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%

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

Ballistic pressure wave contributions to rapid incapacitation in the Strasbourg goat tests

This article presents empirical models for the relationship between peak ballistic pressure wave magnitude and incapacitation times in the Strasbourg goat test data. Using a model with the expected limiting behavior at large and small pressure wave magnitudes, the average incapacitation times are highly correlated (R = 0.91) with peak pressure wave magnitude. The cumulative incapacitation probability as a function of time reveals both fast (t < 5 s) and slow (t > 5 s) incapacitation mechanisms. The fast incapacitation mechanism can be accurately modeled as a function of peak pressure wave magnitude. The slow incapacitation mechanism is presumably due to blood loss via damaged vascular tissue.Comment: Related to traumatic brain injur

Epistemological Distinctions Between Science and History

This article describes epistemological distinctions between science and history. Science investigates models of natural law using repeatable experiments as the ultimate arbiter. In contrast, history investigates past events by considering physical evidence, documentary evidence, and eyewitness testimony. Because questions of natural law are repeatably testable by any audience that exercises due experimental care, models of natural law are inherently more objective and testable with greater certainty than theories of past events.Comment: three page