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At least 1,117 records · Page 62

All sources NASA NTRS DOE OSTI

NASA NTRS2019

Carbon Nanomaterials for Biosensing Applications

Biosensing devices comprised of carbon nanotubes and nanofibers have been developed for astronaut crew point-of-care. Their inherent nanometer scale, high conductivity, wide potential window, good biocompatibility and well-defined surface chemistry make them ideal candidates as biosensor electrodes. Here, we report two studies using carbon nanotube and carbon nanofiber electrodes for biomedical applications. First, a 3x3 electrode device, with each electrode containing 40,000 carbon nanofiber nanoelectrodes was fabricated on silicon using traditional microfabrication processing. The device was demonstrated as a multiplexed immunosensor for simultaneous, label-free detection of cardiac troponin-I, C-reactive protein and myoglobin. Antibodies specific to cardiac troponin-I, C-reactive protein and myoglobin were covalently bound to the CNF surface and were characterized using electrochemical impedance spectroscopy and differential pulse voltammetry. Each step of the modification process resulted in changes in resistance to charge transfer due to the changes at the electrode surface upon antibody immobilization and binding to the specific cardiac protein. The real-time label free detection of the three cardiac markers from pure components and mixtures was demonstrated with high sensitivity, down to 0.2 ng/mL, and good selectivity. Detection in human blood serum did not present false positives from non-specific protein adsorption. More recently, this detection scheme has been applied to inkjet printed carbon nanotube electrodes on Kapton and paper. Printed devices have several unique advantages including simple and inexpensive fabrication. The results demonstrate that these sensors can serve a miniaturized, low cost device for detection of proteins in complex mixtures making this platform a good candidate for early stage diagnosis of myocardial infarction. Future inkjet printed devices can be fabricated have the added advantage in their suitability to be manufactured in an in-space, microgravity environment.

carbon nanotubes↗

NASA NTRS1999

A History of GPS Sounding

The roots of GPS sounding go back to the first days of interplanetary flight. Today we have the almost concurrent emergence of the very element vital to a new global enterprise in GPS sounding: copious high beacons at ideal frequencies bathing the globe; a profusion of low obiters carrying GPS receivers and designed for real-time global data transfer; low-cost microelectronics of unprecedented power; and the occultation techniques itself the most precise and arguably the simplest atmospheric probe yet devised.

occultation↗

NASA NTRS2001

Adenovirus-mediated gene delivery to cells of the magnocellular hypothalamo-neurohypophyseal system

The objective of the present study was to define the optimum conditions for using replication-defective adenovirus (Ad) to transfer the gene for the green fluorescent protein (GFP) to the hypothalamic paraventricular (PVN) and supraoptic (SON) nuclei and cells of the neurohypophysis (NH). As indicated by characterizing cell survival over 15 days in culture and in electrophysiological whole cell patch-clamp studies, viral concentrations up to 2 x 10(7) pfu/coverslip did not affect viability of transfected PVN and NH cultured cells from preweanling rats. At 2 x 10(7) pfu, GFP gene expression was higher (40% of GFP-positive cells) and more sustained (up to 15 days). Using a stereotaxic approach in adult rats, we were able to directly transduce the PVN, SON, and NH and visualize gene expression in coronal brain slices and in the pituitary 4 days after injection of Ad. In animals receiving NH injections of Ad, the virus was retrogradely transported to PVN and SON neurons as indicated by the appearance of GFP-positive neurons in cultures of dissociated cells from those brain nuclei and by polymerase chain reaction and Western blot analyses of PVN and SON tissues. Adenoviral concentrations of up to 8 x 10(6) pfu injected into the NH did not affect cell viability and did not cause inflammatory responses. Adenoviral injection into the pituitary enabled the selective delivery of genes to the soma of magnocellular neurons. The experimental approaches described here provide potentially useful strategies for the treatment of disordered expression of the hormones vasopressin or oxytocin. Copyright 2000 Academic Press.

