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961.
962.
963.
Volker Schurig 《Journal of chromatography. A》2009,1216(10):1723-1736
The retention increment approach is described which quantifies the association equilibria of a selectand and a selector in complexation and inclusion chromatography. A thermodynamic treatment of enantioselectivity based on retention phenomena in chromatography including entropy/enthalpy compensation and the isoenantioselective temperature is advanced. Kinetic parameters of enantiomerization are discussed. Non-linear effects, both existent and elusive, are described and proposed, respectively. The enantioselectivity pertaining to catalysis vs. chromatography is compared and a unified nomenclature is proposed. Through an educational effort, this account is aimed at providing a deeper insight into chemoselective aspects of chromatography thereby stimulating further research of both established and speculative phenomena of the most intriguing manifestation of chemoselectivity, that is, of enantioselectivity. 相似文献
964.
Summary Magnetoelastic wave amplitude, a, was measuredvs. the temperature during thermal cycles in Metglas 2826. When the Curie temperature,T
C, has been reached, theA value vanishes due to the fall of the magnetoelastic coupling in the paramagnetic state. This allows evaluation of theT
c temperature. The latter increases after the iterated thermal treatments while the magnetic anisotropyK
u decreases. Also theA amplitude, measured at room temperature after the subsequent thermal treatments, shows an increasing behaviour. The values
ofK
u
,T
c andA approach saturation after the same number of thermal cycles; this suggests that the structural relaxation produced by annealing
is the microscopic mechanism governing all the three physical quantities. In particular we explain the connection betweenK
u andA by means of the longitudinal magnetostriction.
Riassunto L'ampiezza delle onde magnetoelastiche,A, è stata misurata in funzione della temperatura eseguendo cicli termici nel Metglas 2826. Raggiunta la temperatura di Curie,T C l'ampiezzaA si annulla a causa della transizione dell'accoppiamento magnetoelastico nello stato paramagnetico. Ciò ci mette in grado di misurare la temperaturaT C; quest'ultima aumenta in seguito ai ripetuti trattamenti termici mentre l'anisotropia magneticaK u diminuisce. Anche l'ampiezzaA, misurata a temperatura ambiente dopo i trattamenti termici, mostra un andamento crescente. I valori diK u,T c eA tendono alla saturazione dopo lo stesso numero di cicli termici; ciò suggerisce che il rilassamento strutturale prodotto dalla ricottura è il meccanismo microscopico che regola le tre grandezze fisiche menzionate. In particolare noi mostriamo cheK u eA sono legati dalla magnetostrizione longitudinale.
Резюме Измеряется зависимость амплитуды магнитноупругой волны,A, от температуры в течение температурных циклов в металлическом стекле 2826. При достижении температуры Кюри,T c, величинаA обращается в нуль из-за уменьшения магнитноупругой связи в парамагнитном состоянии. Это позволяет оценить темпаратуру Кюри,T c. Температура Кюри увеличивается после повторных температурных обработок, тогда как магнитная анизотропияK u уменьшается. Также отмечается увеличение амплитудыA, измеренной при комнатной температуре после последовательных температурных обработок. ВеличиныK u,T c иA приближаются к насьщению после одинакового числа температурных циклов. Это результат предполагает, что структурная релаксация, обусловленная отжигом, представляет микроскопический механизм, определяющий все три физические величины. В частности, мы объсняем связь междуK u иA с помощью продольной магнитострикции.相似文献
965.
966.
Magnetic susceptibility and heat capacity due to spin-state excitations in LaCoO3 were analyzed with an irregular solution model composed of Co3+ ions in the low-spin ground state and in the high-spin excited state. An energy-levels diagram proposed by Ropka and Radvanskii
[1] was used for the high-spin excited state. This analysis showed that the entropy of mixing is less than that of ideal solutions
and the enthalpy of mixing is negative, indicating that the high-spin Co ions are arranged as far apart as possible. 相似文献
967.
This study focuses on certain aspects of the quantitivity of adsorptive solid phase microextraction when applied in the form of on-fibre derivatisation with O-(2,3,4,5,6)-pentafluorobenzyl-hydroxylamine hydrochloride (PFBHA) for the determination of carboniles in air samples of relevance in the atmosphere. The study was performed in the high-volume outdoor atmospheric simulation chambers (EUPHORE) located in Valencia (Spain). At short sampling times, the adsorption profiles obtained when only benzaldehyde was inserted in the chamber coincided with those obtained when other carbonylic compounds were also introduced at the same concentration, and this was also the case when the concentration of all the gaseous mixture components was increased considerably from one experiment to another. In a number of experiments applying different conditions, it was proven that all the extraction profiles belonged to the same regression when the fibre responses were plotted against the concentration-time product. A number of calibrations were obtained for benzaldehyde introduced in the chamber alone and in a mixture with three other carboniles at similar concentration values. A statistical test is applied to confirm that they all belonged to the same regression since they shared homogeneous variances. After these tests, the method of SPME on-fibre derivatisation for the determination of carboniles was considered to be safely applicable to quantification. Moreover, the concentration levels at which certain unwanted effects, i.e., displacement, saturation and competition, were observed are a few orders of magnitude higher than their occurrence levels in atmospheric processes. 相似文献
968.
Summary The anisotropy induced by magnetic annealing in a transversal field is correlated with the Young modulus, the longitudinal
magnetostriction and the magnetoelastic coupling coefficient. Subsequently it is shown that the value of the anisotropy deriving
from directional short-range ordering,k
DSRO, can be calculated in an original manner by means of the mentioned parameters. Thisk
DSRO evaluation is in increasing agreement with its directly measured value, when the magnetic-annealing effects approach saturation.
The magnetic heat treatment influences can be described by a small rise of the internal stress, in comparison with conventional
annealing, and a large increase of longitudinal magnetostriction.
Riassunto L'anisotropia indotta da trattamento termico in campo magnetico trasversale si correla con il modulo di elasticità lineare, la magnetostrizione longitudinale ed il coefficiente di accoppiamento magnetoelastico, in provini nastriformi di metallo amorfo. Successivamente si dimostra che l'anisotropia magnetica prodotta per ordine direzionale a corto raggio,k DSRO, può essere calcolata in modo originale attraverso i menzionati parametri fisici. La valutazione, cosí ottenuta in maniera semiteorica, è in crescente accordo con i risultati della misura diretta dik DSRO quanto piú gli effetti del trattamento termomagnetico si avvicinano alla loro saturazione. Detti effetti possono essere sintetizzati in una presenza di stress residui, lievemente maggiore rispetto a quanto avviene dopo il solo trattamento termico, ed in un grande aumento del coefficiente di magnetostrizione longitudinale.
Резюме Анизотропия, индуцированная отжигом в поперечном магнитном поле, коррелирует с модулем Юнга, продольной магнитострикции и коэффициентом магнитоупрутой связи. Показывается, что величина анизотропии, полученная из ориентационного короткодействующего упорядочения,k DSRO, может быть вычислена с помощью вышеуказанных параметров. Эта оценкаk DSRO согласуется с непосредственно измеряемой, величиной, когда происходит насыщение эффектов магнитного отжига. Влияние магнитного теплового эффекта может быть описано с помощвю небольшого увеличения внутреннего напряжения, по сравнению с обычным отжигом, и большого увеличения продольной магнитострикции.相似文献
969.
Summary Brief pressure changes take often place within a liquid chromatography column, e.g., during sample injection. It is shown
that pressure jumps may cause local changes in the composition of a mixed effluent and the rise of system peaks in the chromatogram.
This is a consequence of the dependence of sorption equilibrium on pressure. 相似文献
970.