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排序方式: 共有1833条查询结果,搜索用时 250 毫秒
101.
Pari Mirahmadpour Davood Nematollahi Mohammad Hossein Banitaba Saied Saeed Hosseiny Davarani 《Journal of Inorganic and Organometallic Polymers and Materials》2016,26(2):376-383
Electrochemical synthesis of coordination polymers of Cu(II), [Cu(TDA)]n and [Cu2(BTC)(H2O)6?6H2O]n in which H2TDA is 2,2′-thiodiacetic acid and BTC stands for 1,2,4,5-benzenetetracarboxylate was carried out by the electrochemical oxidation of Cu anode in the presence of H2TDA (a flexible ligand), and 1,2,4,5-benzentetracarboxylic acid (H4BTC) (a rigid ligand) in aqueous solutions. The structure of coordination polymers were characterized by scanning electron microscopy, X-ray powder diffraction, elemental analysis, thermal gravimetric and differential thermal analyses. The crystal structure of the compounds consists of one-dimensional cubical crystal polymeric units of [Cu(TDA)]n and [Cu2(BTC)(H2O)6?6H2O]n. Furthermore, the coordination number of Cu (II) ions in synthesized coordination polymers to be found five. The main advantages of electrosynthesis are the minor synthesis time, the milder conditions and the facile synthesis of coordination polymer coatings. 相似文献
102.
Synthesis and Spark Plasma Sintering of Mg2Si Nanopowder by Mechanical Alloying and Heat Treatment 下载免费PDF全文
Mohammad Khajelakzay Saeed Reza Bakhshi Gholam Hossein Borhani Mazaher Ramazani 《International Journal of Applied Ceramic Technology》2016,13(3):498-505
In this investigation, a two‐step method for the preparation of magnesium silicide (Mg2Si) nanopowder was studied. This method is known as mechanical alloying followed by heat treatment. The results showed that the compositions of the combustion products depended on the milling time, heat treatment temperature, and starting mixtures. Pure Mg2Si nanopowder was formed after short milling time and heat treatment, from Mg and Si powders with the mole ratio of 2.1:1 (Mg:Si) at 500°C in Ar atmosphere. Using the Mg2Si nanopowder, Mg2Si ceramic was produced by spark plasma sintering at 800°C under 50 MPa for 15 min. Composition and structure of reactants and products were examined by X‐ray diffraction (XRD), field emission scanning electron microscopy (FE‐SEM) and high‐resolution transmission electron microscopy (HR‐TEM). 相似文献
103.
In this study, glass flakes were incorporated into the spherical nanosilica component of the dental composites and its effect on the mechanical properties of these composites was investigated. To achieve a good interfacial adhesion between matrix resin and fillers, the particles were surface treated with a silane coupling agent (γ-MPS). Composites with different plate-like and spherical nanoparticle contents were prepared and their mechanical properties, including flexural strength, flexural modulus and fracture toughness were measured. The morphology of the particles and fracture surface of the composites were studied by SEM. The distribution of the flakes in the composite was also monitored using EDXA. Statistical analysis of the data was performed with ANOVA and the Tukey’s post hoc test was at a significance level of 0.05. The results showed that the flexural modulus and fracture toughness of specimens were improved with increasing the glass flake content up to 15 vol % which then declined upon further increase due to the stacking of the flakes on each other. A good interfacial adhesion was observed between matrix resin and particles in the SEM micrographs. The results of this study suggest that incorporation of glass flakes into the dental composites containing spherical nanosilica particles may enhance their mechanical properties. 相似文献
104.
John M. Stormonth‐Darling Anwer Saeed Paul M. Reynolds Nikolaj Gadegaard 《大分子材料与工程》2016,301(8):964-971
Flexible polymers such as poly dimethyl siloxane (PDMS) can be patterned at the micro‐ and nanoscale by casting, for a variety of applications. This replication‐based fabrication process is relatively cheap and fast, yet injection molding offers an even faster and cheaper alternative to PDMS casting, provided thermoplastic polymers with similar mechanical properties can be used. In this paper, a thermoplastic polyurethane is evaluated for its patterning ability with an aim to forming the type of flexible structures used to measure and modulate the contractile forces of cells in tissue engineering experiments. The successful replication of grating structures is demonstrated with feature sizes as low as 100 nm and an analysis of certain processing conditions that facilitate and enhance the accuracy of this replication is presented. The results are benchmarked against an optical storage media grade polycarbonate.
105.
It is well known that the deformation and stress-resistant characteristics of fine-grained soils, especially soft clays, are significantly influenced by the soil softness. It is therefore very important to employ a model which can accurately simulate the effects of this phenomenon. A constitutive model must be able to create a balance among stress paths, the number of parameters, the process of parameter determination, and finally, the simplicity of the computational calculations.The current study investigates the performance of a two-yield surface (cone and cap yield surface) model for soft soils. The efficiency of the cap yield surface has been studied as well. The model has been calibrated by employing the data derived from previous researches for Bangkok clay. The incorporated data have been obtained from the results of CD triaxial, CU triaxial, and oedometer tests. The proposed method for the model calibration can accurately predict the triaxial test results and oedometer test stress path simultaneously. This method for predicting the soil behavior is based on the main soil characteristics taken from common soil mechanics tests. It can be widely employed for engineering practices, especially when complicated soil behavior is encountered. 相似文献
106.
