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Adhesion hysteresis of silane coated microcantilevers (open access)

Adhesion hysteresis of silane coated microcantilevers

The authors have developed a new experimental approach for measuring hysteresis in the adhesion between micromachined surfaces. By accurately modeling the deformations in cantilever beams that are subject to combined interfacial adhesion and applied electrostatic forces, they determine adhesion energies for advancing and receding contacts. They draw on this new method to examine adhesion hysteresis for silane coated micromachined structures and found significant hysteresis for surfaces that were exposed to high relative humidity (RH) conditions. Atomic force microscopy studies of these surfaces showed spontaneous formation of agglomerates that they interpreted as silages that have irreversibly transformed from uniform surface layers at low RH to isolated vesicles at high RH. They used contact deformation models to show that the compliance of these vesicles could reasonably account for the adhesion hysteresis that develops at high RH as the surfaces are forced into contact by an externally applied load.
Date: April 17, 2000
Creator: DE BOER,MAARTEN P.; KNAPP,JAMES A.; MICHALSKE,TERRY A.; SRINIVASAN,U. & MABOUDIAN,R.
Object Type: Article
System: The UNT Digital Library
Air Pollution: Status of Implementation and Issues of the Clean Air Act Amendments of 1990 (open access)

Air Pollution: Status of Implementation and Issues of the Clean Air Act Amendments of 1990

A letter report issued by the General Accounting Office with an abstract that begins "Pursuant to a congressional request, GAO provided information on the 1990 Clean Air Act amendments, focusing on: (1) the status of the Environmental Protection Agency's (EPA) implementation of the requirements established by the 1990 amendments; and (2) views from state governments, local programs, industries that are regulated under the act, and environmental advocacy groups (collectively referred to as stakeholders) on the issues that have either helped or hindered the implementation of the 1990 amendments."
Date: April 17, 2000
Creator: United States. General Accounting Office.
Object Type: Report
System: The UNT Digital Library
Airport Improvement Program Reauthorization Legislation in the 106th Congress (open access)

Airport Improvement Program Reauthorization Legislation in the 106th Congress

This report discusses the Airport Improvement Program (AIP), which provides federal grants to airports for capital development. This report also discusses the Aviation Investment and Reform Act for the 21st Century, also referred to as AIR21, which includes provisions for increases in AIP spending, among other things. Primarily, this report discusses the legislative processes surrounding the enaction of these laws and the various appropriations the laws authorize.
Date: April 17, 2000
Creator: Kirk, Robert S.
Object Type: Report
System: The UNT Digital Library
Altus Times (Altus, Okla.), Vol. 101, No. 29, Ed. 1 Monday, April 17, 2000 (open access)

Altus Times (Altus, Okla.), Vol. 101, No. 29, Ed. 1 Monday, April 17, 2000

Daily newspaper from Altus, Oklahoma that includes local, state, and national news along with advertising.
Date: April 17, 2000
Creator: Bush, Michael
Object Type: Newspaper
System: The Gateway to Oklahoma History
The Alvin Sun (Alvin, Tex.), Vol. 109, No. 32, Ed. 1 Monday, April 17, 2000 (open access)

The Alvin Sun (Alvin, Tex.), Vol. 109, No. 32, Ed. 1 Monday, April 17, 2000

Weekly newspaper from Alvin, Texas that includes local, state, and national news along with advertising.
Date: April 17, 2000
Creator: Schwind, Jim & Holton, Kathleen
Object Type: Newspaper
System: The Portal to Texas History
APMS SVD methodology and implementation (open access)

APMS SVD methodology and implementation

One of the main tasks within the Aviation Performance Measurement System (APMS) program uses statistical methodologies to find atypical flights. With thousands of flights a day and hundreds of parameters being recorded every second for each flight, the amount of data escalates and the ability to find atypical flights becomes more difficult. The purpose of this paper is to explain the method known as single value decomposition (SVD) employed to search for the atypical flights and display useful graphics that facilitate understanding the causes of atypicality for these flights. Other methods could also perform this search and some are planned for future implementation.
Date: April 17, 2000
Creator: Amidan, B. G. & Ferryman, T. A.
Object Type: Report
System: The UNT Digital Library
The Baytown Sun (Baytown, Tex.), Vol. 78, No. 145, Ed. 1 Monday, April 17, 2000 (open access)

