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61.
62.
The present study was designed to identify the objectification processes involved in making sense of the concept of an indefinite integral when studied graphically in a dynamic technological environment. The study focuses on 11 pairs of 17-year-old students familiar with the concept of differentiation but not of integration. The students were asked to explain the possible connection between two linked dynamic graphs: the function and the primitive function graphs. The present study was guided by objectification theory, which considers artifacts to be fundamental to cognition and which views learning as the process of becoming aware of the knowledge that exists within a cultural context. In the course of two rounds of data analysis we identified six elements in the processes of objectification: objectifying the relationships between segments based on the location, inclination, and concavity of the function graph; and on the relationships between the zero, the extreme, and the inflection points in the function graph and the corresponding points in the primitive function graph. 相似文献
63.
Gamal A. Hussein Saied M. Abd El-atty Osama Aly Oraby Abd El-Naser A. Mohamed Ahmed S. Elkorany Ibrahim Eldokany Moawad I. Dessouky El-Sayed M. El-Rabaie Saleh A. Alshebeili F.E. Abd El-Samie 《Optik》2014
Optical code division multiple access (OCDMA) is a promising operational system for future backhaul optical networks especially for switching and optical signal multiplexing. However, OCDMA operation is restricted by multiple access interference (MAI) due to the asynchronous nature of transmission. In this study, we discuss an efficient MAI technique for OCDMA systems that depends not only on using hybrid frequency shift keying (FSK) modulation but also on employing the double padded modified prime code (DPMPC) as a signature sequence. MAI cancellation is performed by subtracting a reference signal from the received signal of the desired user. The simulation results show that the performance of the FSK-OCDMA technique is superior to the performance of the PPM-OCDMA technique. Furthermore, the obtained results illustrate that the FSK-OCDMA technique is able to accommodate a large number of simultaneous active users with low error-rate. 相似文献
64.
Ayman M. Atta Maher A. Elsockary Osama F. Kandil Zakaa M. Mohamed 《Journal of Dispersion Science and Technology》2013,34(1):7-19
Polyethylene acrylic acid copolymer (PEAA) was modified with different types of alkanols and hydroxybenzoic acids to produce three types of esterified grafts. The molecular structures of the synthesized dispersants were performed using 1H NMR analysis. The molecular weights of the synthesized dispersants were determined by GPC technique. The activity of PEAA derivatives as asphaltene stabilizer in the crude oil was evaluated by means of flocculation measurements. The effect of asphaltenes on the rheological behavior of highly asphaltenic crude oils was studied to evaluate the transportation parameters of crude oils. The rheological properties were measured at different temperature ranges of 5°C to 25°C in presence and absence of PEAA additives. It was observed that the PEAA having side chain lengths below C16 show non‐Newtonian pseudoplastic relationships at temperatures from 25°C to 5°C. While, PEAA additives having side chain lengths equal or above C16 show Newtonian relationship even at low temperature (5°C) for all tested crude oils. 相似文献
65.
Arslan HK Shekhah O Wieland DC Paulus M Sternemann C Schroer MA Tiemeyer S Tolan M Fischer RA Wöll C 《Journal of the American Chemical Society》2011,133(21):8158-8161
We report the synthesis of layered [Zn(2)(bdc)(2)(H(2)O)(2)] and [Cu(2)(bdc)(2)(H(2)O)(2)] (bdc = benzdicarboxylate) metal-organic frameworks (MOF) carried out using the liquid-phase epitaxy approach employing self-assembled monolayer (SAM) modified Au-substrates. We obtain Cu and Zn MOF-2 structures, which have not yet been obtained using conventional, solvothermal synthesis methods. The 2D Cu(2+) dimer paddle wheel planes characteristic for the MOF are found to be strictly planar, with the planes oriented perpendicular to the substrate. Intercalation of an organic dye, DXP, leads to a reversible tilting of the planes, demonstrating the huge potential of these surface-anchored MOFs for the intercalation of large, planar molecules. 相似文献
66.
