Showing papers in "Science & Engineering Faculty in 2009"

Accounting for calibration uncertainty in phylogenetic estimation of evolutionary divergence times

Abstract: The estimation of phylogenetic divergence times from sequence data is an important component of many molecular evolutionary studies. There is now a general appreciation that the procedure of divergence dating is considerably more complex than that initially described in the 1960s by Zuckerkandl and Pauling (1962, 1965). In particular, there has been much critical attention toward the assumption of a global molecular clock, resulting in the development of increasingly sophisticated techniques for inferring divergence times from sequence data. In response to the documentation of widespread departures from clocklike behavior, a variety of local- and relaxed-clock methods have been proposed and implemented. Local-clock methods permit different molecular clocks in different parts of the phylogenetic tree, thereby retaining the advantages of the classical molecular clock while casting off the restrictive assumption of a single, global rate of substitution (Rambaut and Bromham 1998; Yoder and Yang 2000).

A comprehensive review of one-dimensional metal-oxide nanostructure photodetectors

Abstract: One-dimensional (1D) metal-oxide nanostructures are ideal systems for exploring a large number of novel phenomena at the nanoscale and investigating size and dimensionality dependence of nanostructure properties for potential applications The construction and integration of photodetectors or optical switches based on such nanostructures with tailored geometries have rapidly advanced in recent years Active 1D nanostructure photodetector elements can be configured either as resistors whose conductions are altered by a charge-transfer process or as field-effect transistors (FET) whose properties can be controlled by applying appropriate potentials onto the gates Functionalizing the structure surfaces offers another avenue for expanding the sensor capabilities This article provides a comprehensive review on the state-of-the-art research activities in the photodetector field It mainly focuses on the metal oxide 1D nanostructures such as ZnO, SnO(2), Cu(2)O, Ga(2)O(3), Fe(2)O(3), In(2)O(3), CdO, CeO(2), and their photoresponses The review begins with a survey of quasi 1D metal-oxide semiconductor nanostructures and the photodetector principle, then shows the recent progresses on several kinds of important metal-oxide nanostructures and their photoresponses and briefly presents some additional prospective metal-oxide 1D nanomaterials Finally, the review is concluded with some perspectives and outlook on the future developments in this area

Kalman filtering for positioning and heading control of ships and offshore rigs

Abstract: In this article, we have described the main components of a ship motion-control system and two particular motion-control problems that require wave filtering, namely, dynamic positioning and heading autopilot. Then, we discussed the models commonly used for vessel response and showed how these models are used for Kalman filter design. We also briefly discussed parameter and noise covariance estimation, which are used for filter tuning. To illustrate the performance, a case study based on numerical simulations for a ship autopilot was considered. The material discussed in this article conforms to modern commercially available ship motion-control systems. Most of the vessels operating in the offshore industry worldwide use Kalman filters for velocity estimation and wave filtering. Thus, the article provides an up-to-date tutorial and overview of Kalman-filter-based wave filtering.

Morphology-dependent stimulated emission and field emission of ordered CdS nanostructure arrays

Abstract: Highly ordered CdS nanostructure arrays were successfully fabricated via a simple two-step metal-organic chemical vapor deposition process. Both stimulated emission and field-emission measurements were carried out in an attempt to understand the correlation between the morphologies, alignments, and emission performances of five ordered CdS nanostructure array types (well-aligned truncated nanocones, nanorods, cleft nanorods, quasi-aligned nanowires, and nanowires). The 1D CdS nanostructures of various types displayed notable differences in stimulated and field-emission performances. The stimulated emission strongly correlated with the structure alignment: the better the alignment, the lower the threshold. Both of the alignments and aspect ratios greatly affected the field-emission properties; the CdS emitters of higher aspect ratio and better alignment exhibited better field-emission performance. Thus the well-aligned CdS nanorod arrays had the lower threshold for stimulated emission, and quasi-aligned nanowire arrays produced the higher field-emission current and possessed the lower turn-on fields.

Electronic and mechanical coupling in bent ZnO nanowires

Abstract: A red shift of the exciton of ZnO nanowires is efficiently produced by bending strain, as demonstrated by a lowtemperature (81 K) cathodoluminescence (CL) study of ZnO nanowires bent into L- or S-shapes. The figure shows a nanowire (Fig. a) with the positions of CL measurements marked. The corresponding CL spectra - revealing a peak shift and broadening in the region of the bend - are shown in Figure b. (Figure Presented).

