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Hoda Molavi Abbas Yousefpour Akbar Mirmostafa Ali Sabzi Sepideh Hamedi Milad Narimani Nazanin Abdi 《Chromatographia》2017,80(7):1129-1135
Methanol in insulating oil has been proposed as a new marker for condition assessment of the solid insulation system of power transformers. In the current work, as a first step of using the new marker, an analytical static headspace gas chromatography/mass spectrometry method has been developed, optimized, and validated to measure methanol and ethanol contents in the insulating mineral oil. The analyzing setup consists of a 6890 N gas chromatograph equipped with a 5973 network mass spectrometer (MS) in the absence of a costly headspace autosampler, and the chromatography separation was performed on a 60 m × 320 µm × 0.5 µm VF-WAXms GC column. Calibration curves have been provided using several concentrations of the alcohols, and also limit of detection (LOD), limit of quantification (LOQ), and relative standard deviation percentage (RSD%) have been determined. 相似文献
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Kojabad Zohreh Deljoo Shojaosadati Seyed Abbas Firoozabadi Seyed Mohammad Hamedi Sepideh 《Journal of Solid State Electrochemistry》2019,23(5):1533-1539
Journal of Solid State Electrochemistry - High selectivity and low impedance are preferred properties for neural microelectrodes. The localized and controlled release of drugs from the... 相似文献
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Mohammad Mahdi Zangeneh Shabnam Bovandi Sepideh Gharehyakheh Akram Zangeneh Parisa Irani 《应用有机金属化学》2019,33(7)
Allium saralicum R.M. Fritsch has been used in Iranian traditional medicine as a remedial supplement for microbial diseases. This paper reports the green synthesis, chemical characterization and antioxidant, cytotoxic, antibacterial and antifungal properties of silver nanoparticles obtained using aqueous extract of A. saralicum leaves. In this synthesis, no surfactants or stabilizers were used. For characterization, UV–visible spectroscopy, transmission electron microscopy, X‐ray diffraction, energy‐dispersive X‐ray spectroscopy and field emission scanning electron microscopy were used. 2,2‐Diphenyl‐1‐picrylhydrazyl was used in experiments to assess the antioxidant potential of the silver nanoparticles, which revealed an impressive prevention in comparison with butylated hydroxytoluene. The synthesized silver nanoparticles at low doses (1–250 μg dl?1) did not show marked cytotoxic activity (against cervical cancer cells (Hela), breast cancer cells (MCF‐7) and human embryonic kidney cells (HEK‐293)). Agar diffusion tests were applied to determine the antibacterial and antifungal characteristics. Compared with all standard antimicrobials, the silver nanoparticles showed higher antibacterial and antifungal activities (p ≤ 0.01). Also, the silver nanoparticles inhibited the growth of all bacteria and fungi at concentrations of 31–250 μg ml?1, and destroyed them at concentrations of 31–500 μg ml?1 (p ≤ 0.01). Because the silver nanoparticles obtained using aqueous extract of A. saralicum leaves have antioxidant, non‐cytotoxic, antifungal and antibacterial potentials, they can be used as a medical supplement or drug. 相似文献
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Christopher Lombardi Dr. Richard P. Rucker Dr. Robert D. J. Froese Dr. Sepideh Sharif Prof. Pier Alexandre Champagne Prof. Michael G. Organ 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(62):14223-14229
The relative rates of arylation of primary alkylamines with different Pd-NHC catalysts have been measured, as have the relative rates of arylation of the secondary aniline product in an attempt to understand the key ligand design features necessary to have high selectivity for the monoarylated amine product. As the substituents on the N-aryl ring of the NHC increase in size, selectivity for monoarylation increases and this is further enhanced by chlorinating the back of the NHC ring. Computations have been performed on the catalytic cycle of this transformation in order to understand the selectivity obtained with the different catalysts. 相似文献
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Despite intense research on the blood oxygenation level-dependent (BOLD) signal underlying functional magnetic resonance imaging, our understanding of its physiological basis is far from complete. In this study, it was investigated whether the so-called poststimulus BOLD signal undershoot is solely a passive vascular effect or actively induced by neural responses. Prolonged static and flickering black-white checkerboard stimulation with isoluminant grey screen as baseline condition were employed on eight human subjects. Within the same region of interest, the positive BOLD time courses for static and flickering stimuli were identical over the entire stimulus duration. In contrast, the static stimuli exhibited no poststimulus BOLD signal undershoot, whereas the flickering stimuli caused a strong BOLD poststimulus undershoot. To ease the interpretation, we performed an additional study measuring both BOLD signal and cerebral blood flow (CBF) using arterial spin labeling. Also for CBF, a difference in the poststimulus period was found for the two stimuli. Thus, a passive blood volume effect as the only contributor to the poststimulus undershoot comes short in explaining the BOLD poststimulus undershoot phenomenon for this particular experiment. Rather, an additional active neuronal activation or deactivation can strongly modulate the BOLD poststimulus behavior. In summary, the poststimulus time course of BOLD signal could potentially be used to differentiate neuronal activity patterns that are otherwise indistinguishable using the positive evoked response. 相似文献
