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151.
Basant Lal Sharma 《The European Physical Journal B - Condensed Matter and Complex Systems》2018,91(5):84
Based on the well known nearest-neighbor tight-binding approximation for graphene, an exact expression for the electronic conductance across a zigzag nanoribbon/armchair nanotube junction is presented for non-interacting electrons. The junction results from the removal of a half-row of zigzag dimers in armchair nanotube, or equivalently by partial rolling of zigzag nanoribbon and insertion of a half-row of zigzag dimers in between. From the former point of view, a discrete form of Dirichlet condition is imposed on a zigzag half-line of dimers assuming the vanishing of wave function outside the physical structure. A closed form expression is provided for the reflection and transmission moduli for the outgoing wave modes for each given electronic wave mode incident from either side of the junction. It is demonstrated that such a contact junction between the nanotube and nanoribbon exhibits negligible backscattering, and the transmission has been found to be nearly ballistic. In contrast to the previously reported studies for partially unzipped carbon nanotubes (CNTs), using the same tight binding model, it is found that due to the “defect” there is certain amount of mixing between the electronic wave modes with even and odd reflection symmetries. But the junction remains a perfect valley filter for CNTs at certain energy ranges. Applications aside from the electronic case, include wave propagation in quasi-one-dimensional honeycomb structures of graphene-like constitution. The paper includes several numerical calculations, analytical derivations, and graphical results, which complement the provision of succinct closed form expressions. 相似文献
152.
Even with the emergence of advanced techniques of separation and identification, it is rarely possible to analyse food without manipulation. The traditional techniques for sample preparation are time consuming and require large amount of reagents, which are expensive, generate considerable waste, contaminate the sample and can enrich it for analytes. The more analytical techniques have become highly developed, the more has sample clean-up become important in order to fully take advantage of them. Due to the multiplicity of food matrices, it is not possible to use one sample preparation technique, so many methods have been proposed for meeting all the requirements. The newest variations of wet digestion, solvent and sorbent extraction and membrane separation are summarised and their most recent applications to food analysis are provided. 相似文献
153.
Ranjeet Kumar J. R. Yadav D. D. Rao Lal Chand 《Journal of Radioanalytical and Nuclear Chemistry》2010,283(3):785-788
Bioassay technique is used for the estimation of actinides present in the body based on their excretion rate through body
fluids. For occupational radiation workers urine assay is the preferred method for monitoring of chronic internal exposure.
Determination of low concentrations of actinides such as plutonium, americium and uranium at low level of mBq in urine by
alpha spectrometry requires pre-concentration of large volumes of urine. This paper deals with standardization of analytical
method for the determination of Pu-isotopes in urine samples using anion exchange resin and 236Pu tracer for radiochemical recovery. The method involves oxidation of urine followed by co-precipitation of plutonium along
with calcium phosphate. Separation of Pu was carried out by Amberlite, IRA-400, anion exchange resin. Pu-fraction was electrodeposited
and activity estimated using tracer recovery by alpha spectrometer. Twenty routine urine samples of radiation workers were
analyzed and consistent radiochemical tracer recovery was obtained in the range 74–96% with a mean and standard deviation
of 85 and 6% respectively. 相似文献
154.
Adamovich MI Aggarwal MM Alexandrov YA Ameeva ZV Andreeva NP Anzon ZV Arora R Badyal SK Bhalla KB Bhasin A Bhatia VS Bubnov VI Burnett TH Cai X Chasnikov IY Chernova LP Chernyavski MM Dressel B Eligbaeva GZ Eremenko LE Friedlander EM Gadzhieva SI Gaitinov AS Ganssauge ER Garpman S Gerassimov SG Gill A Grote JG Gulamov KG Gulyamov UG Gupta VK Hackel S Heckman HH Haung H Judek B Kachroo S Kadyrov FG Kalyachkina GS Kanygina EK Kaul GL Kaur M Kharlamov SP Koss T Kumar V Lal P Larionova VG 《Physical review letters》1990,65(4):412-415
155.
Singh AK Chawla R Rai A Yadav LD 《Chemical communications (Cambridge, England)》2012,48(31):3766-3768
NHC-catalysed azalactone ring-opening and piperidine ring-closing cascade with α,β-unsaturated aldehydes (enals) in a one-pot operation is reported. The present reaction cascade offers a convenient method for a highly diastereoselective synthesis of multifunctionalised piperidines in excellent yields under mild conditions. 相似文献
156.
The flow boiling heat transfer coefficients of R-134a/R-290/R-600a (91%:4.068%:4.932% by mass) refrigerant mixture are experimentally
arrived in two tubes of diameter 9.52 and 12.7 mm. The tests are conducted to target the varied heat flux condition and stratified
flow pattern found in evaporators of refrigerators and deep freezers. The varied heat flux condition is imposed on the refrigerant
using a coaxial counter-current heat exchanger test section. The experiments are performed for mass flow rates of the refrigerant
mixture between 3 and 5 g s−1 and entry temperature between −8.59 and 5.33°C which are bubble temperatures corresponding to a pressure of 3.2 and 5 bar.
The influences of heat flux, mass flow rate, pressure, flow pattern, tube diameter on the heat transfer coefficient are discussed.
The profound effects of nucleate boiling prevailing even at higher vapor qualities in evaporators are highlighted. The heat
transfer coefficient of the refrigerant mixture is also compared with that of R-134a. 相似文献
157.
In this paper, we present a fixed point method to prove generalized Hyers–Ulam stability of derivations in modular spaces. 相似文献
158.
The k-higher Mahler measure of a non-zero polynomial P is the integral of log k |P| on the unit circle. In this note, we consider Lehmer’s question (which is a long-standing open problem for k=1) for k>1 and find some interesting formulas for 2- and 3-higher Mahler measure of cyclotomic polynomials. 相似文献
159.
160.
Adamovich MI Aggarwal MM Alexandrov YA Andreeva NP Anson ZV Arora R Avetyan FA Badyal SK Basova E Bazarov IK Bhalla KB Bhasin A Bhatia VS Bogdanov VG Bubnov VI Burnett TH Cai X Carshiev DA Chasnicov IY Chernova LP Chernyavski MM Eligbaeva GZ Eremenko LE Gaitinov AS Ganssauge ER Garpman S Gerassimov SG Grote JG Gulamov KG Gupta SK Gupta VK Heckman HH Huang H Jacobsson B Judek B Kachroo S Kalyachkina GS Kanygina EK Karabova M Kharlamov SP Kitroo S Koss T Krasnov SA Kumar V Lal P Larionova VG 《Physical review D: Particles and fields》1993,47(9):3726-3732