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Catastrophic failure of contaminated fused silica optics at 355 nm

Description: For years, contamination has been known to degrade the performance of optics and to sometimes initiate laser-induced damage to initiate. This study has W to quantify these effects for fused silica windows used at 355 mm Contamination particles (Al, Cu, TiO{sub 2} and ZrO{sub 2}) were artificially deposited onto the surface and damage tests were conducted with a 3 ns NdYAG laser. The damage morphology was characterized by Nomarski optical microscopy. The results showed that the damage morphology for input and output surface contamination is different. For input surface contamination, both input and output surfaces can damage. In particular, the particle can induce pitting or drilling of the surface where the beam exits. Such damage usually grows catastrophically. Output surface contamination is usually ablated away on the shot but can also induce catastrophic damage. Plasmas are observed during illumination and seem to play an important role in the damage mechanism. The relationship between fluence and contamination size for which catastrophic damage occurred was plotted for different contamination materials. The results show that particles even as small as 10 {micro}m can substantially decrease the damage threshold of the window and that metallic particles on the input surface have a more negative effect than oxide particles.
Date: December 3, 1996
Creator: Genin, F. Y., LLNL
Partner: UNT Libraries Government Documents Department

Sol gel based fiber optic sensor for blook pH measurement

Description: This paper describes a fiber-optic pH sensor based upon sol-gel encapsulation of a self-referencing dye, seminaphthorhodamine-1 carboxylate (SNARF-1C). The simple sol-gel fabrication procedure and low coating leachability are ideal for encapsulation and immobilization of dye molecules onto the end of an optical fiber. A miniature bench-top fluorimeter system was developed for use with the optical fiber to obtain pH measurements. Linear and reproducible responses were obtained in human blood in the pH range 6.8 to 8.0, which encompasses the clinically-relevant range. Therefore, this sensor can be considered for in vivo use.
Date: December 19, 1996
Creator: Grant, S. A. & Glass, R. S.
Partner: UNT Libraries Government Documents Department

Chemical vapor deposition: Stable carbons from low-rank coals

Description: CVD was used to increase the oxidative stability of activated carbons. Activated carbons prepared from Gascoyne lignite (North Dakota) by thermal or KOH activation were subjected to BCl{sub 3} in He at 727 C with or without benzene for alimited period of time followed by annealing in He at 900 C for 3 days. Untreated and acid-washed coal samples were used to assess the effect of minral matter in the coal on the boron coating. The oxidative stability of the boron-modified carbons was determined from the decomposition curves obtained from TGA. Modification of the as-received, KOH-treated carbon yielded oxidatively stable carbons up to an initial temperature of 520 , compared to 350 C for the starting material. Similar results were obtained for the carbonized Gascoyne lignite. Sulfurous acid washing of the Gascoyne significantly enhanced the thermal stability (600 C) of the boron-modified carbon.
Date: July 1, 1996
Creator: Sharma, R.K.; Kulas, R.W. & Olson, E.S.
Partner: UNT Libraries Government Documents Department

