Modal characteristics of a flexible beam with multiple distributed actuators

A flexible structure with surface-bonded piezoceramic patches is modelled using Timoshenko beam theory. Exact mode shapes and natural frequencies associated with the flexural motion are computed for various piezoceramic distributed actuator arrangements. The effects of patch placement and of shear on the modal characteristics are demonstrated using a cantilevered beam as an example. Perfect bonding of the piezoceramic to the beam substructure is assumed, and for the purposes of this paper only passive piezoceramic properties are considered. The modelling technique and results obtained in a closed form are intended to assist investigations into the modelling and control of active structures with surface-bonded piezoceramic actuators. (C) 2003 Elsevier Science Ltd. All rights reserved.

Using FCD Mapper Software and Landsat Images to Assess Forest Canopy Density in Landscapes in Australia and the Philippines

Using Landsat imagery, forest canopy density (FCD) estimated with the FCD Mapper®, was correlated with predominant height (PDH, measured as the average height of the tallest 50 trees per hectare) for 20 field plots measured in native forest at Noosa Heads, south-east Queensland, Australia. A corresponding image was used to calculate FCD in Leyte Island, the Philippines and was validated on the ground for accuracy. The FCD Mapper was produced for the International Tropical Timber Organisation and estimates FCD as an index of canopy density using reflectance characteristics of Landsat Enhanced Thematic (ETM) Mapper images. The FCD Mapper is a ‘semi-expert’ computer program which uses interactive screens to allow the operator to make decisions concerning the classification of land into bare soil, grass and forest. At Noosa, a positive strong nonlinear relationship (r2 = 0.86) was found between FCD and PDH for 15 field plots with variable PDH but complete canopy closure. An additional five field plots were measured in forest with a broken canopy and the software assessed these plots as having a much lower FCD than forest with canopy closure. FCD estimates for forest and agricultural land in the island of Leyte and subsequent field validation showed that at appropriate settings, the FCD Mapper differentiated between tropical rainforest and banana or coconut plantation. These findings suggest that in forests with a closed canopy this remote sensing technique has promise for forest inventory and productivity assessment. The findings also suggest that the software has promise for discriminating between native forest with a complete canopy and forest which has a broken canopy, such as coconut or banana plantation.

Characteristics of undular hydraulic jumps: Experiments and analysis

The writers measured velocity, pressure and energy distributions, wavelengths, and wave amplitudes along undular jumps in a smooth rectangular channel 0.25 m wide. In each case the upstream flow was a fully developed shear flow. Analysis of the data shows that the jump has strong three-dimensional features and that the aspect ratio of the channel is an important parameter. Energy dissipation on the centerline is far from negligible and is largely constrained to the reach between the start of the lateral shock waves and the first wave crest of the jump, in which the boundary layer develops under a strong adverse pressure gradient. A Boussinesq-type solution of the free-surface profile, velocity, and energy and pressure distributions is developed and compared with the data. Limitations of the two-dimensional analysis are discussed.

Adsorption characteristics of carbonized bark for phenol and pentachlorophenol

The potential of using carbonized slash pine bark as a substitute for activated carbon was examined in this study. The bark was carbonized by slow heating in nitrogen for 6.5 h to 672 degrees C. The BET-N-2 surface area, average micropore and mesopore diameter, and micropore volume were 332 m(2) g(-1) 21.7 Angstrom, and 0.125 cm(3) g(-1), respectively. The adsorption capacities for phenol and pentachlorophenol (PCP) at pH 2 and pH 8 were evaluated. The Langmuir equation provided a slightly better fit than the Freundlich equation to two sets of phenol data. The calculated Freundlich constants, K = 0.41 - 0.58 mmol/g/(mmol dm(-3))(1/n) and 1/n = 0.30 - 0.41, were lower and higher, respectively, than literature values for activated carbons. The adsorption capacity of the carbonized bark was much lower for PCP than for phenol. The protonated and anionic PCP isotherms were Type II or III, respectively, in the Brunauer classification. The BET equation provided the best fit to protonated PCP isotherm data. The anionic PCP data were fitted to both the BET model and an equation used in the literature to represent phosphate adsorption on activated carbons. Nonlinear regression of the data for both phenol and PCP adsorption with the Freundlich, Langmuir and BET equations generally gave more accurate parameters, compared with the use of linearized equations to obtain the parameters. (C) 1998 SCI.

An investigation of the effect of powder on the impact characteristics between a ball and a plate using free falling experiments

The study of the mechanisms of mechanical alloying requires knowledge of the impact characteristics between the ball and vial in the presence of milling powders. In this paper, foe falling experiments have br cn used to investigate the characteristics of impact events involved in mechanical milling. The effects of milling conditions, including impact velocity, ball size and powder thickness. on the coefficient of restitution and impact force are studied. It is found that the powder has a significant influence on the impact process due to its porous structure. This effect can be demonstrated using a modified Kelvin model. This study also confirms that the impact force is a relevant parameter for characterising the impact event due to its sensitivity to the milling conditions. (C) 1998 Elsevier Science S.A.

