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Статті в журналах з теми "Functional Gold Clusters"
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Ferrari, Piero, and Klavs Hansen. "Computing gold cluster energies with density functional theory: the importance of correlation." Physical Chemistry Chemical Physics 23, no. 27 (2021): 14830–35. http://dx.doi.org/10.1039/d1cp02084f.
Повний текст джерелаАнотація:
Calculating energy-dependent properties on gold clusters via density functional theory depend critically on the choice of functional. Here we use measured dissociation energies as benchmark data for testing the performance of different functionals.
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Allen, Darnel J., Wayne E. Archibald, John A. Harper, John C. Saputo, and Daniel Torres. "Density Functional Investigation of the Inclusion of Gold Clusters on a CH3S Self-Assembled Lattice on Au(111)." Advances in Chemistry 2016 (October 17, 2016): 1–8. http://dx.doi.org/10.1155/2016/6080343.
Повний текст джерелаАнотація:
We employ first-principles density functional theoretical calculations to address the inclusion of gold (Au) clusters in a well-packed CH3S self-assembled lattice. We compute CH3S adsorption energies to quantify the energetic stability of the self-assembly and gold adsorption and dissolution energies to characterize the structural stability of a series of Au clusters adsorbed at the SAM-Au interface. Our results indicate that the inclusion of Au clusters with less than four Au atoms in the SAM-Au interface enhances the binding of CH3S species. In contrast, larger Au clusters destabilize the self-assembly. We attribute this effect to the low-coordinated gold atoms in the cluster. For small clusters, these low-coordinated sites have significantly different electronic properties compared to larger islands, which makes the binding with the self-assembly energetically more favorable. Our results further indicate that Au clusters in the SAM-Au interface are thermodynamically unstable and they will tend to dissolve, producing Au adatoms incorporated in the self-assembly in the form of CH3S-Au-SCH3 species. This is due to the strong S-Au bond which stabilizes single Au adatoms in the self-assembly. Our results provide solid insight into the impact of adatom islands at the CH3S-Au interface.
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Priyanka, Sumali Bansal, and Keya Dharamvir. "Structure of Small Gold Clusters with Si Doping Using DFT (AunSi, n=1-10, 19)." Journal of Nano Research 24 (September 2013): 203–12. http://dx.doi.org/10.4028/www.scientific.net/jnanor.24.203.
Повний текст джерелаАнотація:
The structures of silicon doped gold clusters AunSi (n = 1-10 and 19) have been investigated using first principle calculations based on density functional theory (DFT). Calculations indicate that the stability of a gold cluster increases with the introduction of a Si atom. In all the low lying geometries, Si prefers peripheral positions. For every ground state configuration with n > 3 (n = 6 and 9 being exceptions) Si has tetra-coordination. In almost all of the tetra coordinated geometries the coordination unit including Si, is in the form of a square pyramid with gold atoms forming the square base. Electronic properties such as HOMO-LUMO gap, ionization potential and electron affinity have also been calculated and support the relative stability of clusters with even n. The study of Au20 cage doped with Si atom has been done .Similar to smaller Si doped gold clusters; the Si atom prefers an exohedral position. The doping of Si atom has enhanced the stability and chemical reactivity of Au20 cluster.
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Alamanova, Denitsa, Yi Dong, Habib ur Rehman, Michael Springborg, and Valeri G. Grigoryan. "Structural and Electronic Properties of Gold Clusters." Computing Letters 1, no. 4 (March 6, 2005): 319–30. http://dx.doi.org/10.1163/157404005776611394.
Повний текст джерелаАнотація:
We study the structure and energetics of AuN clusters by means of parameterfree density-functional calculations (N ≤ 8), jellium calculations (N ≤ 60), embeddedatom calculations (N ≤ 150), and parameterized density-functional calculations (N ≤ 40) in combination with different methods for determining the structure of the lowest total energy. By comparing the results from the different approaches, effects due to geometric packing and those due to the electronic orbitals can be identified. Different descriptors that highlight the results of the analysis are presented and used.
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Bulbula, Shimeles T., and Hagos W. Zeweldi. "Density Functional Study of Electronic and Structural Properties of Gold-Cadmium Selenide/Telluride Nanoclusters." Advances in Materials Science and Engineering 2015 (2015): 1–9. http://dx.doi.org/10.1155/2015/847693.
Повний текст джерелаАнотація:
Semiconductor nanowires are one class of building blocks that show promise for application in nanoscale electronics. Metal-semiconductor nanowire helps to improve the electrical properties or create unique ones. Electronic and structural properties of cadmium selenide/telluride connected to gold electrode clusters have been the focus of this research due to their importance in constructing fast microelectric devices. The simulations were carried out by using VASP (ViennaAb-InitioSimulation Package) which utilizes the method of density functional theory (DFT) and plane wave basis set. Optimization was performed to obtain the minimum energy structure. In this research paper the result shows that the HOMO-LUMO gaps for the minimum energy cadmium selenide/telluride connected to gold electrodes decrease as cluster size increases, whereas the binding energy shows a reverse relationship with the cluster size. However, a few clusters show special properties like AuCd2Se3and AuCd2Te3clusters.
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Vuong, Van Quan, Jenica Marie L. Madridejos, Bálint Aradi, Bobby G. Sumpter, Gregory F. Metha, and Stephan Irle. "Density-functional tight-binding for phosphine-stabilized nanoscale gold clusters." Chemical Science 11, no. 48 (2020): 13113–28. http://dx.doi.org/10.1039/d0sc04514d.
Повний текст джерелаАнотація:
We report a parameterization of the density-functional tight-binding (DFTB) method for the accurate prediction of molecular, electronic and vibrational structure of phosphine-ligated nanoscale gold clusters, metalloids, and gold surfaces.
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Shi, Yong, Cuihua Zhao, Xing Chen, Cuiting Chen, Xi Zhou та Jianhua Chen. "DFT study on the electronic structure and optical properties of an Au-deposited α-Fe2O3 (001) surface". RSC Advances 12, № 9 (2022): 5447–57. http://dx.doi.org/10.1039/d1ra07933f.
Повний текст джерелаАнотація:
The electronic structure and optical properties of gold clusters deposited on an α-Fe2O3 surface were studied by using density functional theory (DFT), with a special emphasis on the influence of Au cluster sizes.
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Zhao, Shuang, YunLi Ren, YunLai Ren, JianJi Wang, and WeiPing Yin. "Density Functional Study of Hydrogen Binding on Gold and Silver−Gold Clusters." Journal of Physical Chemistry A 114, no. 14 (April 15, 2010): 4917–23. http://dx.doi.org/10.1021/jp910230p.
Повний текст джерела
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Chen, Yuheng. "Biosensors Based on Gold Nano-Clusters." Theoretical and Natural Science 4, no. 1 (April 28, 2023): 110–18. http://dx.doi.org/10.54254/2753-8818/4/20220531.