Non-NASA Center↗

DOE OSTI2026

Vicennial metagenomic time series unveils evolutionary dynamics of giant viruses in a freshwater ecosystem

Giant viruses play crucial ecological roles in aquatic ecosystems, yet their evolutionary dynamics in response to environmental changes, particularly in freshwater environments, are not well understood. We analyzed a 20-year time series (2000-2019) of 471 co-assembled metagenomes from Lake Mendota (USA) to reconstruct 1512 giant virus metagenome-assembled genomes, providing insights into viral genome evolution. Viruses in the order Imitervirales dominate the virome, remaining consistent across seasons and years. Our findings reveal gene duplication (23% of genes) and horizontal gene transfer (29% of genes) as key drivers of genomic innovation. A co-occurrence network analysis indicates increased virus-host interactions following the introduction of an invasive predatory zooplankton in 2009, highlighting potential hosts in Bigyra, Perkinsea, and Euglenozoa. While single nucleotide polymorphism analysis shows predominantly purifying selection in viral genes, there is a significant increase in positively selected genes post-invasion, particularly those related to infection. Comparative evolutionary analyses reveal that giant viruses exhibit genome-wide substitution rates similar to co-occurring bacteria but significantly slower than smaller dsDNA phages, suggesting both stability and adaptability. Our study demonstrates that freshwater giant viruses employ various evolutionary strategies to respond to environmental change. These results underscore their significant yet often underappreciated role in freshwater ecosystem dynamics.

Vasquez, Yumary M↗

DOE OSTI2020

Infiltration synthesis of hybrid nanocomposite resists for advanced nanolithography

In this work, we demonstrate a simple ex-situ inorganic infiltration route for transforming standard organic resists into highperformance positive tone hybrid resist platform. A model thin film PMMA-AlOx hybrid resist system has been synthesized by hybridization of PMMA with AlOx and investigated for electron beam lithography. The approach possesses full controllability of the resist performance in terms of critical does, patterning contrast reaching up to 30 and etch resistance for plasma-based pattern transfer processes. The high selectivity Si etching capability demonstrated using a lowtemperature cryo-Si etch process, based on the controlled infiltration outperforms commercial resists and typical hard mask material thermal SiO 2 , with estimated achievable selectivity in excess of ~300. Si nanostructures down to ~30 nm with aspect ratio up to ~17 are also transferred into the Si substrate. Easy implementation and adaptability for different inorganic infiltrations, this platform is well capable of potentially delivering the resist performance and throughput necessary for EUV lithography.

77 NANOSCIENCE AND NANOTECHNOLOGY↗

NASA NTRS1991

Sub-nanosecond clock synchronization and precision deep space tracking

Interferometric spacecraft tracking is accomplished at the NASA Deep Space Network (DSN) by comparing the arrival time of electromagnetic spacecraft signals to ground antennas separated by baselines on the order of 8000 km. Clock synchronization errors within and between DSN stations directly impact the attainable tracking accuracy, with a 0.3 ns error in clock synchronization resulting in an 11 nrad angular position error. This level of synchronization is currently achieved by observing a quasar which is angularly close to the spacecraft just after the spacecraft observations. By determining the differential arrival times of the random quasar signal at the stations, clock synchronization and propagation delays within the atmosphere and within the DSN stations are calibrated. Recent developments in time transfer techniques may allow medium accuracy (50-100 nrad) spacecraft observations without near-simultaneous quasar-based calibrations. Solutions are presented for a global network of GPS receivers in which the formal errors in clock offset parameters are less than 0.5 ns. Comparisons of clock rate offsets derived from GPS measurements and from very long baseline interferometry and the examination of clock closure suggest that these formal errors are a realistic measure of GPS-based clock offset precision and accuracy. Incorporating GPS-based clock synchronization measurements into a spacecraft differential ranging system would allow tracking without near-simultaneous quasar observations. The impact on individual spacecraft navigation error sources due to elimination of quasar-based calibrations is presented. System implementation, including calibration of station electronic delays, is discussed.

Charles Dunn↗

NASA NTRS1999

STS-96 FD Highlights and Crew Activities Report: Flight Day 06

On this sixth day of the STS-96 Discovery mission, the flight crew, Commander Kent V. Rominger, Pilot Rick D. Husband, and Mission Specialists Ellen Ochoa, Tamara E. Jernigan, Daniel T. Barry, Julie Payette, and Valery Ivanovich Tokarev are seen performing logistics transfer activities within the Discovery/International Space Station orbiting complex. Ochoa, Jernigan, Husband and Barry devote a significant part of their day to the transfer of bags of different sizes and shapes from the SPACEHAB module in Discovery's cargo bay to resting places inside the International Space Station. Payette and Tokarev complete the maintenance on the storage batteries. Barry and Tokarev complete installation of the remaining sound mufflers over the fans in Zarya. Barry then measures the sound levels at different positions inside the module. Rominger and Tokarev conduct a news conference with Russian reporters from the Mission Control Center in Moscow.