The Baytown Sun (Baytown, Tex.), Vol. 78, No. 145, Ed. 1 Monday, April 17, 2000

Daily newspaper from Baytown, Texas that includes local, state, and national news along with advertising.
Date: April 17, 2000
Creator: Cash, Wanda Garner
Object Type: Newspaper
System: The Portal to Texas History
Bid Protests: Characteristics of Cases Filed in Federal Courts (open access)

Bid Protests: Characteristics of Cases Filed in Federal Courts

A letter report issued by the General Accounting Office with an abstract that begins "Pursuant to a legislative requirement, GAO provided information on small business bid protests that have been filed in district courts and the United States Court of Federal Claims (COFC) since the Administration Dispute Resolution Act took effect on December 31, 1996, focusing on the: (1) number of bid protest cases filed in the U.S. district courts and COFC between January 1, 1997, and April 30, 1999, that were filed by small businesses, the type of agencies involved, and the amount of the procurement at issue; (2) perceived advantages and disadvantages for small businesses filing bid protest cases in each judicial forum; and (3) characteristics of district court and COFC bid protest cases, particularly those filed by small businesses, that could be used to assess these perceived advantages and disadvantages."
Date: April 17, 2000
Creator: United States. General Accounting Office.
Object Type: Report
System: The UNT Digital Library
A block orthogonalization procedure with constant synchronizationrequirements (open access)

A block orthogonalization procedure with constant synchronizationrequirements

We propose an alternative orthonormalization method that computes the orthonormal basis from the right singular vectors of a matrix. Its advantage are: (a) all operations are matrix-matrix multiplications and thus cache-efficient, (b) only one synchronization point is required in parallel implementations, (c) could be more stable than Gram-Schmidt. In addition, we consider the problem of incremental orthonormalization where a block of vectors is orthonormalized against a previously orthonormal set of vectors and among itself. We solve this problem by alternating iteratively between a phase of Gram-Schmidt and a phase of the new method. We provide error analysis and use it to derive bounds on how accurately the two successive orthonormalization phases should be performed to minimize total work performed. Our experiments confirm the favorable numerical behavior of the new method and its effectiveness on modern parallel computers.
Date: April 17, 2000
Creator: Stathopoulos, Andreas & Wu, Kesheng
Object Type: Article
System: The UNT Digital Library
Bonding and hardness in nonhydrogenated carbon films with moderate sp(3) content (open access)

Bonding and hardness in nonhydrogenated carbon films with moderate sp(3) content

Amorphous carbon films with an s p{sup 3} content up to 25% and a negligible amount of hydrogen have been grown by evaporation of graphite and concurrent Ar{sup +} ion bombardment. The s p{sup 3} content is maximized for Ar{sup +} energies between 200 and 300 eV following a subplantation mechanism. Higher ion energies deteriorate the film due to sputtering and heating processes. The hardness of the films increases in the optimal assisting range from 8 to 18 GPa, and is explained by the crosslinking of graphitic planes through s p {sup 3} connecting site.
Date: April 17, 2000
Creator: Gago, R.; Jimenez, I.; Albella, J. M.; Climent-Font, A.; Caceres, D.; Vergara, I. et al.
Object Type: Article
System: The UNT Digital Library
Catalytic photooxidation of pentachlorophenol using semiconductor nanoclusters (open access)

Catalytic photooxidation of pentachlorophenol using semiconductor nanoclusters

Pentachlorophenol (PCP) is a toxic chlorinated aromatic molecule widely used as fungicide, a bactericide and a wood preservation, and thus ubiquitous in the environment. The authors report photo-oxidation of PCP using a variety of nanosize semiconductor metal oxides and sulfides in both aqueous and polar organic solvents and compare the photo-oxidation kinetics of these nanoclusters to widely studied bulk powders like Degussa P-25 TiO{sub 2} and CdS. They study both the light intensity dependence of PCP photooxidation for nanosize SnO{sub 2} and the size dependence of PCP photooxidation for both nanosize SnO{sub 2} and MoS{sub 2}. They find an extremely strong size dependence for the latter which they attribute to its size-dependent band gap and the associated change in redox potentials due to quantum confinement of the hole-electron pair. The authors show that nanosize MoS{sub 2} with a diameter of d=3.0 nm and an absorbance edge of {approximately}450 nm is a very effective photooxidation catalyst for complete PCP mineralization, even when using only visible light irradiation.
Date: April 17, 2000
Creator: WILCOXON,JESS P.
Object Type: Article
System: The UNT Digital Library
Characterization of degraded EBR-II fuel from the ICPP-603 basin: National spent nuclear fuel program, FY 1999 final report (open access)