Saeed Solaymani Kiomars Sohaili Esmaeil Akhlaghi Yazdinejad 《Electronic Commerce Research》2012,12(3):249-263
In this study, nonlinear Logit and probit models are used to analyse the important factors that impact on the tendency of small- and medium-sized enterprises (SMEs) to use electronic commerce in one of the industrial parks in Kermanshah province of Iran. Furthermore, it identifies the major barriers of e-commerce adoption in these SMEs. The Sample of the study includes 35 SMEs in this province. The results of probit and Logit models suggest that a lower level of the internet service costs, motivates firms to adopt e-commerce. In addition, if the government provides free e-commerce facilities for SMEs, it can encourage SMEs to adopt e-commerce. Furthermore, the results show that due to uncertainty in the e-commerce, producing high-quality products and traditional exports cannot raise the tendency of sample firms to adopt e-commerce. 相似文献
107.
This paper is the second part of a two-part study concerning the dynamics of heat transfer during the nucleation process of FC-72 liquid. The experimental findings on the nature of different heat transfer mechanisms involved in the nucleation process were discussed in part I. In this paper, the experimental results are compared with the existing boiling models. The boiling models based on dominance of a single mechanism of heat transfer did not match the experimental results. However, the Rohsenow model was found to closely predict the heat transfer through the microconvection mechanism that is primarily active outside the bubble/surface contact area. An existing transient conduction model was modified to predict the surface heat transfer during the rewetting process (i.e. transient conduction mechanism). This model takes into account the gradual rewetting of the surface during the transient conduction process rather than a simple sudden surface coverage assumption commonly used in the boiling literature. The initial superheat energy of the microlayer (i.e. microlayer sensible energy) was accurately calculated and found to significantly contribute in microlayer evaporation. This even exceeded the direct wall heat transfer to microlayer at high surface superheat temperatures. A composite model was introduced that closely matches our experimental results. It incorporates models for three mechanisms of heat transfer including microlayer evaporation, transient conduction, microconvection, as well as their influence area and activation time. The significance of this development is that, for the first time, all submodels of the composite correlation were independently verified using experimental results. 相似文献
108.
S.R. Saeed F. Krok M. Szymonski 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》2009,267(16):2752-2756
Structural and compositional modification of InSb(0 0 1) single crystal surfaces induced by oblique incidence 2-5 keV Ar and Xe ion irradiation have been investigated by means of scanning tunneling and atomic force microscopies, and time-of-flight mass spectroscopy of secondary ion emission. In general, ion-induced patterns (networks of nanowires, or ripples) are angle of incidence- and fluence-dependent. Temperature dependences (from 300 to 600 K) of the RMS roughness and of the ripple wavelength have been determined for the samples bombarded with various fluences. Secondary ion emission from an InSb(0 0 1) surface exposed to 4.5 keV Ar+ ions has been investigated with a linear TOF spectrometer working in a static mode. Mass spectra of the sputtered In+, Sb+ and In2+ secondary ions have been measured both for the non-bombarded (0 0 1) surface and for the surface previously exposed to a fluence of 1016 ions/cm2. In+ and In2+ intensities for the irradiated sample are much higher in comparison to the non-bombarded one, whereas Sb+ ions show a reversed tendency. This behavior suggests a significant In-enrichment at the InSb(0 0 1) surface caused by the ion bombardment. 相似文献
109.
A novel modified glassy carbon electrode with a film of nanodiamond-graphite/chitosan is constructed and used for the sensitive voltammetric determination of azathioprine (Aza). The surface morphology and thickness of the film modifier are characterized using atomic force microscopy. The electrochemical response characteristics of the electrode toward Aza are investigated by means of cyclic voltammetry. The modified electrode showed an efficient catalytic role for the electrochemical reduction of Aza, leading to a remarkable decrease in reduction overpotential and enhancement of the kinetics of the electrode reaction with a significant increase of peak current. The effects of experimental variables, such as the deposited amount of modifier suspension, the pH of the supporting electrolyte, the accumulation potential and time were investigated. Under optimal conditions, the modified electrode showed a wide linear response to the concentration of Aza in the range of 0.2-100 μM with a detection limit of 65 nM. The prepared modified electrode showed several advantages: simple preparation method, high stability and uniformity in the composite film, high sensitivity, excellent catalytic activity in physiological conditions and good reproducibility. The modified electrode can be successfully applied to the accurate determination of trace amounts of Aza in pharmaceutical and clinical preparations. 相似文献
110.
SPARCL: an effective and efficient algorithm for mining arbitrary shape-based clusters 总被引:3,自引:3,他引:0
Vineet Chaoji Mohammad Al Hasan Saeed Salem Mohammed J. Zaki 《Knowledge and Information Systems》2009,21(2):201-229
Clustering is one of the fundamental data mining tasks. Many different clustering paradigms have been developed over the years,
which include partitional, hierarchical, mixture model based, density-based, spectral, subspace, and so on. The focus of this
paper is on full-dimensional, arbitrary shaped clusters. Existing methods for this problem suffer either in terms of the memory
or time complexity (quadratic or even cubic). This shortcoming has restricted these algorithms to datasets of moderate sizes.
In this paper we propose SPARCL, a simple and scalable algorithm for finding clusters with arbitrary shapes and sizes, and
it has linear space and time complexity. SPARCL consists of two stages—the first stage runs a carefully initialized version
of the Kmeans algorithm to generate many small seed clusters. The second stage iteratively merges the generated clusters to
obtain the final shape-based clusters. Experiments were conducted on a variety of datasets to highlight the effectiveness,
efficiency, and scalability of our approach. On the large datasets SPARCL is an order of magnitude faster than the best existing
approaches. 相似文献