1,062 research outputs found
Stiffness of clays and silts: Modeling considerations
No full textA large database has recently been published that details the development of new empirical expressions for the stiffness reduction with strain of clays and silts. In this note, the same database is used to examine two major considerations for engineers using these expressions in numerical analyses: the transformation from secant to tangent stiffness and the effect of stress history. (C) 2014 American Society of Civil Engineers.</p
Clays, muds, and shales /
No full textThis book provides a comprehensive and critical summary of clay mineral literature that relates to geology and geologic processes, making it useful both as a reference book for geologists and as a text for the specialist. The book encompasses the full scope of clay-shale geology. An introductory chapter provides basic background terminology and classification. This is followed by a relatively long chapter on the structure and composition of the various clay minerals. Chapter 3 provides an introduction to soil formation, chemical weathering, microbial alteration and the pedogenic formation of clay minerals. Chapters 4 and 5 cover the continental and marine transport, and deposition of clays. Both mechanisms and examples are presented, ranging from biodepositional to the nepheloid layer. Chapter 6 reviews data on the low to high temperature formation of clay minerals from marine volcanics, and the growth of authigenic clays in shallow marine, brackish, and evaporite environments. Chapter 7, Diagenesis Metamorphism, covers both burial diagenesis and the processes occurring during the conversion of shale to clay. Chapter 8 discusses the formation of authigenic-diagenetic formation of clays in sandstones. Chapter 9 describes the temperal distribution of clay minerals in North and South America, Europe, Africa and the Atlantic Ocean. The clay suites are related to factors such as continental drift, tectonics, climate and environment. The final brief chapter covers compaction, lithification and some general features of shales. The book is liberally sprinkled with x-ray patterns, chemical analyses, and SEM and TEM pictures, in addition to hundreds of examples.This book provides a comprehensive and critical summary of clay mineral literature that relates to geology and geologic processes, making it useful both as a reference book for geologists and as a text for the specialist. The book encompasses the full scope of clay-shale geology. An introductory chapter provides basic background terminology and classification. This is followed by a relatively long chapter on the structure and composition of the various clay minerals. Chapter 3 provides an introduction to soil formation, chemical weathering, microbial alteration and the pedogenic formation of clay minerals. Chapters 4 and 5 cover the continental and marine transport, and deposition of clays. Both mechanisms and examples are presented, ranging from biodepositional to the nepheloid layer. Chapter 6 reviews data on the low to high temperature formation of clay minerals from marine volcanics, and the growth of authigenic clays in shallow marine, brackish, and evaporite environments. Chapter 7, Diagenesis Metamorphism, covers both burial diagenesis and the processes occurring during the conversion of shale to clay. Chapter 8 discusses the formation of authigenic-diagenetic formation of clays in sandstones. Chapter 9 describes the temperal distribution of clay minerals in North and South America, Europe, Africa and the Atlantic Ocean. The clay suites are related to factors such as continental drift, tectonics, climate and environment. The final brief chapter covers compaction, lithification and some general features of shales. The book is liberally sprinkled with x-ray patterns, chemical analyses, and SEM and TEM pictures, in addition to hundreds of examples.Background. Structure and Composition. Soils and Weathering. Continental Transport and Deposition. Marine Transport and Deposition. "Authigenic Marine" Physils. Diagenesis Metamorphism. Physils in Sandstones. Evolution of Physils and Continents. Lithification and Petrology. References. Author and Subject Indexes. (Full contents available upon request to the publisher).Includes bibliographical references (pages 723-785).Print version record.Elsevie
Guide to the nature and methods of analysis of the clay fraction of tephras from the South Auckland region, New Zealand.
