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71.
The syntheses of the triesters formed between ethyl bromoacetate and hexahomotrioxacalix[3]naphthalene 8, and its tert-butyl analogue 11, are described. Depending on the conditions employed, cone or partial cone conformers are produced. The conformations appear to have some influence on their complexation in neutral medium, with alkali metal cations. The X-ray structure of the partial cone triester 10 is presented. 相似文献
72.
C. Foin A. Gizon D. Barnéoud J. Genevey J. Gizon D. Santos F. Farget P. Paris C. F. Liang D. Bucurescu A. Płochocki 《The European Physical Journal A - Hadrons and Nuclei》2000,8(4):451-454
The decay of the T
1/2 = 420 ns isomer in 151Er has been reinvestigated. The multipolarities of the decaying transitions have been established by measuring the electron
conversion coefficients. An I
π
= 67/2− assignment is proposed for this isomer with a π[h
112/4
d
32/1
d
52/−1]⊗ν[f
7/2
h
9/2
h
112/−1] configuration. 相似文献
73.
G. Brida M. Genovese M. G. A. Paris F. Piacentini E. Predazzi E. Vallauri 《Optics and Spectroscopy》2007,102(1):90-97
The propagation of pulses of the pump and its second harmonic in a quadratically nonlinear medium whose linear properties are characterized by a negative refractive index at the pump frequency and by a positive refractive index at the harmonic frequency is considered theoretically. In the case of a low intensity of the interacting waves, the pump and second-harmonic pulses propagate in the opposite directions, but sufficiently powerful pulses can form a simulton—a solitary two-frequency wave propagating in a certain direction as a single whole. Solutions to a set of equations are found which describe the steady-state propagation of a solitary wave and of a nonlinear periodic (cnoidal) wave. 相似文献
74.
A. Porzio V. DAuria P.Aniello M.G.A. Paris S. Solimeno 《Optics and Lasers in Engineering》2007,45(4):463
We present a continuous variable quantum communication protocol based on bright continuous-wave twin-beams generated by a type-II OPO. Intensity correlation between the beams is used in conjunction with a binary randomization of polarization to guarantee security and reveal eavesdropping actions. The scheme presented is asymmetric. Bob (the receiver) retains one of the beams and sends the other one to Alice after a random rotation of its polarization. The cryptographic key elements are encoded through amplitude modulation by Alice, who sends back her beam to Bob after a second rotation of the polarization. Eventually, the beams are detected by Bob after a further random polarization rotation. The security of the system and the possibility of revealing the eavesdropping action in the case of an individual attack are demonstrated by evaluating the bit error rates. 相似文献
75.
76.
V. Repän M. Laan P. Paris J. Aarik V. Sammelselg 《Czechoslovak Journal of Physics》1999,49(2):217-224
In the paper the results of experimental study of negative corona in a point – plane gap in a dust-free air flow at atmospheric pressure are presented. Both the low current mode (LCM) of the discharge and Trichel pulses are externally triggered by UV light. Close to the inception voltage of Trichel pulses short-duration current spikes appear besides the steady component of the LCM which indicates to the switch-on of Fowler-Nordheim type emission mechanism. At the inception voltage spike – Trichel pulse transition is recorded. The influence of dielectric layers at the cathode on the discharge parameters is discussed. 相似文献
77.
Ericka Santacruz Gabriela Huelgas Sandra K. Angulo Virginia M. Mastranzo Simón Hernández-Ortega Judit A. Aviña Eusebio Juaristi Cecilia Anaya de Parrodi Patrick J. Walsh 《Tetrahedron: Asymmetry》2009,20(24):2788-2794
New chiral thioureas 1–8 containing 1,2-ethylendiamine or trans-1,2-diaminocyclohexane as the carbon skeleton, and containing an (S)-α-phenylethyl group have been prepared (79–98% yield). Thioureas 1–8 were used as ligands for the zinc-based catalyzed asymmetric hydrosilylation of acetophenone with polymethylhydrosiloxane (PMHS). The best result was achieved with monothiourea 1 (up to 75% ee), in toluene and a catalyst load of 5 mol %. 相似文献
78.
Sara Bogialli Cecilia CiampanellaRoberta Curini Antonio Di CorciaAldo Laganà 《Journal of chromatography. A》2009,1216(40):6810-6815
A simple and rapid method able to determine residues of erythromycin A, tylosin and tilmicosin in whole eggs is presented here. The analytical protocol involves a one-step extraction followed by liquid chromatography (LC)–tandem mass spectrometry. Analytes were extracted from 1 g of egg spiked with an internal standard (josamycin) with acetonitrile. In terms of accuracy, matrix effect and ion signal stability, no extract cleanup was found to be necessary. After partial solvent removal, the final extract was injected into the LC column. Extraction was effective, since absolute recovery of the analyte in egg at their maximum residue limit (MRL) level was 85–102%. Estimated limits of quantification (S/N = 10) were 0.2–0.5 ng/g. Based on the EU Commission Decision 2002/657/EC, the method was in-house validated in terms of ruggedness, specificity, linearity, within-laboratory reproducibility, decision limit (CCα) and detection capability (CCβ). The within-laboratory reproducibility, expressed as RSD (n = 18 at the MRL levels), was not higher than 13%. After validation, a short study on EA depletion in eggs was conducted after administration of this drug to laying hens. 相似文献
79.
80.
Daniel C. Steigerwald Bardia Soltanzadeh Aritra Sarkar Cecilia C. Morgenstern Richard J. Staples Babak Borhan 《Chemical science》2021,12(5):1834
Intermolecular asymmetric haloamination reactions are challenging due to the inherently high halenium affinity (HalA) of the nitrogen atom, which often leads to N-halogenated products as a kinetic trap. To circumvent this issue, acetonitrile, possessing a low HalA, was used as the nucleophile in the catalytic asymmetric Ritter-type chloroamidation of allyl-amides. This method is compatible with Z and E alkenes with both alkyl and aromatic substitution. Mild acidic workup reveals the 1,2-chloroamide products with enantiomeric excess greater than 95% for many examples. We also report the successful use of the sulfonamide chlorenium reagent dichloramine-T in this chlorenium-initiated catalytic asymmetric Ritter-type reaction. Facile modifications lead to chiral imidazoline, guanidine, and orthogonally protected 1,2,3 chiral tri-amines.Intermolecular haloamination reactions are challenging due to the high halenium affinity of the nitrogen atom. This is circumvented by using acetonitrile as an attenuated nucleophile, resulting in an enantioselective halo-Ritter reaction. 相似文献