91 research outputs found
Application of Multivariate Analysis Techniques for Selecting Soil Physical Quality Indicators: A Case Study in Long-Term Field Experiments in Apulia (Southern Italy)
No full textLong-term field experiments and multivariate analysis techniques represent research tools that may improve our knowledge on soil physical quality (SPQ) assessment. These techniques allow us to measure relatively stable soil conditions and to improve soil quality judgment, thereby reducing uncertainties. A monitoring of SPQ under long-term experiments, aimed at comparing crop residue management strategies (burning vs. incorporation of straw, FE1) and soil management (minimum tillage vs. no tillage, FE2), was established during the crop growing season of durum wheat. The relationships between five SPQ indicators (bulk density [BD], macroporosity [PMAC], air capacity [AC], plant available water capacity [PAWC], and relative field capacity [RFC]) were evaluated, and two techniques of multivariate analysis (principal component analysis and stepwise discriminant analysis) were applied to select key indicators for SPQ assessment. According to the used indicators, an SPQ from optimal to intermediate (i.e., not definitely poor) was detected in 65% of the observations in FE1 and in 54% in FE2. The main results showed a significant negative relationship between RFC and AC, and multivariate analysis identified RFC as a key SPQ indicator, mainly in FE2. Plant available water capacity and BD showed the highest discriminating capability in the FE1 dataset. The highest scores of RFC assessment were highlighted for burning and minimum tillage treatments (+1 and +2). An optimal AC range, derived from optimal RFC limits, was obtained and was suggested to better assess the AC of agricultural soils (0.10 ≤ AC ≤ 0.26 cm3 cm-3). © 2019 The Author(s)
Ligand shell morphology of water-soluble mixed-monolayer protected gold nanoparticles
No full textThesis (S.M.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2007.Includes bibliographical references (leaves 41-43).Nanoparticles comprise a versatile class of nanomaterials that consist of particles that have a characteristic length scale less than 100nm. They are on a similar length scale as many biological elements, so it is fitting that they are being used increasingly in biological systems for a variety of applications. Interesting properties of water-soluble metal nanoparticles that could lead to novel biological applications include bio-catalytic, sensing, and light scattering capabilities. We will present here the characterization of novel highly water-soluble gold nanoparticles that can be used as model systems to study the fundamental mechanisms of cellular uptake and intracellular trafficking.by Suelin Chen.S.M
Study of the hadronic current in the neutrino interactions of the OPERA experiment
No full text2011 - 2012The OPERA experiment was designed to observe the appearance of the vr in a pure
beam ofvll (CNGS). The evidence ofthe appearance signal is provided by the detection
of the daughter particles produced in the decay of charged lepton T.
The hadronic decay channel has the largest branching ratio; in order to proficient1y use
it for neutrino oscillation detection, one needs a good knowledge ofthe hadronic current
in the OPERA experimental setup. The present work shows the data-acquisition and the
comparative analysis of a "minimum-bias" sample of interactions to the standard
simulation used in OPERA.
The first chapter of this thesis work is an overview of neutrino physics; in the final part
of the chapter some neutrino experiments are described.
The second chapter focuses on the OPERA detector. The main components of the
detector are explained as well as the physical performance of the experiment.
Data-taking is the subject of the third chapter; the scanning procedure is shown,
followed by the technique used to estimate the momentum of particles in the ECC.
