Showing papers by "Ames Research Center published in 2003"

Carbon Nanotube Sensors for Gas and Organic Vapor Detection

Abstract: A gas sensor, fabricated by the simple casting of single-walled carbon nanotubes (SWNTs) on an interdigitated electrode (IDE), is presented for gas and organic vapor detection at room temperature. The sensor responses are linear for concentrations of sub ppm to hundreds of ppm with detection limits of 44 ppb for NO2 and 262 ppb for nitrotoluene. The time is on the order of seconds for the detection response and minutes for the recovery. The variation of the sensitivity is less than 6% for all of the tested devices, comparable with commercial metal oxide or polymer microfilm sensors while retaining the room-temperature high sensitivity of the SWNT transistor sensors and manufacturability of the commercial sensors. The extended detection capability from gas to organic vapors is attributed to direct charge transfer on individual semiconducting SWNT conductivity with additional electron hopping effects on intertube conductivity through physically adsorbed molecules between SWNTs.

SINGS: The SIRTF Nearby Galaxies Survey

Abstract: The SIRTF Nearby Galaxy Survey is a comprehensive infrared imaging and spectroscopic survey of 75 nearby galaxies. Its primary goal is to characterize the infrared emission of galaxies and their principal infrared-emitting components, across a broad range of galaxy properties and star formation environments. SINGS will provide new insights into the physical processes connecting star formation to the interstellar medium properties of galaxies and provide a vital foundation for understanding infrared observations of the distant universe and ultraluminous and active galaxies. The galaxy sample and observing strategy have been designed to maximize the scientific and archival value of the data set for the SIRTF user community at large. The SIRTF images and spectra will be supplemented by a comprehensive multiwavelength library of ancillary and complementary observations, including radio continuum, H i, CO, submillimeter, BVRIJHK ,H a ,P aa, ultraviolet, and X-ray data. This paper describes the main astrophysical issues to be addressed by SINGS, the galaxy sample and the observing strategy, and the SIRTF and other ancillary data products.

Remote sensing for biodiversity science and conservation

Abstract: Remote-sensing systems typically produce imagery that averages information over tens or even hundreds of square meters – far too coarse to detect most organisms – so the remote sensing of biodiversity would appear to be a fool’s errand. However, advances in the spatial and spectral resolutions of sensors now available to ecologists are making the direct remote sensing of certain aspects of biodiversity increasingly feasible; for example, distinguishing species assemblages or even identifying species of individual trees. In cases where direct detection of individual organisms or assemblages is still beyond our grasp, indirect approaches offer valuable information about diversity patterns. Such approaches derive meaningful environmental parameters from biophysical characteristics that

On the Water−Carbon Interaction for Use in Molecular Dynamics Simulations of Graphite and Carbon Nanotubes

Abstract: A systematic molecular dynamics study shows that the contact angle of a water droplet on graphite changes significantly as a function of the water−carbon interaction energy. Together with the observation that a linear relationship can be established between the contact angle and the water monomer binding energy on graphite, a new route to calibrate interaction potential parameters is presented. Through a variation of the droplet size in the range from 1000 to 17 500 water molecules, we determine the line tension to be positive and on the order of 2 × 10-10 J/m. To recover a macroscopic contact angle of 86°, a water monomer binding energy of −6.33 kJ mol-1 is required, which is obtained by applying a carbon−oxygen Lennard-Jones potential with the parameters eCO = 0.392 kJ mol-1 and σCO = 3.19 A. For this new water−carbon interaction potential, we present density profiles and hydrogen bond distributions for a water droplet on graphite.

