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NASA NTRS1984

A mathematical model for the iron/chromium redox battery

A mathematical model has been developed to describe the isothermal operation of a single anode-separator-cathode unit cell in a redox-flow battery and has been applied to the NASA iron/chromium system. The model, based on porous electrode theory, incorporates redox kinetics, mass transfer, and ohmic effects as well as the parasitic hydrogen reaction which occurs in the chromium electrode. A numerical parameter study was carried out to predict cell performance to aid in the rational design, scale-up, and operation of the flow battery. The calculations demonstrate: (1) an optimum electrode thickness and electrolyte flow rate exist; (2) the amount of hydrogen evolved and, hence, cycle faradaic efficiency, can be affected by cell geometry, flow rate, and charging procedure; (3) countercurrent flow results in enhanced cell performance over cocurrent flow; and (4) elevated temperature operation enhances cell performance.

Fedkiw, P. S.↗

NASA NTRS1986

An analysis of the productivity of a CELSS continuous algal culture system

One of the most attractive aspects of using algal cultures as plant components for a Closed Ecological Life Support Systems (CELSS) is the efficiency with which they can be grown. Although algae are not necessarily intrinsically more efficient than higher plants, the ease which they can be handled and manipulated (more like chemical reagents than plants), and the culturing techniques available, result in much higher growth rates than are usually attainable with higher plants. Furthermore, preliminary experiments have demonstrated that algal growth and physiology is not detectable altered in a microgravity environment, (1) whereas the response of higher plants to zero gravity is unknown. In order to rationally design and operate culture systems, it is necessary to understand how the macroparameters of a culture system, e.g., productivity, are related to the physiological aspects of the algal culture. A first principles analysis of culture system is discussed, and a mathematical model that describes the relationship of culture productivity to the cell concentration of light-limited culture is derived. The predicted productivity vs cell concentration curve agrees well with the experimental data obtained to test this model, indicating that this model permits an accurate prediction of culture productivity given the growth parameters of the system.

Radmer, R.↗

NASA NTRS1988

Finite element (MARC) solution technologies for viscoplastic analyses

A need for development of realistic constitutive models for structural components operating at high temperatures, accompanied by appropriate solution technologies for stress/life analyses of these components is studied. Viscoplastic models provide a better description of inelastic behavior of materials, but their mathematical structure is very complex. The highly nonlinear and stiff nature of the constitutive equations makes analytical solutions difficult. Therefore, suitable solution, finite element or other numerical, technologies must be developed to make these models adaptable for better and rational designs of components. NASA-Lewis has developed several solution technologies and successfully applied them to the solution of a number of uniaxial and multiaxial problems. Some of these solution technologies are described along with the models and representative results. The solution technologies developed and presented encompass a wide range of models, such as, isotropic, anisotropic, metal matrix composites, and single crystal models.

Arya, V. K.↗

NASA NTRS1991

Computer modeling of a hot filament diamond deposition reactor

A commercial fluid mechanics program, FLUENT, has been applied to the modeling of a hot-filament diamond deposition reactor. Streamlines and contours of constant temperature and species concentrations are obtained for practical reactor geometries and conditions. The modeling is presently restricted to two-dimensional simulations and to a chemical mechanism of ten independent homogeneous and surface reactions. Comparisons are made between predicted power consumption, substrate temperature, and concentrations of atomic hydrogen and methyl-radical with values taken from the literature. The results to date indicate that the modeling can aid in the rational design and analysis of practical reactor configurations.

Kuczmarski, Maria A.↗

NASA NTRS1996

Development and Application of Viscoplastic Models in Nonlinear Structural Analysis

A number of numerical solution technologies were developed for advanced analysis capabilities involving the finite element method in advanced constitutive modeling and structural analysis for improved and rational designs of aerospace propulsive systems. These technologies were incorporated into several advanced viscoplastic models and were applied to a wide spectrum of structural engineering problems involving extremes of thermal/mechanical loading. Results of the research performed under the grant were presented at a number of scientific meetings and conferences and have resulted in numerous publications.

