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61.
We study superconducting systems in the regime where superconductivity is destroyed by phase fluctuations. We find that the Nernst effect has a much sharper temperature decay than predicted by Gaussian fluctuations, with an onset temperature that tracks Tc rather than the pairing temperature. We find a close quantitative connection with diamagnetism--the ratio of magnetization to transverse thermoelectric conductivity reaches a fixed value at high temperatures. We interpret measurements on underdoped cuprates in terms of a dilute vortex liquid over a wide temperature range above Tc. 相似文献
62.
We demonstrate that a flowing liquid jet can be controllably split into two separate subfilaments through the application of a sufficiently strong tangential stress to the surface of the jet. In contrast, normal stresses can never split a liquid jet. We apply these results to observations of uncontrolled splitting of jets in electric fields. The experimental realization of controllable jet splitting would provide an entirely novel route for producing small polymeric fibers. 相似文献
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June Cyriac Justin Paulose Mathai George Marupaka Ramesh Ragampeta Srinivas Daryl Giblin Michael L. Gross 《Journal of the American Society for Mass Spectrometry》2014,25(3):398-409
ESI-protonated 1,5-bis-(2-methoxyphenyl)-1,4-pentadien-3-one (1) undergoes a gas-phase Nazarov cyclization and dissociates via expulsions of ketene and anisole. The dissociations of the [M + D]+ ions are accompanied by limited HD scrambling that supports the proposed cyclization. Solution cyclization of 1 was effected to yield the cyclic ketone, 2,3-bis-(2-methoxyphenyl)-cyclopent-2-ene-1-one, (2) on a time scale that is significantly shorter than the time for cyclization of dibenzalacetone. The dissociation characteristics of the ESI-generated [M + H]+ ion of the synthetic cyclic ketone closely resemble those of 1, suggesting that gas-phase and solution cyclization products are the same. Additional mechanistic studies by density functional theory (DFT) methods of the gas-phase reaction reveals that the initial cyclization is followed by two sequential 1,2-aryl migrations that account for the observed structure of the cyclic product in the gas phase and solution. Furthermore, the DFT calculations show that the methoxy group serves as a catalyst for the proton migrations necessary for both cyclization and fragmentation after aryl migration. An isomer formed by moving the 2-methoxy to the 4-position requires relatively higher collision energy for the elimination of anisole, as is consistent with DFT calculations. Replacement of the 2-methoxy group with an OH shows that the cyclization followed by aryl migration and elimination of phenol occurs from the [M + H]+ ion at low energy similar to that for 1. Figure
The role of methoxy group in the Nazarov cyclization of 1,5-bis-(2-methoxyphenyl)-1,4-pentadien-3-one in the gas-phase and condensed phase by June Cyriac, Justin Paulose, M. George, Department of Chemistry, Sacred Heart College, Thevara, Cochin, Kerala, India-682013., M. Ramesh, R. Srinivas, National center for Mass Spectrometry, IICT, Hyderabad, India. Daryl Giblin and Michael L. Gross, Department of Chemistry, Washington University in St.Louis, St.Louis, USA, MO 63130. 相似文献
66.
Bal Sydulu Singu Umashankar Male Palaniappan Srinivasan Srinivas Pabba 《Journal of Solid State Electrochemistry》2014,18(7):1995-2003
Polyaniline sulphate salt titanium dioxide composite (PANI-H2SO4·TiO2) was synthesized by chemical in situ polymerization of aniline in the presence of TiO2. The effect of anionic surfactant (sodium lauryl sulphate) in this reaction was also assessed. During the polymerization reaction, sodium lauryl sulphate (SLS) is converted to dodecyl hydrogen sulphate (DHS) in the presence of acidic medium and gets doped onto polyaniline along with sulphuric acid dopant, i.e. formation of polyaniline-sulphate-dodecyl hydrogen sulphate-titanium dioxide composite (PANI-H2SO4-DHS·TiO2). In the PANI-H2SO4-DHS·TiO2 composite, the presence of DHS is confirmed by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and energy-dispersive X-ray analysis (EDAX) and TiO2 is confirmed by XRD and EDAX results. In PANI-H2SO4-DHS·TiO2 system, the nanoparticle of TiO2 (10–20 nm) is uniformly embedded on nanofibres (20–60 nm) of PANI-H2SO4-DHS, and some part of PANI-H2SO4-DHS·TiO2 forms core–shell morphology, wherein TiO2 is in core and PANI-H2SO4-DHS in shell forms. Stability of PANI-H2SO4-DHS increases due to the incorporation of stable TiO2. Utility of PANI-TiO2 composite was carried out in supercapacitor cell system by performing cyclic voltammetry, galvanostatic charge–discharge and electrochemical impedance spectroscopic techniques in 1 M H2SO4 solution. Very low values of solution resistance, charge transfer resistance and time constant are obtained between 0.2 and 0.6 V. Initial specific capacitance values for the cell carried out at low and high current densities are found to be 280 and 205 F g?1, respectively, and after 1,700 charge–discharge cycles, its retention in the specific capacitance values is found to be the same (65–66 %) with coulombic efficiency of 98–100 %. A capacitor can work even at a high discharge rate. The efficiency of oxidizing and doping power increases with the use of a surfactant. Moreover, the use of a long chain surfactant dopant containing polyaniline as an electrode material plays an important role to increase the performance of the supercapacitor by allowing the electrolyte to easily enter and come out from PANI electrodes. 相似文献
67.
