检索结果-南通市图书馆

Journal of Advanced Ceramics 2016年第2期5卷 103-110页

作者： Y.F.GOMES a.k.freitas R.M.NASCIMENTO M.R.D.BOMIO C.A.PASkOCIMAS F.V.MOTTA Departamento de Engenharia de Materiais Universidade Federal do Rio Grande do Norte 59078-900 Natal/RN Av.Sen.Salgado Filho 3000 CEP 59072-970 Brazil

In this study, the nanostructures of pure ZnO and ZnO:xCe3+ were prepared using statistic design—factorial design 3(3?1)?3-level and mixed-level factorials and fractional with replicates in the central point, totaling 11 experiments. The experiments were performed using the microwave-assisted hydrothermal (MAH) method with Ce3+ concentration of 2 and 4 mol% at 60, 110, and 160 °C for 10, 20, and 30 min. X-ray diffraction (XRD), scanning electron microscopy (SEM), and optical diffuse reflectance were used to characterize the products. The fractional factorial design indicated the optimal design area, and the studies were continued by ridge analysis. The analysis of variance (ANOVA), the Pareto, and the model adjusted to the conditions proposed in this study due to the determination coefficient of 99.9%, variance (R 2), and response surface generated were satisfactory, thus having an optimization in the process of obtaining ZnO doped with Ce.

关键词： hydrothermal ZnO cerium photocatalytic activity factorial design 3(3-1)

Pharmaceutical applications of spouted beds: A review on solid dosage forms

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Particuology 2019年第1期17卷 126-136页

作者： Luis Alexandre Pedro de freitas Faculdade de Ciencias Farmaceuticas de Ribeirao Preto University of Sao PauloVia do Cafe s/n. Campus USPRibeirao Preto14040-903Sao Paulo. Brazil

Spouted beds (SBs) have a long history of successful applications for preparation of solid dosage forms of pharmaceuticals. The well-known versatility of SBs, provided by different design and operational factors, and their efficient mixing of solids allow for engineering of technological characteristics of pharmaceutical solid forms. Particle properties like morphology, size, porosity, flowability, and dissolution rate can be improved by managing geometric and operational conditions for spouting. Drying is probably the most disseminated operation for pharmaceutical processing in SBs, and many studies have investigated drying of medicinal plant extracts such as achiote (Bixa orellana sp.), guarana (Paullinia cupana sp.), passion flower (Passiflora alata D.), and rosemary (Rosmarinus officinalis L.) with excellent pharmacotechnical and stability results. Another important application is coating of tablets and gelatin capsules, and previous studies have shown that SBs and spout–fluid beds may be advantageous over traditional pan coating, especially for polymeric film coating. Recently, an alternative process for improving drug bioavailability has involved preparation of β-cyclodextrin inclusion complexes in SBs. The first study to propose SBs for this pharmaceutical application explored the advantage of obtaining solid forms of inclusion complexes in just one step, and obtained expressive increases in drug solubility. The technique has been applied in subsequent studies on inclusion complexes of the medication carvedilol and uxi (Endopleura uchi L.) extracts.

关键词： Coating Drying Granulation Inclusion Microencapsulation

Oxidative reforming of methane for hydrogen and synthesis gas production:Thermodynamic equilibrium analysis

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 Natural Gas Chemistry 2012年第5期21卷 571-580页

作者： Antonio C.D.freitas Reginaldo Guirardello School of Chemical Engineering University of Campinas (UNICAMP)Av.Albert Einstein 50013083-852Campinas-SPBrazil

A thermodynamic analysis of methane oxidative reforming was carried out by Gibbs energy minimization （at constant pressure and temperature） and entropy maximization （at constant pressure and enthalpy） methods,to determine the equilibrium compositions and equilibrium temperatures,*** cases were treated as optimization problems （non-linear programming formulation）.The GAMS 23.1 software and the CONOPT2 solver were used in the resolution of the proposed *** hydrogen and syngas production were favored at high temperatures and low pressures,and thus the oxygen to methane molar ratio （O 2 /CH 4） was the dominant factor to control the composition of the product *** O 2 /CH 4 molar ratios higher than 0.5,the oxidative reforming of methane presented autothermal behavior in the case of either utilizing O 2 or air as oxidant agent,but oxidation reaction with air possessed the advantage of avoiding peak temperatures in the system,due to change in the heat capacity of the system caused by the addition of *** calculated results were compared with previously published experimental and simulated data with a good agreement between them.

