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51.
Carpino LA Abdel-Maksoud AA Ionescu D Mansour EM Zewail MA 《The Journal of organic chemistry》2007,72(5):1729-1736
Of the three theoretically possible, Bsmoc-related, naphthothiophene sulfone-based amino-protecting groups, the two most readily available derivatives, the alpha- and beta-Nsmoc analogues, have been examined as substitutes for the Bsmoc residue in cases where the latter lead to oily protected amino acids or amino acid fluorides. All of the naphtho systems gave easily handled solid amino acid derivatives. The intermediate sulfone alcohol 11 used as the key reagent for introduction of the alpha-Nsmoc protecting group was readily made from alpha-tetralone (Scheme 1). The corresponding beta-analogue 17 was made similarly on a small scale, but due to the high cost of beta-tetralone, an alternate route involving reaction of rhodanine with alpha-naphthaldehyde was used for large-scale work (Scheme 2). All proteinogenic amino acids were converted to their alpha- and beta-Nsmoc derivatives. Deblocking studies showed that the reactivity toward deblocking by piperidine followed the order alpha-Nsmoc > Bsmoc > beta-Nsmoc. 1H NMR experiments showed that deblocking of the two new systems was mechanistically similar to that previously established for the Bsmoc derivative in that the reaction is initiated by Michael addition to the beta-carbon atom of the alpha,beta-unsaturated sulfone system. Application of alpha- and beta-Nsmoc amino acids to the solid-phase synthesis of two model peptides was examined. An advantage of the alpha-Nsmoc system over the long-known Bsmoc system proved to be the milder conditions needed for the deblocking step relative to the Bsmoc case, which is itself more readily deblocked than the classic Fmoc analogue. 相似文献
52.
van Miltenburg J. C. Mathot V. B. F. van Ekeren P. J. Ionescu L. D. 《Journal of Thermal Analysis and Calorimetry》1999,56(3):1017-1023
The heat capacity of a very low-density polyethylene copolymer (VLDPE) was measured between 10 and 410 K. Using two sets of
literature data for the fully crystalline and the fully amorphous states, crystallinities were calculated as a function of
temperature. During the stabilisation periods in the melting process no equilibrium is reached, because of an exothermic process,
which is attributed to (re)crystallization. Values for the enthalpy of melting and for the heat capacity of the liquid are
given.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
53.
We prove global well-posedness and scattering in H 1 for the defocusing nonlinear Schrödinger equationson the hyperbolic spaces \({\mathbb{H}^d}\), d ≥ 2, for exponents \({\sigma \in (0, 2/(d-2))}\). The main unexpected conclusion is scattering to linear solutions in the case of small exponents σ; for comparison, on Euclidean spaces scattering in H 1 is not known for any exponent \({\sigma \in (1/d, 2/d]}\) and is known to fail for \({\sigma \in (0, 1/d]}\). Our main ingredients are certain noneuclidean global in time Strichartz estimates and noneuclidean Morawetz inequalities.
相似文献
$\left\{\begin{array}{ll}(i\partial_t+\Delta_g)u=u|u|^{2\sigma};\\u(0)=\phi,\end{array}\right.$
54.
The goal of the paper is to prove a perturbative result, concerning the uniqueness of Kerr solutions, a result which we believe
will be useful in the proof of their nonlinear stability. Following the program started in Ionescu and Klainerman (Invent.
Math. 175:35–102, 2009), we attempt to remove the analyticity assumption in the the well known Hawking-Carter-Robinson uniqueness
result for regular stationary vacuum black holes. Unlike (Ionescu and Klainerman in Invent. Math. 175:35–102, 2009), which
was based on a tensorial characterization of the Kerr solutions, due to Mars (Class. Quant. Grav. 16:2507–2523, 1999), we
rely here on Hawking’s original strategy, which is to reduce the case of general stationary space-times to that of stationary
and axi-symmetric spacetimes for which the Carter-Robinson uniqueness result holds. In this reduction Hawking had to appeal
to analyticity. Using a variant of the geometric Carleman estimates developed in Ionescu and Klainerman (Invent. Math. 175:35–102,
2009), in this paper we show how to bypass analyticity in the case when the stationary vacuum space-time is a small perturbation
of a given Kerr solution. Our perturbation assumption is expressed as a uniform smallness condition on the Mars-Simon tensor.
The starting point of our proof is the new local rigidity theorem established in Alexakis et al. (Hawking’s local rigidity
theorem without analyticity. , 2009). 相似文献
55.
Alim Mohammad A. Bak Tadeusz Atanacio Armand J. Ionescu Mihail Kennedy Brendan Price William S. Du Plessis Johan Pourmahdavi Maryam Zhou Meifang Torres Allan Nowotny Janusz 《Ionics》2017,23(12):3517-3531
Ionics - This work reports the effect of tantalum (0.1–1 at.% Ta) on the photocatalytic performance of TiO2 annealed at 1373 and 1673 K in air. It was shown that addition of... 相似文献
56.
