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Human Service Programs: Demonstration Projects Could Identify Ways to Simplify Policies and Facilitate Technology Enhancements to Reduce Administrative Costs (open access)

Human Service Programs: Demonstration Projects Could Identify Ways to Simplify Policies and Facilitate Technology Enhancements to Reduce Administrative Costs

A letter report issued by the Government Accountability Office with an abstract that begins "The cost of administering human service programs has been a long-standing concern among policy makers interested in ensuring that federal programs are run in a cost-efficient manner so that federal funds go directly to helping vulnerable people. Little is known about how administrative costs compare among programs, or about opportunities to better manage these costs. GAO looked at (1) how administrative costs are defined and what rules govern federal and state participation in funding these costs; (2) what is known about the amounts of administrative spending and how they have changed over time; and (3) what opportunities exist at the federal level to help states balance cost savings with program effectiveness and integrity. GAO's review included seven programs: Adoption Assistance, Child Care and Development Fund (CCDF), Child Support Enforcement (CSE), food stamps, Foster Care, Temporary Assistance for Needy Families (TANF), and Unemployment Insurance (UI). To address the questions, GAO reviewed laws, analyzed spending data, and visited five states."
Date: September 19, 2006
Creator: United States. Government Accountability Office.
Object Type: Report
System: The UNT Digital Library
Defense Acquisitions: Better Acquisition Strategy Needed for Successful Development of the Army's Warrior Unmanned Aircraft System (open access)

Defense Acquisitions: Better Acquisition Strategy Needed for Successful Development of the Army's Warrior Unmanned Aircraft System

A letter report issued by the Government Accountability Office with an abstract that begins "Through 2011, the Department of Defense (DOD) plans to spend $20 billion on unmanned aircraft systems, including the Army's "Warrior." Because of congressional concerns that some systems have been more costly and taken more time to produce than predicted, GAO reviewed the Warrior program. This report (1) describes the Army's requirements underlying its decision to acquire Warrior instead of existing systems such as the Air Force's Predator, and (2) assesses whether the Army has established a sound acquisition strategy for the Warrior program."
Date: May 19, 2006
Creator: United States. Government Accountability Office.
Object Type: Report
System: The UNT Digital Library
Commercial Aviation: Costs and Major Factors Influencing Infrastructure Changes at U.S. Airports to Accomodate the New A380 Aircraft (open access)

Commercial Aviation: Costs and Major Factors Influencing Infrastructure Changes at U.S. Airports to Accomodate the New A380 Aircraft

A letter report issued by the Government Accountability Office with an abstract that begins "Airbus S.A.S (Airbus), a European aircraft manufacturer, introduced a new aircraft, the A380 that will be the largest passenger aircraft in the world with expected delivery to its first customers in late 2006. The A380 has a double deck and is expected to seat between 555 and 853 passengers. The A380 is much larger than its competitors with a wingspan of 262 feet, a tail fin about 80 feet high, and a maximum takeoff weight of over 1.2 million pounds. A freight version of the A380 is scheduled for delivery in 2008. Because of the size of the A380, U.S. airports have to make changes to accommodate the aircraft. This may include widening runways and taxiways, or restructuring gate areas to accommodate the additional passengers. This report examines (1) the costs and nature of the changes U.S. airports are making to their infrastructure to accommodate the A380, (2) the funding sources being used to finance these changes, and (3) the major factors influencing the changes being made. The Federal Aviation Administration (FAA) and Airbus provided technical comments on the report. Airbus also commented on the 18 …
Date: May 19, 2006
Creator: United States. Government Accountability Office.
Object Type: Report
System: The UNT Digital Library
Limitations in the Air Force's Proposed Housing Plan for Spangdahlem Air Base, Germany (open access)

Limitations in the Air Force's Proposed Housing Plan for Spangdahlem Air Base, Germany