Cold war historic properties of the 21st Space Wing Air Force Space Command

Description: A Legacy-funded inventory and evaluation of facilities dating to the Cold War era was conducted for the USAF 21{sup ST} Space Wing (AFSPC). The mission of the Wing includes early warning of missile launches and detection and tracking of space objects. The political and military strategic context for these facilities was developed through an overview of Cold War history, subdivided into four major periods: (1) origins of the conflict, (2) confrontation and crisis, (3) sustained superpower balance based on mutual deterrence, and (4) renewed confrontation and collapse of the Soviet Union. The enormous importance of early warning systems in maintaining the balance of power between the USA and the Soviet Union is discussed in more detail as a subset of the general context of the Cold War history to provide additional background for evaluating the 21{sup ST} Space Wing systems. In addition, a history of each installation was prepared and placed in the context of the broader history of the Cold War. For instance, the effort to develop a credible nuclear threat in the early 1950s is represented by the construction of Thule AB as a forward bomber base in 1951. The growing concern with a Soviet ICBM threat in the late 1950s is reflected in the construction of BMEWS at Thule AB and Clear AS during 1958-1961. Development of an antiballistic missile (ABM) system, subsequently abandoned during the 1970s, is represented by the Safeguard System at Cavalier AS. The U.S. response to the Soviet submarine-launched missile capability during the 1970s is embodied in the deployment of phased-array radar systems to cover the ocean flanks of North America at Cape Cod AS (and later at Eldorado AS). The establishment of AFSPC at Peterson AFB in 1982 reflects the increased strategic importance of space in the later phases of the Cold ...
Date: March 1, 1996
Creator: Hoffecker, J.F.; Whorton, M. & Buechler, C.R.
Partner: UNT Libraries Government Documents Department

``Clean`` fuels: Does the new direction make environmental sense?

Description: This paper examines the ramifications of this a three-pronged energy philosophy, with special reference to its expected environmental impact if it is fully implemented as policy. To recapitulate, the three prongs are to rely on a free energy market to determine winners and losers, which could certainly include Reformulated Gasoline (RFG) if it remains relatively cheap and clean; refocus the bulk of government-sponsored transportation energy research toward a ``great leap ahead`` to fully renewable and essentially pollution-free fuels such as hydrogen and fuel cells; and discontinue AFV pump priming. Of special interest is a premise that appears common to all prongs--that none of these measures represents a retreat from environmental goals or accomplishments on record since the National Environmental Policy Act of 1969 was passed.
Date: May 1996
Creator: Saricks, C. L. & Wang, M. Q.
Partner: UNT Libraries Government Documents Department

Intramolecular condensation reactions of {alpha}, {omega}- bis(triethoxy-silyl)alkanes. Formation of cyclic disilsesquioxanes

Description: Under acidic sol-gel polymerization conditions, 1,3-bis(triethoxysilyl)-propane (1) and 1,4-bis(triethoxysilyl)butane (2) were shown to preferentially form cyclic disilsesquioxanes 3 and 4 rather than the expected 1,3-propylene- and 1,4-butylene-bridged polysilsesquioxane gels. Formation of 3 and 4 is driven by a combination of an intramolecular cyclization to six and seven membered rings, and a pronounced reduction in reactivity under acidic conditions as a function of increasing degree of condensation. The ease with which these relatively unreactive cyclic monomers and dimers are formed (under acidic conditions) helps to explain the difficulties in forming gels from 1 and 2. The stability of cyclic disilsesquioxanes was confirmed withe the synthesis of 3 and 4 in gram quantities; the cyclic disilsesquioxanes react slowly to give tricyclic dimers containing a thermodynamically stable eight membered siloxane ring. Continued reactions were shown to perserve the cyclic structure, opening up the possibility of utilizing cyclic disilsesquioxanes as sol-gel monomers. Preliminary polymerization studies with these new, carbohydrate-like monomers revealed the formation of network poly(cyclic disilsesquioxanes) under acidic conditions and polymerization with ring-opening under basic conditions.
Date: August 1, 1996
Creator: Loy, D.A.; Carpenter, J.P.; Myers, S.A.; Assink, R.A.; Small, J.H.; Greaves, J. et al.
Partner: UNT Libraries Government Documents Department

Vitrification of Rocky Flats ash followed by encapsulation in the Defense Waste Processing Facility

Description: The Department of Energy (DOE) manages approximately 10 to 20 metric tons of plutonium in the form of scrap, residues, oxides, ash, metal, sludge, compounds, etc. Not all of this material is chemically stable or is packaging acceptable for storage. Thus, it constitutes a potential hazard to employees and to the public. This paper describes a relatively simple concept for stabilizing most of this type of plutonium by converting it into encapsulated glass. A full-scale hot demonstration of the concept is proposed, in which Rock Flats ash would be vitrified and sealed in small cans, followed by encapsulation of the cans in Defense Waste Processing Facility canisters with high-level glass.
Date: June 1, 1996
Creator: Becker, G.W. Jr. & McKibben, J.M.
Partner: UNT Libraries Government Documents Department