Повний текст джерелаАнотація:
The world is entering an era of strong infectious diseases, and it is urgent to develop a new type of rapid, efficient detection system. This graph specifically illustrates the detection function of the gold nanoparticles, and the gold nanoparticles-based sensor. Gold-based nanoclusters (NCs) which has a small particle size, has a high degree of stability and no impact on the biological activity. Gold-based NCs has a surface plasma resonance effect and produces visible color, which can be detected by observing the color change using the agglomeration reaction of the detected substance with Gold-based NCs. In order to specifically detect certain biomolecules, some functional groups or small DNA molecular chains of nanolodin are usually modified on it to have a selective detection capability. In the review, we introduce a total of four nano-gold applications, for bacteria, viruses, DNA and cancer, also, respectively elaborating some recent Gold-based NCs detection applications.
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Lang, Sandra M., Thorsten M. Bernhardt, Joost M. Bakker, Bokwon Yoon, and Uzi Landman. "Methanol C–O Bond Activation by Free Gold Clusters Probed via Infrared Photodissociation Spectroscopy." Zeitschrift für Physikalische Chemie 233, no. 6 (June 26, 2019): 865–80. http://dx.doi.org/10.1515/zpch-2018-1368.
Повний текст джерелаАнотація:
Abstract The activation of methanol (CD3OD and CD3OH) by small cationic gold clusters has been investigated via infrared multiphoton dissociation (IR-MPD) spectroscopy in the 615–1760 cm−1 frequency range. The C–O stretch mode around 925 cm−1 and a coupled CD3 deformation/C–O stretch mode around 1085 cm−1 are identified to be sensitive to the interaction between methanol and the gold clusters, whereas all other modes in the investigated spectral region remain unaffected. Based on the spectral shift of these modes, the largest C–O bond activation is observed for the mono-gold Au(CD3OD)+ cluster. This activation decreases with increasing the cluster size (number of gold atoms) and the number of adsorbed methanol molecules. Supporting density functional theory (DFT) calculations reveal that the C–O bond activation is caused by a methanol to gold charge donation, whereas the C–D and O–D bonds are not significantly activated by this process. The results are discussed with respect to previous experimental and theoretical investigations of neutral and cationic gold-methanol complexes focusing on the C–O stretch mode.
Дисертації з теми "Functional Gold Clusters"
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Amft, Martin. "Density Functional Theory Studies of Small Supported Gold Clusters and Related Questions : What a Difference an Atom Makes." Doctoral thesis, Uppsala universitet, Materialteori, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-133246.
Повний текст джерелаАнотація:
During the last decades the specific manipulation of matter on the (sub-) nanometer scale, also known as nanoscience, became possible by technologies such as the scanning tunneling microscope. Nanocatalysts, i.e. catalytic active structures of up to a few nanometers in size, belong to this rather new class of materials. Unlike ordinary ’macroscopic’ catalytic materials, the performance of nanocatalysts does not simply scale, for instance, with the surface to volume ratio of the active material. In this Thesis model nanocatalysts are investigated by means of ab-initio density functional theory calculations. In paper I, we explain the experimentally observed catalytic characteristics of small gold clusters, Au1-4, on a regular magnesium oxide terrace towards the oxidation of carbon monoxide by thoroughly studying the adsorption of CO and O2 on these clusters. In the subsequent paper II, we study the feasibility of a catalytic water-mediated CO oxidation reaction on Au1-4/MgO and find that this reaction mechanism is not assessable for Au2,4/MgO and unlikely for Au1,3/MgO. Papers III and IV concentrate on the reactivity of clusters in the gas phase. Particularly, we focus on the relative stability of Au13 isomers and its potential for O2 dissociation (paper III). We find the lowest energy isomers, which contain a triangular prism at their center surrounded by a ring of the remaining seven atoms, to be generally stable upon O2 adsorption. The dissociation of O2 at certain sites of Au13 is found to be exothermic. In paper IV we performed scans of the Born-Oppenheimer potential energy surfaces of neutral and charged Cu3, Ag3, and Au3 to explore the thermally excited vibrations of these trimers. While the Born-Oppenheimer surface of Cu3 exhibits one fairly deep energy minimum, it is comparatively flat with two shallow minima in the case of Ag3. Hence for Ag3 there exist many thermally accessible geometries in a wide range of angles and bond lengths. For Au3, two distinct energy minima appear, being well-separated by a barrier of 180 meV. Already at room temperature, we find bond lengths changes of up to 5% for the studied trimers. Choosing Au3 as a case study for the changed reactivity of thermally excited modes, we find CO to bind up to 150 meV stronger to the excited cluster. Gold deposited on graphene and graphite was observed to form larger aggregates. In paper V, we study the electronic structures, high mobility, and substrate-mediated clustering processes of Au1-4 on graphene. Already in the 1970s is was speculated that dispersion forces, i.e. van der Waals forces, significantly contribute to the adsorption energies of gold atoms on graphite. We accounted for van der Waals interactions in our density functional theory calculations (paper VI) and investigated the influence of these dispersion forces on the binding of copper, silver, and gold adatoms on graphene. While copper and gold show a mixed adsorption mechanism, i.e. chemical binding plus attraction due to the van der Waals forces, silver is purely physisorbed on graphene.Felaktigt tryckt som Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology 719
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Rojas-Cervellera, Víctor. "Ab initio molecular dynamics study of thiolate-protected gold clusters and their interaction with biomolecules." Doctoral thesis, Universitat Politècnica de Catalunya, 2015. http://hdl.handle.net/10803/317382.
Повний текст джерелаАнотація:
Thiolate monolayer-protected gold clusters (AuMPCs) are being used in various biological and biomedical applications due to their unique physical and chemical properties. The fact that gold-sulphur bonds are very stable enables the binding of biomolecules in the surface of gold clusters through a cysteine, an amino acid that contains a thiol group (SH). Specific AuMPCs-peptide conjugates can cross the blood-brain barrier without altering its integrity, opening the door for the treatment of pathologies related to the central nervous system, such as Alzheimer or Parkinson. Moreover, AuMPCs represent an alternative to the traditional fluorescence-based biosensors, due to their optical properties and its ability to bind specific antigens when certain AuMPCs-antibody conjugates are used.
Several synthetic approaches based on the reduction of gold salts have been proposed to synthesize AuMPCs. In 1951 Turkevich and co-workers used sodium citrate for the reduction of chloroauric acid. In 2002 a novel synthetic method was proposed, named solvated metal atom dispersion method. In this method, neutral gold atoms were mixed with alkanethiols, resulting in the formation of AuMPCs, and molecular hydrogen was detected. This finding, together with the first crystallization and X-ray structure determination of Au102(SR)44 by Jadzinsky et.al., triggered a debate in the field, since the protons that were initially present in alkanethiols were not found in the AuMPC structure. One of the main goals of the present Thesis is to elucidate where the alkanethiol hydrogens go during the formation of the AuMPC. To this aim, ab initio metadynamics have been used to unravel the molecular mechanism of the formation of AuMPCs departing from neutral gold clusters and alkanethiols (Chapter III).