Correspondence issued by the Government Accountability Office with an abstract that begins "The Air Force plans to construct 233 military housing units on Spangdahlem Air Base, Germany at a cost of $131.3 million spread over fiscal years 2006-2008, and to fund 270 build-to-lease units nearby at an annual cost of $32,888 per unit over 20 years. The Military Quality of Life and Veterans Affairs Appropriations Act for fiscal year 2006 directed the Secretary of the Air Force to submit to the Committees on Appropriations of both Houses of Congress a report containing a housing plan for Spangdahlem. The House Conference Report accompanying H.R. 2528 stipulated that the report must include a complete cost-benefit analysis of available housing options to include build-to-lease housing, and that none of the funds appropriated for family housing at Spangdahlem--nearly $45.4 million--may be obligated until the Secretary of the Air Force certified to the Appropriations Committees that the report had been completed and received the Committees' response or a 30-day period has elapsed after the Committees receive such report. In response to the mandate, the Air Force issued a report in January 2006 that compared its proposed plan with four other housing options that included a …
Date: May 19, 2006
Creator: United States. Government Accountability Office.
Object Type: Text
System: The UNT Digital Library
Faith-Based and Community Initiative: Improvements in Monitoring Grantees and Measuring Performance Could Enhance Accountability (open access)

Faith-Based and Community Initiative: Improvements in Monitoring Grantees and Measuring Performance Could Enhance Accountability

A letter report issued by the Government Accountability Office with an abstract that begins "The Administration's efforts to improve the federal government's provision of social services through its Faith-Based and Community Initiative have sparked considerable interest. GAO was asked to examine (1) the activities of the initiative-related centers in five federal agencies; (2) the grant award procedures for selected grants; (3) the extent to which selected federal and state agencies are providing information on and ensuring compliance with safeguards designed to protect faith-based organizations (FBO), beneficiaries, and the government; and (4) how the progress of the initiative is being measured. We interviewed government officials administering 10 grant programs and officials from 26 FBOs."
Date: June 19, 2006
Creator: United States. Government Accountability Office.
Object Type: Report
System: The UNT Digital Library
Defense Management: Attention Is Needed to Improve Oversight of DLA Prime Vendor Program (open access)

Defense Management: Attention Is Needed to Improve Oversight of DLA Prime Vendor Program

Correspondence issued by the Government Accountability Office with an abstract that begins "In fiscal year 2005, prime vendor sales accounted for approximately $9 billion of the Defense Logistics Agency's (DLA) total sales and service of $32 billion. Under the prime vendor concept, the Department of Defense (DOD) relies on a distributor of a commercial product line, who provides that product line and incidental services to customers in an assigned region or area of responsibility. Products or services are to be delivered within a specified period of time after order placement. Since 1991, we have identified the use of prime vendors as a best commercial practice for inventory management. Nonetheless, media reports in October 2005, and a hearing before the House Armed Services Committee on November 9, 2005, raised concerns about the use of the prime vendor concept and the prices that DLA was paying for items acquired through a prime vendor. The use of prime vendor contracts is governed by the Federal Acquisition Regulation (FAR) and the Defense Federal Acquisition Regulation Supplement. DLA manages the program and the Director of DLA reports to the Under Secretary of Defense for Acquisition, Technology and Logistics through the Deputy Under Secretary of Defense …
Date: June 19, 2006
Creator: United States. Government Accountability Office.
Object Type: Text
System: The UNT Digital Library
Homeland Security: Management and Coordination Problems Increase the Vulnerability of U.S. Agriculture to Foreign Pests and Disease (open access)

Homeland Security: Management and Coordination Problems Increase the Vulnerability of U.S. Agriculture to Foreign Pests and Disease

A letter report issued by the Government Accountability Office with an abstract that begins "U.S. agriculture generates over $1 trillion in annual economic activity, but concerns exist about the sector's vulnerability to a natural or deliberate introduction of foreign livestock, poultry, and crop pests and disease. Under the Agricultural Quarantine Inspection (AQI) program, international passengers and cargo are inspected at U.S. ports of entry to seize prohibited material and intercept foreign agricultural pests. The Homeland Security Act of 2002 transferred AQI inspections from the U.S. Department of Agriculture (USDA) to the Department of Homeland Security (DHS) and left certain other AQI responsibilities at USDA. GAO examined (1) the extent to which USDA and DHS have changed the inspection program since the transfer, (2) how the agencies have managed and coordinated their responsibilities, and (3) how funding for agricultural inspections has been managed since the transfer."
Date: May 19, 2006
Creator: United States. Government Accountability Office.
Object Type: Report
System: The UNT Digital Library
Alternative Mortgage Products: Impact on Defaults Remains Unclear, but Disclosure of Risks to Borrowers Could Be Improved (open access)