Keith, Theo G., Jr.↗

NASA NTRS1999

Novel Approaches to Cellular Transplantation from the US Space Program

Research in the treatment of type I diabetes is entering a new era that takes advantage of our knowledge in an ever increasing variety of scientific disciplines. Some may originate from very diverse sources, one of which is the Space Program at National Aeronautics and Space Administration (NASA). The Space Program contributes to diabetes-related research in several treatment modalities. As an ongoing effort for medical monitoring of personnel involved in space exploration activities NASA and the extramural scientific community investigate strategies for noninvasive estimation of blood glucose levels. Part of the effort in the space protein crystal growth program is high-resolution structural analysis insulin as a means to better understand the interaction with its receptor and with host immune components and as a basis for rational design of a "better" insulin molecule. The Space Program is also developing laser technology for potential early cataract detection as well as a noninvasive analyses for addressing preclinical diabetic retinopathy. Finally, NASA developed an exciting cell culture system that affords some unique advantages in the propagation and maintenance of mammalian cells in vitro. The cell culture system was originally designed to maintain cell suspensions with a minimum of hydrodynamic and mechanical sheer while awaiting launch into microgravity. Currently the commercially available NASA bioreactor (Synthecon, Inc., Houston, TX) is used as a research tool in basic and applied cell biology. In recent years there is continued strong interest in cellular transplantation as treatment for type I diabetes. The advantages are the potential for successful long-term amelioration and a minimum risk for morbidity in the event of rejection of the transplanted cells. The pathway to successful application of this strategy is accompanied by several substantial hurdles: (1) isolation and propagation of a suitable uniform donor cell population; (2) management of host immune rejection; (3) protection from the autoimmune component of the disease; and (4) anatomic placement of the engrafted cells that permits timely response to blood sugar levels as well as effective release and deployment of insulin. Bioreactor technology may provide some critical advances for surmounting some of these scientific hurdles. The NASA bioreactor is a horizontally rotating cylinder that is completely filled with culture medium. Gaseous exchange is maintained by a concentric cylinder of permeable silicon. In slow rotation (15-25 rpm) particles of small mass such as cells and tissue aggregates remain suspended in the rotating body of fluid. This novel approach suspends cells without stirring thus, allowing objects of different size mass to colocate and interact in a very low shear environment. In fact, analysis of the forces acting on individual cells in the rotating bioreactor reveals that the cells are continuously falling through the fluid medium. The conditions in the bioreactor permit assembly of cells into aggregates. three-dimensional tissue growth, synthesis of intercellular matrix,10 differentiation, and some sinusoid formations that may serve as a surrogate vasculature for larger tissue segments.

Pellis, Neal R.↗

NASA NTRS2001

Friction Stir Welding at MSFC: Kinematics

In 1991 The Welding Institute of the United Kingdom patented the Friction Stir Welding (FSW) process. In FSW a rotating pin-tool is inserted into a weld seam and literally stirs the faying surfaces together as it moves up the seam. By April 2000 the American Welding Society International Welding and Fabricating Exposition featured several exhibits of commercial FSW processes and the 81st Annual Convention devoted a technical session to the process. The FSW process is of interest to Marshall Space Flight Center (MSFC) as a means of avoiding hot-cracking problems presented by the 2195 aluminum-lithium alloy, which is the primary constituent of the Lightweight Space Shuttle External Tank. The process has been under development at MSFC for External Tank applications since the early 1990's. Early development of the FSW process proceeded by cut-and-try empirical methods. A substantial and complex body of data resulted. A theoretical model was wanted to deal with the complexity and reduce the data to concepts serviceable for process diagnostics, optimization, parameter selection, etc. A first step in understanding the FSW process is to determine the kinematics, i.e., the flow field in the metal in the vicinity of the pin-tool. Given the kinematics, the dynamics, i.e., the forces, can be targeted. Given a completed model of the FSW process, attempts at rational design of tools and selection of process parameters can be made.

Nunes, A. C., Jr.↗

NASA NTRS2001

Whole-cell biocomputing

The ability to manipulate systems on the molecular scale naturally leads to speculation about the rational design of molecular-scale machines. Cells might be the ultimate molecular-scale machines and our ability to engineer them is relatively advanced when compared with our ability to control the synthesis and direct the assembly of man-made materials. Indeed, engineered whole cells deployed in biosensors can be considered one of the practical successes of molecular-scale devices. However, these devices explore only a small portion of cellular functionality. Individual cells or self-organized groups of cells perform extremely complex functions that include sensing, communication, navigation, cooperation and even fabrication of synthetic nanoscopic materials. In natural systems, these capabilities are controlled by complex genetic regulatory circuits, which are only partially understood and not readily accessible for use in engineered systems. Here, we focus on efforts to mimic the functionality of man-made information-processing systems within whole cells.

Non-NASA Center↗

NASA NTRS2001

A novel reagentless sensing system for measuring glucose based on the galactose/glucose-binding protein

The galactose/glucose-binding protein (GBP) is synthesized in the cytoplasm of Escherichia coli in a precursor form and exported into the periplasmic space upon cleavage of a 23-amino-acid leader sequence. GBP binds galactose and glucose in a highly specific manner. The ligand induces a hinge motion in GBP and the resultant protein conformational change constitutes the basis of the sensing system. The mglB gene, which codes for GBP, was isolated from the chromosome of E. coli using the polymerase chain reaction (PCR). Since wild-type GBP lacks cysteines in its structure, introducing this amino acid by site-directed mutagenesis ensures single-label attachment at specific sites with a sulfhydro-specific fluorescent probe. Site-directed mutagenesis by overlap extension PCR was performed to prepare three different mutants to introduce a single cysteine residue at positions 148, 152, and 182. Since these residues are not involved in ligand binding and since they are located at the edge of the binding cleft, they experience a significant change in environment upon binding of galactose or glucose. The sensing system strategy is based on the fluorescence changes of the probe as the protein undergoes a structural change on binding. In this work a reagentless sensing system has been rationally designed that can detect submicromolar concentrations of glucose. The calibration plots have a linear working range of three orders of magnitude. Although the system can sense galactose as well, this epimer is not a potential interfering substance since its concentration in blood is negligible. Copyright 2001 Academic Press.