Key to the usage of AuMPCs as biosensors is the better knowledge of their optical properties. The HOMO-LUMO gap, is a physical parameter related with optical properties. Density Functional Theory (DFT) is extensively used to obtain a theoretical value of the HOMO-LUMO gap, although it is known to severely underestimate it with respect to the experimental values. Nevertheless, recent computational studies using DFT have reported values of the HOMO-LUMO gap of AuMPCs in a very close agreement with the experimental ones. However, a simplified model of the real system was used, raising the question whether the agreement between the theoretical and the experimental values is fortuitous due to a compensation of errors. Our goal is to obtain HOMO-LUMO gap values using the whole experimental systems, i.e. peptides as the protecting ligands of the gold core and water as solvent (Chapter IV) to demonstrate that only a realistic model, and not only the use of appropriate DFT functionals, can lead to values comparable to the experimental ones.
In a first step for the understanding of the reactivity of AuMPCs towards proteins, in Chapter V we modelled the binding of AuMPC towards an antibody. This process, known as ligand exchange reaction, is used to label proteins with gold clusters, as reducing agents cannot be used when certain biomolecules are present. Our results show that the neighbouring amino acids of the cysteine that should bind to the gold cluster play an essential role in the reaction.
Finally, we focus on the study of the mechanism of the enzymatic reaction of a glycoprotein, a-1,3-glycosyltransferase. In recent years, our group has investigated the mechanism of one family of glycosyltransferases (GTs), providing its catalytic itinerary. In this thesis we extend this study to another family of GTs to elucidate whether or not a common molecular mechanism operates for GTs. This study represents one step towards the modelling of the more complex glycosyltransferases immobilized by gold nanoparticles, a promising technique for the development of automated glycosynthesis.
The theoretical methods used along this thesis are detailed in Chapter II.Los clústeres de oro protegidos por tiolatos (AuMPCs) se utilizan en varias aplicaciones biológicas y biomédicas debido a sus propiedades físicas y químicas. El hecho de que el enlace oro-azufre sea muy estable permite la unión de biomoléculas en la superficie de los clústeres de oro a través de una cisteína, un aminoácido que contiene un grupo tiol (SH). Sistemas específicos AuMPC-péptido pueden atravesar la barrera hematoencefálica sin alterar su integridad, pudiéndose utilizar para tratar patologías relacionadas con el sistema nervioso central, como el Alzheimer o el Parkinson. Además, los AuMPCs representan una alternativa a los biosensores tradicionales debido a sus propiedades ópticas y su especificidad ante ciertos antígenos cuando se escoge el sistema AuMPC-péptido adecuado. Métodos basados en la reducción de sales de oro han sido propuestos para sintetizar AuMPCs. En 1951 Turkevich y colaboradores usaron citrato sódico para la reducción de ácido cloroáurico. En 2002 un nuevo método sintético fue propuesto, denominado método de dispersión de átomos metálicos solvatados. En este método, átomos de oro neutros se mezclan con alcanotioles, resultando en la formación de AuMPCs e hidrógeno molecular. Este hecho, junto con la primera cristalización y determinación estructural de Au102(SR)44 llevada a cabo por Jadzinsky y colaboradores, desencadenó un gran debate en el campo, ya que los protones que inicialmente estaban presentes en los alcanotioles no se encontraron en la estructura cristalográfica. Uno de los objetivos de esta tesis es encontrar cómo los átomos de hidrógeno forman H2 durante la formación de AuMPCs. Con este fin, se utiliza metadinámica ab initio para descifrar el mecanismo molecular de la formación de AuMPCs partiendo de clústeres de oro neutros y alcanotioles (capítulo III). Clave para el uso de AuMPCs como biosensores es el conocimiento de sus propiedades ópticas. La energía HOMO-LUMO está relacionada con estas propiedades ópticas. La teoría del funcional de la densidad (DFT) ha sido muy utilizada para obtener valores teóricos de la energía HOMO-LUMO, aunque es sabido que subestima este valor con respecto al obtenido experimentalmente. Aún así, estudios computacionales recientes han seguido utilizando DFT para calcular valores de la energía HOMO-LUMO de AuMPCs, y sorprendentemente los valores obtenidos están de acuerdo con los resultados experimentales. Sin embargo, los sistemas estudiados siempre han sido modelos simplificados de los sistemas reales, originando la pregunta de si la coincidencia es fortuita debido a una compensación de errores. Nuestro objetivo es obtener valores de la energía HOMO-LUMO para sistemas utilizados experimentalmente, es decir, péptidos como ligandos y agua como disolvente (capítulo IV) para demostrar que únicamente un modelo realista y no sólo el uso de funcionales DFT adecuados puede dar resultados comparables con los experimentales. Como primer paso para entender la reactividad de AuMPCs frente a proteínas (capítulo V), se ha modelizado la unión de un AuMPC y un anticuerpo. Este proceso, conocido como reacción de intercambio de ligandos, se utiliza para marcar proteínas con clústeres de oro. Nuestros resultados muestran que los aminoácidos del entorno de la cisteína que debe unirse al clúster de oro juegan un papel esencial en la reacción. Finalmente nos centramos en el mecanismo enzimático de una glicoproteína, la a-1,3-glicosiltransferasa. Recientemente nuestro grupo ha investigado el mecanismo de una familia de glicosiltransferasas (GTs), obteniendo su itinerario catalítico. En esta tesis hemos extendido dicho estudio a otra familia de GTs para averiguar si existe un mecanismo común para todas las GTs. Este estudio representa un primer paso para la modelización de sistemas más complejos de GTs inmovilizadas por AuMPCs, una técnica prometedora para el desarrollo de glicosíntesis automatizada. Los métodos teóricos utilizados en la tesis se describen en el capítulo II.
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Vural, Kivilcim Basak. "Adsorption Of Gold Atoms On Anatase Tio2 (100)-1x1 Surface." Master's thesis, METU, 2009. http://etd.lib.metu.edu.tr/upload/3/12610962/index.pdf.
Повний текст джерелаАнотація:
In this work the electronic and structural properties of anatase
TiO2 (100) surface and gold adsorption have been investigated
by using the first-principles calculations based on density
functional theory (DFT). TiO2 is a wide band-gap material and
to this effects it finds numerous applications in technology such
as, cleaning of water, self-cleaning, coating, solar cells and so
on.
Primarily, the relation between the surface energy of the anatase
(100)-1x1 phase and the TiO2-layers is examined. After
an appropriate atomic layer has been chosen according to the
stationary state of the TiO2 slab, the adsorption behavior of
the Au atom and in the different combinations are searched for both
the surface and the surface which is supported by a single Au
atom/atoms. It has been observed that a single Au atom tends to
adsorb to the surface which has an impurity of Au atom or atoms.
Although, the high metal concentration on the surface have increased
the strength of the adsorption, it is indicated that the system
gains a metallic property which is believed to cause problems in the
applications. In addition, the gold clusters of the dimer (Au2)
and the trimer (Au3) have been adsorbed on the surface and
their behavior on the surface is investigate. It is observed that
the interaction between Au atoms in the atomic cluster each other is
stronger than that of gold clusters and the surface.
