Carbon and nitrogen cycling in the Peruvian Andean Amazon

Townsend-Small, Amy The University of Texas at Austin 2008 해외박사(DDOD)

This dissertation consists of several studies conducted at various spatial and temporal scales designed to identify the important processes that affect organic matter (OM) inputs from the Andes mountains to the Amazon headwaters, as well as carbon (C) and nitrogen (N) cycles in the rivers themselves. Andean rivers supplied approximately equal amounts of fine and coarse sediments to the Amazon, but most coarse sediments were retained in the Andean foreland while fine sediments continued downstream. Terrestrial plant delta 13C increased with elevation, but terrestrial soil delta 13C did not and was enriched by 1-3‰ over plants. Particulate organic matter (POM) concentrations were generally low, with periodic high concentrations during storms. There were significant differences in the isotopic composition of POM between seasons (wet vs. dry), reflecting changes in sediment source. During high flow, POM resembled terrestrial materials, but during drier periods there was evidence for a resuspended bottom sediment or algal source. During wet periods, OM content of soils and river POM decreased downstream, but the POM trend was complicated during drier months. Delta14C of POM decreased downstream, suggesting that young, fresh OM introduced in small headwater streams was respired preferentially in rivers or diluted with older material downstream. Fine suspended POM was higher in delta 15N and delta13C than coarse POM, indicating either greater degradation in the fine fraction or sorption of isotopically enriched dissolved OM. Deforestation is reflected in suspended POM in small headwaters, with enrichment in both 13C (due to introduced C4 grasses) and 15N. Epiphytic plants living in forest canopies were delta15N-deplete compared to rooted plants, and the biomass of these epiphytes was so high that their delta15N was reflected in stream POM. Precipitation was a major source of isotopically enriched dissolved organic N (DON) to cloudforests in the central Andes. Inorganic N export from these systems in streams was very low, but this seems to be the result of high demand for DIN by microbes and fine roots in riparian soils, not a high reactivity of dissolved inorganic N (DIN) in the stream. Low deposition of and demand for inorganic N in these forests appear to explain low ambient stream DIN concentrations.

Structure-Function Studies of the Cul3/Rbx1:Keap1 E3 Ubiquitin Ligase Complex

Small, Evan University of Illinois at Chicago 2012 해외박사(DDOD)

Eukaryotic cells have adapted unique mechanisms to respond to environmental stressors. The Nrf2-ARE system is one of these mechanisms and is used to combat chemical stressors such as environmental toxins or endogenous metabolites. Chemopreventive compounds are chemical agents that in low doses cause Nrf2 nuclear accumulation and the subsequent up-regulation of a battery of cytoprotective enzymes which decrease carcinogenesis. These same compounds have been shown to react with and covalently modify components of the ubiquitin E3 ligase complex that directly affects the stability of Nrf2. Determining how this complex's quaternary structure is altered upon reaction with chemopreventive compounds will provide a greater understanding of how the complex functions and is regulated. It is hypothesized that chemopreventive compounds, most of which are electrophilic in nature, react with specific cysteines within the complex to bring about a structural change thereby affecting the ability of the complex to ubiquitinate Nrf2. To test this hypothesis, ultracentrifugation and small angle X-ray scattering experiments were performed to measure the size and shape of the E3 ligase bound to its substrate Nrf2. In addition, the alteration of the size and shape of the Keap1-Nrf2 system upon site-directed mutation or modification by chemopreventive compounds was also performed. Results suggest that upon modification, conformational changes occur within the E3 ligase complex, which alter the ubiquitination of Nrf2. This research was supported by a grant from NCI of the NIH (5PO1 CA48112).

