temperature distribution over the AFE heat shield was calculated for two flight conditions during a nominal AFE trajectory. This study indicates that the surface temperature distribution is sensitive to the nonequilibrium chemistry in the shock layer. Heating distributions over the AFE forebody calculated using nonequilibrium edge properties were similar to values calculated using the VSL program.

The chemistry-climate model ECHAM6.3-HAM2.3-MOZ1.0

NASA Astrophysics Data System (ADS)

Schultz, Martin G.; Stadtler, Scarlet; Schröder, Sabine; Taraborrelli, Domenico; Franco, Bruno; Krefting, Jonathan; Henrot, Alexandra; Ferrachat, Sylvaine; Lohmann, Ulrike; Neubauer, David; Siegenthaler-Le Drian, Colombe; Wahl, Sebastian; Kokkola, Harri; Kühn, Thomas; Rast, Sebastian; Schmidt, Hauke; Stier, Philip; Kinnison, Doug; Tyndall, Geoffrey S.; Orlando, John J.; Wespes, Catherine

2018-05-01

The chemistry-climate model ECHAM-HAMMOZ contains a detailed representation of tropospheric and stratospheric reactive chemistry and state-of-the-art parameterizations of aerosols using either a modal scheme (M7) or a bin scheme (SALSA). This article describes and evaluates the model version ECHAM6.3-HAM2.3-MOZ1.0 with a focus on the tropospheric gas-phase chemistry. A 10-year model simulation was performed to test the stability of the model and provide data for its evaluation. The comparison to observations concentrates on the year 2008 and includes total column observations of ozone and CO from IASI and OMI, Aura MLS observations of temperature, HNO3, ClO, and O3 for the evaluation of polar stratospheric processes, an ozonesonde climatology, surface ozone observations from the TOAR database, and surface CO data from the Global Atmosphere Watch network. Global budgets of ozone, OH, NOx, aerosols, clouds, and radiation are analyzed and compared to the literature. ECHAM-HAMMOZ performs well in many aspects. However, in the base simulation, lightning NOx emissions are very low, and the impact of the heterogeneous reaction of HNO3 on dust and sea salt aerosol is too strong. Sensitivity simulations with increased lightning NOx or modified heterogeneous chemistry deteriorate the comparison with observations and yield excessively large ozone budget terms and too much OH. We hypothesize that this is an impact of potential issues with tropical convection in the ECHAM model.

Particle acceleration in pulsar magnetospheres

NASA Technical Reports Server (NTRS)

Baker, K. B.

1978-01-01

The structure of pulsar magnetospheres and the acceleration mechanism for charged particles in the magnetosphere was studied using a pulsar model which required large acceleration of the particles near the surface of the star. A theorem was developed which showed that particle acceleration cannot be expected when the angle between the magnetic field lines and the rotation axis is constant (e.g. radial field lines). If this angle is not constant, however, acceleration must occur. The more realistic model of an axisymmetric neutron star with a strong dipole magnetic field aligned with the rotation axis was investigated. In this case, acceleration occurred at large distances from the surface of the star. The magnitude of the current can be determined using the model presented. In the case of nonaxisymmetric systems, the acceleration is expected to occur nearer to the surface of the star.

Integrating computational methods to retrofit enzymes to synthetic pathways.

PubMed

Brunk, Elizabeth; Neri, Marilisa; Tavernelli, Ivano; Hatzimanikatis, Vassily; Rothlisberger, Ursula

2012-02-01

Microbial production of desired compounds provides an efficient framework for the development of renewable energy resources. To be competitive to traditional chemistry, one requirement is to utilize the full capacity of the microorganism to produce target compounds with high yields and turnover rates. We use integrated computational methods to generate and quantify the performance of novel biosynthetic routes that contain highly optimized catalysts. Engineering a novel reaction pathway entails addressing feasibility on multiple levels, which involves handling the complexity of large-scale biochemical networks while respecting the critical chemical phenomena at the atomistic scale. To pursue this multi-layer challenge, our strategy merges knowledge-based metabolic engineering methods with computational chemistry methods. By bridging multiple disciplines, we provide an integral computational framework that could accelerate the discovery and implementation of novel biosynthetic production routes. Using this approach, we have identified and optimized a novel biosynthetic route for the production of 3HP from pyruvate. Copyright © 2011 Wiley Periodicals, Inc.

