Academic literature on the topic 'Macroscopic assemblies'

Amphiphilic Janus MXene nanosheets are synthesized for the first time by a one-step transferring method, which can act as promising solid surfactants to stabilize emulsions, and assemble into macroscopic 2D ultrathin MXene films and 3D MXene aerogels.

The frictional collapse of an assembly of equisized spheres is studied by a discrete element model. The macroscopic constitutive response is determined as a function of the level of Coulomb friction between particles. It is found that the level of Coulomb friction has a strong effect upon the relative proportion of sliding and rolling between particles, and consequently upon the macroscopic strength of the granular assembly. The discrete element predictions are shown to be in good agreement with experimental results obtained from triaxial tests on an aggregate of steel spheres. It is demonstrated that the shape of the collapse surface can be adequately represented by the Lade-Duncan continuum model.

Macroscopic cross section generation is key part of core calculation. Commonly, the data are prepared independently without a knowledge of fuel loading pattern. The fuel assemblies are simulated in infinite lattice (with mirror boundary conditions). Rehomogenization method is based on combination of actual neutron flux in fuel assembly with macroscopic data from infinite lattice. Rehomogenization method was implemented into the macrocode Andrea and tested on a reference cases. Cases consist of fuel cases, cases with strong absorber, cases with absorption rods, or cases with reflector assemblies. Testing method is based on a comparisons of homogenized and rehomogenized macroscopic cross sections and later on a comparisons of relative power of each fuel assembly. Above that there is comparison of eigenvalue.