关键词： thermodynamic analysis methane oxidative reforming Gibbs energy minimization entropy maximization hydrogen and syngas production

Gravitational waves from compact objects

在线全文

学校读者我要写书评

暂无评论

Research in Astronomy and Astrophysics 2010年第11期10卷 1071-1099页

作者： José Antonio de freitas Pacheco University of Nice-Sophia Antipolis Observatoire de la Cote d'Azur Laboratoire Cassiopée-UMR 6202 BP 4229-F606304-Nice Cedex 4-France

Large ground-based laser beam interferometers are presently in operation both in the USA （LIGO） and in Europe （VIRGO） and potential sources that might be detected by these instruments are revisited. The present generation of detectors does not have a sensitivity high enough to probe a significant volume of the universe and, consequently, predicted event rates are very low. The planned advanced generation of interferometers will probably be able to detect, for the first time, a gravitational sig- nal. Advanced LIGO and EGO instruments are expected to detect few （some）： binary coalescences consisting of either two neutron stars, two black holes or a neutron star and a black hole. In space, the sensitivity of the planned LISA spacecraft constellation will allow the detection of the gravitational signals, even within a ＂pessimistic＂ range of possible signals, produced during the capture of compact objects by supermassive black holes, at a rate of a few tens per year.

关键词： gravitational waves -- neutron stars -- black holes

Magnetic Tunnel Junction Based on MgO Barrier Prepared by Natural Oxidation and Direct Sputtering Deposition

在线全文

学校读者我要写书评

暂无评论

Nano-Micro Letters 2012年第1期4卷 25-29页

作者： Xiaohong Chen Paulo.P.freitas Engineering Research Center for Nanophotonics and Advanced Instrument Ministry of Education Department of Physics East China Normal University INESC-MN

Magnetic tunnel junctions(MTJs) based on MgO barrier have been fabricated by sputtering single crystal MgO target and metal Mg target, respectively, using magnetic sputtering system Nordiko 2000. MgO barriers have been formed by a multi-step deposition and natural oxidization of Mg layer. Mg layer thickness,oxygen flow rate and oxidization time were adjusted and the tunnel magnetoresistance(TMR) ratio of optimal MTJs is over 60% at annealing temperature 385. The(001) MgO crystal structure was obtained when the separation distance between MgO target and substrate is less than 6 cm. The TMR ratio of most MgO based MTJs are over 100% at the separation distance of 5 cm and annealing temperature 340. The TMR ratios of MTJs are almost zero when the separation distance ranges from 6 to 10 cm, due to the amorphous nature of the MgO film.

关键词： Magnetic tunnel junctions Mg O Crystal structure Magnetic sputtering system

Arbuscular mycorrhizal fungal community assembly in the Brazilian tropical seasonal dry forest

在线全文

学校读者我要写书评

暂无评论

Ecological Processes 2017年第1期6卷 9-18页

作者： Tancredo Augusto Feitosa de Souza Helena freitas Centre for Functional Ecology Department of Life SciencesUniversity of Coimbra3000-456 CoimbraPortugal