Molecules, morphology, and ecology indicate a recent, amphibious ancestry for echidnas

Abstract: The semiaquatic platypus and terrestrial echidnas (spiny anteaters) are the only living egg-laying mammals (monotremes). The fossil record has provided few clues as to their origins and the evolution of their ecological specializations; however, recent reassignment of the Early Cretaceous Teinolophos and Steropodon to the platypus lineage implies that platypuses and echidnas diverged >112.5 million years ago, reinforcing the notion of monotremes as living fossils. This placement is based primarily on characters related to a single feature, the enlarged mandibular canal, which supplies blood vessels and dense electrosensory receptors to the platypus bill. Our reevaluation of the morphological data instead groups platypus and echidnas to the exclusion of Teinolophos and Steropodon and suggests that an enlarged mandibular canal is ancestral for monotremes (partly reversed in echidnas, in association with general mandibular reduction). A multigene evaluation of the echidna–platypus divergence using both a relaxed molecular clock and direct fossil calibrations reveals a recent split of 19–48 million years ago. Platypus-like monotremes (Monotrematum) predate this divergence, indicating that echidnas had aquatically foraging ancestors that reinvaded terrestrial ecosystems. This ecological shift and the associated radiation of echidnas represent a recent expansion of niche space despite potential competition from marsupials. Monotremes might have survived the invasion of marsupials into Australasia by exploiting ecological niches in which marsupials are restricted by their reproductive mode. Morphology, ecology, and molecular biology together indicate that Teinolophos and Steropodon are basal monotremes rather than platypus relatives, and that living monotremes are a relatively recent radiation.

Thermal properties of single-phase Y2SiO5

Abstract: Y2SiO5 is a promising candidate for oxidation-resistant or environmental/thermal barrier coatings (ETBC) due to its excellent high-temperature stability, low elastic modulus and low oxygen permeability. In this paper, we investigated the thermal properties of Y2SiO5 comprehensively, including thermal expansion, thermal diffusivity, heat capacity and thermal conductivity. It is interesting that Y2SiO5 has a very low thermal conductivity (∼1.40 W/m K) but a relatively high linear thermal expansion coefficient ((8.36 ± 0.5) × 10-6 K-1), suggesting compatible thermal and mechanical properties to some non-oxide ceramics and nickel superalloys as ETBC layer. Y2SiO5 is also an ideal EBC on YSZ TBC layer due to their close thermal expansion coefficients. As a continuous source of Y3+, it is predicted that Y2SiO5 EBC may prolong the lifetime of zirconia-based TBC by stopping the degradation aroused by the loss of Y stabilizer.

Periodic TiO2Nanorod Arrays with Hexagonal Nonclose-Packed Arrangements: Excellent Field Emitters by Parameter Optimization

Abstract: Periodic TiO 2 nanorod arrays with hexagonal nonclose-packed (hncp) arrangements are synthesized by pulsed laser deposition (PLD) using polystyrene colloidal monolayers as templates and with subsequent annealing in air. The hncp-array formation is governed by in situ volume shrinkage of amorphous TiO 2 nanorods in the crystallizing process during annealing. The array periodicity can easily be tuned by different sphere sizes of the colloidal template, whereas the distance between neighboring nanorods can be controlled by altering the background gas pressure during the PLD process, at a given periodicity for the nanorod array. Parameter-controlled growth is helpful for investigating and optimizing the parameter-dependent field-emission properties. The hncp nanorod array exhibits an enhanced field-emission (FE) performance compared to both particle films and nanorod arrays with top aggregation. With an increase in periodicity of a hncp nanorod array, the field-enhancement factor decreases and the turn-on FE field increases. FE characteristics can be further enhanced by increasing the distance between adjacent nanorods while maintaining the same periodicity. The parameter-optimized results suggest that the arrays with a smaller periodicity and a larger distance display the best FE performance and could be highly valuable for designing field-emission devices based on these periodic nanorod arrays.