Characterization of degraded EBR-II fuel from the ICPP-603 basin: National spent nuclear fuel program, FY 1999 final report

Characterization data is reported for sodium bonded Experimental Breeder Reactor II (EBR-II) fuel which had been stored underwater in containers since the late 1970's. Sixteen stainless steel storage containers were retrieved from the ICPP-603 storage pool at the Idaho National Engineering and Environmental Laboratory (INEEL) in Idaho. Ten of the containers had leaked water due to improper sealing. In the container chosen for detailed destructive analysis, the stainless steel cladding on the uranium alloy fuel had ruptured and fuel oxide particulate formed and filled the bottom of the container. Headspace gas analysis determined that greater than 99% hydrogen was present. Cesium-137, which had leached out of the fuel during the aqueous corrosion process, dominated the radionuclide source term of the water. The metallic sodium from the fuel element bond had reacted with the water, forming a caustic solution of NaOH.
Date: April 17, 2000
Creator: Pahl, R. G.
Object Type: Report
System: The UNT Digital Library
Characterization of vacuum-multifoil insulation for long-life thermal batteries (open access)

Characterization of vacuum-multifoil insulation for long-life thermal batteries

The use of vacuum multifoil (VMF) container for thermal insulation in long-life thermal batteries was investigated in a proof-of-concept demonstration. An InvenTek-designed VMF container 4.9 inches in diameter by 10 inches long was used with an internally heated aluminum block, to simulate a thermal-battery stack. The block was heated to 525 C or 600 C and allowed to cool while monitoring the temperature of the block and the external case at three locations with time. The data indicate that it should be possible to build an equivalent-sized thermal battery that should last up to six hours, which would meet the requirements for a long-life sonobuoy application.
Date: April 17, 2000
Creator: GUIDOTTI,RONALD A.; REINHARDT,FREDERICK W. & KAUN,THOMAS
Object Type: Article
System: The UNT Digital Library
Constitutive modeling of viscoplastic damage in solder material (open access)

Constitutive modeling of viscoplastic damage in solder material

This paper presents a constitutive modeling of viscoplastic damage in 63Sn-37Pb solder material taking into account the effects of microstructural change in grain coarsening. Based on the theory of damage mechanics, a two-scalar damage model is developed by introducing the damage variables and the free energy equivalence principle. An inelastic potential function based on the concept of inelastic damage energy release rate is proposed and used to derive an inelastic damage evolution equation. The validation of the model is carried out for the viscoplastic material by predicting monotonic tensile behavior and tensile creep curves at different temperatures. The softening behavior of the material under monotonic tension loading can be characterized with the model. The results demonstrate adequately the validity of the proposed viscoplastic constitutive modeling for the solder material.
Date: April 17, 2000
Creator: WEI,YONG; CHOW,C.L.; NEILSEN,MICHAEL K. & FANG,HUEI ELIOT
Object Type: Article
System: The UNT Digital Library
Development of advanced hot-gas desulfurization processes (open access)

Development of advanced hot-gas desulfurization processes

Advanced integrated gasification combined cycle (IGCC) power plants nearing completion, such as Sierra-Pacific, employ a circulating fluidized-bed (transport) reactor hot-gas desulfurization (HGD) process that uses 70-180 {micro}m average particle size (aps) zinc-based mixed-metal oxide sorbent for removing H{sub 2}S from coal gas down to less than 20 ppmv. The sorbent undergoes cycles of absorption (sulfidation) and air regeneration. The key barrier issues associated with a fluidized-bed HGD process are chemical degradation, physical attrition, high regeneration light-off (initiation) temperature, and high cost of the sorbent. Another inherent complication in all air-regeneration-based HGD processes is the disposal of the problematic dilute SO{sub 2} containing regeneration tail-gas. Direct Sulfur Recovery Process (DSRP), a leading first generation technology, efficiently reduces this SO{sub 2} to desirable elemental sulfur, but requires the use of 1-3 % of the coal gas, thus resulting in an energy penalty to the plant. Advanced second-generation processes are under development that can reduce this energy penalty by modifying the sorbent so that it could be directly regenerated to elemental sulfur. The objective of this research is to support the near and long term DOE efforts to commercialize the IGCC-HGD process technology. Specifically we aim to develop: optimized low-cost sorbent materials with …
Date: April 17, 2000
Creator: Jothimurugesan, K.
Object Type: Report
System: The UNT Digital Library