Neutral Atomic Phases of the Interstellar Medium in the Galaxy

Abstract: Much of the interstellar medium in disk galaxies is in the form of neutral atomic hydrogen, H i. This gas can be in thermal equilibrium at relatively low temperatures, Td300 K (the cold neutral medium (CNM)), or at temperatures somewhat less than 10 4 K (the warm neutral medium (WNM)). These two phases can coexist over a narrow range of pressures, PminPPmax. We determine Pmin and Pmax in the plane of the Galaxy as a function of Galactocentric radius R using recent determinations of the gas heating rate and the gas-phase abundances of interstellar gas. We provide an analytic approximation for Pmin as a function of metallicity, far-ultraviolet radiation field, and the ionization rate of atomic hydrogen. Our analytic results show that the existence of Pmin, or the possibility of a two-phase equilibrium, generally requires that H + exceed C + in abundance at Pmin. The abundance of H + is set by EUV/soft X-ray photoionization and by recombination with negatively charged polycyclic aromatic hydrocarbons. In order to assess whether thermal or pressure equilibrium is a realistic assumption, we define a parameter � � tcool=tshock, where tcool is the gas cooling time and tshock is the characteristic shock time or '' time between shocks in a turbulent medium.'' For � < 1 gas has time to reach thermal balance between supernova-induced shocks. We find that this condition is satisfied in the Galactic disk, and thus the two-phase description of the interstellar H i is approximately valid even in the presence of interstellar turbulence. Observationally, the mean density nHi hi is often better determined than the local density, and we cast our results in terms of nHi hi as well. Over most of the disk of the Galaxy, the Hi must be in two phases: the weight of the Hi in the gravitational potential of the Galaxy is large enough to generate thermal pressures exceeding Pmin, so that turbulent pressure fluctuations can produce cold gas that is thermally stable; and the mean density of the H i is too low for the gas to be all CNM. Our models predict the presence of CNM gas to R ' 16 18 kpc, somewhat farther than previous estimates. An estimate for the typical thermal pressure in the Galactic plane for 3 kpcdRd18 kpc is Pth=k ' 1:4 � 10 4 expð� R=5:5 kpcÞ Kc m � 3 . At the solar circle, this gives Pth=k ' 3000 K cm � 3 . We show that this pressure is consistent with the C i*/C itot ratio observed by Jenkins & Tripp and the CNM temperature found by Heiles & Troland. We also examine the potential impact of turbulent heating on our results and provide parameterized expressions for the heating rate as a function of Galactic radius. Although the uncertainties are large, our models predict that including turbulent heating does not significantly change our results and that thermal pressures remain above Pmin to R ' 18 kpc. Subject headings: ISM: clouds — ISM: general — ISM: structure

An overview of ACE-Asia: Strategies for quantifying the relationships between Asian aerosols and their climatic impacts

Abstract: [1] The International Global Atmospheric Chemistry Program (IGAC) has conducted a series of Aerosol Characterization Experiments (ACE) that integrate in situ measurements, satellite observations, and models to reduce the uncertainty in calculations of the climate forcing due to aerosol particles. ACE-Asia, the fourth in this series of experiments, consisted of two focused components: (1) An intensive field study that sought to quantify the spatial and vertical distribution of aerosol concentrations and properties, the processes controlling their formation, evolution, and fate, and the column-integrated radiative effect of the aerosol (late March through May 2001). (2) A longer-term network of ground stations that used in situ and column-integrated measurements to quantify the chemical, physical, and optical properties of aerosols in the ACE-Asia study area and to assess their spatial and temporal (seasonal and interannual) variability (2000–2003). The approach of the ACE-Asia science team was to make simultaneous measurements of aerosol chemical, physical, and optical properties and their radiative impacts in a variety of air masses, often coordinated with satellite overpasses. Three aircraft, two research ships, a network of lidars, and many surface sites gathered data on Asian aerosols. Chemical transport models (CTMs) were integrated into the program from the start, being used in a forecast mode during the intensive observation period to identify promising areas for airborne and ship observations and then later as tools for integrating observations. The testing and improvement of a wide range of aerosol models (including microphysical, radiative transfer, CTM, and global climate models) was one important way in which we assessed our understanding of the properties and controlling processes of Asian aerosols. We describe here the scientific goals and objectives of the ACE-Asia experiment, its observational strategies, the types of observations made by the mobile platforms and stationary sites, the models that will integrate our understanding of the climatic effect of aerosol particles, and the types of data that have been generated. Eight scientific questions focus the discussion. The intensive observations took place during a season of unusually heavy dust, so we have a large suite of observations of dust and its interaction with air pollutants. Further information about ACE-Asia can be found on the project Web site at http://saga.pmel.noaa.gov/aceasia/.

Carbon nanotube growth by PECVD: a review

Abstract: Carbon nanotubes (CNTs), due to their unique electronic and extraordinary mechanical properties, have been receiving much attention for a wide variety of applications. Recently, plasma enhanced chemical vapour deposition (PECVD) has emerged as a key growth technique to produce vertically-aligned nanotubes. This paper reviews various plasma sources currently used in CNT growth, catalyst preparation and growth results. Since the technology is in its early stages, there is a general lack of understanding of growth mechanisms, the role of the plasma itself, and the identity of key species responsible for growth. This review is aimed at the low temperature plasma research community that has successfully addressed such issues, through plasma and surface diagnostics and modelling, in semiconductor processing and diamond thin film growth.

