bluuebunny/crossref_metadata_2025 huggingface dataset:
Augmented Reality Based Maintenance Within Virtual Environments
Authors: Stelzer Ralph , Steindecker Erik , Saske Bernhard , Lässig Stefanie
Published: December 2013

Augmented Reality (AR) is a technology used for maintenance support of existing products. The service instructions are depicted directly into the operator’s vision and enhance his product view while maintaining the item. In order to provide high-quality maintenance support the manuals have to be created and tested at the development stage of the product.

This paper describes a possible solution for testing AR instructions on virtual prototypes by combining AR and Virtual Reality (VR) technology. Technical aspects for combining VR and AR displays are outlined and a combined system is presented. Furthermore, the paper shows the development of a specific test scenario for evaluating the created system and contains design patterns for depicting AR instructions in Virtual Environments. Finally, the usability of the solution is tested by a user study.
Implementations of Deflectors to Improve the Performance of Heat Sinks
Authors: Ramirez-Vazquez J. P. , Hernandez-Guerrero A. , Zuñiga-Cerroblanco J. L. , Rubio-Arana J. C.
Published: December 2013

This work presents a numerical study of the thermal and hydrodynamic behavior of a pin-fin heat sink where deflectors are placed along the flow of the coolant air; the effect of the arrangement of the fins and deflectors in the global performance of the heat sink is investigated. The fin geometry analyzed is rectangular, and the arrangement of the fins is inline. The heat sink is placed in a channel in which air flows, and a constant heat flux is applied at the bottom wall of the heat sink with values equivalent to the heat fluxes generated by current electronic devices. Deflectors are placed in the top of the channel in order to drive the air flow into the front and end of the heat sink. The results for the Nusselt number and for the pressure drop along the heat sink are reported. The best dimension of deflectors and pitch for the arrangement based on the thermal and hydraulic performance is attained.
Evaluation of Drivers Authority in a Structured Set of Driving Tasks and Decisions: Preliminary Results on Vehicle Simulator Study
Authors: Uluer Pınar , Göçmenoğlu Can , Acarman Tankut
Published: December 2013

One of the most challenging factors in the development of autonomous vehicles and advanced driver assistance systems is the imitation of an expert driver system which is the observer and interpreter of the technical system in the related driving scenario. To achieve an expert human-like situational understanding and decision making may be an important feature to fulfill the necessary active safety requirements. In this paper, an exploratory study on a multimodal adaptive driver assistance system is presented. The main goal is to determine the human driver’s attention and authority level in a cognitive model and to trigger the timely warnings according to his/her driving intents and driving skills with respect to the possible driving situation and hazard scenarios. In the previous studies, a fairly restrictive vision-based driver assistance system has been deployed to detect lane departure, blind-spot and to monitor following distance, headway time. This vision-based driver assistance system considers the driver’s driving performance metric sampled during the longitudinal and lateral vehicle control tasks as well as the processed information about the surrounding traffic environment consisting of the interactions with the other vehicles and the road situations. The presented active safety system models the driving task in a cognitive architecture and assesses the cognition of the human driver by modeling the situation awareness of the driver by using fuzzy sets. Each fuzzy set simply represents the expert driver’s perception in both of the longitudinal and lateral traffic. The presented system evaluates the driver’s driving skills and attention level by comparing the expert and human driver’s reactions suited in a finite set of decision and maneuvering task. In case of hazard analysis, the system triggers timely warnings pointing the driver’s attention at the lateral or longitudinal maneuvering tasks depending on the interpreted situation. Introductory experiments are performed with a limited number of participants, the test driving data including the driver’s perception and reaction to the surrounding vehicles and traffic situations are collected by the use of a vehicle simulator. And the presented multimodal adaptive driver assistance system is evaluated by the simulator. The preliminary results seem to be promising.
Handling Localization in Damage Models With the Thick Level Set Approach (TLS)
Authors: Moës Nicolas , Bernard Paul-Emile , Stolz Claude , Chevaugeon Nicolas
Published: December 2013

In this paper, we discuss a new way to model damage growth in solids. A level set is used to separate the undamaged zone from the damaged zone. In the damaged zone, the damage variable is an explicit function of the level set. This function is a parameter of the model. Beyond a critical length, it is assumed that the material is totally damaged, thus allowing a straightforward transition to fracture. The damage growth is expressed as a level set propagation. The configurational force driving the damage front is non local in the sense that it averages information over the thickness in the wake of the front. Three important theoretical advantages of the proposed approach are as follows: (a) The zone for which the materials is fully damaged is located inside a clearly identified domain (given by an iso-level set). (b) The non-locality steps in gradually in the model. At initiation the model is fully local. At initiation, micro-cracks being absent no length scale should prevail. (c) It is straightforward to prove that dissipation is positive. A numerical experiment of the cracking of a multiply perforated plate is discussed.
Design of Training Protocol for Perceptual and Technical Skills in a Minimally Invasive Surgery
Authors: Grosdemouge Cristol , Weyhrauch Peter , Niehaus James , Schwaitzberg Steven , Cao Caroline G. L.
Published: December 2013

