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We consider the one-dimensional steady-state semiconductor deviceequations modelling a pnpn device. There are two relevant scalingsof the equations corresponding to small and large applied voltages.In both scalings, the semiconductor equations can be consideredas singularly perturbed. It turns out that the small-voltagescaling breaks down for current values between two saturationcurrents. In that interval, the large-voltage scaling has tobe employed. For both scalings, we derive the first-order termsof an asymptotic expansion and show that the reduced problemhas a solution. An example verifies that the current-voltagecurves obtained have the expected qualitative structure. 相似文献
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Degassing of bundles of single-walled carbon nanotubes in vacuum at 500 K is found to drive the thermoelectricpower (TEP) strongly negative, indicating that the degassed metallic tubes in a bundle are n type. The magnitude of the negative TEP indicates that important asymmetry in the electronic carbon pi bands exists near the Fermi energy. Easily measurable increases in the TEP ( approximately 5-10 &mgr;V/K) and resistivity ( 2%-10%) are observed at 500 K upon exposure to N2 and He, suggesting that even gas collisions with the nanotube wall can contribute significantly to the transport properties. 相似文献
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Kwaku Adu‐Gyamfi Michael J. Boss Kathleen Lynch‐Davis 《School science and mathematics》2019,119(7):396-404
Previous research has investigated the representational translation practices of high school students, high school teachers, and college preservice teachers in various mathematical contexts including linear functions. Findings from qualitative research has frequently led to new notions about participant work and understanding. Many quantitative research has investigated the degree to which some in these populations correctly perform these translations. However, it seems that only infrequently have empirical research investigated findings from qualitative studies and vice versa, and findings regarding one population are rarely compared with findings of another population. This study (a) empirically explores the frequency of success of preservice teachers (N = 80) regarding representational translations in the context of linear functions, (b) quantifies results from previous qualitative, literature‐based research regarding high school students and teachers, and (c) quantitatively compares the results. This study demonstrates that some mathematical representational translations are more difficult than others. 相似文献
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The effects of negative emotion on different processing periods in spatial and verbal working memory (WM) and the possible brain mechanism of the interaction between negative emotion and WM were explored using a high-time resolution event-related potential (ERP) technique and time-locked delayed matching-to-sample task (DMST). 相似文献6.
Total Synthesis of (6R,10R,13R,14R,16R,17R,19S,20R,21R,24S, 25S,28S,30S,32R,33R,34R,36S,37S,39R)‐Azaspiracid‐3 Reveals Non‐Identity with the Natural Product
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Nathaniel T. Kenton Dr. Daniel Adu‐Ampratwum Dr. Antony A. Okumu Dr. Zhigao Zhang Dr. Yong Chen Dr. Son Nguyen Dr. Jianyan Xu Dr. Yue Ding Dr. Pearse McCarron Dr. Jane Kilcoyne Prof. Dr. Frode Rise Prof. Dr. Alistair L. Wilkins Dr. Christopher O. Miles Prof. Dr. Craig J. Forsyth 《Angewandte Chemie (International ed. in English)》2018,57(3):805-809
A convergent and stereoselective total synthesis of the previously assigned structure of azaspiracid‐3 has been achieved by a late‐stage Nozaki–Hiyama–Kishi coupling to form the C21?C22 bond with the C20 configuration unambiguously established from l ‐(+)‐tartaric acid. Postcoupling steps involved oxidation to an ynone, modified Stryker reduction of the alkyne, global deprotection, and oxidation of the resulting C1 primary alcohol to the carboxylic acid. The synthetic product matched naturally occurring azaspiracid‐3 by mass spectrometry, but differed both chromatographically and spectroscopically. 相似文献
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Darko Kwabena Adu Zondi Nate John Alake Blessing Wisdom Ike Ruchika Chauhan Prof. Rajshekhar Karpoormath 《Electroanalysis》2023,35(3):e202200216
Solvothermally synthesized cobalt sulphide/reduced graphene oxide (CoS/rGO) was used to fabricate an electrochemical sensor for detection of artemisinin. Microscopic techniques were used to characterize CoS/rGO nanocomposite. The electrochemical sensor was fabricated by modifying the surface of glassy carbon electrode with CoS/rGO nanocomposite. [Fe(CN)6]3−/4− was used as a mediator to aid oxidation of artemisinin. Differential pulse voltammetric technique was used for the detection of artemisinin. A linear range of 30–100 μM was used. Experimentally, a detection limit of 0.5 μM was obtained. Therefore, the developed sensor can be used for quality control of artemisinin. 相似文献
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David I. Adu 《Geometriae Dedicata》1988,27(2):227-240
In this paper, we calculate the number, up to homeomorphism, of a certain type of dendrites of order 3. This problem arises out of an attempt to characterize certain congruences of S(X), the semigroup of continuous self maps of a topological space X. The dendrites D under consideration are those which satisfy the condition that for each branch point b of D at least one of the components of D — {b} is either an arc or a triod. To facilitate our calculation we first show that each of such dendrites is homeomorphic to one of an apparently more restricted class. We then classify the dendrites into homeomorphism classes and finally calculate the number of such classes. 相似文献
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Noah Kyame Asare-Donkor Patrick Adu Poku Eric Clement Desmond Kotei Addison David Dotse Wemengah Anthony Apeke Adimado 《Journal of Radioanalytical and Nuclear Chemistry》2018,317(2):675-683
Radon in groundwater and their annual effective dose in the Ashanti region of Ghana have been determined using the continuous grab sampling technique and an AB-5 detector. Mean levels of radon were in the range of 0.51–46.16 Bq L?1. Effective annual doses ranged from 0.18–16.16, 0.13–12.08 and 0.09–8.31 μSv y?1 for infants, children and adults, respectively. These values are significantly lower than the reference level of 0.1 mSv y?1 recommended by the WHO and United Nations Scientific Committee on the Effects of Atomic Radiation for members of the public. 相似文献
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Krishnan Kumar Elias Saion M. K. Halimah Yap CK Muhd Suhaimi Hamzah 《Journal of Radioanalytical and Nuclear Chemistry》2014,301(3):667-676
A study is carried out on the concentrations of rare earth element (REE) elements present in surface mangrove sediments from 10 locations throughout west coast Malaysia. In carrying out the analysis, the best and most convenient method being the instrumental neutron activation analysis (INAA). Samples were obtained, dried, crushed to powdery form and samples prepared for INAA. All the samples for analysis were weighted approximately 150 mg for short irradiation and 200 mg for long irradiation time. As calibration and quality control procedures, blank samples, standard reference material SL-1 were then irradiated with thermal neutron flux of 4 × 1012 cm?2 s?1 at the MINT TRIGA Mark II research reactor which operated at 750 kW by using a pneumatic transport facility. The REE elements of surface sediment samples in this study are Dy, Sm, Eu,Yb, Lu, Tb, La and Ce. It was found that the level of concentrations of all the REE elements varies in the range (0.35–117.4 mg/kg). The geochemical behavior of REEs in surface sediments and normalized pattern (chondrite and shale) has been studied. The degree of sediments contaminations were computed using an enrichment factor. The results showed that the enrichment factor varied in the range (0.75–6.75). 相似文献