Optimal movement in the prey strikes of weakly electric fish: a case study of the interplay of body plan and movement capability

Animal behaviour arises through a complex mixture of biomechanical, neuronal, sensory and control constraints. By focusing on a simple, stereotyped movement, the prey capture strike of a weakly electric fish, we show that the trajectory of a strike is one which minimizes effort. Specifically, we model the fish as a rigid ellipsoid moving through a fluid with no viscosity, governed by Kirchhoff's equations. This formulation allows us to exploit methods of discrete mechanics and optimal control to compute idealized fish trajectories that minimize a cost function. We compare these with the measured prey capture strikes of weakly electric fish from a previous study. The fish has certain movement limitations that are not incorporated in the mathematical model, such as not being able to move sideways. Nonetheless, we show quantitatively that the computed least-cost trajectories are remarkably similar to the measured trajectories. Since, in this simplified model, the basic geometry of the idealized fish determines the favourable modes of movement, this suggests a high degree of influence between body shape and movement capability. Simplified minimal models and optimization methods can give significant insight into how body morphology and movement capability are closely attuned in fish locomotion.     

Solid-solution hardening and Vegard's rule of In1-xGaxSb

The solid-solution hardening of In1-xGaxSb was investigated by means of Vickers indentation microhardness measurements. It shows two hardness peaks and deviates considerably, on that account, from II–VI cation solid solutions which were investigated previously, as well as from solid solutions with preferentially either metallic or ionic bonds known from the literature. Vegard's rule, as a linear lattice parameter–composition relation, is valid for In1-xGaxSb. © 1998 Kluwer Academic Publishers     

Microwave and far-infrared propagation in conductive microstructured composites

In a recent publication [T.E. Huber, L. Luo, Appl. Phys. Lett. 70 (1997) 2502.] we discussed a structural enhancement of the electromagnetic transmission in composites. We showed that densely packed arrays (76% volume fraction) of 10 μm diameter parallel indium wires exhibit an enhanced transmission, of 10³, relative to an indium foil of equal thickness for far-infrared (10 cm⁻¹ < k < 80 cm⁻¹) propagating along the wire length. The absorption increases as k^{0.45 ± 0.07} and is explained by the dynamic Maxwell-Gannett model, which includes eddy current dissipation. It is of considerable practical interest to extend the range of application of these composite properties to the microwave domain. Here we will discuss recent measurements of the transmission of microwaves in wire array composites in the 8–12 GHz frequency range.     

Thermal effects on the forward characteristics of silicon p-i-n diodes at high pulse currents

When applying high pulse currents, the resulting temperature increase in the base regions of p-i-n diodes and thyristors leads to notable changes in the forward characteristics. (I) Decrease of carrier mobility noticeably increases the voltage drop across the diode and tends to limit the current density. (II) When the temperatures are sufficiently high to supply high intrinsic carrier concentrations, the temperature coefficient of the resistivity becomes negative. This can lead to current localization and destruction of the diodes.

To study these effects, the temperature of the base regions was monitored during high pulse currents using thermal i.r. emission. Indication for current limit occurs above 200°C, when the diodes are heated from room temperature. The negative temperature coefficient of the resistivity occurs at temperatures at which the intrinsic carrier concentration has reached the same order of magnitude as the injected carrier density. Simple theoretical treatment yields reasonably good agreement with the experimental results.     

Ejaculatory duct obstruction

The diagnosis, long-range pathophysiology and surgical approach to ejaculatory duct obstruction are presented. Of 5 cases 3 had epididymal extravasation from long-term pressure buildup and secondary epididymal obstruction. This is similar to the epididymal findings after long-term vasectomy.     

Moving current filaments in integrated DMOS transistors under short-duration current stress

Integrated vertical DMOS transistors of a 90-V smart power technology are studied under short-duration current pulses. Movement of current filaments and multiple hot spots observed by transient interferometric mapping under nondestructive snap-back conditions are reported. Device simulations show that the base push-out region associated with the filament can move from cell to cell along the drain buried layer due to the decrease of the avalanche generation rates by increasing temperature. The influence of the termination layout of the source field on the hot-spot dynamics is studied. Conditions for filament motion are discussed. The described mechanisms help homogenizing the time averaged current-density distribution and enhance the device robustness against electrostatic discharges.     

Successful management of low-stage neuroblastoma without adjuvant therapies: a comparison of two decades, 1972 through 1981 and 1982 through 1992, in a single institution

PURPOSE: A review was undertaken of 119 children seen at the Children's Hospital of Philadelphia between 1972 and 1992 to assess the impact of adjuvant therapies for patients with low-stage neuroblastoma (NBL). PATIENTS AND METHODS: Twenty-one of 119 International Neuroblastoma Staging System (INSS) stage 1, 2a, 2b, and 4s patients seen received initial adjuvant treatment postoperatively and 98 did not. The patients were further subdivided according to decade, age, presence of residual disease, and lymph node status. Outcomes were then compared. RESULTS: The event-free survival (EFS) rate for those who received adjuvant therapy was 52% versus 86% for those who did not. The 5-year survival rate was 68% and 94%, respectively. Age (< or > 12 months), extent of residual disease, and status of lymph nodes did not influence survival. Over the two decades, the reasons for selecting treatment changed as new and powerful additional prognostic factors were identified; 71% of patients received no adjuvant treatment in the first decade, compared with 90% in the second. EFS rates for untreated patients by decade were 79% and 89%, and 5-year survival rates were 85% and 98%, respectively. CONCLUSION: It is possible to define most low-stage NBL as favorable-even in patients with positive lymph nodes and gross residual disease-and to omit initial adjuvant treatments successfully.