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Oku, Yoshiaki. "Properties and Functions of Ultrasmall Silver and Gold Clusters on AgBr Microcrystals for Silver Halide Imaging." Kyoto University, 1999. http://hdl.handle.net/2433/181791.
Повний текст джерела
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Burgess, Robertson Wesley. "A TDDFT study of the optical absorption spectra of gold and silver clusters." Thesis, 2012. http://hdl.handle.net/1959.13/936786.
Повний текст джерелаАнотація:
Research Doctorate - Doctor of Philosophy (PhD)The absorption cross-section over the optical range of frequencies of gold and silver clusters of up to 171 atoms was calculated using time-dependent density functional theory. Calculations were performed using the package Octopus and used the explicit time propagation method. The wavefunctions were calculated over a real-space grid and exchange-correlation interactions were including using the local density approximation. Structures were cleaved from a bulk crystal and included high-symmetry structures as well as structures with lower levels of symmetry. The evolution of the absorption spectra over cluster size was investigated and several trends were identified. As cluster size increases the absorption spectra becomes smoother. For gold clusters with more than approximately 70 atoms, the absorption spectra have several common features, including an absorption peak at around 2.5-3.0 eV, commonly attributed to a plasmonic oscillation. Absorption spectra were compared to past calculations and experimental measurements where available. For gold clusters above approximately 150 atoms, the calculated absorption spectra are in reasonable agreement with Mie theory calculations and experimental measurements. The effect of different calculation methods and approximations on the calculated absorption cross-section was also identified. The inclusion of spin-polarisation and the use of an exchange-correlation potential using the generalised gradient approximation had minor impact on the calculated absorption spectra. A new method of analysing the nature of peaks in the absorption spectra was also investigated. This method entailed exciting the system at a single frequency, and analysing the evolution of the electron density over time. This initial investigation indicated a difference in the evolution of the system when it was oscillated at a frequency corresponding to a plasmonic response as compared to a frequency corresponding to an electron hole excitation. This possibly indicates a method for investigating the nature of a plasmonic response in clusters of this size. This thesis demonstrates that with current computing power the optical absorption spectra of metallic clusters can be calculated using time-dependent density functional theory over a continuous range of cluster sizes from several atoms up almost to the point at which classical calculations become accurate. It identifies what calculation parameters are important to the optical absorption spectra for future calculations to agree with classical calculations as more computing power becomes available.
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Ting, Chao-Ming. "Theoretical studies of molecule-substrate interaction at complex gold and silicon oxide surfaces using surface and cluster models." Thesis, 2020. http://hdl.handle.net/1828/12550.
Повний текст джерелаАнотація:
The formation and patterns of a monolayer are determined by the interplay of two fundamental interactions, adsorbate-substrate and intermolecular interactions. The binding strength between adsorbate and substrate affects the mobility of the adsorbate at the surface and the stability of the complex. The intermolecular interaction plays a significant role in the monolayer patterns on the epitaxial layer of the substrate. A monolayer can be formed either by a spontaneous self-assembly, or by fabrication via atomic-layer deposition (ALD). The physical and chemical properties of the resulting monolayer have a broad array of applications in fabricating functional materials for hydrophobic or hydrophilic surfaces, biological sensors, alternating the properties of the substrate, catalysis and forming ordered layered structures. In this dissertation, the investigation focuses primarily on the influence of the surface topology on the binding behaviour of adsorbate-surface complexes. The state of the art DFT-TS method is used to simulate the sulfur-containing amino acids at complex gold surfaces and examine the relationship between the binding strengths and the binding sites with various nearest neighbouring environments. The same method is also used to determine if a chemical reaction will take place for various catalytic silicon precursors at a silicon oxide surface.
Simulating surface chemistry using the DFT-TS method requires intensive com- puting resources, including CPU use and computing time. Another focus of this dissertation is to increase the data generating speed by reducing the size of the sim- ulated systems without altering the outcome. A relatively small gold cluster is used to study the binding behaviours of small organic molecules on the cluster. The same strategy is also used to simulate the chemical reactions between various self-catalying silicon precursors and a water molecule.Graduate
2021-10-21
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Stephens, John Adam. "Simulation tools for predicting the atomic configuration of bimetallic catalytic surfaces." 2012. http://hdl.handle.net/2152/22175.
Повний текст джерелаАнотація:
Transition metal alloys are an important class of materials in heterogeneous catalysis due in no small part to the often greatly enhanced activity and selectivity they exhibit compared to their monometallic constituents. A host of experimental and theoretical studies have demonstrated that, in many cases, these synergistic effects can be attributed to atomic-scale features of the catalyst surface. Realizing the goal of designing -- rather than serendipitously discovering -- new alloy catalysts thus depends on our ability to predict their atomic configuration under technologically relevant conditions. This dissertation presents original research into the development and use of computational tools to accomplish this objective. These tools are all based on a similar strategy: For each of the alloy systems examined, cluster expansion (CE) Hamiltonians were constructed from the results of density functional theory (DFT) calculations, and then used in Metropolis Monte Carlo (MC) simulations to predict properties of interest. Following a detailed description of the DFT+CE+MC simulation scheme, results for the AuPd/Pd(111) and AuPt/Pt(111) surface alloys are presented. These two systems exhibit considerably different trends in their atomic arrangement, which are explicable in terms of their interatomic interactions. In AuPd, a preference for heteronuclear, Au-Pd interactions results in the preferential formation of Pd monomers and other small ensembles, while in AuPt, a preference for homonuclear interactions results in the opposite. AuPd/Pd(100) and AuPt/Pt(100) were similarly examined, revealing not only the effects of the same heteronuclear/homonuclear preferences in this facet, but also a propensity for the formation of second nearest-neighbor pairs of Pd monomers, in close agreement with experiment. Subsequent simulations of the AuPd/Pd(100) surface suggest the application of biaxial compressive strain as a means increasing the population of this catalytically important ensemble of atoms. A method to incorporate the effects of subsurface atomic configuration is also presented, using AuPd as an example. This method represents several improvements over others previously reported in the literature, especially in terms of its simplicity. Finally, we introduce the dimensionless scaled pair interaction, whereby the finite-temperature atomic configuration of any bimetallic surface alloy may be predicted from a small number of relatively inexpensive calculations.text
Книги з теми "Functional Gold Clusters"
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Hardy, Duncan. Associations and the Discourses of Peace, Common Weal, and Empire. Oxford University Press, 2018. http://dx.doi.org/10.1093/oso/9780198827252.003.0008.
