Effects of sphere suspension on echosounder calibrations

Echosounders may be calibrated by suspending a solid metal sphere in the acoustic beam and adjusting the system gain so that the measured target strength (TS) equals the theoretical value for the sphere. The suspension apparatus (i.e. net bag or loop of line glued into a hole, and control lines) may appreciably scatter sound, potentially affecting the sphere-echo intensity and phase, and hence the calibration uncertainty. Here, we characterize the effects of conventional suspension materials and configurations on measurements of sphere TS and recommend approaches to mitigate the observed effects on echosounder calibrations. We show that the effects of suspension lines on both calibration accuracy and precision change with line type and increase with line diameter and acoustic frequencies above ∼100 kHz. Compared to commonly used polyamide (nylon) line, ultra-high-molecular-weight polyethylene (PE) line has an acoustic impedance closer to that of water and therefore has a lessened effect on measurements of sphere TS. The effects may be mitigated in a practical manner using a 0.38-mm diameter, multifilament, PE line for the suspension.

Acoustic and stiffness properties of gillnets as they relate to small cetacean bycatch

Mooney, T. A., Au, W. W. L., Nachtigall, P. E., and Trippel, E. A. 2007. Acoustic and stiffness properties of gillnets as they relate to small cetacean bycatch. – ICES Journal of Marine Science, 64: 1324–1332. Small cetaceans are incidental bycatch in gillnet fisheries. Dolphin and porpoise bycatch has been reduced by the use of barium sulphate-enhanced gillnets. This decreased entanglement is likely the result of either higher acoustic reflectivity or greater stiffness for barium nets. To address these variables, our study quantified the acoustic reflectivity and stiffness of six net types including barium sulphate, iron oxide-enhanced and control demersal gillnets of sizes which typically target cod (Gadus morhua) and monkfish (Lophius americanus). Acoustic reflectivity, or target strength (TS), was assessed using dolphin and porpoise-like sonar signals from 0° to 40°. TS values were used to calculate likely detection ranges. Barium sulphate- and iron oxide-enhanced nets showed increased reflectivity compared with control nets, with the barium sulphate nets generating the highest TS values. Dolphins should detect these nets in time to avoid contact, but porpoises, with typically lower source levels, may not detect nets at a range great enough to avoid entanglement. Barium sulphate line was significantly stiffer than comparable nylon line. All lines lost stiffness when soaked in seawater for 24 h. Barium sulphate nets proved stiffer and more acoustically reflective, and both factors are likely important in reducing harbour porpoise bycatch.

Biomechanical Evaluation of the Suitability of Monofilament Nylon Fishing and Leader Line for Extra-articular Stabilisation of the Canine Cruciate-deficient Stifle

SummaryThe use of monofilament nylon line for extra-articular stabilisation of the cruciate deficient canine stifle is widespread in veterinary surgery. The purpose of this study was twofold: 1) to examine the mechanical behaviour of two forms of monofilament line - standard nylon fishing line (NFL) and nylon leader line (NLL) - when sterilised by steam or ethylene oxide and formed into loops approximating their use in the clinical situation; 2) to compare the mechanical performance of the canine fabellar attachment site to the steel hooks used in the first part of the study.It was found that NLL loops were not affected by sterilisation and had higher failure loads and stiffness than NFL loops. Further testing of 27-kilo - gram-test (kgt) and 36 kgt steam-sterilised NFL and NLL found that of the materials tested, NLL 27 kgt was most suitable as an extra-articular stabiliser of the canine stifle. The performance of the fabellar attachment site was superior to the steel hooks when cycled to 50 N and inferior when cycled to 100 N.The suitability of monofilament nylon fishing line (NFL) and monofilament nylon leader line (NLL) for use as lateral fabel-lotibial sutures (LFTS) in canine cranial cruciate ligament repair was investigated. In vitro testing of loops of the materials was performed with steel hook and fabellar attachment points. Twenty-seven-kilogram test NLL was found to be the most suitable nylon line from which to construct an LFTS.

A Method for Measuring Tension in Small Ligaments: An Application to the Ligaments of the Wrist Carpus

A new technique has been devised for measuring the in situ tension in small ligaments. It is based on measuring the tension in an axially loaded flexible cable with pinned endpoints by deflecting the cable laterally and measuring its lateral load and deformation. Studies were performed in which nylon line and bone ligament bone preparations were placed in a materials tester and loaded in axial tension. Axial load as measured by lateral load and deformation was found to agree with the known load to within 8 percent. The method was sensitive to error in determination of ligament length, nonperpendicularity of the laterally applied load to the long axis of the ligament, and when used in situ, impingement of the ligament on a third bone causing bending. A device, consisting of an LVDT mounted to a rigid frame with its core rod connected to a load cell, was developed. The position of the core rod was controlled by a manual screw drive, and a hook on the other end of the core rod was used to deflect the ligament laterally. This device was applied to the study of tensions in five ligaments of the palmar wrist carpus, in seven cadaver specimens. Results showed that the radioscaphocapitate (RSC) and radiolunate (RL) ligaments had significantly greater tensions than the lunotriquetral (LT), the triquetrocapitate (TC), and scaphocapitate (SC) ligaments. For the four positions of the hand tested, neutral, 14 deg radial and 14 deg ulnar deviation, and 28 deg of extension, ligament tensions were found to be unaffected by position. In all positions tested, all ligaments had measurable tension, demonstrating the importance of ligaments in maintaining the integrity of the wrist carpus.

Scandinavian Thinning Techniques in a Natural Northeastern Softwood Stand

The applicability of Scandinavian thinning techniques to small-diameter northeastern softwood stands was tested in a hemlock stand in central Maine. Cutting used motormanual techniques in which the cutter felled, limbed, bucked and piled 8-ft bolts for extraction to trailside by a small tractor and winch. Sixteen-foot lengths were also cut in order to compare the relative merits of the two sizes. To simulate radio control, the winch was activated by a retractable nylon line that permitted the operator to control it remotely from within the stand. A small, tracked forwarder transported the wood to roadside landings. Total roadside cost of the operation was $42.86 per cord, but a cost of $37.87 is considered attainable. The most expensive and most difficult to improve function is cutting, which is most influenced by the small tree size. In this case, 27.5 trees were cut per cord, compared with 10-15 found in most commercial operations. Costs are unacceptable, but the technique may be viable for woodlot owners with limited equipment and low wage requirements. North. J. Appl. For. 4:38-42, March 1987

Construction of a multipolar electrode system referenced and anchored to endocardium for study of arrhythmias

We developed a Teflon plunge electrode system (Teflon plunge) with important advantages over currently used electrodes. The Teflon plunge consists of an anchor-introducer (anchor) attached to the tip of an 0.8-mm diam epoxy-filled Teflon tube supporting six bipolar recording sites. The plunge is inserted through the myocardium into the ventricular cavity perpendicular to the epicardium. Once in the left ventricular cavity the anchor at the tip of the plunge pivots perpendicular to the long axis of the plunge and seats on the endocardium. It is maintained in position with a 4-0 nylon line (line) that extends from its attachment to the anchor through the body of the plunge to the epicardial end where it is secured with a Ligaclip. Thus the electrode contacts are placed a predetermined distance from the endocardium. When the Ligaclip is released, the plunge is removed from the heart leaving the line in the track of the electrode attached to the anchor as a marker for histological studies. The Teflon plunge will facilitate the evaluation of the role of the endocardium in ventricular arrhythmias by locating recording sites a stable, known distance from the endocardium and by marking the electrode track for histological studies.