40,379 research outputs found
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
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
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
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