C-BN Single-Walled Nanotubes from Hybrid Connection of BN/C Nanoribbons: Prediction by ab initio Density Functional Calculations

Abstract: We demonstrated for the first time by ab initio density functional calculation and molecular dynamics simulation that C0.5(BN)0.5 armchair single-walled nanotubes (NT) are gapless semiconductors and can be spontaneously formed via the hybrid connection of graphene/BN Nanoribbons (GNR/BNNR) at room temperature. The direct synthesis of armchair C0.5(BN)0.5 via the hybrid connection of GNR/BNNR is predicted to be both thermodynamically and dynamically stable. Such novel armchair C0.5(BN)0.5 NTs possess enhanced conductance as that observed in GNRs. Additionally, the zigzag C0.5(BN)0.5 SWNTs are narrow band gap semiconductors, which may have potential application for light emission. In light of recent experimental progress and the enhanced degree of control in the synthesis of GNRs and BNNR, our results highlight an interesting avenue for synthesizing a novel specific type of C0.5(BN)0.5 nanotube (gapless or narrow direct gap semiconductor), with potentially important applications in BNC-based nanodevices.

First principle studies of zigzag AlN nanoribbon

Abstract: Ab initio density functional calculations were performed to study the geometry and electronic structure of a prototypical zigzag AlN nanoribbon. We find that H-terminated zigzag 10-AlN nanoribbons have a non-direct band gap and are nonmagnetic. When a transverse electric field is applied, the band gap decreases monotonically with the strength of field E. Zigzag AlN nanoribbons with the N edge unpassivated display strong spin-polarization close to the Fermi level, which will result in spin-anisotropic transport. These results suggest potential applications for the development of AlN nanoribbon-based nanoelectronics applications.

Self-organized vertically aligned single-crystal silicon nanostructures with controlled shape and aspect ratio by reactive plasma etching

Abstract: The formation of vertically aligned single-crystalline silicon nanostructures via "self-organized" maskless etching in Ar+ H 2 plasmas is studied The shape and aspect ratio can be effectively controlled by the reactive plasma composition In the optimum parameter space, single-crystalline pyramid-like nanostructures are produced; otherwise, nanocones and nanodots are formed This generic nanostructure formation approach does not involve any external material deposition It is based on a concurrent sputtering, etching, hydrogen termination, and atom/radical redeposition and can be applied to other nanomaterials

Galvanic replacement mediated synthesis of hollow Pt nanocatalysts : significance of residual Ag for the H2 evolution reaction

Abstract: With the increasing popularity of the galvanic replacement approach towards the development of bimetallic nanocatalysts, special emphasis has been focused on minimizing the use of expensive metal (e.g. Pt), in the finally formed nanomaterials (e.g. Ag/Pt system as a possible catalyst for fuel cells). However, the complete removal of the less active sacrificial template is generally not achieved during galvanic replacement, and its residual presence may significantly impact on the electrocatalytic properties of the final material. Here, we investigate the hydrogen evolution reaction (HER) activity of Ag nanocubes replaced with different amounts of Pt, and demonstrate how the bimetallic composition significantly affects the activity of the alloyed nanomaterial.

The production of self-organized carbon connections between Ag nanoparticles using atmospheric microplasma synthesis

Abstract: The formation of long self-organized carbon connections (where the length is much greater than the diameter) between Ag nanoparticles on a Si(1 0 0) surface in atmospheric pressure Ar + CH4 microplasmas is demonstrated. A growth scenario explaining the connection nucleation and growth is proposed, and this is supported by numerical simulations which reveal that the electric field pattern around the growing connections affects the surface diffusion of carbon adatoms, the main driving force for the observed self-organization. Results suggest that the microplasma-generated surface charges can be used as effective controls for the self-organized formation of complex carbon-based nano-networks for integrated nanodevices.

Towards reliable perception for unmanned ground vehicles in challenging conditions

Abstract: This work aims to promote reliability and integrity in autonomous perceptual systems, with a focus on outdoor unmanned ground vehicle (UGV) autonomy. For this purpose, a comprehensive UGV system, comprising many different exteroceptive and proprioceptive sensors has been built. The first contribution of this work is a large, accurately calibrated and synchronised, multi-modal data-set, gathered in controlled environmental conditions, including the presence of dust, smoke and rain. The data have then been used to analyse the effects of such challenging conditions on perception and to identify common perceptual failures. The second contribution is a presentation of methods for mitigating these failures to promote perceptual integrity in adverse environmental conditions.