Oriented Circular Dichroism Analysis of Chiral Surface‐Anchored Metal–Organic Frameworks Grown by Liquid‐Phase Epitaxy and upon Loading with Chiral Guest Compounds 下载免费PDF全文
Zhi‐Gang Gu Dr. Jochen Bürck Dr. Angela Bihlmeier Dr. Jinxuan Liu Dr. Osama Shekhah Dr. Peter G. Weidler Dr. Carlos Azucena Zhengbang Wang Stefan Heissler Dr. Hartmut Gliemann Prof. Dr. Wim Klopper Prof. Dr. Anne S. Ulrich Prof. Dr. Christof Wöll 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(32):9879-9882
Oriented circular dichroism (OCD) is explored and successfully applied to investigate chiral surface‐anchored metal–organic frameworks (SURMOFs) based on camphoric acid (D‐ and Lcam) with the composition [Cu2(Dcam)2x(Lcam)2?2x(dabco)]n (dabco=1,4‐diazabicyclo‐[2.2.2]‐octane). The three‐dimensional chiral SURMOFs with high‐quality orientation were grown on quartz glass plates by using a layer‐by‐layer liquid‐phase epitaxy method. The growth orientation, as determined by X‐ray diffraction (XRD), could be switched between the [001] and [110] direction by using either OH‐ or COOH‐terminated substrates. These SURMOFs were characterized by using OCD, which confirmed the ratio as well as the orientation of the enantiomeric linker molecules. Theoretical computations demonstrate that the OCD band intensities of the enantiopure [Cu2(Dcam)2(dabco)]n grown in different orientations are a direct result of the anisotropic nature of the chiral SURMOFs. Finally, the enantiopure [Cu2(Dcam)2(dabco)]n and [Cu2(Lcam)2(dabco)]n SURMOFs were loaded with the two chiral forms of ethyl lactate [(+)‐ethyl‐D ‐lactate and (?)‐ethyl‐L ‐lactate)]. An enantioselective enrichment of >60 % was observed by OCD when the chiral host scaffold was loaded from the racemic mixture. 相似文献
67.
68.
A new naturally occurring ent-kaurane diterpenoid dimer, 15β, 15′β-oxybis (ent-kaur-16-en-19-oic acid) (1) along with six known compounds, 15β-hydroxy-ent-kaur-16-en-19-oic acid (2), 15β-hydroxy-ent-kaur-16-en-19-oate-β-d-glucopyranoside (3), 6-hydroxykaempferol-3, 7-dimethyl ether (4), quercetagetin 3, 7, 3′-trimethyl ether (5), β-sitosterol (6) and β-sitosterol glucoside (daucosterol) (7) were isolated from the aerial parts of Pulicaria inuloides DC. Compounds 2–5 were isolated for the first time from genus Pulicaria. The structures of compounds 1–7 were established on the basis of extensive 1D and 2D NMR spectroscopic techniques in combination with ESI-MS. The antimicrobial activity of the isolated compounds was evaluated against Staphylococcus aureus, Escherichia coli and Candida albicans. Sulphorhodamine B cytotoxic assay against HepG2 (liver cancer) cell line and ABTS antioxidant assay were carried out. 相似文献
69.
H2S Sensors: Fumarate‐Based fcu‐MOF Thin Film Grown on a Capacitive Interdigitated Electrode 下载免费PDF全文
Dr. Omar Yassine Dr. Osama Shekhah Ayalew H. Assen Dr. Youssef Belmabkhout Prof. Khaled N. Salama Prof. Mohamed Eddaoudi 《Angewandte Chemie (International ed. in English)》2016,55(51):15879-15883
Herein we report the fabrication of an advanced sensor for the detection of hydrogen sulfide (H2S) at room temperature, using thin films of rare‐earth metal (RE)‐based metal–organic framework (MOF) with underlying fcu topology. This unique MOF‐based sensor is made via the in situ growth of fumarate‐based fcu ‐MOF (fum‐ fcu ‐MOF) thin film on a capacitive interdigitated electrode. The sensor showed a remarkable detection sensitivity for H2S at concentrations down to 100 ppb, with the lower detection limit around 5 ppb. The fum‐ fcu ‐MOF sensor exhibits a highly desirable detection selectivity towards H2S vs. CH4, NO2, H2, and C7H8 as well as an outstanding H2S sensing stability as compared to other reported MOFs. 相似文献
70.
Santa T Al-Dirbashi OY Ichibangase T Rashed MS Fukushima T Imai K 《Biomedical chromatography : BMC》2008,22(2):115-118
Benzofurazan derivatization reagent, 4-[2-(N,N-dimethylamino)ethylaminosulfonyl]-7-N-methylhydrazino-2,1,3-benzoxadiazole (DAABD-MHz), for aldehydes in liquid chromatography/electrospray ionization-tandem mass spectrometry (LC/ESI-MS/MS), was synthesized. DAABD-MHz reacted with aliphatic aldehydes under mild conditions. The generated derivatives were separated on a reversed-phase column and detected by ESI-MS/MS with detection limits of 30-60 fmol on-column. Upon collision-induced dissociation, a single and intense fragment ion at m/z 151 was observed. These results suggested that DAABD-MHz was suitable as a derivatization reagent in LC/ESI-MS/MS. 相似文献