Severe accident progression perspectives based on IPE results

Description: Accident progression perspectives were gathered from the level 2 PRA analyses (the analysis of the accident after core damage has occurred involving the containment performance and the radionuclide release from the containment) described in the IPE submittals. Insights related to the containment failure modes, the releases associated with those failure modes, and the factors responsible for the types of containment failures and release sizes reported were obtained. Complete results are discussed in NUREG-1560 and summarized here.
Date: August 1, 1996
Creator: Lehner, J.R.; Lin, C.C.; Pratt, W.T. & Drouin, M.
Partner: UNT Libraries Government Documents Department

Dynamical hierarchies - A summary

Description: This paper summarizes some of the problems associated with the generation of higher order emergent structures in formal dynamical systems. In biological systems, higher order hyperstructures occur both in an intuitive and a formal sense: monomers, polymers, membranes, organelles, cells, tissues, organs, etc. constitute an observable hierarchy, apparently generated by the underlying biomolecular process. However, in models and simulations of these systems, it has turned out to be quite difficult to produce higher order emergent structures from first principles. The first problem is to agree on what a higher order structure is. An emergent structure can be defined through an introduction of an observational function. If a property can be observed in the dynamics, but not at the level of the fundamental first order interacting structures, we define it to be emergent. It is well known that second order structures occur relatively easy in simulation, so the problem is how to proceed to third and higher order without external interference. A third order structure is defined through the interaction of second order structures forming a new observable not found at the lower levels.
Date: April 1, 1996
Creator: Rasmussen, S.; Barrett, C.L. & Olesen, M.W.
Partner: UNT Libraries Government Documents Department

Comparison of soft and hard tissue ablation with sub-ps and ns pulse lasers

Description: Tissue ablation with ultrashort laser pulses offers several unique advantages. The nonlinear energy deposition is insensitive to tissue type, allowing this tool to be used for soft and hard tissue ablation. The localized energy deposition lead to precise ablation depth and minimal collateral damage. This paper reports on efforts to study and demonstrate tissue ablation using an ultrashort pulse laser. Ablation efficiency and extent of collateral damage for 0.3 ps and 1000 ps duration laser pulses are compared. Temperature measurements of the rear surface of a tooth section is also presented.
Date: May 1, 1996
Creator: Da Silva, L.B.; Stuart, B.C.; Celliers, P.M.; Feit, M.D.; Glinsky, M.E.; Heredia, N.J. et al.
Partner: UNT Libraries Government Documents Department

Ohmic contacts to Si-implanted and un-implanted n-type GaN

Description: We report on ohmic contacts to Si-implanted and un-implanted n-type GaN on sapphire. A ring shaped contact design avoids the need to isolate the contact structures by additional implantation or etching. Metal layers of Al and Ti/Al were investigated. On un-implanted GaN, post metalization annealing was performed in an RTA for 30 seconds in N{sub 2} at 700, 800, and 900 C. A minimum specific contact resistance (r{sub c}) of 1.4{times}10{sup -5} {Omega}{minus}cm{sup 2} was measured for Ti/Al at an annealing temperature of 800 C. Although these values are reasonably low, variations of 95% in specific contact resistance were measured within a 500 {mu}m distance on the wafer. These results are most likely caused by the presence of compensating hydrogen. Specific contact resistance variation was reduced from 95 to 10% by annealing at 900 C prior to metalization. On Si-implanted GaN, un-annealed ohmic contacts were formed with Ti/Al metalization. The implant activation anneal of 1120 C generates nitrogen vacancies that leave the surface heavily n-type, which makes un-annealed ohmic contacts with low contact resistivity possible.
Date: February 1996
Creator: Brown, J.; Ramer, J.; Zheng, L. F.; Hersee, S. D. & Zolper, J.
Partner: UNT Libraries Government Documents Department

