Preliminary estimates of operating costs for lighter than air transports

A preliminary set of operating cost relationships are presented for airship transports. The starting point for the development of the relationships is the direct operating cost formulae and the indirect operating cost categories commonly used for estimating costs of heavier than air commercial transports. Modifications are made to the relationships to account for the unique features of airships. To illustrate the cost estimating method, the operating costs of selected airship cargo transports are computed. Conventional fully buoyant and hybrid semi-buoyant systems are investigated for a variety of speeds, payloads, ranges, and altitudes. Comparisons are made with aircraft transports for a range of cargo densities

Transport characteristics of L-point and Г-point electrons through GaAs-Ga_(1-x)Ai_xAs-GaAs(111} double heterojunctions

We present here a study on the transport characteristics of L‐point and Γ‐point derived electrons through abrupt GaAs–Ga_(1−x)Al_xAs–GaAs(111) double heterojunctions. The use of complex‐k band structures in the tight‐binding approximation and transfer matrices provide a reasonably accurate description of the wave function at the GaAs–Ga_(1−x)Al_xAs interface. A representation of the wave function in terms of bulk complex‐k Bloch states is used in the GaAs regions where the potential is bulklike. A representation of the wave function in terms of planar orbitals is used in the central Ga_(1−x)Al_xAs region where the potential deviates from its bulk value (i.e., interfacial region). Within this theoretical framework, realistic band structure effects are taken into account and no artificial rules regarding the connection of the wave function across the interface are introduced. The ten‐band tight‐binding model includes admixture in the total wave function of states derived from different extrema of the GaAs conduction band. States derived from the same extremum of the conduction band appear to couple strongly to each other, whereas states derived from different extrema are found to couple weakly. Transport characteristics of incoming L‐point and Γ‐point Bloch states are examined as a function of the energy of the incoming state, thickness of the Ga_(1−x)Al_xAs barrier, and alloy composition x. Transmission through the Ga_(1−x)Al_xAs barrier is either tunneling or propagating depending on the nature of the Bloch states available for strong coupling in the alloy. Since Bloch states derived from different extrema of the conduction band appear to couple weakly to each other, it seems possible to reflect the low velocity L‐point component of the current while transmitting the high velocity Γ‐point component

Quantum Hall ferromagnetism in graphene: a SU(4) bosonization approach

We study the quantum Hall effect in graphene at filling factors \nu = 0 and \nu = \pm, concentrating on the quantum Hall ferromagnetic regime, within a non-perturbative bosonization formalism. We start by developing a bosonization scheme for electrons with two discrete degrees of freedom (spin-1/2 and pseudospin-1/2) restricted to the lowest Landau level. Three distinct phases are considered, namely the so-called spin-pseudospin, spin, and pseudospin phases. The first corresponds to a quarter-filled (\nu =-1) while the others to a half-filled (\nu = 0) lowest Landau level. In each case, we show that the elementary neutral excitations can be treated approximately as a set of n-independent kinds of boson excitations. The boson representation of the projected electron density, the spin, pseudospin, and mixed spin-pseudospin density operators are derived. We then apply the developed formalism to the effective continuous model, which includes SU(4) symmetry breaking terms, recently proposed by Alicea and Fisher. For each quantum Hall state, an effective interacting boson model is derived and the dispersion relations of the elementary excitations are analytically calculated. We propose that the charged excitations (quantum Hall skyrmions) can be described as a coherent state of bosons. We calculate the semiclassical limit of the boson model derived from the SU(4) invariant part of the original fermionic Hamiltonian and show that it agrees with the results of Arovas and co-workers for SU(N) quantum Hall skyrmions. We briefly discuss the influence of the SU(4) symmetry breaking terms in the skyrmion energy.Comment: 16 pages, 4 figures, final version, extended discussion about the boson-boson interaction and its relation with quantum Hall skyrmion

Domain State Occurring in the de Haas-van Alphen Effect in Silver

Hysteresis has been observed in de Haas-van Alphen measurements of the Condon domains in silver, and it shows the first-order nature of the transition to the domain state. The hysteresis, and thus the first-order nature, is manifested in a nonlinear effect where a double-valued response of the amplitude with the applied external field is observed

Carrier transport coefficients across GaAs-GaAIAs (100) interfaces

We present calculations of reflection and transmission coefficients for electrons and holes at (100) interfaces for the GaAs–Ga_(1–x)Al_xAs system. We consider semi‐infinite crystals of the two semiconductors joined at an abrupt or compositionally graded interface. The calculations are performed using the empirical tight binding approximation. The transport coefficients were computed as a function of the components of the incident carrier wavevector normal and parallel to the interface. We have investigated the transport coefficients for incident states near various band minima into different final state channels. The transmission into states with qualitatively similar character to the incident state is found to be much greater than transmission into states of different character. For example, an electron near the X minimum normal to the interface in Ga_(1–xAl_xAs transmits into the X valley of GaAs with much greater probability than it transmits into the Γ minimum of GaAs. We have investigated the dependence of the transport coefficients on alloy composition. The effect of compositional grading of the interface on the transport coefficients has also been investigated

Ground based photometry of potential navigation guide stars

Ground based photometry of potential navigation guide star

Bright star observations using an unfiltered 1P21 phototube

Calibration curves for brighter navigational stars by unfiltered tracking phototube

An economic study of an advanced technology supersonic cruise vehicle

A description is given of the methods used and the results of an economic study of an advanced technology supersonic cruise vehicle. This vehicle was designed for a maximum range of 4000 n.mi. at a cruise speed of Mach 2.7 and carrying 292 passengers. The economic study includes the estimation of aircraft unit cost, operating cost, and idealized cash flow and discounted cash flow return on investment. In addition, it includes a sensitivity study on the effects of unit cost, manufacturing cost, production quantity, average trip length, fuel cost, load factor, and fare on the aircraft's economic feasibility

Pressure distribution of a twin-engine upper-surface blown jet-flap model

An investigation has been made to determine the chordwise and spanwise pressure distributions of a small-scale upper-surface blown jet-augmented flap STOL model. The model was powered by two simulated high-bypass-ratio turbofan engines mounted ahead of and above an unswept-untapered wing in a nacelle having a rectangular nozzle. The results of the investigation are presented as tabulated and plotted chordwise pressure distribution coefficients for nine spanwise stations