This study investigates how the technical and perceptual skills in laparoscopic surgery, typically acquired separately in the initial learning phases, can be trained together. A task analysis and cognitive task analysis were conducted using a cholecystectomy procedure and a fundoplication procedure. An experiment was conducted to examine the interaction of technical and perceptual skill learning. Subjects were divided into three groups based on order of skills training: 1) technical-perceptual-combined skills training order, 2) perceptual-technical-combined skills training order, and 3) combined skills training. After the training sessions, performance was evaluated using the combined skill. Preliminary results indicate that performance of the group trained in the combined skills condition performed equally quickly as those who trained the technical and perceptual skills separately first. In addition, the number of technical errors and perceptual errors committed were lower. This suggests that surgical skills training may be more efficient if perceptual learning is combined with motor skills during the initial phases of training. This has implications for the design of surgical training simulators and surgical education in general.
Application of Discrete Element Simulation to the Crushing of a Food Biopolymer Foam for Mastication Modelling
Authors: Hedjazi Lotfi , Martin Christophe L. , Guessasma Sofiane , Della Valle Guy , Dendievel Rémy
Published: December 2013

The fragmentation behaviour of brittle airy cereal foods is studied both numerically and experimentally. The food item is subjected to severe compression until densification stage. Experimental evidence of typical cellular material behaviour is pointed out by elasticity, cell collapse and densification regimes. Using an accurate description of the cellular structure determined by X-ray tomography, a numerical approach based on discrete element method is proposed in order to better explain the resulting fragmentation. The approach allows to reproduce the deformation stages and predicted results show good agreement with experimental mechanical responses, in terms of maximum force. Moreover, large size fragments are found to form as a consequence of small rupture events.
An Adaptive Remeshing Procedure for Modeling the Clinch Forming Process
Authors: Sahyoun Abdallah , Rassineux Alain , Roëlandt Jean-Marc , Labergère Carl , Saanouni Khémais
Published: December 2013

This work presents the case of a press clinching commonly met in the industry and denoted as TOX. The mechanical strength of the assembly is highly dependent on the final geometry of the clinched joint and among the numerous parameters which govern the process (applied load, lubrication, sheet thickness, friction, mechanical behavior of materials), the tool geometry plays a major role in the evolution of the final shape of the clinched joint. One of the objectives of this work is to provide an accurate numerical evolution of the final geometry of the clinched joint by the use of an adaptive remeshing procedure including error indicators and field variable transfer built by a meshless technique denoted as Diffuse Approximation. The resolution of the updated Lagrangian formulation is based on a static explicit approach (ABAQUS). Our numerical results are validated in comparison with experimental data.
Sources and Potential Utilization of Waste Heat at a Natural Gas Processing Facility in the Middle East
Authors: Eveloy Valerie , Rodgers Peter
Published: December 2013

Waste heat recovery (WHR) has the potential to significantly improve the efficiency of process industries such as in the oil and gas sector, and reduce their environmental impact. The design of an effective WHR strategy requires a comprehensive plant energy audit, but examples of such information are lacking in the published literature. In this paper a detailed energy audit is presented for a major natural gas (NG) processing facility in the Middle East, to identify sources of waste heat and evaluate their potential for on-site recovery. Waste heat sources are quantified and evaluated in terms of grade (i.e., temperature), rate, accessibility (i.e., proximity to potential on-site WHR applications), and impact of potential WHR on the performance and safety of existing facilities. Based on the audit undertaken, conceptual WHR strategies are proposed, focusing on utilities enhancement, i.e., process cooling/heating, electrical/mechanical power generation, and steam production. In addition, to permit the techno-economic feasibility evaluation of the proposed WHR strategies in modeling work undertaken in parallel with this study, the operating parameters of waste heat producing equipment are compiled, along with the cooling/heating loads and electric power/fuel consumption of WHR-enhanced processes.

A total of 689 MW of waste heat is identified in the plant, which consists of 526 MW gas turbine (GT) and 56 MW gas generator exhaust gases, 10 MW flared gases, 5 MW excess process steam, 88 MW process gas air-cooler heat dissipation, 2 MW furnace exhaust gases, and 1 MW steam turbine outlet steam. Waste energy in the form of excess propane cooling capacity is also identified. The total amount of waste heat meeting the rate, grade, accessibility and minimal performance-and-safety-impact criteria defined for potential WHR in this study is of approximately 547 MW, most of which is produced by GTs. Only 174 MW of GT waste heat is presently re-utilized, in addition to excess propane cooling capacity. Novel absorption refrigeration-based WHR strategies are proposed to recover the available GT waste heat. These strategies were found to be thermodynamically and economically feasible in an accompanying study, and to lead to substantial energy and cost savings for the plant.
Prediction Reliability of a Statistical Methodology for Gas Turbine Prognostics
Authors: Venturini Mauro , Puggina Nicola
Published: December 2013

The performance of gas turbines degrades over time and, as a consequence, a decrease in gas turbine performance parameters also occurs, so that they may fall below a given threshold value. Therefore, corrective maintenance actions are required to bring the system back to an acceptable operating condition. In today’s competitive market, the prognosis of the time evolution of system performance is also recommended, in such a manner as to take appropriate action before any serious malfunctioning has occurred and, as a consequence, to improve system reliability and availability. Successful prognostics should be as accurate as possible, because false alarms cause unnecessary maintenance and non-profitable stops.