Повний текст джерелаАнотація:
Associations such as alliances and leagues were not merely functional tools. The rhetoric found in treaties and correspondence suggests that some members of associations perceived their participation as an activity freighted with political and moral significance. Almost all alliance and league foundation treaties and renewals contain appeals to clusters of ideas, centred on the concepts of divinely ordained peace, the common good of the community, and the Holy Roman Empire (conceptually linked, from the late fifteenth century, to the ‘German nation’). These discourses can only be found in this precise form in one other setting: the imperial diets and Empire-wide correspondence and legislation that they produced. This indicates that members of associations claimed to be involving themselves in the most significant and legitimate spheres of political activity in the Empire, even when their immediate objectives were modest and localized, or the legality of their alliances was challenged by other authorities.
Частини книг з теми "Functional Gold Clusters"
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Koyasu, Kiichirou, Keisuke Hirata, and Tatsuya Tsukuda. "Characterization of Chemically Modified Gold/Silver Superatoms in the Gas Phase." In Physical Chemistry of Cold Gas-Phase Functional Molecules and Clusters, 223–53. Singapore: Springer Singapore, 2019. http://dx.doi.org/10.1007/978-981-13-9371-6_8.
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Zanti, Giuseppe, and Daniel Peeters. "Electronic structure analysis of small gold clusters Au m (m ≤ 16) by density functional theory." In Highlights in Theoretical Chemistry, 261–75. Berlin, Heidelberg: Springer Berlin Heidelberg, 2012. http://dx.doi.org/10.1007/978-3-642-41315-5_22.
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Kurashige, W., R. Kumazawa, S. Yoshino, and Y. Negishi. "Thiolate-Protected Gold Clusters as Functional Materials in Photocatalysts." In Encyclopedia of Interfacial Chemistry, 683–96. Elsevier, 2018. http://dx.doi.org/10.1016/b978-0-12-409547-2.13006-9.
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Surono, Sugiyarto, Annisa Eka Haryati, and Joko Eliyanto. "An Optimization of Several Distance Function on Fuzzy Subtractive Clustering." In Frontiers in Artificial Intelligence and Applications. IOS Press, 2021. http://dx.doi.org/10.3233/faia210204.
Повний текст джерелаАнотація:
Fuzzy Subtractive Clustering (FSC) is a technique of fuzzy clustering where the cluster to be formed is unknown. The distance function in the FSC method has an important role in determining the number of points that have the most neighbors. Therefore, this study uses several distance functions. The results obtained indicate that the DBI results indicate that the Euclidean distance has a good cluster evaluation result in the number of clusters 4. Meanwhile, for the PC value the combination of the Minkowski Chebysev distance produces a good PC value in the number of clusters 2.
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Karami, Amin. "A Novel Fuzzy Anomaly Detection Algorithm Based on Hybrid PSO-Kmeans in Content-Centric Networking." In Advances in Computational Intelligence and Robotics, 518–50. IGI Global, 2016. http://dx.doi.org/10.4018/978-1-4666-9474-3.ch017.
Повний текст джерелаАнотація:
In Content-Centric Networks (CCNs) as a promising network architecture, new kinds of anomalies will arise. Usually, clustering algorithms would fit the requirements for building a good anomaly detection system. K-means is a popular anomaly detection method; however, it suffers from the local convergence and sensitivity to selection of the cluster centroids. This chapter presents a novel fuzzy anomaly detection method that works in two phases. In the first phase, authors propose an hybridization of Particle Swarm Optimization (PSO) and K-means algorithm with two simultaneous cost functions as well-separated clusters and local optimization to determine the optimal number of clusters. When the optimal placement of clusters centroids and objects are defined, it starts the second phase. In this phase, the authors employ a fuzzy approach by the combination of two distance-based methods as classification and outlier to detect anomalies in new monitoring data. Experimental results demonstrate that the proposed method can yield high accuracy as compared to preexisting algorithms.
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Hasan Bouzari, Hosein, Rasoul Malekfar, and Laleh Farhang Matin. "A DFT Investigation on Different Graphene Based Substrates on SERS: A Case Study of TiO2 Adsorbed Gold/Graphene." In Graphene – A Wonder Material for Scientists and Engineers [Working Title]. IntechOpen, 2022. http://dx.doi.org/10.5772/intechopen.109033.
Повний текст джерелаАнотація:
In this study, the Raman and the surface-enhanced Raman scattering (SERS) spectra of TiO2 adsorbed on gold/graphene cluster is explained by density functional theory (DFT) calculations. we concentrated on the interaction between TiO2, Au, and graphene, in which graphene is presented as a substrate component in SERS. Results indicate that changing graphene type including pure graphene and B/N-doped graphene enables modifications of interaction between molecule, gold, and graphene cluster. The Raman and SERS spectra of compounds are compared considering the intensity of spectra, which demonstrate the intensity dependence on graphene type which is due to the effects of chemical and electromagnetic properties.
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Tossell, John A., and David J. Vaughan. "Theoretical Methods." In Theoretical Geochemistry. Oxford University Press, 1992. http://dx.doi.org/10.1093/oso/9780195044034.003.0005.
Повний текст джерелаАнотація:
In this chapter, the most important quantum-mechanical methods that can be applied to geological materials are described briefly. The approach used follows that of modern quantum-chemistry textbooks rather than being a historical account of the development of quantum theory and the derivation of the Schrödinger equation from the classical wave equation. The latter approach may serve as a better introduction to the field for those readers with a more limited theoretical background and has recently been well presented in a chapter by McMillan and Hess (1988), which such readers are advised to study initially. Computational aspects of quantum chemistry are also well treated by Hinchliffe (1988). In the section that follows this introduction, the fundamentals of the quantum mechanics of molecules are presented first; that is, the “localized” side of Fig. 1.1 is examined, basing the discussion on that of Levine (1983), a standard quantum-chemistry text. Details of the calculation of molecular wave functions using the standard Hartree-Fock methods are then discussed, drawing upon Schaefer (1972), Szabo and Ostlund (1989), and Hehre et al. (1986), particularly in the discussion of the agreement between calculated versus experimental properties as a function of the size of the expansion basis set. Improvements on the Hartree-Fock wave function using configuration-interaction (CI) or many-body perturbation theory (MBPT), evaluation of properties from Hartree-Fock wave functions, and approximate Hartree-Fock methods are then discussed. The focus then shifts to the “delocalized” side of Fig. 1.1, first discussing Hartree-Fock band-structure studies, that is, calculations in which the full translational symmetry of a solid is exploited rather than the point-group symmetry of a molecule. A good general reference for such studies is Ashcroft and Mermin (1976). Density-functional theory is then discussed, based on a review by von Barth (1986), and including both the multiple-scattering self-consistent-field Xα method (MS-SCF-Xα) and more accurate basis-function-density-functional approaches. We then describe the success of these methods in calculations on molecules and molecular clusters. Advances in density-functional band theory are then considered, with a presentation based on Srivastava and Weaire (1987). A discussion of the purely theoretical modified electron-gas ionic models is followed by discussion of empirical simulation, and we conclude by mentioning a recent approach incorporating density-functional theory and molecular dynamics (Car and Parrinello, 1985).