Multi-robot Cooperation in Space: A Survey

Abstract: This paper reviews the literature related to multi-robot research with a focus on space applications. It starts by examining definitions of, and some of the fields of research, in multi-robot systems. An overview of space applications with multiple robots and cooperating multiple robots is presented. The multi-robot cooperation techniques used in theoretical research as well as experiments are reviewed, and the applicability for space applications is investigated.

Identification of abundant alkyl ether glycerophospholipids in the human lens by tandem mass spectrometry techniques

Abstract: Previous studies have shown that the human lens contains glycerophospholipids with ether linkages. These lipids differ from conventional glycerophospholipids in that the sn-1 substituent is attached to the glycerol backbone via an 1-O-alkyl or an 1-O-alk-1'-enyl ether rather than an ester bond. The present investigation employed a combination of collision-induced dissociation (CID) and ozone-induced dissociation (OzID) to unambiguously distinguish such 1-O-alkyl and 1-O-alk-1'-enyl ethers. Using these methodologies the human lens was found to contain several abundant 1-O-alkyl glycerophos-phoethanolamines, including GPEtn(16:0e/9Z-18:1), GPEtn(11Z-18:1e/9Z-18:1), and GPEtn(18:0e/9Z-18:1), as well as a related series of unusual 1-O-alkyl glycerophosphoserines, including GPSer(16:0e/9Z-18:1), GPSer(11Z-18:1e/9Z-18:1), GPSer(18:0e/9Z-18:1) that to our knowledge have not previously been observed in human tissue. Isomeric 1-O-alk-1'-enyl ethers were absent or in low abundance. Examination of the double bond position within the phospholipids using OzID revealed that several positional isomers were present, including sites of unsaturation at the n-9, n-7, and even n-5 positions. Tandem CID/OzID experiments revealed a preference for double bonds in the n-7 position of 1-O-ether linked chains, while n-9 double bonds predominated in the ester-linked fatty acids [e.g., GPEtn(11Z-18:1e/9Z-18:1) and GPSer(11Z-18:1e/9Z-18:1)]. Different combinations of these double bond positional isomers within chains at the sn-1 and sn-2 positions point to a remarkable molecular diversity of ether-lipids within the human lens.

An adaptive spherical view representation for navigation in changing environments

Abstract: Real-world environments such as houses and offices change over time, meaning that a mobile robot’s map will become out of date. In previous work we introduced a method to update the reference views in a topological map so that a mobile robot could continue to localize itself in a changing environment using omni-directional vision. In this work we extend this longterm updating mechanism to incorporate a spherical metric representation of the observed visual features for each node in the topological map. Using multi-view geometry we are then able to estimate the heading of the robot, in order to enable navigation between the nodes of the map, and to simultaneously adapt the spherical view representation in response to environmental changes. The results demonstrate the persistent performance of the proposed system in a long-term experiment.

Reconstructing annual inflows to the headwater catchments of the Murray River, Australia, using the Pacific Decadal Oscillation

Abstract: Free to read at publisher's site. The Pacific Decadal Oscillation (PDO) is a major forcing of inter-decadal to quasi-centennial variability of the hydroclimatology of the Pacific Basin. Its effects are most pronounced in the extra-tropical regions, while it modulates the El Nino Southern Oscillation (ENSO), the largest forcing of global inter-annual climate variability. Palaeo-PDO indices are now available for at least the past 500 years. Here we show that the > 500 year PDO index of Shen et al. ( 2006) is highly correlated with inflows to the headwaters of Australia's longest river system, the Murray-Darling. We then use the PDO to reconstruct annual inflows to the Murray River back to A. D. 1474. These show penta-decadal and quasi-centennial cycles of low inflows and a possible 500 year cycle of much greater inflow variability. Superimposed on this is the likely influence of recent anthropogenic global warming. We believe this may explain the exceptionally low inflows of the past decade, the lowest of the previous 529 years. Citation: McGowan, H. A., S. K. Marx, J. Denholm, J. Soderholm, and B. S. Kamber (2009), Reconstructing annual inflows to the headwater catchments of the Murray River, Australia, using the Pacific Decadal Oscillation, Geophys. Res. Lett., 36, L06707, doi:10.1029/2008GL037049.