ANNUAL REPORT, JULY 1, 1960

DOE Office of Scientific and Technical Information (OSTI.GOV)

None

1961-10-31

Research facilities, general construction progress, research activities, and administration are discussed and a financial statement is given. Fairly detailed accounts are given of research programs in the fields of physics, accelerator development, instrumentation, applied mathematics, chemistry, nuclear engineering, biology, and medicine. (M.C.G.)

Discrete event performance prediction of speculatively parallel temperature-accelerated dynamics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zamora, Richard James; Voter, Arthur F.; Perez, Danny

Due to its unrivaled ability to predict the dynamical evolution of interacting atoms, molecular dynamics (MD) is a widely used computational method in theoretical chemistry, physics, biology, and engineering. Despite its success, MD is only capable of modeling time scales within several orders of magnitude of thermal vibrations, leaving out many important phenomena that occur at slower rates. The Temperature Accelerated Dynamics (TAD) method overcomes this limitation by thermally accelerating the state-to-state evolution captured by MD. Due to the algorithmically complex nature of the serial TAD procedure, implementations have yet to improve performance by parallelizing the concurrent exploration of multiplemore » states. Here we utilize a discrete event-based application simulator to introduce and explore a new Speculatively Parallel TAD (SpecTAD) method. We investigate the SpecTAD algorithm, without a full-scale implementation, by constructing an application simulator proxy (SpecTADSim). Finally, following this method, we discover that a nontrivial relationship exists between the optimal SpecTAD parameter set and the number of CPU cores available at run-time. Furthermore, we find that a majority of the available SpecTAD boost can be achieved within an existing TAD application using relatively simple algorithm modifications.« less

Discrete event performance prediction of speculatively parallel temperature-accelerated dynamics

DOE PAGES

Zamora, Richard James; Voter, Arthur F.; Perez, Danny; ...

2016-12-01

Due to its unrivaled ability to predict the dynamical evolution of interacting atoms, molecular dynamics (MD) is a widely used computational method in theoretical chemistry, physics, biology, and engineering. Despite its success, MD is only capable of modeling time scales within several orders of magnitude of thermal vibrations, leaving out many important phenomena that occur at slower rates. The Temperature Accelerated Dynamics (TAD) method overcomes this limitation by thermally accelerating the state-to-state evolution captured by MD. Due to the algorithmically complex nature of the serial TAD procedure, implementations have yet to improve performance by parallelizing the concurrent exploration of multiplemore » states. Here we utilize a discrete event-based application simulator to introduce and explore a new Speculatively Parallel TAD (SpecTAD) method. We investigate the SpecTAD algorithm, without a full-scale implementation, by constructing an application simulator proxy (SpecTADSim). Finally, following this method, we discover that a nontrivial relationship exists between the optimal SpecTAD parameter set and the number of CPU cores available at run-time. Furthermore, we find that a majority of the available SpecTAD boost can be achieved within an existing TAD application using relatively simple algorithm modifications.« less

The Interaction of UV-Laser Radiation with Metal and Semiconductor Surfaces

DTIC Science & Technology

1992-05-26

order of magnitude larger than the typical widths of non- 43 R.C. Weast, ed., Handbook of Chemistry and Physics, p. D-185 (CRC Press, 1986). 25 resonant...fundamental chemistry and practical applications of laser chemical processing techniques involved photofragmentation of relatively 28 simple metal-alkyl...pressure of the gas was monitored with a capacitance manometer. A variety of techniques were used in this work to examine the surface-phase chemistry and

Chemistry Division: Annual progress report for period ending March 31, 1987

DOE Office of Scientific and Technical Information (OSTI.GOV)

Not Available

1987-08-01

This report is divided into the following sections: coal chemistry; aqueous chemistry at high temperatures and pressures; geochemistry of crustal processes to high temperatures and pressures; chemistry of advanced inorganic materials; structure and dynamics of advanced polymeric materials; chemistry of transuranium elements and compounds; separations chemistry; reactions and catalysis in molten salts; surface science related to heterogeneous catalysis; electron spectroscopy; chemistry related to nuclear waste disposal; computational modeling of security document printing; and special topics. (DLC)