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Shukla, Madhulata, and Indrajit Sinha. "Catalytic Activation of PVP-Stabilized Gold/Silver Cluster on p- Nitrophenol Reduction: A DFT." In Density Functional Calculations - Recent Progresses of Theory and Application. InTech, 2018. http://dx.doi.org/10.5772/intechopen.72097.
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Doğan, Onur. "Heuristic Approaches in Clustering Problems." In Handbook of Research on Applied Optimization Methodologies in Manufacturing Systems, 107–24. IGI Global, 2018. http://dx.doi.org/10.4018/978-1-5225-2944-6.ch006.
Повний текст джерелаАнотація:
Clustering is an approach used in data mining to classify objects in parallel with similarities or separate according to dissimilarities. The aim of clustering is to decrease the amount of data by grouping similar data items together. There are different methods to cluster. One of the most popular techniques is K-means algorithm and widely used in literature to solve clustering problem is discussed. Although it is a simple and fast algorithm, there are two main drawbacks. One of them is that, in minimizing problems, solution may trap into local minimum point since objective function is not convex. Since the clustering is an NP-hard problem and to avoid converging to a local minimum point, several heuristic algorithms applied to clustering analysis. The heuristic approaches are a good way to reach solution in a short time. Five approaches are mentioned briefly in the chapter and given some directions for details. For an example, particle swarm optimization approach was used for clustering problem. In example, iris dataset including 3 clusters and 150 data was used.
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Arzamazov, Aleksey. "Inmar, the Udmurt God, in Modern Udmurt Literature." In Sator, 151–66. ELM Scholarly Press, 2021. http://dx.doi.org/10.7592/sator.2021.22.06.
Повний текст джерелаАнотація:
One of the productive directions of research into Udmurt literature (and more broadly other Finno-Ugric ‘small’ literary traditions) is the identification and interpretation of multidimensional mythological clusters, textual representativeness and semantic ambivalence. In this work I have focused on only one aspect, the functional and semantic field of a particular character in Udmurt mythology and national poetry at the turn of the 21st century. The chosen mythological character is Inmar/God. The study has predominantly focused on ethnic and futuristic poems by Petr Zakharov, Viktor Shibanov, and Larisa Orekhova, characterised by a high concentration of mythological symbols. The presented research demonstrates how complex the image of Inmar is for direct artistic understanding.
Тези доповідей конференцій з теми "Functional Gold Clusters"
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Sperka, Jirí, Lenka Zajícková, Ondrej Jasek, Annapurna Pamreddy, Josef Havel, Jan Schäfer, and Rüdiger Foest. "Growth of Carbon Materials on Gold Substrate by Plasma Enhanced CVD." In 13th International Conference on Plasma Surface Engineering September 10 - 14, 2012, in Garmisch-Partenkirchen, Germany. Linköping University Electronic Press, 2013. http://dx.doi.org/10.3384/wcc2.395-398.
Повний текст джерелаАнотація:
Carbon is a versatile building element of many interesting materials that have already find practical applications in the form of thin films (diamond, DLC) or potential applications in the form of nanostructures (fullerenes, carbon nanotubes, graphene). For electronics or sensors, it is important to provide a very good contact to the functional structures. Gold is the best choice taking into account its inertness, i. e. oxidation resistance. From this point of view the investigation of the growth of carbon materials on gold is important. The carbon-gold interaction plays an important role in different fields of electronics such as atomic force microscope lithography, bioelectronics or semiconductor industry. Research in this field is developing rapidly e. g. the modification of interface structure and contact resistance between a CNT and gold electrode was recently modified by Joule melting and amorphous C-Au nanocomposite thin films were deposited by dc magnetron co-sputtering. Herein we report on the preparation and characterization of the carbon nanocomposites which were synthesized on gold substrate from methane precursor using low pressure thermal chemical vapor deposition technique and two different plasma-enhanced chemical vapor deposition (PECVD) methods. The former one PECVD proceeded in microwave reactor at low pressure and the latter one was carried out using non-thermal atmospheric pressure plasma jet (ntAPPJ). Presented approach is based on the deposition of carbon material on gold instead of the deposition of gold on carbon material which is more common. Surprisingly, we didnt find similar studies dealing with the synthesis of carbon nanocomposites using direct deposition from hydrocarbon precursor on the gold thin _lm. The surface morphology was studied by high resolution scanning electron microscopy (HRSEM). Depth-structure profile including the film thickness was observed using the focused ion beam ablation. Energy-dispersive X-ray spectroscopy (EDX), infrared reflection absorption spectroscopy (IRRAS) and laser desorption-ionization time of flight mass spectrometry (LDI-TOF MS) were used to study the chemical properties. Gold and carbon related clusters were observed by means of mass spectrometric study.
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Lindsay, H. M., M. Y. Lin, D. A. Weitz, R. Klein, and P. Meakin. "Contribution of rotational diffusion to quasielastic light scattering from fractal clusters." In International Laser Science Conference. Washington, D.C.: Optica Publishing Group, 1986. http://dx.doi.org/10.1364/ils.1986.thi6.
Повний текст джерелаАнотація:
In quasielastic light scattering the decay of the autocorrelation function of the scattered light is due to both translational and rotational diffusion. The clusters formed by the kinetic aggregation of colloids have a random structure, which is scale invariant or fractal. This results in a large contribution from rotational diffusion when the size of the cluster becomes comparable to or greater than 1/q, where q is the scattering vector. We measure the scattering from gold colloid clusters, which are aggregated in two different ways, producing clusters with fractal dimensions of 1.8 and 2.1. Both aggregation mechanisms can be simulated by computer, generating the coordinates of the individual particles comprising the clusters. We use these to calculate the total decay of the autocorrelation function, and explicitly include the contributions of rotational diffusion in terms of the moments of the angular anisotropy to the scattering. We find that, when the cluster size becomes larger than 1/q, the higher-order moments contribute significantly to the total scattering. We discuss the effects of this on the autocorrelation function, as both the cluster size and scattering vectors are varied, the shape of the predicted values of the autocorrelation function is compared with experimental results.
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Cosnita, Daniel alexandru, and Neculai eugen Seghedin. "CLUSTER COMPETITIVENESS PLATFORM." In eLSE 2017. Carol I National Defence University Publishing House, 2017. http://dx.doi.org/10.12753/2066-026x-17-134.
Повний текст джерелаАнотація:
Clusters are regional agglomerations of enterprises (industry), universities and research organisations (RDI), regional/local public authorities and other catalyst institutions gathered around common objectives and goals. Cluster models are strictly linked to measuring their competitiveness based on innovation and internationalisation, as they are regional development instruments in the first place. Several platforms are currently in use at international level measuring cluster competitiveness, created and focused on the very objective they have been defined for. The Cluster Modelling Platform proposes an integrated approach harmonising theoretic considerations and practical aspects of utility aiming at becoming an useful tool for the generation of competitive clusters based on innovation and internationalisation (1); an instrument to measure cluster competitiveness and a consultancy tool (2); a way to evaluate performance of the cluster management team (3); a flexible method allowing assessments both at cluster level and at the level of each member. The evaluation methodology considers both quantitative and qualitative aspects, taking into considerations various indicators such as turnover, exports, employment, innovation (quantitative) and geographical concentration, labour force, strategy, internationalisation and cooperation (qualitative).Qualitative aspects play a validation role, after answers given by peers are being digitalised. In the end, an analogical cluster function is being calculated. As data flow in, the function autocorrects itself in order to give accurate results. Results are being interpreted and recommendations are being provided. The tool is embedded in a user-friendly web-platform. The end beneficiaries are mainly clusters and their members but policy makers can also make a good use of it.
