Review of Magnetic Shark Deterrents: Hypothetical Mechanisms and Evidence for Selectivity

Several papers published since 2006 describe effects of magnetic fields on elasmobranchs and assess their utility in reducing negative interactions between sharks and humans, including bycatch reduction. Most of these repeat a single untested hypothesis regarding physical mechanisms by which elasmobranchs detect magnetic fields and also neglect careful consideration of magnetoreception in teleosts. Several species of teleosts are known to have magnetoreception based in biogenic magnetite, and direct magnetic field detection also has support in several species of elasmobranchs. The overly narrow focus of earlier papers on the unsupported hypothesis that magnetoreception in elasmobranchs is based in the ampullae of Lorenzini creates the impression that all teleosts will be insensitive to magnetic deterrents. However, magnetite based magnetoreception has been demonstrated in several teleosts, and is supported in others. Furthermore, electroreception is present in many teleost species; therefore, the possibility of induction based indirect magnetoreception should be considered. Finally, experiments reported as demonstrating insensitivity in teleost species to magnetic deterrents suffer from inadequate design and sample sizes to reject the hypothesis of magnetic detection in any given species. Since adoption of deterrent hook technologies depends on both deterrent effects in sharks and the absence of effects in target teleosts, the hypothesis of detection in teleost species must be independently tested with adequate sample sizes.Comment: 11 page

Experimental Tests of the Proportionality of Aerodynamic Drag to Air Density for Supersonic Projectiles

Pure theory recognizes the dependence of supersonic drag coefficients on both Mach number and Reynolds number, which includes an implicit dependence of drag coefficient on air density. However, many modern approaches to computing trajectories for artillery and small arms treat drag coefficients as a function of Mach number and assume no dependence on Reynolds number. If drag force is strictly proportional to air density for supersonic projectiles (as suggested by applied theory), the drag coefficient should be independent of air density over a range of Mach numbers. Experimental data to directly support this are not widely available for supersonic projectiles. The experiment determined drag on a 2.59 g projectile from M1.2 to M2.9 using optical chronographs to measure initial and final velocities over a separation of 91.44 m. The free flight determination of drag coefficients was performed at two significantly different atmospheric densities (0.93 kg/m3 and 1.15 kg/m3 ). This experiment supported direct proportionality of aerodynamic drag to air density from M1.2 to M2.9 within the experimental error of 1%-2%

Device for Underwater Laboratory Simulation of Unconfined Blast Waves

Shock tubes simulate blast waves to study their effects in air under laboratory conditions; however, few experimental models exist for simulating underwater blast waves that are needed for facilitating experiments in underwater blast transmission, determining injury thresholds in marine animals, validating numerical models, and exploring mitigation strategies for explosive well removals. This method incorporates an oxy-acetylene driven underwater blast simulator which creates peak blast pressures of about 1860 kPa. Shot-to-shot consistency was fair, with an average standard deviation near 150 kPa. Results suggest peak blast pressures from 460 kPa to 1860 kPa are available by adjusting the distance from the source

Terminal Performance of Lead-Free Pistol Bullets in Ballistic Gelatin Using Retarding Force Analysis from High Speed Video

Due to concerns about environmental and industrial hazards of lead, a number of military, law enforcement, and wildlife management agencies are giving careful consideration to lead-free ammunition. The goal of lead-free bullets is to gain the advantages of reduced lead use in the environment while maintaining equal or better terminal performance. Accepting reduced terminal performance would foolishly risk the lives of military and law enforcement personnel. This paper uses the established technique of studying bullet impacts in ballistic gelatin to characterize the terminal performance of eight commercial off-the- shelf lead-free handgun bullets for comparison with earlier analysis of jacketed lead bullets. Peak retarding force and energy deposit in calibrated ballistic gelatin are quantified using high speed video. The temporary stretch cavities and permanent wound cavities are also characterized. Two factors tend to reduce the terminal performance of these lead-free projectiles compared to similar jacketed lead designs. First, solid copper construction increase barrel friction, which reduces muzzle velocity and energy, and thus reduces the ability of the bullet to exert damaging forces in tissue simulant. Second, the lower density of copper requires a longer bullet for a given mass and caliber, which reduces remaining powder volume in the brass cartridge case, which also tends to reduce muzzle velocity and energy. The results of the present study are consistent with earlier analysis showing that expansion is necessary to maximize the potential for rapid incapacitation of enemy combatants. In spite of some new non-expanding nose designs that moderately increase forces between bullet and tissue, the largest retarding forces and highest incapacitation potential requires expanding bullets which maximize frontal area.Comment: 14 page