Alternative Mortgage Products: Impact on Defaults Remains Unclear, but Disclosure of Risks to Borrowers Could Be Improved

A letter report issued by the Government Accountability Office with an abstract that begins "Alternative mortgage products (AMPs) can make homes more affordable by allowing borrowers to defer repayment of principal or part of the interest for the first few years of the mortgage. Recent growth in AMP lending has heightened the importance of borrowers' understanding and lenders' management of AMP risks. This report discusses the (1) recent trends in the AMP market, (2) potential AMP risks for borrowers and lenders, (3) extent to which mortgage disclosures discuss AMP risks, and (4) federal and selected state regulatory response to AMP risks. To address these objectives, GAO used regulatory and industry data to analyze changes in AMP monthly payments; reviewed available studies; and interviewed relevant federal and state regulators and mortgage industry groups, and consumer groups."
Date: September 19, 2006
Creator: United States. Government Accountability Office.
Object Type: Report
System: The UNT Digital Library
Federal Law Enforcement: Survey of Federal Civilian Law Enforcement Functions and Authorities (open access)

Federal Law Enforcement: Survey of Federal Civilian Law Enforcement Functions and Authorities

A letter report issued by the Government Accountability Office with an abstract that begins "Law enforcement officers (LEOs) within the federal government play a key role in maintaining the safety and security of federal property, employees, and the general public. In this report, we describe the number of LEOs that federal civilian law enforcement components employed as of June 30, 2006; the federal job series classifications the components used to employ LEOs; and the sources of their primary legal authorities. To identify federal components that employ LEOs, we consulted, among other sources, the Federal Citizen Information Center's Cabinet Agencies and Independent Agencies and Commissions Directory; a list of organizations included in the Federal Law Enforcement Training Center (FLETC) 2004-2005 List of Agencies Trained at FLETC; and federal agencies listed in Federal Law Enforcement Officers, 2002, published by the Department of Justice's Bureau of Justice Statistics (BJS). We identified 104 federal civilian law enforcement components and administered two Web-based surveys to each--one survey on the primary authorities and the other survey on the job series classifications. We defined an LEO as an individual authorized to perform any of four specific functions: (1) conduct criminal investigations, (2) execute search warrants, (3) make …
Date: December 19, 2006
Creator: United States. Government Accountability Office.
Object Type: Report
System: The UNT Digital Library
Response to a Posthearing Question Related to GAO's November 16, 2006 Testimony on the Defense Travel System (open access)

Response to a Posthearing Question Related to GAO's November 16, 2006 Testimony on the Defense Travel System

Correspondence issued by the Government Accountability Office with an abstract that begins "On November 16, 2006, GAO testified before the Permanent Subcommittee on Investigations, Committee on Homeland Security and Governmental Affairs, on the results of our audit on the Defense Travel System (DTS). This letter responds to a question from Senator Coburn that we were asked to answer for the record. The question and our response follow."
Date: December 19, 2006
Creator: United States. Government Accountability Office.
Object Type: Text
System: The UNT Digital Library
Indian Issues: Analysis of the Crow Creek Sioux and Lower Brule Sioux Tribes' Additional Compensation Claims (open access)

Indian Issues: Analysis of the Crow Creek Sioux and Lower Brule Sioux Tribes' Additional Compensation Claims