No full textThe manual outlines some of the more common laboratory procedures available for qualitatively and quantitatively analysing the composition of the tephric clays, many of which are difficult to determine because of their short range order or 'amorphous' nature. Techniques described and assessed in terms of their rapidity and quantitativeness include XRD, IR, DTA, TEM and SEM, sodium fluoride reactivity, chemical dissolution analyses, and surface area measurements. No one technique alone produces a definitive clay fraction analysis of tephric deposits. -from Author
CCDC 915406: Experimental Crystal Structure Determination
No full textRelated Article: Benjamin J. Coe, Simon P. Foxon, Madeleine Helliwell, Daniela Rusanova, Bruce S. Brunschwig, Koen Clays, Griet Depotter, Marcin Nyk, Marek Samoc, Dominika Wawrzynczyk, Javier Garín, Jesús Orduna|2013|Chem.-Eur.J.|19|6613|doi:10.1002/chem.20120445
CCDC 915407: Experimental Crystal Structure Determination
No full textRelated Article: Benjamin J. Coe, Simon P. Foxon, Madeleine Helliwell, Daniela Rusanova, Bruce S. Brunschwig, Koen Clays, Griet Depotter, Marcin Nyk, Marek Samoc, Dominika Wawrzynczyk, Javier Garín, Jesús Orduna|2013|Chem.-Eur.J.|19|6613|doi:10.1002/chem.20120445
Moleculaire niet-lineaire optica: gevorderde chromofoorkarakterisatie voor doelgerichte (supra)moleculaire designs ,,
No full textThe coherent, monochromatic and intense light of a laser opened the way to research in nonlinear optics, the field in which this doctoral research is situated. Nonlinear optical (NLO) materials are able to alter the color of light, switch it or change its transmission characteristics, depending on its intensity. The technological applications of such nonlinear optical interactions are myriad. After introducing the general aspects of (non)linear optics in the first chapter, the experimental details of linear absorption, hyper-Rayleigh scattering (HRS) and depolarization ratio measurements are discussed in Chapter 2. The different approaches to deal with the competing process of multi-photon fluorescence in the HRS measurements are discussed in detail.
In Chapter 3, a study on the second-order nonlinear optical properties of organometallic molecular structures with increasing dimensionality is elaborated. The flexible nature of the substitution and oxidation states of transition metal complexes enables their use as donor or acceptor moieties in chromophores. The presence of a metal center allows for other geometries, as a palette of coordination patterns is available for metals. Intrinsically connected to the presence of a transition metal center, these compounds possess reversible redox switching behavior. The NLO properties of one-dimensional, thermally stable ferrocenyl "push-pull" chromophores with an isophorone derived acceptor, ferrocene-diketopyrrolopyrroles and ferrocene-α-cyanostilbenes are discussed, as well as two-ferrocenyl V-shaped chromophores with a rhenium or zinc center and heptametallic octopolar compounds. We have established clear structure-property relations towards molecular optical switches with varying polarization sensitivity.
Chapter 4 deals with the development of porphyrin-based chromophores for bio-medical imaging, more specifically the development of voltage-sensitive dyes to track brain activity when intercalated in the membranes of neurons. In the development of these dyes, function as well as form requirements, i.e. the appropriateness of the compounds for the experimental question and biological target respectively must be taken into account. As an example for nonlinear optical imaging of a cell membrane, a dipolar compound should have amphiphilic properties. Porphyrins can make excellent second-harmonic generation (SHG) dyes to probe voltage changes over neuronal membranes. The finding that the free-base porphyrin core is sufficiently electron-deficient that the hyperpolarizability does not increase on addition of a pyridinium electron-acceptor creates opportunities in the design of new SHG probes. Besides, experimental results show the possibility of elaborating the porphyrin bridge by adding another porphyrin building block to optimize the voltage sensitivity of these extraordinary membrane probes. Dispersion of first and second hyperpolarizability values within the bio-optical transparency window should be mapped and exploited to optimize the possibilities of the SHG probe.
Helically wrapped single-walled carbon nanotubes (SWNTs) are studied in chapter 5. We report for the first time experimental measurements of the first hyperpolarizability of individualized, length-sorted (700 ± 50 nm long) single chirality (6,5) SWNTs. The chiral, opto-electronically active polymers wrap the nanotubes in an exclusively left-handed, single-chain helical fashion and feature PZn2, PZn3 and PZnRuPZn octopolar chromophores as integral parts of the polymer backbone. The non-covalent functionalization of these electronically homogeneous SWNTs by NLO chromophores demonstrates an appealing strategy to design new classes of electro-optic materials that feature enhanced hyperpolarizabilities over the telecommunication-relevant spectral domain.
