Search NASA⌕ Search

SEARCH · Search NASA

Results for “PRESERVATION”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 577 records · Page 32
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

Positivity-preserving numerical schemes for multidimensional advection

This report describes the construction of an explicit, single time-step, conservative, finite-volume method for multidimensional advective flow, based on a uniformly third-order polynomial interpolation algorithm (UTOPIA). Particular attention is paid to the problem of flow-to-grid angle-dependent, anisotropic distortion typical of one-dimensional schemes used component-wise. The third-order multidimensional scheme automatically includes certain cross-difference terms that guarantee good isotropy (and stability). However, above first-order, polynomial-based advection schemes do not preserve positivity (the multidimensional analogue of monotonicity). For this reason, a multidimensional generalization of the first author's universal flux-limiter is sought. This is a very challenging problem. A simple flux-limiter can be found; but this introduces strong anisotropic distortion. A more sophisticated technique, limiting part of the flux and then restoring the isotropy-maintaining cross-terms afterwards, gives more satisfactory results. Test cases are confined to two dimensions; three-dimensional extensions are briefly discussed.

Leonard, B. P.↗
NASA NTRS1992

Dispersion-relation-preserving schemes for computational aeroacoustics

Finite difference schemes that have the same dispersion relations as the original partial differential equations are referred to as dispersion-relation-preserving (DRP) schemes. A method to construct time marching DRP schemes by optimizing the finite difference approximations of the space and time derivatives in the wave number and frequency space is presented. A sequence of numerical simulations is then performed.

Tam, Christopher K. W.↗
NASA NTRS1992

Application of self-preservation in the diurnal evolution of the surface energy budget to determine daily evaporation

Evaporation from natural land surfaces often exhibits a strong variation during the course of a day, mostly in response to the daily variation of radiative energy input at the surface. This makes it difficult to derive the total daily evaporation, when only one or a few instantaneous estimates of evaporation are available. It is often possible to resolve this difficulty by assuming self-preservation in the diurnal evolution of the surface energy budget. Thus if the relative partition of total incoming energy flux among the different components remains the same, the ratio of latent heat flux and any other flux component can be taken as constant through the day. This concept of constant flux ratios is tested by means of data obtained during the First ISLSCP Field Experiment; the instantaneous evaporation values were calculated by means of the atmospheric boundary layer bulk similarity approach with radiosonde profiles and radiative surface temperatures. Good results were obtained for evaporative flux ratios with available energy flux, with net radiation, and with incoming shortwave radiation.

Brutsaert, Wilfried↗
NASA NTRS1993

Dispersion-relation-preserving finite difference schemes for computational acoustics

Time-marching dispersion-relation-preserving (DRP) schemes can be constructed by optimizing the finite difference approximations of the space and time derivatives in wave number and frequency space. A set of radiation and outflow boundary conditions compatible with the DRP schemes is constructed, and a sequence of numerical simulations is conducted to test the effectiveness of the DRP schemes and the radiation and outflow boundary conditions. Close agreement with the exact solutions is obtained.

Tam, Christopher K. W.↗
NASA NTRS1993

Primordial lightning: Evidence preserved in chondrites

An increasing body of evidence suggests that transient heating events were important in forming or modifying many constituents of chondritic meteorites. For example, chondrule compositions and textures imply high cooling rates (approximately 5 to greater than 2000 C/hr) with only limited exposure to elevated temperatures (greater than 1200 C). Similarly, experimental studies of CAI's exhibiting igneous textures suggest cooling rates from 0.5 to 1000 C/hr, and thermal pulses as short as milliseconds may be responsible for CAI rim formation. Additionally, the spectrum of organic compounds observed in chondrites suggests that transient heating may also have played an important role in their formation. The exact nature of these transient events is less clear. A variety of mechanisms have been proposed (e.g., shock melting, drag heating, volcanism, electric discharges, and magnetic reconnection). However, a consensus is lacking as to which or what combination of these mechanisms was responsible for the range of features we observe in chondrites today. Much of the difficulty lies in the inability to identify features unique to any given process. Here we discuss electric discharges ('lightning') as a transient heat source and describe its unique signature preserved in chondrites.

Eisenhour, D.↗
NASA NTRS1993

Largest impact features on Venus: Non-preserved or non-recognizable?

