检索结果-南通市图书馆

Keggin Structure and Surface Acidity of 12-Phosphotungstic Acid Grafted Zr-MCM-48 Mesoporous Molecular Sieves

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

World Journal of Nano Science and Engineering 2012年第3期2卷 134-141页

作者： Zhiqi Wang juan navarrete Dirección de Investigación y Posgrado Instituto Mexicano del Petróleo Eje Lázaro Cárdenas Norte No. 152 México D.F. Mexico The American School Foundation Bondojito No. 21 Col. Las Americas México D.F. Mexico

A zirconium modified MCM-48 mesoporous material was synthesized by surfactant-templated method. Surface grafting Zr-MCM-48 with tungstophosphoric acid led to a great enhancement of both the number of the Br?nsted acid sites and acidity strength in comparison with the bare support. At 100°C, the 30 wt% H3PW12O40/Zr-MCM-48 contained 174 μmol/g Br?nsted acid sites which were 14.5 times greater than that of Zr-MCM-48. The Keggin structure of the grafted heteropolyacid was rather stable after calcination at 400°C for 2 h, approximately 93.3% of Keggin structure in the dispersed heteropolyacid were remained without destruction but slightly distorted in some degree, as evidenced by FTIR characterization and 31P NMR-MAS analysis. This H3PW12O40/Zr-MCM-48 solid with three dimensional mesoporous system, large surface area and very strong Br?nsted acidity will be a promising catalyst for acid catalytic reactions.

关键词： Zr-MCM-48 Surface Acidity Heteropolyacid Spectroscopic Characterization

Prevalence and ecological factors affecting the distribution of plant-parasitic nematodes in Prunus groves in Spain

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Journal of Integrative Agriculture 2024年第2期23卷 566-589页

作者： Ilenia Clavero-Camacho Antonio Archidona-Yuste Carolina Cantalapiedra-navarrete Pablo Castillo juan Emilio Palomares-Rius Institute for Sustainable Agriculture(IAS) Spanish National Research Council(CSIC)Córdoba 14004Spain Andalusian Institute of Agricultural and Fisheries Research and Training(IFAPA) Centro Alameda del ObispoCórdoba 14004Spain

A wide survey was conducted to study plant-parasitic nematodes(PPNs)associated with Prunus groves in *** research aimed to determine the prevalence and distribution of PPNs in Prunus groves,as well as the influence of explanatory variables describing soil,climate and agricultural management in structuring the variation of PPNs community composition.A total of 218 sampling sites were surveyed and 84 PPN species belonging to 32 genera were identified based of an integrative taxonomic *** species considered as potential limiting factors in Prunus production,such as Meloidogyne arenaria,***,***,Pratylenchus penetrans and ***,were identified in this *** soil physico-chemical(C,Mg,N,Na,OM,P,pH and clay,loamy sand and sandy loam texture classes),four climate(Bio04,Bio05,Bio13 and Bio14)and four agricultural management variables(grove-use history less than 10 years,irrigation,apricot seedling rootstock,and Montclar rootstock)were identified as the most influential variables driving spatial patterns of PPNs *** particular,younger plantations showed higher values for species richness and diversity indices than groves cultivated for more than 20 years with Prunus *** study increases the knowledge of the distribution and prevalence of PPNs associated with Prunus rhizosphere,as well as on the influence of explanatory variables driving the spatial structure PPNs communities,which has important implications for the successful design of sustainable management strategies in the future in this agricultural system.

关键词： nematodes Meloidogyne Pratylenchus Paratylenchus rootstock distribution soil grove-use almond peach

Consolidation of Ancient Raw Materials Using a Reversible, Elastic, Soft Polymer

维普期刊数据库

同方期刊数据库评论

在线全文

学校读者我要写书评

暂无评论

Advances in Materials Physics and Chemistry 2012年第1期2卷 37-42页

作者： juan Manuel navarrete Gustavo Leonardo Martínez Faculty of Chemistry Inorganic and Nuclear Chemistry Department National University of Mexico Mexico City Mexico National Coordination to Restore the Cultural Inheritance National Institute of Anthropology and History Mexico City Mexico