For these reasons, a prognostic methodology, developed by the authors, is applied in this paper to assess its prediction reliability for several degradation scenarios typical of gas turbine performance deterioration. The methodology makes use of the Monte Carlo statistical method to provide, on the basis of the recordings of past behavior, a prediction of future availability, i.e. the probability that the considered machine or component can be found in the operational state at a given time in the future. The analyses carried out in this paper aim to assess the influence of the degradation scenario on methodology prediction reliability, as a function of a user-defined threshold and minimum value allowed for the parameter under consideration. A technique is also presented and discussed, in order to improve methodology prediction reliability by means a correction factor applied to the time points used for methodology calibration.

The results presented in this paper show that, for all the considered degradation scenarios, the prediction error is lower than 4% (in most cases, it is even lower than 2%), if the availability is estimated for the next trend, while it is not higher than 12%, if the availability is estimated five trends ahead. The application of a proper correction factor allows the prediction errors after five trends to be reduced to approximately 5%.
On Uncertainty Propagation in Mass, Damping and Stiffness Matrices Identification of Mechanical Systems
Authors: Medina Luis U. , Díaz Sergio E. , Feng Ningsheng , Hahn Eric J.
Published: December 2013

The accuracy in estimating the mass, damping and stiffness matrices for mechanical systems depends on the error propagation through the stages involved in the parameter identification, i.e. excitation and response measurements, signal processing and modeling stages. Robust algorithms are available to estimate the system’s parameters in the presence of “noisy” measurements. However, uncertainties in the identified parameters of mechanical systems have not been usually reported or have simply been overlooked in the identification strategy. An overall uncertainty occurs for each identified parameter, and it may be defined in terms of error propagation. The recognition of relevant error contributions is the key to accomplishing parameter error estimation in the identification process, a task that may imply subtle aspects. An approach is proposed for uncertainty estimation in mass, stiffness and damping matrices for linearized mechanical systems. This approach is formulated as an extension of the accepted practice for evaluating experimental uncertainty for a scalar measurand. Typical error sources throughout the identification stages are also discussed. The suggested approach may be applied to identify mechanical systems in the frequency domain, and is independent of the algorithm used to estimate the system parameters. Practical limitations of the suggested approach are also discussed.
Study on the Sampling Quality of Wetness Measurement Probe for Thermodynamic Methods
Authors: Wang Xinjun , Liao Gaoliang , Zhu Ding , Yao Jinling , Bai Xiaowei
Published: December 2013

Software FLUENT was applied to conduct the numerical calculations of the sampling velocity at the sampling nozzle inlet of the wetness measurement probe and the trajectories of water droplets in the steam flow. The steam wetness of samples and the percentage of the droplets with different diameters entering the sampling nozzle were ascertained. The results showed that wetness measurement probe affected the flow of vapor phase at some degrees. Especially, there was a deflection of stream line nearby the sampling nozzle. It was showed that the isokinetic sampling could not be accomplished because of the viscosity of vapor. The larger the angle between the steam flow direction and the center line of the sampling nozzle was, the lower the average sampling velocity at sampling nozzle inlet section was. The percentage of water droplets captured by sampling nozzle increased with the augmentation of water droplet diameters. When the water droplet diameter was 5μm, the sampling nozzle would capture all water droplets in the corresponding area of the sampling nozzle inlet. When the sampling nozzle was dead against the upper stream, the wetness of sample extracted by sampling nozzle was lower than that of the measured steam. In contrast, the wetness of sample was larger than that of the measured steam when the angle between the sampling nozzle and upper stream was ± 5° or ± 10° respectively. The results have showed that the wetness error increased with the augmentation of sampling nozzle diameters, the vapor velocity and the angle between upper steam and center line of the sampling nozzle.
Damage Parameter Assessment for Energy Based Fatigue Life Prediction Methods
Authors: Holycross Casey M. , Wertz John N. , Letcher Todd , Shen M.-H. Herman , Scott-Emuakpor Onome E. , George Tommy J.
Published: December 2013

An energy-based method used to predict fatigue life and critical life of various materials has been previously developed, correlating strain energy dissipated during monotonic fracture to total cyclic strain energy dissipation in fatigue fracture. This method is based on the assumption that the monotonic strain energy and total hysteretic strain energy to fracture is equivalent. The fracture processes of monotonic and cyclic failure modes can be of stark contrast, with ductile and brittle fracture dominating each respectively. This study proposes that a more appropriate damage parameter for predicting fatigue life may be to use low cycle fatigue (LCF) strain energy rather than monotonic energy. Thus, the new damage parameter would capture similar fracture processes and cyclic behavior. Round tensile specimens machined from commercially supplied Al 6061-T6511 were tested to acquire LCF failure data in fully reversed loading at various alternating stresses. Results are compared to both monotonic and cyclic strain energy dissipation to determine if LCF strain energy dissipation is a more suitable damage parameter for fatigue life prediction.
Stochastic Integration Methods: Comparison and Application to Reliability Analysis
Authors: Paffrath M. , Wever U.
Published: December 2013

