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Microgravity Research Opportunities for the 1990s: Appendix A
Microgravity Research Opportunities
for the 1990s
A
Glossary
Advective: A mode of heat and species transport associated with the directed
motion of a fluid as often induced by volume changes accompanying phase
transformations.
Anisotropic: The variation of some material property with respect to direction or
spatial orientation.
REPORT MENU
NOTICE
MEMBERSHIP Austenite: The high-temperature phase in steel consisting of carbon dissolved in
PREFACE face-centered cubic iron.
EXECUTIVE SUMMARY
PART I
Batch technique: One of several strategies for crystallization in which a
CHAPTER 1
supersaturated condition for one dissolved component is established by mixing
CHAPTER 2
solutions and other additives into a single batch solution. In the typical application,
PART II
this solution is then left undisturbed during precipitation of the supersaturated
CHAPTER 3
component in the form of crystals.
CHAPTER 4
CHAPTER 5
CHAPTER 6 Biochemical assays: Methods of detecting and monitoring protein or other
CHAPTER 7 biological activities. The activity of an enzyme, for example, may be monitored by
PART III
the disappearance of reactants or the appearance of products from the reaction it
CHAPTER 8
catalyzes.
APPENDIX A
APPENDIX B
Biological macromolecule: One of a diversity of large molecules (relative
molecular weights typically 5000 or more) characteristic of biological systems, such
as proteins, nucleic acids (e.g., DNA), and polysaccharides.
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Microgravity Research Opportunities for the 1990s: Appendix A
Biomimetic synthesis: Synthesis by processes that mimic those found in
biological systems. An example is the composite organic mineral structure of
abalone shell.
Bridgman: A technique for effecting bulk crystal growth by application of a
temperature gradient to a solution of the components.
Calorimetry: A classical measurement technique based on the temperature
change observed in a material arising from the admission or release of a known
quantity of heat energy.
Cell fusion: The merging of more than one cell into a single entity surrounded by a
composite membrane, with concomitant mixing of cell contents.
Cell matrix: A structural component organizing and shaping cells in organs and
tissue. A common molecular component of mammalian matrix is collagen.
Chemotaxis: A behavioral response of certain living organisms mediated by
interactions of a receptor with a specific chemical that causes movement of the
organism in response to a gradient in concentration of the chemical. An example is
the movement of certain bacteria toward the source of a soluble nutrient.
Chromatography: A collection of methods for separating solution components by
differential flow rates through a porous medium due to differences in size, charge,
or binding affinity for the medium.
Coercivity: The magnitude of the magnetic field intensity required to reverse the
magnetic induction from one state of magnetization to its opposing orientation.
Commercial enzymes: Although biological materials have been used in generating
products of commercial value for centuries, in recent times the sources of the utility
of some of these materials have been identified as enzymes, an example of which
is rennin, an enzyme used in commercial cheese production. More recently, interest
has grown in the design and manufacture of enzyme products with commercial
value. An example is the engineering of thermostable protein-degrading enzymes
such as subtilisin as additives conferring improved stain-removing properties on
laundry products.
Constitutive equations: Equations that relate electric displacement with electric
field intensity and magnetic induction with magnetic field intensity.
Containerless: The description of materials processes carried out in microgravity
that precludes the need for a supporting vessel or crucible and thereby eliminates
sources of contamination at high temperatures.
Convective: A mode of heat and species transport in fluid systems caused by bulk
(macroscopic) motion of the fluid.
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Cuprate superconductors: A class of high-temperature superconductors based
on layered intermetallic compounds containing copper oxide and metals such as
yttrium, barium, and bismuth.
CVD: Chemical vapor deposition.
Czochralski method: A technique for effecting bulk crystal growth in which a
"seed" crystal grows by its gradual withdrawal from a stationary melt phase.
Dendritic: A branched, tree-like, form of crystal growth, commonly occurring in the
solidification of metals and alloys during casting and welding.
Diffusivity: The transport coefficient that relates the net flux of species or heat
flowing in response to a gradient of the concentration or temperature, respectively,
established in the material.