The importance of target-oriented development, taking into account both form and function requirements, is clear from the very different approaches of chromophore molecular design in chapters 3, 4 and 5. We explored higher dimensionality as well as extension along one dimension and supramolecular chirality in the domain of molecular optical switches, biological imaging as well as optical telecommunication.status: Publishe
Holle sferen als bouwstenen voor nieuwe nanostructuren en gefunctionaliseerde colloïdale fotonische kristallen ,,
No full textstatus: Publishe
Influence of plasticity and porewater salinity on shrinkage and water retention characteristics of biochar‐engineered clays
No full textFunding Information: The first author is grateful for the support by USDOE (United States Department of Education) GAANN (Graduate Assistance in Areas of National Need). The corresponding author acknowledges the startup research grant provided by the School of Engineering, Aalto University for supporting this research work. Publisher Copyright: © 2023 The Authors. Soil Science Society of America Journal published by Wiley Periodicals LLC on behalf of Soil Science Society of America.Clay-engineered barriers might be subjected to soil salinization issues under climate change. A recently emerged desalinization method is achieved by modifying clays using biochar. However, unsaturated soil responses of biochar-engineered clays in saline environments under drought conditions remain unknown. This study aims to investigate soil shrinkage and water retention characteristics of biochar-amended kaolin and bentonite under saline conditions. Soil shrinkage and water retention tests were conducted on clays (with and without biochar addition) with various porewater salinity (i.e., 0%–10%). Physiochemical properties (including zeta potential and porewater pH) were measured to interpret particle–fluid interactions. Shrinkage characteristics of kaolin and bentonite exhibited sensitivity and insensitivity to the porewater salinity, respectively. This phenomenon was explained by hydrogen-sodium ion exchange and deprotonation phenomenon occurring on kaolin and bentonite, respectively. Biochar significantly alleviated the salinity-induced shrinkage of clays by increasing the shrinkage limit of kaolin and bentonite by 6%–14% and 50%–107%, respectively (p < 0.05). This was attributed to the porous structure and hydrophilic functionality of biochar that immobilized sodium ions through ion exchange and protonation reactions. The air entry value of clays significantly increased with porewater salinity and biochar addition due to the reduction of void ratio and enhanced capillarity, respectively. An empirical equation was proposed to predict the shrinkage limit of clay in various saline conditions. It highlighted that the application of biochar-engineered clays could contribute to the desalination and the improvement of resistance to shrinkage damage in hydro-chemical barriers.Peer reviewe
Controle over de voortplanting van licht door defectmodes en magnetische effecten in fotonische kristallen.
No full textThe aim of this work was to take the existing photonics crystals experience in this lab, and build on that to create new structures. This includes both enhancements of work that has been done before, and also making new materials and ways to influence the optical properties. Photonic crystals, by themselves, already have some special optical properties. The materials are essentially structures with a periodic variation of the index of refraction on a scale similar to the wavelength of electromagnetic radiation one wants to influence. The sizes cover a very broad range --- much of the early work was done in the microwave region, with the near infrared being tested using semiconductor devices. Our work mainly focuses on the visible light region of the electromagnetic spectrum, and the type of photonic crystal we use is the artificial opal, a synthetic structure created by the self-assembly of close-packed spherical monodisperse colloids, with a structure similar to that of the naturally occurring opal.The spheres stack in a close-packed crystal ordering (generally considered to be face-centered cubic), and this highly regular structure leads to the appearance of Bragg reflections, so the material will reflect different wavelengths of light in different directions. For large structures of this type, an analogy with semiconductors can be made, as the periodic variation of the index of refraction has an influence on photons travelling through the material, which is similar to the influence electrons experience from periodic potential variations in semiconductor crystals. Band diagrams can be made for photonic crystals, showing band gaps like those in semiconductors, energy levels where no photon propagation may occur. This insight led to research into photonic crystals as the optical analogue of semiconductor technology, now an important subject in photonics. Just like electronics, the introduction of modifications (defects) into the structure is often essential to obtain the desired behaviour. A material that passes no electrons or photons may have its uses, but a material that can selectively pass some and block others, or guide them into specific paths, promises far more advanced applications (in the long term possibly including optical computers).A first part of this study was based on the study of defect layers in synthetic opal crystals. Initially the defects were made out of spheres like those forming the main opal, but of different size. The defect would thus be made of the same material as the bulk crystal, but due to a size mismatch a phase difference would be introduced to the light propagating through the samples. Further research successfully explored the possibility of introducing other materials inside the structure to create sharper and bigger defects, creating optical cavities bounded by photonic crystals. These structures may prove useful in future research involving fluorescence.The other (and arguably more ambitious) part of these modifications is the introduction of magnetic materials into photonic crystals. This opens the road towards tuning the optical properties of the crystals using magnetic fields, leading to the possibility of the crystal having different properties for light beams travelling in opposite directions (useful in, for example, optical isolators that pass light in one direction and block it in the other). We succeeded in creating magnetic photonic crystals using only wet chemical and self-assembly techniques and characterise them. This included using Faraday rotation measurements to verify their magneto-optical properties, which were found to differ significantly from those of nonmagnetic reference samples.status: Publishe
Octopolaire materialen voor tweede orde niet-lineair optische toepassingen.
