排序方式: 共有46条查询结果,搜索用时 218 毫秒
31.
A. T. Farsoni B. Alemayehu A. Alhawsawi E. M. Becker 《Journal of Radioanalytical and Nuclear Chemistry》2013,296(1):63-68
A phoswich detector with two scintillation layers has been designed and assembled at Oregon State University. This detector is able to identify and reject Compton events and ultimately reduce the Compton continuum in gamma energy spectra. In this detector, CsI(Tl) crystal is used to primarily detect photoelectric events. The CsI(Tl) crystal is partially surrounded by a BGO crystal layer to capture and identify Compton-scattered photons. Both crystals are optically coupled to a single photomultiplier tube. A real-time, FPGA-based digital pulse shape analysis was developed to discriminate and reject Compton-induced pulses from the CsI(Tl) crystal. All the digital pulse processing functions including pulse shape discrimination analysis, pile-up rejection and energy measurement were implemented in an on-board FPGA device. In this paper, the results of recent measurements using radioactive lab sources will be presented and discussed. 相似文献
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Alemayehu H. Bedane Mladen Eić Madjid Farmahini-Farahani Huining Xiao 《Cellulose (London, England)》2016,23(3):1537-1552
The theory of mass transport in porous media is of fundamental importance for different applications such as food, paper packaging, textiles, and wood for building materials. In this study, a theoretical water vapor transport model has been developed for cellulose-based materials, such as paper and regenerated cellulose film. Pore diffusivities were determined from the dynamic moisture breakthrough experiments comprising a stack of paper sheets and regenerated cellulose films in a configuration similar to a packed adsorption column. Other mass transfer parameters were determined from transient moisture uptake rate measurements. The model incorporates pore and surface diffusion as a lump parameter into a variable effective diffusion coefficient. The mass transport, involving both pore and surface diffusions, is evaluated independently. The theoretical water vapor transmission rates (WVTRs) obtained from the model were compared with experimentally determined WVTRs measured under steady-state conditions. The theoretical model, based on intrinsic diffusion, stipulates higher WVTR values compared to the experimental results. However, the theoretical water vapor transfer rates agree well with the experimental results when external mass transfer resistance is incorporated in the model. 相似文献
34.
Alemayehu Mekonnen 《Tetrahedron》2006,62(5):852-856
An efficient and highly selective synthesis of bicyclic-α-keto aziridines from 2-bromo-2-cyclopentenone and aliphatic primary amines mediated by phase transfer catalysts (PTCs) in water at room temperature is demonstrated. Bicyclic-α-keto-aziridines are highly strained and reactive compounds that can be used in the synthesis of biologically active compounds. Therefore, the present strategy with its mild reaction conditions opens up a new entry to the synthesis of unusual aziridines using inexpensive reagents. 相似文献
35.
Sisal (Agave sisalana) fiber was extracted by manual process. These fibers were subjected to surface coating with conducting polyaniline, through in situ oxidative polymerization. The polyaniline modified sisal fibers were characterized by thermal, spectroscopic and microscopic techniques. It was shown that the fiber was coated with polyaniline through in situ oxidative polymerization and the latter had a smoothing effect on the surface as compared to uncoated sisal fiber. Besides, it was confirmed that polyaniline was deposited in conductive form of emeraldine salt. This in turn verified the introduction of active functionalities to the system, which is helpful to tune up surface chemistry of polyaniline for water treatment applications. 相似文献
36.
Cuijing Liu Junjun Hou Mingzheng Yan Prof. Jianqi Zhang Haftu Gebrekiros Alemayehu Wei Zheng Pengchao Liu Prof. Zhiyong Tang Prof. Lianshan Li 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2024,136(15):e202320137
Membrane separation of aromatics and aliphatics is a crucial requirement in chemical and petroleum industries. However, this task presents a significant challenge due to the lack of membrane materials that can endure harsh solvents, exhibit molecular specificity, and facilitate easy processing. Herein, we present a novel approach to fabricate a covalent triazine framework (CTF) membrane by employing a mix-monomer strategy. By incorporating a spatial monomer alongside a planar monomer, we were able to subtly modulate both the pore aperture and membrane affinity, enabling preferential permeation of aromatics over aliphatics with molecular weight below 200 Dalton (Da). Consequently, we achieved successful all-liquid phase separation of aromatic/aliphatic mixtures. Our investigation revealed that the synergistic effects of size sieving and the affinity between the permeating molecules and the membrane played a pivotal role in separating these closely resembling species. Furthermore, the membrane exhibited remarkable robustness under practical operating conditions, including prolonged operation time, various feed compositions, different applied pressure, and multiple feed components. This versatile strategy offers a feasible approach to fabricate membranes with molecule selectivity toward aromatic/aliphatic mixtures, taking a significant step forward in addressing the grand challenge of separating small organic molecules through membrane technology. 相似文献