Single-Crystalline ZnS Nanobelts as Ultraviolet-Light Sensors

Abstract: [*] Dr. X. S. Fang, Prof. Y. Bando, Dr. U. K. Gautam, Dr. C. Y. Zhi, Dr. B. D. Liu, Dr. T. Y. Zhai, Prof. D. Golberg International Center for Young Scientists (ICYS) and World Premier International Center for Materials Nanoarchitectonics (MANA) National Institute for Materials Science (NIMS) Namiki 1-1, Tsukuba, Ibaraki 305-0044 (Japan) E-mail: fang.xiaosheng@nims.go.jp; xshfang@yahoo.cn Dr. M. Y. Liao, Prof. Y. Koide Sensor Materials Center, NIMS Namiki 1-1, Tsukuba, Ibaraki 305-0044 (Japan)

A Survey of Control Allocation Methods for Underwater Vehicles

Abstract: A control allocation system implements a function that maps the desired control forces generated by the vehicle motion controller into the commands of the different actuators. In this article, a survey of control allocation methods for over-actuated underwater vehicles is presented. The methods are applicable for both surface vessels and underwater vehicles. The paper presents a survey of control allocation methods with focus on mathematical representation and solvability of thruster allocation problems. The paper is useful for university students and engineers who want to get an overview of state-of-the art control allocation methods as well as advance methods to solve more complex problems.

Self-organized carbon connections between catalyst particles on a silicon surface exposed to atmospheric-pressure Ar + CH4 microplasmas

Abstract: Ag nanoparticles and Fe-coated Si micrograins were separately deposited onto Si(1 0 0) surfaces and then exposed to an Ar + CH4 microplasma at atmospheric pressure. For the Ag nanoparticles, self-organized carbon nanowires, up to 400 nm in length were produced, whereas for the Fe-coated Si micrograins carbon connections with the length up to 100 μm were synthesized on the plasma-exposed surface area of about 0.5 mm2. The experiment has revealed that long carbon connections and short nanowires demonstrate quite similar behavior and structure. While most connections/nanowires tended to link the nearest particles, some wires were found to 'dissolve' into the substrate without terminating at the second particle. Both connections and nanowires are mostly linear, but long carbon connections can form kinks which were not observed in the carbon nanowire networks. A growth scenario explaining the carbon structure nucleation and growth is proposed. Multiscale numerical simulations reveal that the electric field pattern around the growing connections/nanowires strongly affects the surface diffusion of carbon adatoms, the main driving force for the observed self-organization in the system. The results suggest that the microplasma-generated surface charges can be used as effective controls for the self-organized formation of complex carbon-based nano-networks for integrated nanodevices.

Modelling business process variability for design-time configuration

Abstract: A reference process model represents multiple variants of a common business process in an inte-grated and reusable manner. It is intended to be individualized in order to fit the requirements of a specific organization or project. This practice of individualizing reference process models provides an attractive alternative with respect to designing process models from scratch. In particular, it en-ables the reuse of proven practices. This chapter introduces techniques for representing variability in the context of reference process models, as well as techniques that facilitate the individualization of reference process models with respect to a given set of requirements.

The Quantum Probability Ranking Principle for Information Retrieval

Abstract: While the Probability Ranking Principle for Information Retrieval provides the basis for formal models, it makes a very strong assumption regarding the dependence between documents. However, it has been observed that in real situations this assumption does not always hold. In this paper we propose a reformulation of the Probability Ranking Principle based on quantum theory. Quantum probability theory naturally includes interference effects between events. We posit that this interference captures the dependency between the judgement of document relevance. The outcome is a more sophisticated principle, the Quantum Probability Ranking Principle, that provides a more sensitive ranking which caters for interference/dependence between documents’ relevance.

Submarine deposition of volcaniclastic material from the 1995-2005 eruptions of Soufriere Hills volcano, Montserrat

Abstract: Soufriere Hills volcano, Montserrat, has been erupting since 1995. During the current eruption, a large part of the material produced by the volcano has been transported into the sea, modifying the morphology of the submarine flanks of the volcano. We present a unique set of swath bathymetric data collected offshore from Montserrat in 1999, 2002 and 2005. From 1999 to 2002, pyroclastic flows associated with numerous dome collapses entered the sea to produce 100 Mm3 deposit. From 2002 to 2005, the 290 Mm3 submarine deposit is mainly from the 12–13 July 2003 collapse. These data allow us to estimate that, by May 2005, at least 482 Mm3 of material had been deposited on the sea floor since 1995. We compare on-land characteristics and volumes of dome collapse events with the submarine deposits and propose a new analysis of their emplacement on the submarine flanks of the volcano. The deposition mechanism shows a slope dependence, with the maximum thickness of deposit before the break in the slope, probably because of the type of the dense granular flow involved. We conclude that from 1995 to 2005 more than 75% of the erupted volume entered the sea.

