Test of a Method to Calculate Near-Bank Velocity and Boundary Shear Stress

Detailed knowledge of the flow and boundary shear stress fields near the banks of natural channels is essential for making accurate calculations of rates of near-bank sediment transport and geomorphic adjustment. This paper presents a high-resolution laboratory data set of velocity and boundary shear stress measurements and uses it to test a relatively simple, fully predictive, numerical method for determining these distributions across the cross-section of a straight channel. The measurements are made in a flume with a fairly complex cross-section that includes a simulated, cobble-roughened floodplain. The method tested is that reported by Kean and Smith in Riparian Vegetation and Fluvial Geomorphology in 2004, which is modified here to include the effects of drag on clasts located in the channel. The calculated patterns of velocity and boundary shear stress are shown to be in reasonable agreement with the measurements. The principal differences between the measured and calculated fields are the result of secondary circulations, which are not included in the calculation. Better agreement with the structure of the measured streamwise velocity field is obtained by distorting the calculated flow field with the measured secondary flow. Calculations for a variety of narrower and wider configurations of the original flume geometry are used to show how the width-to-depth ratio affects the distribution of velocity and boundary shear stress across the channel.     

An analytic method to compute the stress dependence on the dimensions and its influence in the characteristics of triple gate devices

Triple-gate devices are considered a promising solution for sub-20 nm era. Strain engineering has also been recognized as an alternative due to the increase in the carriers mobility it propitiates. The simulation of strained devices has the major drawback of the stress non-uniformity, which cannot be easily considered in a device TCAD simulation without the coupled process simulation that is time consuming and cumbersome task. However, it is mandatory to have accurate device simulation, with good correlation with experimental results of strained devices, allowing for in-depth physical insight as well as prediction on the stress impact on the device electrical characteristics. This work proposes the use of an analytic function, based on the literature, to describe accurately the strain dependence on both channel length and fin width in order to simulate adequately strained triple-gate devices. The maximum transconductance and the threshold voltage are used as the key parameters to compare simulated and experimental data. The results show the agreement of the proposed analytic function with the experimental results. Also, an analysis on the threshold voltage variation is carried out, showing that the stress affects the dependence of the threshold voltage on the temperature.     

Arsenic adsorption on goethite nanoparticles produced through hydrazine sulfate assisted synthesis method

Goethite nanoparticles synthesized using hydrazine sulfate as a modifying agent were evaluated for As(V) adsorption capacity. The nanoparticles were characterized for their morphological and structural features. The precipitated goethite particles were spherical with particle size of less than 10 nm. Batch adsorption study was carried out systematically varying parameters such as pH, contact time, initial As(V) concentration and adsorbent doses. The Langmuir isotherm represented the equilibrium data well and the estimated monolayer adsorption capacity at ambient temperature was 76 mg/g, which is significantly higher than most of the adsorbents reported in the literature. Adsorption kinetic data were better represented by the pseudo-second order kinetic model. Intra-particle diffusion played a significant role in the rate controlling process in the initial hour. Desorption study showed that the loaded adsorbent could be regenerated when treated with dilute sodium hydroxide solution of pH 13.     

Size-dependent dry deposition of airborne polybrominated diphenyl ethers in urban Guangzhou, China

Gaseous and size-segregated particulate PBDEs (specifically BDE-47, -99, -183, -207, and -209) in the air were measured in urban Guangzhou at 100 and 150 m above the ground in daytime and at night in August and December 2010, to assess dry deposition of these contaminants accurately with regards to influences of meteorological factors but without confounding surface effects. Particulate PBDEs were more abundant at night than in daytime, and slightly higher in winter than in summer, likely from varying meteorological conditions and atmospheric boundary layers. More than 60% of particulate-phase PBDEs was contained in particles with an aerodynamic diameter (D(p)) below 1.8 μm, indicating long-range transport potential. The average daily particle dry deposition fluxes of PBDEs in August ranged from 2.6 (BDE-47) to 88.6 (BDE-209) ng m(-2) d(-1), while those in winter ranged from 2.0 (BDE-47) to 122 (BDE-209) ng m(-2) d(-1). Deposition fluxes of all PBDE congeners were significantly higher in daytime than at night for both months, due to the effect of diurnal variability of meteorological factors. In addition, mean overall particle deposition velocities of individual BDE congeners ranged from 0.11 to 0.28 cm s(-1). These values were within a factor of 2 of assumed values previously used in southern China and the Laurentian Great Lakes, suggesting that such assumptions were reasonable for sites with similar particulate size distributions and PBDE sources. Dry deposition velocities of PBDEs were lower at night than those in the daytime, probably reflecting higher mechanical and thermal turbulence during daytime. Dry deposition of particulate-bound PBDEs is influenced by short-term temporal variability from meteorological factors, and also by particulate size fractions.     

