GEOS axial booms

A booms and mechanisms subsystem was designed, developed, and qualified for the geostationary scientific satellite GEOS. Part of this subsystem consist of four axial booms consisting of one pair of 1 m booms and one pair of 2.5 m booms. Each of these booms is carrying one bird cage electric field sensor. Alignment accuracy requirements led to a telescopic type solution. Deployment is performed by pressurized nitrogen. At deployment in orbit two of these booms showed some anomalies and one of these two deployed only about 80%. Following this malfunction a detailed failure investigation was performed resulting in a design modification of some critical components as release mechanism, guide sleeves of the telescopic elements, and pressure system

Construction of Nonlinear Symplectic Six-Dimensional Thin-Lens Maps by Exponentiation

The aim of this paper is to construct six-dimensional symplectic thin-lens transport maps for the tracking program SIXTRACK, continuing an earlier report by using another method which consistes in applying Lie series and exponentiation as described by W. Groebner and for canonical systems by A.J. Dragt. We firstly use an approximate Hamiltonian obtained by a series expansion of the square root. Furthermore, nonlinear crossing terms due to the curvature in bending magnets are neglected. An improved Hamiltonian, excluding solenoids, is introduced in Appendix A by using the unexpanded square root mentioned above, but neglecting again nonlinear crossing terms...Comment: 57 pages, late

Unifying Magnons and Triplons in Stripe-Ordered Cuprate Superconductors

Based on a two-dimensional model of coupled two-leg spin ladders, we derive a unified picture of recent neutron scattering data of stripe-ordered La_(15/8)Ba_(1/8)CuO_4, namely of the low-energy magnons around the superstructure satellites and of the triplon excitations at higher energies. The resonance peak at the antiferromagnetic wave vector Q_AF in the stripe-ordered phase corresponds to a saddle point in the dispersion of the magnetic excitations. Quantitative agreement with the neutron data is obtained for J= 130-160 meV and J_cyc/J = 0.2-0.25.Comment: 4 pages, 4 figures included updated version taking new data into account; factor in spectral weight corrected; Figs. 2 and 4 change

Integrated structure/control law design by multilevel optimization

A new approach to integrated structure/control law design based on multilevel optimization is presented. This new approach is applicable to aircraft and spacecraft and allows for the independent design of the structure and control law. Integration of the designs is achieved through use of an upper level coordination problem formulation within the multilevel optimization framework. The method requires the use of structure and control law design sensitivity information. A general multilevel structure/control law design problem formulation is given, and the use of Linear Quadratic Gaussian (LQG) control law design and design sensitivity methods within the formulation is illustrated. Results of three simple integrated structure/control law design examples are presented. These results show the capability of structure and control law design tradeoffs to improve controlled system performance within the multilevel approach

Bound hole states in a ferromagnetic (Ga,Mn)As environment

A numerical technique is developed to solve the Luttinger-Kohn equation for impurity states directly in k-space and is applied to calculate bound hole wave functions in a ferromagnetic (Ga,Mn)As host. The rich properties of the band structure of an arbitrarily strained, ferromagnetic zinc-blende semiconductor yields various features which have direct impact on the detailed shape of a valence band hole bound to an active impurity. The role of strain is discussed on the basis of explicit calculations of bound hole states.Comment: 9 pages, 10 figure

The fate of orbitons coupled to phonons

The key feature of an orbital wave or orbiton is a significant dispersion, which arises from exchange interactions between orbitals on distinct sites. We study the effect of a coupling between orbitons and phonons in one dimension using continuous unitary transformations (CUTs). Already for intermediate values of the coupling, the orbiton band width is strongly reduced and the spectral density is dominated by an orbiton-phonon continuum. However, we find sharp features within the continuum and an orbiton-phonon anti-bound state above. Both show a significant dispersion and should be observable experimentally.Comment: 7 pages, 7 figures; strongly enlarged, comprehensive revised version according to the referees' suggestions, in pres

Thermodynamics of Adiabatically Loaded Cold Bosons in the Mott Insulating Phase of One-Dimensional Optical Lattices

In this work we give a consistent picture of the thermodynamic properties of bosons in the Mott insulating phase when loaded adiabatically into one-dimensional optical lattices. We find a crucial dependence of the temperature in the optical lattice on the doping level of the Mott insulator. In the undoped case, the temperature is of the order of the large onsite Hubbard interaction. In contrast, at a finite doping level the temperature jumps almost immediately to the order of the small hopping parameter. These two situations are investigated on the one hand by considering limiting cases like the atomic limit and the case of free fermions. On the other hand, they are examined using a quasi-particle conserving continuous unitary transformation extended by an approximate thermodynamics for hardcore particles.Comment: 10 pages, 6 figure

VHF Radar Observations in the Stratosphere and Mesosphere During a Stratospheric Warming

The SOUSY-VHF-radar was used to carry out measurements during minor and a major stratospheric warming in February and March 1980, respectively. Echoes have been received from the stratosphere up to an altitude of about 30 km continuously during day and night, whereas echoes from the mesosphere were restricted to the daytime and occurred sporadically at different heights within the altitude range from 60 to 90 km. The three dimensional velocity vector was derived from Doppler measurements made in three different antenna beam directions with a height resolution of 1.5 km. In particular, the results obtained during disturbed conditions show the change of the zonal winds at mesospheric heights from westerly to easterly. A spectral analysis reveals a diurnal and a weaker semidiurnal tide of the zonal wind component