Organocatalytic Asymmetric Mannich Cyclization of Hydroxylactams with Acetals: Total Syntheses of (−)‐Epilupinine, (−)‐Tashiromine,and (−)‐Trachelanthamidine 下载免费PDF全文
Dr. Dipankar Koley Yarkali Krishna Kyatham Srinivas Afsar Ali Khan Ruchir Kant 《Angewandte Chemie (International ed. in English)》2014,53(48):13196-13200
An asymmetric, organocatalytic, one‐pot Mannich cyclization between a hydroxylactam and acetal is described to provide fused, bicyclic alkaloids bearing a bridgehead N atom. Both aliphatic and aromatic substrates were used in this transformation to furnish chiral pyrrolizidinone, indolizidinone, and quinolizidinone derivatives in up to 89 % yield and 97 % ee. The total syntheses of (?)‐epilupinine, (?)‐tashiromine, and (?)‐trachelanthamidine also achieved to demonstrate the generality of the process. 相似文献
68.
Srinivas Cheruku Chaithra Nagaraju Poornima Shetty Swarup Hassan A Sandhya Nagarakere C 《合成通讯》2020,50(10):1486-1494
AbstractWe have developed an economical and efficient method for the synthesis of medicinally and synthetically important indole-based triarylmethanes by using indoles and benzhydrols in the presence of propylphosphonic anhydride (T3P®). This methodology is an alternate approach for the C–C bond formation with good to excellent yields. In this T3P-mediated dehydration approach, the by-product is highly soluble in water, so that it can be done at larger scale also. In addition to that this efficient protocol has several advantages such as mild reaction conditions, short reaction time and operational simplicity. We have successfully synthesized pyrrole, imidazothiadiazole and imidazolo pyridine based triarylmethanes also. 相似文献
69.
Leiming Zhu Leonard Himmel Jean Michél Merkes Prof. Dr. Fabian Kiessling Prof. Dr. Magnus Rueping Dr. Srinivas Banala 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(19):4232-4235
Atropisomerism has been observed in a variety of biaryl compounds and meso-aryl substituted porphyrins. However, in porphyrins, this phenomenon had been shown only with o-substituted 6-membered aromatic groups at the meso-position. We show herein that a 5-membered heteroaromatic (N-mesyl-pyrrol-2-yl) group at the meso-position leads to atropisomerism. In addition, we report a ‘one-pot’ synthetic route for the synthesis of ‘all-pyrrolic’ porphyrin (APP) with several N-protection groups (Boc, Cbz, Ms and Ts). Among these groups, we found that only the Ms group gave four individually separable atropisomers of meso-tetra(N-Ms-pyrrol-2-yl) porphyrin. Furthermore, the reductive removal of Cbz- was achieved to obtain meso-tetra(pyrrol-2-yl) porphyrin. Thus, our synthetic procedure provides an easy access to a group of APPs and stable atropisomers, which is expected to expand the application of novel APP-based materials. 相似文献
70.
Jyoti Kannoujia Pavan Kumar Bangalore Srinivas Kantevari Prabhakar Sripadi 《Journal of mass spectrometry : JMS》2020,55(10)
The HPLC‐DAD and GC/MS methods were successfully used for the identification and characterization of the impurities in an agrochemical insecticide, bifenthrin technical. Three impurities ranging from 0.175%–0.541% were detected by the HPLC‐DAD method. The LC/MS technique with ESI or APCI source failed to detect the impurities detected by HPLC‐DAD, due to lack of ionization in ESI or APCI. The three impurities were enriched by prep‐HPLC, and then their structures were elucidated based on the GC/EIMS and CIMS data. The EI mass spectra of bifenthrin and its impurities displayed molecular ion and provided structure indicative fragment ions; the CIMS data further confirmed their molecular weight. The identity of the impurity 1 was further confirmed by the synthesis of the authentic sample followed by NMR and GC/MS data. 相似文献