Analysis of hypervelocity impacts: The tungsten case

The atomistic mechanisms of damage initiation during high velocity (v up to 9 km/s, kinetic energies up to 200 keV) impacts of W projectiles on a W surface have been investigated using parallel molecular-dynamics simulations involving large samples (up to 40 million atoms). Various aspects of the impact at high velocities, where the projectile and part of the target materials undergo massive plastic deformation, breakup, melting, and vaporization, are analyzed. Different stages of the penetration process have been identified through a detailed examination of implantation, crater size and volume, sputtered atoms, and dislocations created by the impacts. The crater volume increases linearly with the kinetic energy for a given impactor; and the total dislocation length increases with the kinetic energy but depends itself on the size of the impactor. Furthermore, the total dislocation length is less dependent of the fine details of the interatomic potential. The results are rationalized based on the physical properties of bcc W.

On-Orbit Geometric Calibration from the Relative Motion of Stars for Geostationary Cameras

Affected by the vibrations and thermal shocks during launch and the orbit penetration process, the geometric positioning model of the remote sensing cameras measured on the ground will generate a displacement, affecting the geometric accuracy of imagery and requiring recalibration. Conventional methods adopt the ground control points (GCPs) or stars as references for on-orbit geometric calibration. However, inescapable cloud coverage and discontented extraction algorithms make it extremely difficult to collect sufficient high-precision GCPs for modifying the misalignment of the camera, especially for geostationary satellites. Additionally, the number of the observed stars is very likely to be inadequate for calibrating the relative installations of the camera. In terms of the problems above, we propose a novel on-orbit geometric calibration method using the relative motion of stars for geostationary cameras. First, a geometric calibration model is constructed based on the optical system structure. Then, we analyze the relative motion transformation of the observed stars. The stellar trajectory and the auxiliary ephemeris are used to obtain the corresponding object vector for correcting the associated calibration parameters iteratively. Experimental results evaluated on the data of a geostationary experiment satellite demonstrate that the positioning errors corrected by this proposed method can be within ±2.35 pixels. This approach is able to effectively calibrate the camera and improve the positioning accuracy, which avoids the influence of cloud cover and overcomes the great dependence on the number of the observed stars.

Penetration of Chitosan into the Single Walled Armchair Carbon Nanotubes: Atomic Scale Insight

(1) Background: Currently, nanomaterials have been broadly used in various applications including engineering, medicine and biology. One of the carbon allotropes such as carbon nanotubes (CNTs) implemented for fabrication of nanocomposite materials due to the hypersensitivity. The combined design of nanomaterial with chitosan (CS) and CNT expands the field of exploitation from biosensing and tissue engineering to water desalination. Therefore, the penetration of CS into CNT provides a valuable insight into the interactions between CS and CNT. (2) Methods: We performed molecular dynamics simulations, applying the umbrella sampling method, in order to calculate the potential mean force between CS and CNT. (3) Results: The estimated penetration free energies showed that CS is favorable to the penetration into CNT cavities. However, the penetration nature differs depending on the CNT’s architecture. (4) Conclusions: Our finding revealed the CS penetration process into CNT with nanoscale precision. The investigation results assist in a better understanding of the nanocomposite materials based on CS-CNT.

Modeling of penetration process of fragments in ballistic gelatin

Modeling the penetration process in soft tissue simulant is the basis for evaluating the damaging efficiency of projectiles. To investigate the penetration dynamics of fragments in gelatin, this paper presented a model describing both the penetration resistance and the temporary cavity dynamics. The modeling process was set up using the law of energy conversion and conservation. The equations for the movement of the penetrator and the movement of the target medium are closely combined through sharing the same set of parameters. Penetration experiments were conducted using fragments of two different shapes: cylinder and rhombus. By comparing with the experimental results, the parameters in the present model were estimated and discussed thoroughly. The present model can predict the movement of the penetrator and the cavity expansion in the target with satisfactory accuracy.

The Analysis on the Relationship between Dating and the Gel-ink Material Penetration of Handwriting along Z Direction on Paper

Scanning electron microscopy (SEM) technology has been widely used in forensic science, which promotes the development of interdisciplinary science. This paper used SEM to observe the penetration degree of common black gel-ink on paper. The penetration morphology of the different black brands gel-ink has been observed. The relationship between the penetration process of gel-ink material and the dating of document has been observed after determining the measuring position. The results showed that the penetration depth of ink along Z direction on paper is significantly different, the penetration speed of ink is also different, which presents regular variety and gradually reaches a relatively stable state over time. The application of SEM will provide a useful exploration for judging the ink dating.

Quantitative description of a contractile macromolecular machine

Contractile injection systems (CISs) [type VI secretion system (T6SS), phage tails, and tailocins] use a contractile sheath-rigid tube machinery to breach cell walls and lipid membranes. The structures of the pre- and postcontraction states of several CISs are known, but the mechanism of contraction remains poorly understood. Combining structural information of the end states of the 12-megadalton R-type pyocin sheath-tube complex with thermodynamic and force spectroscopy analyses and an original modeling procedure, we describe the mechanism of pyocin contraction. We show that this nanomachine has an activation energy of 160 kilocalories/mole (kcal/mol), and it releases 2160 kcal/mol of heat and develops a force greater than 500 piconewtons. Our combined approach provides a quantitative and experimental description of the membrane penetration process by a CIS.

Research on Increasing the Degree of Individual Protection against Bullets through the use of Ceramic Materials

The protection of forces in the new world conflicts has become a particularly important issue for all the world’s armies. Therefore, ensuring an optimal level of protection, combined with maintaining freedom of movement in the tactical field has become a very important topic for research teams. This goal can be achieved by using materials in the protection of forces with a relatively low mass, but to ensure a substantial reduction in the kinetic energy of ballistic penetrators. In this paper are presented some considerations on how the ballistic penetration process is affected by the presence of ceramic materials.