A 3-phase AC plasma torch has been developed and aims at overcoming some limits of the classical DC torches in terms of efficiency, cost and reliability. However, the arc behavior in 3-phase plasma torch remains poorly explored. This paper is dedicated to the high speed video camera at 100,000 frames per second and electrical signal analyses of arcs behavior in a 3-phase AC arc plasma torch. First, a reference case at 150 A, in nitrogen as working gas, has been deeply analyzed. Afterwards, a parametric study based on current and inter-electrode gap has been carried out. Results show that only one arc can exist at a given time and arcs rotate by switching from a pair of electrodes to another one, following the maximal electrical gap potential. However, a particular “abnormal” arc behavior was sometimes observed. Indeed, the arc motion within the inter-electrode gap increases the heat exchange and stabilizes the 3-phase discharge whereas the system is unbalanced when the arc is in the periphery. The analysis highlights that the arc motion is strongly influenced by the electrode jet velocity and repulsive Lorentz forces. The parametric study shows that the current increases both jet velocity and arc discharge stability. Elsewhere, the increase of the inter-electrode gap can also stabilizes the electrical 3-phase arc discharge. Furthermore, the correlation between arc motion and current waveform is highlighted. This work is likely to open the way toward a better understanding of 3-phase discharges in the perspective of their further optimization. 相似文献
Artificial implants and biomaterials lack the natural defense system of our body and, thus, have to be protected from bacterial adhesion and biofilm formation. In addition to the increasing number of implanted objects, the resistance of bacteria is also an important problem. Silver ions are well‐known for their antimicrobial properties, yet not a lot is known about their mode of action. Silver is expected to interact on many levels, thus the development of silver resistance is very difficult. Nevertheless, some bacteria are able to resist silver, even at higher concentrations. One such defense mechanism of bacteria against heavy‐metal intoxication includes an efflux system. SilE, a periplasmic silver‐binding protein that is involved in this defense mechanism, has been shown to possess numerous histidine functions, which strongly bind to silver atoms, as demonstrated by ourselves previously. Herein, we address the question of how histidine binds to silver ions as a function of pH value. This property is important because the local proton concentration in cells varies. Thus, we solved the crystal structures of histidine–silver complexes at different pH values and also investigated the influence of the amino‐acid configuration. These results were completed by DFT calculations on the binding strength and packing effects and led to the development of a model for the mode of action of SilE. 相似文献
The rare‐earth‐metal? hydride complexes [{(1,7‐Me2TACD)LnH}4] (Ln=La 1 a , Y 1 b ; (1,7‐Me2TACD)H2=1,7‐dimethyl‐1,4,7,10‐tetraazacyclododecane, 1,7‐Me2[12]aneN4) were synthesized by hydrogenolysis of [{(1,7‐Me2TACD)Ln(η3‐C3H5)}2] with 1 bar H2. The tetrameric structures were confirmed by 1H NMR spectroscopy and single‐crystal X‐ray diffraction of compound 1 a . Both complexes catalyze the dehydrogenation of secondary amine? borane Me2NH ? BH3 to afford the cyclic dimer (Me2NBH2)2 and (Me2N)2BH under mild conditions. Whilst the complete conversion of Me2NH ? BH3 was observed within 2 h with lanthanum? hydride 1 a , the yttrium homologue 1 b required 48 h to reach 95 % conversion. Further reactions of compound 1 a with Me2NH ? BH3 in various stoichiometric ratios gave a series of intermediate products, [{(1,7‐Me2TACD)LaH}4](Me2NBH2)2 ( 2 a ), [(1,7‐Me2TACDH)La(Me2NBH3)2] ( 3 a ), [(1,7‐Me2TACD)(Me2NBH2)La(Me2NBH3)] ( 4 a ), and [(1,7‐Me2TACD)(Me2NBH2)2La(Me2NBH3)] ( 5 a ). Complexes 2 a , 3 a , and 5 a were isolated and characterized by multinuclear NMR spectroscopy and single‐crystal X‐ray diffraction studies. These intermediates revealed the activation and coordination modes of “Me2NH ? BH3” fragments that were trapped within the coordination sphere of a rare‐earth‐metal center. 相似文献
We report a new synthesis and our study of the mechanism of formation of substituted 1-trifluoromethyl and 1-perfluoroalkyl-3-(phenylamino)prop-2-en-1-one starting from 3-(R-phenoxy)-3-perfluoroalkyl-prop-2-enals and arylamines. Reactivity study of the intermediates confirmed that 3-perfluoroalkyl-N,N′-diphenyl-1,5-diazapentadienes are the synthetic intermediates of the synthesis of 2-perfluoroalkylquinolines. The mechanism of the reaction of 1-trifluoromethyl and 1-perfluoroalkyl-3-(phenylamino)prop-2-en-1-one with POCl3 was studied. To our knowledge this is the first detection and isolation of N,N′-diaryldiazapentadiene derivatives as intermediates in the Combes F-alkyl substituted quinoline synthesis starting from enaminoketones. Finally, we succeeded isolating and identifying unsymmetrically substituted 2-perfluorolakyldiazapentadiene. 相似文献
