Flow effects with cross-blown lifting jets of V/STOL aircraft and their reactions on aerodynamical forces and moments of the airframe

Systematic basic studies on the close and distant effects of cross blown single and twin lifting jets were performed with the aid of a principle model. The different effects are described in detail. The number of the experimental parameters is reduced to the most essential ones: (1) the angle of attack, (2) the flight and the jet velocities as well as the jet diameter, (3) the distance between the twin jets, (4) the location of the wing relative to the jets and the fuselage, and (5) the ground distance. The results of systematic pressure distribution measurements on the fuselage surface are studied, especially in the close vicinity of the jet exits. From these results, functions on the influence of the parameters are deduced

Annual report 2006 // Institute of Radiochemistry

[no abstract available

Hall resistance in the hopping regime, a "Hall Insulator"?

The Hall conductivity and resistivity of strongly localized electrons at low temperatures and at small magnetic fields are obtained. It is found that the results depend on whether the conductivity or the resistivity tensors are averaged to obtain the macroscopic Hall resistivity. In the second case the Hall resistivity always {\it diverges} exponentially as the temperature tends to zero. But when the Hall resistivity is derived from the averaged conductivity, the resulting temperature dependence is sensitive to the disorder configuration. Then the Hall resistivity may approach a constant value as $T\to 0$. This is the Hall insulating behavior. It is argued that for strictly dc conditions, the transport quantity that should be averaged is the resistivity.Comment: Late

Electron-Electron Interactions and the Hall-Insulator

Using the Kubo formula, we show explicitly that a non-interacting electron system can not behave like a Hall-insulator, {\it ie.,} a DC resistivity matrix $\rho_{xx}\rightarrow\infty$ and $\rho_{xy}=$finite in the zero temperature limit, as has been observed recently in experiment. For a strongly interacting electron system in a magnetic field, we illustrate, by constructing a specific form of correlations between mobile and localized electrons, that the Hall resistivity can approximately equal to its classical value. A Hall-insulator is realized in this model when the density of mobile electrons becomes vanishingly small. It is shown that in non-interacting electron systems, the zero-temperature frequency-dependent conductacnce generally does not give the DC conductance.Comment: 11 pages, RevTeX3.

Influence of clinical and gait analysis experience on reliability of observational gait analysis (Edinburgh Gait Score Reliability)

AbstractObjectivesTreatment complexity of cerebral palsy (CP) patients imposes outcome evaluation studies, which may include objective technical analysis and more subjective functional evaluation. The Edinburgh Gait Score (EGS) was proposed as an additive or alternative when complex instrumented three-dimensional gait analysis is not available. Our purposes were to apply a translated EGS to standard video recordings of independent walking spastic diplegic CP patients, to evaluate its intraobserver and interobserver reliability with respect to gait analysis familiar and not familiar observers.MethodsTen standard video recordings acquired during routine clinical gait analysis were examined by eight observers gait analysis interpretation experienced or not, out of various specialities, two times with a two weeks interval. Kappa statistics and intraclass correlation coefficient were calculated.ResultsBetter reliability was observed for foot and knee scores than in proximal segments with significant differences between stance and swing phase. Significantly better results in gait analysis trained observers underlines the importance to either be used to clinical gait analysis interpretation, or to benefit of video analysis training before observational scoring.ConclusionVisual evaluation may be used for outcome studies to explore clinical changes in CP patients over time and may be associated to other validated evaluation tools

Superconductors with Magnetic Impurities: Instantons and Sub-gap States

When subject to a weak magnetic impurity potential, the order parameter and quasi-particle energy gap of a bulk singlet superconductor are suppressed. According to the conventional mean-field theory of Abrikosov and Gor'kov, the integrity of the energy gap is maintained up to a critical concentration of magnetic impurities. In this paper, a field theoretic approach is developed to critically analyze the validity of the mean field theory. Using the supersymmetry technique we find a spatially homogeneous saddle-point that reproduces the Abrikosov-Gor'kov theory, and identify instanton contributions to the density of states that render the quasi-particle energy gap soft at any non-zero magnetic impurity concentration. The sub-gap states are associated with supersymmetry broken field configurations of the action. An analysis of fluctuations around these configurations shows how the underlying supersymmetry of the action is restored by zero modes. An estimate of the density of states is given for all dimensionalities. To illustrate the universality of the present scheme we apply the same method to study `gap fluctuations' in a normal quantum dot coupled to a superconducting terminal. Using the same instanton approach, we recover the universal result recently proposed by Vavilov et al. Finally, we emphasize the universality of the present scheme for the description of gap fluctuations in d-dimensional superconducting/normal structures.Comment: 18 pages, 9 eps figure

Sliding motion of a two-dimensional Wigner crystal in a strong magnetic field

We study the sliding state of a two-dimensional Wigner crystal in a strong magnetic field and a random impurity potential. Using a high-velocity perturbation theory, we compute the nonlinear conductivity, various correlation functions, and the interference effects arising in combined AC + DC electric effects, including the Shapiro anomaly and the linear response to an AC field. Disorder is found to induce mainly transverse distortions in the sliding state of the lattice. The Hall resistivity retains its classical value. We find that, within the large velocity perturbation theory, free carriers which affect the longitudinal phonon modes of the Wigner crystal do not change the form of the nonlinear conductivity. We compare the present sliding Wigner crystal in a strong magnetic field to the conventional sliding charge-density wave systems. Our result for the nonlinear conductivity agrees well with the $I-V$ characteristics measured in some experiments at low temperatures or large depinning fields, for the insulating phases near filling factor $\nu$ = 1/5. We summarize the available experimental data, and point out the differences among them.Comment: appeared in RPB vol. 50, 4600 (1994); LaTex file; 3 figures available from [email protected]

Growth rate after limb deformity correction by the Ilizarov method with or without knee joint distraction: Lengthening in 30 children followed for at least 2 years

Background and purpose Growth inhibition and stimulation have both been reported after juvenile limb lengthening. Distraction of a joint usually suspends and unloads the growth plate and may stimulate growth. We investigated the influence of knee joint distraction on the speed of growth after limb lengthening