Evaluation of Salmon Spawning Below Bonneville Dam, Annual Report October 2005 - September 2006. (open access)

Evaluation of Salmon Spawning Below Bonneville Dam, Annual Report October 2005 - September 2006.

Since FY 2000, scientists at Pacific Northwest National Laboratory (PNNL) have conducted research to assess the extent of spawning by chum salmon (Oncorhynchus keta) and fall Chinook salmon (O. tshawytscha) in the lower mainstem Columbia River. Their work supports a larger project funded by the Bonneville Power Administration (BPA) aimed at characterizing the physical habitat used by mainstem fall Chinook and chum salmon populations. Multiple collaborators in addition to PNNL are involved in the BPA project--counterparts include the Washington Department of Fish and Wildlife (WDFW), U.S. Fish and Wildlife Service (USFWS), Pacific States Marine Fisheries Commission (PSMFC), U.S. Geological Survey (USGS), and Oregon Department of Fish and Wildlife (ODFW). Data resulting from the individual tasks each agency conducts are providing a sound scientific basis for developing strategies to operate the Federal Columbia River Power System (FCRPS) in ways that will effectively protect and enhance the chum and tule fall Chinook salmon populations--both listed as threatened under the Endangered Species Act (ESA). Fall Chinook salmon, thought to originate from Bonneville Hatchery, were first noted to be spawning downstream of Bonneville Dam by WDFW biologists in 1993. Known spawning areas include gravel beds on the Washington side of the river near Hamilton …
Date: September 21, 2007
Creator: Arntzen, Evan V.; Mueller, Robert P. & Murray, Christopher J.
Object Type: Report
System: The UNT Digital Library
Contemporary Instrumentation and Application of Charge Exchange Neutral Particle Diagnostics in Magnetic Fusion Experiments (open access)

Contemporary Instrumentation and Application of Charge Exchange Neutral Particle Diagnostics in Magnetic Fusion Experiments

An overview of the developments post-circa 1980's of the instrumentation and application of charge exchange neutral particle diagnostics on Magnetic Fusion Energy experiments is presented.
Date: July 21, 2007
Creator: S.S. Medley, A.J.H. Donné, R. Kaita, A.I. Kislyakov, M.P. Petrov, and A.L. Roquemore
Object Type: Report
System: The UNT Digital Library
Segue between Favorable and Unfavorable Solvation (open access)

Segue between Favorable and Unfavorable Solvation

Solvation of small and large clusters are studied by simulation, considering a range of solvent-solute attractive energy strengths. Over a wide range of conditions, both for solvation in the Lennard-Jones liquid and in the SPC model of water, it is shown that the mean solvent density varies linearly with changes in solvent-solute adhesion or attractive energy strength. This behavior is understood from the perspective of Weeks theory of solvation [Ann. Rev. Phys. Chem. 2002, 53, 533] and supports theories based upon that perspective.
Date: March 21, 2007
Creator: Maibaum, Lutz & Chandler, David
Object Type: Article
System: The UNT Digital Library
Compensatory Paracrine Mechanisms That Define The Urothelial Response to Injury in Partial Bladder Outlet Obstruction (open access)

Compensatory Paracrine Mechanisms That Define The Urothelial Response to Injury in Partial Bladder Outlet Obstruction

Diseases and conditions affecting the lower urinary tract are a leading cause of dysfunctional sexual health, incontinence, infection, and kidney failure. The growth, differentiation, and repair of the bladder's epithelial lining are regulated, in part, by fibroblast growth factor (FGF)-7 and -10 via a paracrine cascade originating in the mesenchyme (lamina propria) and targeting the receptor for FGF-7 and -10 within the transitional epithelium (urothelium). The FGF-7 gene is located at the 15q15-q21.1 locus on chromosome 15 and four exons generate a 3.852-kb mRNA. Five duplicated FGF-7 gene sequences that localized to chromosome 9 were predicted not to generate functional protein products, thus validating the use of FGF-7-null mice as an experimental model. Recombinant FGF-7 and -10 induced proliferation of human urothelial cells in vitro and transitional epithelium of wild-type and FGF-7-null mice in vivo.To determine the extent that induction of urothelial cell proliferation during the bladder response to injury is dependent on FGF-7, an animal model of partial bladder outlet obstruction was developed. Unbiased stereology was used to measure the percentage of proliferating urothelial cells between obstructed groups of wild-type and FGF-7-null mice. The stereological analysis indicated that a statistical significant difference did not exist between the two groups, …
Date: June 21, 2007
Creator: Bassuk, James; Lendvay, Thomas S.; Sweet, Robert; Han, Chang-Hee; Soygur, Tarkan; Cheng, Jan-Fang et al.
Object Type: Article
System: The UNT Digital Library
Atmospheric Climate Model Experiments Performed at Multiple Horizontal Resolutions (open access)

