检索结果-南通市图书馆

American Journal of Analytical Chemistry 2022年第7期13卷 241-254页

作者： Salomon Madjitoloum Betoloum abel mbaiogaoun Severin Mbaihougadobe Emmanuel Talla Department of Chemistry Faculty of Exact and Applied Sciences (FSEA) University of N’Djamena N’Djamena The Republic of Chad Department of Chemistry Faculty of Science University of Ngaoundéré (UN) Ngaoundéré The Republic of Cameroon

The present work deals with the research of chemical constituents and evaluation of antioxidant properties of Bebotho propolis. From the ethyl acetate extract, we isolated, using various chromatographic techniques, a mixture of two identical compounds (isomers) indexed PBy4a and PByb. The structures of these compounds were elucidated by means of spectroscopic analysis techniques (MS, IR, 1H-NMR, 13C-NMR, HMBC and HSQC) and by comparison of the spectral data with those described in the literature. Thus, these compounds were identified to a mixture of two chromones namely 5,7-dihydroxy-2-methylchromone-6-C-α-D-glucopyranoside and 5,7-dihydroxy-2-methylchromone-8-C-β-D-glucopyranoside, first reported in propolis. The study of the antiradical power, chelating power and the quantification of phenolic compound of these same extracts, showed interesting properties that propolis extracts have to scavenge free radicals.

关键词： Isolation Propolis Chelating Power 5 7-Dihydroxy-2-Methylchromone-6-C-α-D-Glucopyranoside and 5 7-Dihydroxy-2-Methylchromone-8-C-β-D-Glucopyranoside

A TWO-SURFACE MODEL DESCRIBING RATCHETTING BEHAVIORS AND TRANSIENT HARDENING UNDER NONPROPORTIONAL LOADING

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Acta Mechanica Sinica 1996年第4期12卷 368-376页

作者：陈旭 A.abel Dept.of Chemical Engineering Tianjin UniversityTianjin300072China School of Civil and Mining Engineering The University of SydneyNSW 2006Australia

A new superposed rule of Mroz's kinematic hardening rule and Ziegler's kinematic hardening rule based on two-surface model is proposed in the paper. Some experimental results on ratchetting of 2014-T6 aluminum alloy are predicted very well under multiaxial loading. In addition the conformability of the model is discussed for transient cyclic hardening under two kinds of nonproportional cyclic loading paths., i.e. square and rhombic path.

关键词： nonproportional loading multiaxial loading ratchetting two-surface model cyclic hardening

Combustion Irreversibilities: Numerical Simulation and Analysis

在线全文

学校读者我要写书评

暂无评论

Journal of Thermal Science 2012年第4期21卷 377-383页

作者： Valter Silva abel Rouboa CITAB/Engineering Department School of Science and Technology of University of U TAD Mechanical Engineering and Applied Mechanics Department University of PennsylvaniaPhiladelphia

An exergy analysis was performed considering the combustion of methane and agro-industrial residues produced in Portugal (forest residues and vines pruning). Regarding that the irreversibilities of a thermodynamic process are path dependent, the combustion process was considering as resulting from different hypothetical paths each one characterized by four main sub-processes: reactant mixing, fuel oxidation, internal thermal energy exchange (heat transfer), and product mixing. The exergetic efficiency was computed using a zero dimensional model developed by using a Visual Basic home code. It was concluded that the exergy losses were mainly due to the internal thermal energy exchange sub-process. The exergy losses from this sub-process are higher when the reactants are preheated up to the ignition temperature without previous fuel oxidation. On the other hand, the global exergy destruction can be minored increasing the pressure, the reactants temperature and the oxygen content on the oxidant stream. This methodology allows the identification of the phenomena and processes that have larger exergy losses, the understanding of why these losses occur and how the exergy changes with the parameters associated to each system which is crucial to implement the syngas combustion from biomass products as a competitive technology.

关键词： Exergy Combustion paths Combustion sub-processes Exergetic efficiency Visual Basic Syngas

Compact High-Velocity Atmospheric Pressure Dielectric Barrier Plasma Jet in Ambient Air

在线全文

学校读者我要写书评

暂无评论

Plasma Science and Technology 2015年第1期17卷 14-19页

作者： Annette MEINERS Michael LECK Bernd abel University of Applied Science and Arts Department of Science and Technology Leibniz-Institut für Oberflachenmodifizierung(IOM) Wilhelm-Ostwald-Institut für Physikalische und Theoretische Chemie Universitat Leipzig

In this paper,a non-thermal atmospheric pressure plasma jet at high streaming velocity operating with ambient air is *** the present technological approach,the employment of air poses a significant *** high oxygen concentration in air results in a reduced concentration of reactive species in combination with a short species *** plasma jet assembly presented here contains a special dielectric barrier with a high secondary emission *** this way,the electron density and in turn the density of reactive species is *** addition,the plasma jet assembly is equipped with a short *** leads to a higher voltage across the discharge gap and in turn to an increased density of reactive plasma *** plasma jet is formed within and emitted by a small conical nozzle.A high-speed gas flow with gas velocity of 340 m/s was achieved at the end of the *** the jet the concentration of toxic and unwanted neutral plasma species like O3 or NOx is significantly reduced because of the shorter residence time within the *** range of short-lived active plasma species is in turn considerably *** jet efficiency and action range measured through the oxidation of a test surface were determined by measuring the increase of surface tension of a polypropylene substrate via contact angle measurements after plasma *** modeling of the plasma plume indicates that oxygen atoms are in fact the main active species in the plasma plume.