A letter report issued by the Government Accountability Office with an abstract that begins "From 1946 to 1966, the government constructed the Fort Randall and Big Bend Dams as flood control projects on the Missouri River in South Dakota. The reservoirs created behind the dams flooded about 38,000 acres of the Crow Creek and Lower Brule Indian reservations. The tribes received compensation when the dams were built and additional compensation in the 1990s. The tribes are seeking a third round of compensation based on a consultant's analysis. The Congress provided additional compensation to other tribes after two prior GAO reports. For those reports, GAO found that one recommended approach to providing additional compensation would be to calculate the difference between the tribe's final asking price and the amount that was appropriated by the Congress, and then to adjust it using the inflation rate and an interest rate to reflect a range of current values. GAO was asked to assess whether the tribes' consultant followed the approach used in GAO's prior reports. The additional compensation amounts calculated by the tribes' consultant are contained in H.R. 109 and S. 374."
Date: May 19, 2006
Creator: United States. Government Accountability Office.
Object Type: Report
System: The UNT Digital Library
Federal Autism Activities: Funding for Research Has Increased, but Agencies Need to Resolve Surveillance Challenges (open access)

Federal Autism Activities: Funding for Research Has Increased, but Agencies Need to Resolve Surveillance Challenges

A letter report issued by the Government Accountability Office with an abstract that begins "Autism is a developmental disorder involving communication and social impairment. It has no known cause or cure, and its prevalence is unknown. The Children's Health Act of 2000 required the Department of Health and Human Services (HHS) and HHS agencies to conduct activities related to autism research, surveillance, and coordination. This report provides information on (1) the National Institutes of Health's (NIH) and the Centers for Disease Control and Prevention's (CDC) autism activities and these agencies' funding of autism activities, (2) programs that federal agencies have under way to support services for people with autism and concerns related to providing services, and (3) coordination of federal autism activities."
Date: July 19, 2006
Creator: United States. Government Accountability Office.
Object Type: Report
System: The UNT Digital Library
DOD Payments to Small Business: Implementation and Effective Utilization of Electronic Invoicing Could Further Reduce Late Payments (open access)

DOD Payments to Small Business: Implementation and Effective Utilization of Electronic Invoicing Could Further Reduce Late Payments

A letter report issued by the Government Accountability Office with an abstract that begins "The National Defense Authorization Act for Fiscal Year 2004 requires GAO to report on the timeliness of Department of Defense (DOD) payments made to small businesses. GAO's report focuses on (1) whether, at DOD payment centers for which data were available, small business invoices were more likely to be paid late; (2) whether systemic weaknesses in DOD payment processes result in late payments to contractors--including small business contractors; and (3) the impact of late payments on small businesses. To calculate timeliness rates, GAO used the data DOD was able to provide for 9 of its 20 vendor payment locations as well as its one contract pay location. GAO used a case study approach for the third objective because data limitations did not permit the use of statistically reliable sampling techniques for assessing the experiences of DOD small business contractors as a whole. Case study contractors were selected because they experienced a high frequency of late payments and may not be reflective of all small businesses."
Date: May 19, 2006
Creator: United States. Government Accountability Office.
Object Type: Report
System: The UNT Digital Library
Immigration Enforcement: Weaknesses Hinder Employment Verification and Worksite Enforcement Efforts (open access)

Immigration Enforcement: Weaknesses Hinder Employment Verification and Worksite Enforcement Efforts

Testimony issued by the Government Accountability Office with an abstract that begins "The opportunity for employment is one of the most important magnets attracting illegal immigrants to the United States. The Immigration Reform and Control Act (IRCA) of 1986 established an employment eligibility verification process and a sanctions program for fining employers for noncompliance. Few modifications have been made to the verification process and sanctions program since 1986, and immigration experts state that a more reliable verification process and a strengthened worksite enforcement capacity are needed to help deter illegal immigration. This testimony is based on GAO's August 2005 report on the employment verification process and worksite enforcement efforts. In this testimony, GAO provides observations on (1) the current employment verification process and (2) U.S. Immigration and Customs Enforcement's (ICE) priorities and resources for the worksite enforcement program and the challenges it faces in implementing that program."
Date: June 19, 2006
Creator: United States. Government Accountability Office.
Object Type: Text
System: The UNT Digital Library
Particulate Matter: EPA Needs to Make More Progress in Addressing the National Academies' Recommendations on Estimating Health Benefits (open access)

