Ballistic Conditions Research Articles

Structure of aluminum atomic chains

First-principles density functional calculations reveal that aluminum can form planar chains in zigzag and ladder structures. The most stable one has equilateral triangular geometry with four nearest neighbors; the other stable zigzag structure has wide bond angle and allows for two nearest neighbors. An intermediary structure has the ladder geometry and is formed by two strands. All these planar geometries are, however, more favored energetically than the linear chain. We found that by going from bulk to a chain the character of bonding changes and acquires directionality. The conductance of zigzag and linear chains is 4e^2/h under ideal ballistic conditions.

Fluctuations in the number of irreversibly adsorbed particles

Fluctuations in the number of colloid particles adsorbed irreversibly under pure diffusion transport conditions were determined as a function of surface density and ionic strength of the suspension. The experiments were carried out for monodisperse polystyrene latex particles of micrometer size range adsorbing irreversibly at mica surface. The surface density of adsorbed particles at various areas was determined using the direct microscope observation method. A new experimental cell was used enabling in situ observations of particles adsorption under conditions of negligible gravity effects. It was found that the particle density fluctuations for high ionic strength were in a good agreement with the theoretical results derived from the random sequential adsorption (RSA) model. Also, the theoretical results stemming from the equilibrium scaled particle theory reflected the experimental data satisfactorily. For lower ionic strength a deviation from the hard sphere behavior was experimentally demonstrated. This effect due to the repulsive electrostatic interactions was interpreted in terms of the effective hard particle concept. The universal dependence of variance on particle density obtained in this way was found in a good agreement with the RSA model for all ionic strength. These results proved that fluctuations in particle density of monolayer formed under diffusional conditions differ fundamentally from these obtained under ballistic transport conditions.

Chain composites under ballistic impact conditions

An existing family of composites of steel chains in resin matrices that exhibit delocalized failure and high levels of energy absorption under static tensile loading has been tested under high-velocity impact conditions. Panels of chain composites were shot with anti-personnel rounds in an instrumented test range. The tests demonstrate that the lockup mechanism operates at strain rates approaching 10 4 s −1, with delocalized damage extending in several cases from the impact site to the edge of the test panel. Estimates of the energy absorbed per unit volume under impact conditions range from 30 to 75 MJ/m 2, approximately 50–60% higher than values measured in static tension for the same composites. The enhancement of energy absorption is tentatively attributed to strengthening of the resin at high strain rates. Implications of the tests for designing ballistic protection are discussed.

Evaluation of Knee Extensor Muscles under Non-Isokinetic Conditions in Elderly Subjects

This paper describes the application of the inverse dynamic method developed by Bosco and colleagues for measuring the mechanical properties of knee extensor muscles under ballistic conditions. Twenty elderly men performed a series of maximal ballistic leg extensions at different loads. Accurate measurements of friction and inertial effects during the movement were used to calculate the torque and power produced during extension. The error of the results was 6.2–45.3% when the friction and inertial effects were neglected. The torque-angular velocity relationships were linear (r = 0.92 to 0.99, p < .001). The peak measurements obtained were in agreement with published isokinetic values. This new ergometer allows assessment of movements similar to those performed in day-to-day activities and can be used. without training, by elderly or disabled subjects.

Frequency response of spine extensors during rapid isometric contractions: effects of muscle length and tension

During muscle contraction, electrical activity necessarily precedes force output, yet models that utilize processed electromyograms sometimes predict force as preceding EMG under rapid ballistic loading conditions. The purpose of this study was to define the frequency response transfer function of the upper and lower erector spinae musculature, at different lengths and tensions, using rectified, low pass filtered EMG. This would enable accurate estimates of force from the processed electromyogram, specifically during impulsive contractions. Abdominal and erector spinae EMG were measured in synchrony with impulsive low back moments in five men. EMG signals were rectified and low pass filtered repeatedly with cut-off frequencies from 1 to 3 Hz at 0.5 Hz increments in order to quantify the frequency response. It was found that EMG signals processed through a simple, Butterworth low pass filter could not produce the measured force output without an additional time shift. These shifts were quantified by cross-correlating EMG and force with increments of 1 ms. In order to define the transfer function of EMG to force, optimal cut-off frequencies were selected two ways: quantitatively by searching for maximum cross correlations coefficients, and qualitatively. Results indicated that the frequency response of both the upper and lower erector spinae can be modelled with a cut-off frequency between 2 and 2.5 Hz and that these values are not significantly modulated by changes in muscle length or tension.