Atmospheric Climate Model Experiments Performed at Multiple Horizontal Resolutions

This report documents salient features of version 3.3 of the Community Atmosphere Model (CAM3.3) and of three climate simulations in which the resolution of its latitude-longitude grid was systematically increased. For all these simulations of global atmospheric climate during the period 1980-1999, observed monthly ocean surface temperatures and sea ice extents were prescribed according to standard Atmospheric Model Intercomparison Project (AMIP) values. These CAM3.3 resolution experiments served as control runs for subsequent simulations of the climatic effects of agricultural irrigation, the focus of a Laboratory Directed Research and Development (LDRD) project. The CAM3.3 model was able to replicate basic features of the historical climate, although biases in a number of atmospheric variables were evident. Increasing horizontal resolution also generally failed to ameliorate the large-scale errors in most of the climate variables that could be compared with observations. A notable exception was the simulation of precipitation, which incrementally improved with increasing resolution, especially in regions where orography plays a central role in determining the local hydroclimate.
Date: December 21, 2007
Creator: Phillips, T.; Bala, G.; Gleckler, P.; Lobell, D.; Mirin, A.; Maxwell, R. et al.
Object Type: Report
System: The UNT Digital Library
Toward a Deeper Understanding of Plutonium (open access)

Toward a Deeper Understanding of Plutonium

Plutonium is a very complex element lying near the middle of the actinide series. On the lower atomic number side of Pu is the element neptunium; its 5f electrons are highly delocalized or itinerant, participating in metallic-like bonding. The electrons in americium, the element to the right of Pu, are localized and do not participant significantly in the bonding. Plutonium is located directly on this rather abrupt transition. In the low-temperature {alpha} phase ground state, the five 5f electrons are mostly delocalized leading to a highly dense monoclinic crystal structure. Increases in temperature take the unalloyed plutonium through a series of five solid-state allotropic phase transformations before melting. One of the high temperature phases, the close-packed face centered cubic {delta} phase, is the least dense of all the phases, including the liquid. Alloying the Pu with Group IIIA elements such as aluminum or gallium retains the {delta} phase in a metastable state at ambient conditions. Ultimately, this metastable {delta} phase will decompose via a eutectoid transformation to {alpha} + Pu{sub 3}Ga. These low solute-containing {delta}-phase Pu alloys are also metastable with respect to low temperature excursions or increases in pressure and will transform to a monoclinic crystal structure at low …
Date: June 21, 2007
Creator: Schwartz, A J & Wolfer, W G
Object Type: Article
System: The UNT Digital Library
Analysis of the Costs of a Backlog Project in Response to Recommendation 2 of the 2004 Archives and History Office Program Review Committee Report (open access)

Analysis of the Costs of a Backlog Project in Response to Recommendation 2 of the 2004 Archives and History Office Program Review Committee Report