Mining distance-based outliers in near linear time with randomization and a simple pruning rule

Abstract: Defining outliers by their distance to neighboring examples is a popular approach to finding unusual examples in a data set. Recently, much work has been conducted with the goal of finding fast algorithms for this task. We show that a simple nested loop algorithm that in the worst case is quadratic can give near linear time performance when the data is in random order and a simple pruning rule is used. We test our algorithm on real high-dimensional data sets with millions of examples and show that the near linear scaling holds over several orders of magnitude. Our average case analysis suggests that much of the efficiency is because the time to process non-outliers, which are the majority of examples, does not depend on the size of the data set.

Carbon Nanotube Nanoelectrode Array for Ultrasensitive DNA Detection

Abstract: A nanoelectrode array based on vertically aligned multiwalled carbon nanotubes (MWNTs) embedded in SiO2 is used for ultrasensitive DNA detection. Characteristic electrochemical behaviors are observed for measuring bulk and surface-immobilized redox species. Sensitivity is dramatically improved by lowering the nanotube density. Oligonucleotide probes are selectively functionalized to the open ends of nanotubes. The hybridization of subattomole DNA targets can be detected by combining such electrodes with Ru(bpy)32+ mediated guanine oxidation.

Functional profiling of a human cytomegalovirus genome

Abstract: Human cytomegalovirus (HCMV), a ubiquitous herpesvirus, causes a lifelong subclinical infection in healthy adults but leads to significant morbidity and mortality in neonates and immunocompromised individuals. Its ability to grow in different cell types is responsible for HCMV-associated diseases, including mental retardation and retinitis, and vascular disorders. To globally assess viral gene function for replication in cells, we determined the genomic sequence of a bacterial artificial chromosome (BAC)-based clone of HCMV Towne strain and used this information to delete each of its 162 unique ORFs and generate a collection of viral mutants. The growth of these mutants in different cultured cells was examined to systematically investigate the necessity of each ORF for replication. Our results showed that 45 ORFs are essential for viral replication in fibroblasts and 117 are nonessential. Some genes were found to be required for viral replication in retinal pigment epithelial cells and microvascular endothelial cells, but not in fibroblasts, indicating their role as tropism factors. Interestingly, several viral mutants grew 10- to 500-fold better than the parental strain in different cell types, suggesting that the deleted ORFs encode replication temperance or repressing functions. Thus, HCMV encodes supportive and suppressive growth regulators for optimizing its replication in human fibroblasts, epithelial, and endothelial cells. Suppression of viral replication by virus-encoded temperance factors represents a novel mechanism for regulating the growth of an animal virus, and may contribute to HCMV's optimal infection of different tissues and successful proliferation among the human population.

Generalized symbolic execution for model checking and testing

Abstract: Modern software systems, which often are concurrent and manipulate complex data structures must be extremely reliable. We present a novel framework based on symbolic execution, for automated checking of such systems. We provide a two-fold generalization of traditional symbolic execution based approaches. First, we define a source to source translation to instrument a program, which enables standard model checkers to perform symbolic execution of the program. Second, we give a novel symbolic execution algorithm that handles dynamically allocated structures (e.g., lists and trees), method preconditions (e.g., acyclicity), data (e.g., integers and strings) and concurrency. The program instrumentation enables a model checker to automatically explore different program heap configurations and manipulate logical formulae on program data (using a decision procedure). We illustrate two applications of our framework: checking correctness of multi-threaded programs that take inputs from unbounded domains with complex structure and generation of non-isomorphic test inputs that satisfy a testing criterion. Our implementation for Java uses the Java PathFinder model checker.

Mars-like soils in the Atacama Desert, Chile, and the dry limit of microbial life

Abstract: The Viking missions showed the martian soil to be lifeless and depleted in organic material and indicated the presence of one or more reactive oxidants. Here we report the presence of Mars-like soils in the extreme arid region of the Atacama Desert. Samples from this region had organic species only at trace levels and extremely low levels of culturable bacteria. Two samples from the extreme arid region were tested for DNA and none was recovered. Incubation experiments, patterned after the Viking labeled-release experiment but with separate biological and nonbiological isomers, show active decomposition of organic species in these soils by nonbiological processes.

