Influence of Calcined Bauxite Aggregate on the Resistance of Cement Composites Subjected to Small Caliber Deformable Projectile Impact

This paper presents an experimental investigation on the influence of calcined bauxite aggregate (CBA) on the resistance of cement composites subjected to small caliber deformable projectile impact at a designed velocity of 400 m/s. The deformable projectile was made from copper with a purity of 99.5% and a diameter of 8.0 mm. Compared to mixtures with conventional coarse granite aggregate and/or siliceous fine aggregate, the incorporation of either fine or coarse CBA or their combination is beneficial in reducing the depth of penetration (DOP), equivalent crater diameter (CD), and crater volume (CV) caused by deformable projectile impact. CBA is found to be more effective in controlling the DOP and CV in comparison to the CD. Replacing of conventional aggregate with CBA leads to more severe damage to the projectiles (e.g., projectile length reduction, diameter increase, and mass loss). Relative effective hardness is an effective indicator to the deformation potential and penetration capacity of a deformable projectile to impact cement composites incorporating CBA.

Numerical Investigation of Penetration Characteristics of Preformed Spherical Fragments at Hyper Velocity

Numerical investigation of penetration characteristics of 6mm SS304 preformed spherical fragments released from a Fragment Generator Warhead (FGW) impacting on Steel 1006 target plate of 1 mm, 3 mm and 6 mm thick in velocity range 1000 m/s to 5000 m/s and impact angle between 0° and 75°, has been carried out using the explicit code LS-Dyna which is predominantly used for solving impact problems. The simulation model employs a strain rate dependent plasticity model viz. Johnson-Cook model supplemented by Gruneisen Equation of State (EoS), to capture the large strain encountered in target plate due to impact of a spherical fragment at high velocities. The simulation model results are presented in terms of crater diameter on the target plate normalised over original fragment diameter. Empirical equations are available in literature to estimate the normalised crater diameter under the same impact conditions employed in simulation models. The simulation model results have been validated with experimental data available in literature and also found to be in good agreement with the results obtained from empirical equations. The effectiveness of the erosion contact algorithm over Smoothed Particle Hydrodynamics (SPH) method in LS-Dyna to reasonably predict the behaviour of the target material at high velocities of impact is demonstrated in the current study.

Hydrogel sphere impact cratering, spreading and bouncing on granular media

The impact of a hydrogel sphere onto a granular target results in both the deformation of the sphere and the formation of a prominent topographic feature known as an impact crater on the granular surface. We investigate the crater formation and scaling, together with the spreading diameter and post-impact dynamics of spheres by performing a series of experiments, varying the Young's modulus $Y$ and impact speed $U_{0}$ of the hydrogel spheres, and the packing fraction and grain size of the granular target. We determine how the crater diameter and depth depend on $Y$ and show the data to be consistent with those from earlier experiments using droplets and hard spheres. Most specifically, we find that the crater diameter data are consistent with a power law, where the power exponent changes more sharply when $Y$ becomes less than 200 Pa. Next, we introduce an estimate for the portion of the impact kinetic energy that is stored as elastic energy during impact, and thus correct the energy that remains available for crater formation. Subsequently, we determine the deformation of the hydrogel spheres and find that the normalized spreading diameter data are well collapsed introducing an equivalent velocity from an energy balance of the initial kinetic energy against surface and elastic energy. Finally, we observe that under certain intermediate values for the Young's modulus and impact velocities, the particles rebound from the impact crater. We determine the phase diagram and explain our findings from a comparison of the elastocapillary spreading time and the impact duration.

Er:YAG laser-induced damage to a dental composite in simulated clinical scenarios for inadvertent irradiation: an in vitro study