Electrofusion: Cell fusion facilitated by application of electric fields.
Electromagnetic levitator: A device consisting of a high-frequency coil that
provides a magnetic lifting force and heating for a conducting material placed within
the coil.
Electroosmosis: Transport across a semipermeable membrane driven by
electrical potential difference.
Electrophoresis: Separation of charged molecules based on differential mobilities
in an imposed electrostatic field.
Electrowinning: The process of recovery of metallics from low-grade ores by
leaching the mineral with an acidic solution followed by electrolytic precipitation.
Ellipsometry: An optical technique used for determining the index of refraction and
other optical properties of the surface of a material by analyzing the elliptically
polarized light reflected from the surface.
Embryogenesis: The collection of complex developmental processes involved in
going from ovum to embryo.
Emissivity: The optical property of a material body that relates the absorbed
energy flux for a given wavelength to that of a perfectly absorbing substance.
Endocrine cell: A cell from one of a number of different glands that secrete
molecules, known as hormones, that influence the behavior of other cells.
Epitaxy: The growth on a crystalline substrate of a crystalline layer with an ordered
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structure that is determined by the crystal structure of the substrate. As used in this
report, the epitaxial layer has the same structure as the substrate.
Eutectic: A thermodynamic reaction in which a liquid transforms into two solid
phases upon cooling.
Fermentation: A process involving enzymatically controlled breakdown of nutrients
in the absence of air by living organisms such as yeast.
Flammability limit: Mixture ratio limits of fuel to oxidizer above and below which a
propagating flame will not sustain itself.
g-jitter (gravity-jitter): The spectral range of oscillatory accelerations arising from
crew motions, machinery, rocket firings, and so on, occurring in orbiting spacecraft.
GBP: Gravity Probe-B—an experimental test of magnetogravitational effects
predicted by Einstein's general theory of relativity.
Genome: The collection of genetic material that encodes all of the components, the
assembly, and the development of an organism.
Glovebox: A hermetically sealed environment accessible to hand manipulation by
gloves that are an integral part of the environmental enclosure.
Glycoprotein: A protein that is modified after synthesis by the attachment of
oligomeric assemblages of carbohydrate. The attachment sites and the nature of
the attached carbohydrate are determined by the action of enzymes.
Heterostructure: Term usually applied to semiconductors. A multilayered, single-
crystal structure with the layers having different compositions, but with nearly defect-
free interfaces as the result of being either lattice matched or thin enough that
stress has not been relieved by the formation of defects.
Hybridoma: A fused cell combining a cell with desired properties with a cancer cell
that confers reproductive immortality on the fusion product.
Hydrothermal growth: Synthesis in high-pressure aqueous systems at
temperatures above 100°C.
Hypereutectic: Describing compositions of an alloy that are above the eutectic
point.
Hysteresis: The memory effect exhibited in some property by systems changing
from one state to another, such as from the magnetized to the unmagnetized
condition.
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Immiscibility: The property of liquid alloys over certain temperatures, pressures,
and compositions by which they separate into distinct phases, such as oil and water
at room temperature and atmospheric pressure.
Immunoglobulins: Proteins whose function it is to recognize and bind to
dangerous or foreign molecules, matter, or cells, and to flag them for destruction or
elimination.
Incongruent melting: Melting with decomposition.
Intercellular communication: The process by which cells influence the behavior of
other cells in a multicellular organism. Communication occurs most commonly by
chemical means and involves the interactions of a bewildering variety of secreted
chemicals with specific cellular receptors.
Intermetallic: Referring to phases of nearly fixed atomic proportions, usually
exhibiting limited mutual solubility, and occurring away from the ends of the phase
diagram.
Isoelectronic: Having the same electronic structure.
Isostatic pressing: A process for consolidating powders by application of pressure
equally from all sides.
Lambda point: For 4He, the temperature (2.1780 K), at atmospheric pressure, at
which the transformation between the fluids helium I and helium II takes place. At
this point the heat capacity of the system increases without limit as the transition
temperature is approached from above or below.
Landau-Darrieus instability: A fluid interface instability occurring when there is a
density difference across the interface and mass transport across the interface.