SLAC Archives and History Office (AHO) backlog of unprocessed material is over 3,000 cubic feet and growing. Because much of this material was directly transferred to off-site storage, the provenance and contents are a mystery. The costs of off-site storage, lack of knowledge of the contents, and the impending federal regulations in 2009 concerning storage facilities all suggest the need for a long-term plan for the backlog. AHO presents these options to SLAC management: (1) Continue with the status quo, adding new accessions to OffSite Records Management, LLC (hereinafter referred to as OffSite) storage; (2) Pull the backlog back a segment at a time for box-level processing, determine what is in each box, get rid of extraneous material, and return what is left to OffSite storage; (3) Gradually retrieve the backlog for thorough, folder-level processing and then transfer to the Federal Records Center in San Bruno (hereinafter referred to as FRC) or the Archives side of the operations at the National Archives and Records Administration in San Bruno (hereinafter referred to as NARA); and (4) Gradually retrieve the backlog for a combination of box-level processing with return to OffSite storage and thorough folder-level processing with transfer to FRC or NARA.
Date: December 21, 2007
Creator: O'Hara, Laura
Object Type: Report
System: The UNT Digital Library
GENERATING THE RIGHT PCB DATA DETERMINATION OF AROCLORS VERSUS PCB CONGENERS (open access)

GENERATING THE RIGHT PCB DATA DETERMINATION OF AROCLORS VERSUS PCB CONGENERS

Polychlorinated biphenyls (PCBs) are a major environmental concern due to their ubiquity and tendency to bio-accumulate. as well as their persistence and toxicity. As the cleanup of waste and contaminated soil progresses at U.S. Department of Energy (DOE) sites, the costs for accurate PCB data are increasing. PCBs are actually a broad name for a group of 209 individual compounds known as congeners. PCBs were originally produced in the United States as specific mixtures of congeners known as Aroclors'. PCBs can be analyzed and quantified either as Aroclor mixtures or as individual congeners. Aroclor analysis, which is the more common analytical method applied to PCBs. has been in use for decades, and in general, most cleanup regulations are based on total PCB concentrations using Aroclor analyses. Congener analysis is relatively new to environmental cleanup and restoration due to both technical issues and associated cost. The benefits of congener analysis are that it allows a more direct analysis of the risk of the PCBs. The World Health Organization (WHO) has identified twelve specific congeners as dioxin-like with toxicity ranging from 0.00003 to 0.1 times the standard 2,3,7.8-Tetrachlorodibenzo-p-dioxin (2.3.7.8-TCDD) toxicity. This paper defines Aroclors and congeners and compares the current application and …
Date: November 21, 2007
Creator: CT, NARQUIS & AL, PRIGNANO
Object Type: Article
System: The UNT Digital Library
Interpretation of Recent Temperature Trends in California (open access)

Interpretation of Recent Temperature Trends in California

Regional-scale climate change and associated societal impacts result from large-scale (e.g. well-mixed greenhouse gases) and more local (e.g. land-use change) 'forcing' (perturbing) agents. It is essential to understand these forcings and climate responses to them, in order to predict future climate and societal impacts. California is a fine example of the complex effects of multiple climate forcings. The State's natural climate is diverse, highly variable, and strongly influenced by ENSO. Humans are perturbing this complex system through urbanization, irrigation, and emission of multiple types of aerosols and greenhouse gases. Despite better-than-average observational coverage, we are only beginning to understand the manifestations of these forcings in California's temperature record.
Date: September 21, 2007
Creator: Duffy, P B; Bonfils, C & Lobell, D
Object Type: Article
System: The UNT Digital Library
ELECTRON AVALANCHE MODEL OF DIELECTRIC-VACUUM SURFACE BREAKDOWN (open access)

ELECTRON AVALANCHE MODEL OF DIELECTRIC-VACUUM SURFACE BREAKDOWN

The model assumes that an 'initiating event' results in positive ions on the surface near the anode and reverses the direction of the normal component of electric field so that electrons in vacuum are attracted to the dielectric locally. A sequence of surface electron avalanches progresses in steps from the anode to the cathode. For 200 kV across 1 cm, the spacing of avalanches is predicted to be about 13 microns. The time for avalanches to step from the anode to the cathode is predicted to be about a ns.
Date: February 21, 2007
Creator: Lauer, E J
Object Type: Article
System: The UNT Digital Library
End-Of-Life Vehicle Recycling: State of the Art of Resource Recovery From Shredder Residue. (open access)

End-Of-Life Vehicle Recycling: State of the Art of Resource Recovery From Shredder Residue.