Inadvertent Er:YAG laser irradiation occurs in dentistry and may harm restorative materials in teeth. The aim of this in vitro study was to quantify Er:YAG laser-induced damage to a nanohybrid composite in simulated clinical scenarios for inadvertent direct and indirect (reflection) laser irradiation. The simulation was performed by varying the output energy (OE;direct˃indirect) reaching the specimen and the operating distance (OD;direct˂indirect). Composite specimens were irradiated by an Er:YAG laser. The ablation threshold was determined and clinically relevant parameters were applied (n = 6 for each OE/OD combination) for direct (OE: 570 mJ/OD: 10 mm, OE: 190 mJ/OD: 10 mm) and indirect irradiation (OE: 466 mJ/OD: 15 mm, OE: 57 mJ/OD: 15 mm, OE: 155 mJ/OD: 15 mm, OE: 19 mJ/OD: 15 mm). The extent of damage in the form of craters was evaluated using a laser scanning microscope (LSM) and a conventional light microscope (LM). The ablation threshold was determined to be 2.6 J/cm2. The crater diameter showed the highest value (LM: 1075 ± 18 µm/LSM: 1082 ± 17 µm) for indirect irradiation (reflectant:dental mirror) (OE: 466 mJ/OD: 15 mm). The crater depth showed the highest and comparable value for direct (OE: 570 mJ/OD: 10 mm; LSM: 89 ± 2 µm) and indirect irradiation (OE: 466 mJ/OD: 15 mm; LSM: 90 ± 4 µm). For each OD, the crater diameter, depth, and volume increased with higher laser fluence. However, the OD—and thus the laser spot diameter—also had an enlarging effect. Thus, indirect irradiation (reflectant:dental mirror) with only 47% of the laser fluence of direct irradiation led to a larger diameter and a comparable depth. The three-dimensional extent of the crater was large enough to cause roughening, which may lead to plaque accumulation and encourage caries, gingivitis, and periodontitis under clinical conditions. Clinicians should be aware that reflected irradiation can still create such craters.

Сlassification and characteristic of inclusions in the Severny Kolchim meteorite (H3.4)

Research subject. Fragments of the Severny Kolchim meteorite.Materials and methods. The study was performed in the Geoanalyst Centre for Collective Use, Institute of Geology and Geochemistry, UB RAS. The clast and inclusions were studied using a scanning electron microscope JSM-6390LV from JEOL with an energy dispersing attachment INCA Energy 450 X-Max 80. The bulk chondrule compositions were obtained by EDS analysis of whole chondrule areas in thin sections. The composition of minerals was studied using an electron microprobe analyser Cameca SX100 equipped with five wavelength spectrometers. The concentrations of trace elements in olivine were measured using a mass spectrometer with inductively coupled plasma NexION 300S (PerkinElmer) with a laser ablation attachment NWR 213 (ESI) at a crater diameter of 25 microns.Results. According to the revealed set of petrographic and mineralogical features, the meteorite was clarified as H3.4. In addition, this meteorite can be further classified as genomict breccia. In the Severny Kolchim meteorite, a 6×6 mm clast fragment composed of chondrite H3.9 was studied. This inclusion has a slightly higher degree of S2 shock transformations compared to the host rock. Refractory forsterite-rich objects were found and studied. These inclusions are composed of low-ferroan forsterite (f = 0.004–0.2, f – ratio Fe/(Fe + Mg)mol).Conclusion. The porphyry olivine chondrules consisting of refractory forsterite and high-calcium glass in mesostasis are likely to be parental to the refractory forsterite-rich inclusions. Al-rich chondrules and pyroxene chondrule with tridymite identified in the matrix of the chondrite are likely to be xenogenic, originating from the formation area of enstatite chondrites.

Jadeite and its relatives: fake news or a real tool to constrain shock conditions?

Jadeite is frequently reported in shocked meteorites, displaying a variety of textures and grain sizes that suggest formation by either solid-state transformation or by crystallization from a melt. Sometimes, jadeite has been identified solely on the basis of Raman spectra. Here we argue that additional characterization is needed to confidently identify jadeite and distinguish it from related species. Based on chemical and spectral analysis of three new occurrences, complemented by first-principles calculations, we show that related pyroxenes in the chemical space (Na)M2(Al)M1(Si2)TO6 – (Ca)M2(Al)M1(AlSi)TO6 – (□)M2(Si)M1(Si2)TO6 with up to 2.25 atoms Si per formula unit have spectral features similar to jadeite. However, their distinct stability fields and synthesis pathways, considered together with textural constraints, have specific implications for precursor phases and estimates of impactor size, encounter velocity, and crater diameter. A reassessment of reported jadeite occurrences puts in a new light many previous conclusions about the shock histories preserved in particular meteorites.

Nesting and hatching behaviour of Olive Ridley Turtles Lepidochelys olivacea (Eschscholtz, 1829) (Reptilia: Cryptodira: Cheloniidae) on Dr. Abdul Kalam Island, Odisha, India