Ensemble: 2000-04-17 - Les Petits Violons

Concert presented at the UNT College of Music Recital Hall.
Date: April 17, 2000
Creator: Les Petits Violons
Object Type: Sound
System: The UNT Digital Library
The equilibrium state of hydrogen in gallium nitride: Theory and experiment (open access)

The equilibrium state of hydrogen in gallium nitride: Theory and experiment

Formation energies and vibrational frequencies for H in wurtzite GaN were calculated from density functional theory and used to predict equilibrium state occupancies and solid solubilities for p-type, intrinsic, and n-type material. The solubility of deuterium (D) was measured at 600--800 C as a function of D{sub 2} pressure and doping and compared with theory. Agreement was obtained by reducing the H formation energies 0.2 eV from ab-initio theoretical values. The predicted stretch-mode frequency for H bound to the Mg acceptor lies 5% above an observed infrared absorption attributed to this complex. It is concluded that currently recognized H states and physical processes account for the equilibrium behavior of H examined in this work.
Date: April 17, 2000
Creator: Myers, Samuel M., Jr.; Wright, Alan F.; Petersen, Gary A.; Seager, Carleton H.; Wampler, William R.; Crawford, Mary H. et al.
Object Type: Article
System: The UNT Digital Library
The Express-Star (Chickasha, Okla.), Ed. 1 Monday, April 17, 2000 (open access)

The Express-Star (Chickasha, Okla.), Ed. 1 Monday, April 17, 2000

Daily newspaper from Chickasha, Oklahoma that includes local, state, and national news along with advertising.
Date: April 17, 2000
Creator: Bush, Kent
Object Type: Newspaper
System: The Gateway to Oklahoma History
Federal Advertising Contracts: Distribution to Small Disadvantaged Businesses (open access)

Federal Advertising Contracts: Distribution to Small Disadvantaged Businesses

Correspondence issued by the General Accounting Office with an abstract that begins "Pursuant to a congressional request, GAO reviewed the distribution of federal contract dollars for advertising services to small disadvantaged businesses (SDB), focusing on: (1) the goals established for federal contracting with small minority-owned and women-owned businesses; (2) trend data on the distribution of prime advertising obligations for fiscal years 1994 through 1998; (3) information on the distribution of and competition for advertising contracts with fiscal year (FY) 1998 obligations; and (4) information on the distribution of subcontract awards to SDBs for selected advertising contracts."
Date: April 17, 2000
Creator: United States. General Accounting Office.
Object Type: Text
System: The UNT Digital Library
First passage failure: Analysis alternatives (open access)

First passage failure: Analysis alternatives

Most mechanical and structural failures can be formulated as first passage problems. The traditional approach to first passage analysis models barrier crossings as Poisson events. The crossing rate is established and used in the Poisson framework to approximate the no-crossing probability. While this approach is accurate in a number of situations, it is desirable to develop analysis alternatives for those situations where traditional analysis is less accurate and situations where it is difficult to estimate parameters of the traditional approach. This paper develops an efficient simulation approach to first passage failure analysis. It is based on simulation of segments of complex random processes with the Karhunen-Loeve expansion, use of these simulations to estimate the parameters of a Markov chain, and use of the Markov chain to estimate the probability of first passage failure. Some numerical examples are presented.
Date: April 17, 2000
Creator: PAEZ,THOMAS L.; NGUYEN,H.P. & WIRSCHING,PAUL H.
Object Type: Article
System: The UNT Digital Library
The Impact of Solution Agglomeration on the Deposition of Self-Assembled Monolayers (open access)

The Impact of Solution Agglomeration on the Deposition of Self-Assembled Monolayers