Diameter and Geometry Control of Vertically Aligned SWNTs through Catalyst Manipulation

NASA Astrophysics Data System (ADS)

Xiang, Rong; Einarsson, Erik; Okawa, Jun; Murakami, Yoichi; Maruyama, Shigeo

2009-03-01

We present our recent progress on manipulating our liquid-based catalyst loading process, which possesses greater potential than conventional deposition in terms of cost and scalability, to control the diameter and morphology of single-walled carbon nanotubes (SWNTs). We demonstrate that the diameter of aligned SWNTs synthesized by alcohol catalytic CVD can be tailored over a wide range by modifying the catalyst recipe. SWNT arrays with an average diameter as small as 1.2 nm were obtained by this method. Additionally, owing to the alignment of the array, the continuous change of the SWNT diameter during a single CVD process can be clearly observed and quantitatively characterized. We have also developed a versatile wet chemistry method to localize the growth of SWNTs to desired regions via surface modification. By functionalizing the silicon surface using a classic self-assembled monolayer, the catalyst can be selectively dip-coated onto hydrophilic areas of the substrate. This technique was successful in producing both random and aligned SWNTs with various patterns. The precise control of the diameter and morphology of SWNTs, achieved by simple and scalable liquid-based surface chemistry, could greatly facilitate the application of SWNTs as the building blocks of future nano-devices.

ZnO synthesis by high vacuum plasma-assisted chemical vapor deposition using dimethylzinc and atomic oxygen

NASA Astrophysics Data System (ADS)

Barnes, Teresa M.; Hand, Steve; Leaf, Jackie; Wolden, Colin A.

2004-09-01

Zinc oxide thin films were produced by high vacuum plasma-assisted chemical vapor deposition (HVP-CVD) from dimethylzinc (DMZn) and atomic oxygen. HVP-CVD is differentiated from conventional remote plasma-enhanced CVD in that the operating pressures of the inductively coupled plasma (ICP) source and the deposition chamber are decoupled. Both DMZn and atomic oxygen effuse into the deposition chamber under near collisionless conditions. The deposition rate was measured as a function of DMZn and atomic oxygen flux on glass and silicon substrates. Optical emission spectroscopy and quadrupole mass spectrometry (QMS) were used to provide real time analysis of the ICP source and the deposition chamber. The deposition rate was found to be first order in DMZn pressure and zero order in atomic oxygen density. All films demonstrated excellent transparency and were preferentially orientated along the c-axis. The deposition chemistry occurs exclusively through surface-mediated reactions, since the collisionless transport environment eliminates gas-phase chemistry. QMS analysis revealed that DMZn was almost completely consumed, and desorption of unreacted methyl radicals was greatly accelerated in the presence of atomic oxygen. Negligible zinc was detected in the gas phase, suggesting that Zn was efficiently consumed on the substrate and walls of the reactor.

Purdue Rare Isotope Measurement Laboratory

NASA Astrophysics Data System (ADS)

Caffee, M.; Elmore, D.; Granger, D.; Muzikar, P.

2002-12-01

The Purdue Rare Isotope Measurement Laboratory (PRIME Lab) is a dedicated research and service facility for accelerator mass spectrometry. AMS is an ultra-sensitive analytical technique used to measure low levels of long-lived cosmic-ray-produced and anthropogenic radionuclides, and rare trace elements. We measure 10Be (T1/2 = 1.5 My), 26Al (.702 My), 36Cl (.301 My), and 129I (16 My), in geologic samples. Applications include dating the cosmic-ray-exposure time of rocks on Earth's surface, determining rock and sediment burial ages, measuring the erosion rates of rocks and soils, and tracing and dating ground water. We perform sample preparation and separation chemistries for these radio-nuclides for our internal research activities and for those external researchers not possessing this capability. Our chemical preparation laboratories also serve as training sites for members of the geoscience community developing these techniques at their institutions. Research at Purdue involves collaborators among members of the Purdue Departments of Physics, Earth and Atmospheric Sciences, Chemistry, Agronomy, and Anthropology. We also collaborate and serve numerous scientists from other institutions. We are currently in the process of modernizing the facility with the goals of higher precision for routinely measured radio-nuclides, increased sample throughput, and the development of new measurement capabilities for the geoscience community.

