The roller coaster flight strategy of bar-headed geese conserves energy during Himalayan migrations.

The physiological and biomechanical requirements of flight at high altitude have been the subject of much interest. Here, we uncover a steep relation between heart rate and wingbeat frequency (raised to the exponent 3.5) and estimated metabolic power and wingbeat frequency (exponent 7) of migratory bar-headed geese. Flight costs increase more rapidly than anticipated as air density declines, which overturns prevailing expectations that this species should maintain high-altitude flight when traversing the Himalayas. Instead, a "roller coaster" strategy, of tracking the underlying terrain and discarding large altitude gains only to recoup them later in the flight with occasional benefits from orographic lift, is shown to be energetically advantageous for flights over the Himalayas.

Interpretation of body-mounted accelerometry in flying animals and estimation of biomechanical power.

An idealized energy fluctuation model of a bird's body undergoing horizontal flapping flight is developed, focusing on the biomechanical power discernible to a body-mounted accelerometer. Expressions for flight body power constructed from root mean square dynamic body accelerations and wingstroke frequency are derived from first principles and presented in dimensionally appropriate units. As wingstroke frequency increases, the model generally predicts a gradual transition in power from a linear to an asymptotically cubic relationship. However, the onset of this transition and the degree to which this occurs depends upon whether and how forward vibrations are exploited for temporary energy storage and retrieval. While this may vary considerably between species and individual birds, it is found that a quadrature phase arrangement is generally advantageous during level flight. Gravity-aligned vertical acceleration always enters into the calculation of body power, but, whenever forward acceleration becomes relevant, its contribution is subtractive. Several novel kinematic measures descriptive of flapping flight are postulated, offering fresh insights into the processes involved in airborne locomotion. The limitations of the model are briefly discussed, and departures from its predictions during ascending and descending flight evaluated. These findings highlight how body-mounted accelerometers can offer a valuable, insightful and non-invasive technique for investigating the flight of free-ranging birds and bats.

In vitro acid reactivity of three commercial antacid tablets.

The in vitro acid reactivity of three commercial brands of aluminum and magnesium hydroxide antacid tablets was determined by two methods. A pH-stat test was used to examine the rate and extent of acid neutralization at a constant pH of 3.0. A modified Rossett-Rice test was used to record the length of time during which the antacid products maintained the pH of a simulated gastric solution at between 3.0 and 5.0. Acid neutralization by product A was faster and more complete than that by product B or C. The percent of theoretical acid consuming capacity at 30 minutes of product A (86.8%) was significantly greater than that of product B (56.1%) and product C (57.0%) tablets. The 32-minute Rosett-Rice time A was significantly longer than the 16- and 12-minute times of products B and C, respectively. The differences observed may be attributed to different reactivities of the raw materials used in the products, or formulation and processing variables. It is not known how the data relate to in vivo performance.

Chelates of dicumarol I: Preparation and structure identification of magnesium chelate.

A magnesium chelate of dicumarol was prepared by reacting a suspension of dicumarol and magnesium oxide in 50% water-methanol. GLC, thermogravimetric, and elemental analyses showed that this compound has a 2:1 ligand-metal stoichiometry with 2 moles of water associated with the complex. Although the chelate does not melt, two endothermic peaks at 205 and 274 degrees were observed in the thermogram, in contrast to a single endothermic peak corresponding to a melting point of 288 degrees for dicumarol. IR spectroscopy indicated that the magnesium is bonded between the carbonyl at C-2 and the oxygen at C-4' (or vice versa).