Supersymmetry: Theory

Description: If supersymmetric particles are discovered at high-energy colliders, what can one hope to learn about them? In principle, the properties of supersymmetric particles can give a window into the physics of grand unification, or of other aspects of interactions at very short distances. In this article, the author sketches out a systematic program for the experimental study of supersymmetric particles and point out the essential role that e{sup +}e{sup {minus}} linear colliders will play in this investigation.
Date: March 1, 1996
Creator: Peskin, M.E.
Partner: UNT Libraries Government Documents Department

Ensuring critical event sequences in high integrity software by applying path expressions

Description: The goal of this work is to extend the use of existing path expression theory and methodologies to ensure that critical software event sequences are maintained even in the face of malevolent attacks and harsh or unstable operating environments. This will be accomplished by providing dynamic fault management measures directly to the software developer and to their varied development environments. This paper discusses the perceived problems, a brief overview of path expressions, and the author`s proposed extension areas. The authors discuss how the traditional path expression usage and implementation differs from the intended usage and implementation.
Date: July 1, 1996
Creator: Kidd, M.E.C.
Partner: UNT Libraries Government Documents Department

Fast neutron radiography research at ANL-W

Description: Thirty-seven different elements were tested for their suitability as converter screens for direct and indirect fast neutron radiography. The use of commercial X-ray scintillator screens containing YTaO{sub 4}, LaOBr:Tm, YTaO{sub 4}:Nb, YTaO{sub 4}:Tm, CaWO{sub 4}, BaSO{sub 4}:Sr, and GdO{sub 2}S:Tb was also explored for direct fast neutron radiography. For the indirect radiographic process, only one element, holmium, was found to be better than copper. Iron was also found to work as well as copper. All other elements that were tested were inferior to copper for indirect fast neutron radiography. For direct fast neutron radiography, the results were markedly different. Copper was found to be a poor material to sue, as thirty-two of the elements performed better than the copper. Tantalum was found to be the best material to use. Several other materials that also performed remarkably well include, in order of decreasing utility, gold, lutetium, germanium, dysprosium, and thulium. Several interesting results were obtained for the commercial X-ray scintillator screens. Most notably, useful radiographs were produced with all of the various scintillation screens. However, the screens containing YTaO{sub 4}:Nb offered the greatest film densities for the shortest exposure times. Screens using GdSO{sub 4}:Tb provided the best resolution and clearest images at the sacrifice of exposure time. Also, as previous researchers found, scintillator screens offered significantly shorter exposure times than activation foils.
Date: June 1, 1996
Creator: Klann, R.T. & Natale, M.D.
Partner: UNT Libraries Government Documents Department

III-Nitride ion implantation and device processing

Description: Ion implantation doping and isolation has played a critical role in realizing high performance photonic and electronic devices in all mature semiconductor materials; this is also expected for binary III-Nitride materials (InN, GaN, AlN) and their alloys as epitaxy improves and more advanced device structures fabricated. This paper reports on recent progress in ion implantation doping of III-Nitride materials that has led to the first demonstration of a GaN JFET (junction field effect transistor). The JFET was fabricated with all ion implantation doping; in particular, p-type doping of GaN with Ca has been demonstrated with an estimated acceptor ionization energy of 169 meV. O-implantation has also been studied and shown to yield n-type conduction with an ionization energy of {similar_to}29 meV. Neither Ca or O display measurable redistribution during a 1125 C, 15 s activation anneal which sets an upper limit on their diffusivity at this temperature of 2.7{times}10{sup {minus}13}cm{sup 2}/s.
Date: June 1, 1996
Creator: Zolper, J.C.; Shul, R.J.; Baca, A.G.; Pearton, S.J.; Abernathy, C.R.; Wilson, R.G. et al.
Partner: UNT Libraries Government Documents Department

