Increasing Thickness (increasing + thickness)

Distribution by Scientific Domains

Selected Abstracts

Modelling of air drying of fresh and blanched sweet potato slices

Kolawole O. Falade
Summary Effects of blanching, drying temperatures (50,80 °C) and thickness (5, 10 and 15 mm) on drying characteristics of sweet potato slices were investigated. Lewis, Henderson and Pabis, Modified Page and Page models were tested with the drying patterns. Page and Modified Page models best described the drying curves. Moisture ratio vs. drying time profiles of the models showed high correlation coefficient (R2 = 0.9864,0.9967), and low root mean squared error (RMSE = 0.0018,0.0130) and chi-squared (,2 = 3.446 × 10,6,1.03 × 10,2). Drying of sweet potato was predominantly in the falling rate period. The temperature dependence of the diffusion coefficient (Deff) was described by Arrhenius relationship. Deff increased with increasing thickness and air temperature. Deff of fresh and blanched sweet potato slices varied between 6.36 × 10,11,1.78 × 10,9 and 1.25 × 10,10,9.75 × 10,9 m2 s,1, respectively. Activation energy for moisture diffusion of the slices ranged between 11.1 and 30.4 kJ mol,1. [source]

Modelling of diffraction from fibre texture gradients in thin polycrystalline films

M. Birkholz
Crystallographic textures in thin polycrystalline films typically exhibit a rotational symmetry, i.e. they occur as a fibre texture with the texture pole being orientated in the direction of the substrate normal. As a further characteristic of thin-film textures, it was often observed that the degree of preferred orientation increases with increasing thickness. It is shown in this work how a fibre texture gradient may be modelled in kinematical X-ray diffraction and which effects it has on the intensity mapping of the IHKL reflection, when the HKL pole is the fibre axis. A general expression for IHKL is derived for a depth-dependent fibre texture that is based on the finite Laplace transform of the texture distribution. The concept is outlined for the cosn, function to model the tilt-angle dependence of intensity, with the parameter n denoting the degree of texture. It is found that the measured intensity distribution sensitively depends on the ratio of texture gradient over X-ray attenuation coefficient. For particular cases, it is found that the maximum intensity may occur for non-zero tilt angles and thus arise at a different tilt angle from the pole of the fibre texture. [source]


ABSTRACT An experimental investigation on the influence of sample size and shape on heat and mass transport parameters under natural convection air-drying is presented. Potato cylinders with length of 0.05 m and thicknesses of 0.005, 0.008, 0.010 and 0.016 m, and circular slices with diameter of 0.05 m and thickness of 0.01 m were dried in a laboratory scale hot-air cabinet dryer. Results indicate that each transport parameter exhibits a linear relationship with sample thickness. Convective heat and mass transfer coefficients (hcand hm) decreased whereas moisture diffusion coefficient (Deff) increased with increasing thickness. Considering no sample shrinkage effect in the parameter analysis, for the thickness range considered, the values of hcare found to be underestimated in the range of 29.0,30.6%, whereas those of hmand Deff are overestimated in the range of 33.7,38.0% and 75.9,128.1%, respectively. Using Levenberg,Marquardt algorithm for optimization, a correlation for Biot number for mass transfer (Bim) as a function of drying time and sample thickness is proposed. A close agreement was observed between dimensionless moisture contents predicted by this relation and those obtained from experiments for different sample thicknesses at drying air temperature of 60C. For the same thickness and drying conditions, circular slices caused an increase in each transport parameter significantly. [source]

The origin of the high ideality factor in AlGaN-based quantum well ultraviolet light emitting diodes

K. B. Lee
Abstract The ideality factor of AlGaN-based quantum well ultraviolet light emitting diodes (LEDs) is found to be dependent on both material quality and the presence of electron blocking layer (EBL). The ideality factor of the 340,nm LEDs decreases from 6.9 to 4.9 in the low bias regime (1,,,V,,,2) as the structural dislocation density reduces from 5,×,109 to 9,×,108,cm,2. Moreover, the ideality factor of the 310,nm LEDs decreases with increasing thickness of the AlGaN EBL which is placed between the barrier after the QW and the p-type layer. The slope of the I,V characteristics is temperature independent, indicating that the carrier tunneling is the dominant mechanism. The characteristic tunneling energy extracted from the I,V characteristics decreases from the order of 200 to around 100,meV as the dislocation density in the LED is reduced and with the insertion of a 10,nm EBL. This is attributed to the suppression of deep level states assisted electron tunneling into p-type layer. [source]

Initial growth stages of MOVPE InN studied by AFM and specular reflectivity

A. van der Lee
Abstract The initial growth of InN grown by MOVPE was investigated by a combination of atomic force microscopy (AFM) and X-ray specular reflectivity for five different thin films ranging from 57 to 750 Å. Both AFM and specular reflectivity measurements show that during the initial growth the surface is not completely covered but that instead a discontinuous layer resembling quasi two-dimensional islands is formed. Dots with heights between 30 and 100 nm appear at the same time; the number density of these dots decreases with increasing thickness. At 750 Å the surface is completely covered and obtains a granular aspect. The surface coverage of the discontinuous wetting layer is discussed in relation with the apparent porosity calculated from the specular reflectivity data. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