Aging of ancient raw materials usually finish with disintegration, which starts on surface of walls to progress toward the inside mass of a huge variety of mineral compounds. This is particularly harmful when antique buildings keep mural paintings, which suffers destruction before the wall itself. Same case appears on sculptures and monuments, whose surfaces are often attacked by living organisms which start a deterioration process previous to complete disintegration. The main factor to produce these unwanted effects is humidity, either rain for materials exposed to open air, or underground humidity going up by capillarity of minerals, in this case represented by porosity of associated salts forming the material. This paper describes a method to measure easily the relative porosity of diverse raw materials at laboratory level, by using a radioactive labeled solution, and also a procedure to reduce their porosity of those minerals. The efficiency of this procedure is measured in the same way, and so the results obtained at laboratory level have encouraged its use at real scale, where it has been quite successful for a number of materials in a limited span of five years.

关键词： Consolidation Preservation Humidity Ancient Materials

Assessment of Present and Future Radioactive Contamination at Global Scale

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Journal of Chemistry and Chemical Engineering 2012年第11期6卷 1010-1015页

作者： juan Manuel navarrete Miguel Angel ZUNiga Guillermo Espinosa Jose Ignacio Golzarri Faculty of Chemistry National University of Mexico Mexico City 04510 Mexico Institute of Physics National University of Mexico Mexico City 04510 Mexico

As a result of more than two thousand nuclear tests performed since 1945, two war actions and few accidents in nuclear reactor, it does already exist a radioactive contamination at global scale. This contamination has been accumulated mainly in marine sediments, because sea is about 80% of planet surface, and solid fission products released by nuclear explosions are transported by wind first and then by rain to liquid and solid portions on earth, while gaseous fission products are diffused in the atmosphere. In this way, heavy, high yielding fission products, such as 137Cs, get marine sediments, where they are found mixed with heavy radioactive natural elements such as U, Th and their also radioactive decay products. But since alkaline are so abundant on earth, it is also found natural radioactive isotope 4~K, 0.0118% of isotopes forming K element, with half life 1.28 ~ l09, in the time range of planet age and elements origin. So, one easy way to assess both the importance and evaluation of radioactive contamination at global scale should be to establish a RCF （radioactive contamination factor） as a percentage of 137Cs contaminant radioactivity in marine sediments, compared to 4~K natural radioactivity present from the very beginning of earth, both expressed as Bq per gram of sediment. In the frame of these rather general considerations, a research project has started in Mexico whose varied purposes are： to characterize sea regions in both vast littorals in the country, by its natural 4~K radioactivity present in sea salts, as well as to determine if 137Cs traces produced by recent radioactive contamination have reached their coasts. Also, to assess the 137Cs traces already present in marine sediments as a result of more than two thousand nuclear test explosions performed till now, rather than contamination produced by four main accidents in nuclear reactors during the last 60 years. It is proposed a radioactive contamination factor obtained from samples taken up in

关键词： Contaminant natural radioactivity relation coefficient.

Isobars Separation (137Cs-137mBa-137Ba) from Marine Sediments, in Order to Evaluate Directly Their Radioactive Contamination by Mass Spectrometry

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

World Journal of Nuclear Science and Technology 2020年第1期10卷 32-38页

作者： Karla Fernández juan Manuel navarrete Miguel Angel Zúñ iga Ernesto Hernández Department of Inorganic and Nuclear Chemistry Faculty of ChemistryNational Autonomous University of MexicoMexico CityMexico

Marine sediments contamination by fission product 137Cs-137mBa is a fact since the period 1945-65, when plus than two thousand atomic explosion tests were performed mainly in the southern seas, earth region with minor population density. However, marine flows have produced dissemination of this radioactive pair through the sea bottom all over the world, at different levels, because the sea movement and natural decaying of radioactive pair: parent 137Cs (t1/2 = 30.17 years) and daughter 137mBa (t1/2 = 2.55 minutes). Radioactive detection of these contaminants, compared as percentage with that of natural 40K (t1/2 = 1.28 × 109 years, 0.0118% of elementary K) leads to radiation contamination factor (RCF), as one possible unit to measure the radioactive contamination intensity in different regions, as well to determine if there is some other possible source of this contaminant, for example water cooling from power nuclear reactors when it is discharged at sea. However, radioactive detection always implies an unavoidable statistical variation, which makes more difficult to appreciate the changes as function of time and region. But at beginning of this century, mass spectrometry has got impressive advances, which makes it much more precise and sensible than radioactive detection [1]. This paper attempts to measure with other units the radioactive contamination: 137Cs atoms number per gram of sample, instead radioactivity, which could be more direct and with minor standard deviation that radioactive detection, solving at same time the isobars separation: 137Cs versus 137mBa plus elementary 137Ba (11.23% of Ba element).

