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排序方式: 共有142条查询结果,搜索用时 15 毫秒
101.
102.
火焰原子吸收光谱法测定鱼腥草、西洋参和茯苓中的铜含量 总被引:1,自引:0,他引:1
用硝酸-高氯酸混合酸(4∶1)消化鱼腥草、西洋参和茯苓,在波长324.8nm处,利用火焰原子吸收光谱法测定鱼腥草、西洋参和茯苓中铜的含量。线性回归方程为A=0.1708C 0.0004,相关系数r=0.9997,线性范围为0—5μg/mL,检出限为0.0035μg/mL,测定结果的相对标准偏差为0.09%,加标回收率为98.0%—104.2%。 相似文献
103.
V. Bellani C. Bocchi T. Ciabattoni S. Franchi P. Frigeri P. Galinetto M. Geddo F. Germini G. Guizzetti L. Nasi M. Patrini L. Seravalli G. Trevisi 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,56(3):217-222
This work deals with the strain relaxation mechanism in InGaAs metamorphic buffers (MBs) grown on GaAs substrates and overgrown
by InAs quantum dots (QD). The residual strain is measured by using Raman scattering and X-ray diffraction, both in Reciprocal
Space Map and in single ω-2θ scan modes (ω and θ being the incidence angles on the sample surface and on the scattering planes,
respectively). By relating the GaAs-like longitudinal optical phonon frequency ωLO of InGaAs MBs to the in-plane residual strain ε measured by means of photoreflectance (PR), the linear ε-vs.-ωLO working curve is obtained. The results of Raman and XRD measurements, as well as those obtained by PR, are in a very satisfactory
agreement. The respective advantages of the techniques are discussed. The measurements confirm that strain relaxation depends
on the thickness t of the buffer layer following a ~t-1/2 power law, that can be explained by an energy-balance model. 相似文献
104.
S. Franchi A. Bosacchi E. Gombia R. Mosca A. Carnera A. Gasparotto 《Journal of Crystal Growth》1995,150(1-4):261-265
We correlate the Si concentration measured by secondary ion mass spectrometry (SIMS) and the net donor concentration in GaAs:Si grown by atomic layer molecular beam epitaxy (ALMBE); Si was supplied during: (a) both the As and the Ga subcycles, (b) the As subcycle, and (c) the Ga subcycle; the layers were grown at temperatures in the 300-530°C range. The results show that Si incorporation and its compensation depend on the Si-supply scheme and that the extent of compensation decreases with the growth temperature. We also study the deep levels in the ALMBE GaAs grown under the above conditions. Our results show the occurrence of M1, M3 and M4 levels with concentrations that are: (i) essentially independent of both the Si supply scheme and the ALMBE growth temperature, (ii) close to those of MBE GaAs grown at 600°C, and (iii) up to 2 orders of magnitude lower than that of GaAs prepared by molecular beam epitaxy (MBE) at similar temperatures. 相似文献
105.
Alice Franchi Marco Pedrazzi Alessandro Alberto Casazza Enrico Millo Gianluca Damonte Annalisa Salis Nara Liessi Franco Onofri Antonella Marte Silvia Casagrande Roberta De Tullio Patrizia Perego Monica Averna 《Molecules (Basel, Switzerland)》2020,25(19)
We have recently demonstrated that bioactive molecules, extracted by high pressure and temperature from olive pomace, counteract calcium-induced cell damage to different cell lines. Here, our aim was to study the effect of the same extract on murine cortical neurons, since the preservation of the intracellular Ca2+-homeostasis is essential for neuronal function and survival. Accordingly, we treated neurons with different stimuli in order to evoke cytotoxic glutamatergic activation. In these conditions, the high-pressure and temperature extract from olive pomace (HPTOPE) only abolished the effects of N-methyl-d-aspartate (NMDA). Particularly, we observed that HPTOPE was able to promote the neuron rescue from NMDA-induced cell death. Moreover, we demonstrated that HPTOPE is endowed with the ability to maintain the intracellular Ca2+-homeostasis following NMDA receptor overactivation, protecting neurons from Ca2+-induced adverse effects, including aberrant calpain proteolytic activity. Moreover, we highlight the importance of the extraction conditions used that, without producing toxic molecules, allow us to obtain protecting molecules belonging to proanthocyanidin derivatives like procyanidin B2. In conclusion, we can hypothesize that HPTOPE, due to its functional and nontoxic properties on neuronal primary culture, can be utilized for future therapeutic interventions for neurodegeneration. 相似文献
106.
Lorenzo Gualandi Paola Franchi Elisabetta Mezzina Stephen M. Goldup Marco Lucarini 《Chemical science》2021,12(24):8385
Biradical spin probes can provide detailed information about the distances between molecules/regions of molecules because the through-space coupling of radical centres, characterised by J, is strongly distance dependent. However, if the system can adopt multiple configurations, as is common in supramolecular complexes, the shape of the EPR spectrum is influenced not only by J but also the rate of exchange between different states. In practice, it is often hard to separate these variables and as a result, the effect of the latter is sometimes overlooked. To demonstrate this challenge unequivocally we synthesised rotaxane biradicals containing nitronyl nitroxide units at the termini of their axles. The rotaxanes exchange between the available biradical conformations more slowly than the corresponding non-interlocked axles but, despite this, in some cases, the EPR spectra of the axle and rotaxane remain remarkably similar. Detailed analysis allowed us to demonstrate that the similar EPR spectral shapes result from different combinations of J and rates of conformational interconversion, a phenomenon suggested theoretically more than 50 years ago. This work reinforces the idea that thorough analysis must be performed when interpreting the spectra of biradicals employed as spin probes in solution.Using a rotaxane biradical, we unambiguously demonstrate the need consider both J and rate of conformational interconversion carefully when interpreting the spectra of such systems when they are employed as spin probes in solution. 相似文献
107.
Mileo E Franchi P Gotti R Bendazzoli C Mezzina E Lucarini M 《Chemical communications (Cambridge, England)》2008,(11):1311-1313
The combined use of selected nitroxides and EPR spectroscopy has been proved to be suitable for studying the partitioning rate of a given substrate in cyclodextrin-micelle systems. 相似文献
108.
G. Muoz-Matutano B. Aln J. Martínez-Pastor L. Seravalli P. Frigeri S. Franchi 《Superlattices and Microstructures》2008,43(5-6):494
Photoluminescence and excitation of photoluminescence spectroscopy have been performed for two kinds of single InAs self-assembled quantum dots grown on GaAs. The presence of unintentional impurities (donors and acceptors) offers the possibility to switch from negative to positively charged excitons by selectively exciting impurity related optical transitions. 相似文献
109.
We consider groups Γ of automorphisms of a groupG acting by means of power automorphisms on the factors of a normal series inG with lengthm. We show that [G, Γ] is nilpotent with class at mostm and that this bound is best possible. Moreover, such a Γ is parasoluble with paraheight at most 1/2m(m+3)+1, provided Γ′ is periodic. We give best possible bound in the case where the series is a central one. 相似文献
110.
In this paper, we fully extend to the Heisenberg group endowed with its intrinsic Carnot-Carathéodory metric and perimeter
the classical De Giorgi's rectifiability divergence theorems.
Received: 27 March 2000 / Revised version: 13 December 2000 / Published online: 24 September 2001 相似文献