2011/2012
Carbon nanotubes (CNTs) possess important physical and chemical properties, such as high electrical and thermal conductivity, large surface area, high mechanical strength and chemical stability, that made them important in the construction of novel biomaterials, biosensors, transistors and conductive layers. However, an unsettled issue pertinent to the construction of such CNT-based materials is their precise localization and controllable spatial organization. As result, the development of new protocols for patterning CNTs on substrates or disperse them in biological media have become increasingly important in their processing. In this direction, several approaches have being developed, among them, the inclusion of non-covalent bond such electrostatic, hydrophobic, hydrogen bonding, metal coordination and π-π interactions. The aim of this thesis was to evaluate H-bonding interactions as directional, reliable and predictable non-covalent attractive forces between complementary H-donor (D) and H-acceptor (A) moieties to control the self-organization process of CNTs for the construction of macroscopic materials. In the Introduction (Chapter 1), an overview on CNTs is given, explaining their main features and the key issues associated with their manipulation. The different existing possibilities for CNT functionalization are described, focusing the attention on the covalent approach exploited in this thesis, namely the diazonium salt-based arylation reaction. The main characterization techniques used are then described, illustrating their advantages and their limitations. Subsequently, the existing literature on macroscopic CNT assemblies is given. Examples include super-strong 1D CNT fibers, highly flexible 2D CNT films and compressible 3D CNT arrays or foams. Finally, molecular-recognition events, able to direct the assembly of macroscopic structures, are described focusing on the possibility of translate this supramolecular approach on the assembly of CNT architectures. In Chapter 2 the utilization of an acridine-derived Zn(II)-cyclen complex as a multidentate ligand for recognizing thymidine-derived multiwalled carbon nanotube derivatives (Td-MWCNTs) is reported. The effectiveness of the Zn(II)-cyclen recognition has been confirmed through a combination of analytical techniques such as Kaiser test, TGA-MS, IR, X-Ray photoemission spectroscopy, TEM, UV-Vis absorption and fluorescence spectroscopy. Taken all together, the different characterization techniques have unambiguously shown the 1:1 recognition of the nucleoside by a Zn(II)-cyclen complex and confirmed that the Td moieties preserve their recognition properties also in presence of CNTs. In Chapter 3 nucleosides moieties (Thymidine, T; Adenosine, A; Cytidine, C; Guanosine, G) were covalently attached to MWCNTs as supramolecular motifs, N-MWCNTs (N=A, T, G, C). Then, the complementary nucleobase pair nanohybrids T-MWCNTs/A-MWCNTs and G-MWCNTs/C-MWCNTs were mixed together and the supramolecularly self-assembly was followed by characterization techniques such as TEM, TGA and IR spectroscopy. The successful recognition process allows the fabrication of freestanding homogeneous membranes by a simple vacuum filtration methodology. The electronic conduction properties of the resulting N-MWCNT films were measured. Finally, the intrinsic conductivity of pristine MWCNTs was restored in the films by the thermal removal of the organic functionalization moieties, as verified by resistivity and TGA measurements. Finally, in Chapter 4, a versatile and simple method for the construction of macroscopic structures based on CNT/Polymer composites is demonstrated. Ureidopyrimidinone (UPy) moieties were covalently attached to MWCNTs as supramolecular motifs (UPy-MWCNTs) and the novel nanohybrid compound was characterized by TGA, IR, TEM, UV-visible and 1H-NMR spectroscopy. Then the self-assembly of UPy-MWCNTs with different polymers bearing UPy moieties (Bis-UPy 1, Bis-UPy 2), trough quadruple complementary DDAA•AADD H-bonding motif, allowed the fabrication of a 2D free standing film and of a supramolecular gel using the method of solution blending. In conclusion the present thesis demonstrates that organic molecules covalently grafted to CNT surface as supramolecular motifs can control the self-assembly of CNTs by H-bonding recognition. This strategy can be used for the construction of supramolecular architectures to create new nanodevices. In particular we have demonstrated that the self-organizzation of functionalized CNTs lead to a versatile and simple method for the construction of macroscopic structures based on pure MWCNTs or on CNT/Polymer composites.