关键词： plasma jet atmospheric plasma dielectric barrier radicals plasma modeling

A new species of Atelopus(Amphibia:Bufonidae)from eastern Panama

在线全文

学校读者我要写书评

暂无评论

Zoological Research 2021年第3期42卷 272-279页

作者： Milan Vesely abel Batista Department of Zoology Faculty of Natural SciencesPalacky UniversityOlomouc 77146Czech Republic Universidad Autónoma de Chiriquí Ciudad Universitaria El Cabrero DavidChiriquí427Panama Asociacion ADOPTA el Bosque Panamá Gamboa 119xPanama Fundacion Los Naturalistas DavidChiriquí426-01459Panama

A new species of the genus Atelopus,Atelopus fronterizo ***.,from eastern Panama is described herein based on molecular,morphological,and bioacoustic *** new species can be distinguished from its congeners occurring in the region by a combination of the following characters:(1)phalangeal reduction in thumb;(2)SVL(females only)(35.1-50.1;n=13),HW/SVL(0.23-0.34;n=59),EYND/HW(0.27-0.39;n=60),TIBL/SVL(0.41-0.56;n=58),and HAL/SVL(0.22-0.28;n=49);(3)dorsal color pattern with green or yellow background and extensive dark olive blotches forming transversal bands or mottling;(4)advertisement call duration 176-235 ms with 19-34 pulses,average pulse rate 131.69 pulses/s,and dominant frequency 2422.50-2606.50 *** new species is nested within the Central American clade of *** minimum Kimura‐2‐parameter(K2P)genetic divergence between Atelopus fronterizo *** its most phylogenetically similar congeners(*** and ***)is>2.6%for 16S and>4.9%for COI(Table 1).The phylogenetic relationship is strongly supported by ultrafast bootstrap values for the maximum-likelihood trees of both genetic markers(16S,96;COI,100,Figure 1A).Bayesian analysis of the concatenated sequences resulted in a tree with similar topology and high posterior probability support(0.99;Supplementary Figure S1).In addition,haplotype networks inferred from COI and 16S(Supplementary Figure S2)showed a well-separated clade containing the new species(two for COI,four for 16S).

关键词： 16S Figure eastern

Purification of solar cell silicon materials through filtration

在线全文

学校读者我要写书评

暂无评论

Rare Metals 2006年第Z1期25卷 180-185页

作者： CIFTJA Arjan ENGH Thorvald abel KVITHYLD Anne Department of Materials Science and Engineering Norwegian University of Science and Technology Trondheim N-7491 Norway

Silicon is the material most commonly used in the manufacturing of photovoltaic (PV) cells. In the current study, laboratory experiments of purification of solar cell silicon materials through filtration are carried out. Inclusion removal from silicon was investigated. The purpose is to achieve clean silicon materials for solar cells. Silicon samples and filter samples were analyzed using microscope observation, EPMA, and X-ray detection. Silicon nitride (Si3N4) and silicon carbide (SiC) particles are the main non-metallic inclusions present in top-cut silicon scrap. Almost all inclusions larger than 10 μm can be removed from silicon by the porous foam filter. In mass fraction, more than 90% inclusions are removed. Si3N4 particles are mainly removed on the top surface of the filter, and SiC particles are mainly removed by entering the pores and attaching to the filter material. SiC inclusions are not only simply attached on the surface of the filter material, but are found also inside the filter material. There are SiC bridges near the filter materials. These bridges may fill the spaces between filter material, and this will further retard inclusions passing through the filter. Three-dimensional turbulent fluid flow and inclusion motion in the filter was calculated. Both experimental observation and fluid flow simulation indicate that most of the inclusions are entrapped at the upper part of the filter.

关键词： solar cell silicon inclusions filtration nitrides carbides fluid flow

Model of acceptance of Web 2.0 technologies for increased participation in learning activities A case study of a Scottish university

在线全文

学校读者我要写书评

暂无评论

International Journal of Intelligent Computing and Cybernetics 2015年第3期8卷 208-221页