Non-NASA Center↗

NASA NTRS2016

Automating Microbial Directed Evolution For Bioengineering Applications

From a micro-biology perspective, directed evolution is a technique that uses controlled environmental pressures to select for a desired phenotype. Directed evolution has the distinct advantage over rational design of not needing extensive knowledge of the genome or pathways associated with a microorganism to induce phenotypes. However, there are currently limitations to the applicability of this technique including being time-consuming, error-prone, and dependent on existing assays that may lack selectivity for the given phenotype. The AADEC (Autonomous Adaptive Directed Evolution Chamber) system is a proof-of-concept instrument to automate and improve the technique such that directed evolution can be used more effectively as a general bioengineering tool. A series of tests using the automated system and comparable by-hand survival assay measurements have been carried out using UV-C radiation and Escherichia coli cultures in order to demonstrate the advantages of the AADEC versus traditional implementations of directed evolution such as random mutagenesis. AADEC uses UV-C exposure as both a source of environmental stress and mutagenesis, so in order to evaluate the UV-C tolerance obtained from the cultures, a manual UV-C exposure survival assay was developed alongside the device to compare the survival fractions at a fixed dosage. This survival assay involves exposing E. coli to UV-C radiation using a custom-designed exposure hood to control the flux and dose. Surviving cells are counted then transferred to the next iteration and so on for several iterations to calculate the survival fractions for each exposure iteration.This survival assay primarily serves as a baseline for the AADEC device, allowing quantification of the differences between the AADEC system over the manual approach. The primary data of comparison is survival fractions; this is obtained by optical density and plate counts in the manual assay and by optical density growth curve fits pre- and post-exposure in the automated case. This data can then be compiled to calculate trends over the iterations to characterize increasing UV-C resistance of the E.coli strains. The observed trends are statistically indistinguishable through several iterations from both sources.

Bioengineering↗

NASA NTRS2021

Anion-Assisted Delivery of Multivalent Cations to Inert Electrodes

To understand and control key electrochemical processes - metal plating, corrosion, intercalation, etc. requires molecular-scale details of the active species at electrochemical interfaces and their mechanisms for de-solvation from the electrolyte. Using free energy sampling techniques we reveal the interfacial speciation of divalent cations in ether-based electrolytes and mechanisms for their delivery to an inert graphene electrode interface. Surprisingly, we find that anion solvophobicity drives a high population of anion-containing species to the interface that facilitate the delivery of divalent cations, even to negatively charged electrodes. Our simulations indicate that cation desolvation is greatly facilitated by cation-anion coupling. We propose anion solvophobicity as a molecular-level descriptor for rational design of electrolytes with increased efficiency for electrochemical processes limited by multivalent cation desolvation.

Electrochemical interfaces↗

NASA NTRS2022

Free Energy Landscapes for Elucidating the Structural Consequences of Exon-20 mutations on the ErbB Family of Protein Kinases

The ErbB family of protein kinases plays an important role in major cellular functions and consequently mutations in the functional regions of these proteins are implicated in several types of cancer growths. To envision rational design of small molecule drugs that target the diseased proteins it is important to quantify the structural effects of the mutations, as some of these mutants render the protein resistant to tyrosine kinase inhibitors (TKIs). Herein we use advanced sampling techniques and long-timescale molecular dynamics simulations to predict the effect of major exon 20 mutations on the ErbB family, specifically EGFR and HER2 proteins. Exon 20 mutations have been clinically known to induce TKI resistance, though the mechanisms of such an effect is poorly understood. By mapping out the free energy landscape of the mutants and comparing them against the wild-type, we elucidate the structural differences in the binding pocket region that alter the nature of drug-protein interactions. We believe that these insights will play a pivotal role in developing small molecule drugs that overcome the TKI resistance.

Ashwin Ravichandran↗

NASA NTRS1978

Practical design of low-cost large space structures

The practical design of low-cost space structures involves the use of approaches that reduce the cost of the design and development effort itself. Such approaches include: (1) design with criteria arrived at rationally; (2) design for simplicity, repeatability, and modularity; (3) assembly without adjustments; (4) design for testability on the ground; (5) the attainment of structural efficiency by configuration and material choice rather than by squeezing down on the design margins; and (6) prefabrication and preassembly before launch. Attention is given to truss platform designs, and the Seasat Extendible Support Structure is discussed as a particular example.