Developing Construction Management Events in Situational Simulations

Abstract: The challenge and promise of educational computer simulations are to provide user experiences that allow for immersion into a dynamic system in which participants discover the ramifications of their decisions in a complex environment. Researchers at the University of Washington, in collaboration with Michigan Technological University, are developing situational simulations to meet the needs of construction management education. This article explores the development of simulation events where simulation variables are changed due to an event, and then the player is challenged to interact with the simulation by making decisions that impact the project outcome. A simulation event includes the player's experience, variables altered by the event, and variables changed by the player. This article defines the concept of simulation events within the context of situational simulations; explains how events are triggered, represented, and handled within the simulation and database; describes how players engage with the simulation; and identifies the challenges of incorporating the social dynamics of project management into the simulation environment.     

An autopsy study of a fouled reverse osmosis membrane element used in a brackish water treatment plant

The fouling of a spiral wound reverse osmosis (RO) membrane after nearly 1 year of service in a brackish water treatment plant was investigated using optical and electron microscopic methods, Fourier transform infrared spectroscopy (FTIR) and inductively coupled plasma atomic emission spectrometry (ICP-AES). Both the top surface and the cross-section of the fouled membrane were analysed to monitor the development of the fouling layer. It has been found that the extent of fouling was uneven across the membrane surface with regions underneath or in the vicinity of the strands of the feed spacer being more severely affected. Fouling appeared to have developed through different stages. In particular, it consisted of an initial thin fouling layer of an amorphous matrix with embedded particulate matter. The amorphous matrix comprised organic-Al-P complexes and the particulate matter was mostly aluminium silicates. Subsequently, as the fouling layer reached a thickness of about 5-7microm, further amorphous material, which is suggested to include extracellular polymeric substances such as polysaccharides, started to deposit on top of the existing fouling layer. This secondary amorphous material did not seem to contain any particulate matter nor any inorganic elements within it, but acted as a substrate upon which aluminium silicate crystals grew exclusively in the absence of other foulants, including natural organic matter (NOM).     

Bilayer graphene grown on 4H-SiC (0001) step-free mesas

We demonstrate the first successful growth of large-area (200 × 200 μm(2)) bilayer, Bernal stacked, epitaxial graphene (EG) on atomically flat, 4H-SiC (0001) step-free mesas (SFMs) . The use of SFMs for the growth of graphene resulted in the complete elimination of surface step-bunching typically found after EG growth on conventional nominally on-axis SiC (0001) substrates. As a result heights of EG surface features are reduced by at least a factor of 50 from the heights found on conventional substrates. Evaluation of the EG across the SFM using the Raman 2D mode indicates Bernal stacking with low and uniform compressive lattice strain of only 0.05%. The uniformity of this strain is significantly improved, which is about 13-fold decrease of strain found for EG grown on conventional nominally on-axis substrates. The magnitude of the strain approaches values for stress-free exfoliated graphene flakes. Hall transport measurements on large area bilayer samples taken as a function of temperature from 4.3 to 300 K revealed an n-type carrier mobility that increased from 1170 to 1730 cm(2) V(-1) s(-1), and a corresponding sheet carrier density that decreased from 5.0 × 10(12) cm(-2) to 3.26 × 10(12) cm(-2). The transport is believed to occur predominantly through the top EG layer with the bottom layer screening the top layer from the substrate. These results demonstrate that EG synthesized on large area, perfectly flat on-axis mesa surfaces can be used to produce Bernal-stacked bilayer EG having excellent uniformity and reduced strain and provides the perfect opportunity for significant advancement of epitaxial graphene electronics technology.     

Electron-Nuclear Recoil Discrimination by Pulse Shape Analysis

In the framework of the “ULTIMA” project, we use ultra cold superfluid ³He bolometers for the direct detection of single particle events, aimed for a future use as a dark matter detector. One parameter of the pulse shape observed after such an event is the thermalization time constant τ _b . Until now it was believed that this parameter only depends on geometrical factors and superfluid ³He properties, and that it is independent of the nature of the incident particles. In this report we show new results which demonstrate that a difference for muon- and neutron events, as well as events simulated by heater pulses exist. The possibility to use this difference for event discrimination in a future dark matter detector will be discussed.      

An architecture for stable, analyzable Internet routing

In today's Internet, individuals, campuses, and organizations obtain IP connectivity from transit providers. Internet interprovider routing is governed by bilateral traffic exchange agreements between providers. Such independently established policies can adversely impact the stability and analyzability of Internet routing. We describe an architecture for coordinating Internet routing policies. This architecture allows providers to publish high-level specifications of their policies, and to analyze the effects of their policies on Internet routing. Several pieces of the architecture have been implemented and are in production use; we also discuss the experiences gleaned from these deployments