I Nanotubi di Carbonio (CNTs) presentano importanti proprietà fisico-chimiche, come alta conducibilità elettrica e termica, ampia area superficiale, elevata forza meccanica e stabilità chimica, che li rendono interessanti per la costruzione di nuovi biomateriali, biosensori, transistor e film conduttivi. Tuttavia la loro localizzazione, organizzazione spaziale e manipolazione rimangono problemi irrisolti legati alla costruzione di materiali a base di nanotubi di carbonio. Lo sviluppo di nuovi protocolli per la deposizione controllata di CNTs su substrati o la loro dispersione in materiali biologici sono diventati sempre più di interesse. In questa direzione, diversi approcci sono in fase di sviluppo, tra cui l’esplorazione di legami non-covalenti, quali interazioni elettrostatiche, idrofobiche, legami a idrogeno, legami coordinativi e interazioni π-π. Lo scopo di questa tesi è stato valutare l’uso di interazioni a idrogeno come forze attrattive non-covalenti, direzionali e prevedibili, tra porzioni complementari H-donatori (D) e H-accettori (A) per controllare l'auto-organizzazione dei CNTs per la costruzione di materiali macroscopici. Nell'Introduzione (Capitolo 1), viene fatta una breve panoramica dei CNTs, spiegando le loro caratteristiche principali e le problematiche associate alla loro manipolazione. Vengono descritte le diverse strategie per la funzionalizzazione dei CNTs, focalizzando l'attenzione sull’ approccio covalente sfruttato in questa tesi, vale a dire la reazione di arilazione basata sui sali di diazonio. Vengono anche presentate le principali tecniche di caratterizzazione utilizzate, illustrando i loro vantaggi ed i loro limiti. Successivamente, viene riportata la letteratura esistente sulle strutture macroscopiche a base di CNTs. Gli esempi includono fibre 1D, film 2D e strutture 3D. Infine, vengono descritti alcuni processi di riconoscimento molecolare, in grado di dirigere l'assemblaggio di strutture macroscopiche, concentrandosi sulla possibilità di applicare questo approccio supramolecolare nell'assemblaggio di architetture di CNTs. Nel Capitolo 2 è stato riporto l'impiego di un complesso di acridina-Zn(II)-ciclano come legante multidentato per il riconoscimento di frammenti timidinici legati covalentemente alla superficie di CNTs (Td-MWCNTs). L'efficacia del riconoscimento supramolecolare è stato confermato attraverso una combinazione di tecniche analitiche quali il Kaiser test, TGA-MS, IR, XPS, TEM, assorbimento UV-Vis e spettroscopia di fluorescenza. Nel loro insieme, le diverse tecniche di caratterizzazione hanno dimostrato inequivocabilmente il riconoscimento 1:1 tra il nucleoside ed il complesso Zn(II)-ciclano, ed hanno confermato che le porzioni timidiniche conservano le loro proprietà di riconoscimento anche in presenza di CNTs. Nel Capitolo 3 i quattro nucleosidi (timidina, T; adenosina, A; citidina, C; guanosina, G) sono stati legati covalentemente a CNTs come pendagli supramolecolari, N-MWCNTs (N = A, T, G, C). I nanoibridi portanti coppie di nucleobasi complementari, T-MWCNTs/A-MWCNTs e G-MWCNTs/C-MWCNTs, sono stati mescolati insieme e l’ auto-riconoscimento supramolecolare è stato analizzato con diverse tecniche di caratterizzazione come TEM e spettroscopia IR. Il processo di riconoscimento ha permesso la fabbricazione di membrane omogenee, utilizzando una semplice metodologia di filtrazione sotto vuoto. Le proprietà di conduzione elettrica dei risultanti film di N-MWCNTs sono state misurate. Infine, nelle membrane è stata restaurata la conducibilità intrinseca dei CNTs attraverso la rimozione termica delle funzionalizzazioni organiche, come verificato dalle misure di resistività e dalle analisi TGA. Nel Capitolo 4, infine,è stato dimostriamo un metodo versatile e semplice per la costruzione di strutture macroscopiche basate su compositi di nanotubi e polimeri. Pendagli di Ureidopirimidinoni (UPy) sono stati covalentemente legati alle pareti dei CNTs come motivi supramolecolari (UPy-MWCNTs) ed il nuovo nanoibrido è stato caratterizzato attraverso TGA, IR, TEM, assorbimento UV-visibile e 1H-NMR. L'auto-assemblaggio di UPy-MWCNTs con diversi polimeri recanti frammenti UPy (Bis-UPy 1, Bis-UPy 2) ha permesso la realizzazione di un film bidimensionale e di un gel supramolecolare, attraverso la formazione di legami a idrogeno complementari quadrupli DDAA•AADD. In conclusione la presente tesi dimostra che le molecole organiche legate covalentemente alla superficie dei CNTs come motivi supramolecolari sono in grado di controllare l'auto-assemblaggio dei nanotubi attraverso il riconoscimento a legame a idrogeno. Questa strategia può essere usata per la costruzione di architetture supramolecolari per creare nuovi nanodispositivi. In particolare è stato dimostrato che l'auto-organizzazione di CNTs funzionalizzati risulta un metodo versatile e semplice per la costruzione di strutture macroscopiche a base di soli CNTs o di compositi nanotubi/polimeri.
XXV Ciclo
1983