Front surface structured targets for enhancing laser-plasma interactions

NASA Astrophysics Data System (ADS)

Snyder, Joseph; George, Kevin; Ji, Liangliang; Yalamanchili, Sasir; Simonoff, Ethan; Cochran, Ginevra; Daskalova, Rebecca; Poole, Patrick; Willis, Christopher; Lewis, Nathan; Schumacher, Douglass

2016-10-01

We present recent progress made using front surface structured interfaces for enhancing ultrashort, relativistic laser-plasma interactions. Structured targets can increase laser absorption and enhance ion acceleration through a number of mechanisms such as direct laser acceleration and laser guiding. We detail experimental results obtained at the Scarlet laser facility on hollow, micron-scale plasma channels for enhancing electron acceleration. These targets show a greater than three times enhancement in the electron cutoff energy as well as an increased slope temperature for the electron distribution when compared to a flat interface. Using three-dimensional particle-in-cell (PIC) simulations, we have modeled the interaction to give insight into the physical processes responsible for the enhancement. Furthermore, we have used PIC simulations to design structures that are more advantageous for ion acceleration. Such targets necessitate advanced target fabrication methods and we describe techniques used to manufacture optimized structures, including vapor-liquid-solid growth, cryogenic etching, and 3D printing using two-photon-polymerization. This material is based upon work supported by the Air Force Office of Scientific Research under Award Number FA9550-14-1-0085.

Sub-nanometer surface chemistry and orbital hybridization in lanthanum-doped ceria nano-catalysts revealed by 3D electron microscopy.

PubMed

Collins, Sean M; Fernandez-Garcia, Susana; Calvino, José J; Midgley, Paul A

2017-07-14

Surface chemical composition, electronic structure, and bonding characteristics determine catalytic activity but are not resolved for individual catalyst particles by conventional spectroscopy. In particular, the nano-scale three-dimensional distribution of aliovalent lanthanide dopants in ceria catalysts and their effect on the surface electronic structure remains unclear. Here, we reveal the surface segregation of dopant cations and oxygen vacancies and observe bonding changes in lanthanum-doped ceria catalyst particle aggregates with sub-nanometer precision using a new model-based spectroscopic tomography approach. These findings refine our understanding of the spatially varying electronic structure and bonding in ceria-based nanoparticle aggregates with aliovalent cation concentrations and identify new strategies for advancing high efficiency doped ceria nano-catalysts.

Monolayer of Hydrazine Facilitates the Direct Covalent Attachment of C60 Fullerene to a Silicon Surface.

PubMed

Gao, Fei; Teplyakov, Andrew V

2017-09-05

The development of oxygen-free organic-inorganic interfaces has led to new schemes for the functionalization of silicon surfaces with nitrogen-based chemical groups. However, building layers of large structures directly on this functionalized surface has remained elusive. This work confirms the path to form a stable interface between silicon and buckminsterfullerene C 60 based on covalent chemical bonds. The starting point for this modification is the hydrazine-reacted Si(111) surface with the diamine functionality, which is further reacted directly with the C 60 molecules. The chemistry of this process is confirmed spectroscopically and microscopically and can be used to form organic-inorganic interfaces separated by a single layer of nitrogen.

Self-referenced directional enhanced Raman scattering using plasmon waveguide resonance for surface and bulk sensing

NASA Astrophysics Data System (ADS)

Wan, Xiu-mei; Gao, Ran; Lu, Dan-feng; Qi, Zhi-mei

2018-01-01

Surface plasmon-coupled emission has been widely used in fluorescence imaging, biochemical sensing, and enhanced Raman spectroscopy. A self-referenced directional enhanced Raman scattering for simultaneous detection of surface and bulk effects by using plasmon waveguide resonance (PWR) based surface plasmon-coupled emission has been proposed and experimentally demonstrated. Raman scattering was captured on the prism side in Kretschmann-surface plasmon-coupled emission. The distinct penetration depths (δ) of the evanescent field for the transverse electric (TE) and transverse magnetic (TM) modes result in different detected distances of the Raman signal. The experimental results demonstrate that the self-referenced directional enhanced Raman scattering of the TE and TM modes based on the PWR can detect and distinguish the surface and bulk effects simultaneously, which appears to have potential applications in researches of chemistry, medicine, and biology.