Source record↗

NASA NTRS2006

A Quasi-Laue Neutron Crystallographic Study of D-Xylose Isomerase

Hydrogen atom location and hydrogen bonding interaction determination are often critical to explain enzymatic mechanism. Whilst it is difficult to determine the position of hydrogen atoms using X-ray crystallography even with subatomic (less than 1.0 Angstrom) resolution data available, neutron crystallography provides an experimental tool to directly localise hydrogeddeuteriwn atoms in biological macromolecules at resolution of 1.5-2.0 Angstroms. Linearisation and isomerisation of xylose at the active site of D-xylose isomerase rely upon a complex hydrogen transfer. Neutron quasi-Laue data were collected on Streptomyces rubiginosus D-xylose isomerase crystal using the LADI instrument at ILL with the objective to provide insight into the enzymatic mechanism (Myles et al. 1998). The neutron structure unambiguously reveals the protonation state of His 53 in the active site, identifying the model for the enzymatic pathway.

Meilleur, Flora↗

NASA NTRS2014

Design Improvements and X-Ray Performance of a Time Projection Chamber Polarimeter for Persistent Astronomical Sources

The design of the Time-Projection Chamber (TPC) Polarimeter for the Gravity and Extreme Magnetism Small Explorer (GEMS) was demonstrated to Technology Readiness Level 6 (TRL-6)3 and the flight detectors fabricated, assembled and performance tested. A single flight detector was characterized at the Brookhaven National Laboratory Synchrotron Light Source with polarized X-rays at 10 energies from 2.3-8.0 keV at five detector positions. The detector met all of the GEMS performance requirements. Lifetime measurements have shown that the existing flight design has 23 years of lifetime4, opening up the possibility of relaxing material requirements, in particular the consideration of the use of epoxy, to reduce risk elsewhere. We report on design improvements to the GEMS detector to enable a narrower transfer gap that, when operated with a lower transfer field, reduces asymmetries in the detector response. In addition, the new design reduces cost and risk by simplifying the assembly and reducing production time. Finally, we report on the performance of the narrow-gap detector in response to polarized and unpolarized X-rays.

GEMS↗

DOE OSTI2021

Shockley-Queisser analysis of the temperature-efficiency correlation of solar cells in the presence of non-radiative heat transfer

An empirical negative T cell − η correlation has been widely applied, without careful justifications, to evaluate the efficiency ( η ) increase of solar cells due to their temperature ( T cell ) decrease. Here, a framework is introduced to simultaneously compute T cell and η . This model confirms the negative T cell − η correlation if the above-bandgap absorptivity ( α I ) is not suppressed in the optimization of the sub-bandgap reflectivity ( ρ II ) or the infrared emissivity, otherwise it may suggest a positive correlation. It further gives a guideline to enhance η of silicon cells under typical conditions: every 1% increase of α I is equivalent to a 57% increase of ρ II .

14 SOLAR ENERGY↗

DOE OSTI2021

Mechanisms of water oxidation on heterogeneous catalyst surfaces

Water oxidation, an essential step in photosynthesis, has attracted intense research attention. Understanding the reaction pathways at the electrocatalyst/water interface is of great importance for the development of water oxidation catalysts. How the water is oxidized on the electrocatalyst surface by the positive charges is still an open question. This review summarizes current advances in studies on surface chemistry within the context of water oxidation, including the intermediates, reaction mechanisms, and their influences on the reaction kinetics. The Tafel analyses of some electrocatalysts and the rate-laws relative to charge consumption rates are also presented. Moreover, how the multiple charge transfer relies on the intermediate coverage and the accumulated charge numbers is outlined. Finally, the intermediates and rate-determining steps on some water oxidation catalysts are discussed based on density functional theories.

14 SOLAR ENERGY↗

DOE OSTI2025

Multiphysics Running-In Simulations for Pebble-Bed Reactors with Griffin

Griffin, a Multiphysics Object-Oriented Simulation Environment (MOOSE)–based application targeting transient modeling of advanced reactors, has been used recently to model pebble-bed reactors (PBRs). The modeling effort has focused thus far on equilibrium core calculations. A new capability to simulate the running-in phase of PBR operation has been added to Griffin. This work demonstrates the new capability with a coupled multiphysics running-in simulation. Griffin computes power densities in the core at each time step of the running-in simulation and passes these to Pronghorn, which models fluid flow and heat transfer to calculate pebble surface temperatures. These surface temperatures are used along with the power densities in a heat conduction model to compute average fuel and moderator temperatures, which are passed back to Griffin and accounted for with temperature-dependent cross sections. This work also describes a novel methodology for determining appropriate pebble feed rates and control rod positioning during the running-in simulation. Furthermore, the RZ-geometry model used in this work requires minimal computational resources and can be used for optimization and uncertainty studies in future works.