Particulate Matter: EPA Needs to Make More Progress in Addressing the National Academies' Recommendations on Estimating Health Benefits

Testimony issued by the Government Accountability Office with an abstract that begins "Scientific evidence links exposure to particulate matter--a widespread form of air pollution--to serious health problems, including asthma and premature death. Under the Clean Air Act, the Environmental Protection Agency (EPA) periodically reviews the appropriate air quality level at which to set national standards to protect the public against the health effects of six pollutants, including particulate matter. EPA proposed revisions to the particulate matter standards in January 2006 and issued a regulatory impact analysis of the revisions' expected costs and benefits. The estimated benefits of air pollution regulations have been controversial in the past, and a 2002 National Academies report to EPA made recommendations aimed at improving the estimates for particulate matter and other air pollution regulations. This testimony is based on GAO's July 2006 report Particulate Matter: EPA Has Started to Address the National Academies' Recommendations on Estimating Health Benefits, but More Progress Is Needed (GAO-06-780). GAO determined whether and how EPA applied the National Academies' recommendations in its estimates of the health benefits expected from the January 2006 proposed revisions to the particulate matter standards."
Date: July 19, 2006
Creator: United States. Government Accountability Office.
Object Type: Text
System: The UNT Digital Library
Rail Transit: Observations on FTA's State Safety Oversight Program (open access)

Rail Transit: Observations on FTA's State Safety Oversight Program

Testimony issued by the Government Accountability Office with an abstract that begins "The U.S. rail transit system is a vital component of the nation's transportation infrastructure, carrying millions of people daily. Unlike most transportation modes, safety and security oversight of rail transit is the responsibility of state-designated oversight agencies following Federal Transit Administration (FTA) requirements. In addition, in 2001, Congress passed the Aviation and Transportation Security Act, giving the Transportation Security Administration (TSA) authority for security over all transportation modes, including rail transit. This testimony is based on ongoing work for this subcommittee's committee--the House Committee on Transportation and Infrastructure. I describe (1) how the State Safety Oversight program is designed; (2) what is known about the impact of the program on rail safety and security; and (3) challenges facing the program. I also provide information about oversight of transit systems that cross state boundaries. To address these issues, we reviewed program documents and interviewed stakeholders including officials from FTA, TSA, the National Transportation Safety Board, and the American Public Transportation Association. We also surveyed state oversight and transit agencies covered by FTA's program, interviewing 24 of the 25 oversight agencies and 37 of 42 transit agencies across the country."
Date: July 19, 2006
Creator: United States. Government Accountability Office.
Object Type: Text
System: The UNT Digital Library
Nuclear Regulatory Commission: Preliminary Observations on Its Process to Oversee the Safe Operation of Nuclear Power Plants (open access)

Nuclear Regulatory Commission: Preliminary Observations on Its Process to Oversee the Safe Operation of Nuclear Power Plants

Testimony issued by the Government Accountability Office with an abstract that begins "The Nuclear Regulatory Commission (NRC) has the responsibility to provide oversight to ensure that the nation's 103 commercial nuclear power plants are operated safely. While the safety of these plants has always been important, since radioactive release could harm the public and the environment, NRC's oversight has become even more critical as the Congress and the nation consider the potential resurgence of nuclear power in helping to meet the nation's growing energy needs. Prior to 2000, NRC was criticized for having a safety oversight process that was not always focused on the most important safety issues and in some cases, was overly subjective. To address these and other concerns, NRC implemented a new oversight process--the Reactor Oversight Process (ROP). NRC continues to modify the ROP to incorporate feedback from stakeholders and in response to other external events. This testimony summarizes information on (1) how NRC oversees nuclear power plants, (2) the results of the ROP over the past several years, and (3) the aspects of the ROP that need improvement and the status of NRC's efforts to improve them. This testimony discusses preliminary results of GAO's work. GAO …
Date: June 19, 2006
Creator: United States. Government Accountability Office.
Object Type: Text
System: The UNT Digital Library
Puerto Rico: Fiscal Relations with the Federal Government and Economic Trends during the Phaseout of the Possessions Tax Credit (open access)