Uniformity studies of inductively coupled plasma etching in fabrication of HgCdTe detector arrays

NASA Astrophysics Data System (ADS)

Bommena, R.; Velicu, S.; Boieriu, P.; Lee, T. S.; Grein, C. H.; Tedjojuwono, K. K.

2007-04-01

Inductively coupled plasma (ICP) chemistry based on a mixture of CH 4, Ar, and H II was investigated for the purpose of delineating HgCdTe mesa structures and vias typically used in the fabrication of second and third generation infrared photo detector arrays. We report on ICP etching uniformity results and correlate them with plasma controlling parameters (gas flow rates, total chamber pressure, ICP power and RF power). The etching rate and surface morphology of In-doped MWIR and LWIR HgCdTe showed distinct dependences on the plasma chemistry, total pressure and RF power. Contact stylus profilometry and cross-section scanning electron microscopy (SEM) were used to characterize the anisotropy of the etched profiles obtained after various processes and a standard deviation of 0.06 μm was obtained for etch depth on 128 x 128 format array vias. The surface morphology and the uniformity of the etched surfaces were studied by plan view SEM. Atomic force microscopy was used to make precise assessments of surface roughness.

Surface Chemistry and Nano-/Microstructure Engineering on Photocatalytic In2S3 Nanocrystals.

PubMed

Berestok, Taisiia; Guardia, Pablo; Portals, Javier Blanco; Estradé, Sònia; Llorca, Jordi; Peiró, Francesca; Cabot, Andreu; Brock, Stephanie L

2018-06-05

Colloidal nanocrystals (NCs) compete with molecular catalysts in the field of homogenous catalysis, offering easier recyclability and a number of potentially advantageous functionalities, such as tunable band gaps, plasmonic properties, or a magnetic moment. Using high-throughput printing technologies, colloidal NCs can also be supported onto substrates to produce cost-effective electronic, optoelectronic, electrocatalytic, and sensing devices. For both catalytic and technological application, NC surface chemistry and supracrystal organization are key parameters determining final performance. Here, we study the influence of the surface ligands and the NC organization on the catalytic properties of In 2 S 3 , both as a colloid and as a supported layer. As a colloid, NCs stabilized by inorganic ligands show the highest photocatalytic activities, which we associate with their large and more accessible surfaces. On the other hand, when NCs are supported on a substrate, their organization becomes an essential parameter determining performance. For instance, NC-based films produced through a gelation process provided five-fold higher photocurrent densities than those obtained from dense films produced by the direct printing of NCs.

Ferroelectric based catalysis: Switchable surface chemistry

NASA Astrophysics Data System (ADS)

Kakekhani, Arvin; Ismail-Beigi, Sohrab

2015-03-01

We describe a new class of catalysts that uses an epitaxial monolayer of a transition metal oxide on a ferroelectric substrate. The ferroelectric polarization switches the surface chemistry between strongly adsorptive and strongly desorptive regimes, circumventing difficulties encountered on non-switchable catalytic surfaces where the Sabatier principle dictates a moderate surface-molecule interaction strength. This method is general and can, in principle, be applied to many reactions, and for each case the choice of the transition oxide monolayer can be optimized. Here, as a specific example, we show how simultaneous NOx direct decomposition (into N2 and O2) and CO oxidation can be achieved efficiently on CrO2 terminated PbTiO3, while circumventing oxygen (and sulfur) poisoning issues. One should note that NOx direct decomposition has been an open challenge in automotive emission control industry. Our method can expand the range of catalytically active elements to those which are not conventionally considered for catalysis and which are more economical, e.g., Cr (for NOx direct decomposition and CO oxidation) instead of canonical precious metal catalysts. Primary support from Toyota Motor Engineering and Manufacturing, North America, Inc.