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Veličković, Suzana, and Xianglei Kong. "„Superalkali” clusters, production, potential application like energy storage materials." In 8th International Conference on Renewable Electrical Power Sources. SMEITS, 2020. http://dx.doi.org/10.24094/mkoiee.020.8.1.15.
Повний текст джерелаАнотація:
One of the major developments of the past century was the recognition of clusters as building blocks of new materials. “Superalkali” clusters because of their ionization energies which lower than alkaline atoms, present the excellent reducing agents; hence, they are recognized as good can-didates for the synthesis of unusually compounds. “Superalkalis”, plays an important role in the chemistry and material science because of their potential to serve as structural units for the assem-bly of novel nanostructured functional materials, such as nonlinear optical materials, hydrogen storage materials, as well as an excellent reduction reagent for decreasing emissions of carbon dioxide, nitrogen oxides, and molecular nitrogen. One way to get a cluster is to use unconventional methods. To date, the mass spectrometry has proven itself a crucial method, which has no alterna-tive, in the field of the production “superalkali” clusters. However, in order to obtain these clus-ters, it is necessary to make modifications of the mass spectrometers available on the market. With-in this paper, the possibilities of obtaining “superalkali” clusters by combining two classical meth-ods of mass spectrometry such as, Knudsen cell and the surface ionization within a magnetic mass spectrometer will be presented. The modified classic surface ionization mass spectrometry has con-firmed to be an efficient and inexpensive method for obtaining these clusters.
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Davidson, Jacob D., and N. C. Goulbourne. "Electromechanical Coupling in Ionic Polymer-Metal Composites." In ASME 2010 International Mechanical Engineering Congress and Exposition. ASMEDC, 2010. http://dx.doi.org/10.1115/imece2010-39582.
Повний текст джерелаАнотація:
Ionic polymer-metal composites (IPMCs) are smart materials which function as soft sensors and actuators. When a small DC voltage (1–5 V) is applied to an IPMC in a cantilever configuration, ion and solvent transport through the thickness of the polymer membrane causes the transducer to bend towards the anode. For device development and use in engineering applications, actuation is often described at a higher level in terms of an electromechanical coupling between the ionic charge distribution and the stresses developed in the IPMC. In this work we derive a set of relationships describing the coupling response by starting with basic considerations of polymer microstructure and local interactions during actuation. A micromechanical modeling framework is employed in order to account for the material microstructure. Using a generalized expression for electrostatic cluster pressure which takes into account clusters recombining to form larger cluster upon expansion, we define an effective local stiffness which varies with both solvent uptake and charge density in the boundary layers. An equilibrium relationship between solvent uptake and charge density is determined by considering the free energy of the homogenized polymer as the sum of elastic, electrostatic, and chemical components. Stress developed in the boundary layers is then calculated from changes in local stiffness and solvent uptake with respect to charge density. The resulting relationship for electromechanical coupling is found to be in good agreement with previous empirical models, thus serving as a model validation and demonstrating why certain forms for electromechanical coupling can be used to explain a variety of experimental observations. Specifically, we see that stress developed in the boundary layers is well described as a quadratic polynomial in charge density due to the form of the electrostatic cluster pressures.
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Sousa Júnior, Edilson, Airton Carneiro Freitas, Ricardo Rabelo, and Welflen Santos. "Estimation of Radial Basis Function Network Centres via Informational Forces." In Congresso Brasileiro de Inteligência Computacional. SBIC, 2021. http://dx.doi.org/10.21528/cbic2021-85.
Повний текст джерелаАнотація:
The Radial Basis Function Network centres determination is a open problem. In this work, the cluster centres are determined by a proposed gradient algorithm using the information forces acting on each data point. These centres are applied to a Radial Basis Function Network for data classification. A threshold is established based on Information Potential to classify the outliers. Combined, the threshold and the centres determined by information forces show good results in comparison to a similar Network with a k-means clustering algorithm.
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Yuan, Yuan, and Diana-Andra Borca-Tasciuc. "The Influence of Coating and Agglomeration on Specific Absorption Rate of Iron Oxide Nanoparticles." In ASME 2011 9th International Conference on Nanochannels, Microchannels, and Minichannels. ASMEDC, 2011. http://dx.doi.org/10.1115/icnmm2011-58217.
Повний текст джерелаАнотація:
Magnetic nanofluids can be remotely heated by alternating magnetic field and have significant potential for cancer hyperthermia therapy. The heat generated by magnetic nanoparticles is typically quantified by the specific absorption rate (SAR), which represents the thermal power per unit mass of magnetic material generated in the presence of an alternating magnetic field. During hyperthermia treatment, heat dosage of tumor tissue correlates with slowing tumor growth. The therapeutic ratios of cancer can be increased with the use of biofunctionalized magnetic nanoparticles that have higher SAR for modest amplitudes of magnetic field[1]. Hence, understanding the factors that control the heat generation of magnetic nanoparticle suspensions is important to design fluids with optimized biocompatibility and functionality. In all biomedical applications, the nanoparticles must be coated on the surface to prevent their agglomeration [2], enhance biocompatibility and allow targeting to a specific area. Existing studies have shown that the SAR of nanoparticles may change in the presence of functional coating[3–5]. However, while these studies show that the coating may affect the heat generation rate, there is a limited understanding on the mechanisms that cause that changes of SAR. Hence, it is important to carry out a systematic investigation of nanoparticles similar in size but with different organic coating relevant to biomedical applications to obtain a more complete picture of the mechanisms contributing to changes in SAR. In this work, we present a review of our efforts in this area. Specifically, in our studies we are investigating the correlation between the magnetic and physical properties of commercially available nanoparticles systems and their heat generation rate. The susceptibility and SAR of suspensions of coated and uncoated iron oxide nanoparticles of similar particle size are measured. The coatings selected are highly relevant to biomedical applications and include amine and carboxyl functionalization as well as bioaffine ligands such as protein and biotin. The particle and cluster size was determined from transmission electron microscope (TEM), X-Ray diffraction (XRD) and Dynamic light scattering (DLS). TEM and DLS studies suggested that clusters exist in samples. A summary of all morphological properties together with pH of each suspension is shown in Table.1. The AC magnetic susceptibility of the suspensions was measured as a function of frequency with an in-house made apparatus. Finally SAR was determined by heating the suspension in a commercial induction system and measuring the temperature rise as function of time with a fiber optic sensor. Following these measurements, the SAR values were predicted in two ways: 1) based on measured AC susceptibility and 2) based on particle physical and magnetic properties, starting from Debye model for susceptibility. The normalized predicted and experimental SAR values for all samples are also shown in Table 1. From Table 1, it was found that pH may influence aggregation as described in Ref [6], which indicated that at pH about 2 nanoparticles are highly charged preventing their aggregation while in pH in 6–10 suspensions aggregations are more significant. Normalized SAR of nanoparticle system with aggregations seems to be not related to