Learning assumptions for compositional verification

Abstract: Compositional verification is a promising approach to addressing the state explosion problem associated with model checking. One compositional technique advocates proving properties of a system by checking properties of its components in an assume-guarantee style. However, the application of this technique is difficult because it involves non-trivial human input. This paper presents a novel framework for performing assume-guarantee reasoning in an incremental and fully automated fashion. To check a component against a property, our approach generates assumptions that the environment needs to satisfy for the property to hold. These assumptions are then discharged on the rest of the system. Assumptions are computed by a learning algorithm. They are initially approximate, but become gradually more precise by means of counterexamples obtained by model checking the component and its environment, alternately. This iterative process may at any stage conclude that the property is either true or false in the system. We have implemented our approach in the LTSA tool and applied it to a NASA system.

Calculation of Si nanowire thermal conductivity using complete phonon dispersion relations

Abstract: The lattice thermal conductivity of crystalline Si nanowires is calculated. The calculation uses complete phonon dispersions, and does not require any externally imposed frequency cutoffs. No adjustment to nanowire thermal conductivity measurements is required. Good agreement with experimental results for nanowires wider than 35 nm is obtained. A formulation in terms of the transmission function is given. Also, the use of a simpler, nondispersive ``Callaway formula,'' is discussed from the complete dispersions perspective.

