Boundary work in knowledge teams.

The purpose of this article is to promote an open systems perspective on team research. The authors develop a model of team boundary activities: boundary spanning, buffering, and reinforcement. The model examines the relationship between these boundary activities and team performance, the moderating effects of organizational contextual factors, and the mediating effect of team psychological safety on the boundary work–performance relationship. These relationships were empirically tested with data collected from 64 software development teams. Boundary spanning, buffering, and boundary reinforcement were found to relate to team performance and psychological safety. Both relationships are moderated by the team’s task uncertainty and resource scarcity. The implications of the findings are offered for future research and practice. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Towards a water–energy–food nexus policy: realizing the blue and green virtual water of agriculture in Jordan

Virtual water is an important addendum to how we view a country's water resources. This study examines the virtual water embedded in Jordan's agricultural produce and its impact on future water–energy–food policies. Blue and green virtual waters are calculated from data on rainfall, crop patterns, yields, and water requirements at the district level. Results highlight the advantages of blue water usage in the Jordan Valley and of harnessing more available green water in the Highlands, with both displaying low energy impact. Results also emphasize the high groundwater usage and energy footprint in the Desert regions, signalling a need to rein in groundwater extraction and take advantage of solar power.     

Wavelet Denoising of TSD Deflection Slope Measurements for Improved Pavement Structural Evaluation

Continuous deflection devices (CDDs) can safely measure pavement deflection (or other related properties) while traveling at highway speed, which reduces traffic disruption. CDD measurements are contaminated with relatively high noise levels compared to stop‐and‐go devices such as the Falling Weight Deflectometer. In this article, we use wavelet transform denoising to remove the noise and estimate the true deflection slope measurements obtained from the Traffic Speed Deflectometer. Results show that failure to denoise deflection slope measurements can lead to calculated Effective Structural Number values that are highly variable (unstable). Attempting to filter these highly variable measurements can lead to erroneous results. We also use wavelet transform denoising to identify localized weak spots such as those that are caused by pavement reflection cracking. Identifying weak spots with wavelets is possible because wavelets are spatially adaptive to local features. In contrast, a linear filter is not capable of adapting to local features.     

Autolanding a Power-off UAV Using On-line Optimization and Slip Maneuvers

This paper tackles the final stages of autolanding a fixed-wing Unmanned Air Vehicle (UAV) in a power-fail emergency scenario. We applied the principle of Nonlinear Model Predictive Control (NMPC) to plan trajectories that respect the aircraft’s limits, and react on disturbances and environmental changes in real-time. However, thanks to judicious problem formulations, our algorithm optimizes—in each time step—the whole horizon of the landing trajectory, and settles a dynamic compromise between the different touchdown requirements. Furthermore, the algorithm is powered by a novel method that utilizes slip maneuvers to achieve adequate energy control notwithstanding the absence of specialized drag control devices. Thus, precise touchdown point is attained even in the presence of strong wind shear and large initial errors. All design parameters are optimized off-line over a wide spectrum of conditions using Genetic Algorithm (GA). Monte-Carlo simulation of the optimized design shows excellent landing performance and high success rate on both flat and sloping terrains.     

Evaluation of repeatability and reproducibility of continuous friction measuring equipment (CFME) using cross-correlation

Lack of sufficient friction between tyre and pavement is known to be one of the contributing factors in vehicle crashes. The application of new technologies can be used to determine the low friction areas or vulnerable accident sites at both the project and network levels. Continuous friction devices are one of the newest systems currently used in European countries that have recently been introduced to the United States. Continuous friction measuring devices are designed to measure the friction under conditions similar to those produced by an anti-lock braking system. Although continuous friction measuring equipment (CFME) provides valuable information about surface friction, processing of the relatively large amount of data produced is time-consuming. Traditional methods such as comparing the average friction provide a quick and simple data analysis method; however, they neglect other important characteristics such as friction spatial variation and low friction spots. This study proposes a methodology based on cross-correlation to compare CFME measurements. The data used in the study were collected during the annual rodeo that took place at the Virginia Smart Road. Two GripTester and one Dynatest 6875H Highway Friction Tester were used for data collection. Cross-correlation was used to synchronise the measurements. Repeatability and reproducibility of the measurements were evaluated based on the maximum cross-correlation value.     

Kinetics of nitrate and perchlorate reduction in ion-exchange brine using the membrane biofilm reactor (MBfR)

Several sources of bacterial inocula were tested for their ability to reduce nitrate and perchlorate in synthetic ion-exchange spent brine (30-45 g/L) using a hydrogen-based membrane biofilm reactor (MBfR). Nitrate and perchlorate removal fluxes reached as high as 5.4 g N m⁻² d⁻¹ and 5.0 g ClO₄ m⁻² d⁻¹, respectively, and these values are similar to values obtained with freshwater MBfRs. Nitrate and perchlorate removal fluxes decreased with increasing salinity. The nitrate fluxes were roughly first order in H₂ pressure, but roughly zero-order with nitrate concentration. Perchlorate reduction rates were higher with lower nitrate loadings, compared to high nitrate loadings; this is a sign of competition for H₂. Nitrate and perchlorate reduction rates depended strongly on the inoculum. An inoculum that was well acclimated (years) to nitrate and perchlorate gave markedly faster removal kinetics than cultures that were acclimated for only a few months. These results underscore that the most successful MBfR bioreduction of nitrate and perchlorate in ion-exchange brine demands a well-acclimated inoculum and sufficient hydrogen availability.     

Effect of pre-heating duration and temperature conditioning on the rheological properties of bitumen

It is well known that overheating asphalt bitumen can lead to oxidation and stiffening. While heating bitumen is an essential protocol in sample preparation, it is important to identify the oven setting time and temperature for lab testing. Current AASHTO standards do not specify exact oven settings for bitumen sample preparation prior to laboratory testing. This study is evaluating the effect of oven heating duration and pouring temperature during sample preparation in the rheological properties of neat and polymer-modified bitumen (PMB). Rheological properties are measured using Rotational Viscometer, Dynamic Shear Rheometer and Bending Beam Rheometer at grade-specific testing temperatures. A neat bitumen PG64-22 and two PMB PG70-22 and 76-22 in un-aged (original) and aged conditions were tested at two temperatures: 143 °C and 185 °C for 1/2, 2 and 4 h. The effect of short-term aging by rolling thin film oven was also investigated. To investigate the rheological properties over a wide range of temperatures, temperature sweep testing was conducted from 35 °C to 110 °C at a 10 rad/s frequency. The results suggest that there was no significant difference in the viscosity, complex modulus and creep stiffness for the tested bitumen. The RTFO aging index, absolute drop of complex viscosity and temperature aging indices were used to evaluate the bitumen preparation settings. The study recommends using the 143 °C and 2-h heating for proper preparation prior to standard lab testing. The study also investigated the aging influence in rheological properties for neat and PMB using the black diagram, DSR function map, and critical-stiffness temperature.