Griffin↗

DOE OSTI2025

Specifications of Legacy U(Pu)Zr Metallography Data

The DOE Nuclear Energy Advanced Reactor Technologies (ART) Program has supported the creation of several databases with information describing the safety performance of fast reactors, components, and fuels. This growing collection of legacy experimental data, operating data, and analysis is available online to registered users. Metallography data is one of the most important types of PIE data being collected, organized and stored in several ART Fast Reactor Databases (https://frdb.ne.anl.gov), including the Fuels Irradiation & Physics Database (FIPD), Out-of-Pile Transient Database (OPTD), and TREAT (the Transient Reactor Test Facility) Experimental Relational Database (TREXR). These databases contain three main sets of metallography data. The first set is the metallography data from Experimental Breeder Reactor-II (EBR-II) and Fast Flux Test Facility (FFTF) irradiated fuel pins measured in the Hot Fuel Examination Facility (HFEF); the second set is the metallography data from EBR-II irradiated fuel pins measured in the Alpha-Gamma Hot Cell Facility (AGHCF); the third set is the metallography data from transient tested fuel pins (the transients tests include the out-of-pile tests and TREAT tests) measured in AGHCF. Since both the second and third sets of data were measured in AGHCF, they are governed by the same specification. The metallography data in the databases are digital images scanned from either positive or negative photos. The quality of the images, including their resolution and contrast, relies on the preserved quality of the pictures and the scanning conditions. To analyze the microstructure of a fuel pin, a series of preparatory steps must be undertaken. These include sectioning, epoxy mounting, mechanical grinding and polishing, and often etching. The resulting samples were then transferred to a secondary hot cell, or glovebox (depending the strength of radiation field) for microscopy examination. The specifications provided herein focus on the metallography examinations. The sample grinding, polishing and etching processes are also discussed. The procedures involving sectioning and epoxy mounting are out of the scope of the current specification; details can be found in the corresponding operation manuals. If more data are collected and added to the ART Fast Reactor Databases, this specification will be updated to accommodate the additional data.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗

DOE OSTI2026

Measurement of the Dispersion in the CeC Beamlines

The coherent electron cooling requires to match the relativistic factors of the hadron and electron beam within 10 -4 accuracy. Initial matching is based on the energy measurement of the electron beam using solenoid with accuracy about 10 -3 (the hadron relativistic factor can be found from the revolution frequency). Further matching is done with observation of the recombination rate with fine tuning based on the cooling rate. The last two steps require change of the electron energy which is achieved by change of the linac voltage. The interaction of the hadron and electron beams is affected by the transverse overlap of two beams. To minimize the effect, we need zero dispersion in the common section. The merge of the beams a dogleg transfer line is used containing two dipoles and three quadrupoles. The zeroing of dispersion is performed by settings of the quadrupoles. We have developed two ways to measure the dispersion. In the first mostly commonly used we change both dipoles by the same value creating the mismatch between the electron energy and bending magnet. In the compensated dogleg the position in the second dipole should not change, and the trajectory angle will change by the same amount as deflecting angle but in opposite direction. Therefore, the trajectory in the common section will not change. The value of the dispersion can be calculated from the beam displacement divided by the relative chang of the dipoles’ current. The second method is based on the change of the electron beam energy using linac. This method requires electron orbit alignment with linac axis to avoid beam steering. The results are shown in Fig.1 and Fig. 2. The first figure shows the dispersion prior the correction, and the second figure after the correction.

43 PARTICLE ACCELERATORS↗

NASA NTRS1986

A lateral guidance algorithm to reduce the post-aerobraking burn requirements for a lift-modulated orbital transfer vehicle

A lateral guidance algorithm which controls the location of the line of intersection between the actual and desired orbital planes (the hinge line) is developed for the aerobraking phase of a lift-modulated orbital transfer vehicle. The on-board targeting algorithm associated with this lateral guidance algorithm is simple and concise which is very desirable since computation time and space are limited on an on-board flight computer. A variational equation which describes the movement of the hinge line is derived. Simple relationships between the plane error, the desired hinge line position, the position out-of-plane error, and the velocity out-of-plane error are found. A computer simulation is developed to test the lateral guidance algorithm for a variety of operating conditions. The algorithm does reduce the total burn magnitude needed to achieve the desired orbit by allowing the plane correction and perigee-raising burn to be combined in a single maneuver. The algorithm performs well under vacuum perigee dispersions, pot-hole density disturbance, and thick atmospheres. The results for many different operating conditions are presented.

