Military Academy

About: Military Academy is a based out in . It is known for research contribution in the topics: Population & Context (language use). The organization has 2478 authors who have published 3003 publications receiving 33188 citations.

Experimental techniques for ballistic pressure measurements and recent development in means of calibration

Abstract: This paper presents a study carried out with the commonly used experimental techniques of ballistic pressure measurement. The comparison criteria were the peak chamber pressure and its standard deviation inside specific weapon/ammunition system configurations. It is impossible to determine exactly how precise either crusher, direct or conformal transducer methods are, as there is no way to know exactly what the actual pressure is; Nevertheless, the combined use of these measuring techniques could improve accuracy. Furthermore, a particular attention has been devoted to the problem of calibration. Calibration of crusher gauges and piezoelectric transducers is paramount and an essential task for a correct determination of the pressure inside a weapon. This topic has not been completely addressed yet and still requires further investigation. In this work, state of the art calibration methods are presented together with their specific aspects. Many solutions have been developed to satisfy this demand; nevertheless current systems do not cover the whole range of needs, calling for further development effort. In this work, research being carried out for the development of suitable practical calibration methods will be presented. The behavior of copper crushers under different high strain rates by the use of the Split Hopkinson Pressure Bars (SHPB) technique is investigated in particular. The Johnson-Cook model was employed as suitable model for the numerical study using FEM code

Curved quantum waveguides in uniform magnetic fields

Abstract: A theoretical study of a planar electronic waveguide with a uniformly curved section in the perpendicular homogeneous magnetic field $\mathbf{B}$ is presented within the envelope function approximation. Utilizing analytical solutions in each part of the waveguide, exact expressions are derived for the scattering and reflection matrices and for the transcendental equation defining bound-state energies. It is shown that in the magnetic field a propagation threshold in the continuously curved channel is always smaller than its counterpart for the straight arm which means that bound states in the uniform magnetic field always exist. Their energies do not depend on the direction of the field, and at high magnetic intensities they approach the lowest Landau level. For the transport in the fundamental mode an interaction of a quasibound level split off from the higher-lying threshold as a result of the bend, with its degenerate continuum counterpart, causes a dip in the transmission. In the magnetic field, contrary to the field-free case, conductance in the minimum ${G}_{\mathit{min}}$, generally, ceases to be zero. It is shown that growing magnetic fields cause ${G}_{\mathit{min}}$ to saturate to $2{e}^{2}∕h$ which means that a quasibound level formed as a result of the bend is completely dissolved by the increasing $\mathbf{B}$; however, this transformation is very different for the different bend angles and radii. In particular, quasibound states of the fundamental propagation mode survive stronger fields for the smaller bend angles which is explained by the larger total magnetic flux through the curved section where these levels are formed. Since a magnetic length ${l}_{B}={(\ensuremath{\hbar}∕eB)}^{1∕2}$ is inversely proportional to the square root of $B$, states for the waveguide with a smaller radius also survive stronger fields, and their asymptotic approach to the dissolution possesses nonmonotonic ${G}_{\mathit{min}}$ dependence on the magnetic field with minimum conductance again reaching zero for some special values of $B$. Vortex structure of the currents flowing in the waveguide near the resonance is strongly affected by the field. In particular, small magnetic intensities change zero-field vortices in the straight arms into the magnetic antivortices which correspond to the interacting with each other surface currents flowing along opposite walls of the channel. Increasing the magnetic field suppresses the formation of the vortices pushing currents to the outer (inner) walls in the straight (bent) section. For fields larger than the saturation magnetic intensity, the only consequence of the bend is a strong surface current near the convex wall of the bend, and the electronic flow along the junctions between straight and curved parts.

Powerful Antibacterial Peptides from Egg Albumin Hydrolysates.

Abstract: Native egg albumin (NEA) was isolated from hen eggs and hydrolyzed by pepsin to produce hydrolyzed egg albumin (HEA). HEA was chemically characterized and screened for its antibacterial activity against 10 pathogenic bacteria (6 Gram (+) and 4 Gram (-)). The SDS-PAGE pattern of NEA showed molecular weights of hen egg albumin subunits ranging from 30 to 180 kDa. The highest intensive bands appeared at a molecular mass of about 50 and 97 kDa. Ultra-performance liquid chromatography (UPLC) of the peptic HEA revealed 44 peptides, 17 of them were dipeptides, and the other 27 fractions corresponded to bigger peptides (3-9 amino acids). The dipeptides and big peptides represented 26% and 74% of the total hydrolysate, respectively. The MIC of HEA was about 100 μg/L for Listeria monocytogenes, Bacillus cereus, Staphylococcus aureus, Salmonella typhimurium, Streptococcus pyogenes, and Klebsiella oxytoca and 150 μg/L for Pseudomonas aeruginosa, Bacillus subtilis, and Listeria ivanovii and 200 μg/L for Escherichia coli. L. monocytogenes was the most sensitive organism to HEA. Mixtures of HEA with antibiotics showed more significant antibacterial activity than individually using them. Transmission electron microscopy (TEM) revealed various signs of cellular deformation in the protein-treated bacteria. HEA may electrostatically and hydrophobically interact with the cell wall and cell membrane of the susceptible bacteria, engendering large pores and pore channels leading to cell wall and cell membrane disintegration. Higher cell permeability may, thus, occur, leading to cell emptiness, lysis, and finally death. Alternatively, no toxicity signs appeared when HEA was administrated to Wistar Albino rats as one single dose (2000, 5000 mg/kg body weight) or repeated daily dose (500 and 2500 mg/kg body weight/day) for 28 days to disclose the possible toxicity hazards. HEA did not produce any death.

MUSCOP: Mission-Based UAV Swarm Coordination Protocol

Abstract: Nowadays, Unmanned Aerial Vehicles (UAVs) have become the preferred, and sometimes the only support tool when facing critical scenarios such as earthquakes, search and rescue missions, and border surveillance. In these scenarios, deploying a UAV swarm instead of a single UAV can provide additional benefits when, for example, cargo carrying requirements exceed the lifting power of a single UAV, or when the deployment of several UAVs simultaneously can accelerate the accomplishment of the mission, and broaden the covered area. To this aim, in this paper we present MUSCOP, a protocol that allows multiple UAVs to perfectly coordinate their flight when performing planned missions. Experimental results show that the proposed protocol is able to achieve a high degree of swarm cohesion independently of the swarm formation adopted, and even in the presence of very lossy channels, achieving minimal synchronization delays and very low position offsets with regard to the ideal case.