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1.
R. Gerbaldo G. Ghigo G. Giunchi L. Gozzelino F. Laviano E. Mezzetti 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(3):297-300
We present results from an extended magneto-optical (MO) analysis of two samples cut from high-density pellets of MgB2. The first sample was studied in order to show that no matter how large the sample is and despite the bulk granularity, the
material enters into a critical state in a crystal-like fashion. The second sample was chosen for the quantitative analysis.
A numerical approach based on an inverted 2D Biot-Savart model was used to calculate the current paths across the homogeneous
polycrystalline bulk, as well as in the vicinity and across some morphological defects. Local current densities in the homogeneous
part were estimated as a function of the applied magnetic field at different temperatures, in three regimes: below full penetration,
at full penetration and above full penetration, respectively. A hypothesis of interpretation of the apparent absence of magnetic
granularity inside the polycrystalline microstructure is presented. It is related to a critical state likely reached by a
network of strongly coupled Josephson junctions.
Received 31 May 2001 and Received in final form 5 December 2001 相似文献
2.
3.
Sunto Fissata una superficie algebrica liscia X sopra un campo algebricamente chiuso e di caratteristica 0, e una curva ridotta C su X, si introduce, per ogni -upla di numeri naturali m1,..., m, uno schema W=W(C, m1,..., m), parametrizzante le curve del sistema lineare ¦C¦ con punti multipli ordinari di molteplicità almeno m1,..., m. Si studia W in relazione con la configurazione delie singolarità e delle componenti irriducibili di C. Si prova in particolare un teorema di «virtuale connessione», che permette di stabilire l'esistenza di curve irriducibili in alcuni di tali schemi W.
Membro del G.N.S.A.G.A. del C.N.R. 相似文献
Membro del G.N.S.A.G.A. del C.N.R. 相似文献
4.
Dominik Huber P. G. Anil Kumar Paul S. Pregosin Igor S. Mikhel Antonio Mezzetti 《Helvetica chimica acta》2006,89(8):1696-1715
Chloride abstraction from the half‐sandwich complexes [RuCl2(η6‐p‐cymene)(P*‐κP)] ( 2a : P* = (Sa,R,R)‐ 1a = (1Sa)‐[1,1′‐binaphthalene]‐2,2′‐diyl bis[(1R)‐1‐phenylethyl)]phosphoramidite; 2b : P* = (Sa,R,R)‐ 1b = (1Sa)‐[1,1′‐binaphthalene]‐2,2′‐diyl bis[(1R)‐(1‐(1‐naphthalen‐1‐yl)ethyl]phosphoramidite) with (Et3O)[PF6] or Tl[PF6] gives the cationic, 18‐electron complexes dichloro(η6‐p‐cymene){(1Sa)‐[1,1′‐binaphthalene]‐2,2′‐diyl {(1R)‐1‐[(1,2‐η)‐phenyl]ethyl}[(1R)‐1‐phenylethyl]phosphoramidite‐κP}ruthenium(II) hexafluorophosphate ( 3a ) and [Ru(S)]‐dichloro(η6‐p‐cymene){(1Sa)‐[1,1′‐binaphthalene]‐2,2′‐diyl {(1R)‐1‐[(1,2‐η)‐naphthalen‐1‐yl]ethyl}[(1R)‐1‐(naphthalen‐1‐yl)ethyl]phosphoramidite‐κP)ruthenium(II) hexafluorophosphate ( 3b ), which feature the η2‐coordination of one aryl substituent of the phosphoramidite ligand, as indicated by 1H‐, 13C‐, and 31P‐NMR spectroscopy and confirmed by an X‐ray study of 3b . Additionally, the dissociation of p‐cymene from 2a and 3a gives dichloro{(1Sa)‐[1,1′‐binaphthalene]‐2,2′‐diyl [(1R)‐(1‐(η6‐phenyl)ethyl][(1R)‐1‐phenylethyl]phosphoramidite‐κP)ruthenium(II) ( 4a ) and di‐μ‐chlorobis{(1Sa)‐[1,1′‐binaphthalene]‐2,2′‐diyl [(1R)‐1‐(η6‐phenyl)ethyl][(1R)‐1‐phenylethyl]phosphoramidite‐κP}diruthenium(II) bis(hexafluorophosphate) ( 5a ), respectively, in which one phenyl group of the N‐substituents is η6‐coordinated to the Ru‐center. Complexes 3a and 3b catalyze the asymmetric cyclopropanation of α‐methylstyrene with ethyl diazoacetate with up to 86 and 87% ee for the cis‐ and the trans‐isomers, respectively. 相似文献
5.
