850 research outputs found
An analysis of bipropellant neutralization for spacecraft refueling operations
Refueling of satellites on orbit with storable propellants will involve venting part or all of the pressurant gas from the propellant tanks. This gas will be saturated with propellant vapor, and it may also have significant amounts of entrained fine droplets of propellant. The two most commonly used bipropellants, monomethyl hydrazine (MMH) and nitrogen tetroxide (N2O4), are highly reactive and toxic. Various possible ways of neutralizing the vented propellants are examined. The amount of propellant vented in a typical refueling operation is shown to be in the range of 0.2 to 5% of the tank capacity. Four potential neutralization schemes are examined: chemical decomposition, chemical reaction, condensation and adsorption. Chemical decomposition to essentially inert materials is thermodynamically feasible for both MMH and N2O4. It would be the simplest and easiest neutralization method to implement. Chemical decomposition would require more complex control. Condensation would require a refrigeration system and a very efficent phase separator. Adsorption is likely to be much heavier. A preliminary assessment of the four neutralization shemes is presented, along with suggested research and development plans
Oriented Quantum Algebras and Coalgebras, Invariants of Oriented 1-1 Tangles, Knots and Links
In this paper we study oriented quantum coalgebras which are structures
closely related to oriented quantum algebras. We study the relationship between
oriented quantum coalgebras and oriented quantum algebras and the relationship
between oriented quantum coalgebras and quantum coalgebras. We show that there
are regular isotopy invariants of oriented 1-1 tangles and of oriented knots
and links associated to oriented and twist oriented quantum coalgebras
respectively. There are many parallels between the theory of oriented quantum
coalgebras and the theory of quantum coalgebra
On Filamentations and Virtual Knots
In this paper, we discuss filamentations on oriented chord diagrams. When a
filamentation cannot be realized on an oriented chord diagram, then the
corresponding flat virtual knot is non-trivial. If a flat knot diagram is
non-trivial, then any virtual diagram whose shadow is the flat diagram must
also be non-trivial. We introduce a class of flat diagrams for which no
filamentations exist. This class gives the first example of an infinite set of
virtual knots for which the Jones polynomial and the fundamental group both
evaluate trivially. The related generalized Alexander polynomials for the
virtual knots in this class turn out to be distinct, proving that the class is
indeed infinite.Comment: Corrected/Updated version. 34 pages, 12 figures, 2 tables, latex
document, xypic required to compil
Oriented Quantum Algebras and Invariants of Knots and Links
In GT/0006019 oriented quantum algebras were motivated and introduced in a
natural categorical setting. Invariants of knots and links can be computed from
oriented quantum algebras, and this includes the Reshetikhin-Turaev theory for
Ribbon Hopf algebras. Here we continue the study of oriented quantum algebras
from a more algebraic perspective, and develop a more detailed theory for them
and their associated invariants.Comment: LAteX document, 45 pages, 17 figure
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