We observe counter-intuitive spin segregation in an inhomogeneous sample of ultra-cold, noncondensed Rubidium atoms in a magnetic trap. We use spatially selective microwave spectroscopy to verify a model that accounts for the differential forces on two internal spin states. In any simple understanding of the cloud dynamics, the forces are far too small to account for the dramatic transient spin polarizations observed. The underlying mechanism remains to be elucidated.

We designed and constructed a simplified experimental system to create a Bose-Einstein condensate in 87 Rb. Our system has several novel features including a mechanical atom transfer mechanism and a hybrid Ioffe-Pritchard magnetic trap. The apparatus has been designed to consistently produce a stable condensate even when it is not well optimized.

The release of stored elastic energy often drives rapid movements in animal systems, and plant components employing this mechanism should be able to move with similar speed. Here we describe how the flower stamens of the bunchberry dogwood (Cornus canadensis) rely on this principle to catapult pollen into the air as the flower opens explosively. Our high-speed video observations show that the flower opens in less than 0.5 ms--to our knowledge, the fastest movement so far recorded in a plant.

No abstract

Sphagnum spores, which have low terminal velocities, are carried by turbulent wind currents to establish colonies many kilometers away. However, spores that are easily kept aloft are also rapidly decelerated in still air; thus, dispersal range depends strongly on release height. Vascular plants grow tall to lift spores into sufficient wind currents for dispersal, but nonvascular plants such as Sphagnum cannot grow sufficiently high. High-speed videos show that exploding capsules of Sphagnum generate vortex rings to efficiently carry spores high enough to be dispersed by turbulent air currents. Spores launched ballistically at similar speeds through still air would travel a few millimeters and not easily reach turbulent air. Vortex rings are used by animals; here, we report vortex rings generated by plants.

There was an error published in J. Exp. Biol. 213, 2551-2556 The two mite species studied were incorrectly identified as members of the family Teneriffiidae. Both are actually members of the closely related family Erythracaridae. Species 1 is Paratarsotomus macropalpis (Banks 1916) while the species identification of Species 2 remains undetermined. We are grateful to Dr Mark Judson (Museum of Natural History, Paris) for spotting the misidentification and providing the identification for P. macropalpis.The authors apologize sincerely to readers for this error.

Fruits of (Acanthaceae) explosively launch small (2.5 mm diameter × 0.46 mm thick), disc-shaped seeds at velocities over 15 m s, reaching distances of up to 7 m. Through high-speed video analysis, we observe that seeds fly with extraordinary backspin of up to 1660 Hz. By modelling the seeds as spinning discs, we show that flying with backspin is stable against gyroscopic precession. This stable backspin orientation minimizes the frontal area during flight, decreasing drag force on the seeds and thus increasing dispersal distance. From high-speed video of the seeds' flight, we experimentally determine drag forces that are 40% less than those calculated for a sphere of the same volume and density. This reduces the energy costs for seed dispersal by up to a factor of five.

The Southern California endemic mite Paratarsotomus macropalpis was filmed in the field on a concrete substrate and in the lab to analyze stride frequency, gait and running speed under different temperature conditions and during turning. At ground temperatures ranging from 45 to 60°C, mites ran at a mean relative speed of 192.4±2.1 body lengths (BL) s , exceeding the highest previously documented value for a land animal by 12.5%. Stride frequencies were also exceptionally high (up to 135 Hz), and increased with substrate temperature. Juveniles exhibited higher relative speeds than adults and possess proportionally longer legs, which allow for greater relative stride lengths. Although mites accelerated and decelerated rapidly during straight running (7.2±1.2 and −10.1±2.1 m s −2 , respectively), the forces involved were comparable to those found in other animals. Paratarsotomus macropalpis employs an alternating tetrapod gait during steady running. Shallow turns were accomplished by a simple asymmetry in stride length. During tight turns, mites pivoted around the tarsus of the inside third leg (L3), which thus behaved like a grappling hook. Pivot turns were characterized by a 42% decrease in turning radius and a 40% increase in angular velocity compared with non-pivot turns. The joint angle amplitudes of the inner L2 and L3 were negligible during a pivot turn. While exceptional, running speeds in P. macropalpis approximate values predicted from inter-specific scaling relationships.