Range discrimination by big brown bats (Eptesicus fuscus) using altered model echoes: implications for signal processing

The sonar emissions of two big brown bats (Eptesicus fuscus) were modeled to create a "normal" echolocation signal for each bat which was then used as an artificial echo to synthesize a phantom target. The bat's task was to indicate which of two phantom targets (presented singly) was the "near" target and which the "far" target. Threshold range discrimination at a nominal target distance of 80 cm was about 0.6 cm for both bats. The normal signal was then modified to change the relative energy in each harmonic, the signal duration, the curvature of the frequency sweep, the absolute frequency, the phase of the second and third harmonics relative to the first, or the Doppler shift of the signal. To determine which modifications affected ranging performance, the altered models were used in tests of range discrimination that were interleaved on a day-to-day basis with tests using the normal model. Of the 12 modifications tested, only those changing the curvature of the frequency sweep affected performance. This result appears not to be predicted by current models of echo processing in FM bats. Eptesicus may be able to compensate for certain types of distortions of a returning echo, an ability possibly related to Doppler tolerance or to the characteristics of the natural variation in a bat's emissions.     

Polyurethane/Dermatan Sulfate Copolymers as Hemocompatible,Non‐Biofouling Materials

The range of application of polyurethanes has been limited by their poor hemocompatibility and inability to resist non‐specific binding of biomolecules and cells. In this work, a non‐adhesive PU‐based material was synthesized via the copolymerization of PU with dermatan sulfate. Incorporation of DS into the PU backbone dramatically increased material hydrophilicity and decreased protein adsorption. The in vitro adhesion of several cell types, including platelets, also significantly decreased with increasing DS content. Both the physical and biological properties of the DS contributed to the anti‐adhesive properties of the PU/DS copolymer, and this anti‐adhesive nature of PU/DS renders this new biomaterial attractive for blood‐contacting or non‐fouling applications.

     

Unusual asymmetry in halobenzenes,a solid-state,gas-phase and theoretical investigation

The molecular structures of 1-Br-4-F-C₆H₄ and 1-Cl-4-F-C₆H₄ have been studied in the gas phase using gas electron diffraction (GED) and ab initio methods. The structure of 1-Cl,4-F-C₆H₄ in the crystalline phase has also been studied, but whilst the gaseous structures were found to possess C _2v symmetry, the solid-state structure was found to be quite distorted, with three molecules in the asymmetric unit. These fragments only possess C _s symmetry in the plane of the molecules, as opposed to the C _2v symmetry observed in the gas phase. The bonding motifs within the solid-state structure are very unusual and unexpected, with quite different C–F bond lengths for the three moieties, and are a result of weak hydrogen-halogen interactions within the structure.