Evaluation of a computer-generated perspective tunnel display for flight path following

The display was evaluated by monitoring pilot performance in a fixed base simulator with the vehicle dynamics of a CH-47 tandem rotor helicopter. Superposition of the predicted future vehicle position on the tunnel image was also investigated to determine whether, and to what extent, it contributes to better system performance (the best predicted future vehicle position was sought). Three types of simulator experiments were conducted: following a desired trajectory in the presence of disturbances; entering the trajectory from a random position, outside the trajectory; detecting and correcting failures in automatic flight. The tunnel display with superimposed predictor/director symbols was shown to be a very successful combination, which outperformed the other two displays in all three experiments. A prediction time of 4 to 7 sec. was found to optimize trajectory tracking for the given vehicle dynamics and flight condition. Pilot acceptance of the tunnel plus predictor/director display was found to be favorable and the time the pilot needed for familiarization with the display was found to be relatively short

Spin-Current Relaxation Time in Spin-Polarized Heisenberg Paramagnets

We study the spatial Fourier transform of the spin correlation function G_q(t) in paramagnetic quantum crystals by direct simulation of a 1d lattice of atoms interacting via a nearest-neighbor Heisenberg exchange Hamiltonian. Since it is not practical to diagonalize the s=1/2 exchange Hamiltonian for a lattice which is of sufficient size to study long-wavelength (hydrodynamic) fluctuations, we instead study the s -> infinity limit and treat each spin as a vector with a classical equation of motion. The simulations give a detailed picture of the correlation function G_q(t) and its time derivatives. At high polarization, there seems to be a hierarchy of frequency scales: the local exchange frequency, a wavelength-independent relaxation rate 1/tau that vanishes at large polarization P ->1, and a wavelength-dependent spin-wave frequency proportional to q^2. This suggests a form for the correlation function which modifies the spin diffusion coefficients obtained in a moments calculation by Cowan and Mullin, who used a standard Gaussian ansatz for the second derivative of the correlation function.Comment: 6 pages, 3 figure

Pathological regional blood flow in opiate-dependent patients during withdrawal: A HMPAO-SPECT study

The aims of the present study were to investigate regional cerebral blood flow (rCBF) in heroin-dependent patients during withdrawal and to assess the relation between these changes and duration of heroin consumption and withdrawal data. The rCBF was measured using brain SPECT with Tc-99m-HMPAO in 16 heroin-dependent patients during heroin withdrawal. Thirteen patients received levomethadone at the time of the SPECT scans. The images were analyzed both visually and quantitatively, a total of 21 hypoperfused brain regions were observed in 11 of the 16 patients. The temporal lobes were the most affected area, hypoperfusions of the right and left temporal lobe were observed in 5 and 5 patients, respectively. Three of the patients had a hypoperfusion of the right frontal lobe, 2 patients showed perfusion defects in the left frontal lobe, right parietal lobe and left parietal lobe. The results of the quantitative assessments of the rCBF were consistent with the results of the qualitative findings. The stepwise regression analysis showed a significant positive correlation (r = 0.54) between the dose of levomethadone at the time of the SPECT scan and the rCBF of the right parietal lobe. Other significant correlations between clinical data and rCBF were not found. The present results suggest brain perfusion abnormalities during heroin withdrawal in heroin-dependent patients, which are not due to the conditions of withdrawal

Suppression of biodynamic interference in head-tracked teleoperation

The utility of helmet-tracked sights to provide pointing commands for teleoperation of cameras, lasers, or antennas in aircraft is degraded by the presence of uncommanded, involuntary heat motion, referred to as biodynamic interference. This interference limits the achievable precision required in pointing tasks. The noise contributions due to biodynamic interference consists of an additive component which is correlated with aircraft vibration and an uncorrelated, nonadditive component, referred to as remnant. An experimental simulation study is described which investigated the improvements achievable in pointing and tracking precision using dynamic display shifting in the helmet-mounted display. The experiment was conducted in a six degree of freedom motion base simulator with an emulated helmet-mounted display. Highly experienced pilot subjects performed precision head-pointing tasks while manually flying a visual flight-path tracking task. Four schemes using adaptive and low-pass filtering of the head motion were evaluated to determine their effects on task performance and pilot workload in the presence of whole-body vibration characteristic of helicopter flight. The results indicate that, for tracking tasks involving continuously moving targets, improvements of up to 70 percent can be achieved in percent on-target dwelling time and of up to 35 percent in rms tracking error, with the adaptive plus low-pass filter configuration. The results with the same filter configuration for the task of capturing randomly-positioned, stationary targets show an increase of up to 340 percent in the number of targets captured and an improvement of up to 24 percent in the average capture time. The adaptive plus low-pass filter combination was considered to exhibit the best overall display dynamics by each of the subjects