作者： abel Usoro Razep Echeng University of the West of Scotland PaisleyUK

Purpose–The purpose of this paper is to find out how to encourage the use of Web 2.0 in learning in higher education by investigating factors that would relate to and would encourage such ***/methodology/approach–Three existing theories of technology acceptance underpinned this research and six constructs selected from these existing theories and one new construct from a pilot study were used to develop a conceptual model which constructs were operationalized into an online questionnaire(open and closed ended questions).Copies of this questionnaire were electronically distributed to all students in a higher institution of learning in *** total,203 *** and regression analyses were performed on the quantitative data collected so as to validate the research model.A focus group of ten volunteer students provided opportunity for a follow-up interview that produced in-depth information which provided strategies for enhancing the use of Web 2.0 tools for learning in higher ***–All the factors of the model,except perceived ease of use,positively relate significantly with use *** factors are perceived usefulness,facilitating conditions,motivation,prior knowledge,performance expectancy and social *** limitations/implications–The study was performed at only one institution in *** implication of the study is that predictor variables(mentioned above in the findings)of the model should be taken into consideration when introducing Web 2.0 to students of higher *** implications–In the paper are discussed specific strategies and these include assigning roles to users with little participation,checking to ensure irregular users have access and e-mailing them to encourage ***/value–This is apparently the first time the key technology acceptance models have been synthesised and tested in Scotland with regards to the acceptance of Web 2.0 tools in learning in higher

关键词： Web 2.0 e-Learning Technology acceptance Higher education Scottish university Learning participation

The utilization of algorithms for cloud internet of things application domains:a review

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Frontiers of Computer Science 2021年第3期15卷 137-163页

作者： Edje E.abel Muhammad Shafie Abd LATIFF Department of Computer Science Universiti Teknologi MalaysiaJohor 81310Malaysia Department of Computer Science Delta State UniversityDelta State PMB 01Nigeria

Cloud internet of things(IoT)is an emerging technology that is already impelling the daily activities of our ***,the enormous resources(data and physical features of things)generated from Cloud-enabled IoT sensing devices are lacking suitable managerial *** research surveys on Cloud IoT mainly focused on its fundamentals,definitions and layered architecture as well as security *** by the current literature,none of the existing researches is yet to provide a detailed analysis on the approaches deployed to manage the heterogeneous and dynamic resource data generated by sensor devices in the cloud-enabled IoT ***,to bridge this gap,the existing algorithms designed to manage resource data on various CloudloT application domains are investigated and *** emergence of CloudloT,followed by previous related survey articles in this field,which motivated the current study is ***,the utilization of simulation environment,highlighting the programming languages and a brief description of the simulation pack-ages adopted to design and evaluate the performance of the algorithms are *** utilization of diverse network communication protocols and gateways to aid resource dissemina-tion in the cloud-enabled IoT network infrastructure are also *** future work as discussed in previous researches,which pave the way for future research directions in this field is also presented,and ends with concluding remarks.

关键词： internet of things sensing devices radio frequency identification network communication protocols gateways cloud platform

When invasive ants meet: effects of outbreeding on queen performance in the tramp ant Cardiocondyla itsukii

在线全文

学校读者我要写书评

暂无评论

Insect Science 2019年第2期26卷 333-340页

作者： Jurgen Heinze Sabine Frohschammer abel Bernadou LS Zoologie/Evolutionsbiologie Universitat Regensburg Regensburg Germany

Most disturbed habitats in the tropics and subtropics harbor numerous species of invasive ants, and occasionally the same species has been introduced repeatedly from multiple geographical sources. We examined how experimental crossbreeding between sexuals from different populations affects the fitness of queens of the tramp ant Cardiocondyla itsukii, which is widely distributed in Asia and the Pacific Islands. Eggs laid by queens that mated with nestmate males had a higher hatchi ng rate than eggs laid by queens mated to males from neighboring (Hawaii x Kauai) or distant introduced populations (Hawaii/Kauai x Okinawa). Furthermore, inbreeding queens had a Ion ger lifespan and produced a less female-biased offspring sex ratio than queens from allopatric mating. This suggests that the genetic divergence between different source populations may already be so large that in case of multiple invasions eventual crossbreeding might negatively affect the fitness of tramp ants.

关键词： Cardiocondyla longevity outbreeding depression reproductive success tramp ants

On-surface synthesis of covalent coordination polymers on micrometer scale

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Nano Research 2017年第3期10卷 933-940页

作者： Mathieu Koudia Elena Nardi Olivier Siri Mathieu abel Aix Marseille UniversitY CNRS IM2NP UMR 7334 13397 Marseille France Aix Marseille UniversitY CNRS CINaM UMR 7325 13288 Marseille France

On-surface synthesis under ultrahigh vacuum provides a promising strategy to control matter at the atomic level, with important implications for the design of new two-dimensional materials having remarkable electronic, magnetic, or catalytic properties. This strategy must address the problem of limited extension of the domains due to the irreversible nature of covalent bonds, which prevents the ripening of defects. We show here that extended materials can be produced by a controlled co-deposition process. In particular, co-deposition of quinoid zwitterion molecules with iron atoms on a Ag（111） surface held at 570 K allows the formation of micrometer-sized domains based on covalent coordination bonds. This work opens up the construction of micrometer-scale single-layer covalent coordination materials under vacuum conditions.

关键词： on-surface synthesis scanning tunnelingmicroscopy (STM) two-dimensional polymer covalent organic frameworks