Conventional explanation of a lack of impact craters with diameters greater than 300 km on Venus is that they formed during the intense bombardment era and had lunar-like morphology, but they are not preserved now because of rapid viscous relaxation of their topograpy and/or high endogenous reworking of surface. Other explanation invokes failure to recognize these larger craters because of their non-lunar-like morphology from the moment of formation, since larger gravity of Venus relatively to the Moon results in that largest craters on Venus may form within the mass of shock melted material while comparably sized lunar craters would be still almost 'dry'. To test this hypothesis, morphologies and rim-crest diameters of the largest peak-ring and Orientale-type basins and all larger impact features on Moon, Mercury, Mars, and Venus were compiled and compared to rim crest diameters of model craters with different melt volume/transient-cavity volume ratios. Results show that the final diameters of model craters formed at depth of melting about twice of transient cavity depth correspond to changeover from a planet-similar morphology of all the smaller basins on any terrestrial planet to a planet-specific morphology of all the larger basins on the Moon, Mercury, and Mars. On Venus, these largest impact features are not found and instead, a Venus-specific morphology of the largest concentric coronae appears in this size range. The coronae were suggested to form over sites of mantle upwelling and modified by subsequent volcanism and gravitational relaxation. The results here suggest that mantle upwelling - the first and necessary step of the corona formation models - may be induced by impact event (as a result of transient cavity collapse) and operated under cover of hot, slowly cooled impact melt in the areas of thinned crust and/or thermally active regions.

Nikolaeva, Olga V.↗
NASA NTRS1995

Solutions of the benchmark problems by the dispersion-relation-preserving scheme

The 7-point stencil Dispersion-Relation-Preserving scheme of Tam and Webb is used to solve all the six categories of the CAA benchmark problems. The purpose is to show that the scheme is capable of solving linear, as well as nonlinear aeroacoustics problems accurately. Nonlinearities, inevitably, lead to the generation of spurious short wave length numerical waves. Often, these spurious waves would overwhelm the entire numerical solution. In this work, the spurious waves are removed by the addition of artificial selective damping terms to the discretized equations. Category 3 problems are for testing radiation and outflow boundary conditions. In solving these problems, the radiation and outflow boundary conditions of Tam and Webb are used. These conditions are derived from the asymptotic solutions of the linearized Euler equations. Category 4 problems involved solid walls. Here, the wall boundary conditions for high-order schemes of Tam and Dong are employed. These conditions require the use of one ghost value per boundary point per physical boundary condition. In the second problem of this category, the governing equations, when written in cylindrical coordinates, are singular along the axis of the radial coordinate. The proper boundary conditions at the axis are derived by applying the limiting process of r approaches 0 to the governing equations. The Category 5 problem deals with the numerical noise issue. In the present approach, the time-independent mean flow solution is computed first. Once the residual drops to the machine noise level, the incident sound wave is turned on gradually. The solution is marched in time until a time-periodic state is reached. No exact solution is known for the Category 6 problem. Because of this, the problem is formulated in two totally different ways, first as a scattering problem then as a direct simulation problem. There is good agreement between the two numerical solutions. This offers confidence in the computed results. Both formulations are solved as initial value problems. As such, no Kutta condition is required at the trailing edge of the airfoil.

Tam, Christopher K. W.↗
NASA NTRS1996

Singularity Preserving Numerical Methods for Boundary Integral Equations

In the past twelve months (May 8, 1995 - May 8, 1996), under the cooperative agreement with Division of Multidisciplinary Optimization at NASA Langley, we have accomplished the following five projects: a note on the finite element method with singular basis functions; numerical quadrature for weakly singular integrals; superconvergence of degenerate kernel method; superconvergence of the iterated collocation method for Hammersteion equations; and singularity preserving Galerkin method for Hammerstein equations with logarithmic kernel. This final report consists of five papers describing these projects. Each project is preceeded by a brief abstract.