关键词： Isobars Separation 137Cs-137mBa-137Ba

Potassium Concentration by Natural ^40K-^40Ar Y Rays Detection in Four Basic Diet Products （Milk, Eggs, Wheat and Corn）

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Journal of Life Sciences 2011年第8期5卷 614-617页

作者： juan Manuel navarrete Trinidad Martinez Luis Cabrera Pilar Lizarraga Miguel Angel Zuniga Michelle Camacho Faculty of Chemistry Building D National University of Mexico CU Mexico City ZC 04510 Mexico

The purpose of this paper is double： first to measure the natural radioactivity in any food by detecting the omnipresent radiation of ^40K, and then to use this date to obtain the concentration of the important mineral nutrient K, by dividing the specific activity of the sample （Bq/g） by the specific activity of elementary K （31.19 Bq/g）. The method implies the γ rays detection emitted by natural ^40K-^40Ar present in foodstuff, by using a 3 × 3＂ low background NaI （TI） scintillation detector coupled to a PC charged with the Maestro Program. When this detection system is calibrated in order to determine its efficiency for 1461 KeV γrays emitted during ^40K-^40Ar decaying, it is possible to measure easily and with enough precision the specific activity due to natural ^40K present in any foodstuff. Once this figure is divided by the constant value of ^40K specific activity of elementary K, the concentration of this element in the foodstuff sample is established. This paper describes the procedure and shows the results obtained with four basic diet products： milk （powdered, light and cream）, eggs （yellow and white）, wheat （whole and refined flour） and corn （whole and cornstarch flour）. The possible application of this study seems to be to establish the necessary threshold to evaluate the importance of any possible radioactive contamination, as well as to measure the concentration of the mineral nutrient K in foodstuff, by means of an easy, practicable method. Also, it might be useful as an experiment for teaching purposes.

关键词： Radioactivity nourishment potassium concentration ^40K-^40Ar Y rays.

Determination of Radioactive Contaminant ¹³⁷Cs (Fission Product) and Comparison with Natural ⁴⁰K Present in Mexican Strawberries

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Journal of Geoscience and Environment Protection 2022年第7期10卷 257-265页

作者： Fridda Concepción Fuentes Gama juan Manuel navarrete Tejero Alejandro Ramírez Chávez Miguel Ángel Zúñiga Pérez Department of Inorganic and Nuclear Chemistry Faculty of Chemistry National Autonomous University of Mexico Mexico City Mexico

Several previous papers have been published about radioactive contamination in Mexican soil, marine sediments and foodstuffs. Ever since, results have been according to expectation, mainly consisting of natural isotopes in small concentration. Continuous research leads with the surprising finding of fission product 137Cs (t1/2 = 30 years) in strawberries produced in different states, about 2000 km away from each other. Never before, such contaminant has been observed in foodstuffs, produced in this country. The aim of this work is to report the presence of 137Cs in Mexican strawberries and compare the activity of such contaminant with the natural radioactivity of 40K (t1/2 = 1.28 × 109 years), through gamma spectrometry. Eventually, the specific activity of 137Cs observed in samples FM4, FM5 and FBC is respectively 0.7, 0.8 and 0.3 Bq/kg. The limits established in CODEX-STAN-193-1995 for 137Cs are 1000 Bq/kg, so all samples meet the recommendation. It’s presence now in vegetables result with enough interest to be known and considered in the near future to measure the possible effect that radioactive contamination could reach after nearly 80 years from second world war, where no nuclear test has been performed, nuclear accident occurred, neither nuclear weapon has ever been used.

关键词： Radioactive Contamination

Production of Carbon Nanotubes and Hydrogen Catalyzed with Ni/MCM-41 Catalysts

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Keggin Structure and Surface Acidity of 12-Phosphotungstic Acid Grafted Zr-MCM-48 Mesoporous Molecular Sieves

Green and Sustainable Chemistry（绿色与可持续化学） 2012年第3期

作者： Zhiqi Wang juan navarrete

来源：评论

学校读者我要写书评

暂无评论