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941.
Peter Šafář Jozefína Žúžiová Štefan Marchalín Eva Tóthová Nadežda Prónayová Ľubomír Švorc Viktor Vrábel Adam Daïch 《Tetrahedron: Asymmetry》2009,20(5):626-634
Chiral tetra- and hexahydro[1]benzothieno[2,3-f]indolizines 3–5, 9, and 11 were synthesized easily from benzo[b]thiophene-2-carboxaldehyde (1) and (S)-glutamic acid (2) in good overall yields and both high enantio- and diastereomeric purities. Applying a diastereoselective reductive desulfurization of benzo[b]thiophene followed by lactam reduction, epimeric alcohols 4a and 4b were readily converted into (7R or S,8aS)-phenylindolizidinols 6a,c. During these studies, the reduction of benzothienoindolizines 3–5, 9, 11, and 12, was investigated and the results obtained are also discussed. 相似文献
942.
Loïc de Carlan Didier Baltès Jean-Marc Bordy Josiane Daures Frank Delaunay Aimé Ostrowsky Soizic Sorel 《Accreditation and quality assurance》2009,14(11):613-618
The relevant standard quantity for radiation therapy is the absorbed dose to water. This quantity refers to the amount of
energy locally absorbed in a small volume of water divided by the mass of this volume. The aim of this paper is to present
a short overview on the establishment of traceability to national standards of absorbed doses delivered to patients in radiation
therapy. The approach used at LNE-LNHB, the French national metrology laboratory for ionizing radiation, to determine the
reference value of absorbed dose to water is presented and the chain of traceability from the reference value to the treatment
of the patient is described. 相似文献
943.
Loïc Sorbier Elisabeth Rosenberg Claude Merlet Xavier Llovet 《Mikrochimica acta》2000,132(2-4):189-199
We examine the influence of the sample porosity on the X-ray emission from mesoporous alumina bombarded with kilovolt electrons.
Experimental results show that there is a loss of X-rays (Al Kα and O Kα) from those samples when compared to a fully dense
mono-crystalline alumina (sapphire), which depends on the X-ray line, the measurement time and the embedding medium. Both
geometrical and charging effects may be responsibl e for this signal loss. Monte Carlo simulations of the X-ray intensity
emitted from porous alumina, using different models to describe sample porosity, show that the geometrical effect of porosity
itself cannot account for the X-ray loss. Charge trapping effect and/or its combination with porosity is therefore expected
to be the major cause of the signal loss. 相似文献
944.
We consider a tree-shaped network of vibrating elastic strings, with feedback acting on the root of the tree. Using the d’Alembert
representation formula, we show that the input-output map is bounded, i.e. this system is a well-posed system in the sense
of G. Weiss (Trans. Am. Math. Soc. 342 (1994), 827–854). As a consequence we prove that the strings networks are not exponentially stable in the energy space. Moreover,
we give explicit polynomial decay estimates valid for regular initial data. 相似文献
945.
N. Safta A. Sakly H. Mejri M. A. Zaïdi 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,53(1):35-38
In this paper, we present a theoretical study of the quantized electronic states in Cd1-xZnxS quantum dots. The shape of the confining
potential, the subband energies and their eigen envelope wave functions are
calculated by solving a one-dimensional Schr?dinger equation.
Electrons and holes are assumed to be confined in dots having a flattened
cylindrical geometry with a finite barrier height at the boundary. Optical
absorption measurements are used to fit the bandgap edge of the
Cd1-xZnxS nanocrystals. An analysis of the electron band
parameters has been made as a function of Zn composition. Two main features
were revealed: (i) a multiplicity in Cd1-xZnxS quantum dots with
different crystalline sizes has been found to fit accurately experimental
data in the composition range 0 ≤x ≤0.2; (ii) the fit did not,
however, show a multiplicity for x higher than 0.4. On the other hand, we
have calculated the energy level structure of coupled Cd1-xZnxS
semiconductor quantum dots using the tight-binding approximation. As is
found the Zn composition x = 0.4 is expected to be the most favorable to
give rise a superlattice behavior for the Cd1-xZnxS quantum dots
studied. 相似文献
946.
The theory of Nambu–Poisson structures on manifolds is extended to the context of Lie algebroids in a natural way based on the derived bracket associated with the Lie algebroid differential. A new way of combining Nambu–Poisson structures and triangular Lie bialgebroids is described in this work. Also, we introduce the concept of a higher order Dirac structure on a Lie algebroid. This allows to describe both Nambu–Poisson structures and Dirac structures on manifolds in the same setting. 相似文献
947.
Journal of Evolution Equations - 相似文献
948.
Quinton L Gilles N Smargiasso N Kiehne A De Pauw E 《Journal of the American Society for Mass Spectrometry》2011,22(11):1891-1897
This study describes the structural characterization of a totally new family of peptides from the venom of the snake green
mamba (Dendroaspis angusticeps). Interestingly, these peptides differ in several points from other already known mamba toxins. First of all, they exhibit
very small molecular masses, ranging from 1.3 to 2.4 kDa. The molecular mass of classical mamba toxins is in the range of
7 to 25 kDa. Second, the new peptides do not contain disulfide bonds, a post-translational modification commonly encountered
in animal toxins. The third difference is the very high proportion of proline residues in the sequence accounting for about
one-third of the sequence. Finally, these new peptides reveal a carbohydrate moiety, indicating a glycosylation in the sequence.
The last two features have made the structural characterization of the new peptides by mass spectrometry a real analytical
challenge. Peptides were characterized by a combined use of MALDI- TOF/TOF and nanoESI-IT-ETD experiments to determine not
only the peptide sequence but also the composition and the position of the carbohydrate moiety. Anyway, such small glycosylated
and proline-rich toxins are totally different from any other known snake peptide and form, as a consequence, a new family
of peptides. 相似文献
949.
Le Pleux L Pellegrin Y Blart E Odobel F Harriman A 《The journal of physical chemistry. A》2011,115(20):5069-5080
A series of multiporphyrin clusters has been synthesized and characterized in which there exists a logical gradient for either energy or electron transfer between the porphyrins. A central free-base porphyrin (FbP), for example, is equipped with peripheral zinc(II) porphyrins (ZnP) which act as ancillary light harvesters and transfer excitation energy to the FbP under visible light illumination. Additional energy-transfer steps occur at the triplet level, and the series is expanded by including magnesium(II) porphyrins and/or tin(IV) porphyrins as chromophores. Light-induced electron transfer is made possible by incorporating a gold(III) porphyrin (AuP(+)) into the array. Although interesting by themselves, these clusters serve as control compounds by which to understand the photophysical processes occurring within a three-stage dendrimer comprising an AuP(+) core, a second layer formed from four FbP units, and an outer layer containing 12 ZnP residues. Here, illumination into a peripheral ZnP leads to highly efficient electronic energy transfer to FbP, followed by charge transfer to the central AuP(+). Charge recombination within the resultant charge-shift state is intercepted by secondary hole transfer to the ZnP, which occurs with a quantum yield of around 20%. The final charge-shift state survives for some microseconds in fluid solution at room temperature. 相似文献
950.
The intramolecular reaction of secondary amines with tethered alkenes using NIS was studied, which gave insight into the kinetic vs. thermodynamic control of the iodoaminocyclization and the regioselectivity of the aziridinium ring-opening reactions, and led to functionalized piperidines. 相似文献