A central part of stochastic computations (e.g. of moments or of failure probabilities) is the evaluation of multi-dimensional integrals. The crude Monte-Carlo method is often too expensive in terms of computation time. In this paper a comparison of methods is made for a collection of test examples. The considered methods are numerical sparse grid methods either known from literature or some further development of known methods. Apart from some academic test examples, the performance of the methods is studied for integrals arising in the area of stochastic crack growth.
Comparison Between Numerical and Experimental Dynamic Coefficients of a Hybrid Aerostatic Bearing
Authors: Hassini Mohamed Amine , Arghir Mihai , Frocot Manuel
Published: December 2013

Hybrid journal bearings are considered since many years as a possible replacement for ball bearings in turbo-pumps used by the aerospace industry. Due to flow regimes dominated by inertia and due to the nature of the lubricant (cryogenic fluids), the prediction of the linearized dynamic coefficients in these bearings must be based on the compressible bulk-flow equations. Theoretical models based on these equations were validated for hybrid bearings working with water or for liquid or gas annular seals. Validations for hybrid compressible bearings are missing. Experimental data obtained for an air lubricated hybrid aerostatic bearing designed with shallow pockets were recently presented; the data consist of linearized dynamic coefficients obtained for rotation speeds up to 50 krpm and up to 7 bar feeding pressure. The present work introduces a consolidated numerical approach for predicting static and linearized dynamic characteristics. Theoretical predictions are based on bulk flow equations in conjunction with CFD analysis. It was found that for a given feeding pressure, the value of the pressure downstream the orifice has a major influence on all results. Special care was then taken for describing the complex flow in the feeding system and the orifice. Three dimensional CFD was employed because the bulk-flow equations are inappropriate in this part of the bearing. The pressure downstream the orifice stemming from CFD results and the feeding pressure were next imposed in the bulk flow model and the equivalent area of the orifice was obtained from the numerical solution of the steady flow in the bearing. Since the pockets of the hybrid bearing are shallow, this equivalent area is considered as being the harmonic average of the orifice cross section area and of the cylindrical curtain area located between the orifice and the rotor. The comparisons between theoretical dynamic coefficients and experimental data validated this approach of the equivalent area of the orifice.
Hole-Pattern and Honeycomb Seal Rotordynamic Forces: Validation of CFD-Based Prediction Techniques
Authors: Krogh Nielsen Kenny , Jønck Kasper , Underbakke Harald
Published: December 2013

This paper deals with modeling of hole-pattern and honeycomb seals. These are frequently used as balance piston seals in high pressure centrifugal compressor applications as they have the potential to facilitate superior rotordynamic damping characteristics while providing good leakage control. On the other hand it is also well-established that the rotordynamic performance of hole-pattern and honeycomb seals is very sensitive to convergence and divergence in the streamwise direction.

The ISOTSEAL bulk-flow code has shown difficulties in predicting the rotordynamic coefficients for convergent seal geometries or in cases with negative preswirl. This has lead to increased interest in CFD-based analysis of seal dynamics. CFD-based models generally have less assumptions and are applicable for complex geometries or operating ranges not covered by bulk-flow codes.

The CFD-based Instationary Perturbation Model (IPM) is utilized for the analysis of the hole-pattern and honeycomb seals. The rotordynamic forces are obtained by means of a time-dependent perturbation of the rotor position with respect to the stator. A sequence of perturbation frequencies is utilized to obtain the frequency dependence of the rotordynamic seal force coefficients.

A strong effort has been put into validating the CFD-based perturbation modeling techniques against published experimental seal test data and the paper describes selected validation cases. A constant-clearance hole-pattern seal and a convergent honeycomb seal are analyzed and the results are compared to experimental results. The frequency dependence of the rotordynamic stiffness and damping characteristics of the seals is very well-captured for both types of seals.

