Space Shuttle Booster Wing Geometry Trade Studies

The subsonic aircraft mode of a Space Shuttle booster establishes design requirements on airbreathing engine size and flyback fuel allotment. Trade study results show the influence of wing geometry variations on the flyback systems weight (wing, jet engine and flyback fuel weight) of a canard Space Shuttle booster. The influence of such wing geometry parameters as aspect ratio and wing area is discussed. Wing weight trends with wing geometry, obtained from conventional cargo, bomber and fighter airplane weight histories, are correlated with predicted values for Space Shuttle wings where structural span, load factor, and other design parameters are taken into account. For other than cruise performance reasons, a lower limit of wing area is defined; the influence of other phases of the booster mission profile, including launch, entry, and landing is presented. Aspect ratio, however, is influenced primarily by cruise performance and cost considerations. The influence of ground rules, such as choice of flyback fuel, headwind profile, and required range is discussed

Spin exchange interaction with tunable range between graphene quantum dots

We study the spin exchange between two electrons localized in separate quantum dots in graphene. The electronic states in the conduction band are coupled indirectly by tunneling to a common continuum of delocalized states in the valence band. As a model, we use a two-impurity Anderson Hamiltonian which we subsequently transform into an effective spin Hamiltonian by way of a two-stage Schrieffer-Wolff transformation. We then compare our result to that from a Coqblin-Schrieffer approach as well as to fourth order perturbation theory.Comment: 8 pages, 3 figure

Graphene zigzag ribbons, square lattice models and quantum spin chains

We present an extended study of finite-width zigzag graphene ribbons (ZGRs) based on a tight-binding model with hard-wall boundary conditions. We provide an exact analytic solution that clarifies the origin of the predicted width dependence on the conductance through junctions of ribbons with different widths. An analysis of the obtained solutions suggests a new description of ZGRs in terms of coupled chains. We pursue these ideas further by introducing a mapping between the ZGR model and the Hamiltonian for N-coupled quantum chains as described in terms of 2N Majorana fermions. The proposed mapping preserves the dependence of ribbon properties on its width thus rendering metallic ribbons for N odd and zero-gap semiconductor ribbons for N even. Furthermore, it reveals a close connection between the low-energy properties of the ZGR model and a continuous family of square lattice model Hamiltonians with similar width-dependent properties that includes the $\pi-$flux and the trivial square lattice models. As a further extension, we show that this new description makes it possible to identify various aspects of the physics of graphene ribbons with those predicted by models of quantum spin chains (QSCs)

Propulsion system ignition overpressure for the Space Shuttle

Liquid and solid rocket motor propulsion systems create an overpressure wave during ignition, caused by the accelerating gas particles pushing against or displacing the air contained in the launch pad or launch facility and by the afterburning of the fuel-rich gases. This wave behaves as a blast or shock wave characterized by a positive triangular-shaped first pulse and a negative half-sine wave second pulse. The pulse travels up the space vehicle and has the potential of either overloading individual elements or exciting overall vehicle dynamics. The latter effect results from the phasing difference of the wave from one side of the vehicle to the other. This overpressure phasing, or delta P environment, because of its frequency content as well as amplitude, becomes a design driver for certain panels (e.g., thermal shields) and payloads for the Space Shuttle. The history of overpressure effects on the Space Shuttle, the basic overpressure phenomenon, Space Shuttle overpressure environment, scale model overpressure testing, and techniques for suppressing the overpressure environments are considered

Relation between design requirements and building performance simulation

The aim of this paper is to reveal the relation between basic design requirements and the use of building performance simulation in current design practice. As a starting point to focus future research on building performance simulation a number of interviews with building design practitioners were conducted to find the answer to the question: "What general information can be obtained on the building design requirements, providing a background for the context in which future building performance simulation tools or support environments will be used?" The results of the interviews with world leading building services professionals are elaborated focusing on the relationship of value drivers and design requirements, which prescribe the building performance. The literature review on architectural programming together with the outcomes of the interviews will reveal whether the value drivers such as flexibility, functionality and sustainability are identified in the program of requirements, accommodating the client’s expectation on the building performance or not. The results are summarized and interpreted suggesting alternatives for the use of building performance simulation