A method for testing bullets at reduced velocity

Reconstruction of shooting events occasionally requires testing of bullets at velocities significantly below the typical muzzle velocity of cartridge arms. Trajectory, drag, and terminal performance depend strongly on velocity, and realistic results require accurately reconstructing the velocity. A method is presented for testing bullets at reduced velocities by loading the bullet into a sabot and firing from a muzzle loading rifle with a suitably reduced powder charge. Powder charges can be safely reduced to any desirable level when shooting saboted bullets from a muzzleloader; in contrast, cartridge arms can only be safely operated within a narrow window of powder charges/muzzle velocities. This technique is applicable to a wide range of both pistol and rifle bullets at velocities from 700 ft/s to 2000 ft/s

Apparent measurement errors in "Development of biomechanical response corridors of the thorax to blunt ballistic impacts"

"Development of biomechanical response corridors of the thorax to blunt ballistic impacts" (Bir, C., Viano, D., King, A., 2004, Journal of Biomechanics 37, 73-79.) contains apparent measurement errors. Areas under several force vs. time (Fig. 2) and force vs. deflection curves (Fig.4) differ significantly from the momentum and kinetic energy changes, respectively. These differences violate Newton's second law and the work-energy theorem

An Acoustic Method for Determining Ballistic Coefficients

This paper presents a method for using a PC soundcard, microphone and a chronograph to determine bullet BC with an accuracy of 6%. This is useful when a second chronograph is unavailable or when the projectile accuracy is insufficient to use a far chronograph.Comment: Related to forensic science (shooting event reconstruction

Impossible? Publication Quality Research with the Weakest 10% of Incoming Freshmen

Undergraduate research is widely regarded as a high impact practice. However, usually only the highest achieving students are rewarded with undergraduate research opportunities. This paper reports on the successful implementation of a student research program offering the weakest 10% of incoming freshmen opportunities to conduct original research in one of several science or engineering disciplines with the possibility of publication if the research and report meet a suitable standard, defined as earning an A on the final research project report in the introductory math course. The opportunity has been offered now for two years to incoming cadets at the United States Air Force Academy who are placed in Basic Math. The cadets placed in this course score in the bottom 5% of incoming cadets on the math placement exam. During the second semester of their freshman year, cadets enrolled in Calculus 1 are also offered a similar research opportunity. About 10% of cadets are enrolled in this course each Spring, the 5% who began in Basic Math and matriculate to Calculus 1 and the 5% who failed Calculus 1 in their first attempt. During the first four semesters, the program has yielded 22 cadet papers which have been published or are currently under review and expected to be published. This represents approximately 38% of the projects in the program, because the majority of the projects do not earn As and are not suitable for publication. Over 80% of the cadet co-authors on the publication quality papers are minorities, women, and/or intercollegiate athletes.Comment: 12 page

The Truth About Ballistic Coefficients

The ballistic coefficient of a bullet describes how it slows in flight due to air resistance. This article presents experimental determinations of ballistic coefficients showing that the majority of bullets tested have their previously published ballistic coefficients exaggerated from 5-25% by the bullet manufacturers. These exaggerated ballistic coefficients lead to inaccurate predictions of long range bullet drop, retained energy and wind drift.Comment: related to forensic science (shooting event reconstructions

Acoustic measurement of potato cannon velocity

This article describes measurement of potato cannon velocity with a digitized microphone signal. A microphone is attached to the potato cannon muzzle and a potato is fired at an aluminum target about 10 m away. The potato's flight time can be determined from the acoustic waveform by subtracting the time in the barrel and time for sound to return from the target. The potato velocity is simply the flight distance divided by the flight time.Comment: 3 page