Nonlinear mixing behavior of the three-dimensional Rayleigh-Taylor instability at a decelerating interface. (open access)

Nonlinear mixing behavior of the three-dimensional Rayleigh-Taylor instability at a decelerating interface.

We report results from the first experiments to explore the evolution of the Rayleigh-Taylor (RT) instability from intentionally three-dimensional (3D) initial conditions at an embedded, decelerating interface in a high-Reynolds-number flow. The experiments used {approx}5 kJ of laser energy to produce a blast wave in polyimide and/or brominated plastic having an initial pressure of {approx}50 Mbars. This blast wave shocked and then decelerated the perturbed interface between first material and a lower-density, C foam. This caused the formation of a decelerating interface with an Atwood number {approx}2/3, producing a long-term positive growth rate for the RT instability. The initial perturbations were a 3D perturbation in an ''egg-crate'' pattern with feature spacings of 71 {micro}m in two orthogonal directions and peak-to-valley amplitudes of 5 {micro}m. The resulting RT spikes were observed to overtake the shock waves at the undisturbed, ''free-fall'' rate, and to subsequently deliver material from behind the interface to the forward shock. This result is unanticipated by prior simulations and models.
Date: March 19, 2004
Creator: Robey, H.; Remington, B.; Edwards, M.; Perry, T.; Wallace, R. J.; Louis, H. et al.
Object Type: Article
System: The UNT Digital Library
Targeting a Novel Plasmodium falciparum Purine Recycling Pathway with Specific Immucillins (open access)

Targeting a Novel Plasmodium falciparum Purine Recycling Pathway with Specific Immucillins

Plasmodium falciparum is unable to synthesize purine bases and relies upon purine salvage and purine recycling to meet its purine needs. We report that purines formed as products of the polyamine pathway are recycled in a novel pathway in which 5'-methylthioinosine is generated by adenosine deaminase. The action of P. falciparum purine nucleoside phosphorylase is a convergent step of purine salvage, converting both 5'-methylthioinosine and inosine to hypoxanthine. We used accelerator mass spectrometry to verify that 5'-methylthioinosine is an active nucleic acid precursor in P. falciparum. Prior studies have shown that inhibitors of purine salvage enzymes kill malaria, but potent malaria-specific inhibitors of these enzymes have not previously been described. 5'-methylthio-Immucillin-H, a transition state analogue inhibitor that is selective for malarial over human purine nucleoside phosphorylase, kills P. falciparum in culture. Immucillins are currently in clinical trials for other indications and may have application as antimalarials.
Date: May 19, 2004
Creator: Ting, L; Shi, W; Lewandowicz, A; Singh, V; Mwakingwe, A; Birck, M R et al.
Object Type: Article
System: The UNT Digital Library
Development of colorimetric solid Phase Extraction (C-SPE) for in-flight Monitoring of spacecraft Water Supplies (open access)

Development of colorimetric solid Phase Extraction (C-SPE) for in-flight Monitoring of spacecraft Water Supplies

Although having recently been extremely successful gathering data on the surface of Mars, robotic missions are not an effective substitute for the insight and knowledge about our solar system that can be gained though first-hand exploration. Earlier this year, President Bush presented a ''new course'' for the U.S. space program that shifts NASA's focus to the development of new manned space vehicles to the return of humans to the moon. Re-establishing the human presence on the moon will eventually lead to humans permanently living and working in space and also serve as a possible launch point for missions into deeper space. There are several obstacles to the realization of these goals, most notably the lack of life support and environmental regeneration and monitoring hardware capable of functioning on long duration spaceflight. In the case of the latter, past experience on the International Space Station (ISS), Mir, and the Space Shuttle has strongly underscored the need to develop broad spectrum in-flight chemical sensors that: (1) meet current environmental monitoring requirements on ISS as well as projected requirements for future missions, and (2) enable the in-situ acquisition and analysis of analytical data in order to further define on-orbit monitoring requirements. Additionally, systems …
Date: December 19, 2004
Creator: Gazda, Daniel Bryan
Object Type: Thesis or Dissertation
System: The UNT Digital Library
VA Medical Centers: Further Operational Improvements Could Enhance Third-Party  Collections (open access)

VA Medical Centers: Further Operational Improvements Could Enhance Third-Party Collections

A letter report issued by the Government Accountability Office with an abstract that begins "In the face of growing demand for veterans' health care, GAO and the Department of Veterans Affairs Office of Inspector General (OIG) have raised concerns about the Veterans Health Administration's (VHA) ability to maximize its third-party collections to supplement its medical care appropriation. GAO has testified that inadequate patient intake procedures, insufficient documentation by physicians, a shortage of qualified billing coders, and insufficient automation diminished VA's collections. In turn, the OIG reported that VA missed opportunities to bill, had billing backlogs, and did inadequate follow-up on bills. While VA has made improvements in these areas, GAO was asked to review internal control activities over third-party billings and collections at selected medical centers to assess whether they were designed and implemented effectively."
Date: July 19, 2004
Creator: United States. Government Accountability Office.
Object Type: Report
System: The UNT Digital Library
Extremophiles 2004 (open access)

Extremophiles 2004

None
Date: September 19, 2004
Creator: Robb, Frank
Object Type: Article
System: The UNT Digital Library
General Management Laws: A Compendium (open access)

General Management Laws: A Compendium

This report is a companion to CRS Report RL32388, General Management Laws: Major Themes and Management Policy Options. In combination, these reports have three main objectives: (1) to identify and describe the major management laws under which the executive branch of the federal government is required to operate, including their rationale, design, and scope; (2) to assist Members of Congress and their staff in oversight of executive branch management; and (3) to help Congress when considering potential changes to the management laws themselves, as well as other legislation, including authorization statutes and appropriations.
Date: May 19, 2004
Creator: Brass, Clinton T.
Object Type: Report
System: The UNT Digital Library