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排序方式: 共有1053条查询结果,搜索用时 31 毫秒
1.
Dr. Antonio M. Rodríguez Dr. Pilar Prieto Prof. Antonio de la Hoz Prof. Ángel Díaz-Ortiz D. Raúl Martín Prof. José I. García 《ChemistryOpen》2015,4(3):308-317
The aim of this work was to determine the parameters that have decisive roles in microwave-assisted reactions and to develop a model, using computational chemistry, to predict a priori the type of reactions that can be improved under microwaves. For this purpose, a computational study was carried out on a variety of reactions, which have been reported to be improved under microwave irradiation. This comprises six types of reactions. The outcomes obtained in this study indicate that the most influential parameters are activation energy, enthalpy, and the polarity of all the species that participate. In addition to this, in most cases, slower reacting systems observe a much greater improvement under microwave irradiation. Furthermore, for these reactions, the presence of a polar component in the reaction (solvent, reagent, susceptor, etc.) is necessary for strong coupling with the electromagnetic radiation. We also quantified that an activation energy of 20–30 kcal mol−1 and a polarity (μ) between 7–20 D of the species involved in the process is required to obtain significant improvements under microwave irradiation. 相似文献
2.
Design and development of a two‐dimensional system based on hydrophilic and reversed‐phase liquid chromatography with on‐line sample treatment for the simultaneous separation of excreted xenobiotics and endogenous metabolites in urine
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Diego García‐Gómez Encarnación Rodríguez‐Gonzalo Rita Carabias‐Martínez 《Biomedical chromatography : BMC》2015,29(8):1190-1196
In the present work we describe a two‐dimensional liquid chromatographic system (2D‐LC) with detection by mass spectrometry (MS) for the simultaneous separation of endogenous metabolites of clinical interest and excreted xenobiotics deriving from exposure to toxic compounds. The 2D‐LC system involves two orthogonal chromatographic modes, hydrophilic interaction liquid chromatography (HILIC) to separate polar endogenous metabolites and reversed‐phase (RP) chromatography to separate excreted xenobiotics of low and intermediate polarity. Additionally, the present proposal has the novelty of incorporating an on‐line sample treatment based on the use of restricted access materials (RAMs), which permits the direct injection of urine samples into the system. The work is focused on the instrumental coupling, studying all possible options and attempting to circumvent the problems of solvent incompatibility between the RAM device and the two chromatographic columns, HILIC and RP. The instrumental configuration developed, RAM‐HILIC‐RPLC‐MS/MS, allows the simultaneous assessment of urinary metabolites of clinical interest and excreted compounds derived from exposure to toxic agents with minimal sample manipulation. Thus, it may be of interest in areas such as occupational and environmental toxicology in order to explore the possible relationship between the two types of compounds. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
3.
The notion of Kuratowski convergence is applied to describe a kind of convergence in the context of holomorphic functions. We associate it to a convenient topology, explore its relation with the compact-open topology, thus providing a new set theoretic point of view of this classic topology, and present it in the framework of set-valued mappings. 相似文献
4.
Let a text of u characters over an alphabet of size σ be compressible to n phrases by the LZ78 algorithm. We show how to build a data structure based on the Ziv–Lempel trie, called the LZ-index, that takes 4nlog2n(1+o(1)) bits of space (that is, 4 times the entropy of the text for ergodic sources) and reports the R occurrences of a pattern of length m in worst case time O(m3logσ+(m+R)logn). We present a practical implementation of the LZ-index, which is faster than current alternatives when we take into consideration the time to report the positions or text contexts of the occurrences found. 相似文献
5.
We consider the problems of (1) longest common subsequence (LCS) of two given strings in the case where the first may be shifted by some constant (that is, transposed) to match the second, and (2) transposition-invariant text searching using indel distance. These problems have applications in music comparison and retrieval. We introduce two novel techniques to solve these problems efficiently. The first is based on the branch and bound method, the second on bit-parallelism. Our branch and bound algorithm computes the longest common transposition-invariant subsequence (LCTS) in time O((m2+loglogσ)logσ) in the best case and O((m2+logσ)σ) in the worst case, where m and σ, respectively, are the length of the strings and the size of the alphabet. On the other hand, we show that the same problem can be solved by using bit-parallelism and thus obtain a speedup of O(w/logm) over the classical algorithms, where the computer word has w bits. The advantage of this latter algorithm over the present bit-parallel ones is that it allows the use of more complex distances, including general integer weights. Since our branch and bound method is very flexible, it can be further improved by combining it with other efficient algorithms such as our novel bit-parallel algorithm. We experiment on several combination possibilities and discuss which are the best settings for each of those combinations. Our algorithms are easily extended to other musically relevant cases, such as δ-matching and polyphony (where there are several parallel texts to be considered). We also show how our bit-parallel algorithm is adapted to text searching and illustrate its effectiveness in complex cases where the only known competing method is the use of brute force. 相似文献
6.
Gonzalo Contreras 《Bulletin of the Brazilian Mathematical Society》1995,26(2):211-228
We find some estimates for the derivatives of equilibrium states of subshifts of finite type. We prove the differentiability (with respect to the potential) of integrals of certain discontinuous functions for the equilibrium state of a potential.research supported by CNPq, Brazil 相似文献
7.
Roberto D. Galvão Luis Gonzalo Acosta Espejo Brian Boffey 《Annals of Operations Research》2006,143(1):31-44
A study has been carried out aimed at reducing perinatal mortality in the municipality of Rio de Janeiro through a better
distribution of health care facilities. The algorithmic aspects are detailed elsewhere and here the emphasis is on practical
issues and difficulties encountered.
A 3-level hierarchical model was developed. Both uncapacitated and capacitated versions are briefly described together with
some results based on actual data. The project brought to light many contradictions between OR theory and practice in developing
countries and, unfortunately, the models developed were not implemented by the municipality health authorities. Possible reasons
for this outcome are analysed. 相似文献
8.
Peter D. Verhaert Maria C. Prieto Conaway Tonya M. Pekar Ken Miller 《International journal of mass spectrometry》2007,260(2-3):177
Direct tissue imaging was performed on dissected insect tissue using a MALDI ion trap to visualize endogenous neuropeptides. Coupling tissue imaging to tandem MSn allows for the identification of previously known species and the ability to identify new ones by de novo sequencing, as searchable databases for insects are sparse. Direct tissue imaging is an attractive technique for the study of neuropeptides as minimal sample preparation is required prior to mass spectrometry. We successfully identified neuropeptides present in the corpora cardiaca and allata of Acheta domesticus (the house cricket). Diagnostic fragments at low m/z were used to distinguish between lipids and neuropeptides. The distribution of peptides appears to be more differentially localized than that of phospholipids, which seem to be more evenly distributed within the tissue. 相似文献
9.
We analyze the polarization changes introduced by a rotated Dove prism on the linearly polarized light, using the Jones calculus and the exact ray trace analysis. The state of polarization changes from the linear to a mildly elliptical one when a plane wave front passes through a rotated Dove prism: its semi-major axis is nearly parallel to the input plane of polarization, for any angle of prism rotation. The interferogram contrast remains high for all shearing angles in spite of polarization changes when the Dove prism is incorporated into a rotational shearing interferometer. These results are confirmed experimentally. 相似文献
10.