Lewis number: Nondimensional number consisting of the ratio of the thermal and
mass diffusivities.
Liposomes: Aqueous compartments enclosed by lipid bilayer membranes. Artificial
liposomes are constructed to encapsulate substances for controlled delivery in
biological systems.
Liquid-liquid diffusion: A method of crystallization in which two different solutions,
miscible or immiscible, are brought in contact to form an interface, with or without
the benefit of a semipermeable membrane. Subsequent diffusion across the
interface establishes a supersaturated condition for one of the dissolved
components, typically a protein, resulting in precipitation of that component in the
form of crystals.
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Liquidus: The curve giving the compositions and temperatures at which a liquid
and a crystalline phase may coexist in thermodynamic equilibrium.
LPE: Lambda-point experiment-a high-resolution determination of the heat capacity
of liquid 4He at superfluid transition ( -point).
Macromolecular: Referring to large molecules such as those found in biological
systems, where a relative molecular weight of 2000 to 5000 daltons or greater is
implied, or those studied by polymer sciences.
Macrosegregation: The redistribution of solute atoms between the solid and liquid
phases during solidification, with redistribution occurring over distances that are
large compared to the size scale of the solid-liquid microstructure.
Martensite: A hard, metastable phase occurring spontaneously in certain rapidly
cooled (quenched) steels, consisting of iron and carbon with a tetragonal crystal
structure.
Membrane: A semipermeable molecular barrier. The most well known example, the
cell membrane, surrounds the cell and separates the interior from external
surroundings. The typical biological membrane is a bilayer of lipid molecules
exposing polar head groups to both exterior and interior.
Mesoscopic: Referring to a scale of size characterizing the microstructure of
materials that typically fall in the range 10-5 to 10-2 cm (i.e., intermediate between
microscopic and macroscopic).
Metastable: The thermodynamic condition of a phase or assembly of matter in
which the minimum energy state is not accessible without first passing through a
state of higher energy. Such states can persist for long periods of time.
Monoclonal antibody: A single specific immunoglobulin antibody reproduced in an
immortalized cell line by artificial methods.
Monodispersions: Polymer systems that are homogeneous in molecular weight.
Monomer: A molecule consisting of a group of atoms that constitute the chain
repeat of a polymer.
Monotectic: A thermodynamic reaction in which a liquid alloy, upon cooling,
separates into a new liquid phase and a crystalline phase.
Nanomaterials: Generic designation of bulk solid and thin film materials prepared
by special processing methods to consist of ultrafine crystallites with diameters of
less than 10-8 m. Such materials have a preponderant number of their atoms in
interfacial locations and as a consequence display unusual properties.
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Nanostructures: An arrangement of almost atomically thin, contiguous layers of
semiconducting materials, usually operating as an optoelectronic device. Such
devices often exhibit unusual behavior based on quantum effects that depend on
the reduced dimensions of the crystalline layers.
Nucleic acid (sequence): A linear polymer of a mixture of four purine- or
pyrimidine-ribose-phosphate monomers. Depending on the type of ribose, the
nucleic acid is either DNA or RNA. In genetically active DNA or RNA, the sequence
of purines and pyrimidines, taken in triplets, encodes the sequence of amino acids
in a protein.
Oligomers: Polymers made up of two, three, or four monomer units.
Organelle: One of several kinds of distinct particulate bodies, either entirely
membranous or an organized unit surrounded by a membrane, found within cells.
Most organelles-the cell nucleus is an example-are associated with important cell
functions, and the cells that contain them (eukaryotic cells) are reckoned to be more
advanced than those without (prokaryotic cells).
Ostwald ripening: The general thermodynamic and kinetic tendency of dispersed
collections of fine particles to interact and lower their energy by exhibiting shrinkage
and eventual disappearance of smaller particles and simultaneous growth and
dominance of larger particles.
Peptide: Part or all of a protein. Any chemical entity including a peptide bond (i.e.,
a bond joining amino and carboxylate groups by elimination of a water molecule).