Each year, more than 50 million vehicles reach the end of their service life throughout the world. More than 95% of these vehicles enter a comprehensive recycling infrastructure that includes auto parts recyclers/dismantlers, remanufacturers, and material recyclers (shredders). Today, about 75% of automotive materials are profitably recycled via (1) parts reuse and parts and components remanufacturing and (2) ultimately by the scrap processing (shredding) industry. The process by which the scrap processors recover metal scrap from automobiles involves shredding the obsolete automobiles, along with other obsolete metal-containing products (such as white goods, industrial scrap, and demolition debris), and recovering the metals from the shredded material. The single largest source of recycled ferrous scrap for the iron and steel industry is obsolete automobiles. The non-metallic fraction that remains after the metals are recovered from the shredded materials (about 25% of the weight of the vehicle)--commonly called shredder residue--is disposed of in landfills. Over the past 10 to 15 years, a significant amount of research and development has been undertaken to enhance the recycle rate of end-of-life vehicles (ELVs), including enhancing dismantling techniques and improving remanufacturing operations. However, most of the effort has focused on developing technology to recover materials, such as …
Date: March 21, 2007
Creator: Jody, B. J.; Daniels, E. J. & Systems, Energy
Object Type: Report
System: The UNT Digital Library
Charm Spectroscopy at BaBar (open access)

Charm Spectroscopy at BaBar

We present a mini-review on charm spectroscopy at the BABAR experiment. We first report on the c{bar s} meson spectrum, and present precise measurements of the D{sub s1}(2536) meson as well as the properties of the many new states discovered since 2003 (D*{sub s0}(2317), D{sub s1}(2460), D*{sub sJ}(2860), and D{sub sJ}(2700) mesons). We then discuss about charmed baryons observed recently in the BABAR experiment: {Omega}{sub c}{sup 0} and {Omega}*{sub c}{sup 0} css baryons, {Lambda}{sub c}(2940){sup +} udc baryon and the {Xi}{sub c} usc/dsc baryons.
Date: December 21, 2007
Creator: Poireau, Vincent
Object Type: Article
System: The UNT Digital Library
Technical justification for a request to reclassify the former CCC/USDA facility at Canada, Kansas. (open access)

Technical justification for a request to reclassify the former CCC/USDA facility at Canada, Kansas.

Contamination in groundwater at Canada, Kansas, was discovered in 1997, during limited private well sampling near former grain storage facilities of the Commodity Credit Corporation, U.S. Department of Agriculture (CCC/USDA). Subsequent investigations by the Kansas Department of Health and Environment (KDHE) confirmed carbon tetrachloride and nitrate concentrations in groundwater above the respective maximum contaminant levels (MCLs) of 5.0 {micro}g/L and 10.0 mg/L. The KDHE investigations identified both the former CCC/USDA grain storage facility and a private grain storage facility as likely sources for the carbon tetrachloride contamination. The CCC/USDA funded extension of a rural water district line to provide a permanent alternate water supply, and the KDHE has conducted long-term monitoring under the State Water Plan. This document presents an analysis of the available information for the Canada site, acquired in previous investigations and the long-term KDHE monitoring. This analysis forms the technical justification for a request to reclassify the former CCC/USDA grain storage facility at Canada as a site requiring no further action under the Intergovernmental Agreement (IGA) between the KDHE and the USDA's Farm Service Agency. The KDHE's long-term water level monitoring results indicate a consistent groundwater flow direction to the east-southeast. Consequently, the wells with the highest …
Date: December 21, 2007
Creator: LaFreniere, L. M.
Object Type: Report
System: The UNT Digital Library
Unified Model of Dynamic Forced Barrier Crossing in Single Molecules (open access)

Unified Model of Dynamic Forced Barrier Crossing in Single Molecules

Thermally activated barrier crossing in the presence of an increasing load can reveal kinetic rate constants and energy barrier parameters when repeated over a range of loading rates. Here we derive a model of the mean escape force for all relevant loading rates--the complete force spectrum. Two well-known approximations emerge as limiting cases; one of which confirms predictions that single-barrier spectra should converge to a phenomenological description in the slow loading limit.
Date: June 21, 2007
Creator: Friddle, R W
Object Type: Article
System: The UNT Digital Library
Microscopic Approaches to Nuclear Structure: Configuration Interaction (open access)