Estimating the effects of air pollution on buildings and structures: The US experience since 1985 and some lessons for the future

Description: Damage to the built environment has always been the foster child of the environmental movement in the United States. Although the Clean Air Act includes damage to materials as one of the welfare effects to be considered when setting secondary air quality standards, the main activity by the U.S. Environmental Protection Agency (EPA) in this discipline seems to be the periodic review of literature required to assemble the official documents needed to review these standards. The one important exception was the National Acid Precipitation Assessment Program (NAPAP), which included a materials damage research activity amounting to a few percent of its total $500 million budget. The 1990 NAPAP State of Science and Technology Report includes three of its twenty-seven chapters on this topic, in addition to portions of the chapter on economic valuation methods. The 1990 NAPAP Integrated Assessment Report debated the economic importance of damage to galvanized steel and to carbonate stone buildings, discussed confounding and mitigating factors for damage to paints, and listed some priorities for assessment of damage to cultural resources. However, in contrast to NAPAP`s views, one independent assessment was that {open_quotes}The NAPAP study found that, at current levels, the major negative effects of acid deposition are probably reduced visibility and accelerated deterioration of outdoor cultural resources{close_quotes}. Since the 1990 reports and the passage of the 1990 Clean Air Act Amendments, NAPAP has contracted to a fraction of its former size. NAPAP now produces a biennial Report to Congress; release of the 1994 report is reported to be imminent. This paper will attempt to review what was accomplished by NAPAP with respect to economic assessment of materials damage and the supporting research and will then go on to postulate some guidelines for future assessments.
Date: January 1, 1996
Creator: Lipfert, F.W.
Partner: UNT Libraries Government Documents Department

Properties of H, O and C in GaN

Description: The electrical properties of the light ion impurities H, O and C in GaN have been examined in both as-grown and implanted material. H is found to efficiently passivate acceptors such as Mg, Ca and C. Reactivation occurs at {ge} 450 C and is enhanced by minority carrier injection. The hydrogen does not leave the GaN crystal until > 800 C, and its diffusivity is relatively high ({approximately} 10{sup {minus}11} cm{sup 2}/s) even at low temperatures (< 200 C) during injection by wet etching, boiling in water or plasma exposure. Oxygen shows a low donor activation efficiency when implanted into GaN, with an ionization level of 30--40 meV. It is essentially immobile up to 1,100 C. Carbon can produce low p-type levels (3 {times} 10{sup 17} cm{sup {minus}3}) in GaN during MOMBE, although there is some evidence it may also create n-type conduction in other nitrides.
Date: April 1, 1996
Creator: Pearton, S.J.; Abernathy, C.R. & Lee, J.W.
Partner: UNT Libraries Government Documents Department

The waveform correlation event detection system project: Issues in system refinement, tuning, and operation

Description: The goal of the Waveform Correlation Event Detection System (WCEDS) Project at Sandia Labs has been to develop a prototype of a full-waveform correlation based seismic event detection system which could be used to assess potential usefulness for CTBT monitoring. The current seismic event detection system in use at the IDC is very sophisticated and provides good results but there is still significant room for improvement, particularly in reducing the number of false events (currently being nearly equal to the number of real events). Our first prototype was developed last year and since then we have used it for extensive testing from which we have gained considerable insight. The original prototype was based on a long-period detector designed by Shearer (1994), but it has been heavily modified to address problems encountered in application to a data set from the Incorporated Research Institutes for Seismology (IRIS) broadband global network. Important modifications include capabilities for event masking and iterative event detection, continuous near-real time execution, improved Master Image creation, and individualized station pre-processing. All have been shown to improve bulletin quality. In some cases the system has detected marginal events which may not be detectable by traditional detection systems, but definitive conclusions cannot be made without direct comparisons. For this reason future work will focus on using the system to process GSETT3 data for comparison with current event detection systems at the IDC.
Date: August 1, 1996
Creator: Young, C.J.; Beiriger, J.I.; Harris, J.M.; Moore, S.G.; Trujillo, J.R.; Withers, M.M. et al.
Partner: UNT Libraries Government Documents Department

