10 Matching Results

Search Results

Advanced search parameters have been applied.

Electron Diffraction Determination of Nanoscale Structures

Description: Dominant research results on adsorption on gold clusters are reviewed, including adsorption of H{sub 2}O and O{sub 2} on gold cluster cations and anions, kinetics of CO adsorption to middle sized gold cluster cations, adsorption of CO on Au{sub n}{sup +} with induced changes in structure, and H{sub 2}O enhancement of CO adsorption.
Date: March 1, 2013
Creator: Parks, Joel H
Partner: UNT Libraries Government Documents Department

Coherent Anti-Stokes Raman Scattering Spectroscopy of Single Molecules in Solution

Description: During this funding period, we have developed two breakthrough techniques. The first is stimulated Raman scattering microscopy, providing label-free chemical contrast for chemical and biomedical imaging based on vibrational spectroscopy. Spontaneous Raman microscopy provides specific vibrational signatures of chemical bonds, but is often hindered by low sensitivity. We developed a three-dimensional multiphoton vibrational imaging technique based on stimulated Raman scattering (SRS). The sensitivity of SRS imaging is significantly greater than that of spontaneous Raman microscopy, which is achieved by implementing high-frequency (megahertz) phase-sensitive detection. SRS microscopy has a major advantage over previous coherent Raman techniques in that it offers background-free and readily interpretable chemical contrast. We demonstrated a variety of biomedical applications, such as differentiating distributions of omega-3 fatty acids and saturated lipids in living cells, imaging of brain and skin tissues based on intrinsic lipid contrast, and monitoring drug delivery through the epidermis. This technology offers exciting prospect for medical imaging. The second technology we developed is stimulated emission microscopy. Many chromophores, such as haemoglobin and cytochromes, absorb but have undetectable fluorescence because the spontaneous emission is dominated by their fast non-radiative decay. Yet the detection of their absorption is difficult under a microscope. We use stimulated emission, which competes effectively with the nonradiative decay, to make the chromophores detectable, as a new contrast mechanism for optical microscopy. We demonstrate a variety of applications of stimulated emission microscopy, such as visualizing chromoproteins, non-fluorescent variants of the green fluorescent protein, monitoring lacZ gene expression with a chromogenic reporter, mapping transdermal drug distribu- tions without histological sectioning, and label-free microvascular imaging based on endogenous contrast of haemoglobin. For all these applications, sensitivity is orders of magnitude higher than for spontaneous emission or absorption contrast, permitting nonfluorescent reporters for molecular imaging. Although we did not accomplish the original goal of detecting single-molecule ...
Date: January 18, 2012
Creator: Sunney Xie, Wei Min, Chris Freudiger, Sijia Lu
Partner: UNT Libraries Government Documents Department

"Quantum Field Theory and QCD"

Description: This grant partially funded a meeting, "QFT & QCD: Past, Present and Future" held at Harvard University, Cambridge, MA on March 18-19, 2005. The participants ranged from senior scientists (including at least 9 Nobel Prize winners, and 1 Fields medalist) to graduate students and undergraduates. There were several hundred persons in attendance at each lecture. The lectures ranged from superlative reviews of past progress, lists of important, unsolved questions, to provocative hypotheses for future discovery. The project generated a great deal of interest on the internet, raising awareness and interest in the open questions of theoretical physics.
Date: February 25, 2006
Creator: Jaffe, Arthur M.
Partner: UNT Libraries Government Documents Department

Final Technical Report

Description: This research consisted of a theoretical investigation of the properties of surface-based nanostructures, having as a main goal the deeper understanding of the atomic-scale mechanisms responsible for the formation and stability of such structures. This understanding will lead to the design of improved systems for applications in diverse areas such as novel electronic devices, sensors, field-effect transistors, substrates with enhanced hydro-phobic (water repelling) or hydro-philic (water absorbing) behavior for coatings of various surfaces used in bioengineering, flexible displays, organic photovoltaics, etc. The research consisted of developing new theoretical methodologies and applying them to a wide range of interesting physical systems. Highlights of the new methodologies include techniques for bridging different scales, from the quantum-mechanical electronic level to the meso-scopic level of large molecular structures such as DNA, carbon nanotubes and two-dimensional assemblies of organic molecules. These methodologies were successfully applied to investigate interactions between systems that are large on the atomic scale (reaching the scale of microns in length or milliseconds in time), but still incorporating all the essential elements of the atomic-scale structure. While the research performed here did not address applications directly, the implications of its finding are important in guiding experimental searches and in coming up with novel solutions to important problems. In this sense, the results of this work can be incorporated in the design of many useful applications. Specifically, in addition to elucidating important physical principles on how nano-structures are stabilized on surfaces, we have used our theoretical investigations to make predictions for useful applications in the following fields: a) we proposed new types of nanotubes that can overcome the limitations of the carbon nanotubes whose properties depend sensitively on the structure which cannot be controlled experimentally; b) we showed how carbon nanotubes can be employed in optical determination of the DNA base sequence, an ...
Date: February 2, 2009
Creator: Kaxiras, Efthimios
Partner: UNT Libraries Government Documents Department