Puerto Rico: Fiscal Relations with the Federal Government and Economic Trends during the Phaseout of the Possessions Tax Credit

A chapter report issued by the Government Accountability Office with an abstract that begins "The federal possessions tax credit, which was designed to encourage U.S. corporate investment in Puerto Rico and other insular areas, expires this year. Proponents of continued federal economic assistance to Puerto Rico have presented a variety of proposals for congressional consideration. In response to a request from the U.S. Senate Committee on Finance, this study compares trends in Puerto Rico's principal economic indicators with those for the United States; reports on changes in the activities and tax status of the corporations that have claimed the possessions tax credit; explains how fiscal relations between the federal government and Puerto Rico differs from the federal government's relations with the states and other insular areas; and compares the taxes paid to all levels of government by residents of Puerto Rico, the states, and other insular areas. GAO used the latest data available from multiple federal and Puerto Rican government agencies. Data limitations are noted where relevant. Key findings are based on multiple measures from different sources. GAO is not making any recommendations in this report. In comments on this report the Governor of Puerto Rico said the report will …
Date: May 19, 2006
Creator: United States. Government Accountability Office.
Object Type: Report
System: The UNT Digital Library
Purchase Cards: Control Weaknesses Leave DHS Highly Vulnerable to Fraudulent, Improper, and Abusive Activity (open access)

Purchase Cards: Control Weaknesses Leave DHS Highly Vulnerable to Fraudulent, Improper, and Abusive Activity

Testimony issued by the Government Accountability Office with an abstract that begins "In the wake of the 2005 hurricanes in the Gulf Region, GAO and the Department of Homeland Security Office of Inspector General (DHS OIG) initiated a number of audits and investigations addressing the federal government's response to those events. Department of Homeland Security (DHS) cardholders made thousands of transactions related to hurricane rescue and relief operations. GAO, working with DHS OIG, interviewed DHS personnel and reviewed purchase card policies and procedures to assess the control environment. GAO and DHS OIG conducted statistical tests from a random sample of transactions and performed data mining on all DHS purchase card transactions for a 5-month period beginning in June 2005. GAO and DHS OIG looked at all transactions in this period because the database did not distinguish hurricane related from routine purchases. GAO and DHS OIG used the testing results to determine the extent of control weaknesses and identify instances of fraud, waste, and abuse. This testimony addresses whether (1) DHS's control environment and management of purchase card usage were effective; (2) DHS's key internal control activities operated effectively and provided reasonable assurance that purchase cards were used appropriately; and (3) …
Date: July 19, 2006
Creator: United States. Government Accountability Office.
Object Type: Text
System: The UNT Digital Library
Small Business Innovation Research: Agencies Need to Strengthen Efforts to Improve the Completeness, Consistency, and Accuracy of Awards Data (open access)

Small Business Innovation Research: Agencies Need to Strengthen Efforts to Improve the Completeness, Consistency, and Accuracy of Awards Data

A letter report issued by the Government Accountability Office with an abstract that begins "The Small Business Innovation Research (SBIR) program was created to increase the use of small businesses to meet federal research needs and commercialize the results of this research. To monitor the program, the Small Business Administration (SBA) requires participating agencies to provide, in a standard format, specific data on all SBIR awards they make. SBA then compiles these data into a database known as Tech-Net. Congress also required SBA to create, by 2001, a restricted and more comprehensive database that would provide information for government agencies to use in evaluating the program. GAO was asked to identify the (1) types of data that agencies report to SBA for inclusion in the Tech-Net database, (2) extent to which these data are provided in a standard format, (3) extent to which SBA has established the government-use database, and (4) extent to which SBIR agencies have developed and implemented techniques to track commercialization of SBIR projects. GAO reviewed 8 of the 11 agencies participating in SBIR."
Date: October 19, 2006
Creator: United States. Government Accountability Office.
Object Type: Report
System: The UNT Digital Library
International Energy: International Forums Contribute to Energy Cooperation within Constraints (open access)