Introduction:Here,we compare the arbuscular mycorrhizal fungal(AMF)community composition in soils from the root zone of the exotic invasive species Prosopis juliflora(EXO soils)and soils from the root zone of the native species Mimosa tenuiflora(NAT soils)from five locations in the Brazilian tropical seasonal dry forest,Paraíba,Brazil,using morphological ***:AMF community composition in EXO and NAT soils were *** phosphorus,diversity index,spore abundance,and species richness were the main factors differing between the EXO and NAT *** general,the most dominant order present in the soils were Glomerales(44.8%)and Gigasporales(41.4%).The most abundant AMF genus in all studied soils was ***:Differences in AMF community composition were associated with(1)differences in the dominant plant species(*** ***)and(2)changes in soil chemical factors(soil,pH,total organic carbon,total nitrogen,and available P)in EXO *** results contribute to a deeper view of the AMF communities in exotic soils and open new perspectives for ecological processes involving AMF species and exotic plant species in the Brazilian tropical seasonal dry forest.

关键词： Glomeromycota AMF community AMF diversity Native plant species Exotic plant species Caatinga

Quantum effects on dislocation motion from ring-polymer molecular dynamics

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

npj Computational Materials 2018年第1期4卷 198-203页

作者： Rodrigo freitas Mark Asta Vasily V.Bulatov Department of Materials Science and Engineering University of CaliforniaBerkeleyCA 94720USA Lawrence Livermore National Laboratory LivermoreCA 94550USA Materials Sciences Division Lawrence Berkeley National LaboratoryBerkeleyCA 94720USA Department of Materials Science and Engineering Stanford UniversityStanfordCA 94305USA

Quantum motion of atoms known as zero-point vibration was recently proposed to explain a long-standing discrepancy between theoretically computed and experimentally measured low-temperature plastic strength of iron and possibly other metals with high atomic *** finding challenges the traditional notion that quantum motion of atoms is relatively unimportant in solids comprised of heavy *** we report quantum dynamic simulations of quantum effects on dislocation motion within the exact formalism of Ring-Polymer Molecular Dynamics(RPMD).To extend the reach of quantum atomistic simulations to length and time scales relevant for extended defects in materials,we implemented RPMD in the open-source code LAMMPS thus making the RPMD method widely available to the *** use our RPMD/LAMMPS approach for direct calculations of dislocation mobility and its effects on the yield strength ofα-*** simulation results establish that quantum effects are noticeable at temperatures below 50 k but account for only a modest(≈13% at T=0 k)overall reduction in the Peierls barrier,at variance with the factor of two reduction predicted earlier based on the more approximate framework of harmonic transition state *** results confirm that zero-point vibrations provide ample additional agitation for atomic motion that increases with decreasing temperature,however its enhancing effect on dislocation mobility is largely offset by an increase in the effective atom size,an effect known as quantum dispersion that has not been accounted for in the previous calculations.

关键词： theory quantum motion

Melting behavior and globular microstructure formation in semi-solid CoCrCuxFeNi high-entropy alloys

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 Materials Science & Technology 2020年第17期52卷 207-217页

作者： kaio Niitsu Campo Caio Chaussêde freitas Leonardo Fanton Rubens Caram University of Campinas School of Mechanical EngineeringSPBrazil

High-entropy alloys can be compelling raw materials for semi-solid *** the present study,the influence of the Cu content on the melting behavior and semi-solid microstructure of CoCrCuxFeNi(x=0,1,2,3)alloys was ***-melted samples were cross-rolled at room temperature and then isothermally treated at 1175℃in the semi-solid state for 300 *** characterization showed that the alloys containing Cu were formed by two fcc ***,the increase in Cu content also led to an increase in the volumetric fraction of the Cu-rich *** solidification,this phase,which is the last to form,nucleates and epitaxially grows on the Cu-lean *** the studied CoCrCuFeNi alloys exhibited the same melting *** Cu-rich phase melts at approximately 1120℃,whereas the Culean phase melts at approximately 1350℃,providing a suitable processing temperature range of more than 200℃.The semi-solid microstructures were considerably refined and globular regardless of the alloy composition,being suitable for semi-solid ***,each fcc phase exhibited roughly the same composition under the different processing *** Cu content in the Cu-lean phase was approximately 10 at.%,while Co,Cr,Fe,and Ni were in an approximately equiatomic ***,the Cu content was between 80 at.%and 86 at.%in the Cu-rich *** isothermal treatment of the CoCrCu3FeNi alloy at a higher temperature(1300℃)only caused the globules to *** conclusion,this work showed that these alloys can be potential candidates for semi-solid processing.