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Many people worldwide are exposed to extreme levels of fluoride in drinking water. It is, therefore, critical to develop inexpensive, locally available, and environmentally friendly adsorbents for fluoride-laden water defluoridation. In the current study, virgin scoria (volcanic rock) from Ethiopia, was modified with zirconium oxide and used as an adsorbent in a fixed-bed column aiming at the removal of fluoride from water. The adsorption capability of zirconium oxide-coated scoria (ZrOCSc) was compared with unmodified virgin scoria (VSco). XRD, FTIR, XRF, SEM, ICP-OES, and the pHPZC tests were evaluated to explore the adsorption mechanisms. Thermal analysis of VSco and ZrOCSc revealed lower total weight losses of 2.3 and 3.2 percent, respectively, owing to the removal of water molecules and OH species linked to metal oxides contained in the material. The effect of test conditions such as the pH of the solution and the influent flow rate on the adsorption capacity of the adsorbent was carefully studied. ZrOCSc exhibited the maximum removal capacity of 58 mg/kg, which was 4.46 times higher than the observations for VSco (13 mg/kg) at pH 2, and an initial flow rate of 1.25 mL/min. Breakthrough time increased with decreasing initial pH and flow rate. The adsorption experimental data under various test conditions were examined by the Thomas and Adams–Bohart models. Both models were found very effective in describing the experimental data with a correlation coefficient (R2) of ≥0.976 (ZrOCSc) and ≥0.967 (VSco). Generally, coating VSco with zirconium oxide improved the adsorption performance of VSco; hence, a ZrOCSc-packed fixed bed could be employed for the decontamination of high levels of fluoride from groundwater. However, further examination of the adsorbent using natural groundwater is advisable to produce a definitive conclusion. 相似文献
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Ting Li Brian Albee Matti Alemayehu Rocio Diaz Leigha Ingham Shawn Kamal Maritza Rodriguez Sandra Whaley Bishnoi 《Analytical and bioanalytical chemistry》2010,398(2):689-700
A comparative assessment of the 48-h acute toxicity of aqueous nanoparticles synthesized using the same methodology, including
Au, Ag, and Ag–Au bimetallic nanoparticles, was conducted to determine their ecological effect in freshwater environments
through the use of Daphnia magna, using their mortality as a toxicological endpoint. D. magna are one of the standard organisms used for ecotoxicity studies due to their sensitivity to chemical toxicants. Particle suspensions
used in toxicity testing were well-characterized through a combination of absorbance measurements, atomic force or electron
microscopy, flame atomic absorption spectrometry, and dynamic light scattering to determine composition, aggregation state,
and particle size. The toxicity of all nanoparticles tested was found to be dose and composition dependent. The concentration
of Au nanoparticles that killed 50% of the test organisms (LC50) ranged from 65–75 mg/L. In addition, three different sized Ag nanoparticles (diameters = 36, 52, and 66 nm) were studied
to analyze the toxicological effects of particle size on D. magna; however, it was found that toxicity was not a function of size and ranged from 3–4 μg/L for all three sets of Ag nanoparticles
tested. This was possibly due to the large degree of aggregation when these nanoparticles were suspended in standard synthetic
freshwater. Moreover, the LC50 values for Ag–Au bimetallic nanoparticles were found to be between that of Ag and Au but much closer to that of Ag. The bimetallic
particles containing 80% Ag and 20% Au were found to have a significantly lower toxicity to Daphnia (LC50 of 15 μg/L) compared to Ag nanoparticles, while the toxicity of the nanoparticles containing 20% Ag and 80% Au was greater
than expected at 12 μg/L. The comparison results confirm that Ag nanoparticles were much more toxic than Au nanoparticles,
and that the introduction of gold into silver nanoparticles may lower their environmental impact by lowering the amount of
Ag which is bioavailable. 相似文献
39.
The purpose of this paper is to prove the existence of common fixed points for two pairs of occasionally weakly compatible selfmaps satisfying property (E. A)/common property (E. A) using an inequality involving quadratic terms. 相似文献
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Adane Woldemedhin Kalsido Beteley Tekola Meshesha Beshah M. Behailu Esayas Alemayehu 《Molecules (Basel, Switzerland)》2021,26(23)
Using small-scale batch tests, various researchers investigated the adsorptive removal of fluoride using low-cost clay minerals, such as Bentonite. In this study, Column adsorption studies were used to investigate the removal of fluoride from aqueous solution using acid-treated Bentonite (ATB). The effects of initial fluoride concentration, flow rates, and bed depth on fluoride removal efficiency (R) and adsorption capability (qe) in continuous settings were investigated, and the optimal operating condition was determined using central composite design (CCD). The model’s suitability was determined by examining the relationship between experimental and expected response values. The analysis of variance was used to determine the importance of independent variables and their interactions. The optimal values were determined as the initial concentration of 5.51 mg/L, volumetric flow rate of 17.2 mL/min and adsorbent packed-bed depth of 8.88 cm, with % removal of 100, adsorptive capacity of 2.46 mg/g and desirability of 1.0. This output reveals that an acid activation of Bentonite has made the adsorbent successful for field application. 相似文献