Microscopic Approaches to Nuclear Structure: Configuration Interaction

The configuration interaction (CI) approach to solving the nuclear many-body problem, also known as the interacting shell model, has proven to be powerful tool in understanding the structure of nuclei. The principal criticism of past applications of the shell model is the reliance on empirical tuning to interaction matrix elements. If an accurate description of nuclei far from the valley of stability, where little or no data is available, a more fundamental approach is needed. This starts with recent ab initio approaches with effective interactions in the no-core shell model (NCSM). Using effective-field theory for guidance, fully ab initio descriptions of nuclei up to {sup 16}O with QCD based NN, NNN, and NNNN interactions will be possible within the next five years. An important task is then to determine how to use these NCSM results to develop effective interactions to describe heavier nuclei without the need to resort to an empirical retuning with every model space. Thus, it is likely that more traditional CI applications utilizing direct diagonalization and more fundamental interactions will be applicable to nuclei with perhaps up to one hundred constituents. But, these direct diagonalization CI applications will always be computationally limited due to the rapid increase …
Date: September 21, 2007
Creator: Ormand, W E
Object Type: Article
System: The UNT Digital Library
Negative Transconductance in Apertured Electron Guns (open access)

Negative Transconductance in Apertured Electron Guns

Passing an electron beam through an aperture can serve to reduce the beam current or change the transverse beam profile. For a sufficiently intense beam, space charge will drive a radial expansion of the beam, which may cause the current passing through the aperture to increase even though the current arriving at the aperture is decreasing. When a gridded electron gun is used, this may be expressed by stating that the transconductance of the apertured gun is negative. Here we explain this effect, and explore some of the key factors governing when it can occur and influencing its strength.
Date: September 21, 2007
Creator: Harris, J R & O'Shea, P G
Object Type: Article
System: The UNT Digital Library
Object Classification at the Nearby Supernova Factory (open access)

Object Classification at the Nearby Supernova Factory

We present the results of applying new object classification techniques to the supernova search of the Nearby Supernova Factory. In comparison to simple threshold cuts, more sophisticated methods such as boosted decision trees, random forests, and support vector machines provide dramatically better object discrimination: we reduced the number of nonsupernova candidates by a factor of 10 while increasing our supernova identification efficiency. Methods such as these will be crucial for maintaining a reasonable false positive rate in the automated transient alert pipelines of upcoming large optical surveys.
Date: December 21, 2007
Creator: Aragon, Cecilia R.; Bailey, Stephen; Aragon, Cecilia R.; Romano, Raquel; Thomas, Rollin C.; Weaver, B. A. et al.
Object Type: Article
System: The UNT Digital Library
Discrimination Report: ESTCP UXO Discrimination Study, ESTCPProject #MM-0437 (open access)

Discrimination Report: ESTCP UXO Discrimination Study, ESTCPProject #MM-0437

The FY06 Defense Appropriation contains funding for the 'Development of Advanced, Sophisticated, Discrimination Technologies for UXO Cleanup' in the Environmental Security Technology Certification Program. In 2003, the Defense Science Board observed: 'The problem is that instruments that can detect the buried UXOs also detect numerous scrap metal objects and other artifacts, which leads to an enormous amount of expensive digging. Typically 100 holes may be dug before a real UXO is unearthed! The Task Force assessment is that much of this wasteful digging can be eliminated by the use of more advanced technology instruments that exploit modern digital processing and advanced multi-mode sensors to achieve an improved level of discrimination of scrap from UXOs.' Significant progress has been made in discrimination technology. To date, testing of these approaches has been primarily limited to test sites with only limited application at live sites. Acceptance of discrimination technologies requires demonstration of system capabilities at real UXO sites under real world conditions. Any attempt to declare detected anomalies to be harmless and requiring no further investigation require demonstration to regulators of not only individual technologies, but of an entire decision making process. This discrimination study was be the first phase in what is …
Date: December 21, 2007
Creator: Gasperikova, Erika; Smith, J. Torquil; Morrison, H. Frank & Becker, Alex
Object Type: Report
System: The UNT Digital Library
Characterization of Direct-Push Vadose Zone Sediments from the 241-B and 241-BX Tank Farms (open access)