Finally the IPM method was applied to a convergent hole-pattern seal to investigate the effects of eccentricity on the rotordynamic coefficients. The results are consistent with available experimental data.
Microturbine Recuperation: Turbulators and Their Effect on Power Density and Thermal Efficiency
Authors: Dorman Kaylee M. , Quintero Sergio Arias , Tran Lucky V. , Ricklick Mark , Kapat J. S.
Published: December 2013

Microturbines have proven to be a vital part of the distributed power generation field due to their low emissions, compact size, high reliability and low maintenance. However, microturbines operate at low pressure ratios and relatively low turbine inlet temperatures that limit cycle efficiency. In order to overcome these limitations, microturbines often utilize a recuperator or regenerator to achieve the optimal balance between improved heat rates and reduced pressure ratios across the turbine. Recuperator design aims to achieve maximum effectiveness while staying reasonably compact, which creates the need to study novel heat transfer surfaces for compact heat exchanger application. In this study, experimental data of heat transfer augmentation and friction factor augmentation values for various turbulator geometries is used to determine the required heat exchanger volume to achieve 85%, 90%, and 95% effectiveness. A parametric analysis of various recuperator channel surface areas and turbulator geometry data will be utilized to determine the feasibility of increasing thermal efficiency while remaining compact to avoid large, negative effects on power density for a hypothetical gas turbine modeled after the Turbine Technologies, Ltd. SR-30 Turbo-Jet Engine. The turbulators considered in this study consist of 4 wedges, 4 ribs, and a dimpled geometry. The results will highlight the applicability of surface features in recuperator designs that can improve overall efficiency for microturbines. Results present the power density, thermal efficiency, and specific fuel consumption as functions of heat exchanger channel Reynolds number for heat exchangers implementing different turbulators. It is shown that dimples at low Reynolds numbers yield 85% effectiveness with only a 8% reduction in power density and 90% effectiveness with only a 12% reduction in power density. Ribs and wedges also perform well but suffer from high pressure losses due to their obtrusive design.
Waterless TiO2 atomic layer deposition using titanium tetrachloride and titanium tetraisopropoxide
Authors: Anderson Virginia R. , Cavanagh Andrew S. , Abdulagatov Aziz I. , Gibbs Zachary M. , George Steven M.
Published: December 2013

The surface chemistry for TiO2 atomic layer deposition (ALD) typically utilizes water or other oxidants that can oxidize underlying substrates such as magnetic disks or semiconductors. To avoid this oxidation, waterless or oxidant-free surface chemistry can be used that involves titanium halides and titanium alkoxides. In this study, waterless TiO2 ALD was accomplished using titanium tetrachloride (TiCl4) and titanium tetraisopropoxide (TTIP). In situ transmission Fourier transform infrared (FTIR) studies were employed to study the surface species and the reactions during waterless TiO2 ALD. At low temperatures between 125 and 225  °C, the FTIR absorbance spectra revealed that the isopropoxide species remained on the surface after TTIP exposures. The TiCl4 exposures then removed the isopropoxide species and deposited additional titanium species. At high temperatures between 250 and 300  °C, the isopropoxide species were converted to hydroxyl species by β-hydride elimination. The observation of propene gaseous reaction product by quadrupole mass spectrometry (QMS) confirmed the β-hydride elimination reaction pathway. The TiCl4 exposures then easily reacted with the hydroxyl species. QMS studies also observed the 2-chloropropane and HCl gaseous reaction products and monitored the self-limiting nature of the TTIP reaction. Additional studies examined the waterless TiO2 ALD growth at low and high temperature. Quartz crystal microbalance measurements observed growth rates of ∼3 ng/cm2 at a low temperature of 150  °C. Much higher growth rates of ∼15 ng/cm2 were measured at a higher temperature of 250  °C under similar reaction conditions. X-ray reflectivity analysis measured a growth rate of 0.55 ± 0.05 Å/cycle at 250  °C. X-ray photoelectron depth-profile studies showed that the TiO2 films contained low Cl concentrations <1 at. %. This waterless TiO2 ALD process using TiCl4 and TTIP should be valuable to prevent substrate oxidation during TiO2 ALD on oxygen-sensitive substrates.
Corrosion of Iron by Sulfate-Reducing Bacteria: New Views of an Old Problem
Authors: Enning Dennis , Garrelfs Julia
Published: December 2013

About a century ago, researchers first recognized a connection between the activity of environmental microorganisms and cases of anaerobic iron corrosion. Since then, such microbially influenced corrosion (MIC) has gained prominence and its technical and economic implications are now widely recognized. Under anoxic conditions (e.g., in oil and gas pipelines), sulfate-reducing bacteria (SRB) are commonly considered the main culprits of MIC. This perception largely stems from three recurrent observations. First, anoxic sulfate-rich environments (e.g., anoxic seawater) are particularly corrosive. Second, SRB and their characteristic corrosion product iron sulfide are ubiquitously associated with anaerobic corrosion damage, and third, no other physiological group produces comparably severe corrosion damage in laboratory-grown pure cultures. However, there remain many open questions as to the underlying mechanisms and their relative contributions to corrosion. On the one hand, SRB damage iron constructions indirectly through a corrosive chemical agent, hydrogen sulfide, formed by the organisms as a dissimilatory product from sulfate reduction with organic compounds or hydrogen (“chemical microbially influenced corrosion”; CMIC). On the other hand, certain SRB can also attack iron via withdrawal of electrons (“electrical microbially influenced corrosion”; EMIC),
viz
., directly by metabolic coupling. Corrosion of iron by SRB is typically associated with the formation of iron sulfides (FeS) which, paradoxically, may reduce corrosion in some cases while they increase it in others. This brief review traces the historical twists in the perception of SRB-induced corrosion, considering the presently most plausible explanations as well as possible early misconceptions in the understanding of severe corrosion in anoxic, sulfate-rich environments.
Measurement of Ice Nucleation-Active Bacteria on Plants and in Precipitation by Quantitative PCR
Authors: Hill Thomas C. J. , Moffett Bruce F. , DeMott Paul J. , Georgakopoulos Dimitrios G. , Stump William L. , Franc Gary D.
Published: December 2013