This work reports the successful production of macroscopic assemblies of aligned single walled carbon nanotubes (SWNTs) via filtration in a magnetic field of 25 Tesla. Such assemblies allow an unprecedented capability to characterize and manipulate aligned nanotubes. Surface areas in excess of 100 cm 2 and thicknesses in excess of seven microns thick were produced. A density within a factor of two of close packing was achieved. These assemblies exhibit anisotropy in reflection of polarized light, Raman resonance, electrical transport, and thermal transport. This provides a macroscopic window to exploring the properties of SWNTs and paves the way for many potential applications. This thesis also describes experiments using a combination of electrical and chemical methods, including DC electric fields, amine-derivatization of gold, and thiol-derivatization of SWNTs. These latter experiments preceded the filtration work and provided an essential basis for conceptualizing the successful filtration approach.

Nanoscale building blocks, such as nanocrystals and one-dimensional (1D) nanostructures, have attracted tremendous attention due to their peculiar and fascinating properties. It is necessary to assemble the low dimensional nanoscale building blocks into macroscopic nanostructured architectures for potential applications in energy storage, separation, catalysis, computation, sensing, etc. This dissertation demonstrates synthesis, characterization and applications of macroscopic hierarchical metal or semiconductor (e.g., Pt, CdSe) nanowire networks. These nanowire networks were synthesized by electrodeposition within the pores of highly-ordered mesoporous silica template followed by removal of the silica template, resulting in robust nanowire networks with replicated mesopore structure. The nanowire diameter (3-10 nm) and network mesostructures (e.g. 2D, 3D and superstructures) are controlled by the pore size and the mesostructure of the silica template. As-synthesized metal nanowires self support to form networks with high electrochemical active surface area, which are further applied in enzymatic glucose sensing. Semiconductor CdSe nanowire networks show tunable optical properties dependent on nanowire diameter and have been demonstrated as a good electron acceptor in CdSe nanowire network/polymer photovoltaic devices. The dissertation also describes self-assembly behavior of composite mesostructures under physical confined environment. Novel mesostructures and mesostructured nanowire superstructures have been achieved by the confined assembly and the replication procedure mentioned above. Our approach provides an easy and efficient way to synthesize macroscopic hierarchical nanowire networks with well-controlled diameter and mesoscale arrangement, which will be of great interest for sensor, photovoltaic, and other applications
acase@tulane.edu

碩士
國立中央大學
土木工程研究所
94
This study performs experimental work with cylinders on the conveyor belt to simulate the initial process of landslide induced debris flow.The experimental set up consists of three parts: microscopic overturn deformation and macroscopic fluidization. The kinetic of angular velocity and displacement of the overturn process on the top layer of the cylinders is studied. The change of porosity before and after the overturn is analyzed at different velocities (i.e. 5.08cm/s, 10.16cm/s,15.24 cm/s,20.32 cm/s), and slopes (i.e. 0°, 5°, 10°,15°, 20°),respectively. The particle image algorithm is used to study the deformation on the bottom of the assemble cylinders by shearing force. The change of porosity before and after the failure is analyzed at different velocities (i.e. 4.17cm/s, 12.34cm/s), and slopes (i.e. 0°, 20°). We establish a method to measure the deformation, angular velocity and porosity of particles. The experimental results show that region of the shearing zone increases as the velocity of the conveyor belt, increases. Different belt velocities (i.e. 4.17cm/s, 12.34cm/s) affect the thickness of fluidization, and lead to two opposite results on the decay rate of PVC, and steel layers under the same experimental conditions. The sequence of cylinders flowing out the confined zone is strongly related to the gap clearance. When the gap is raised, the leading side of cylinders will flow out first while the gap becomes low, the tailing side and bottom parts of cylinders will flow out first.

Even though the general framework of statistical mechanics is ultimately targeted at the description of macroscopic systems, it is illustrative to apply it first to some simple systems: a harmonic oscillator, a rotor, and a spin in a magnetic field. These applications serve to illustrate how a key function associated with the Gibbs state, the so-called partition function, is calculated in practice, how the entropy function is obtained via a Legendre transformation, and how such systems behave in the limits of high and low temperatures. After discussing these simple systems, this chapter considers a first example where multiple constituents are assembled into a macroscopic system: a basic model of a paramagnetic salt. It also investigates the size of energy fluctuations and how—in the case of the paramagnet—these fluctuations scale with the number of constituents.

Nonlinear optical (NLO) materials have gained much attention during the last two decades owing to their potentiality in the field of optical data storage, optical information processing, optical switching, and telecommunication. NLO responsive macroscopic devices possess extensive applications in our day to day life. Such devices are considered as assemblies of several macroscopic components designed to achieve specific functions. The extension of this concept to the molecular level forms the basis of molecular devices. In this context, the design of NLO switches, that is, molecules characterized by their ability to alternate between two or more chemical forms displaying contrasts in one of their NLO properties, has motivated many experimental and theoretical works. Thus, this chapter focuses on the rational design of molecular NLO switches based on stimuli and materials with extensive examples reported in the literature. The factors affecting the efficiency of optical switches are discussed. The device fabrication of optical switches and their efficiency based on the optical switch, internal architecture, and substrate materials are described. In the end, applications of switches and future prospectus of designing new molecules with references are suitably discussed.