concentration, different from the well dispersed system[7]. The carboxyl coated sample has smallest diameter and show the lowest SAR, as reported in Ref[8]. The results of suspensions of uncoated iron oxide nanoparticles as well as particles coated with amine groups show that normalized experimental SAR (NSARE) agrees relatively well with calculated SAR using experimental susceptibility (NSARC_χ″E); poor agreement was found when experimental susceptibility was substituted with calculated one (NSART_χ″C) using Debye model, which is developed for non-interacting magnetic particles. These results suggest that the coating do not have a direct effect on SAR. On the other hand, agglomeration, which was present in both samples, may lead to dipolar interaction between nanoparticles and enhancement in magnetic properties and SAR. For carboxyl coated sample which has negligible clustering, showed no temperature increase and zero imaginary part of susceptibility. Therefore, good agreement between Debye-model based predictions of SAR and experimental results were obtained in this sample. However, unexpected results were obtained for bioaffine ligands coated sample, where the experimental SAR values are higher than the SAR values determined based on experimental susceptibility. Protein coated sample, which has the larger clusters among the two samples, has a heat generation rate is 6 times higher than the prediction. Meanwhile, the biotin coated sample which has relatively smaller clusters show only a small increase in heat generation rate. A possible explanation for these results is the loss of superparamagnetic character and an opening in hysteresis loop at test frequency for suspensions with large clusters, which may increase the dissipated power above that produced by the relaxation heat losses [9]. Above results show that coating had little effect on SAR. On the other hand, aggregations and clusters may significantly affect SAR, possibly due to dipolar interaction between nanoparticles in suspensions with relatively small clusters or loss of superparmagnetic characters when very large clusters are present.
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Wong, Eric K. L., and Geraldine L. Richmond. "Laser excitation spectroscopy: a probe of metal ion binding in polymers." In International Laser Science Conference. Washington, D.C.: Optica Publishing Group, 1986. http://dx.doi.org/10.1364/ils.1986.fg6.
Повний текст джерелаАнотація:
The structure and the function of many macromolecules and organic polymers are dependent on the specific sites bound to metal ions. Metal binding in some ionic polymers is in the form of ionic clusters. The objective of our laser-induced fluorescence studies is to gain a better understanding of the structure and binding properties of these clusters by using europium ions as probes. Eu(III) has many unique spectral properties which make it a good luminescent probe of the metal binding in polymers. The energy, fluorescence quantum yield, and lifetime of the excited state of the 7F0 → 5D0 transition near 580 nm are very sensitive to the environment of the ions. By studying this transition in detail, it is possible to obtain unique optical information about the metal–molecule interaction. Metal binding in the perfluorosulfonate membrane, Nation (DuPont), has been studied here as function of such parameters as metal ion concentration and pH. The resulting excitation spectra show multiple peaks corresponding to different ionic environments. The results of these experiments are discussed in terms of the known macroscopic binding properties of this film.
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Mabuchi, Takuya, and Takashi Tokumasu. "Molecular Dynamics Study of Proton and Water Transport in Nafion Membrane." In ASME 2013 11th International Conference on Nanochannels, Microchannels, and Minichannels. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/icnmm2013-73084.
Повний текст джерелаАнотація:
Polymer electrolyte fuel cells (PEFCs) are highly expected as a next-generation power supply system due to the purity of its exhaust gas, its high power density and high efficiency. The polymer electrolyte membrane is a critical component for the performance of the PEFCs and it is important to understand the nanostructure in the membrane to enhance proton transport. We have performed an atomistic analysis of the vehicular transport of hydronium ions and water molecules in the nanostructure of hydrated Nafion membrane by systematically changing the hydration level which provides insights into a connection between the nanoscopic and mesoscopic structure of ion clusters and the dynamics of hydronium ions and water molecules in the hydrated Nafion membrane. In this study, classical molecular dynamics simulations are implemented using a model of Nafion membrane which is based on DREIDING force field and newly modified and validated by comparing the density, water diffusivity, and Nafion morphology with experimental data. The simulated final density after the annealing procedure agrees with experiment within 1.3 % for various water contents and the trends that density decreases with increasing hydration level are reproduced. In addition to determination of diffusion coefficients of solvent molecules as a function of hydration level (from λ = 1 up to λ = 18), we have also calculated radial distribution functions and static structure factors not only to clarify the structure of water molecules and hydronium ions around the first solvation shell of sulfonate groups but also to validate the mesoscopic periodic structure among water clusters. The diffusion coefficient of water molecules increases with increasing hydration level and is found to be in good agreement with experimental data. The diffusion coefficient of hydronium ions has showed that general trends in the experimental data are reproduced by the simulations although the classical models have the limitation of probing hydronium dynamics. The static structure factors of liquid molecules at low wave length provide insights into the periodic structure of the inter-water clusters. These results are consistent with the Gebel’s model based on small-angle X-ray scattering that considers the dry membrane to be made of isolated spherical ionic clusters of radius ∼7.5 Å that swell with increasing hydration.
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Gavrea mazur, Iuliana. "QUALITY EVALUATION OF THE PRESCHOOL EDUCATION SYSTEM IN IASI." In eLSE 2016. Carol I National Defence University Publishing House, 2016. http://dx.doi.org/10.12753/2066-026x-16-094.
Повний текст джерелаАнотація:
The interest shown to the children of pre-school education increased due to the benefits which the students had by participating in the preschool education and they achieved the necessary abilities in school. The investments in good quality pre-school education had benefits on the long term because they contributed to the increase not only of the social inclusion and the employment of workforce, but also to the poverty reduction. The pre-school education systems within the European Union support investments in pre-school education programs offered to the children who come from disadvantaged environments, who would be insufficiently prepared for school, and they act as a helping instrument for the entire school system. The aim of this paper is the quality evaluation of the preschool education according to the main quality dimensions: human resources, equipment and financing sources. In order to emphasize the relation between the quality dimensions of the preschool education, we apply the cluster analysis, while for the evaluation of the differences among the kindergarten clusters we use ANOVA. The kindergarten, as a formal education service, ensures the child's development, with the help of the family and of the community, in the learning process, and takes into account the psychological features. At the pre-school age, all the education functions are centered on the formation of the student through the transmission of information with a moral, religious, cultural and scientific character, according to the age's particularities. The results of this study show that the good training of the teachers and the better equipment in education explains the higher level of preschool participation, thus reflecting a quality of the preschool education system. The significance of this study consists in highlighting the necessity for the preparation of the pre-school child according to the cognitive, physical, socio-emotional development, in order to integrate in the school activity.