Growth of Epitaxial Nanowires at the Junctions of Nanowalls

Abstract: Interfacing semiconducting nanostructures with conducting or insulating substrates to attain a three-dimensional (3D) integrated platform is highly desirable for advanced nanoscale electronics and optoelectronics applications ( [1][1] ). As such, the assembly and synthesis of these nanostructures, which demonstrate multiple dimensionality, using a bottom-up approach would be useful. Taking ZnO as an example, we show here that high crystallinity 1D and 2D nanostructures can be epitaxially and vertically grown into 3D architectures on both conducting and insulating single crystalline substrates. Our objective was to grow vertically well-aligned 2D and 1D semiconducting nanostructures for nanoelectronics and nanosensor applications. Using a carbothermal reduction process and gold (Au)-catalyzed epitaxial growth ( [2][2] – [4][3] ), we have been able to reproducibly grow hierachically well-ordered and vertically aligned 2D and 1D ZnO nanostructures on electrically conducting, highly oriented pyrolytic graphite (HOPG) and on insulating (1120) sapphire substrates. We achieve these by specifically controlling either the spacing between the catalyst spots or the thickness of the catalyst thin film. When the Au film thickness is maintained above the threshold limit of 15 A, we obtained highly intricate quasi-3D nanostructures ([Fig. 1A][4] and inset), which are composed of an array of vertical 1D nanowires on top of a 2D network of intricate “nanowalls.” The scanning electron microscope (SEM) (top view) further reveals a random honeycomb-like pattern, resembling typical structures observed from anodization of thin-film aluminum. The nanowires are observed to grow from the “nodes” of the nanowalls. The average diameters of the nanowires and the thickness of the nanowalls are of the same order of magnitude (∼80 nm). The hexagonal facets (0001) of the nanowires ( [4][3] ) are clearly visible in the SEM images. This suggests that epitaxial growth of the nanowires occurs at the nodes of the nanowalls, which are themselves assembled epitaxially on the substrates and presumably also have their c -plane parallel to the substrates. The nanowalls have essentially vertical side wall profiles. By controlling the growth time, 2D nanowalls ([Fig. 1B][4]) could be obtained before onset of the 1D nanowires. When the catalyst thickness is kept below the threshold limit of 15 A, discrete individual free-standing 1D nanowires are obtained ([Fig. 1C][4]). ![ Fig. 1. ][5] Fig. 1. Zinc oxide nanowalls and nanowires. ( A ) SEM image of quasi-3D ZnO nanostructures grown on a sapphire using ∼40 to 50 A Au thin film as the catalyst. The inset shows a SEM perspective view. ( B ) 2D ZnO nanowalls on a sapphire with a height ∼5 μm. ( C ) An array of free-standing 1D ZnO nanowires on a HOPG substrate using ∼15 A Au ultrathin film as the catalyst. ( D ) Schematic illustration showing the growth mechanism of ZnO nanowalls and nanowires. The first four sketches are top views; the last, a perspective view. Vertical growth of the ZnO nanostructures are observed as a result of the good epitaxial lattice match of the c plane of ZnO with the hexagonal basal plane of HOPG and (\batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(11{\bar{2}}0\) \end{document}) plane of sapphire. Unlike the governing mechanism in the growth of carbon nanowalls ( [5][6] ), the observed growth phenomena appear to be a result of the interplay between the dynamic wetting behavior and thermal-enhanced surface diffusion of gold adatoms on the substrates. The limited wettability between the substrate and Au film facilitates the formation of Au network patterns at an elevated temperature, in contrast to totally isolated droplets that form due to a total incompatibility or a continuous film that forms due to a complete wetting. Control experiments with different growth durations but without ZnO and carbon feed-stock have been performed and examined under an atomic force microscope (AFM). Consistency in the AFM granulometry results has suggested aggregation of the Au nanograins forming larger particulates with narrow grain boundaries within complex channeled Au networks that resemble the 2D nanowall patterns, as depicted in [Fig. 1D][4]. We believe that, with improved wetting to the substrate, ZnO epitaxial growth is initiated along the grain boundaries because these are the most thermodynamically active sites for saturation and precipitation of the Zn atoms (green arrows). As the ZnO nanowalls continue to grow via vapor-liquid-solid (VLS) mechanism, the surface energy at the nodes increases with resultant Au atoms diffusing and accumulating at the nodes (red arrows) for overall energy compensation. At a critical saturation point, 1D nanowires begin to grow from the nodes via the same mechanism. In the 1D individual nanowire growth, the Au nanoparticles are typically well-separated and the surface diffusion length may not be extended enough to allow a continuous network formation. Though it is well known that nanowires are useful in many electronics and optoelectronics applications, the nanowalls and high surface-to-volume ratio nanostructures with multiple dimensionality may be useful in applications in energy storage or conversion and data storage and memory devices. Supporting Online Material [www.sciencemag.org/cgi/content/full/300/5623/1249/DC1][7] Materials and Methods Fig. S1 1. [↵][8] International Technology Roadmap for Semiconductors 2001 (Semiconductor Industry Association, San Jose, CA, 2001); available at 2. [↵][9] H. T. Ng et al. , Appl. Phys. Lett. 82, 2023 (2003). [OpenUrl][10][CrossRef][11] 3. Materials and methods are available as supporting material on Science Online. 4. [↵][12] M. Huang et al ., Science 292, 1897 (2001). [OpenUrl][13][Abstract/FREE Full Text][14] 5. [↵][15] Y. Wu, P. Qiao, T. Chong, Z. Shen, Adv. Mater. 14, 64 (2002). [OpenUrl][16] [1]: #ref-1 [2]: #ref-2 [3]: #ref-4 [4]: #F1 [5]: pending:yes [6]: #ref-5 [7]: http://www.sciencemag.org/cgi/content/full/300/5623/1249/DC1 [8]: #xref-ref-1-1 "View reference 1 in text" [9]: #xref-ref-2-1 "View reference 2 in text" [10]: {openurl}?query=rft.jtitle%253DAppl.%2BPhys.%2BLett.%26rft.volume%253D82%26rft.spage%253D2023%26rft_id%253Dinfo%253Adoi%252F10.1063%252F1.1564870%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx [11]: /lookup/external-ref?access_num=10.1063/1.1564870&link_type=DOI [12]: #xref-ref-4-1 "View reference 4 in text" [13]: {openurl}?query=rft.jtitle%253DScience%26rft.stitle%253DScience%26rft.issn%253D0036-8075%26rft.aulast%253DHuang%26rft.auinit1%253DM.%2BH.%26rft.volume%253D292%26rft.issue%253D5523%26rft.spage%253D1897%26rft.epage%253D1899%26rft.atitle%253DRoom-Temperature%2BUltraviolet%2BNanowire%2BNanolasers%26rft_id%253Dinfo%253Adoi%252F10.1126%252Fscience.1060367%26rft_id%253Dinfo%253Apmid%252F11397941%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx [14]: /lookup/ijlink/YTozOntzOjQ6InBhdGgiO3M6MTQ6Ii9sb29rdXAvaWpsaW5rIjtzOjU6InF1ZXJ5IjthOjQ6e3M6ODoibGlua1R5cGUiO3M6NDoiQUJTVCI7czoxMToiam91cm5hbENvZGUiO3M6Mzoic2NpIjtzOjU6InJlc2lkIjtzOjEzOiIyOTIvNTUyMy8xODk3IjtzOjQ6ImF0b20iO3M6MjM6Ii9zY2kvMzAwLzU2MjMvMTI0OS5hdG9tIjt9czo4OiJmcmFnbWVudCI7czowOiIiO30= [15]: #xref-ref-5-1 "View reference 5 in text" [16]: {openurl}?query=rft.jtitle%253DAdv.%2BMater.%26rft.volume%253D14%26rft.spage%253D64%26rft.atitle%253DADV%2BMATER%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx

GridFlow: workflow management for grid computing

Abstract: Grid computing is becoming a mainstream technology for large-scale distributed resource sharing and system integration. Workflow management is emerging as one of the most important grid services. In this work, a workflow management system for grid computing, called GridFlow, is presented, including a user portal and services of both global grid workflow management and local grid sub-workflow scheduling. Simulation, execution and monitoring functionalities are provided at the global grid level, which work on top of an existing agent-based grid resource management system. At each local grid, sub-workflow scheduling and conflict management are processed on top of an existing performance prediction based task scheduling system. A fuzzy timing technique is applied to address new challenges of workflow management in a cross-domain and highly dynamic grid environment. A case study is given and corresponding results indicate that local and global grid workflow management can coordinate with each other to optimise workflow execution time and solve conflicts of interest.

Temperature and moisture conditions for life in the extreme arid region of the Atacama desert: four years of observations including the El Nino of 1997-1998

Abstract: The Atacama along the Pacific Coast of Chile and Peru is one of the driest and possibly oldest deserts in the world. It represents an extreme habitat for life on Earth and is an analog for life in dry conditions on Mars. We report on four years (September 1994-October 1998) of climate and moisture data from the extreme arid region of the Atacama. Our data are focused on understanding moisture sources and their role in creating suitable environments for photosynthetic microorganisms in the desert surface. The average air temperature was 16.5 degrees C and 16.6 degrees C in 1995 and 1996, respectively. The maximum air temperature recorded was 37.9 degrees C, and the minimum was -5.7 degrees C. Annual average sunlight was 336 and 335 W m(-2) in 1995 and 1996, respectively. Winds averaged a few meters per second, with strong fohn winds coming from the west exceeding 12 m s(-1). During our 4 years of observation there was only one significant rain event of 2.3 mm, which occurred near midnight local time. We suggest that this event was a rainout of a heavy fog. It is of interest that the strong El Nino of 1997-1998 brought heavy rainfall to the deserts of Peru, but did not bring significant rain to the central Atacama in Chile. Dew occurred at our station frequently following high nighttime relative humidity, but is not a significant source of moisture in the soil or under stones. Groundwater also does not contribute to surface moisture. Only the one rain event of 2.3 mm resulted in liquid water in the soil and beneath stones for a total of only 65-85 h over 4 years. The paucity of liquid water under stones is consistent with the apparent absence of hypolithic (under-stone) cyanobacteria, the only known primary producers in such extreme deserts.

Phonon transport in nanowires coated with an amorphous material: An atomistic Green’s function approach

Abstract: An approach is presented for the atomistic study of phonon transport in real dielectric nanowires via Green's functions. The formalism is applied to investigate the phonon flow through nanowires coated by an amorphous material. Examples for a simple model system and for real Si nanowires coated by silica are given. New physical results emerge for these systems, regarding the character of the transition from ballistic to diffusive transport, the low-temperature thermal conductance, and the influence of the wire-coating interface on the thermal transport. An efficient treatment of phonon scattering by the amorphous coating is also developed, representing a valuable tool for the investigation of thermal conduction through amorphous-coated nanowires.