The Effects of Interactive Stratospheric Chemistry on Antarctic and Southern Ocean Climate Change in an AOGCM

NASA Technical Reports Server (NTRS)

Li, Feng; Newman, Paul; Pawson, Steven; Waugh, Darryn

2014-01-01

Stratospheric ozone depletion has played a dominant role in driving Antarctic climate change in the last decades. In order to capture the stratospheric ozone forcing, many coupled atmosphere-ocean general circulation models (AOGCMs) prescribe the Antarctic ozone hole using monthly and zonally averaged ozone field. However, the prescribed ozone hole has a high ozone bias and lacks zonal asymmetry. The impacts of these biases on model simulations, particularly on Southern Ocean and the Antarctic sea ice, are not well understood. The purpose of this study is to determine the effects of using interactive stratospheric chemistry instead of prescribed ozone on Antarctic and Southern Ocean climate change in an AOGCM. We compare two sets of ensemble simulations for the 1960-2010 period using different versions of the Goddard Earth Observing System 5 - AOGCM: one with interactive stratospheric chemistry, and the other with prescribed monthly and zonally averaged ozone and 6 other stratospheric radiative species calculated from the interactive chemistry simulations. Consistent with previous studies using prescribed sea surface temperatures and sea ice concentrations, the interactive chemistry runs simulate a deeper Antarctic ozone hole and consistently larger changes in surface pressure and winds than the prescribed ozone runs. The use of a coupled atmosphere-ocean model in this study enables us to determine the impact of these surface changes on Southern Ocean circulation and Antarctic sea ice. The larger surface wind trends in the interactive chemistry case lead to larger Southern Ocean circulation trends with stronger changes in northerly and westerly surface flow near the Antarctica continent and stronger upwelling near 60S. Using interactive chemistry also simulates a larger decrease of sea ice concentrations. Our results highlight the importance of using interactive chemistry in order to correctly capture the influences of stratospheric ozone depletion on climate change over Antarctic and the Southern Ocean.

Correlations between the interfacial chemistry and current-voltage behavior of n-GaAs/liquid junctions

NASA Technical Reports Server (NTRS)

Tufts, Bruce J.; Casagrande, Louis G.; Lewis, Nathan S.; Grunthaner, Frank J.

1990-01-01

Correlations between the surface chemistry of etched, (100) oriented n-GaAs electrodes and their subsequent photoelectrochemical behavior have been probed by high-resolution X-ray photoelectron spectroscopy. GaAs photoanodes were chemically treated to prepare either an oxide-free near stoichiometric surface, a surface enriched in zero-valent arsenic or a substrate-oxide terminated surface. The current-voltage (I-V) behavior of each surface type was subsequently monitored in contact with several electrolytes.

Various fates of neuronal progenitor cells observed on several different chemical functional groups

NASA Astrophysics Data System (ADS)

Liu, Xi; Wang, Ying; He, Jin; Wang, Xiu-Mei; Cui, Fu-Zhai; Xu, Quan-Yuan

2011-12-01

Neuronal progenitor cells cultured on gold-coated glass surfaces modified by different chemical functional groups, including hydroxyl (-OH), carboxyl (-COOH), amino (-NH2), bromo (-Br), mercapto (-SH), - Phenyl and methyl (-CH3), were studied here to investigate the influence of surface chemistry on the cells' adhesion, morphology, proliferation and functional gene expression. Focal adhesion staining indicated in the initial culture stage cells exhibited morphological changes in response to different chemical functional groups. Cells cultured on -NH2 grafted surface displayed focal adhesion plaque and flattened morphology and had the largest contact area. However, their counter parts on -CH3 grafted surface displayed no focal adhesion and rounded morphology and had the smallest contact area. After 6 days culture, the proliferation trend was as follows: -NH2 > -SH> -COOH> - Phenyl > - Br > -OH> -CH3. To determine the neural functional properties of the cells affected by surface chemistry, the expression of glutamate decarboxylase (GAD67), nerve growth factor (NGF) and brainderived neurotrophic factor (BDNF) were characterized. An increase of GAD67 expression was observed on -NH2, -COOH and -SH grafted surfaces, while no increase in NGF and BDNF expression was observed on any chemical surfaces. These results highlight the importance of surface chemistry in the fate determination of neuronal progenitor cells, and suggest that surface chemistry must be considered in the design of biomaterials for neural tissue engineering.

Benzotriazole a Corrosion Inhibitor for Antiques: Some Practical Surface Chemistry.

ERIC Educational Resources Information Center

Walker, Robert

1980-01-01

Describes the structure and inhibitive properties of Benzotriazole. The chemical may be employed as an inhibitor to reduce corrosion of articles during storage or display. It may be applied to copper and copper-based antiques as well as to silver and other metals. (Author/JN)

Building ultramicropores within organic polymers based on a thermosetting cyanate ester resin.