The word ‘crystal’ is derived from the Greek root ‘krustallos’ meaning ‘clear ice’. Like ice, crystals are chemically well defined, and many among of them are of transparent and glittering appearance, like quartz, which was for a long time the archetype. Often they are beautiful geometrical solids with regular faces and sharp edges, which probably explains why crystallinity, even in the figurative meaning, is taken as a symbol of perfection and purity. From the physical point of view, crystals are regular three-dimensional arrays of atoms, ions, molecules, or molecular assemblies. Ideal crystals can be imagined as infinite and perfect arrays in which the building blocks (the asymmetric units) are arranged according to well-defined symmetries (forming the 230 space groups) into unit cells that are repeated in the three-dimensions by translations. Experimental crystals, however, have finite dimensions. An implicit consequence is that a macroscopic fragment from a crystal is still a crystal, because the orderly arrangement of molecules within such a fragment still extends at long distances. The practical consequence is that crystal fragments can be used as seeds (Chapter 7). In laboratory-grown crystals the periodicity is never perfect, due to different kinds of local disorders or long-range imperfections like dislocations. Also, these crystals are often of polycrystalline nature. The external forms of crystals are always manifestations of their internal structures and symmetries, even if in some cases these symmetries may be hidden at the macroscopic level, due to differential growth kinetics of the crystal faces. Periodicity in crystal architecture is also reflected in their macroscopic physical properties. The most straightforward example is given by the ability of crystals to diffract X-rays, neutrons, or electrons, the phenomenon underlying structural chemistry and biology (for introductory texts see refs 1 and 2), and the major aim of this book is to present the methods employed to produce three-dimensional crystals of biological macromolecules, but also two-dimensional crystals (Chapter 12), needed for diffraction studies. Other properties of invaluable practical applications should not be overlooked either, as is the case of optical and electronic properties which are at the basis of non-linear optics and modern electronics (for an introduction to physical properties of molecular crystals see ref. 3).

Abstract Contrary to fracture, plastic deformation is usually associate to smooth flow and one would not expect to observe any avalanche behavior. Nevertheless, plastic instabilities with strong and widely fluctuating deformation jumps have been known for long time. These are typically attributed to the interplay between dislocation and diffusing solute atoms. Experiments have shown that in plastically deformed ice single crystals, acoustic emission displays power law amplitude distributions. This behavior is due to the collective motion of interacting dislocations and can be reproduced by numerical simulations. In presence of immobile solute atoms or other defects, dislocations display a depinning transition in response to external stress. The remarkable nature of the dislocation mutual interactions is also responsible for a similar jamming transition even without intrinsic pinning. In this chapter, we first introduce the basic concepts of continuum plasticity, which represent the macroscopic reference frame of the present discussion. We then discuss the physics of dislocation assemblies in presence of pinning and report on the basic phenomenology of the yielding transition which is ruled by dislocation mutual interactions. Finally, we review the properties of plastic deformation in amorphous materials and glasses.

Formation and characterization of organic thin film assemblies intended for use in biomolecular devices, such as biosensors, is currently a very active area of research. We have been investigating techniques for creating macroscopically ordered protein films formed by covalent bonding between a unique site on the protein and an appropriately derivatized substrate surface. Assemblies consisting of heme proteins immobilized on substrates coated with self-assembled monolayers and Langmuir-Blodgett are being examined. Macroscopic film order is probed using a combination of total internal reflectance fluorescence and planar integrated optical waveguide-attenuated total reflection spectroscopies, from which the orientation distribution of heme tilt angles in the protein film is determined.

Hemicyanine dyes containing long alkyl chains have attracted considerable attention in recent years due to their significance as possible optoelectronic and molecular electronic materials. With large non-linear molecular polarizabilities, amphiphilic hemicyanines are readily incorporated into Langmuir-Bludgett monolayer and multilayer films, forming artificial molecular assemblies with preferred spatial and orientational order [1,2], In contrast to centrosymmetric bulk materials, in which the individual effects are canceled, and the overall bulk second-order susceptibility vanishes [1], highly aligned structures ensure non-zero macroscopic second-order susceptibilities, χ(2). In addition molecular assemblies of these materials have been shown to be characterized by extended electronic states in which the relationship between molecular structure and delocalization of the electronic states is a matter of current interest.