Neutralizing Carbonic Acid in Deep Carbonate Strata below the North Atlantic

Description: Our research is aimed at investigating several technical issues associated with carbon dioxide sequestration in calcium carbonate sediments below the sea floor through laboratory experiments and chemical transport modeling. Our goal is to evaluate the basic feasibility of this approach, including an assessment of optimal depths, sediment types, and other issues related to site selection. Through laboratory and modeling efforts, we are studying the flow of liquid carbon dioxide and carbon dioxide-water mixtures through calcium carbonate sediments to better understand the geomechanical and structural stability of the sediments during and after injection. Our modeling efforts in the first year show that the idea is feasible, but requires more sophisticated analysis of fluid flow at high pressure in deep sea sediments. In addition, we are investigating the kinetics of calcium carbonate dissolution in the presence of CO{sub 2}-water fluids, which is a critical feature of the system as it allows for increased permeability during injection. Our experimental results from the first year of work have shown that the kinetics are likely to be fast enough to create dissolution which will affect permeability. However, additional experiments are needed at high pressures, which will be a focus for years 2 and 3. We are also investigating the possibility of carbon dioxide hydrate formation in the pore fluid, which might complicate the injection procedure by reducing sediment permeability but might also provide an upper seal in the sediment-pore fluid system, preventing release of CO{sub 2} into the deep ocean, particularly if depth and temperature at the injection point rule out immediate hydrate formation. Finally, we are in the beginning stages of an economic analysis to estimate costs of drilling and gas injection, site monitoring as well as the availability of potential disposal sites with particular emphasis on those sites that are within the 200-mile ...
Date: December 1, 2005
Creator: Schrag, Daniel P.
Partner: UNT Libraries Government Documents Department

Growth and Dissolution of Iron and Manganese Oxide Films

Description: Growth and dissolution of Fe and Mn oxide films are key regulators of the fate and transport of heavy metals in the environment, especially during changing seasonal conditions of pH and dissolved oxygen. The Fe and Mn are present at much higher concentrations than the heavy metals, and, when Fe and Mn precipitate as oxide films, heavy metals surface adsorb or co-precipitate and are thus essentially immobilized. Conversely, when the Fe and Mn oxide films dissolve, the heavy metals are released to aqueous solution and are thus mobilized for transport. Therefore, understanding the dynamics and properties of Fe and Mn oxide films and thus on the uptake and release of heavy metals is critically important to any attempt to develop mechanistic, quantitative models of the fate, transport, and bioavailablity of heavy metals. A primary capability developed in our earlier work was the ability to grow manganese oxide (MnO{sub x}) films on rhodochrosite (MnCO{sub 3}) substrate in presence of dissolved oxygen under mild alkaline conditions. The morphology of the films was characterized using contact-mode atomic force microscopy. The initial growth began by heteroepitaxial nucleation. The resulting films had maximum heights of 1.5 to 2 nm as a result of thermodynamic constraints. Over the three past years, we have investigated the effects of MnO{sub x} growth on the interactions of MnCO{sub 3} with charged ions and microorganisms, as regulated by the surface electrical properties of the mineral. In 2006, we demonstrated that MnO{sub x} growth could induce interfacial repulsion and surface adhesion on the otherwise neutral MnCO{sub 3} substrate under environmental conditions. Using force-volume microscopy (FVM), we measured the interfacial and adhesive forces on a MnO{sub x}/MnCO{sub 3} surface with a negatively charged silicon nitride tip in a 10-mM NaNO3 solution at pH 7.4. The interfacial force and surface adhesion of MnOx ...
Date: December 22, 2008
Creator: Martin, Scot T.
Partner: UNT Libraries Government Documents Department