Characterization of Direct-Push Vadose Zone Sediments from the 241-B and 241-BX Tank Farms

Geochemical tests provide evidence for the transit of a plume of caustic waste solution through the sediment column at the Hanford 241-B and -BX Tank Farms. Direct-push samples recovered from boreholes surrounding Tanks 241-B-110 and 241-BX-102 and related waste transfer lines and diversion boxes included sediments typical of those previously recovered from other localities on the Hanford Site. The Hanford formation sediments are dominantly quartzo-feldspathic sands strewn with lithic fragments, displaying a range of particle size distributions and sorting characteristics. Some moderately well-sorted, fine-grained lithologies are interpreted as lenticular bodies irregularly dispersed in coarser-grained, more poorly sorted sediments. Tier I tests conducted on the vadose zone sediments revealed an inverse correlation between moisture content and sediment size fraction (i.e., there is greater moisture content in finer-grained sediments). The Tier I tests also showed that the pore water solutions were likely sodium-rich, moderately saline, and possessed higher pH values than background (untainted) sediments. These data are characteristic of sediments that have encountered sodium-rich, saline, caustic waste solution, as documented in other reports at other suspect contamination sites around Hanford. Analyses of solutions from 1:1 water extracts reveal relatively balanced cation and anion concentrations, indicating that most of the geochemical species have …
Date: December 21, 2007
Creator: Brown, Christopher F.; Icenhower, Jonathan P.; Um, Wooyong; Bjornstad, Bruce N.; Valenta, Michelle M.; Iovin, Cristian et al.
Object Type: Report
System: The UNT Digital Library
Soil Sampling to Demonstrate Compliance with Department of Energy Radiological Clearance Requirements for the McGee Ranch-Riverlands and North Slope Units of the Hanford Reach National Monument (open access)

Soil Sampling to Demonstrate Compliance with Department of Energy Radiological Clearance Requirements for the McGee Ranch-Riverlands and North Slope Units of the Hanford Reach National Monument

The Hanford Reach National Monument (HRNM) was created by presidential proclamation in 2000. It is located along the Columbia River in south central Washington and consists of five distinct units. The McGee Ranch-Riverlands and the North Slope units are addressed in this report. North Slope refers to two of the HRNM units: the Saddle Mountain Unit and the Wahluke Slope Unit. The Saddle Mountain and Wahluke Slope Units are located north of the Columbia River, while the McGee Ranch-Riverlands Unit is located south of the Columbia River and north and west of Washington State Highway 24. To fulfill internal U.S. Department of Energy (DOE) requirements prior to any radiological clearance of land, the DOE must evaluate the potential for residual radioactive contamination on this land and determine compliance with the requirements of DOE Order 5400.5. Authorized limits for residual radioactive contamination were developed based on the DOE annual exposure limit to the public (100 mrem) using future potential land-use scenarios. The DOE Office of Environmental Management approved these authorized limits on March 1, 2004. Historical soil monitoring conducted on and around the HRNM indicated soil concentrations of radionuclides were well below the authorized limits (Fritz et al. 2003). However, the …
Date: September 21, 2007
Creator: Fritz, Brad G.; Dirkes, Roger L. & Napier, Bruce A.
Object Type: Report
System: The UNT Digital Library
Kansas Advanced Semiconductor Project (open access)

Kansas Advanced Semiconductor Project

KASP (Kansas Advanced Semiconductor Project) completed the new Layer 0 upgrade for D0, assumed key electronics projects for the US CMS project, finished important new physics measurements with the D0 experiment at Fermilab, made substantial contributions to detector studies for the proposed e+e- international linear collider (ILC), and advanced key initiatives in non-accelerator-based neutrino physics.
Date: September 21, 2007
Creator: Baringer, P.; Bean, A.; Bolton, T.; Horton-Smith, G.; Maravin, Y.; Ratra, B. et al.
Object Type: Report
System: The UNT Digital Library
Chiral perturbation theory with tensor sources (open access)