Self-assembled monolayers (SAMS) are commonly produced by immersing substrates in organic solutions containing trichlorosilane coupling agents. Unfortunately, such deposition solutions can also form alternate structures including inverse micelles and lamellar phases. The formation of alternate phases is one reason for the sensitivity of SAM depositions to factors such as the water content of the deposition solvent. If such phases are present, the performance of thin films used for applications such as minimization of friction and stiction in micromachines can be seriously compromised. Inverse micelle formation has been studied in detail for depositions involve 1H-, 1H-, 2H-, 2H-perfluorodecyltrichlorosilane (FDTS) in isooctane. Nuclear magnetic resonance experiments have been used to monitor the kinetics of hydrolysis and condensation reactions between water and FDTS. Light scattering experiments show that when hydrolyzed FDTS concentrations reach a critical concentration, there is a burst of nucleation to form high concentrations of spherical agglomerates. Atomic force microscopy results show that the agglomerates then deposit on substrate surfaces. Deposition conditions leading to monolayer formation involve using deposition times that are short relative to the induction time for agglomeration. After deposition, inverse micelles can be converted into lamellar or monolayer structures with appropriate heat treatments if surface concentrations are relatively …
Date: April 17, 2000
Creator: Bunker, Bruce C.; Carpick, Robert W.; Assink, Roger A.; Thomas, Michael L.; Hankins, Matthew G.; Voigt, James A. et al.
Object Type: Article
System: The UNT Digital Library
Impedance Studies on Li-Ion Cathodes (open access)

Impedance Studies on Li-Ion Cathodes

This paper describes the author's 2- and 3-electrode impedance results of metal oxide cathodes. These results were extracted from impedance data on 18650 Li-ion cells. The impedance results indicate that the ohmic resistance of the cell is very nearly constant with state-of-charge (SOC) and temperature. For example, the ohmic resistance of 18650 Li-ion cells is around 60 m{Omega} for different SOCS (4.1V to 3.0V) and temperatures from 35 C to {minus}20 C. However, the interfacial impedance shows a modest increase with SOC and a huge increase of between 10 and 100 times with decreasing temperature. For example, in the temperature regime (35 C down to {minus}20 C) the overall cell impedance has increased from nearly 200 m{Omega} to 8,000 m{Omega}. Most of the increase in cell impedance comes from the metal oxide cathode/electrolyte interface.
Date: April 17, 2000
Creator: Nagasubramanian, Ganesan
Object Type: Article
System: The UNT Digital Library
Internet-based calibration of a multifunction calibrator (open access)

Internet-based calibration of a multifunction calibrator

A new way of providing calibration services is evolving which employs the Internet to expand present capabilities and make the calibration process more interactive. Sandia National Laboratories and the National Institute of Standards and Technology are collaborating to set up and demonstrate a remote calibration of multifunction calibrators using this Internet-based technique that is becoming known as e-calibration. This paper describes the measurement philosophy and the Internet resources that can provide real-time audio/video/data exchange, consultation and training, as well as web-accessible test procedures, software and calibration reports. The communication system utilizes commercial hardware and software that should be easy to integrate into most calibration laboratories.
Date: April 17, 2000
Creator: Bunting Baca, Lisa A.; Duda, Leonard E., Jr.; Walker, Russell M.; Oldham, Nile & Parker, Mark
Object Type: Article
System: The UNT Digital Library
Investigation of elevated temperature aging effects on lithium-ion cells (open access)

Investigation of elevated temperature aging effects on lithium-ion cells

Electrical and chemical measurements have been made on 18650-size lithium-ion cells that have been exposed to calendar and cycle life aging at temperatures up to 70 C. Aging times ranged from 2 weeks at the highest temperature to several months under more moderate conditions. After aging, the impedance behavior of the cells was reversed from that found originally, with lower impedance at low state of charge and the total impedance was significantly increased. Investigations using a reference electrode showed that these changes are primarily due to the behavior of the cathode. Measurements of cell impedance as a function of cell voltage reveal a pronounced minimum in the total impedance at approximately 40--50% state-of-charge (SOC). Chemical analysis data are presented to support the SOC assignments for aged and unaged cells. Electrochemical impedance spectroscopy (EIS) data have been recorded at several intermediate states of charge to construct the impedance vs. open circuit voltage curve for the cell. This information has not previously been available for the LiNi{sub 0.85}Co{sub 0.15}O{sub 2} cathode material. Structural and chemical analysis information obtained from cell components removed during postmortems will also be discussed in order to reveal the true state of charge of the cathode and to …
Date: April 17, 2000
Creator: Jungst, Rudolph G.; Nagasubramanian, Ganesan & Ingersoll, David
Object Type: Article
System: The UNT Digital Library