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Visually evoked intrinsic optical signals (IOSs) were measured in vivo for the first time to our knowledge from all retina layers of the chicken retina with a combined functional optical coherence tomography and electroretinography (ERG) system. IOS traces were recorded from a small volume in the retina with 3.5 μm axial resolution and 7 ms time resolution. Comparison of the IOS and ERG traces shows a correlation between the positive and negative IOS measured from different retinal layers and the timing of the a and b waves in the ERG recording. 相似文献
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In this work a modified form of the Ghotbi–Vera Mean Spherical Approximation model (MGV-MSA) has been used to correlate the mean ionic activity coefficients (MIAC) for a number of symmetric and asymmetric aqueous electrolyte solutions at 25 °C. In the proposed model the hard sphere as well as the electrostatic contributions to the MIAC and the osmotic coefficient of the previously GV-MSA model has been modified. The results of the proposed model for the MIAC of the electrolyte solutions studied in this work are used to directly calculate the values of the osmotic coefficients without introducing any new adjustable parameter. In the MGV-MSA model the cation diameter as well as the relative permittivity of water depends on the electrolyte concentration. Having considered such dependency for both cation and relative permittivity for water in an electrolyte solution the modification of the GV-MSA has been made. It should be stated that in the MGV-MSA model the anion diameter in the solution similar to that in the GV-MSA model remains constant and independent of the electrolyte concentration. The results obtained from the proposed model have been favorably compared with those of the GV-MSA model. The results showed that the MGV-MSA model can more accurately correlate the MIAC of the single electrolyte solutions than those of the GV-MSA model. The same comparison has been observed in case of the osmotic coefficients for the electrolyte solutions studied in this work. It should be noted that in order to do an unequivocal comparison between the results obtained from the models used in this work the same minimization procedure and the same experimental data for the MIAC and the osmotic coefficients have been used. Also it should be mentioned that in the MGV-MSA model the conversion from the McMillan–Mayer (MM) framework to that of the Lewis–Randall (LR) has been performed. It has been concluded that such transformation can affect the results in particular at higher electrolyte concentrations. 相似文献
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Utilizing pure amine hydrogen bonding is a novel approach for constructing two‐dimensional (2D) networks. Further, such systems are capable of undergoing structural modifications due to changes in pH. In this study, we designed a 2D network of triaminobenzene (TAB) molecules that by varying the pH from neutral to acidic, form either ordered or disordered structures on Au(111) surface as revealed in scanning tunneling microscopy images. In near‐neutral solution (pH ≈5.5), protonation of TAB generates charged species capable of forming H‐bonds between amine groups of neighboring molecules resulting in the formation of a 2D supramolecular structure on the electrified surface. At lower pH, due to the protonation of the amine groups, intermolecular hydrogen bonding is no longer possible and no ordered structure is observed on the surface. This opens the possibility to employ pH as a chemical trigger to induce a phase transition in the 2D molecular network of triaminobenzene molecules. 相似文献
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Dr. Zhihai Li Dr. Manuel Smeu Sepideh Afsari Dr. Yangjun Xing Prof. Mark A. Ratner Prof. Eric Borguet 《Angewandte Chemie (International ed. in English)》2014,53(4):1098-1102
Sensors play a significant role in the detection of toxic species and explosives, and in the remote control of chemical processes. In this work, we report a single‐molecule‐based pH switch/sensor that exploits the sensitivity of dye molecules to environmental pH to build metal–molecule–metal (m‐M‐m) devices using the scanning tunneling microscopy (STM) break junction technique. Dyes undergo pH‐induced electronic modulation due to reversible structural transformation between a conjugated and a nonconjugated form, resulting in a change in the HOMO–LUMO gap. The dye‐mediated m‐M‐m devices react to environmental pH with a high on/off ratio (≈100:1) of device conductivity. Density functional theory (DFT) calculations, carried out under the non‐equilibrium Green’s function (NEGF) framework, model charge transport through these molecules in the two possible forms and confirm that the HOMO–LUMO gap of dyes is nearly twice as large in the nonconjugated form as in the conjugated form. 相似文献