Chiral perturbation theory with tensor sources

We construct the most general chirally-invariant Lagrangian for mesons in the presence of external sources coupled to the tensor current \bar psi sigma_mu nu psi. In order to have only even terms in the chiral expansion, we consider the new source of O(p2). With this choice, we build the even-parity effective Lagrangian up to the p6-order (NLO). While there are only 4 new terms at the p4-order, at p6-order we find 78 terms for n_f=2 and 113 terms for n_f=3. We provide a detailed discussion on the different mechanisms that ensure that our final set of operators is complete and non-redundant. We also examine the odd-parity sector, to conclude that the first operators appear at the p8-order (NNLO).
Date: May 21, 2007
Creator: Cata, Oscar; Cata, Oscar & Mateu, Vicent
Object Type: Article
System: The UNT Digital Library
Temporal Development of Ion Beam Mean Charge State in PulsedVacuum Arc Ion Sources (open access)

Temporal Development of Ion Beam Mean Charge State in PulsedVacuum Arc Ion Sources

Vacuum arc ion sources, commonly also known as "Mevva" ionsources, are used to generate intense pulsed metal ion beams. It is knownthat the mean charge state of the ion beam lies between 1 and 4,depending on cathode material, arc current, arc pulse duration, presenceor absence of magnetic field at the cathode, as well background gaspressure. A characteristic of the vacuum arc ion beam is a significantdecrease in ion charge state throughout the pulse. This decrease can beobserved up to a few milliseconds, until a "noisy" steady-state value isestablished. Since the extraction voltage is constant, a decrease in theion charge state has a proportional impact on the average ion beamenergy. This paper presents results of detailed investigations of theinfluence of arc parameters on the temporal development of the ion beammean charge state for a wide range of cathode materials. It is shown thatfor fixed pulse duration, the charge state decrease can be reduced bylower arc current, higher pulse repetition rate, and reduction of thedistance between cathode and extraction region. The latter effect may beassociated with charge exchange processes in the dischargeplasma.
Date: June 21, 2007
Creator: Oks, Efim M.; Yushkov, Georgy Yu. & Anders, Andre
Object Type: Article
System: The UNT Digital Library
Development of an ultra-high resolution diffraction grating for soft x-rays (open access)

Development of an ultra-high resolution diffraction grating for soft x-rays

Resonant Inelastic X-ray Scattering (RIXS) is the one of themost powerful methods for investigation of the electronic structure ofmaterials, specifically of excitations in correlated electron systems.However the potential of the RIXS technique has not been fully exploitedbecause conventional grating spectrometers have not been capable ofachieving the extreme resolving powers that RIXS can utilize. State ofthe art spectrometers in the soft x-ray energy range achieve ~;0.25 eVresolution, compared to the energy scales of soft excitations andsuperconducting gap openings down to a few meV. Development ofdiffraction gratings with super high resolving power is necessary tosolve this problem. In this paper we study the possibilities offabrication of gratings of resolving power of up to 106 for the 0.5 1.5KeV energy range. This energy range corresponds to all or most of theuseful dipole transitions for elements of interest in most correlatedelectronic systems, i.e., oxygen K-edge of relevance to all oxides, thetransition metal L2,3 edges, and the M4,5 edges of the rare earths.Various approaches based on different kinds of diffraction gratings suchas deep-etched multilayer gratings, and multilayer coated echelettes arediscussed. We also present simulations of diffraction efficiency for suchgratings, and investigate the necessary fabricationtolerances.
Date: August 21, 2007
Creator: Voronov, Dmitriy L.; Cambie, Rossana; Feshchenko, Ruslan M.; Gullikson, Eric M.; Padmore, Howard A.; Vinogradov, Alexander V. et al.
Object Type: Article
System: The UNT Digital Library