Penetration and Perforation of Composite Sandwich Panels by Hemispherical and Conical Projectiles

The results of penetration and perforation tests carried out on composite sandwich panels with GRP skins and PVC foam cores using hemispherical-ended and conical-nosed indenters/projectiles under quasi-static, drop-weight, and ballistic impact conditions, with impact velocities up to 305 m/s, are described. Load-displacement characteristics under quasi-static loading are presented and the ballistic limits as well as perforation energies are determined. A classification of the sandwich panel responses based on the panel thickness-to-projectile diameter ratio is deduced. General empirical formulas that predict the dynamic perforation energies for FRP laminates and composite sandwich panels loaded by hemispherical-ended projectiles are derived. The empirical equations correlate well with available experimental data. It is shown that, to a first approximation, the formulas obtained for hemispherical-ended projectiles are also applicable to conical-nosed projectiles.

Quasi-static impact damage in confined ceramic tiles

The effect of confinement on the failure mechanisms in dense alumina tiles during the penetration of a projectile was investigated and the role played by lateral mechanical confinement in inhibiting some failure modes was examined. Alumina tiles were placed in a confinement frame which simply and accurately allows high biaxial compressive pre-stresses. The confinement frame is a modular system which enables the application of various boundary conditions on the impacted tile to be generated. Tile samples were supported by semi-infinite support blocks made of steel or aluminum, and were confined by steel wedges. In the tests carried out under ballistic penetration conditions, the confined tiles were impacted by 0.3 cal. NATO AP (armor piercing) projectiles. These contained a hardened steel cone-shaped core with a sharp tip. In this investigation, the effect of reflected stress waves was small or even negligible, since the tile/support impedance mismatch was low, so that quasi-static failure mechanisms predominated. The effect of tile thickness on the damage mechanisms was also examined. Under the described test conditions, the major failure modes were radial cracks, cone crack, and fragmentation of the cone. Confined tiles exhibited reduced damage; damage in the form of radial cracks was reduced, and cone crack and fragmentation of the cone were inhibited. Based on the theory of a plate on an elastic foundation, the quasi-static loads that initiate the radial cracks were formulated. This model assists in understanding the initial damage mechanism.

Origin of conductance quantization

It is well known that for an ideal one-dimensional conductor under ballistic transport conditions the conductance is transversally quantized in steps of 2 e 2/ h as the constriction width is varied. We essentially obtain this quantization by invoking the uncertainty principle in conjunction with the definition of transport in the quantum limit. The finite resistance of a perfect conductor, which has been previously understood in terms of contact effects, can thus also be viewed as having a quantum mechanical origin in the uncertainty principle. Having analyzed the quantization using simple arguments, we observe that the quantized Hall resistance shows similar step structure, and hence may be similarly motivated.

Effect of long-range Coulomb interaction on shot-noise suppression in ballistic transport

We present a microscopic analysis of shot-noise suppression due to long-range Coulomb interaction in semiconductor devices under ballistic transport conditions. An ensemble Monte Carlo simulator self-consistently coupled with a Poisson solver is used for the calculations. A wide range of injection-rate densities leading to different degrees of suppression is investigated. A sharp tendency of noise suppression at increasing injection densities is found to scale with a dimensionless Debye length related to the importance of space-charge effects in the structure.

Improved ballistic transient transformation conditions for tomato fruit allow identification of organ-specific contributions of I-box and G-box to the RBCS2 promoter activity.

An improved protocol for the ballistic transient transformation of developing tomato (Lycopersicon esculentum) fruits is reported, which allows high-resolution cis-analysis of fruit-specific transcriptional activation. The tomato RBCS2 promoter fused to the firefly luciferase gene was used as a model system for this study. Osmotic treatment of fruit slices before, during and after particle bombardment, together with the optimization of bombardment conditions, resulted in a 100-fold increase in RBCS2 promoter-driven transient luciferase expression compared with previously reported protocols. Under these conditions, the transformed RBCS2 promoter was shown to be properly regulated in a developmental fashion. A cis-analysis of the RBCS2 promoter was performed. A 37 bp domain is required for high-level RBCS2 promoter activity both in leaves and young fruits. Two conserved sequence elements within this domain, an I-box element (GATAAG) and a G-box element (CACGTG), are necessary for its activity in leaves. In contrast, in young fruits, the G-box is the single dominant cis-acting element. These findings are discussed with respect to the proposed functions of G-box and I-box binding factors in regulating plant genes in different organs.

