Echolocating bats emit a highly directional sonar sound beam in the field

Bats use echolocation or biosonar to navigate and find prey at night. They emit short ultrasonic calls and listen for reflected echoes. The beam width of the calls is central to the function of the sonar, but directionality of echolocation calls has never been measured from bats flying in the wild. We used a microphone array to record sounds and determine horizontal directionality for echolocation calls of the trawling Daubenton's bat, Myotis daubentonii, flying over a pond in its natural habitat. Myotis daubentonii emitted highly directional calls in the field. Directionality increased with frequency. At 40 kHz half-amplitude angle was 25°, decreasing to 14° at 75 kHz. In the laboratory, M. daubentonii emitted less intense and less directional calls. At 55 kHz half-amplitude angle was 40° in the laboratory versus 20° in the field. The relationship between frequency and directionality can be explained by the simple piston model. The model also suggests that the increase in the emitted intensity in the field is caused by the increased directionality, focusing sound energy in the forward direction. The bat may increase directionality by opening the mouth wider to emit a louder, narrower beam in the wild

Free surface flows emerging from beneath a semi-infinite plate with constant vorticity

The free surface flow past a semi-infinite horizontal plate in a finite-depth fluid is considered. It is assumed that the fluid is incompressible and inviscid and that the flow approaches a uniform shear flow downstream. Exact relations are derived using conservation of mass and momentum for the case where the downstream free surface is flat. The complete nonlinear problem is solved numerically using a boundary integral method and these waveless solutions are shown to exist only when the height of the plate above the bottom is greater than the height of the uniform shear flow. Interesting results are found for various values of the constant vorticity. Solutions with downstream surface waves are also considered, and nonlinear results of this type are compared with linear results found previously. These solutions can be used to model the flow near the stern of a (two-dimensional) ship

Please Welcome Our First Academic Editor-in-Chief

The PLoS Biology Editors explain the background to Jonathan Eisen's appointment as the journal's first Academic Editor-in-Chief

Magnitude and implications of spontaneous hemodynamic variability in primary pulmonary hypertension

The pulmonary artery (PA) pressure and pulmonary resistance at rest have been noted to vary spontaneously in patients with primary pulmonary hypertension. To evaluate this variation, in 12 patients (8 women, 4 men, aged 43 +/- 13 years), hourly measurements were made for 6 consecutive hours of heart rate, systemic and PA pressures, cardiac output, systemic and pulmonary resistance. After these baseline measurements the patients were tested with hydralazine and nifedipine therapy. Spontaneous variability in pulmonary pressures and resistances occurred in each patient, with the amount of variation (coefficient of variation) in PA pressure averaging 8% and in total pulmonary resistance 13% over the 6 hours. The patients with the most variability in mean PA pressure also had the most variability in cardiac output (r = 0.69, P = 0.02). Variability also correlated with the severity of the disease, as the patients with the highest total pulmonary resistances also had the most variation for that factor (r = 0.91, p < 0.01). The amount of variability did not correlate, however, with the acute response to either hydralazine or nifedipine administration. Based on the average coefficients of variation in these 12 patients, estimates were obtained of the percent change needed for an observed change to be attributed to a drug effect with 95% confidence. From these estimates, it was projected that for a single patient, a mean change in pulmonary resistance of 36% or a mean change in PA pressure of 22% would be required in order to attribute the changes to a drug effect. Thus, spontaneous hemodynamic variability is a common phenomenon in patients with primary pulmonary hypertension and may account for substantial changes in PA pressure and pulmonary resistance at rest.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/25855/1/0000418.pd

The simulation of the activity dependent neural network growth

It is currently accepted that cortical maps are dynamic constructions that are altered in response to external input. Experience-dependent structural changes in cortical microcurcuts lead to changes of activity, i.e. to changes in information encoded. Specific patterns of external stimulation can lead to creation of new synaptic connections between neurons. The calcium influxes controlled by neuronal activity regulate the processes of neurotrophic factors released by neurons, growth cones movement and synapse differentiation in developing neural systems. We propose a model for description and investigation of the activity dependent development of neural networks. The dynamics of the network parameters (activity, diffusion of axon guidance chemicals, growth cone position) is described by a closed set of differential equations. The model presented here describes the development of neural networks under the assumption of activity dependent axon guidance molecules. Numerical simulation shows that morpholess neurons compromise the development of cortical connectivity.Comment: 10 pages, 2 figure