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141.
Several samples of hematite, one a natural specimen, are considered in order to study the specific effect of the morphology on the magnetic structure and especially on the Morin transition. It seemed that mainly the weak-ferromagnetic contribution is affected by the morphology, as well as the transition temperature and region. 相似文献
142.
F. De Corte M. Dejaeger S. M. Hossain D. Vandenberghe A. De Wispelaere P. Van den Haute 《Journal of Radioanalytical and Nuclear Chemistry》2005,263(3):659-663
Summary Recently, in our laboratory an intercomparison was made of methods for the annual radiation dose determination (assessed from direct radiation counting and/or from the measurement of the K, Th and U contents) applied to luminescence dating of loess and sand sediment, whereby the emphasis was put on their precision and accuracy. Although these properties are important, the duration of the measurement is also a practically relevant aspect. Indeed, direct alpha, beta and gamma-counting can last a week or more, and the determination of K, Th and U via NAA can take up to three weeks to enable proper gamma-ray spectrometry of the long-lived 233 Th/233Pa. Therefore, in the present work the performance of k0-based epiCd-NAA (ENAA, with irradiation under a cadmium cover) when applied to sediments is compared to k0-NAA. As concluded, with the use of k0-ENAA the analysis turnaround time could be considerably reduced from ~3 weeks to ~ 2.5days, while maintaining satisfactory accuracy, precision and determination sensitivity. 相似文献
143.
A series of vulpinic acids differing by the aryl or heteroaryl groups placed in the ester α-position were prepared by Suzuki-Miyaura cross-coupling involving a common iodide and the corresponding aryl boronates. The preparation of the iodide precursor from (+)-dimethyl l-tartrate required four steps: the esterification of one hydroxyl group, a Dieckmann cyclization allowing the construction of the tetronic acid moiety, a dehydration leading to the installation of the exocyclic double bond and lastly, an N-iodosuccinimide-mediated iodation of the alkene obtained. 相似文献
144.
145.
Marnix Vangheluwe Thierry Verbiest Guy Koeckelberghs 《Journal of polymer science. Part A, Polymer chemistry》2008,46(14):4817-4829
New functionalized, (a)chiral poly(phenylene‐alt‐bithiophene)s were prepared and their chiroptical properties were studied. The polymers were prepared by a Stille coupling reaction and were functionalized with protected carboxylic acid and amino functions (tert‐butyl ester and BOC respectively). The polymers are present as well conjugated rigid rods in solution, which (chirally) aggregate in nonsolvents and film. In a next step, the protecting group (tert‐butyl ester in case of the carboxylic acid) was removed. Aggregation of this polymer can be induced by addition of amines; if chiral amines are used, the polymer chains chirally stack. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4817–4829, 2008 相似文献
146.
We continue the study of G. Castelnuovo on the group of birational transformations of the complex plane that fix each point
of a curve of genus > 1 ; we use adjoint linear system of the curve as Castelnuovo does. We prove that these groups are abelian,
and that these are either finite, of order 2 or 3, or conjuguate to a subgroup of the de Jonquières group. We show also that
these results do not generalise to curves of genus ≤ 1.
*Partiellement soutenu par le CNPq-Brasil et la Section de Mathématiques de l'Université de Genève. 相似文献
147.
148.
Florent Benaych-Georges Thierry Cabanal-Duvillard 《Journal of Theoretical Probability》2010,23(2):447-465
Recently, Ben Arous and Voiculescu considered taking the maximum of two free random variables and brought to light a deep
analogy with the operation of taking the maximum of two independent random variables. We present here a new insight on this
analogy: its concrete realization based on random matrices giving an interpolation between classical and free settings. 相似文献
149.
Julien Barré Freddy Bouchet Thierry Dauxois Stefano Ruffo 《Journal of statistical physics》2005,119(3-4):677-713
We discuss a method to solve models with long-range interactions in the microcanonical and canonical ensemble. The method closely follows the one introduced by R.S. Ellis, Physica D 133:106 (1999), which uses large deviation techniques. We show how it can be adapted to obtain the solution of a large class of simple models, which can show ensemble inequivalence. The model Hamiltonian can have both discrete (Ising, Potts) and continuous (HMF, Free Electron Laser) state variables. This latter extension gives access to the comparison with dynamics and to the study of non-equilibrium effects. We treat both infinite range and slowly decreasing interactions and, in particular, we present the solution of the α-Ising model in one-dimension with 0
⩽ α < 1. 相似文献
150.
R. M. Persoons E. De Grave P. M. A. De Bakker R. E. Vandenberghe H. H. A. Smit 《Hyperfine Interactions》1990,54(1-4):661-666
Spectra for three members of the spinel system Mg1+t
Fe2(1−t)Ti
t
O4, witht=0.5, 0.6 and 0.7, all showing re-entrant spin-glass-like behavior, were collected at temperatures down to 1.6 K and decomposed
in A- and B-site components, both having a broad distribution of hyperfine fields. The numerical results suggest a more pronounced
spin canting on A sites as compared to B sites. From spectra recorded at 4.2 K in an applied field of 6 T, and analysed with
a sum of two bi-dimensional distributions of hyperfine fields and canting angles, the existence of reversed A-site spins is
evidenced. The number of such spins increases with increasing magnetic dilution.
Senior Research Associate at the National Fund for Scientific Research, Belgium 相似文献