Catalytic activities and coking characteristics of oxides-supported Ni catalysts for CH4 reforming with carbon dioxide

Catalytic activities and deactivation characteristics of oxides-supported nickel catalysts for the reaction of methane reforming with carbon dioxide were investigated. The dynamic carbon deposition on various nickel catalysts was also studied by a thermogravimetric method. Among the catalysts prepared, Ni/La2O3, Ni/alpha-Al2O3, Ni/SiO2, and Ni/CeO2 showed very high CH4 and CO2 conversions and moderate deactivation whereas Ni/MgO and Ni/TiO2 had lower conversions when the Ni reduction was conducted at 500 degrees C. When Ni/MgO catalyst was reduced at 800 degrees C, it exhibited not only comparable conversions of CH4 and CO2 with other active catalysts but also much longer period of stability without deactivation. The amount of carbon deposited in Ni-based catalysts varied depending on the nature of support and followed the order of Ni/La2O3 > Ni/alpha-Al2O3 > Ni/SiO2 > Ni/MgO > Ni/CeO2 at 700 degrees C. The carbons formed on the catalyst surface showed different structural and chemical properties, and these in turn affected the catalytic activity of the catalysts.

Overflow characteristics of circular weirs: Effects of inflow conditions

The most common types of weirs are the broad-crested weir, the sharp-crested weir, the circular-crested weir, and nowadays, the ogee crest weir, Advantages of the cylindrical weir shape include the stable overflow pattern, the ease to pass floating debris, the simplicity of design compared to ogee crest design, and the associated lower costs. in this study, the writers describe new experiments of circular weir overflows, with eight cylinder sizes, for several weir heights and for five types of inflow conditions: partially developed inflow, fully developed inflow, upstream ramp, upstream undular hydraulic jump, and upstream (breaking) hydraulic jump. Within the range of the experiments, the cylinder size, the weir height DIR and the presence of an upstream ramp had no effect on the discharge coefficient, flow depth at crest, and energy dissipation. But the inflow conditions had substantial effects on the discharge characteristics and flow properties at the crest. Practically, the results indicate that discharge measurements with circular weirs are significantly affected by the upstream flow conditions.

Educational characteristics of students with high or low self-concept

In response to methodological concerns associated with previous research into the educational characteristics of students with high or low self-concept, the topic was re-examined using a significantly more representative sample and a contemporary self-concept measure. From an initial screening of 515 preadolescent, coeducational students in 18 schools, students significantly high or low in self-concept were compared using standardized tests in reading, spelling, and mathematics, and teacher interviews to determine students' academic and nonacademic characteristics. The teachers were not informed of the self-concept status of the students. Compared to students with low self-concept, students with high self-concept were rated by teachers as being more popular, cooperative, and persistent in class, showed greater leadership, were lower in anxiety, had more supportive families, and had higher teacher expectations for their future success. Teachers observed that students with low self-concept were quiet and withdrawn, while peers with high self-concept were talkative and more dominating with peers. Students with lower self-concepts were also lower than their peers in reading, spelling, and mathematical abilities. The findings support the notion that there is an interactive relationship between self-concept and achievement. (C) 1998 John Wiley & Sons, Inc.

Adsorption characteristics of phenolic compounds onto coal-reject-derived adsorbents

Carbonaceous adsorbents were prepared by heat treatment of coal reject at 600 degrees C, after chemical treatment in HNO3, H2SO4, and NaOH at 25 and 75 degrees C. Pore structure characterization and the phenol adsorption capacities of the adsorbents showed that nitric acid pretreatment significantly enhanced the surface properties, consequently the adsorption capacities of the adsorbents. A number of samples were subsequently prepared by carbonizing coal reject at 600 degrees C, after pretreatment in HNO3 under various conditions. The acid concentration, residence time, and reaction temperature were varied to obtain adsorbents with various pore structures. The adsorption capacities of the derived adsorbents for phenol, p-nitrophenol, and benzene were measured to gain further insights into the pore structure evolution. Adsorption isotherms of phenol, p-nitrophenol, and p-chlorophenol on the best adsorbent prepared were determined and correlated with theoretical isotherm equations, such as the Langmuir, Freundlich, and Redlich-Peterson equations.

Characteristics of long-term cannabis users in Sydney, Australia

Two hundred long-term cannabis users (58% male) were interviewed on their characteristics and experience of use. Respondents had been regularly using cannabis for an average of 11 years and more than half used daily (56%). The most common route of administration was in a waterpipe, and nearly all (93%) smoked the flowering heads ot the plant. One in 5 (21%) had a cannabis-related conviction. The benefits of use were perceived to be its relaxing, mood-enhancing effects, and its ability to alter consciousness. The most commonly cited negative aspects of use were cost, negative psychological effects and legal status. Polydrug use was common, with alcohol and tobacco almost universally used on a regular basis. More than half the drinkers in the sample were consuming alcohol at hazardous or harmful levels.

Remotely sensed estimates of vegetation structural characteristics in restored wetlands, Southern California

Traditional field sampling approaches for ecological studies of restored habitat can only cover small areas in detail, con be time consuming, and are often invasive and destructive. Spatially extensive and non-invasive remotely sensed data can make field sampling more focused and efficient. The objective of this work was to investigate the feasibility and accuracy of hand-held and airborne remotely sensed data to estimate vegetation structural parameters for an indicator plant species in a restored wetland. High spatial resolution, digital, multispectral camera images were captured from an aircraft over Sweetwater Marsh (San Diego County, California) during each growing season between 1992-1996. Field data were collected concurrently, which included plant heights, proportional ground cover and canopy architecture type, and spectral radiometer measurements. Spartina foliosa (Pacific cordgrass) is the indicator species for the restoration monitoring. A conceptual model summarizing the controls on the spectral reflectance properties of Pacific cordgrass was established. Empirical models were developed relating the stem length, density, and canopy architecture of cordgrass to normalized-difference-vegetation-index values. The most promising results were obtained from empirical estimates of total ground cover using image data that had been stratified into high, middle, and low marsh zones. As part of on-going restoration monitoring activities, this model is being used to provide maps of estimated vegetation cover.