Finally, the fourth chapter presents the data analysis. [edited by Author]XI n.s
Synthesis, characterization, and fractionation of cell penetrating gold nanoparticles
No full textThesis (S.M.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2010.Includes bibliographical references (p. 42-43).Analytical Ultracentrifugation (AUC) is a powerful tool to obtain statistically relevant size and shape measurements for macromolecular systems. Metal nanoparticles coated by a ligand shell of thiolated molecules provide diverse functionality, from targeted cellular delivery to the formation of complex assemblies. Here I show that AUC can be used to determine particle size distribution, ligand shell density, shape, and hydrodynamic radius. It can also be used to probe complex mixtures of nanoparticle assemblies, from 2D dimers and chains, to 3D trimers, tetramers, and higher order assemblies, from a consideration of their hydrodynamic shape factor and its relation to the sedimentation coefficient. With AUC, the ease of sample preparation, ligand shell information, and dramatic increase in sample size are improvements compared with electron microscopy, and the ability to probe multiple, discrete absorbing wavelengths and globally analyze with interference information offers a measured improvement compared with dynamic light scattering (DLS). This work describes multiple calibrations and considerations as well as theoretical contributions concerning the application of AUC to nanoparticle systemsby Randy Carney.S.M
Evaporative printing of organic materials and metals and development of organic memories
No full textThesis (S.M.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2004.Includes bibliographical references (p. 125-132).The advantages of directed printing make it the ideal fabrication tool for the ubiquitous electronic technologies of the future. However, direct printing techniques such as ink-jet technology, are currently limited to materials that can be processed in solution. We developed a novel micro-machined print head capable of expanding the capabilities of inkjet printing to metals and molecules that are suited for evaporative deposition. Deposition of metals is particularly desirable advantage of the proposed printer. We demonstrate arbitrary organic and metal patterns by printing, with the line width modulated by controlling the micro-machined shutter. With the challenges and solutions for ambient pressure printing are also studied. Additionally, the printer can be used for organic crystal formation, and controlled doping. In the second part of the thesis we examine charge trapping and storage in organic thin film devices. We demonstrate that by controlled doping, we can engineer charge storage in active organic electronic devices. Charge trapping in organic hetero-junction structures results in two distinct phenomena that both manifest as a memory behavior. Trapped charge can (1) increase the carrier mobility in organic structures, (2) generate current during the de-trapping process. Both processes are demonstrated in practical structures.by Sung Hoon Kang.S.M
General approach for the application of Supramolecular NanoStamping (SuNS) to surfaces of all types
No full textThesis (S.M.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2007.Includes bibliographical references (leaves 77-83).To novel ideas must correspond novel fabrication techniques, that enable the transfer of technologies from laboratories to the market. The success of microelectronics for example can not be separated from the success of the revolutionary manufacturing technology that has fed its expansion. The same is now true for nano- and biotechnologies that, to a large extent, have yet to find the technologies that will best answer their processing needs. The question is to find an approach that will enable the production of devices with the required resolution, complexity and versatility, together with the necessary reliability and potential for high-throughput. Supramolecular NanoStamping (SuNS), a DNA based lithography technique developed in our group, is trying to answer to this set of requirements. In this thesis, I present a new development in this lithography technique, expanding its application to a broad new range of substrates in a substrate-independent fashion. This work, which I conducted during the course of my master, proves the ability of SuNS to adapt to very diverse environments and applications.by Sarah Thévenet.S.M
Effects of doping single and double walled carbon nanotubes with nitrogen and boron
No full textThesis (S.M.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2006.Includes bibliographical references (p. 135-143).Controlling the diameter and chirality of carbon nanotubes to fine tune their electronic band gap will no longer be enough to satisfy the growing list of characteristics that future carbon nanotube applications are starting to require. Controlling their band gap, wall reactivity and mechanical properties is imperative to make them functional. The solution to these challenges is likely to lie in smart defect engineering. Defects of every kind can induce significant changes on the intrinsic properties of carbon nanotubes. In this context, this thesis analyzes the effects of doping single and double walled carbon nanotubes with nitrogen and boron. We describe the synthesis of N-doped single-walled carbon nanotubes (N-SWNTs), that agglomerate in bundles and form long strands (<10cm), via the thermal decomposition of ferrocene/ethanol/benzylamine (FEB) solutions in an Ar atmosphere at 950°C. Using Raman spectroscopy, we noted that as the N content is increased in the starting FEB solution, the growth of large diameter tubes is inhibited. We observed that the relative electrical conductivity of the strands increases with increasing nitrogen concentration. Thermogravimetric analysis (TGA) showed novel features for highly doped tubes, that are related to chemical reactions on N sites.