Ice nucleation-active (INA) bacteria may function as high-temperature ice-nucleating particles (INP) in clouds, but their effective contribution to atmospheric processes, i.e., their potential to trigger glaciation and precipitation, remains uncertain. We know little about their abundance on natural vegetation, factors that trigger their release, or persistence of their ice nucleation activity once airborne. To facilitate these investigations, we developed two quantitative PCR (qPCR) tests of the
ina
gene to directly count INA bacteria in environmental samples. Each of two primer pairs amplified most alleles of the
ina
gene and, taken together, they should amplify all known alleles. To aid primer design, we collected many new INA isolates. Alignment of their partial
ina
sequences revealed new and deeply branching clades, including sequences from
Pseudomonas syringae
pv.
atropurpurea
,
Ps. viridiflava
,
Pantoea agglomerans
,
Xanthomonas campestris
, and possibly
Ps. putida
,
Ps. auricularis
, and
Ps. poae
. qPCR of leaf washings recorded ∼10
8
ina
genes g
−1
fresh weight of foliage on cereals and 10
5
to 10
7
g
−1
on broadleaf crops. Much lower populations were found on most naturally occurring vegetation. In fresh snow,
ina
genes from various INA bacteria were detected in about half the samples but at abundances that could have accounted for only a minor proportion of INP at −10°C (assuming one
ina
gene per INA bacterium). Despite this, an apparent biological source contributed an average of ∼85% of INP active at −10°C in snow samples. In contrast, a thunderstorm hail sample contained 0.3 INA bacteria per INP active at −10°C, suggesting a significant contribution to this sample.
Replicon-Dependent Differentiation of Symbiosis-Related Genes in Sinorhizobium Strains Nodulating Glycine max
Authors: Guo Hui Juan , Wang En Tao , Zhang Xing Xing , Li Qin Qin , Zhang Yan Ming , Tian Chang Fu , Chen Wen Xin
Published: December 2013

In order to investigate the genetic differentiation of
Sinorhizobium
strains nodulating
Glycine max
and related microevolutionary mechanisms, three housekeeping genes (
SMc00019
,
truA
, and
thrA
) and 16 symbiosis-related genes on the chromosome (7 genes), pSymA (6 genes), and pSymB (3 genes) were analyzed. Five distinct species were identified among the test strains by calculating the average nucleotide identity (ANI) of
SMc00019-truA-thrA
:
Sinorhizobium fredii
,
Sinorhizobium sojae
,
Sinorhizobium
sp. I,
Sinorhizobium
sp. II, and
Sinorhizobium
sp. III. These species assignments were also supported by population genetics and phylogenetic analyses of housekeeping genes and symbiosis-related genes on the chromosome and pSymB. Different levels of genetic differentiation were observed among these species or different replicons.
S. sojae
was the most divergent from the other test species and was characterized by its low intraspecies diversity and limited geographic distribution. Intergenic recombination dominated the evolution of 19 genes from different replicons. Intraspecies recombination happened frequently in housekeeping genes and symbiosis-related genes on the chromosome and pSymB, whereas pSymA genes showed a clear pattern of lateral-transfer events between different species. Moreover, pSymA genes were characterized by a lower level of polymorphism and recombination than those on the chromosome and pSymB. Taken together, genes from different replicons of rhizobia might be involved in the establishment of symbiosis with legumes, but these symbiosis-related genes might have evolved differently according to their corresponding replicons.
Revealing the Genetic Basis of Natural Bacterial Phenotypic Divergence
Authors: Freddolino Lydia , Goodarzi Hani , Tavazoie Saeed
Published: December 2013

Divergent phenotypes for distantly related strains of bacteria, such as differing antibiotic resistances or organic solvent tolerances, are of keen interest both from an evolutionary perspective and for the engineering of novel microbial organisms and consortia in synthetic biology applications. A prerequisite for any practical application of this phenotypic diversity is knowledge of the genetic determinants for each trait of interest. Sequence divergence between strains is often so extensive as to make brute-force approaches to identifying the loci contributing to a given trait impractical. Here we describe a global linkage analysis approach, GLINT, for rapid discovery of the causal genetic variants underlying phenotypic divergence between distantly related strains of
Escherichia coli
. This general strategy will also be usable, with minor modifications, for revealing genotype-phenotype associations between naturally occurring strains of other bacterial species.
The Uptake Hydrogenase in the Unicellular Diazotrophic Cyanobacterium Cyanothece sp. Strain PCC 7822 Protects Nitrogenase from Oxygen Toxicity
Authors: Zhang Xiaohui , Sherman Debra M. , Sherman Louis A.
Published: December 2013

