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Nanoparticle Based Surface-Enhanced Raman Spectroscopy (open access)

Nanoparticle Based Surface-Enhanced Raman Spectroscopy

Surface-enhanced Raman scattering is a powerful tool for the investigation of biological samples. Following a brief introduction to Raman and surface-enhanced Raman scattering, several examples of biophotonic applications of SERS are discussed. The concept of nanoparticle based sensors using SERS is introduced and the development of these sensors is discussed.
Date: January 3, 2005
Creator: Talley, Chad E.; Huser, Thomas R.; Hollars, Christopher W.; Jusinski, Leonard; Laurence, Ted & Lane, Stephen M.
System: The UNT Digital Library
Facile Synthesis of a Crystalline, High-Surface Area SnO2 Aerogel (open access)

Facile Synthesis of a Crystalline, High-Surface Area SnO2 Aerogel

We report the preparation of a novel monolithic SnO{sub 2} aerogel using a straightforward sol-gel technique. TEM and XRD analysis show that the as-prepared material is comprised of interconnected, randomly oriented crystalline (rutile) SnO{sub 2} nanoparticles {approx}3-5 nm in size. As a result, the low-density SnO{sub 2} monolith ({approx}97% porous) exhibits a very high surface area of 383 m{sup 2}/g. /XANES spectroscopy at the Sn M{sub 4,5} edge reveals that the electronic structure of the SnO{sub 2} aerogel is similar to that of tetragonal SnO rather than SnO{sub 2} or {beta}-Sn, and that the undercoordinated surface atoms in the material introduce additional Sn-related electronic states close to the conduction band minimum.
Date: January 3, 2005
Creator: Baumann, T. F.; Kucheyev, S. O.; Gash, A. E. & Satcher, J. H. Jr.
System: The UNT Digital Library
Vehicular Storage of Hydrogen in Insulated Pressure Vessels (open access)

Vehicular Storage of Hydrogen in Insulated Pressure Vessels

This paper describes the development of an alternative technology for storing hydrogen fuel onboard automobiles. Insulated pressure vessels are cryogenic-capable pressure vessels that can accept cryogenic liquid fuel, cryogenic compressed gas or compressed gas at ambient temperature. Insulated pressure vessels offer advantages over conventional H{sub 2} storage approaches. Insulated pressure vessels are more compact and require less carbon fiber than GH{sub 2} vessels. They have lower evaporative losses than LH{sub 2} tanks, and are much lighter than metal hydrides. After outlining the advantages of hydrogen fuel and insulated pressure vessels, the paper describes the experimental and analytical work conducted to verify that insulated pressure vessels can be used safely for vehicular H{sub 2} storage. The paper describes tests that have been conducted to evaluate the safety of insulated pressure vessels. Insulated pressure vessels have successfully completed a series of DOT, ISO and SAE certification tests. A draft procedure for insulated pressure vessel certification has been generated to assist in a future commercialization of this technology. An insulated pressure vessel has been installed in a hydrogen fueled truck and it is currently being subjected to extensive testing.
Date: January 3, 2005
Creator: Aceves, S. M.; Berry, G. D.; Martinez-Frias, J. & Espinosa-Loza, F.
System: The UNT Digital Library
Stable CSR in storage rings: A model (open access)

Stable CSR in storage rings: A model

A comprehensive historical view of the work done on coherent synchrotron radiation (CSR) in storage rings is given in reference [1]. Here we want just to point out that even if the issue of CSR in storage rings was already discussed over 50 years ago, it is only recently that a considerable number of observations have been reported. In fact, intense bursts of coherent synchrotron radiation with a stochastic character were measured in the terahertz frequency range, at several synchrotron light source storage rings [2-8]. It has been shown [8-11], that this bursting emission of CSR is associated with a single bunch instability, usually referred as microbunching instability (MBI), driven by the fields of the synchrotron radiation emitted by the bunch itself. Of remarkably different characteristics was the CSR emission observed at BESSY II in Berlin, when the storage ring was tuned into a special low momentum compaction mode [12, 13]. In fact, the emitted radiation was not the quasi-random bursting observed in the other machines, but a powerful and stable flux of broadband CSR in the terahertz range. This was an important result, because it experimentally demonstrated the concrete possibility of constructing a stable broadband source with extremely high …
Date: January 3, 2005
Creator: Sannibale, Fernando; Byrd, John M.; Loftsdottir, Agusta; Venturini, Marco; Abo-Bakr, Michael; Feikes, Jorge et al.
System: The UNT Digital Library
Erratum for: Master equation and Fokker-Planck methods for void nucleation and growth in irradiation swelling, Vacancy cluster evolution and swelling in irradiated 316 stainless steel and Radiation swelling behavior and its dependence on temperature, dose (open access)

Erratum for: Master equation and Fokker-Planck methods for void nucleation and growth in irradiation swelling, Vacancy cluster evolution and swelling in irradiated 316 stainless steel and Radiation swelling behavior and its dependence on temperature, dose