No full textIn this work, the molecular and supramolecular second-order nonlinear optical (SONLO) properties of octopolar chromophores are studied. Molecules of octopolar symmetry are noncentrosymmetric, a fundamental requirement for efficient SONLO structures, and nonpolar. The main research interest in these systems lies in their ability to spontaneously adopt noncentrosymmetric crystal structures, as opposed to traditionally studied dipolar chromophores. A typical recurring motif are extended C3-symmetric pi-systems, substituted with electron donating and electron accepting groups. In this work, we have studied several series of octopolar chromophores, derived from this motif. The main goal was to gain insight in the structure-function relationship of the studied systems, related to their molecular SONLO properties. In other words: how can we tune the molecular SONLO response by chemical synthesis, i.e. the introduction of various molecular functionalities? Since technological applications ultimately rely on bulk materials, we also studied the bulk properties of a series of compounds, and explored how we can control the supramolecular organization, determining the SONLO response, by molecular engineering. After introducing the field of linear and nonlinear optics, and the employed characterization methods, we discuss a very broad interdisciplinary study of the electronic structure and corresponding molecular properties of a series of thienylethynyl octopolar compounds. A variety of spectroscopic techniques is used to study the structure-function relationship of these compounds. These results are backed-up by theoretical calculations. The SONLO response of the compounds shows a subtle modulation depending on the nature of the substituents and is shown to depend on the charge-transfer character from the core to the periphery, as effected by the electron donating/accepting character from the side groups. The experimental SONLO results are reproduced well by theoretical calculations and allow for a qualitative comparison between various models. In the next chapter we present a study on the linear and nonlinear optical properties of a series of hexaazatriphenylene (HAT) molecules. The electron deficient HAT core is extended with peripheral electron donating groups of different strength. Furthermore the effect of the spacer (double or triple carbon-carbon bonds) connecting the core to its periphery is investigated. Linear and nonlinear optical spectroscopy, electrochemistry and theoretical modeling provide insight in the electronic properties of these molecules, revealing a distinct influence of the different spacers and the mesomeric effect of the donor groups on the charge-transfer properties and ultimately the SONLO response. In a fifth chapter, an extensive series of triindoles with different conjugation length and peripheral substituents is investigated by linear and nonlinear optical spectroscopy, in combination with electrochemistry. A study of the first hyperpolarizability of these compounds reveals an unusually strong wavelength dependence that cannot be explained by the conventional three-level model for octopoles. To explain for this behaviour, we carried out an extensive study at multiple wavelengths and were able to model the full wavelength dependence of the first hyperpolarizability by a theoretical analysis using Thomas-Kuhn sum rules. We show that the unusually strong dispersion can be understood in terms of the mixing of higher excited states through the nonlinear optical interaction. This study reveals that dispersive effects can have a much greater influence on the SONLO response than was assumed so far. In chapter 6, a series of donor-acceptor substituted 1,3,5 trisalkynylbenzenes is studied. The molecular properties are explored by linear and nonlinear spectroscopy. The charge-transfer character of the chromophores is reflected in the linear regime. The introduction of strong electron accepting groups results in an increased SONLO response. In a second part we studied the bulk properties of a series of nitrated analogues, that display discotic liquid crystalline mesophases at higher temperatures. The bulk SONLO response, depends on the length and nature of the alkoxy side chains, driving the supramolecular organization. The introduction of chiral side groups, in an effort to promote a chiral crystal packing, is investigated and shown to lead to a considerable SONLO response in the crystalline state. The crystal structure of these compounds is determined by polarized SHG microscopy. For a series with achiral side chains of different length, longer side chains lead to centrosymmetric structures. The crystalline state of an analogue with shorter side chains exhibits a large SONLO response. The symmetry is determined by polarized SHG microscopy. Surprisingly, a chiral point group was found for the achiral analogues as well, critically confirmed by circular dichroism spectroscopy. Finally, we present an image analysis formalism, based on straightforward polarized second-harmonic generation microscopy tests. This convenient formalism allows assessing the local organization and homogeneity of crystalline structures, of crucial importance for technological applications, with high resolution and sensitivity.status: Publishe
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