Cyanothece
sp. strain PCC 7822 is a unicellular, diazotrophic cyanobacterium that can produce large quantities of H
2
when grown diazotrophically. This strain is also capable of genetic manipulations and can represent a good model for improving H
2
production from cyanobacteria. To this end, a knockout mutation was made in the
hupL
gene (Δ
hupL
), and we determined how this would affect the amount of H
2
produced. The Δ
hupL
mutant demonstrated virtually no nitrogenase activity or H
2
production when grown under N
2
-fixing conditions. To ensure that this mutation only affected the
hupL
gene, a complementation strain was constructed readily with wild-type properties; this indicated that the original insertion was only in
hupL
. The mutant had no uptake hydrogenase activity but had increased bidirectional hydrogenase (Hox) activity. Western blotting and immunocytochemistry under the electron microscope indicated that the mutant had neither HupL nor NifHDK, although the
nif
genes were transcribed. Interestingly, biochemical analysis demonstrated that both HupL and NifH could be membrane associated. The results indicated that the
nif
genes were transcribed but that NifHDK was either not translated or was translated but rapidly degraded. We hypothesized that the Nif proteins were made but were unusually susceptible to O
2
damage. Thus, we grew the mutant cells under anaerobic conditions and found that they grew well under N
2
-fixing conditions. We conclude that in unicellular diazotrophs, like
Cyanothece
sp. strain PCC 7822, the HupLS complex helps remove oxygen from the nitrogenase, and that this is a more important function than merely oxidizing the H
2
produced by the nitrogenase.
Blast a Biofilm: A Hands-On Activity for School Children and Members of the Public
Authors: Marlow Victoria L. , MacLean Tristan , Brown Helen , Kiley Taryn B. , Stanley-Wall Nicola R.
Published: December 2013

Microbial biofilms are very common in nature and have both detrimental and beneficial effects on everyday life. Practical and hands-on activities have been shown to achieve greater learning and engagement with science by young people (1, 4, 5). We describe an interactive activity, developed to introduce microbes and biofilms to school age children and members of the public. Biofilms are common in nature and, as the favored mode of growth for microbes, biofilms affect many parts ofeveryday life. This hands-on activity highlights the key concepts of biofilms by allowing participants to first build, then attempt to ‘blast,’ a biofilm, thus enabling the robust nature of biofilms to become apparent. We developed the blast-a-biofilm activity as part of our two-day Magnificent Microbes event, which took place at the Dundee Science Centre-Sensation in May 2010 (6). This public engagement event was run by scientists from the Division of Molecular Microbiology at the University of Dundee. The purpose of the event was to use fun and interesting activities to make both children and adults think about how fascinating microbes are. Additionally, we aimed to develop interactive resources that could be used in future events and learning environments, of which the blast-a-biofilm activity is one such resource. Scientists and policy makers in the UK believe engaging the public with research ensures that the work of universities and research institutes is relevant to society and wider social concerns and can also help scientists actively contribute to positive social change (2). The activity is aimed at junior school age children (9–11 years) and adults with little or no knowledge of microbiology. The activity is suitable for use at science festivals, science clubs, and also in the classroom, where it can serve as a tool to enrich and enhance the school curriculum.
A Survey Tool for Assessing Student Expectations Early in a Semester
Authors: Schmitt Karl R. B. , Larsen Elise A. , Miller Matthew , Badawy Abdel-Hameed A. , Dougherty Mara , Sharma Artesha Taylor , Hrapczynski Katie , Andrew Andrea , Robertson Breanne , Williams Alexis , Kramer Sabrina , Benson Spencer
Published: December 2013

Quality learning is fostered when faculty members are aware of and address student expectations for course learning activities and assessments. However, faculty often have difficulty identifying and addressing student expectations given variations in students’ backgrounds, experiences, and beliefs about education. Prior research has described significant discrepancies between student and faculty expectations that result from cultural backgrounds (1), technological expertise (2), and ‘teaching dimensions’ as described by Trudeau and Barnes (4). Such studies illustrate the need for tools to identify and index student expectations, which can be used to facilitate a dialogue between instructor and students. Here we present the results of our work to develop, refine, and deploy such a tool.
Ozone air pollution and ischaemic stroke occurrence: a case-crossover study in Nice, France
Authors: Suissa Laurent , Fortier Mikael , Lachaud Sylvain , Staccini Pascal , Mahagne Marie-Hélène
Published: December 2013

Objectives

Relationship between low-level air pollution and stroke is conflicting. This study was conducted to document the relationship between outdoor air pollution and ischaemic stroke occurrence.

Design

Time-stratified case-crossover analysis.

Setting

University Hospital of Nice, France.

Participants

All consecutive patients with ischaemic stroke living in Nice admitted in the University Hospital of Nice (France) between January 2007 and December 2011.