Predicting protein functions from redundancies in large-scale protein interaction networks

Abstract: Interpreting data from large-scale protein interaction experiments has been a challenging task because of the widespread presence of random false positives. Here, we present a network-based statistical algorithm that overcomes this difficulty and allows us to derive functions of unannotated proteins from large-scale interaction data. Our algorithm uses the insight that if two proteins share significantly larger number of common interaction partners than random, they have close functional associations. Analysis of publicly available data from Saccharomyces cerevisiae reveals >2,800 reliable functional associations, 29% of which involve at least one unannotated protein. By further analyzing these associations, we derive tentative functions for 81 unannotated proteins with high certainty. Our method is not overly sensitive to the false positives present in the data. Even after adding 50% randomly generated interactions to the measured data set, we are able to recover almost all (≈89%) of the original associations.

High-Accuracy ab Initio Rotation-Vibration Transitions for Water

Abstract: The spectrum of water vapor is of fundamental importance for a variety of processes, including the absorption and retention of sunlight in Earth's atmosphere. Therefore, there has long been an urgent need for a robust and accurate predictive model for this spectrum. In our work on the high-resolution spectrum of water, we report first-principles calculations that approach experimental accuracy. To achieve this, we performed exceptionally large electronic structure calculations and considered a variety of effects, including quantum electrodynamics, which have routinely been neglected in studies of small many-electron molecules. The high accuracy of the resulting ab initio procedure is demonstrated for the main isotopomers of water.

Nanomechanics of carbon nanotubes and composites

Abstract: Computer simulation and modeling results for the nanomechanics of carbon nanotubes and carbon nanotube-polyethylene composite materials are described and compared with experimental observations Young’s modulus of individual single-wall nanotubes is found to be in the range of 1 TPa within the elastic limit At room temperature and experimentally realizable strain rates, the tubes typically yield at about 5–10% axial strain; bending and torsional stiffness and different mechanisms of plastic yielding of individual single-wall nanotubes are discussed in detail For nanotube-polyethylene composites, we find that thermal expansion and diffusion coefficients increase significantly, over their bulk polyethylene values, above glass transition temperature, and Young’s modulus of the composite is found to increase through van der Waals interaction This review article cites 54 references @DOI: 101115/11538625#

Noncovalent functionalization of carbon nanotubes by aromatic organic molecules

Abstract: The interaction between carbon nanotubes and organic molecules including benzene (C6H6), cyclohexane (C6H12), and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ: C8N2O2Cl2) have been studied using first principles calculations. The equilibrium tube-molecule distance, adsorption energy, and charge transfer are obtained. The hybridization between the DDQ molecular level and nanotube valence bands transforms the semiconducting tube into a metallic one. Coupling of π electrons between tubes and aromatic molecules are observed. Our results show that noncovalent functionalization of carbon nanotubes by aromatic molecules is an efficient way to control the electronic properties of carbon nanotubes.

Model-based diagnosis of hybrid systems

Abstract: Recent years have seen a proliferation of embedded systems that combine a digital (discrete) supervisory controller with an analog (continuous) plant. Diagnosing faults in such hybrid systems, require techniques that are different from those used for discrete and continuous systems. In addition, these algorithms have to be deployed online to meet the real time requirements of embedded systems. This paper presents a methodology for online tracking and diagnosis of hybrid systems. We demonstrate the effectiveness of the approach with experiments conducted on the fuel transfer system of fighter aircraft.

Constraint-Based Attribute and Interval Planning

Abstract: In this paper we describe Constraint-based Attribute and Interval Planning (CAIP), a paradigm for representing and reasoning about plans. The paradigm enables the description of planning domains with time, resources, concurrent activities, mutual exclusions among sets of activities, disjunctive preconditions and conditional effects. We provide a theoretical foundation for the paradigm, based on temporal intervals and attributes. We show how the plans are naturally expressed by networks of constraints, and show that the process of planning maps directly to dynamic constraint reasoning. We describe compatibilities, a compact mechanism for describing planning domains. We also demonstrate how this framework incorporates the use of constraint representation and reasoning technology to improve planning. Finally, we describe EUROPA, an implementation of the CAIP framework.

Reflection of guided modes in a semiconductor nanowire laser

Abstract: We analyze the waveguiding properties of semiconductor (GaN, ZnO, CdS) single nanowire lasers which were recently demonstrated experimentally. In particular, we compute the reflectivity for a few lowest-order guided modes (HE11, TE01, and TM01) from the nanowire facets. The reflectivity is shown to depend strongly on the mode type, lasing frequency and radius of the nanowire. By using the computed reflectivities, we make realisic estimates of the threshold gain and quality factor for the nanowire lasers. Our results shed light on the lasing mechanism of the nanowire lasers.