排序方式: 共有50条查询结果,搜索用时 46 毫秒
1.
光照与彩陶俑表面色变关系的实验研究 总被引:1,自引:0,他引:1
本文以秦彩俑表面色彩为研究对象,通过光照实验与色彩变化的色度测量,分析了光照引起彩俑颜料色变的规律,为秦彩俑这一大型重点文物的色彩保护提供了科学理论依据. 相似文献
2.
We give a self‐contained proof of the preservation theorem for proper countable support iterations known as “tools‐preservation”, “Case A” or “first preservation theorem” in the literature. We do not assume that the forcings add reals. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
3.
Linsinger TP Gawlik BM Trapmann S Lamberty A Emons H 《Analytical and bioanalytical chemistry》2004,378(5):1168-1174
Over the years, the nature of CRMs has changed considerably. Recently, more and more CRMs have been certified in their "natural" form, that is processed as little as possible, with analytes at their natural concentration level. This and the trend towards certified properties other than the concentrations of clearly defined molecules/elements have made guaranteeing stability of CRMs and estimating a shelf life an even more important issue for reference material producers than it has been before. One way to meet this challenge is to take more care in processing, storage and dispatch of CRMs. At IRMM, approximately 20 % of the RMs are stored at –20 °C or below and about 10% require cooled transportation. In addition, increased efforts for assessing stability are needed. Shelf lives are estimated using addition of an uncertainty component based on real-temperature stability studies rather than by accelerated stability studies. These pre-certification efforts are complemented by a stability-monitoring program, which at IRMM includes 80 % of the non-nuclear and non-isotopic materials. Although the costs for these efforts are high in absolute terms, they are only a minor and indispensable contribution to the total costs of CRM production. 相似文献
4.
《Operations Research Letters》2022,50(2):160-167
In this paper, sufficient conditions for preservation of several transform orders under a typical family of semiparametric distributions are made. The preservation properties are developed to compare mixture semiparametric distributions. Possible applications of the achieved results to compare scale family of distributions and also compare coherent systems with dependent but identical components and series and parallel systems with randomized number of components are provided. 相似文献
5.
We study quasi-periodic tori under a normal-internal resonance, possibly with multiple eigenvalues. Two non-degeneracy conditions play a role. The first of these generalizes invertibility of the Floquet matrix and prevents drift of the lower dimensional torus. The second condition involves a Kolmogorov-like variation of the internal frequencies and simultaneously versality of the Floquet matrix unfolding. We focus on the reversible setting, but our results carry over to the Hamiltonian and dissipative contexts. 相似文献
6.
We will construct several models where there are no strongly meager sets of size 20.
First author partially supported by NSF grant DMS 0200671.Second author partially supported by Israel Science Foundation and NSF grant DMS 0072560. Publication 807.
Mathematics Subject Classification (2000):03E15, 03E20 相似文献
7.
We show that the existential preservation theorem fails for two-variable first-order logic FO2. It is known that for all k ≥ 3, FOk does not have an existential preservation theorem, so this settles the last open case, answering a question of Andreka, van Benthem, and Németi. In contrast, we prove that the homomorphism preservation theorem holds for FO2. 相似文献
8.
Henni Vanda Yuntao Dai Erica G. Wilson Robert Verpoorte Young Hae Choi 《Comptes Rendus Chimie》2018,21(6):628-638
Natural deep eutectic solvents (NADESs) are defined as mixtures of certain molar ratios of natural compounds such as sugars, organic acids, amino acids, and organic bases that are abundant in organisms. The melting points of these mixtures are considerably lower than those of their individual ingredients and far below ambient temperature. The first publications on the NADES concept in 2011 created a great expectation regarding their potential as green solvents that could replace conventional organic solvents in a wide range of applications. This was largely because many of the drawbacks of conventional synthetic ionic liquids (ILs) and deep eutectic solvents (DESs), particularly their toxicity and environmental hazards, could be solved using NADESs. Throughout the last 7 years, the interest in NADESs has increased enormously as reflected by the exponential growth of the number of related publications. The research on NADESs has rapidly expanded particularly into the evaluation of the feasibility of their application in diverse fields such as the extraction of (targeted) bioactive compounds from natural sources, as media for enzymatic or chemical reactions, preservatives of labile compounds, or as vehicles of non–water-soluble compounds for pharmaceutical purposes. Along with the exploration of these potential applications, there have been a large number of other studies related to their physicochemical features, the search for new NADESs, the research into the interactions between NADES components or with solutes, the recovery of solutes from NADES solutions, and the ways of circumventing inherent problems of NADESs such as their high viscosity and the consequent difficulties in handling them. This article contains a review of the applications of NADESs as extraction solvents, reaction media, and preservative, providing also a perspective of their future. 相似文献
9.
The preservation of arsenic species in water samples is an indispensable method to avoid their changes during storage, if it is not possible to analyse them immediately. The aim of this investigation was to demonstrate the limitations of the suggested method by using phosphoric acid as a preservation agent. The samples remain stable for 3 months, even if they show evidence of high concentrations of iron or manganese. Critical is an increasing pH > 3. Theoretically, a precipitation of strengite (Fe3(PO4)2) could occur, which should be avoided. Phosphoric acid with a final concentration of 10 mM is recommended as a preservation agent, combined with keeping the samples cool (6 °C) and dark. Filtration of samples before preservation may be carried out with respect to the analytical aim to distinguish between the total and soluble fraction (without colloids). It was shown that filtered and non-filtered samples can be preserved by utilising the above mentioned scheme. 相似文献
10.
Archives of voice recordings could provide a source of information for voice scientists and clinicians interested in voice analysis and in cultural and historical changes of vocal styles and qualities. Large collections of sound recordings exist that could be used as databases for such inquiries, although no comprehensive list of such collections currently exists. A preliminary survey of major collections is presented. Voice scientists and voice archivists have many common areas of interest in the recording, reproduction, copying, and analysis of sound. The Recording and Research Center, as part of its ongoing research in establishment of standards for voice analysis, has begun an archive of laboratory recordings. A protocol for recording trained, normal, abnormal, and neurologically impaired voices is in development. This survey of sound archives will continue as well. 相似文献