In the present work a modular pathway towards the synthesis of a new versatile MRI contrast agent is reported and its physico-chemical properties are described. Two different functional groups were attached on two arms of the gadolinium 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetate (DOTA) in order to get a platform able to bind one probe designed to target specific biological marker and a fluorescent molecule likely to be used for optical imaging. The nuclear magnetic relaxation dispersion (NMRD) profile, the oxygen-17 relaxometric NMR study and stability assessment versus transmetalation of the Gd-complex show that this new contrast agent has a relaxivity and transmetalation stability similar to Gd–DOTA. 相似文献
Nanosized titanium dioxide (TiO2) is one of the most interesting and valuable nanomaterials for the construction industry but also in health care applications, food, and consumer goods, e.g., cosmetics. Therefore, the properties associated with this material are described in detail. Despite its widespread use, the analytical determination and characterization of nanosized metal oxides is not as straightforward as the comparatively easy-to-detect metallic nanoparticles (e.g., silver or gold). This study presents the method development and the results of the determination of tissue titanium (Ti) levels after treatment of rats with the nanosized TiO2. Total Ti levels were chosen to evaluate the presence and distribution of TiO2 nanoparticles. A procedure consisting of incubation with a mixture of nitric acid (HNO3) and hydrofluoric acid (HF), and heating was developed to digest tissues and TiO2 nanomaterials in order to determine the total Ti content by inductively coupled plasma mass spectrometry (ICPMS). For the inter-laboratory comparison, altogether four laboratories analyzed the same samples upon digestion using the available ICPMS equipment. A major premise for any toxicokinetic study is the possibility to detect the chemical under investigation in biological samples (tissues). So, the study has to be performed with a dose high enough to allow for subsequent tissue level measurement of the chemical under investigation. On the other hand, dose of the chemical applied should not induce over toxicity in the animal as this may affect its absorption, distribution, metabolism, and excretion. To determine a non-toxic TiO2 dosage, an acute toxicity study in rats was performed, and the organs obtained were evaluated for the presence of Ti by ICPMS. Despite the differences in methodology and independent of the sample preparation and the ICPMS equipment used, the results obtained for samples with Ti concentrations >4 μg Ti/g tissue agreed well.
Figure
Major Ti concentrations in micrograms per gram of organ as determined by different laboratories. 相似文献
The functionalization of zinc oxide (ZnO) nanoparticles by poly(3‐hexylthiophene) (P3HT) brush is completed by the combination of a mussel inspired biomimetic anchoring group and Huisgen cyclo‐addition “click chemistry.” Herein, the direct coupling of an azide modified catechol derivative with an alkyne end‐functionalized P3HT is described. This macromolecular binding agent is used to access core@corona ZnO@P3HT with a stable and homogeneous conjugated organic corona. Preliminary photoluminescence measurement proves an efficient electron transfer from the donor P3HT to the acceptor ZnO nanoparticles upon grafting, thus demonstrating the potential of such a combination in organic electronics.
An ion chromatography system employing a low-cost three-dimensional printed absorbance detector for indirect ultraviolet detection towards portable phosphate analysis of environmental and industrial waters has been developed. The optical detection cell was fabricated using stereolithography three-dimensional printing of nanocomposite material. Chromatographic analysis and detection of phosphate were carried out using a CS5A 4 × 250 mm analytical column with indirect ultraviolet detection using a 255 nm light-emitting diode. Isocratic elution using a 0.6 mM potassium phthalate eluent combined with 1.44 mM sodium bicarbonate was employed at a flow rate of 0.75 mL/min. A linear calibration range of 0.5 to 30 mg/L PO43− applicable to environmental and wastewater analysis was achieved. For retention time and peak area repeatability, relative standard deviation values were 0.68 and 4.09%, respectively. Environmental and wastewater samples were analyzed with the optimized ion chromatography platform and the results were compared to values obtained by an accredited ion chromatograph. For the analysis of environmental samples, relative errors of <14 % were achieved. Recovery analysis was also carried out on both freshwater and wastewater samples and recovery results were within the acceptable range for water analysis using standard ion chromatography methods. 相似文献