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排序方式: 共有254条查询结果,搜索用时 15 毫秒
91.
The effective action formulation of lattice QCD is extended to incorporate baryons. At strong coupling we find a generalized σ model where the baryons obtain their mass via a non-vanishing vacuum expectation value 〈¯ΦΦ〉. The SU(3) effective potential is worked out for Susskind fermions taking into account the influence of the baryons, and the results are compared with the U(3) theory. The large-N behavior of the SU(N) theory is studied as well. A loop expansion method is proposed for dealing with general multi-component baryon fields in both Susskind's and Wilson's fermion formulations. 相似文献
92.
Jaap J.D. de Jong Theodora D. Tiemersma-Wegeman Wesley R. Browne Kingo Uchida Ben L. Feringa 《Tetrahedron》2008,64(36):8324-8335
The synthesis and characterisation of a series of chiral and achiral low molecular weight organogelators (LMWGs) based on bis-amide substituted dithienylethene photochromic switches is reported. The LMWGs gelate a range of solvents depending on the specific functionalisation of the hydrogen bonding amide groups. In mixtures of chiral and achiral LMWGs the stereochemical outcome of the chiral aggregation is determined by the chiral LMWG molecules in most cases. However, for the first time we demonstrate that the stereochemical outcome of the aggregation can be influenced by the achiral LWMG molecules in some cases. Furthermore specific π-π (and/or van der Waals) interactions of chiral LMWGs 1-3o with the solvent allow the solvent to influence the control of chirality of aggregation. This influence of the solvent has a dramatic effect on whether four- or two-gel states are available. 相似文献
93.
Bergwerff JA Lysova AA Espinosa-Alonso L Koptyug IV Weckhuysen BM 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(8):2363-2374
An indirect magnetic resonance imaging (MRI) method has been developed to determine in a noninvasive manner the distribution of paramagnetic Co2+ complexes inside Co/Al2O3 catalyst extrudates after impregnation with Co2+/citrate solutions of different pH and citrate concentrations. UV/Vis/NIR microspectroscopic measurements were carried out simultaneously to obtain complementary information on the nature of the Co2+ complexes. In this way, it could be confirmed that the actual distribution of Co2+ inside the extrudates could be derived from the MRI images. By combining these space- and time-resolved techniques, information was obtained on both the strength and the mode of interaction between [Co(H2O)6]2+ and different Co2+ citrate complexes with the Al2O(3) support. Complexation of Co2+ by citrate was found to lead to a stronger interaction of Co with the support surface and formation of an eggshell distribution of Co2+ complexes after impregnation. By addition of free citrate and by changing the pH of the impregnation solution, it was possible to obtain the rather uncommon egg-yolk and egg-white distributions of Co2+ inside the extrudates after impregnation. In other words, by carefully altering the chemical composition and pH of the impregnation solution, the macrodistribution of Co2+ complexes inside catalyst extrudates could be fine-tuned from eggshell over egg white and egg yolk to uniform. 相似文献
94.
Retra K Bleijerveld OB van Gestel RA Tielens AG van Hellemond JJ Brouwers JF 《Rapid communications in mass spectrometry : RCM》2008,22(12):1853-1862
One of the major challenges in lipidomics is to obtain as much information about the lipidome as possible. Here, we present a simple yet universal high-performance liquid chromatography/tandem mass spectrometry (HPLC/MS/MS) method to separate molecular species of all phospholipid classes in one single run. The method is sensitive, robust and allows lipid profiling using full scan mass spectrometry, as well as lipid class specific scanning in positive and negative ionisation mode. This allows high-throughput processing of samples for lipidomics, even if different types of MS analysis are required. Excellent separation of isobaric and even isomeric species is achieved, and original levels of lyso-lipids can be determined without interference from lyso-lipids formed from diacyl species by source fragmentation. As examples of application of this method, more than 400 phospholipid species were identified and quantified in crude phospholipid extracts from rat liver and the parasitic helminth Schistosoma mansoni. 相似文献
95.
Two-dimensional photoelectron spectroscopy has been used to supply process-specific labels to multiphoton ionization events. Employing these tags, the authors can construct excitation and photoelectron spectra along predefined excitation routes in the neutral manifold and ionization routes to the ionic manifold from one single two-dimensional photoelectron spectrum. These results offer a novel way to elucidate the vibronic and dynamic properties of excited and ionic states. 相似文献
96.
97.
98.
Joost Rooze Evgeny V. Rebrov Jaap C. Schouten Jos T.F. Keurentjes 《Ultrasonics sonochemistry》2013,20(1):1-11
The physics and chemistry of nonlinearly oscillating acoustic cavitation bubbles are strongly influenced by the dissolved gas in the surrounding liquid. Changing the gas alters among others the luminescence spectrum, and the radical production of the collapsing bubbles. An overview of experiments with various gas types and concentration described in literature is given and is compared to mechanisms that lead to the observed changes in luminescence spectra and radical production. The dissolved gas type changes the bubble adiabatic ratio, thermal conductivity, and the liquid surface tension, and consequently the hot spot temperature. The gas can also participate in chemical reactions, which can enhance radical production or luminescence of a cavitation bubble. With this knowledge, the gas content in cavitation can be tailored to obtain the desired output. 相似文献
99.
There are parallels between de Bruijn’s early work in analysis and that of the author. However, Dick’s work soon became much broader and deeper. While the present paper reviews several topics of common interest, its main content is a short version of Dick’s important article related to Riemann’s Hypothesis, entitled ‘The roots of trigonometric integrals’ [N.G. de Bruijn, The roots of trigonometric integrals, Duke Math. J. 17 (1950) 197–226]. The associated ‘de Bruijn–Newman constant’ is also discussed. 相似文献
100.
Hoek-van den Hil EF Beekmann K Keijer J Hollman PC Rietjens IM van Schothorst EM 《Analytical and bioanalytical chemistry》2012,402(3):1389-1392
Flavonoids are bioactive food compounds with potential lipid-lowering effects. Commercially available enzymatic assays are
widely used to determine free fatty acid (FFA) and triglyceride (TG) levels both in vivo in plasma or serum and in vitro in
cell culture medium or cell lysate. However, we have observed that various flavonoids interfere with peroxidases used in these
enzymatic assays, resulting in incorrect lower FFA and TG levels than actually present. Furthermore, addition of isorhamnetin
or the major metabolite of the flavonoid quercetin in human and rat plasma, quercetin-3-O-glucuronide, to murine serum also resulted in a significant reduction of the detected TG levels, while a trend was seen for
FFA levels. It is concluded that when applying these assays, vigilance is needed and alternative analytical methods, directly
assessing FFA or TG levels, should be used for studying the biological effects of flavonoids on FFA and TG levels. 相似文献