A model for stripping multicomponent vapor from unsaturated soil with free and trapped residual nonaqueous phase liquid

We present a model for the multicomponent vapor transport due to air venting in an unsaturated zone in the presence of free and trapped phases of residual nonaqueous phase liquid (NAPL). On the microscale the soil particles are assumed to form spherical aggregates with micropores filled with-immobile water, trapped phases of NAPL and air. The interaggregate space is occupied with mobile air, and a thin film of free NAPL adheres on the aggregate surface. While the free NAPL can readily be in equilibrium with macropore vapor, the mass transfer from immobile phases inaggregates is rate-limited by aqueous diffusion. This model enables us to predict the vapor concentrations of various chemical species and the free NAPL saturation over the macroscale, based on the detailed understanding of the aqueous concentrations of the species and the trapped NAPL saturation within the aggregates. The model is compared favorably with some experimental data of sparging multicomponent vapor out of an intact core taken from a contaminated site. The distinctive features of multicomponent transport, clearly exhibited by the data, are further examined in the simulations of a hypothetical case of three-aromatic vapor transport under a radial flow field. It is found that while the vapor concentration of the most volatile component drops monotonically with time, those of the less volatile may rise as their mole fractions in the NAPL increase. The vapor concentration of a heavy component may have a local maximum at the evaporation front of the free NAPL. In the case of radial flow the free NAPL has two receding evaporation fronts. Condensation of the heavy component downstream of the far front causes a temporary increase of its total concentration there. With trapped NAPL and soil aggregation the macroscale transport is retarded, and the effluent concentrations end up in noticeable tailing.published_or_final_versio

Analysis of the technology acceptance model in examining students' behavioural intention to use an e-portfolio system

In recent years, instructors have had an increasing interest in integrating Internet based technologies into their classroom as part of the learning environment. Compared to studies on other information systems, student users' behaviour towards e-portfolios have not been assessed and thoroughly understood. This paper analyses the Technology Acceptance Model (TAM) in order to examine students' behavioural intention to use an electronic portfolio system, meaning how students use and appropriate it within the specific framework of a course. An E-Portfolio Usage Questionnaire was developed using existing scales from prior TAM instruments and modified where appropriate. Seventy-two participants completed the survey questionnaire measuring their responses to perceived usefulness (PU), perceived ease of use (PEOU), attitudes towards usage (ATU) and behavioural intention to use (BIU) the e-portfolio system. The results of the study indicated that students' perceived ease of use (PEOU) had a significant influence on attitude towards usage (ATU). Subsequently, perceived ease of use (PEOU) had the strongest significant influence on perceived usefulness (PU). The research further demonstrated that individual characteristics and technological factors may have a significant influence on instructors to adopt e-portfolios into their courses. Results suggest that TAM is a solid theoretical model where its validity can extend to an e-portfolio context.published_or_final_versio

Energy loss of monoenergetic positrons passing through a thin carbon foil

In this paper, the measurements of energy loss and energy loss straggling for 1-10 keV monoenergetic positrons passing through thin carbon foils of different thicknesses ranging from 1.0 to 5.0 μg/cm 2 are presented. The stopping power dE/dx and positron transmission coefficient as a function of incident positron energy and foil thickness have also been investigated. Particularly, the experimental results obtained are compared with those from Monte Carlo simulation and theory with a view to providing a way to determine the actual thickness of a carbon foil. The ratio of the energy straggling to the foil thickness seems to have a linear relation with the beam energy. © 2011 Elsevier B.V. All rights reserved.postprin

Thickness dependence of positron induced secondary electron emission in forward geometry from thin carbon foils

Secondary electron (SE) emission from thin carbon foils induced by 1-20 keV positrons has been investigated over a range of nominal foil thicknesses from 1.0to5.0μg/cm 2. The measurement of SEs was carried out in forward geometry using a microchannel plate as a detector. The SE yield γ has been measured as a function of beam energy and compared with our Monte Carlo simulation results. We also present in this paper the material parameter Λ=γ/(dE/dx) and the emitted SE energy spectra. For incident positron energy of 5 keV or higher, the distribution is found to be characterized by the Sickafus form, AE- m and m is close to 1. For low energy incident positrons, however, another form, Bexp(-E/t), is proposed for describing the SE distribution. © 2011 Elsevier B.V. All rights reserved.postprin

Au/n-ZnO rectifying contact fabricated with hydrogen peroxide pretreatment

Au contacts were deposited on n -type ZnO single crystals with and without hydrogen peroxide pretreatment for the ZnO substrate. The Au/ZnO contacts fabricated on substrates without H2 O2 pretreatment were Ohmic and those with H2 O2 pretreatment were rectifying. With an aim of fabricating a good quality Schottky contact, the rectifying property of the Au/ZnO contact was systemically investigated by varying the treatment temperature and duration. The best performing Schottky contact was found to have an ideality factor of 1.15 and a leakage current of ∼ 10-7 A cm-2. A multispectroscopic study, including scanning electron microscopy, positron annihilation spectroscopy, deep level transient spectroscopy, x-ray photoelectron spectroscopy, and photoluminescence, showed that the H2 O2 treatment removed the OH impurity and created Zn-vacancy related defects hence decreasing the conductivity of the ZnO surface layer, a condition favorable for forming good Schottky contact. However, the H2 O2 treatment also resulted in a deterioration of the surface morphology, leading to an increase in the Schottky contact ideality factor and leakage current in the case of nonoptimal treatment time and temperature. © 2008 American Institute of Physics.published_or_final_versio

Adverse effects if TERT-CLPTM1L and double-strand breaks repair contribute to risk for NPC

Epidemiology - Poster Presentations - Proffered Abstracts - Poster Presentations - Molecular and Genetic Epidemiology of Lung, Head and Neck, and Gastrointestinal Cancers: abstract no. 4148This journal suppl. entitled: Proceedings: AACR Annual Meeting 2014; April 5-9, 2014 ...BACKGROUND AND AIMS: The genetic etiology of NPC and mechanisms for inherited susceptibility remain unclear. Only modest low-penetrance effects of cancer-predisposing common variant SNPs were previously identified in the few large-scale NPC association studies reported. Most NPC association studies focused on single or limited candidate genes with modest sample sizes. Systematic and comprehensive study designs for evaluation of higher order gene-gene interactions are scanty. A large-scale NPC case-control SNP association study was performed to examine the genetic risk factors for NPC development. In order to elucidate the ...postprin

Nitrogen doped-ZnO/n-GaN heterojunctions

Nitrogen-doped ZnO nanorods were prepared by electrodeposition using two different Zn precursors (zinc nitrate and zinc acetate), while all other growth conditions (dopant precursor, concentration, growth temperature, and bias) were identical. We have shown that the precursor used affects the properties of the ZnO nanorods, and that the presence of rectifying properties in n-GaN/N:ZnO heterojunctions is strongly related to the use of nitrate precursor for ZnO growth. The difference in the properties of ZnO obtained from two precursors is attributed to the differences in native defect and impurity concentrations, which could affect the electronic properties of the samples. © 2011 American Institute of Physics.published_or_final_versio

Effects of Ving Tsun Chinese martial art training on upper extremity muscle strength and eye-hand coordination in community-dwelling middle-aged and older adults: A pilot study

published_or_final_versio

Yttrium-90 radioembolization for advanced inoperable hepatocellular carcinoma

published_or_final_versio

Prognostication of serial post-intensity-modulated radiation therapy undetectable plasma EBV DNA for nasopharyngeal carcinoma

published_or_final_versio