A universal thermal conductance of charge carriers

A universal thermal conductance of charge carriersK=2π2 k B 2 T/(3h) is rigorously derived within a correlation-function formalism. Similar to the case of the universal electrical conductanceG=2e 2 /h this result pertains to one-dimensional, ballistic, and degenerate conditions for non-interacting particles.

Current-driven excitation of magnetic multilayers

A new mechanism is proposed for exciting the magnetic state of a ferromagnet. Assuming ballistic conditions and using WKB wave functions, we predict that a transfer of vectorial spin accompanies an electric current flowing perpendicular to two parallel magnetic films connected by a normal metallic spacer. This spin transfer drives motions of the two magnetization vectors within their instantaneously common plane. Consequent new mesoscopic precession and switching phenomena with potential applications are predicted.

A comparative study of the energy resolution achievable with digital signal processors in X-ray spectroscopy

Interest for digital processing of signals from radiation detectors is subject to a growing attention due to its intrinsic adaptivity, easiness of calibration, etc. This work compares two digital processing methods: a multiple-delay-line (DL)/sup N/ filter and a least-mean-squares (LMS) adaptive filter for applications in high resolution X-ray spectroscopy. The signal pulse, as appears at the output of a proper analog conditioning circuit, is digitized: the samples undergo a digital filtering procedure. Both digital filters take advantage of the possibility of synthesizing the best possible weighting function with respect to the actual noise conditions. A noticeable improvement of more than 10% in energy resolution has been achieved with both systems with respect to state-of-the-art systems based on analog circuitry. In particular, the two digital processors are shown to be the best choice respectively: for on-line use with critical ballistic deficit conditions and for very-high-resolution spectroscopy systems, ultimately limited by 1/f noise.

Kinematics, Kinetics, and Muscle Activation during Explosive Upper Body Movements

The aim of this study was to investigate the kinematics, kinetics, and neural activation of the traditional bench press movement performed explosively and the explosive bench throw in which the barbell was projected from the hands. Seventeen male subjects completed three trials with a bar weight of 45% of the subject's previously determined 1RM. Performance was significantly higher during the throw movement compared to the press for average velocity, peak velocity, average force, average power, and peak power. Average muscle activity during the concentric phase for pectoralis major, anterior deltoid, triceps brachii, and biceps brachii was higher for the throw condition. It was concluded that performing traditional press movements rapidly with light loads does not create ideal loading conditions for the neuromuscular system with regard to explosive strength production, especially in the final stages of the movement, because ballistic weight loading conditions where the resistance was accelerated throughout the movement resulted in a greater velocity of movement, force output, and EMG activity.

Observation of double-gap-edge Andreev reflection at Si/Nb interfaces by point-contact spectroscopy.

Andreev reflection point-contact spectroscopy is performed on a bilayer consisting of 50-nm degenerately doped Si backed with Nb. Due to the short mean free path both injection into and transport across the Si layer are diffusive, in contrast to the ballistic conditions prevailing in clean metal layers. Nevertheless a large Andreev signal is observed in the point-contact characteristics, not reduced by elastic scattering in the Si layer or by interface scattering, but only limited by the transmission coefficient of the metal-semiconductor point contact. Two peaks in the Andreev reflection probability are visible, marking the values of the superconducting energy gap at the interface on the Nb and Si sides. This interpretation is supported by a method of solving the Bogolubov equations analytically using a simplified expression for the variation of the order parameter close to the interface. This observation enables a comparison with theoretical predictions of the gap discontinuity in the proximity effect. It is found that the widely used de Gennes model does not agree with the experimental data.