Peritectic: A thermodynamic reaction in which a solid, upon heating, decomposes
to a liquid phase and a new crystalline phase.
pH: The negative logarithm (base 10) of the hydrogen ion concentration. In an
aqueous solution, the accessible range of pH is from 1 to 14 by virtue of the
dissociation of water. Acidic conditions have pH values lower than 7; basic, higher.
Phase partitioning: Fractionation of mixtures based on differential solubilities of
components in two or more immiscible phases.
Polymerization: Chemical process in which individual monomers are converted
into polymers.
Polymers: Substances made up of large molecules formed by the union of simple
molecules.
Polymorphic: One of many possible crystallographic forms for a solid material of
given chemical composition.
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Polyphase: A mixture or microstructure containing two or more coexisting phases.
Precipitant: A compound or solution that, when added to the solution of a
component that is to be precipitated, establishes a supersaturated condition for that
component and causes the desired precipitation.
Protein activity: The ability of a protein to perform its function. This function may
require one or more of several different kinds of activities. If the protein is an
enzyme, its activity is measured by its ability to catalyze a specific biochemical
reaction. If the protein is a receptor on a cell surface, its activity is measured as its
ability to recognize and bind a specific ligand and to transduce that ligand-binding
event as a chemical signal within the cell.
Proteins: Heterogeneous linear polymers of amino acids connected by peptide
bonds in sequences specified by the genetic messages encoded in DNA. In
aqueous environments, these molecules typically adopt characteristic three-
dimensional folded structures that endow them with the properties required for the
functions they perform.
Pyrolysis: Gasification of a condensed-phase substance with, perhaps, chemical
change by the application of heat.
Rayleigh-Taylor instability: The instability of the interface separating two fluids
having different densities when the lighter fluid is accelerated toward the heavier
fluid.
Receptor-ligand interactions: The collection of phenomena comprising and
attending the recognition and binding of a receptor to a specific ligand molecule and
the transduction of that event through the cell membrane.
Recombinant DNA techniques: The collection of techniques that are the basis for
genetic engineering capabilities. Included are isolation of a specific RNA message,
cloning of DNA complementary to the message, insertion of this DNA into
transferable genetic elements, and infection of a foreign host cell with these genetic
elements for expression of the selected gene.
Reynolds number: A dimensionless number indicating the ratio of inertial to
viscous forces in a fluid flow.
Ribosome: The assembly of proteins that translates a genetic instruction in the
form of an RNA message and synthesizes the encoded protein.
Shadowgraph, schlieren: Methods of making visible the disturbances in fluid flows
by refracting light through density gradients in the fluids.
Sintering: The process of powder particle bonding and coalescence by diffusion.
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Solutal: Referring to alloy additions and/or chemical impurities, such as solutal
convection.
SQUID: Superconducting Quantum Interference Device that provides state-of-the-
art magnetic field measurements.
Stoichiometry: The whole-number relationship between the number of moles of
each element constituting a chemical compound.
Stokes regime: Flows with a Reynolds number of less than 1.
Superalloys: Any of the complex nickel-based alloys used for high-temperature
service in gas turbines and jet engines.
Supercool: Referring to the persistence of a (metastable) liquid phase at
temperatures below the normal melting point, where, strictly speaking, only the
crystalline form is thermodynamically stable.
Thermocapillary: Referring to changes in surface tension due to temperature
variations that can generate fluid motions.
Thermodiffusion: The transport of matter induced by application of a temperature
gradient.
Thermophoresis: The kinetic phenomenon in which a small particle or molecule
moves spontaneously and collinearly to the applied thermal gradient.
Thermosolutal: Referring to combined convection effects arising from density
gradients associated with alloy additions and temperature.
Virus: One of a complex variety of parasitic particles capable of replicating itself by
infection of a host cell and consisting in its simplest form of an RNA or DNA
genome surrounded by a coat of viral protein.
Viscoelastic: Referring to mechanical behavior in which both fluid-like (viscous)
and solid-like (elastic) characteristics are exhibited.
Weldments: A generic term referring to joints and connections between like and
unlike materials made without mechanical fasteners, usually by fusing the materials
together.
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