Alessandro Passera Prof. Dr. Antonio Mezzetti 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(1):193-197
The bis(carbonyl) manganese(I) complex [Mn(CO)2( 1 )]Br ( 2 ) with a chiral (NH)2P2 macrocyclic ligand ( 1 ) catalyzes the asymmetric transfer hydrogenation of polar double bonds with 2-propanol as the hydrogen source. Ketones (43 substrates) are reduced to alcohols in high yields (up to >99 %) and with excellent enantioselectivities (90–99 % ee). A stereochemical model based on attractive CH–π interactions is proposed. 相似文献
6.
Arnald Grabulosa Alberto Mannu Antonio Mezzetti Guillermo Muller 《Journal of organometallic chemistry》2012,696(26):4221-4228
A family of eight neutral, pseudotetrahedral piano-stool ruthenium complexes C, of the type [RuCl2(p-cymene)(PArPhR)] (Ar = 1-naphthyl, 9-phenanthryl and 2-biphenylyl; R = Me, i-Pr, OMe, –CH2SiMe3 and –CH2SiPh3) have been prepared and characterised, including the X-ray crystal structure for C6 (Ar = 2-biphenylyl; R = i-Pr). These complexes catalyse the asymmetric hydrogen transfer reaction of acetophenone in refluxing 2-propanol in the presence of potassium tert-butoxyde, reaching full conversions and up to 45% ee after 24 h towards the S enantiomer of 1-phenylethanol. Cationic complexes formed upon treatment of C with one equivalent of AgSbF6 or (Et3O)PF6 are active in the cyclopropanation reaction of styrene and α-methylstyrene by ethyl diazoacetate. Low to moderate conversions (up to 58%), diastereoselectivities (up to 40% de), and moderate enantioselectivities (up to 69% ee) have been found. For both reactions, bulky complexes and C6 in particular lead to the best results. 相似文献
7.
[RuCl2(PPh3)3] reacts with thallium(I) fluoride to give either [Tl(mu-F)3Ru(PPh3)3] (1) or [Tl(mu3-F)(mu2-Cl)2Ru2(mu2-Cl)(mu2-F)(PPh3)4] (2) depending on the excess of TlF used. Both 1 and 2 were fully characterized, including X-ray structure determinations. Complex 1 reacts with dihydrogen to form the known ruthenium hydride complex [Ru(H)2(H2)(PPh3)3] upon hydrogenolysis of the Ru-F bond. The reaction of 1 with activated alkyl bromides (R-Br) gives the corresponding alkyl fluorides and the trinuclear complex [Tl(mu3-F)(mu2-F)(mu2-X)Ru2(mu2-Br)(mu2-F)(PPh3)4] (X=Br, F) (3), whose structure closely resembles that of 2. However, 1 is not active as catalyst for the nucleophilic fluorination of R-Br in the presence of thallium fluoride. The effect of the bridging coordination mode of fluoride on the Ru-F bond is discussed in terms of the HSAB principle, which suggests a more general model for predicting the stability of d6 and d8 complexes containing hard ligands (such as fluoro, oxo, and amido). 相似文献
8.
F. Demichelis G. Kaniadakis E. Mezzetti P. Mpawenayo A. Tagliaferro E. Tresso P. Rava G. Della Mea 《Il Nuovo Cimento D》1987,9(4):393-408
Summary Two sets ofa-SiC:H films were deposited by glow discharge in an Ar-SiH4-CH4 atmosphere to investigate the effect of a variable CH4/SiH4 ratio on the physical properties. The composition of the films was determined by resonant nuclear reaction and by Rutherford
backscattering measurements, the optical gap and the index of refraction by transmissivity measurements in the visible-UV-NIR
range, the bonding configuration by IR transmissivity measurements and the resistivity and the photo-conductivity by electrical
measurements in the dark and under a 500 W/m2 illumination. Results indicate that with increasing carbon content the refractive index decreases systematically over all
wavelengths, the energy gap increases, the dark resistivity increases, the bonding configuration becomes dominated by carbon-containing
chains and the structure more disordered.