A phenomenological study of the mechanical properties of long-fiber filled injection-molded thermoplastic composites

V. K. Stokes
Tensile and flexural tests on specimens cut from rectangular injection-molded plaques show that long-fiber filled thermoplastic composites are complex, non-homogeneous, anistropic material systems. Like all fiber-filled materials, they exhibit through-thickness nonhomogeneity as indicated by differences between tensile and flexural properties. The in-plane orientation of fibers in through-thickness layers causes the material to have in-plane anisotropic properties. However, these long-fiber filled materials exhibit an unexpectedly large level of in-plane nonhomogeneity. Also, the effective mechanical properties of these materials are strongly thickness dependent. The thinnest plaques exhibit the largest differences between the flow and cross-flow tensile properties. These differences decrease with increasing thickness. A methodology for part design with this class of materials is discussed. [source]

Combined effect of temperature and thickness on work of fracture parameters of unplasticized PVC film

A. Arkhireyeva
The combined effect of temperature and thickness on the essential work of fracture (EWF) parameters for an unplasticized poly(vinyl chloride) (uPVC) film was investigated using double edge notched tension specimens. It was found that for the range of temperatures (23°C to 60°C) and thicknesses (0.15 mm to 0.40 mm) studied here, specific essential work of fracture (we) was independent of temperature at each thickness but increased with thickness at each temperature. It was found that at each temperature, we and its yielding (we,y) and necking/tearing components (we,nt), all increased linearly with increasing thickness. However, whilet we showed no significant variation with respect to temperature, its yielding component (we,y) decreased and its necking/tearing component increased (we,nt) with increasing temperature. It was found that estimated values of we and its components we,y and we,nt via crack opening displacement values were by and large unsatisfactory, being either much higher or lower than the directly measured values. [source]

Fine Root Distribution in a Lower Montane Rain Forest of Panama

BIOTROPICA, Issue 3 2009
Dirk Hölscher
ABSTRACT In a Panamanian lower montane rain forest we: (1) analyzed the vertical and horizontal distribution of fine roots; and (2) assessed the relationship of fine root mass to thickness of the soil organic layer, soil pH, and soil-extractable nitrogen. The soil in the study area has developed on volcanic ash deposits and was classified as Hapludand. In randomly distributed samples, the median fine root mass (biomass and necromass, diam , 2 mm) to a depth of 100 cm mineral soil was 544 g/m2, 41 percent of which was found in the organic layer. Fine root mass was approximately twice as high in the vicinity of stems of the tree species Oreomunnea mexicana (1069 g/m2) and the palm species Colpothrinax aphanopetala (1169 g/m2) and was associated with thick organic layers. The median thickness of the soil organic layer in a larger random sample (N= 64) was 8 cm with a considerable variation (interquartile range: 7 cm). In these samples, the density of fine root biomass was correlated with the concentration of extractable nitrogen (r= 0.33, P= 0.011), and on an areal basis, fine root biomass in the organic layer increased with increasing thickness of the organic layer (r= 0.63, P < 0.001) and decreasing pHKCl (r=,0.33, P < 0.01). Fine root biomass in the upper mineral soil did not show significant correlations with any of the studied parameters. RESUMEN En un bosque panameño bajo montano tropical (1) analizamos la distribución horizontal y vertical de las raíces finas, y (2) evaluamos la relación de la masa de las raíces finas con el espesor de la capa de suelo orgánico, pH del suelo, y nitrógeno extraíble del suelo. El suelo del área de estudio se ha desarrollado en depósitos de ceniza volcánica y fue clasificado como Hapludand. En muestras distribuidas aleatoriamente, la media de la masa de raíces finas (biomasa y masa necrosada, diámetro , 2 mm) a una profundidad de 100 cm del suelo mineral fue 544 g/m2, 41 por ciento de las cuales fueron encontradas en suelo orgánico. La masa de raíces finas fue aproximadamente el doble en la vecindad entre los pies de especies de árboles Oreomunnea mexicana (1069 g/m2) y especies de palmera Colpothrinax aphanopetala (1169 g/m2) y fue asociada con el espesor de capa orgánica. El espesor mediano de la capa de suelo orgánico en una amplia muestra aleatoria (N= 64) fue 8 cm con una considerable variación (intervalo entre cuartilas: 7 cm). En estas muestras, la densidad de raíces finas fue correlacionada con la concentración de nitrógeno extraíble (r= 0.33, P= 0.011), y en base al área, la biomasa de raíces finas en la capa orgánica aumentó con el incremento del espesor de la capa orgánica (r= 0.63, P < 0.001) y decrecimiento del pHKCl (r=,0.33, P < 0.01). La biomasa de raíces finas en el suelo mineral superior no mostró ninguna significante correlación con los parámetros estudiados. [source]