Herman, G. C.↗

NASA NTRS1989

On the Nature of Navier-stokes Turbulence

Several turbulent and nonturbulent solutions of the Navier-Stokes equations are obtained. The unaveraged equations are used numerically in conjunction with tools and concepts from nonlinear dynamics, including time series, phase portraits, Poincare sections, largest Liapunov exponents, power spectra, and strange attractors. Initially neighboring solutions for a low-Reynolds-number fully developed turbulence are compared. The solutions, separate exponentially with time, having a positive Liapunov exponent. Thus the turbulence is characterized as chaotic. In a search for solutions which contrast with the turbulent ones, the Reynolds number is reduced. Several qualitatively different flows are noted. These are, fully chaotic, complex period, weakly chaotic, simple periodic, and fixed-point. Of these, only the fully chaotic flows are classified as turbulent. Those flows have both a positive Liapunov exponent and Poincare sections without pattern. By contrast, the weakly chaotic flows have some pattern in their Poincare sections. The fixed-point and periodic flows are nonturbulent, since turbulence, is both time-dependent and aperiodic. Turbulent solutions are obtained in which energy cascades from large to small-scale motions. In general, the spectral energy transfer takes place between wavenumber bands that are considerably separated. The special transfer can occur either as a result of nonlinear turbulence self-interaction or by interaction of turbulence with mean gradients. Turbulent systems are compared with those studied in kinetic theory. The two types of systems are fundamentally different (continuous and dissipative as opposed to discrete and conservative), but there are similarities. For instance, both are nonlinear and show sensitive dependence on initial conditions. Also, the turbulent and molecular stress tensors are identical if the macroscopic velocities for the turbulent stress are replaced by molecular velocities.

Deissler, Robert G.↗

NASA NTRS1992

A dual purpose optical truss laser metrology system for a space-based far-IR segmented telescope: Figure maintenance and pointing control

To obtain imaging performance as for monolithic mirrors, large segmented reflectors used for astronomy must be actively aligned and pointed to extreme levels of precision. A system concept for a dual purpose optical truss laser metrology system is described which is used for both figure and alignment maintenance and telescope pointing. A two-stage figure active control approach was developed for several proposed spaceborne far infrared segmented telescopes, one of which is the 10-20 meters Large Deployable Reflector (LDR). The first active control stage, the figure initialization control system, aligns the optical elements (i.e., the primary segments, secondary and focal plane assembly) based on images obtained. The second stage, the figure maintenance control system, maintains the alignment between re-initializations using measurements provided by laser interferometers arranged in an optical truss configuration. It measures the relative positions and alignments of the telescope segments so that a controller can reposition them appropriately. The application of this optical truss for figure maintenance control is the subject of the first part of this paper. The second portion of this paper discusses the application of the optical truss to telescope pointing. Here, the laser metrology system is used to transfer pointing information from an external fine guidance sensor (FGS) to the telescope optical boresight as defined by the primary mirror, secondary mirror, and focal plane assembly. Thus, any alignment variations between the two boresights can be observed and accounted for.

Lau, Kenneth↗

NASA NTRS1996

Biomechanically Induced and Controller Coupled Oscillations Experienced on the F-16XL Aircraft During Rolling Maneuvers

During rapid rolling maneuvers, the F-16 XL aircraft exhibits a 2.5 Hz lightly damped roll oscillation, perceived and described as 'roll ratcheting.' This phenomenon is common with fly-by-wire control systems, particularly when primary control is derived through a pedestal-mounted side-arm controller. Analytical studies have been conducted to model the nature of the integrated control characteristics. The analytical results complement the flight observations. A three-degree-of-freedom linearized set of aerodynamic matrices was assembled to simulate the aircraft plant. The lateral-directional control system was modeled as a linear system. A combination of two second-order transfer functions was derived to couple the lateral acceleration feed through effect of the operator's arm and controller to the roll stick force input. From the combined systems, open-loop frequency responses and a time history were derived, describing and predicting an analogous in-flight situation. This report describes the primary control, aircraft angular rate, and position time responses of the F-16 XL-2 aircraft during subsonic and high-dynamic-pressure rolling maneuvers. The analytical description of the pilot's arm and controller can be applied to other aircraft or simulations to assess roll ratcheting susceptibility.

Smith, John W.↗