M. A. Idris Z. A. Z. Jamal S. B. Jamaludin N. Nafarizal A. K. Othman M. Z. Sahdan M. P. Zakaria M. Ionescu J. Nowotny 《Ionics》2014,20(4):581-592
The present work considers the application of oxide semiconductors in the conversion of solar energy into the chemical energy required for water purification (removal of microbial cells and toxic organic compounds from water) and the generation of solar hydrogen fuel by photoelectrochemical water splitting. The first part of this work considers the concept of solar energy conversion by oxide semiconductors and the key performance-related properties, including electronic structure, charge transport, flat band potential and surface properties, which are responsible to the reactivity and photoreactivity of oxides with water. The performance of oxide systems for solar energy conversion is briefly considered in terms of an electronic factor. The progress of research in the formation of systems with high performance is considered in terms of specific aspects of nanotechnology, leading to the formation of systems with high performance. The nanotechnology approach in the development of high-performance photocatalysts is considered in terms of the effect of surface energy associated with the formation of nanostructured system on the formation of surface structures that exhibit outstanding properties. The unresolved problems that should be tackled in better understanding of the effect of nanostructures on properties and performance of oxide semiconductors in solar energy conversion are discussed. This part is summarised by a list of unresolved problems of crucial importance in the formation of systems with enhanced performance. This work also formulates the questions that must be addressed in order to overcome the hurdles in the formation of oxide semiconductors with high performance in water purification and the generation of solar fuel. The research strategy in the development of oxide systems with high performance, including photocatalysts for solar water purification and photoelectrodes for photoelectrochemical water splitting, is considered. The considerations are focused on the systems based on titanium dioxide of different defect disorder as well as its solid solutions and composites. 相似文献
57.
Emine Kayhan Ravi Mohan Prasad Dr. Alexander Gurlo Dr. Oktay Yilmazoglu Dr. Jörg Engstler Dr. Emanuel Ionescu Songhak Yoon Prof. Dr. Anke Weidenkaff Prof. Dr. Jörg J. Schneider 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(47):14996-15003
Low‐layered, transparent graphene is accessible by a chemical vapor deposition (CVD) technique on a Ni‐catalyst layer, which is deposited on a <100> silicon substrate. The number of graphene layers on the substrate is controlled by the grain boundaries in the Ni‐catalyst layer and can be studied by micro Raman analysis. Electrical studies showed a sheet resistance (Rsheet) of approximately 1435 Ω per □, a contact resistance (Rc) of about 127 Ω, and a specific contact resistance (Rsc) of approximately 2.8×10?4 Ω cm2 for the CVD graphene samples. Transistor output characteristics for the graphene sample demonstrated linear current/voltage behavior. A current versus voltage (Ids–Vds) plot clearly indicates a p‐conducting characteristic of the synthesized graphene. Gas‐sensor measurements revealed a high sensor activity of the low‐layer graphene material towards H2 and CO. At 300 °C, a sensor response of approximately 29 towards low H2 concentrations (1 vol %) was observed, which is by a factor of four higher than recently reported. 相似文献
58.
Manickam Minakshi Pritam Singh David Ralph Dominique Appadoo Mark Blackford Mihail Ionescu 《Ionics》2012,18(6):583-590
The structural characteristics of olivine-type lithium orthophosphate Li(Mg0.5Ni0.5)PO4 synthesized via solid-state reaction have been studied using X-ray diffraction, ion beam technique, scanning electron microscopy, infrared spectroscopy, transmission electron microscopy and energy dispersive X-ray analysis. The parent LiNiPO4 compound can be synthesized in olivine structure without any evidence of secondary phases as impurities. The structural quality of the parent LiNiPO4 in the absence of secondary component phases resulted in the formation of hexagonal closed packed structure. The olivine analogue compound containing mixed M (M?=?Mg, Ni) cations, Li(Mg0.5Ni0.5)PO4 contained Li3PO4 as a second phase upon synthesis, however a carbothermal reduction method produced a single-phase compound. The redox behaviour of carbon-coated Li(Mg0.5Ni0.5)PO4 cathode in aqueous lithium hydroxide as the electrolyte showed reversible lithium intercalation. 相似文献
59.
Delia Ionescu 《PAMM》2006,6(1):813-814
A new approach to nonlinear RLC circuits, which is based on the geometric Birkhoffian formalism, is described in this note. The configuration space and a special Pfaffian form, called Birkhoffian, are obtained from the constitutive relations of the involved resistors, inductors and capacitors and from Kirchhoff's laws. No assumptions are placed upon the topology of the network. Properties of the corresponding Birkhoffian such as its regularity, or its dissipativeness, are discussed in this context. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
60.