Abstract A model for crack nucleation in layered electronic assemblies under thermal cycling is developed in this paper. The present model includes three scales: (i) at the microscale or the mechanism level, the damage mechanisms such as diffusive void growth or fatigue cracks, determine the damage growth rate; (2) at an intermediate mesoscale, the localized damage bands are modeled as variable stiffness springs connecting undamaged materials; and (iii) at the macroscale or the continuum level, the localized damage band growing in an otherwise undamaged material is modeled as an array of dislocations. The three scales are then combined together to incorporate damage mechanisms into continuum analysis. Traditional fracture mechanics provides a crack propagation model based on pre-existing cracks. The present work provides an approach for predicting crack nucleation. The proposed model is then utilized to investigate crack nucleations in three-layered electronic assemblies under thermal cycling. The damage is observed to accumulate rapidly in the weakest regions of the band. Estimates are obtained for critical time or critical number of cycles at which a macroscopic crack will nucleate in these assemblies under thermal cycling. This critical number of cycles is found to be insensitive to the size of the damage cluster, but decreases rapidly as the local excess damage increases.

Abstract This paper describes a variant shape model and its application to tolerance analysis. To realize a high-precision mechanism at low cost, designers specify various types of tolerances selectively, often in combination on a single face. We propose a solid model that has attributes at points scattered over its faces. In this model, the macroscopic geometry is represented as a B-rep solid model, and the microscopic geometry (manufacturing errors and clearances) as attributes. The model can represent a wide variational class, such as shapes with form errors. We use it to present a method for generating a deviant shape model having a specified set of geometric errors. After deviant part shapes have been generated, they are assembled virtually in such a way that they do not interfere with each other and that the physical conditions of the attachment are satisfied. Through a large number of deviant assemblies, a product’s performance is analyzed statistically and quantitatively.

In statistical physics of dilute gases maximum entropy methods are widely used for theoretical predictions of macroscopic quantities in terms of microscopic quantities. In this study an analogous approach to the mechanics of quasi-static deformation of granular materials is proposed. The reasoning is presented that leads to the definition of an entropy that is appropriate to quasi-static deformation of granular materials. This entropy is formulated in terms of contact quantities, since contacts constitute the relevant microscopic level for granular materials that consist of semirigid particles. The proposed maximum entropy approach is then applied to two cases. The first case deals with the probability density functions of contact forces in a two-dimensional assembly with frictional contacts under prescribed hydrostatic stress. The second case deals with the elastic behaviour of two-dimensional assemblies of non-rotating particles with bonded contacts. For both cases the probability density functions of contact forces are determined from the proposed maximum entropy method, under the constraints appropriate to the case. These constraints form the macroscopic information available about the system. With the probability density functions for contact forces thus determined, theoretical predictions of macroscopic quantities can be made. These theoretical predictions are then compared with results obtained from two-dimensional Discrete Element simulations and from experiments.

A 3D neutron kinetic code DiFis is designed for steady-state and transition calculation for cores with hexagonal fuel assemblies. The code uses traditional time-dependent diffusion equations in a two-group approximation and takes into account six delayed group neutron precursors. A variation finite element method is used for solution of diffusion equations. The thermal-hydraulic model of the code is based on an “average” fuel rod model. Each fuel assembly contains such a rod, which provides heat transfer from a fuel pellet through the gas gap and the cladding to the coolant. The thermal-hydraulic model is used for feedback correction of macroscopic nuclear cross-sections. The code DiFis has been used for the AER-DYN-002 benchmark problem, which describes an eccentric control rod ejection at hot zero power condition in a VVER-440 type reactor. The only feedback mechanism taken into account is a Doppler one. Comparison with well-known nodal kinetic codes shows acceptable accuracy of DiFis. As an example of transition calculation, a VVER-1000 core behavior during fast power reduction is described.