This paper reports the nesting, impact of lunar phase and rainfall on mass nesting, hatching, and hatchling behaviour of L. olivacea in Dr. Abdul Kalam Island, Bhadrak District, Odisha. The study site is a well-known rookery for this species. A study of 15 mass nesting events between 2003 and 2020 using Rayleigh’s test indicated that the onset of mass nesting was not uniform across a lunar month, but was most intense towards the beginning of the fourth quarter moon (mean lunar day = 22.44). Also, rainfall and mass-nesting data from 2015 to 2020 revealed that ≥3.2 mm rainfall in February delayed mass nesting from the second fortnight of February to the end of the first fortnight of March. Sporadic nesting continued after hatching commenced in May, and continued until the end of May 2020, with an average of three turtles nesting each day. At night, a cohort of hatchlings from individual nests emerged synchronously. Before emergence they remained a little beneath the sand surface in airy-shallow pits. During hatchling emergence these pits fill with sand, leaving depressions described as “emergence craters” in recent literature on L. olivacea. To study hatchling emergence 30 such craters were examined in May 2020, and the numbers of emerged hatchlings per cohort varied from 28 to 182. Of 30 craters examined, 28 were circular and two were elliptical, with diameters varying between 10 and 26 cm. Pearson’s correlation coefficient between the numbers of emerged hatchlings and crater diameter was 0.38. Hatchlings took 17 min 22 sec (SD= ±5min 30 sec) on average to reach the sea from a mean distance of 34.6m.

Decrease in Volcano Jet Noise Peak Frequency from Crater Expansion

<p>Volcanic jet noise is the sound, often below the human audible range (<20 Hz and termed infrasound), generated by momentum-driven fluid flow through a volcanic vent. Assuming the self-similarity of jet flows and audible jet noise extends to infrasonic volcanic jet noise, the Strouhal number, <em>St=D<sub>j</sub>f/U<sub>j</sub></em>, connects frequency changes, <em>f</em>, to changes in the jet length (expanded jet diameter, <em>D<sub>j</sub></em>) and/or velocity scale (jet velocity, <em>U<sub>j</sub></em>). We examine the infrasound signal characteristics from the June 2019 VEI 4 eruptions of Raikoke, Kuril Islands and Ulawun, Papua New Guinea volcanoes with changes in crater geometry. We use data from the International Monitoring System (IMS) infrasound network and pre- and post-eruption satellite data (RADARSAT-2 and PlanetScope imaging for Raikoke and Ulawun, respectively). During both eruptions we observe a decrease in infrasound peak frequency during the transition to a Plinian phase, which remains through the end of the eruptions. The RADARSAT-2 data show a qualitative increase in the crater area at Raikoke; quantitative analysis is limited by shadows. At Ulawun, however, we estimate an increase in crater area from ~35,000 m<sup>2</sup> on May 25, 2019 to ~66,000 m<sup>2</sup> on July 17, 2019. We assume a constant Strouhal number and use the crater diameter as a proxy for expanded jet diameter. Our analysis suggests that the increase in crater diameter alone cannot account for the decrease in peak frequency during the Ulawun eruption. This suggests that the jet velocity also increased, which fits satellite data, and or the fluid properties (e.g. particle loading, nozzle geometry and roughness, etc.) changed. This is reasonable as the Ulawun eruption went Plinian, which likely involved an increase in jet velocity and erosion of the crater walls. This is the first study to corroborate the decrease in infrasound peak frequency with documented increase in crater area. The fortuitous satellite overpass timing, clear skies, and high spatial resolution enabled the quantitative examination of the Ulawun eruption.</p>

The effect of sample surface roughness on the microanalysis of microchip laser-induced breakdown spectroscopy

In the microanalysis of laser-induced breakdown spectroscopy, the influence of surface roughness on spectral stability and quantitative analysis capability was studied for the first time when the laser ablation crater diameter was approximately 10 μm.

SURFACE MODIFICATION OF BIOMATERIAL FABRIC USING SUPERCRITICAL N2 JET

Textile biomaterials have been largely used over the last decades as vascular grafts, hernia meshes and heart valve leaflet [1-2]. Once implanted in vivo, the natural porosity of textile materials tends to induce exaggerated tissue ingrowth, which may prevent the implants from remaining flexible [3]. One hypothesized way to limit the foreign body reaction process is to increase the material surface roughness [4]. Supercritical N2 jet particle projection is a novel technique to provide enough velocity to micro particles to induce plastic deformation on the textile impacted surface. The aim of this study is to investigate the influence of micro particles laden supercritical N2 jet projection parameters like jet static pressure, standoff distance and particle size on the roughness of PET fabric surfaces. Results bring out that particles projected by the jet N2 SC generate craters on the surface of monofilament as well as multifilament fabric, allowing topographical modifications at the yarn scale. We found that larger particles induce larger crater diameters. Moreover, increasing the static jet pressure from 300 to 1000 bars further allows increase in the crater diameter. For a pressure of 500 bar, the standoff distance must be greater than 300 mm in order to obtain significant roughness values without breaking the PET monofilament fabrics. Thus, this treatment increased the roughness of the monofilament fabric from 0.78 μm to 1.22 μm. The results obtained in this work show that it is possible to create a roughness on a PET fabric using the N2 jet technology.