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We obtain a simple derivation of Korzhik's result on the burst distribution of a linear code. 相似文献
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Escoubet S Gastaldi S Timokhin VI Bertrand MP Siri D 《Journal of the American Chemical Society》2004,126(39):12343-12352
Thiols mediate the radical isomerization of allylic amines into enamines. The reaction results in the cleavage of the allylic C-N bond, after treatment with aqueous HCl. The mechanism involves the abstraction of an allylic hydrogen alpha to nitrogen by thiyl radical, followed by a return hydrogen transfer from the thiol to the carbon gamma to nitrogen in the intermediate allylic radical. The scope and limitations of the reaction with respect to the nature of the thiol, to the structure of the allylic chain, and to the nature of the substituents at nitrogen were investigated. The experimental results were interpreted on the ground of DFT calculations of the C-Halpha BDE in the starting allylic amines, and of the C-Hgamma BDE in the resulting enamines. The efficiency of the initial hydrogen transfer is the first requirement for the reaction to proceed. A balance must be found between the S-H BDE and the two above-mentioned C-H BDEs. The incidence of stereoelectronic factors was analyzed through NBO calculations performed on the optimized geometries of the starting allylic amines. Additional calculations of the transition structures and subsequent tracing of the reaction profiles were performed for the abstraction of Halpha from both the allyl and the prenyl derivatives by p-TolS(*). The latter allowed us to estimate the rate constant for the abstraction of hydrogen by thiyl radical from an N-prenylamine and an N-allylamine. 相似文献
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R. Bracco E. Canessa M. R. Cimberle C. Ferdeghini M. Putti A. S. Siri 《Il Nuovo Cimento D》1987,9(3):289-300
Summary We have performed quantum Hall effect measurements on commercial low-mobilityn-channel MOSFETs. The channel resistancevs. electron concentration has the expected oscillating behaviour and gives the quantized values for the Hall resistance, at
least in the region of higher mobility. One class of the tested samples gave a surprising behaviour, both in QHE and in field
effect mobility measurements: this is thought to be due to uncontrolled differences in the diffusion zones at the interface
between the channel and the contacts. In particular, we attribute the deformation of the QHE curves to the onset of a thermoelectromotive
force which is present in the electron gas even if the sample is isothermal. A clear evidence for thermoelectric effects is
given by measurements made on a high-quality Hall geometry MOSFET.
Riassunto Abbiamo eseguito misure di effetto Hall quantistico su MOSFET commerciali di bassa mobilità a canalen. Le curve di resistenza di canale in funzione della tensione di gate presentano l'atteso andamento oscillante e danno i valori quantizzati, almeno nelle regioni di maggiore mobilità. Una categoria di campioni ha mostrato andamenti sorprendenti, sia in misure di QHE che in misure di mobilità per effetto di campo: riteniamo che ciò sia dovuto a differenze incontrollabili nelle regioni di diffusione alle interfacce tra i contatti e il canale. In particolare, attribuiamo la deformazione delle curve di QHE all'instaurarsi di forze termoelettromotrici, che sono presenti nel gas elettronico nonostante i campioni siano isotermi. Misure eseguite su un MOSFET a geometria Hall di alta qualità forniscono una chiara evidenza dell'esistenza di effetti termoelettrici.
Резюме Проводятся измерения квантового эффекта Холла на коммерческих MOSFET с малой подвижностью вn-канале. Зависмость сопротивления канала от концентрации электронов обнаруживает осцилляторное поведение и дает квантованные значения сопротивления Холла, по крайней мере, в области высокой подвижности. Один класс исследованных образцов обнаруживает удивительное поведение при измерении квантового эффекта Холла и при измерении зависимости подвижности от поля. Такое поведение, по-видимому, обусловлено неконтролируемыми различиями в зонах диффузии между каналом и контактами. В частности, мы приписываем деформацию кривых квантового эффекта Холла возникновению термоэлектродвижущей силы, которая присутствует в электронном газе, даже в изотермических образцах. Приводятся подтверждения для термоэлектрических эффектов, проводя измерения эффекта Холла в MOSFET с высокой подвижностью.相似文献
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Nechab M Campolo D Maury J Perfetti P Vanthuyne N Siri D Bertrand MP 《Journal of the American Chemical Society》2010,132(42):14742-14744
The cascade rearrangement of chiral enediynes 1c-e, involving successively 1,3-proton shift, Saito-Myers cyclization, 1,5-hydrogen atom transfer, and intramolecular coupling of the resulting biradical, proceeded at 80 °C to form tri- and tetracyclic heterocycles possessing a quaternary stereogenic center with a very high level of memory of chirality. 相似文献
18.
The uncontrolled accumulation of biological materials on the surface of medical devices through protein adsorption or cell adhesion causes adverse biological reactions in the living host system, leading to complications. In this study, poly(ethylene glycol) (PEG) is successfully grafted onto polyurethane (PU) surfaces by using a new strategy through a simple and efficient transurethanization reaction. The PEG hydroxyl group is deprotonated and then reacted with the PU surface to provide antiadhesive hydrophilic surfaces in a single step. Surface analysis techniques proved the grafting to be efficient and the formation of a hydrophilic polymeric layer at the surface of PU. Biological assays showed that the surface modification induced lower protein adsorption, cell, platelet, and bacterial adhesion than untreated surfaces, showing a potential for biomedical applications. 相似文献
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Dynamics of Fluorescent Dyes Attached to G‐Quadruplex DNA and their Effect on FRET Experiments 下载免费PDF全文
Siri Søndergaard Dr. Mikayel Aznauryan Emil K. Haustrup Prof. Birgit Schiøtt Prof. Victoria Birkedal Prof. Ben Corry 《Chemphyschem》2015,16(12):2562-2570
FRET spectroscopy is a promising approach for investigating the dynamics of G‐quadruplex DNA folds and improving the targeting of G‐quadruplexes by potential anticancer compounds. To better interpret such experiments, classical and replica‐exchange molecular dynamics simulations and fluorescence‐lifetime measurements are used to understand the behavior of a range of Cy3‐based dyes attached to the 3′ end of G‐quadruplex DNA. The simulations revealed that the dyes interact extensively with the G‐quadruplex. Identification of preferred dye positions relative to the G‐quadruplex in the simulations allows the impact of dye–DNA interactions on FRET results to be determined. All the dyes show significant deviations from the common approximation of being freely rotating and not interacting with the host, but one of the Cy3 dye analogues is slightly closer to this case. 相似文献