Kaneko, Hideaki↗
NASA NTRS1996

Specimen Sample Preservation for Cell and Tissue Cultures

The era of the International Space Station with its longer duration missions will pose unique challenges to microgravity life sciences research. The Space Station Biological Research Project (SSBRP) is responsible for addressing these challenges and defining the science requirements necessary to conduct life science research on-board the International Space Station. Space Station will support a wide range of cell and tissue culture experiments for durations of 1 to 30 days. Space Shuttle flights to bring experimental samples back to Earth for analyses will only occur every 90 days. Therefore, samples may have to be retained for periods up to 60 days. This presents a new challenge in fresh specimen sample storage for cell biology. Fresh specimen samples are defined as samples that are preserved by means other than fixation and cryopreservation. The challenge of long-term storage of fresh specimen samples includes the need to suspend or inhibit proliferation and metabolism pending return to Earth-based laboratories. With this challenge being unique to space research, there have not been any ground based studies performed to address this issue. It was decided hy SSBRP that experiment support studies to address the following issues were needed: Fixative Solution Management; Media Storage Conditions; Fresh Specimen Sample Storage of Mammalian Cell/Tissue Cultures; Fresh Specimen Sample Storage of Plant Cell/Tissue Cultures; Fresh Specimen Sample Storage of Aquatic Cell/Tissue Cultures; and Fresh Specimen Sample Storage of Microbial Cell/Tissue Cultures. The objective of these studies was to derive a set of conditions and recommendations that can be used in a long duration microgravity environment such as Space Station that will permit extended storage of cell and tissue culture specimens in a state consistent with zero or minimal growth, while at the same time maintaining their stability and viability.

Meeker, Gabrielle↗
NASA NTRS1996

Knowledge Engineering for Preservation and Future use of Institutional Knowledge

This Project has two main thrusts-preservation of special knowledge and its useful representation via computers. NASA is losing the expertise of its engineers and scientists who put together the great missions of the past. We no longer are landing men on the moon. Some of the equipment still used today (such as the RL-10 rocket) was designed decades ago by people who are now retiring. Furthermore, there has been a lack, in some areas of technology, of new projects that overlap with the old and that would have provided opportunities for monitoring by senior engineers of the young ones. We are studying this problem and trying out a couple of methods of soliciting and recording rare knowledge from experts. One method is that of Concept Maps which produces a graphical interface to knowledge even as it helps solicit that knowledge. We arranged for experienced help in this method from John Coffey of the Institute of Human and Machine Technology at the University of West Florida. A second method which we plan to try out in May, is a video-taped review of selected failed missions (e.g., the craft tumbled and blew up). Five senior engineers (most already retired from NASA) will, as a team, analyze available data, illustrating their thought processes as they try to solve the problem of why a space craft failed to complete its mission. The session will be captured in high quality audio and with at least two video cameras. The video can later be used to plan future concept mapping interviews and, in edited form, be a product in itself. Our computer representations of the amassed knowledge may eventually, via the methods of expert systems, be joined with other software being prepared as a suite of tools to aid future engineers designing rocket engines. In addition to representation by multimedia concept maps, we plan to consider linking vast bodies of text (and other media) by hypertexting methods.

Moreman, Douglas↗
NASA NTRS1996

Preserving Symmetry in Preconditioned Krylov Subspace Methods

We consider the problem of solving a linear system Ax = b when A is nearly symmetric and when the system is preconditioned by a symmetric positive definite matrix M. In the symmetric case, one can recover symmetry by using M-inner products in the conjugate gradient (CG) algorithm. This idea can also be used in the nonsymmetric case, and near symmetry can be preserved similarly. Like CG, the new algorithms are mathematically equivalent to split preconditioning, but do not require M to be factored. Better robustness in a specific sense can also be observed. When combined with truncated versions of iterative methods, tests show that this is more effective than the common practice of forfeiting near-symmetry altogether.

Chan, Tony F.↗
NASA NTRS1996

Amino Acid Racemization and the Preservation of Ancient DNA

The extent of racemization of aspartic acid, alanine, and leucine provides criteria for assessing whether ancient tissue samples contain endogenous DNA. In samples in which the D/L ratio of aspartic acid exceeds 0.08, ancient DNA sequences could not be retrieved. Paleontological finds from which DNA sequences purportedly millions of years old have been reported show extensive racemization, and the amino acids present are mainly contaminates. An exception is the amino acids in some insects preserved in amber.