关键词： Semi-solid processing Thixoforming High-entropy alloys Microstructure

Descriptors-based machine-learning prediction of cetane number using quantitative structure–property relationship

在线全文

学校读者我要写书评

暂无评论

Energy and AI 2024年第3期17卷 168-178页

作者： Rodolfo S.M.freitas Xi Jiang School of Engineering and Materials Science Queen Mary University of LondonMile End RoadLondonE14NSUK

The physicochemical properties of liquid alternative fuels are important but difficult to measure/predict, especially when complex surrogate fuels are concerned. In the present work, machine learning is used to develop quantitative structure–property relationship models. The fuel chemical structure is represented by molecular descriptors, allowing the linking of important features of the fuel composition and key properties of fuel utilization. Feature selection is employed to select the most relevant features that describe the chemical structure of the fuel and several machine learning algorithms are tested to construct interpretable models. The effectiveness of the methodology is demonstrated through the development of accurate and interpretable predictive models for cetane numbers, with a focus on understanding the link between molecular structure and fuel properties. In this context, matrix-based descriptors and descriptors related to the number of atoms in the molecule are directly linked with the cetane number of hydrocarbons. Furthermore, the results showed that molecular connectivity indices play a role in the cetane number for aromatic molecules. Also, the methodology is extended to predict the cetane number of ester and ether molecules, leveraging the design of alternative fuels towards fully sustainable fuel utilization.

关键词： Chemical descriptors Quantitative structure-property relationship Machine learning Cetane number Fuel design

A longitudinal analysis of the U.S. Air Force Reserve Officers’ Training Corps physical fitness assessment

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Military Medical Research 2020年第2期7卷 166-173页

作者： Cameron SMackey Jason MDe freitas Applied Neuromuscular Physiology Laboratory Oklahoma State University192 CRCStillwaterOK 74078USA

Background:The *** Force physical fitness assessment(PFA)is used to determine the overall fitness of their *** is currently unknown to what extent the PFA scores of Reserve Officers’Training Corps(ROTC)cadets are affected by mandatory physical *** purpose of this investigation was to longitudinally examine the PFAs of ROTC cadets over a four-year period,evaluate the results across class ranks,and evaluate the sensitivity of the classification of the ***:Air Force ROTC cadets performed the PFAs(abdominal circumference,1-min pushups,1-min sit-ups,and a 1.5-mile run)in both the spring(n=26)and fall(n=22)*** were compiled over a four-year period(Spring 2014–Fall 2017)and were performed in accordance with Air Force Instruction 36–2905.A oneway repeated measures ANOVA was performed separately for the fall and spring groups for each dependent variable across the 4 ***,a one-way between groups ANOVA was performed for each dependent variable during the time point(fall 2015;n=46)with the most recorded cadets for each class ***:Longitudinal assessments revealed a main effect of time(P=0.010)on abdominal circumference;cadets had a smaller abdominal circumference in their freshman year than in their senior year.A main effect of time(P=0.006)was also observed on sit-up quantity;cadets performed more sit-ups in their junior year than in their freshman *** between class ranks during the same year(between-subjects ANOVA)revealed a main effect of class rank on sit-up quantity(P=0.003);the freshmen completed fewer repetitions than the sophomores(P=0.018)and the juniors did(P=0.001).Conclusions:The results indicated that only the sit-up component showed differences between class *** findings suggest that the Air Force PFA may not be sensitive enough to detect changes in physical fitness or distinguish between class ranks regarding physical performance,even after years of *** limitation may b

关键词： Class ranks Fitness assessment Military Physical training ROTC