PubMed

Zhang, Bufeng; Wang, Zhonggang

2009-09-07

Ultramicropores with high surface areas (>530 m(2) g(-1)) and narrow micropore size distribution (4-6 A) were engineered within a new cyanate ester resin, extending the microporous concept (<20 A) to general thermosetting resins in the area of polymer chemistry.

Ethers on Si(001): A Prime Example for the Common Ground between Surface Science and Molecular Organic Chemistry.

PubMed

Pecher, Lisa; Laref, Slimane; Raupach, Marc; Tonner, Ralf

2017-11-20

By using computational chemistry it has been shown that the adsorption of ether molecules on Si(001) under ultrahigh vacuum conditions can be understood with classical concepts of organic chemistry. Detailed analysis of the two-step reaction mechanism-1) formation of a dative bond between the ether oxygen atom and a Lewis acidic surface atom and 2) nucleophilic attack of a nearby Lewis basic surface atom-shows that it mirrors acid-catalyzed ether cleavage in solution. The O-Si dative bond is the strongest of its kind, and the reactivity in step 2 defies the Bell-Evans-Polanyi principle. Electron rearrangement during C-O bond cleavage has been visualized with a newly developed method for analyzing bonding, which shows that the mechanism of nucleophilic substitutions on semiconductor surfaces is identical to molecular S N 2 reactions. Our findings illustrate how surface science and molecular chemistry can mutually benefit from each other and unexpected insight can be gained. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Reactions at surfaces in the atmosphere: integration of experiments and theory as necessary (but not necessarily sufficient) for predicting the physical chemistry of aerosols.

PubMed

Finlayson-Pitts, Barbara J

2009-09-28

While particles have significant deleterious impacts on human health, visibility and climate, quantitative understanding of their formation, composition and fates remains problematic. Indeed, in many cases, even qualitative understanding is lacking. One area of particular uncertainty is the nature of particle surfaces and how this determines interactions with gases in the atmosphere, including water, which is important for cloud formation and properties. The focus in this Perspective article is on some chemistry relevant to airborne particles and especially to reactions occurring on their surfaces. The intent is not to provide a comprehensive review, but rather to highlight a few selected examples of interface chemistry involving inorganic and organic species that may be important in the lower atmosphere. This includes sea salt chemistry, nitrate and nitrite ion photochemistry, organics on surfaces and heterogeneous reactions of oxides of nitrogen on proxies for airborne mineral dust and boundary layer surfaces. Emphasis is on the molecular level understanding that can only be gained by fully integrating experiment and theory to elucidate these complex systems.

Chemistry Modeling for Aerothermodynamics and TPS

NASA Technical Reports Server (NTRS)

Wang, Dunyou; Stallcop, James R.; Dateo, Christopher e.; Schwenke, David W.; Halicioglu, Timur; Huo, winifred M.

2005-01-01

Recent advances in supercomputers and highly scalable quantum chemistry software render computational chemistry methods a viable means of providing chemistry data for aerothermal analysis at a specific level of confidence. Four examples of first principles quantum chemistry calculations will be presented. Study of the highly nonequilibrium rotational distribution of a nitrogen molecule from the exchange reaction N + N2 illustrates how chemical reactions can influence rotational distribution. The reaction C2H + H2 is one example of a radical reaction that occurs during hypersonic entry into an atmosphere containing methane. A study of the etching of a Si surface illustrates our approach to surface reactions. A recently developed web accessible database and software tool (DDD) that provides the radiation profile of diatomic molecules is also described.

Chemistry Modeling for Aerothermodynamics and TPS

NASA Technical Reports Server (NTRS)

Wang, Dun-You; Stallcop, James R.; Dateo, Christopher E.; Schwenke, David W.; Haliciogiu, Timur; Huo, Winifred

2004-01-01

Recent advances in supercomputers and highly scalable quantum chemistry software render computational chemistry methods a viable means of providing chemistry data for aerothermal analysis at a specific level of confidence. Four examples of first principles quantum chemistry calculations will be presented. The study of the highly nonequilibrium rotational distribution of nitrogen molecule from the exchange reaction N + N2 illustrates how chemical reactions can influence the rotational distribution. The reaction C2H + H2 is one example of a radical reaction that occurs during hypersonic entry into a methane containing atmosphere. A study of the etching of Si surface illustrates our approach to surface reactions. A recently developed web accessible database and software tool (DDD) that provides the radiation profile of diatomic molecules is also described.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Perriot, Romain; Dholabhai, Pratik P.; Uberuaga, Blas P.