Poinar, Hendrik N.↗
NASA NTRS2000

Hopanoid Biomarker Preservation In Coniform (Phormidium) Stromatolites in Siliceous Thermal Springs, Yellowstone National Park

The microbial communities that characterize modem hydrothermal ecosystems serve as modern analogs to those thought to have dominated early environments on Earth and possibly Mars. The importance of such hydrothermal systems as targets in exploring for an early biosphere on Mars is well established. Such work provides an important basis for the analysis of Martian samples associated with such environments. The surviving molecular structure and isotopic signature of diagnostic lipid biomarkers found as chemical fossils can provide a link between modern bacterially dominated ecosystems and their ancient counterparts. We are interested in the processes involved in the deposition and/or degradation of organic material in moderately thermal, silicifying microbial mats, particularly as this relates to the potential for preservation of some biomarker components known to be more highly resistant to microbial degradation. Several excellent biomarker molecules are associated with the cyanobacteria that dominate these mats, particularly the 2-methylbacteriohopanepolyols (2-MeBHP). These compounds are ubiquitous on Earth and are not easily degraded in nature, a fact documented by their detection in ancient Earth rocks dating back as far as 2,700 Ma.

Jahnke, Linda L.↗
NASA NTRS2000

Computation of Transonic Nozzle Sound Transmission and Rotor Problems by the Dispersion-Relation-Preserving Scheme

The transonic nozzle transmission problem and the open rotor noise radiation problem are solved computationally. Both are multiple length scales problems. For efficient and accurate numerical simulation, the multiple-size-mesh multiple-time-step Dispersion-Relation-Preserving scheme is used to calculate the time periodic solution. To ensure an accurate solution, high quality numerical boundary conditions are also needed. For the nozzle problem, a set of nonhomogeneous, outflow boundary conditions are required. The nonhomogeneous boundary conditions not only generate the incoming sound waves but also, at the same time, allow the reflected acoustic waves and entropy waves, if present, to exit the computation domain without reflection. For the open rotor problem, there is an apparent singularity at the axis of rotation. An analytic extension approach is developed to provide a high quality axis boundary treatment.

Tam, Christopher K. W.↗
NASA NTRS2001

Urine Preservative

Disclosed is CPG, a combination of a chlorhexidine salt (such as chlorhexidine digluconate, chlorhexidine diacetate, or chlorhexidine dichloride) and n-propyl gallate that can be used at ambient temperatures as a urine preservative.

Scott M Smith↗
NASA NTRS2004

Preserving the Pyramid of STI Using Buckets

The product of research projects is information. Through the life cycle of a project, information comes from many sources and takes many forms. Traditionally, this body of information is summarized in a formal publication, typically a journal article. While formal publications enjoy the benefits of peer review and technical editing, they are also often compromises in media format and length. As such, we consider a formal publication to represent an abstract to a larger body of work: a pyramid of scientific and technical information (STI). While this abstract may be sufficient for some applications, an in-depth use or analysis is likely to require the supporting layers from the pyramid. We have developed buckets to preserve this pyramid of STI. Buckets provide an archive- and protocol-independent container construct in which all related information objects can be logically grouped together, archived, and manipulated as a single object. Furthermore, buckets are active archival objects and can communicate with each other, people, or arbitrary network services. Buckets are an implementation of the Smart Object, Dumb Archive (SODA) DL model. In SODA, data objects are more important than the archives that hold them. Much of the functionality traditionally associated with archives is pushed down into the objects, such as enforcing terms and conditions, negotiating display, and content maintenance. In this paper, we discuss the motivation, design, and implication of bucket use in DLs with respect to grey literature.

Nelson, Michael L.↗
NASA NTRS1994

Amino acid racemization in amber-entombed insects: implications for DNA preservation

DNA depurination and amino acid racemization take place at similar rates in aqueous solution at neutral pH. This relationship suggests that amino acid racemization may be useful in accessing the extent of DNA chain breakage in ancient biological remains. To test this suggestion, we have investigated the amino acids in insects entombed in fossilized tree resins ranging in age from <100 years to 130 million years. The amino acids present in 40 to 130 million year old amber-entombed insects resemble those in a modern fly and are probably the most ancient, unaltered amino acids found so far on Earth. In comparison to other geochemical environments on the surface of the Earth, the amino acid racemization rate in amber insect inclusions is retarded by a factor of >10(4). These results suggest that in amber insect inclusions DNA depurination rates would also likely be retarded in comparison to aqueous solution measurements, and thus DNA fragments containing many hundreds of base pairs should be preserved. This conclusion is consistent with the reported successful retrieval of DNA sequences from amber-entombed organisms.

NASA Discipline Exobiology↗