We have recently discovered an error in our void nucleation code used in three prior publications [1-3]. A term was omitted in the model for vacancy re-emission that (especially at high temperature) affects void nucleation and growth during irradiation as well as void annealing and Ostwald ripening of the size distribution after irradiation. The omission was not immediately detected because the calculations predict reasonable void densities and swelling behaviors when compared to experiment at low irradiation temperatures, where void swelling is prominent. (Comparable neutron irradiation experiments are less prevalent at higher temperatures, e.g., > 500 C.)
Date: January 3, 2005
Creator: Surh, M. P.; Sturgeon, J. B. & Wolfer, W. G.
System: The UNT Digital Library
Up-scaling analysis with rigorous error estimates for poromechanics in random polycrystals of porous laminates (open access)

Up-scaling analysis with rigorous error estimates for poromechanics in random polycrystals of porous laminates

A detailed analytical model of random polycrystals of porous laminates has been developed. This approach permits detailed calculations of poromechanics constants as well as transport coefficients. The resulting earth reservoir model allows studies of both geomechanics and fluid permeability to proceed semi-analytically. Rigorous bounds of the Hashin-Shtrikman type provide estimates of overall bulk and shear moduli, and thereby also provide rigorous error estimates for geomechanical constants obtained from up-scaling based on a self-consistent effective medium method. The influence of hidden or unknown microstructure on the final results can then be evaluated quantitatively. Descriptions of the use of the model and some examples of typical results on the poromechanics of such a heterogeneous reservoir are presented.
Date: January 3, 2005
Creator: Berger, E. L.
System: The UNT Digital Library
A Comparison of Detailed Level and Superconfiguration Models of Neon (open access)

A Comparison of Detailed Level and Superconfiguration Models of Neon

The superconfiguration (SC) approach to collisional-radiative modeling can significantly decrease the computational demands of finding non-LTE level populations in complex systems. However, it has not yet been fully determined whether the statistical averaging of SC models leads to a significant loss of accuracy. The present work compares results from two independent models: a detailed-level accounting (DLA) model based on HULLAC data and the SC model MOST. The relatively simple level structures of the K- and L-shell ions of the neon test system ensure a tractable number of levels in the DLA model but challenge the statistical assumptions of the SC approach. Nonetheless, we find fair agreement between the two models for average ion charges, SC populations, and various effective temperatures.
Date: January 3, 2005
Creator: Hansen, S B; Fournier, K B; Bauche-Arnoult, C; Bauche, J & Peyrusse, O
System: The UNT Digital Library
Vulnerability And Risk Assessment Using The Homeland-Defense Operational Planning System (HOPS) (open access)

Vulnerability And Risk Assessment Using The Homeland-Defense Operational Planning System (HOPS)

For over ten years, the Counterproliferation Analysis and Planning System (CAPS) at Lawrence Livermore National Laboratory (LLNL) has been a planning tool used by U.S. combatant commands for mission support planning against foreign programs engaged in the manufacture of weapons of mass destruction (WMD). CAPS is endorsed by the Secretary of Defense as the preferred counterproliferation tool to be used by the nation's armed services. A sister system, the Homeland-Defense Operational Planning System (HOPS), is a new operational planning tool leveraging CAPS expertise designed to support the defense of the U.S. homeland. HOPS provides planners with a basis to make decisions to protect against acts of terrorism, focusing on the defense of facilities critical to U.S. infrastructure. Criticality of facilities, structures, and systems is evaluated on a composite matrix of specific projected casualty, economic, and sociopolitical impact bins. Based on these criteria, significant unidentified vulnerabilities are identified and secured. To provide insight into potential successes by malevolent actors, HOPS analysts strive to base their efforts mainly on unclassified open-source data. However, more cooperation is needed between HOPS analysts and facility representatives to provide an advantage to those whose task is to defend these facilities. Evaluated facilities include: refineries, major ports, …
Date: January 3, 2005
Creator: Durling, Jr., R L; Price, D E & Spero, K K
System: The UNT Digital Library
Imaging Lithium Atoms at Sub-Angstrom Resolution (open access)

Imaging Lithium Atoms at Sub-Angstrom Resolution

John Cowley and his group at ASU were pioneers in the use of transmission electron microscopy (TEM) for high-resolution imaging. Three decades ago they achieved images showing the crystal unit cell content at better than 4A resolution. Over the years, this achievement has inspired improvements in resolution that have enabled researchers to pinpoint the positions of heavy atom columns within the cell. More recently, this ability has been extended to light atoms as resolution has improved. Sub-Angstrom resolution has enabled researchers to image the columns of light atoms (carbon, oxygen and nitrogen) that are present in many complex structures. By using sub-Angstrom focal-series reconstruction of the specimen exit surface wave to image columns of cobalt, oxygen, and lithium atoms in a transition metal oxide structure commonly used as positive electrodes in lithium rechargeable batteries, we show that the range of detectable light atoms extends to lithium. HRTEM at sub-Angstrom resolution will provide the essential role of experimental verification for the emergent nanotech revolution. Our results foreshadow those to be expected from next-generation TEMs with CS-corrected lenses and monochromated electron beams.
Date: January 3, 2005
Creator: O'Keefe, Michael A. & Shao-Horn, Yang
System: The UNT Digital Library