Riassunto Sono stati realizzati film dia-SiC:H mediante glow-discharge in atmosfera Ar-SiH4-CH4 con differenti rapporti CH4/SiH4. La concentrazione di H nei film è stata determinate usando la reazione di risonanza1H(15N, αγ)12C ed il contenuto di carbonio mediante spettrometria Rutherford-backscattering. Da misure di trasmittanza e riflettanza nella zona UV-visibile-vicino IR sono state ricavate le costanti ottiche, l'indice di rifrazione, la costante dielettrica, il coefficiente di assorbimento e il gap ottico. Un esame delle bande degli spettri vibrazionali dei vari legami CH, CSi e SiH ottenuti mediante misure di trasmissione nell'IR ha fornito un'interpretazione sulla struttura dei film. Sono state anche realizzate misure di conduttività di buio e di fotoconduttività sotto illuminamento di 500 W/m2. I risultati indicano che all'aumentare del contenuto di carbonio l'indice di rifrazione diminuisce sistematicamente per tutte le lunghezze d'onda, il gap ottico aumenta, la conduttività di buio diminuisce e nella configurazione strutturale tendono a prevalere le catene contenenti il carbonio.
Резюме Ъыли осаждены две системы пленокa-SiC:H в атмосфере Ar-SiH4-CH4, чтобы исследовать переменного отношения CH4/SiH4 на физические свойства. Состав пленок определяется с помощью резонансных ядерных реакций и измерений обратного резерфордовского рассеяния. Также определяются оптичззкся щеяь и показатель преломления с помщяю иемерений пронисаемости в видимойультрафиолетовой-близкой инфракрасной области, конфигурацуя связи с помощью измерений инфракрасной проницаемости и удельное сопротивление и фотопроводимость с помошью єлектрических измерений в темноте м при освешении 500 Bt/M2. Полученные результаты покасывают, что с увеличением содержания углерода показатель преомления систематически уменьшается для всех длин волн, єнергетическая щель увеличивается, темновое сопротивление увеличивается, конфигурация связи становится доминирующей за счет углерод-содержащих цепочек и структура становится более разориентировнной.相似文献
9.
Tina Osswald Antonio Mezzetti Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(4):1388-1397
The like and unlike isomers of phosphoramidite (P*) ligands are found to react differently with iridium(I), which is a key to explaining the apparently inconsistent results obtained by us and other research groups in a variety of catalytic reactions. Thus, the unlike diastereoisomer (aR,S,S)‐[IrCl(cod)( 1 a )] ( 2 a ; cod=1,5‐cyclooctadiene, 1 a =(aR,S,S)‐(1,1′‐binaphthalene)‐2,2′‐diyl bis(1‐phenylethyl)phosphoramidite) forms, upon chloride abstraction, the monosubstituted complex (aR,S,S)‐[Ir(cod)(1,2‐η‐ 1 a ,κP)]+ ( 3 a ), which contains a chelating P* ligand that features an η2 interaction between a dangling phenyl group and iridium. Under analogous conditions, the like analogue (aR,R,R)‐ 1 a′ gives the disubstituted species (aR,R,R)‐[Ir(cod)( 1 a′ ,κP)2]+ ( 4 a′ ) with monodentate P* ligands. The structure of 3 a was assessed by a combination of X‐ray and NMR spectroscopic studies, which indicate that it is the configuration of the binaphthol moiety (and not that of the dangling benzyl N groups) that determines the configuration of the complex. The effect of the relative configuration of the P* ligand on its iridium(I) coordination chemistry is discussed in the context of our preliminary catalytic results and of apparently random results obtained by other groups in the iridium(I)‐catalyzed asymmetric allylic alkylation of allylic acetates and in rhodium(I)‐catalyzed asymmetric cycloaddition reactions. Further studies with the unlike ligand (aS,R,R)‐(1,1′‐binaphthalene)‐2,2′‐diyl bis{[1‐(1‐naphthalene‐1‐yl)ethyl]phosphoramidite} ( 1 b ) showed a yet different coordination mode, that is, the η4‐arene–metal interaction in (aS,R,R)‐[Ir(cod)(1,2,3,4‐η‐ 1 b ,κP)]+ ( 3 b ). 相似文献
10.
Summary A model for determination and optimization of the fundamental parameters defining the quality of amorphous solar cells in
which optical, electrical and recombination properties are specified is developed. It can be applied to any amorphous solar-cell
systems. This paper gives theoretical expressions and describes an iterative method of numerical calculation for the current
density of different cells. Results of computer calculations based on this model are presented.
Riassunto In questo lavoro si presenta un modello per la determinazione e l'ottimizzazione dei parametri fondamentali atti a definire la qualità delle celle solari amorfe, specificando le proprietà ottiche, elettriche e di ricombinazione. Esso può essere applicato a qualunque sistema di celle solari amorfe. Sono fornite le espressioni teoriche ed è descritto un metodo iterativo per il calcolo numerico della densità di corrente di alcuni tipi di celle. Sono anche presentati i risultati ottenuti da calcoli eseguiti col computer e basati su questo modello.相似文献