Main outcome measure

Association (adjusted OR) between daily levels of outdoor pollutants (ozone (O3), nitrogen dioxide (NO2), particulate matter (PM10) and sulfur dioxide (SO2)) and ischaemic stroke occurrence.

Results

1729 patients with ischaemic stroke (mean age: 76.1±14.0 years; men: 46.7%) were enrolled. No significant association was found between stroke occurrence and short-term effects of all pollutants tested. In stratified analysis, we observed significant associations only between recurrent (n=280) and large artery ischaemic stroke (n=578) onset and short-term effect of O3exposure. For an increase of 10 µg/m3of O3level, recurrent stroke risk (mean D-1, D-2 and D-3 lag) was increased by 12.1% (95% CI 1.5% to 23.9%) and large artery stroke risk (mean D-3 and D-4 lag) was increased by 8% (95% CI 2.0% to 16.6%). Linear dose–response relationship for both subgroups was found.

Conclusions

Our results confirm the relationship between low-level O3exposure and ischaemic stroke in high vascular risk subgroup with linear exposure–response relation, independently of other pollutants and meteorological parameters. The physiopathological processes underlying this association between ischaemic stroke and O3exposure remain to be investigated.
Associations between race, lifecourse socioeconomic position and prevalence of diabetes among US women and men: results from a population-based panel study
Authors: Insaf T Z , Strogatz D S , Yucel R M , Chasan-Taber L , Shaw B A
Published: December 2013

Background

Few studies have examined the degree to which racial disparities in the development of diabetes are accounted by differences in lifecourse socioeconomic position (SEP). We assessed the association between race, lifecourse SEP measures and prevalence of diabetes in a representative US sample of black and white adults.

Methods

A generalised estimating equations approach was used with a sample of 3497 adults from the Americans’ Changing Lives study. Sex-specific models were calculated to compute prevalence ratios (PR) for associations of race and SEP with self-reported diagnoses of diabetes.

Results

For men, childhood and adult SEP were unrelated to diabetes, and adjustment for lifecourse SEP had little effect on the excess diabetes in blacks (PR=1.56, 95% CI 1.11 to 2.21). Adjustment for measures of lifecourse SEP reduced the PR for the association between race and diabetes in women from 1.96 (95% CI 1.52 to 2.54) to 1.40 (95% CI 1.04 to 1.87) with the respondent's education responsible for most of the reduction in the association. However, diabetes was also inversely associated with father's education, and low SEP throughout the lifecourse was associated with a nearly threefold increase in diabetes (PR=2.89, 95% CI 2.10 to 3.99).

Conclusions

Racial disparities in diabetes existed among both men and women, but lifecourse SEP was related to diabetes only among women. The pathway and cumulative hypotheses for lifecourse SEP effects on diabetes may be especially salient for women.
Selection of reference genes for quantitative real-time PCR in Cocos nucifera during abiotic stress
Authors: Xia Wei , Liu Zheng , Yang Yaodong , Xiao Yong , Mason Annaliese S. , Zhao Songlin , Ma Zilong
Published: December 2013

Reverse transcription quantitative real-time polymerase chain reaction (PCR) is a widely used and reproducible method for studying gene expression changes. However, its accuracy and reliability is highly dependent on the normalization step. Cocos nucifera L., a perennial palm with a long productive life span, is frequently exposed to soil and atmospheric drought and other stresses. In applying gene expression analysis to understand coconut stress responses, validation of suitable reference genes is an important first step. In this study, seven putative reference genes were identified from coconut transcriptome data. The stability of these putative reference genes was assessed in a diverse set of 18 coconut samples subject to cold, drought, and high-salinity treatment and representing different endosperm developmental stages. Using statistical algorithms geNorm, NormFinder, and BestKeeper, eEF1-α and UBC10 genes were identified as stable reference genes in all stress treatments and endosperm development stages, consistent with validated reference genes in rice (Oryza sativa L.), potato (Solanum tuberosum L.), and other species. Further validation of analyzed reference genes by normalization of a C-repeat binding factor (CBF)-like gene in cold-treatment samples indicated that the less stable reference genes produced different results from the more stable reference genes, with weaker variation or higher expression levels of a target gene. Our results will be beneficial for further research on molecular mechanisms of stress resistance.
Genetic Engineering and Breeding of Drought-Resistant Crops
Authors: Hu Honghong , Xiong Lizhong
Published: December 2013

Drought is one of the most important environmental stresses affecting the productivity of most field crops. Elucidation of the complex mechanisms underlying drought resistance in crops will accelerate the development of new varieties with enhanced drought resistance. Here, we provide a brief review on the progress in genetic, genomic, and molecular studies of drought resistance in major crops. Drought resistance is regulated by numerous small-effect loci and hundreds of genes that control various morphological and physiological responses to drought. This review focuses on recent studies of genes that have been well characterized as affecting drought resistance and genes that have been successfully engineered in staple crops. We propose that one significant challenge will be to unravel the complex mechanisms of drought resistance in crops through more intensive and integrative studies in order to find key functional components or machineries that can be used as tools for engineering and breeding drought-resistant crops.