BUGLE-96: A revised multigroup cross section library for LWR applications based on ENDF/B-VI Release 3

Description: A revised multigroup cross-section library based ON ENDF/B-VI Release 3 has been produced for light water reactor shielding and reactor pressure vessel dosimetry applications. This new broad-group library, which is designated BUGLE-96, represents an improvement over the BUGLE-93 library released in February 1994 and is expected to replace te BUGLE-93 data. The cross-section processing methodology is the same as that used for producing BUGLE-93 and is consistent with ANSI/ANS 6.1.2. As an added feature, cross-section sets having upscatter data for four thermal neutron groups are included in the BUGLE-96 package available from the Radiation Shielding Information Center. The upscattering data should improve the application of this library to the calculation of more accurate thermal fluences, although more computer time will be required. The incorporation of feedback from users has resulted in a data library that addresses a wider spectrum of user needs.
Date: May 1, 1996
Creator: White, J.E.; Ingersoll, D.T.; Slater, C.O. & Roussin, R.W.
Partner: UNT Libraries Government Documents Department

Remediating the INEL`s buried mixed waste tanks

Description: The Idaho National Engineering Laboratory (INEL), formerly the National Reactor Testing Station (NRTS), encompasses 890 square miles and is located in southeast Idaho. In 1949, the United States Atomic Energy Commission, now the Department of Energy (DOE), established the NRTS as a site for the building and testing of nuclear facilities. Wastes generated during the building and testing of these nuclear facilities were disposed within the boundaries of the site. These mixed wastes, containing radionuclides and hazardous materials, were often stored in underground tanks for future disposal. The INEL has 11 buried mixed waste storage tanks regulated under the Comprehensive Environmental Response, Compensation and Liability Act (CERCLA) ranging in size from 400 to 50,000 gallons. These tanks are constructed of either stainless or carbon steel and are located at 3 distinct geographic locations across the INEL. These tanks have been grouped based on their similarities in an effort to save money and decrease the time required to complete the necessary remediation. Environmental Restoration and Technology Development personnel are teaming in an effort to address the remediation problem systematically.
Date: February 28, 1996
Creator: Kuhns, D.J.; Matthern, G.E. & Reese, C.L.
Partner: UNT Libraries Government Documents Department

Glass material oxidation and dissolution system: Converting miscellaneous fissile materials to glass

Description: The cold war and the development of nuclear energy have resulted in significant inventories of miscellaneous fissile materials (MFMs). MFMs include (1) plutonium scrap and residue, (2) miscellaneous spent nuclear fuel (SNF), (3) certain hot cell wastes, and (4) many one-of-a-kind materials. Major concerns associated with the long-term management of these materials include: safeguards and nonproliferation issues; health, environment, and safety concerns. waste management requirements; and high storage costs. These issues can be addressed by converting the MFMs to glass for secure, long-term storage or repository disposal; however, conventional glass-making processes require oxide-like feed materials. Converting MFMs to oxide-like materials with subsequent vitrification is a complex and expensive process. A new vitrification process has been invented, the Glass Material Oxidation and Dissolution System (GMODS), which directly converts metals, ceramics, and amorphous solids to glass; oxidizes organics with the residue converted to glass; and converts chlorides to borosilicate glass and a secondary sodium chloride (NaCl) stream. Laboratory work has demonstrated the conversion of cerium (a plutonium surrogate), uranium, Zircaloy, stainless steel, multiple oxides, and other materials to glass. However, significant work is required to develop GMODS further for applications at an industrial scale. If implemented, GMODS will provide a new approach to manage these materials.
Date: March 19, 1996
Creator: Forsberg, C.W. & Ferrada, J.J.
Partner: UNT Libraries Government Documents Department