International Energy: International Forums Contribute to Energy Cooperation within Constraints

A letter report issued by the Government Accountability Office with an abstract that begins "Rising oil prices, resulting from growth in energy consumption by rapidly developing Asian nations and by most industrialized nations, have increased concern about competition over oil and natural gas resources. In particular, Congress expressed interest in how the United States participates in energy cooperation through international forums. GAO was asked to review: (1) what are the key international energy forums in which the United States pursues energy cooperation, (2) what are some of the key emerging energy market issues that are important for international energy cooperation, and (3) how is the United States addressing these issues through its participation in these forums. GAO's work is based on contacts with agency officials and energy experts and review of documents."
Date: December 19, 2006
Creator: United States. Government Accountability Office.
Object Type: Report
System: The UNT Digital Library
Novel Metal Hydroxide Derivatives Containing Chemically Bound Organophosphorus or Polyphosphate Species as Flame Retardants (open access)

Novel Metal Hydroxide Derivatives Containing Chemically Bound Organophosphorus or Polyphosphate Species as Flame Retardants

Patent relating to novel metal hydroxide derivatives containing chemically bound organophosphorus or polyphosphate species as flame retardants.
Date: March 29, 2006
Creator: Braterman, Paul S.; D'Souza, Nandika & Dharia, Amit
Object Type: Patent
System: The UNT Digital Library
Application of the TraPPE force field to predicting isothermal pressure-volume curves at high pressures and high temperatures (open access)

Application of the TraPPE force field to predicting isothermal pressure-volume curves at high pressures and high temperatures

Knowledge of the thermophysical properties of materials at extreme pressure and temperature conditions is essential for improving our understanding of many planetary and detonation processes. Significant gaps in what is known about the behavior of materials at high density and high temperature exist, largely due to the limitations and dangers of performing experiments at the necessary extreme conditions. Modeling these systems through the use of equations of state and particle-based simulation methods significantly extends the range of pressures and temperatures that can be safely studied. The reliability of such calculations depends on the accuracy of the models used. Here we present an assessment of the united-atom version of the TraPPE (Transferable Potentials for Phase Equilibria) force field and single-site exp-6 representations for methane, methanol, oxygen, and ammonia at extreme conditions. As shown by Monte Carlo simulations in the isobaric-isothermal ensemble, the TraPPE models, despite being parameterized to the vapor-liquid coexistence curve (i.e. relatively mild conditions), perform remarkably well in the high pressure/high temperature regime. The single-site exp-6 models can fit experimental data in the high pressure/temperature regime very well, but the parameters are less transferable to ambient conditions.
Date: May 19, 2006
Creator: Eggimann, B L; Siepmann, J I & Fried, L E
Object Type: Article
System: The UNT Digital Library
An optimal point spread function subtraction algorithm for high-contrast imaging: a demonstration with angular differential imaging (open access)

An optimal point spread function subtraction algorithm for high-contrast imaging: a demonstration with angular differential imaging

Direct imaging of exoplanets is limited by bright quasi-static speckles in the point spread function (PSF) of the central star. This limitation can be reduced by subtraction of reference PSF images. We have developed an algorithm to construct an optimal reference PSF image from an arbitrary set of reference images. This image is built as a linear combination of all available images and is optimized independently inside multiple subsections of the image to ensure that the absolute minimum residual noise is achieved within each subsection. The algorithm developed is completely general and can be used with many high contrast imaging observing strategies, such as angular differential imaging (ADI), roll subtraction, spectral differential imaging, reference star observations, etc. The performance of the algorithm is demonstrated for ADI data. It is shown that for this type of data the new algorithm provides a gain in sensitivity by up 22 to a factor 3 at small separation over the algorithm previously used.
Date: September 19, 2006
Creator: Lafreniere, D; Marois, C; Doyon, R; Artigau, E & Nadeau, D
Object Type: Article
System: The UNT Digital Library