The comparison of inequality : the semantics and syntax of the comparative particle in English

Small, George William Distributed by the Johns Hopkins University Press 1924 국내석사

Towards successful implementation of advanced manufacturing technology : a process-factors-process approach

Small, Michael Hilary Cleveland State University 1993 국내박사

ESSAYS IN SELF-PORTRAITURE : A COMPARATIVE STUDY OF SELF-PORTRAITURE IN THE WORKS OF REMBRANDT AND MONTAIGNE

SMALL, ANDREW THOMAS University of North Carolinaat Chapel Hill 1991 해외박사

ESCLAVE, NEGRE, NOIR : THE REPRESENTATION OF BLACKS IN LATE 18TH AND 19TH-CENTURY FRENCH ART (EIGHTEENTH CENTURY, NINETEENTH CENTURY)

SMALLS, JAMES University of California 1991 해외박사

The open semiclassical approximation to the density matrix and its application to the Wigner function

Small, Michael Solomon University of California, Berkeley 2008 해외박사(DDOD)

The semiclassical initial value representation (IVR) provides a way to incorporate quantum dynamical effects into classical molecular dynamics simulations. Application of the IVR to large systems depends on its ability to be formulated in a monte carlo setting. In this work, we focus on the simplest (and most approximate) IVR, known as the linearized semiclassical IVR (LSC) which is equivalent to Wigner's classical model. The LSC approximation combines an exact treatment of quantum statistics with dynamics approximated by classical mechanics. The main computational obstacle of the LSC approximation is that it requires the Fourier transform of the thermal density matrix. Therefore, all applications of LSC to large systems require a Gaussian approximation to the density matrix so that this Fourier transform may be computed analytically. Previous works with the LSC approximation have obtained such a Gaussian approximation by employing a quadratic approximation for the potential or by using the thermal Gaussian approximation (TGA) to the density matrix. In this work, we present a Gaussian semiclassical approximation to the density matrix which we call the open semiclassical approximation. The advantage of this approximation is that it may be directly applied to the potential energy. It does not require the potential to be approximated as a sum of two body terms, as does TGA. The implementation of the open semiclassical approximation requires the relaxation of the random paths that appear in the path integral representation of the density matrix to minimum action classical trajectories and the subsequent evaluation of blocks of the action Hessian for these trajectories. We present efficient numerical methods to perform these tasks. Additionally we show how this approximation leads to an expression for the Wigner function that may be implemented together with existing path integral monte carlo methods.

Ultra-low latency optical packet switching networks

Small, Benjamin A Columbia University 2006 해외박사(DDOD)

A novel paradigm for high-capacity, low-latency optical packet switching (OPS) interconnection network architectures is enunciated, appropriate for applications in high-performance computing, storage area networks, and telecommunications core routers. This design capitalizes on the immense bandwidth provided by optical signal encoding and transmission over contemporary fiberoptic components, and avoids common pitfalls and shortcomings of photonic technologies, especially the complexity of all-optical logic devices and the absence of robust optical buffers and registers. The structure of a single-packet 2-by-2 photonic switching node which is based on semiconductor optical amplifiers (SOAs) is introduced; packets traverse the node entirely in the optical domain while optical header information is extracted and digital electronic circuitry cooperatively computes the routing decision to be executed by the SOAs. The switching node exhibits almost perfect optical transparency to multiple-wavelength optical packets over nearly the whole ITU C-band. The packet structure is itself unique, containing designated header wavelengths with simple one-bit encoding, in addition to multiple wavelengths modulated at extremely high data rates for packet payload encoding. Empirical measurements quantify the switching node's minimal impact on the optically encoded signals, including a receiver power penalty of just 0.2 dB and a noise figure of 7.0 dB. A first prototype of the Data Vortex architecture provides 12 input ports and 12 output ports and comprises 36 switching nodes. Because the distributed multiple-stage network topology is based on a banyan routing structure while incorporating a deflection routing scheme, it is ideal for implementation with optical components. The architecture presented here differs markedly from conventional designs in that it capitalizes fully on the high-bandwidth nature of multiple-wavelength optical transmission in a scheme that also leverages the benefits of high-speed electronics, and thus requires no sophisticated optical processing nor buffering. The implemented system is capable of routing packets with 160 Gbps of bandwidth over 16 discrete payload wavelengths in approximately 100 ns while maintaining practically error-free signal integrity over an optical power dynamic range of more than 6 dB. Further experimental measurements investigate the OPS interconnection network's flexibility and robustness in terms of optical signal quality and network timing. Numerous demonstrations and subsequent empirical investigations support the scalability of the implemented architecture and serve to substantiate the merits of the proposed OPS network architectural paradigm.