Hedgepeth, J. M.↗

NASA NTRS1984

Structural optimization of large ocean-going structures

Ocean-going vehicles and platforms are among the largest structures in the world and are subjected to relatively harsh conditions of motions and loads. Some of them, such as semi-submersible platforms, are a relatively new type of structure and hence there is no formal, well evolved and established structural design code as there is for more traditional structures. More recently, efforts have also been made to develop a design method of this type for ships and other ocean structures. One of the many advantages of a rationally based design method is versatility; it can be used for structures that have widely differing purposes, measures of merit, shapes and sizes. The purpose is to describe a rationally based design method that has been developed within the field of ocean structures, in order that persons dealing with other types of structure can judge whether and to what extent its various features may be useful for those other types. Also, even though some features may not be applicable they might stimulate some useful ideas.

Hughes, O. F.↗

NASA NTRS1986

Control of H2S emissions using an ozone oxidation process: Preliminary results

The problem of eliminating industrial emission odors does not have a simple solution, and consequently has not been researched extensively. Therefore, an experimental research program regarding oxidation of H2S through ozone was undertaken to verify the applicable limits of the procedure and, in addition, was designed to supply a useful analytical means of rationalizing the design of reactors employed in the sector.

Defaveri, D.↗

NASA NTRS1985

Nutritional Criteria for Military Rations and Effects of Prolonged Feeding on Acceptability

Broad nutritional policies for operational rations are designed to insure that the nutritional content of the rations served will sustain combat effectiveness. Concern exists that these rations, although nutritionally complete, would become monotonous because of limited variety causing nutrient intake to decrease and body weight losses to occur with adverse effects on morale and combat effectiveness. Whenever possible, troops are now fed one or two hot meals per day containing fresh foods and a much greater variety of foods than are available in packaged rations. A laboratory test was conducted with student volunteers and the results are discussed.

Schnakenberg, D.↗

NASA NTRS1974

Nonproportional loading limit for structures

The design of most structures involves ensuring integrity for several independent loading conditions. Often, it is rational to design these, exploiting the ductility of the materials to reduce structural costs. Then, ensuring integrity evokes the need for nonmonotonic limit analyses. A groundwork is laid for implementing these analyses. An alternate limit load characterization to that of Greenberg is provided, a mathematical statement of the problem leading to both monotonic (proportional) and nonmonotonic limit loads values is formulated, a direct limit load analysis procedure for analysis within a finite-element framework is described, and limit loads for sets of simple structures are evaluated. A direct limit analysis process is described, and monotonic limit loads are characterized. The process furnishes 'exact' values of limit loads with increasing efficiency as the number of structural elements and force redundancy decreases. Tests show that the accuracy of predicting nonmonotonic limit loads is very sensitive to the number of degrees of freedom in the analysis compared with the total number in the model.

Melosh, R. J.↗

NASA NTRS1991

Lunar crane system

In many lunar construction scenarios, mechanical cranes in some form will be indispensible in moving large masses around with various degrees of fine positioning. While thorough experience exists in the use of terrestrial cranes new thinking is required about the design of cranes to be used in extraterrestrial construction. The primary driving force for this new thinking is the need to automate the crane system so that space cranes can be operated as telerobotic machines with a large number of automatic capabilities. This is true because in extraterrestrial construction human resources will need to be critically rationed. The design problems of mechanisms and control systems for a lunar crane must deal with at least two areas of performance. First, the automated crane must be capable of maneuvering a large mass, so that when the mass arrives at the target position there are only small vibrations. Secondly, any residue vibrations must be automatically damped out and a fine positioning must be achieved. For extraterrestrial use there are additional challenges to a crane design - for example, to design a crane system so that it can be transformed for other construction uses. This initial project in crane design does not address such additional issues, although they may be the subject of future CSC research. To date the Center has designed and analyzed many mechanisms. The fundamental problem of trade-offs between passively stabilizing the load and actively controlling the load by actuators was extensively studied. The capability of 3D dynamics modeling now exists for such studies. A scaled model of a lunar crane was set up and it has been most fruitful in providing basic understanding of lunar cranes. Due to an interesting scaling match-up, this scaled model exhibits the load vibration frequencies one would expect in the real lunar case. Using the analytical results achieved to date, a laboratory crane system is now being developed as a test bed for verifying a wide variety of mechanisms and control designs. Future development will be aimed at making the crane system a telerobotic test bed into which external sensors such as computer vision systems, and other small robotic devices such as CSC lunar rovers, will be integrated.

Mikulas, Martin M., Jr.↗