Real-Time Gene Expression Profiling of Live Shewanella Oneidensis Cells

Description: The overall objective of this proposal is to make real-time observations of gene expression in live Shewanella oneidensis cells with high sensitivity and high throughput. Gene expression, a central process to all life, is stochastic because most genes often exist in one or two copies per cell. Although the central dogma of molecular biology has been proven beyond doubt, due to insufficient sensitivity, stochastic protein production has not been visualized in real time in an individual cell at the single-molecule level. We report the first direct observation of single protein molecules as they are generated, one at a time in a single live E. coli cell, yielding quantitative information about gene expression [Science 2006; 311: 1600-1603]. We demonstrated a general strategy for live-cell single-molecule measurements: detection by localization. It is difficult to detect single fluorescence protein molecules inside cytoplasm - their fluorescence is spread by fast diffusion to the entire cell and overwhelmed by the strong autofluorescence. We achieved single-molecule sensitivity by immobilizing the fluorescence protein on the cell membrane, where the diffusion is much slowed. We learned that under the repressed condition protein molecules are produced in bursts, with each burst originating from a stochastically-transcribed single messenger RNA molecule, and that protein copy numbers in the bursts follow a geometric distribution. We also simultaneously published a paper reporting a different method using β-glactosidase as a reporter [Nature 440, 358 (2006)]. Many important proteins are expressed at low levels, inaccessible by previous proteomic techniques. Both papers allowed quantification of protein expression with unprecedented sensitivity and received overwhelming acclaim from the scientific community. The Nature paper has been identified as one of the most-cited papers in the past year [http://esi-topics.com/]. We have also an analytical framework describing the steady-state distribution of protein concentration in live cells, considering that protein production occurs ...
Date: March 30, 2009
Creator: Xie, Xiaoliang Sunney
Partner: UNT Libraries Government Documents Department

Microtextured Silicon Surfaces for Detectors, Sensors & Photovoltaics

Description: With support from this award we studied a novel silicon microtexturing process and its application in silicon-based infrared photodetectors. By irradiating the surface of a silicon wafer with intense femtosecond laser pulses in the presence of certain gases or liquids, the originally shiny, flat surface is transformed into a dark array of microstructures. The resulting microtextured surface has near-unity absorption from near-ultraviolet to infrared wavelengths well below the band gap. The high, broad absorption of microtextured silicon could enable the production of silicon-based photodiodes for use as inexpensive, room-temperature multi-spectral photodetectors. Such detectors would find use in numerous applications including environmental sensors, solar energy, and infrared imaging. The goals of this study were to learn about microtextured surfaces and then develop and test prototype silicon detectors for the visible and infrared. We were extremely successful in achieving our goals. During the first two years of this award, we learned a great deal about how microtextured surfaces form and what leads to their remarkable optical properties. We used this knowledge to build prototype detectors with high sensitivity in both the visible and in the near-infrared. We obtained room-temperature responsivities as high as 100 A/W at 1064 nm, two orders of magnitude higher than standard silicon photodiodes. For wavelengths below the band gap, we obtained responsivities as high as 50 mA/W at 1330 nm and 35 mA/W at 1550 nm, close to the responsivity of InGaAs photodiodes and five orders of magnitude higher than silicon devices in this wavelength region.
Date: May 19, 2005
Creator: Carey, JE & Mazur, E
Partner: UNT Libraries Government Documents Department

Race, Genetics and Medicine: New Information, Enduring Questions

Description: Final Report on Conference held on April 9, 2005 and its Sequelae The Conference, “Race, Genetics and Medicine: New Information, Enduring Questions,” was held on Saturday, April 9, 2005 in the Science Center, Lecture Hall D at Harvard University, Cambridge, MA. Approximately 150 people attended. The audience was composed mainly of college and graduate school science students and postdoctoral fellows, some science and medical school faculty, science teachers at various levels, journalists and interested members of the public. The keynote speaker and the panelists reflected different academic disciplines (genetics, medicine, anthropology, sociology) and a CEO of a biotechnology company with background in medicine and law. They also presented different perspectives on the utility of race concepts in medicine and even on the use of the word “race.” While the talks often involved descriptions of genetic approaches that were not simple to explain, the speakers did an effective job of getting across the gist of studies that have been carried out on these issues. Although no consensus was reached, the conference gave the audience the opportunity to understand the issues and to have the tools to follow the debates in the future. Our strongest feedback was from attendees who had heard of the race and genetics issues through various media, but did not have a sense of what they were really about. They reported to us that they now felt they understood the basis of these discussions. Our post-conference activities have been successfully completed. While we had proposed to make available transcripts of the talks to the public through a Website, some of the speakers would not agree to have their presentations available in this way. Therefore, we asked permission from the DOE to use the funds to prepare classroom lesson plans for high school students to discuss the issues. These ...
Date: August 1, 2008
Creator: Beckwith, Jonathan R.
Partner: UNT Libraries Government Documents Department

Economic and Energy Development in China: Policy Options and Implications for Climate Change

Description: The Harvard University Center for the Environment and partner institutions in China established a multidisciplinary program of integrated research on energy-related environmental issues, local air pollution and global climate change, in China and their role in U.S.-Chinese relations. Major research streams included: (a) developing a dynamic, multi-sector model of the Chinese economy that can estimate energy use, emission, and health damages from pollution, and using this model to simulate broad economic effects of market-based pollution-control policies; (b) developing a regionally disaggregated model of technology and investment choice in the Chinese electric power sector; (c) applying an atmospheric chemical tracer transport model to investigate carbon uptake in Eurasis (notably China) and North America, and to inform observational strategies for CO{sub 2} in China and elsewhere.
Date: January 23, 2003
Creator: McElroy, M. B. & Nielsen, C.
Partner: UNT Libraries Government Documents Department