Direct observation of the gas phase reaction of the cyclohexyl radical with dioxygen using a distonic radical ion approach

Abstract: Alkylperoxyl radicals are intermediates in the oxidation Of hydrocarbons. The reactive nature of these intermediates, however, has made therin elusive to direct observation and isolation. We have employed ion trap mass spectrometry to synthesize and characterize 4-carboxylatocyclohexyl radical anions ((center dot)C(6)H(10)-CO(2)(-)) and observe their reactivity in the presence of dioxygen. The resulting reaction is facile (k = 1.8 x 10(-10) cm(3) molecule(-1) s(-1) or 30% of calculated collision rate) and results in (i) the addition Of O(2) to form stabilized 4-carboxylatocyclohexylperoxyl radical anions ((center dot)OO-C(6)H(10)-CO(2)(-)), providing the first direct observation of a cyclohexylperoxyl radical, and (ii) elimination of HO(2)(center dot) and HO(center dot) radicals consistent with recent laser-induced fluorescence studies of the reaction of neutral cyclohexyl radicals with O(2). Electronic structure calculations at the B3LYP/6-31+G(d) level of theory reveal viable pathways for the observed reactions showing that formation of the peroxyl radical is exothermic by 37 kcal mol(-1) with subsequent transition states its low as -6.6 kcal mol(-1) (formation of HO(2)(center dot)) and -9.1 kcal mol(-1) (formation of HO(center dot)) with respect to the entrance channel. The combined computational and experimental data Suggest that the structures of the reaction products correspond to cyclohexenes and epoxides from HO(2)(center dot) and HO(center dot) loss, respectively, while alternative pathways leading to cyclohexanone or ring-opened isomers ate not observed, Activation of the charged peroxyl radical (center dot)OO-C(6)H(10)-CO(2)(-) by collision induced disassociation also results in the loss Of HO(2)(center dot) and HO(center dot) radicals confirming that these products are directly connected to the peroxyl radical intermediate.

Vertical Alignment of Process Models – How Can We Get There?

Abstract: There is a wide variety of drivers for business process modelling initiatives, reaching from business evolution and process optimisation over compliance checking and process certification to process enactment. That, in turn, results in models that differ in content due to serving different purposes. In particular, processes are modelled on different abstraction levels and assume different perspectives. Vertical alignment of process models aims at handling these deviations. While the advantages of such an alignment for inter-model analysis and change propagation are out of question, a number of challenges has still to be addressed. In this paper, we discuss three main challenges for vertical alignment in detail. Against this background, the potential application of techniques from the field of process integration is critically assessed. Based thereon, we identify specific research questions that guide the design of a framework for model alignment.

A stochastic neighborhood conditional autoregressive model for spatial data

Abstract: A spatial process observed over a lattice or a set of irregular regions is usually modeled using a conditionally autoregressive (CAR) model. The neighborhoods within a CAR model are generally formed deterministically using the inter-distances or boundaries between the regions. An extension of CAR model is proposed in this article where the selection of the neighborhood depends on unknown parameter(s). This extension is called a Stochastic Neighborhood CAR (SNCAR) model. The resulting model shows flexibility in accurately estimating covariance structures for data generated from a variety of spatial covariance models. Specific examples are illustrated using data generated from some common spatial covariance functions as well as real data concerning radioactive contamination of the soil in Switzerland after the Chernobyl accident.

Scheduling a flow-shop with combined buffer conditions

Abstract: In this paper, No-Wait, No-Buffer, Limited-Buffer, and Infinite-Buffer conditions for the flow-shop problem (FSP) have been investigated. These four different buffer conditions have been combined to generate a new class of scheduling problem, which is significant for modelling many real-world scheduling problems. A new heuristic algorithm is developed to solve this strongly NP-hard problem. Detailed numerical implementations have been analysed and promising results have been achieved.