Adjustments of wingbeat frequency and air speed to air density in free-flying migratory birds.

Birds adjust their flight behaviour to the physical properties of the air. Lift and drag, the two major properties in aerodynamics, are highly dependent on air density. With decreasing air density drag is reduced and lift per wingbeat decreases. According to flight mechanical theory, wingbeat frequency and air speed should increase with decreasing air density, i.e. increasing flight altitude. Although wind tunnel experiments have shed light on many aspects of avian flight, the effect of air density remained ambiguous, because air density could not be adjusted in wind tunnels, until now. By means of radar we recorded tracks of several thousand free-flying individual birds during nocturnal migration. From these tracks we derived wingbeat frequencies and air speeds covering air densities from 0.84 kg m(-3) to 1.13 kg m(-3), corresponding to an altitudinal range of about 3000 m. We demonstrate here with this sample of nocturnal migrants that: (1) wingbeat frequency decreases with air density (which corresponds to an increase in flap-gliding flyers by 0.4 Hz km(-1) and in bounding flyers by 1.1 Hz km(-1)), (2) reducing wingbeat frequency to equivalent sea level values did not abolish the dependency on air density, as expected by flight mechanical theory, and (3) bounding flyers show a higher response in their flight behavioural adjustments to changes in air density than flap-gliding flyers. With respect to air speed flap-gliding flyers increase their air speed by 1.0 m s(-1) km(-1) and bounding flyers by 1.4 m s(-1) km(-1).

Multiple oscillators are causing parkinsonian and essential tremor.

The tremors of Parkinson's disease (PD) and essential tremor (ET) are traditionally considered to depend on a central oscillator producing rhythmic activation of the motoneurones of all extremities. To test this hypothesis, we have compared electromyographic tremor activity in different muscles of the affected limbs using cross spectral analysis, including coherence and phase. Surface electromyographic recordings from both arms, legs, and the neck were analyzed in 22 patients with PD and 28 patients with ET. Volume conduction between neighboring muscles producing artificial "coherence" has been found to be an important methodologic problem. We have developed a mathematical test to exclude data that could distort the results. According to this test, 10% or 25% of muscle combinations from the same limb had to be excluded from further analysis in PD or ET, respectively. In both, patients with PD and ET, we found a considerable number of muscle combinations oscillating at virtually the same frequency (delta frequency <0.4 Hz) without showing a significant coherence. Thus, the frequency difference between different muscles is not sufficient to measure the correlation between two muscles. Significant coherencies between muscles within the same arm or leg were found in 70% or 90% of patients with PD or ET, respectively, whereas only one patient with PD and not a single patient with ET showed significant coherencies between muscles from different limbs. The phase between coherent muscles of the same arm of patients with PD showed a preference of either a reciprocal alternating pattern for antagonistic muscles in forearm flexor and upper arm extensor as opposed to a co-contraction pattern between the hand flexors and the triceps brachii. In patients with ET such clear differences were lacking. We conclude that multiple oscillators are responsible for the tremor in different extremities of patients with PD and ET. Differences between PD and ET concerning the phase relation within the arm may either be related to the topography within the basal ganglia or to differently involved-spinal pathways.

Dynamics of F=2 spinor Bose-Einstein condensates.

We experimentally investigate and analyze the rich dynamics in F=2 spinor Bose-Einstein condensates of 87Rb. An interplay between mean-field driven spin dynamics and hyperfine-changing losses in addition to interactions with the thermal component is observed. In particular, we measure conversion rates in the range of 10(-12) cm(3) s(-1) for spin-changing collisions within the F=2 manifold and spin-dependent loss rates in the range of 10(-13) cm(3) s(-1) for hyperfine-changing collisions. We observe polar behavior in the F=2 ground state of 87Rb, while we find the F=1 ground state to be ferromagnetic. We further see a magnetization for condensates prepared with nonzero total spin.