Giant crystals inside mitochondria of equine chondrocytes

The present study reports for the first time the presence of giant crystals in mitochondria of equine chondrocytes. These structures show dark contrast in TEM images as well as a granular substructure of regularly aligned 12 nm small units. Different zone axes of the crystalline structure were analysed by means of Fourier transformation of lattice-resolution TEM images proving the crystalline nature of the structure. Elemental analysis reveals a high content of nitrogen referring to protein. The outer shape of the crystals is geometrical with an up to hexagonal profile in cross sections. It is elongated, spanning a length of several micrometres through the whole cell. In some chondrocytes, several crystals were found, sometimes combined in a single mitochondrion. Crystals were preferentially aligned along the long axis of the cells, thus appearing in the same orientation as the chondrocytes in the tissue. Although no similar structures have been found in the cartilage of any other species investigated, they have been found in cartilage repair tissue formed within a mechanically stimulated equine chondrocyte construct. Crystals were mainly located in superficial regions of cartilage, especially in joint regions of well-developed superficial layers, more often in yearlings than in adult horses. These results indicate that intramitochondrial crystals are related to the high mechanical stress in the horse joint and potentially also to the increased metabolic activity of immature individuals.(VLID)353386

Thermoelectric Response of an Interacting Two-Dimensional Electron Gas in Quantizing Magnetic Field

We present a discussion of the linear thermoelectric response of an interacting electron gas in a quantizing magnetic field. Boundary currents can carry a significant fraction of the net current passing through the system. We derive general expressions for the bulk and boundary components of the number and energy currents. We show that the local current density may be described in terms of ``transport'' and ``internal magnetization'' contributions. The latter carry no net current and are not observable in standard transport experiments. We show that although Onsager relations cannot be applied to the local current, they are valid for the transport currents and hence for the currents observed in standard transport experiments. We relate three of the four thermoelectric response coefficients of a disorder-free interacting two-dimensional electron gas to equilibrium thermodynamic quantities. In particular, we show that the diffusion thermopower is proportional to the entropy per particle, and we compare this result with recent experimental observations.Comment: 18 pages, 2 postscript figures included. Revtex with epsf.tex and multicol.sty. In the revised version, the comparison with experimental observations at $\nu=1/2, 3/2$ is extended to include the possibility of corrections due to weak impurity scattering. The conclusions that we reach regarding the applicability of the composite fermion model at these filling fractions are not affecte

First measurement of the Non-instantaneous response Time of a χ(3) nonlinear optical effect

The third harmonic of a few-cycle pulse, generated at different dielectric surfaces, is investigated using interferometric frequency-resolved optical gating. We present direct experimental evidence for a non-instantaneous nonlinear response in a TiO2 thin film whereas surface third-harmonic generation in a SiO2 sample does not show any indication for non-instanteneity. To the best of our knowledge, this constitutes the first report of a non-instantaneous nonlinear optical response of a dielectric optical material

Action research and democracy

This contribution explores the relationship between research and learning democracy. Action research is seen as being compatible with the orientation of educational and social work research towards social justice and democracy. Nevertheless, the history of action research is characterized by a tension between democracy and social engineering. In the social-engineering approach, action research is conceptualized as a process of innovation aimed at a specific Bildungsideal. In a democratic approach action research is seen as research based on cooperation between research and practice. However, the notion of democratic action research as opposed to social engineering action research needs to be theorized. So called democratic action research involving the implementation by the researcher of democracy as a model and as a preset goal, reduces cooperation and participation into instruments to reach this goal, and becomes a type of social engineering in itself. We argue that the relationship between action research and democracy is in the acknowledgment of the political dimension of participation: ‘a democratic relationship in which both sides exercise power and shared control over decision-making as well as interpretation’. This implies an open research design and methodology able to understand democracy as a learning process and an ongoing experiment