Guidance and targeting for the strategic target system

Guidance algorithms and targeting procedures for the Strategic Target System (STARS) launch vehicle are described. The STARS vehicle is a three-stage booster, based partly on retired Polaris A3 missile assets, which is intended to support development and testing of the Strategic Defense Initiative by delivering target payloads to the vicinity of the Kwajalein Atoll. STARS will be launched from the Kauai Test Facility located on Kauai, Hawaii. The STARS guidance objective is to deliver payloads to a prescribed target location with intercontinental ballistic missile re-entry conditions. The guidance problem is complicated by the fact that all three stages lack thrust termination or other velocity control mechanisms, and by range safety requirements for one or more out-of-plane turns. Mission objectives are achieved with a combination of guidance algorithms. The original Polaris guidance is used during the atmospheric ascent phase. The powered explicit guidance used by the Space Shuttle is later employed to execute an out-of-plane turn and to place the third stage as closely as possible onto the desired coast trajectory. Third-stage guidance is a modified Lambert procedure formulated to eliminate the target miss due to off-nominal ascent phase performance.

The ballistic impact characteristics of aramid fabrics: The influence of interface friction

This study reports the effect of the surface friction characteristics of aramid fabrics with respect to their static deformation behaviour and their ballistic capture performance. Various fabric weaves were studied and differing levels of interfibre-interyarn friction within the fabrics were achieved by the removal (Soxhlet extraction) or the addition (polydimethyl-siloxane treatment) of surface lubricants. Simple interyarn friction measurements have been performed, as well as fabric penetration studies, both quasi-statistically and under high speed ballistic conditions. A simple thin elastic plate model was found to described adequately the quasi-static response of the fabrics to a normal indentation deformation. A simulation of the ballistic deformation process in fabrics was devised on the basis of this first-order model of the quasi static indentation process. The predictions of the relative fabric ballistic captive performance, derived from this model, were found to be in reasonable agreement with the results obtained directly from the ballistic studies. The investigation has also shown that the interface frictional work dissipated at the filament-filament and yarn-yarn junctions is a critical factor in determining the static tensile yarn and (transverse) fabric stiffness. The changes in these static parameters is considered to be the origin of the subtle changes observed in the ballistic performance of the corresponding fabrics.

Study on turbulence in interior ballistics flows

The compressible, viscous, turbulent gas expansion flow behind an accelerating projectile moving in a gun tube is investigated by solving the Navier-Stokes equations. For future theoretical investigations of the heat transfer from the hot gases to the walls, a reliable modeling of the turbulence is needed. Turbulence is described by two algebraic models, namely, the models by Cebeci-Smith-Mosinskis and Baldwin-Lomax, as well as by a one-equation model for the turbulent kinetic energy. Computational results obtained by application of these models are compared to experimental data obtained with two low-pressure gun simulators. Also, numerical predictions are reported for the flow behind a projectile under more realistic interior ballistic conditions.

Mass determination of a small body in solar system by using a test-mass during a fly-by

The mass estimation of small bodies in the solar system—such as comets or minor planets—with an accuracy sufficient to get scientific information is difficult. The ground-based range-rate measurements are not practicable for bodies smaller than 100 km diameter. A proof mass, ejected from the spacecraft before the flyby and whose relative trajectory is determined with onboard measurements can give very good results even for small bodies. This paper presents the expected accuracy of mass determination depending on ballistic conditions (relative velocity and closest approach), type and accuracy of measurements (range, optical).

The crater radial growth rate under ballistic impact conditions

Popular applications of impact dynamics involve the penetration/perforation of metallic or non-metallic materials by either explosively driven shaped-charge devices or gun launched kinetic energy penetrators. With typical impact velocities ranging from 1 to 8 km/s, the projectile/jet penetrates the impacted (target) material forming a crater within a few hundred microseconds. A knowledge of the crater formation process is prerequisite to the complete understanding of the impact penetrator/target interaction. In particular, the crater growth rate, from its initial to its final value, is addressed in this paper. Motion orthogonal to the penetration trajectory is treated with a suitably approximated equation of motion, yield condition and constitutive relationship. An exact solution is obtained for the resulting non-linear differential equation with the specified initial conditions. These conditions are available from the experimental data. With specified initial conditions, the predicted cavity radius and velocity history is compared with the available experimental data. When the initial conditions are not known a priori, a method for obtaining them is given and comparison is made with experimental data. Parametric studies indicative of the dependency of the key variables are given. Finally, conclusions regarding the accuracy and the applicability of the model are presented.