Pyrochlores, a class of complex oxides with formula A 2B 2O 7, are one of the candidates for nuclear waste encapsulation, due to the natural occurrence of actinide-bearing pyrochlore minerals and laboratory observations of high radiation tolerance. In this work, we use atomistic simulations to determine the role of surfaces, chemical interfaces, and cation disorder on the plutonium immobilization properties of pyrochlores as a function of pyrochlore chemistry. We find that both Pu 3+ and Pu 4+ segregate to the surface for the four low-index pyrochlore surfaces considered, and that the segregation energy varies with the chemistry of the compound.more » We also find that pyrochlore/pyrochlore bicrystals A 2B 2O 7/A 2'B 2'O 7 can be used to immobilize Pu 3+ and Pu 4+ either in the same or separate phases of the compound, depending on the chemistry of the material. Finally, we find that Pu 4+ segregates to the disordered phase of an order/disorder bicrystal, driven by the occurrence of local oxygen-rich environments. However, Pu 3+ is weakly sensitive to the oxygen environment, and therefore only slightly favors the disordered phase. This behavior suggests that, at some concentration, Pu incorporation can destabilize the pyrochlore structure. Together, these results provide new insight into the ability of pyrochlore compounds to encapsulate Pu and suggest new considerations in the development of waste forms based on pyrochlores. Particularly, the phase structure of a multi-phase pyrochlore composite can be used to independently getter decay products based on their valence and size.« less

Electron acceleration by surface plasma waves in double metal surface structure

NASA Astrophysics Data System (ADS)

Liu, C. S.; Kumar, Gagan; Singh, D. B.; Tripathi, V. K.

2007-12-01

Two parallel metal sheets, separated by a vacuum region, support a surface plasma wave whose amplitude is maximum on the two parallel interfaces and minimum in the middle. This mode can be excited by a laser using a glass prism. An electron beam launched into the middle region experiences a longitudinal ponderomotive force due to the surface plasma wave and gets accelerated to velocities of the order of phase velocity of the surface wave. The scheme is viable to achieve beams of tens of keV energy. In the case of a surface plasma wave excited on a single metal-vacuum interface, the field gradient normal to the interface pushes the electrons away from the high field region, limiting the acceleration process. The acceleration energy thus achieved is in agreement with the experimental observations.

Covalent Surface Modifications of Carbon Nanotubes.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pavia Sanders, Adriana; O'Bryan, Greg

A report meant to document the chemistries investigated by the author for covalent surface modification of CNTs. Oxidation, cycloaddition, and radical reactions were explored to determine their success at covalently altering the CNT surface. Characterization through infrared spectroscopy, Raman spectroscopy, and thermo gravimetric analysis was performed in order to determine the success of the chemistries employed. This report is not exhaustive and was performed for CNT surface modification exploration as it pertains to the "Next Gen" project.

COSMIC-RAY-MEDIATED FORMATION OF BENZENE ON THE SURFACE OF SATURN'S MOON TITAN

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhou Li; Zheng Weijun; Kaiser, Ralf I.

2010-08-01

The aromatic benzene molecule (C{sub 6}H{sub 6})-a central building block of polycyclic aromatic hydrocarbon molecules-is of crucial importance for the understanding of the organic chemistry of Saturn's largest moon, Titan. Here, we show via laboratory experiments and electronic structure calculations that the benzene molecule can be formed on Titan's surface in situ via non-equilibrium chemistry by cosmic-ray processing of low-temperature acetylene (C{sub 2}H{sub 2}) ices. The actual yield of benzene depends strongly on the surface coverage. We suggest that the cosmic-ray-mediated chemistry on Titan's surface could be the dominant source of benzene, i.e., a factor of at least two ordersmore » of magnitude higher compared to previously modeled precipitation rates, in those regions of the surface which have a high surface coverage of acetylene.« less