排序方式: 共有156条查询结果,搜索用时 0 毫秒
141.
Ion Grosu Luminita Muntean Loïc Toupet Gerard Plé Monica Pop Mirela Balog Sorin Mager Elena Bogdan 《Monatshefte für Chemie / Chemical Monthly》2002,133(5):631-641
Summary. The synthesis and stereochemistry of new 1,3-dioxane derivatives of 1,4-diacetylbenzene are reported. The anancomeric structure
of these compounds, the axial orientation of the aryl group for both 1,3-dioxane rings, and the cis and trans isomerism of some of these compounds is discussed considering data of conformational analysis, NMR investigations, and single
crystal X-ray diffractometry.
Received September 12, 2001. Accepted (revised) November 5, 2001 相似文献
142.
AbstractThermochromic inks, materials that change color at a certain temperature, are increasingly used on papers and other materials in the areas of design, commercials, and security printing. Pseudo-estrogen bisphenol A (BPA) may be one of their main compounds present in mass fractions of up to several percent. In this work, the mass fractions of BPA in thermochromic prints on seven types of paper were determined. Migration of BPA from the surface of the thermochromic print to artificial sweat solutions was investigated as well. Total amount of BPA in papers with thermochromic prints was determined by an HPLC-UV method with ultrasonic-assisted extraction in methanol developed and validated in this work. Total amount of BPA, which ranged from 0.126 to 0.778?mg/g, was compared with the amounts extracted under the same conditions in two artificial human sweat solutions, which differed in chemical composition, ionic strength, and pH-value. Mass fractions of BPA extracted with artificial sweat solutions were from 0.047 to 0.175?mg/g with respect to the mass of the paper. On average, the mass fraction of BPA was four times less when extracted with artificial sweat solutions than the maximal amount extracted with methanol. The amounts of extracted BPA raise a concern of health risk through dermal exposure to BPA from thermochromic prints on paper. 相似文献
143.
144.
145.
146.
Mirela Kohr G. P. Raja Sekhar Wolfgang L. Wendland 《Mathematical Methods in the Applied Sciences》2008,31(9):1065-1097
In this paper we obtain an indirect boundary integral method in order to prove existence and uniqueness of the classical solution to a boundary value problem for the Stokes–Brinkman-coupled system, which describes an unbounded Stokes flow past a porous body in terms of Brinkman's model. Therefore, one assumes that the flow inside the body is governed by the continuity and Brinkman equations. Some asymptotic results in both cases of large and, respectively, of low permeability are also obtained. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
147.
On the transmission problems for the Oseen and Brinkman systems on Lipschitz domains in compact Riemannian manifolds 下载免费PDF全文
Robert Gutt Mirela Kohr Cornel Pintea Wolfgang L. Wendland 《Mathematische Nachrichten》2016,289(4):471-484
The purpose of this work is to show the well‐posedness in L2‐Sobolev spaces of the Poisson‐transmission problem for the Oseen and Brinkman systems on complementary Lipschitz domains in a compact Riemannian manifold. The Oseen system appears as a perturbation of order one of the Stokes system, given in terms of the Levi‐Civita connection, while the Brinkman system is a zero order perturbation of the Stokes system. The technical details of this paper rely on the layer potential theory for the Stokes system and the invertibility of some perturbed zero index Fredholm operators by a first order differential operator given in terms of the Levi‐Civita connection. The compactness of this differential operator requires to restrict ourselves to low dimensional compact Riemannian manifolds. 相似文献
148.
In this paper we use the method of boundary integral equations to treat some transmission problems for Brinkman-type operators on Lipschitz and C 1 domains in Riemannian manifolds. 相似文献
149.
Different partial hypergroupoids are associated with binary relations defined on a set H. In this paper we find sufficient and necessary conditions for these hypergroupoids in order to be reduced hypergroups. Given two binary relations ρ and σ on H we investigate when the hypergroups associated with the relations ρ∩σ, ρ∪σ and ρσ are reduced. We also determine when the cartesian product of two hypergroupoids associated with a binary relation is a reduced hypergroup. 相似文献
150.
Mihaela Alexandra Bogdan Simona Bungau Delia Mirela Tit Dana Carmen Zaha Aurelia Cristina Nechifor Tapan Behl Dorina Chambre Andreea Ioana Lupitu Lucian Copolovici Dana Maria Copolovici 《Molecules (Basel, Switzerland)》2021,26(14)
Chemical composition, antioxidant capacity, and antimicrobial activity of lavender essential oils (LEOs) extracted from three different varieties of Lavandula angustifolia Mill. (1-Moldoveanca 4, 2-Vis magic 10, and 3-Alba 7) have been determined. These plants previously patented in the Republic of Moldova were cultivated in an organic agriculture system in the northeastern part of Romania and then harvested in 3 consecutive years (2017–2019) to obtain the essential oils. From the inflorescences in the complete flowering stage, the LEOs were extracted by hydrodistillation. Then, their composition was analyzed by gas chromatography coupled with mass spectrometry (GC-MS) and by Fourier Transformed Infrared spectroscopy (FT-IR). The major identified constituents are as follows: linalool (1: 32.19–46.83%; 2: 29.93–30.97%; 3: 31.97–33.77%), linalyl acetate (1: 17.70–35.18%; 2: 27.55–37.13%; 3: 28.03–35.32%), and terpinen-4-ol (1: 3.63–7.70%; 2: 3.06–7.16%; 3: 3.10–6.53%). The antioxidant capacity as determined by ABTS and DPPH assays indicates inhibition, with the highest activity obtained for LEO var. Alba 7 from 2019. The in vitro antimicrobial activities of the LEOs and combinations were investigated as well, by using the disk diffusion method and minimum inhibitory concentration (MIC) against the Gram-positive bacterial strain Staphylococcus aureus (ATCC 6538), Gram-negative Pseudomonas aeruginosa (ATCC 27858), Escherichia coli (ATCC 25922), the yeast Candida albicans (ATCC 10231), and clinical isolates. Our results have shown that LEOs obtained from the three studied varieties of L. angustifolia manifest significant bactericidal effects against tested microorganisms (Staphylococcus aureus and Escherichia coli), and antifungal effects against Candida albicans. The mixture of LEOs (Var. Alba 7) and geranium, respectively, in tea tree EOs, in different ratios, showed a significant enhancement of the antibacterial effect against all the studied strains, except Pseudomonas aeruginosa. 相似文献