Extreme genomic variation in a natural population

Small, Kerrin Shannon Stanford University 2007 해외박사(DDOD)

The genome sequence of the urochordate Ciona savignyi was determined with a standard whole genome shotgun strategy, but an extraordinarily high degree of polymorphism resulted in a fractured assembly wherein allelic sequences from the same genomic region assembled into separate contigs. Each locus of the sequenced individual is thus represented twice in the original assembly, and contigs contain no information to indicate which of the two 'haplomes' (haploid genomes) they belong to, or to which other contigs they are allelic. We have generated a global whole genome alignment of the C. savignyi assembly with itself in order to construct a highly contiguous and non-redundant reference sequence of the C. savignyi genome. Our C. savignyi reference sequence exhibits a threefold improvement in N50 and a sixfold reduction in contig breaks compared to the initial assembly, and has facilitated gene annotation of the C. savignyi genome. Sequence gaps and misassemblies have been dramatically reduced by utilizing information from both aligned alleles in a given region. The global alignment of the two haplomes allowed for genome-wide characterization of the heterozygosity of the sequenced individual. We demonstrate extreme per-base heterozygosity for insertions and deletions (16.6%), inversions (1.96%), mobile element activity (11.4%), and single nucleotide polymorphisms (SNPs; 4.5%). We show that the cause for the high rate of heterozygosity is a large effective population size rather than elevated mutation rates and, consistent with the large effective population size, we find evidence of strong purifying selection. These results constitute the first in-depth insight into the dynamics of highly polymorphic genomes and provide important empirical support of population genetic theory as it pertains to population size, heterozygosity, and natural selection.

Thermoelectric transport in nanoscale materials

Small, Joshua P Columbia University 2006 해외박사(DDOD)

Measurements of thermoelectric transport coefficients yield important information regarding fundamental properties of a system in addition to the information supplied from the electronic transport measurements. In this thesis we re port gate dependent and temperature dependent conductance ( G) and thermo-electric power (TEP) measurements made in three different basic nanomaterials: single-walled nanotubes (SWNTs), multi-walled nanotubes (MWNTs), and silicon nanowires (SiNWs). There are two means of generating a thermoelectric voltage: carrier diffusion and phonon drag. Gate dependent measurements of metallic SWNTs verified the use of the mesoscopic Mott formula, the equation governing diffusive thermoelectric voltage, used to relate TEP with the conductance. We find phonon drag negligible in graphene based systems. In the semi-conducting SWNT we observed high valued and variable TEP. In addition, the TEP behaves according to a simple Schottky barrier (SB) controlled transport model where transport takes place by quantum mechanical tunneling through the barrier, or thermal activation over it, depending on the value of the gate electric field. We also observe saw-tooth oscillations of the TEP in weakly contacted SWNTs at temperatures below the charging energy, indicative of Coulomb blockade transport. Importantly, we made quantitative measurements of the TEP oscillation amplitude, agreeing well with theory. In the MWNT, the Mott formula describes well the TEP within a framework of multiple parallel channels. We observe TEP weighting in this parallel system. In conjunction with conductance measurements, by probing the TEP in SWNTs we are able to extract the number of shells participating in electrical transport. These results agree well with figures obtained independently in controlled breakdown experiments, and the temperature dependent results may prove useful for investigation of the intershell interaction energy. We also investigate TEP in the SiNW, where TEP response appears similar to that of the semi-conducting SWNT, but with subtle differences. In the SiNW, both SB and bulk controlled transport contribute to the overall TEP, and must be considered within a series transport model, weighted appropriately by their length. These measurements give us insight into the SiNW transport properties.