(cont.) We also carried out resonance Raman studies of the coalescence process of double walled carbon nanotubes in conjunction with high resolution transmission electron microscope (HRTEM) experiments on the same samples, heat treated to a variety of temperatures and either undoped or Boron doped. As the heat treatment temperatures are increased (to 1300°C) a Raman mode related to carbon-carbon chains (w = 1855cm-1) is observed before DWNT coalescence occurs. These chains are expected to be 3-5 atoms long and they are established covalently between adjacent DWNTs. The sp carbon chains trigger nanotube coalescence via a zipper mechanism and the chains disappear once the tubes merge. Other features of the Raman spectra were analyzed as a function of heat treatment with special emphasis on the metallic or semiconducting nature of the layers constituting the DWNTs. DWNTs whose outer wall is metallic tend to interact more with the dopant and their outer tubes are the predominant contributors to the line shape of the G and G' bands.(cont.) The metallic or semiconducting nature of the layers of the DWNTs does not affect their coalescence temperature. All the experiments and analysis presented in this thesis are the result of a collaborative effort between Professor Dresselhaus' group at MIT and its international collaborators, including Professor Endo's group at Shinshu University, Nagano, Japan, Professors Pimenta's and Jorio's group at the Federal University of Minas Gerais, Belo Horizonte, Brazil, and Professors M. and H. Terrones' group at IPICYT, San Luis Potosi, Mexico.by Federico Villalpando Paéz.S.M
Controlling the structure of 2D NPSCs from long-range order to anisotropy by tailoring ligand interactions
No full textThesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2012.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from student submitted PDF version of thesis.Includes bibliographical references.Ligand-stabilized nanoparticles (NPs) assembled into long-range ordered arrays, also known as "nanoparticle supracrystals (NPSCs)", are expected to provide a powerful general platform for designing new types of solids. In particular, the NPs are themselves self-assembled structures consisting of a core and a self-assembled monolayer of ligand molecules surrounding it. The self-assembled structure of the NPs themselves determines the structure of the self-assembled supracrystals. Ligands are of special interest in this respect, because it is an important component for the NP system which play a major role in the design of self-assembly of the complex matter and also provide a powerful entry into the supracrystal engineering. The increasing ability to control the way in which ligand molecules associate gives means for the designed generation of supraparticle architectures in the self-assembly. In spite of this, elucidation of how the ligands play a role in affecting the structural behavior of NPSCs remains largely unrevealed. In this thesis, the effect of ligands for the two dimensional (2D) self-assembled NPSCs structure was investigated. The key materials advancement that enables this work is that we have been able to synthesize monodisperse gold NPs of same core size but different ligand molecules. Additionally, a new method for monolayer film processing has been developed to prepare the 2D NPSCs, based on a Langmuir assembly through successive compression cycles. Importantly, as there is little effect exhibited by solvent interactions in the NPs structure obtained from this approach, the corresponding NPs structural variation in this work is truly driven by the different ligand interactions in NPSCs. Specifically, we show that such ligand interactions have direct consequences on the ordering and symmetry of the assembled NPSCs structures. Here, we report on a set of NPSC arrays in which small changes in either the NP ligand environment or the ligand configuration geometry induce significant variations in the order parameters of the crystal. First, we show that the packing organization of a 2D NPSC array of hydrophobic alkanethiol ligands varies with subtle chemical changes in the system, leading to a transition between long-range to short-range (almost glassy) ordered phases. The balance between long and short-range order is driven by small differences in intermolecular interpenetration of the ligand molecules, that can be related to ligand conformational and that can be rigorously the experimentally measured. Second, we show the first 2D NPSC structures to have unique anisotropic symmetry due to the interaction between amphiphilic NP ligand shells. It is understood that the ligand interactions on NPs through their unique molecular configuration of amphiphilic ligands may provide the anisotropic feature in the orientational alignment of NPSC symmetry.by Jin Young Kim.Ph.D
Amino acids modulate liquid-liquid phase separation in vitro and in vivo by regulating protein-protein interactions
No full textCopyright © 2024 the Author(s). Published by PNAS.Liquid-liquid phase separation (LLPS) is an intracellular process widely used by cells for many key biological functions. It occurs in complex and crowded environments, where amino acids (AAs) are vital components. We have found that AAs render the net interaction between proteins more repulsive. Here, we find that some AAs efficiently suppress LLPS in test tubes (in vitro). We then screen all the proteinogenic AAs and find that three specific AAs, including proline, glutamine, and glycine, significantly suppressed the formation of stress granules (SGs) in U2OS and HeLa cell lines (in vivo) irrespective of stress types. We also observe the effect in primary fibroblast cells, a viable cell model for neurodegenerative disorders. Kinetic studies by live-cell microscopy show that the presence of AAs not only slows down the formation but also decreases the saturating number and prevents the coalescence of SGs. We finally use sedimentation-diffusion equilibrium analytical ultracentrifuge (SE-AUC) to demonstrate that the suppression effects of AAs on LLPS may be due to their modulation in protein-protein and RNA-RNA interactions. Overall, this study reveals an underappreciated role of cellular AAs, which may find biomedical applications, especially in treating SG-associated diseases.SUNMI
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