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•Dynamic compression characteristics and reaction behavior of W-Zr reactive material are investigated.•Hypervelocity impact experiments of long rods on multi-spaced plates are ...performed.•The debris clouds during the impact process are recorded with a high-speed camera.•Damage properties of the multi-spaced plates with long rods are obtained and compared.•W-Zr reactive material has the damage effects of kinetic and chemical energy.
The damage or penetration research of the long rods has attracted more and more attention from scholars worldwide. In this article, the dynamic compression tests of W-Zr reactive material are performed. Six experiments of the long rods impacting the multi-spaced plates at hypervelocity are carried out on a two-stage light gas gun. Two kinds of long rods, inert 40CrNi2MoA steel and W-Zr reactive material, are used. The initial impact speed ranges from 2040 m/s to 3200 m/s. According to results, W-Zr reactive material reacts at the strain rate of 2200 s−1 and higher, whose strength limit is related to the strain rate. The long rods can produce debris clouds when hitting the multi-spaced plates at the speed of 2040 m/s and higher, causing large perforation and great damaged area in the subsequent plates. The perforations and damaged areas of the multi-spaced plates depend on the specific kinetic energy of the long rods. The violent reaction behavior of the W-Zr reactive material helps to cause large perforation and damaged area of the subsequent plates than inert materials. It proves that the damage ability of the W-Zr reactive material is stronger than that of the inert material with a similar density.
Streptococcus mutans (S. mutans) is generally regarded as a major contributor to dental caries because of its ability to synthesize extracellular polysaccharides (EPS) that aid in the formation of ...plaque biofilm. The VicRKX system of S. mutans plays an important role in biofilm formation. The aim of this study was to investigate the effects of vicK gene on specific characteristics of EPS in S. mutans biofilm. We constructed single-species biofilms formed by different mutants of vicK gene. Production and distribution of EPS were detected through atomic force microscopy, scanning electron microscopy and confocal laser scanning microscopy. Microcosmic structures of EPS were analyzed by gel permeation chromatography and gas chromatography-mass spectrometry. Cariogenicity of the vicK mutant was assessed in a specific pathogen-free rat model. Transcriptional levels of cariogenicity-associated genes were confirmed by quantitative real-time polymerase chain reaction. The results showed that deletion of vicK gene suppressed biofilm formation as well as EPS production, and EPS were synthesized mostly around the cells. Molecular weight and monosaccharide components underwent evident alterations. Biofilms formed in vivo were sparse and contributed a decreased degree of caries. Moreover, expressional levels of genes related to EPS synthesis were down-regulated, except for gtfB. Our report demonstrates that vicK gene enhances biofilm formation and subsequent caries development. And this may due to its regulations on EPS metabolism, like synthesis or microcosmic features of EPS. This study suggests that vicK gene and EPS can be considered as promising targets to modulate dental caries.
The need to improve the protection capability of spacecraft shield structure is urgent, owing to the deterioration of space environment caused by orbital debris. Reactive material is a kind of ...impact-induced energetic composites, and using reactive material to protect spacecraft against hypervelocity impact of orbital debris is a new way. In this paper, the dynamic compression experiments of PTFE (polytetrafluoroethylene)/Al (aluminum) and PTFE (polytetrafluoroethylene)/Ti (titanium) reactive materials were carried out. The mechanical properties and impact-induced reaction characteristics of PTFE/Al and PTFE/Ti were compared. The experiments of projectiles with hypervelocity impact on Whipple shields with PTFE/Al, PTFE/Ti and Al2024 as bumper respectively were carried out by using two-stage light-gas gun, and the protective capability of these two reactive materials against hypervelocity impact are compared. The experimental results show that the protective capability of PTFE/Al and PTFE/Ti reactive materials is better than that of Al2024, and the protective capability of PTFE/Al reactive material is better than that of PTFE/Ti. Through theoretical calculation and numerical simulation, the reasons for the difference of protective capability of different reactive materials are analyzed, and the ballistic limit curves of Whipple shield structures are compared.
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•Through hypervelocity impact experiments，the resistances of reactive materials to hypervelocity impact were compared.•The reasons of different resistance to hypervelocity impact are analyzed by theoretical calculation.•The ballistic limit curves of reactive material Whipple shields and Al2024 Whipple shield are compared.
Streptococcus mutans
constantly coexists with
Candida albicans
in plaque biofilms of early childhood caries (ECC). The progression of ECC can be influenced by the interactions between
S. mutans
and
...C. albicans
through exopolysaccharides (EPS). Our previous studies have shown that
rnc
, the gene encoding ribonuclease III (RNase III), is implicated in the cariogenicity of
S. mutans
by regulating EPS metabolism. The
DCR1
gene in
C. albicans
encodes the sole functional RNase III and is capable of producing non-coding RNAs. However, whether
rnc
or
DCR1
can regulate the structure or cariogenic virulence of the cross-kingdom biofilm of
S. mutans
and
C. albicans
is not yet well understood. By using gene disruption or overexpression assays, this study aims to investigate the roles of
rnc
and
DCR1
in modulating the biological characteristics of dual-species biofilms of
S. mutans
and
C. albicans
and to reveal the molecular mechanism of regulation. The morphology, biomass, EPS content, and lactic acid production of the dual-species biofilm were assessed. Quantitative real-time polymerase chain reaction (qRT-PCR) and transcriptomic profiling were performed to unravel the alteration of
C. albicans
virulence. We found that both
rnc
and
DCR1
could regulate the biological traits of cross-kingdom biofilms. The
rnc
gene prominently contributed to the formation of dual-species biofilms by positively modulating the extracellular polysaccharide synthesis, leading to increased biomass, biofilm roughness, and acid production. Changes in the microecological system probably impacted the virulence as well as polysaccharide or pyruvate metabolism pathways of
C. albicans
, which facilitated the assembly of a cariogenic cross-kingdom biofilm and the generation of an augmented acidic milieu. These results may provide an avenue for exploring new targets for the effective prevention and treatment of ECC.
Three types of multi-wall shielding were experimentally investigated for their performances under the high-velocity impact of a cm-size cylindrical projectile by using a two-stage light-gas gun. The ...three shields contained the same two aluminum bumpers but different rear walls, which were 7075-T651 aluminum (Al) plate, boron carbide (B4C)/Al 7075-T651/Kevlar composite plate and B4C/ultra-high molecular weight polyethylene (UHMW-PE) composite plate. The impact test was carried out using a cylindrical shape of 6 g mass 7075-T651 Al projectile in a speed range (1.6 to 1.9 km/s) to achieve an effective shield configuration. A numerical simulation was undertaken by using ANSYS Autodyn-3D and the results of this were in good agreement with the experimental results. Meanwhile, both the experimental and the numerical simulation results indicated that B4C/UHMW-PE composite plates performed a better interception of the high-velocity projectiles within the specific speed range and could be considered as a good configuration for intercepting large fragments in shielding design.
Impact cratering experiments were performed on semi-infinite concrete targets with 7 mm-diameter 40CrNiMo steel long-rod projectiles at impact velocities ranging from 2117 m/s to 3086 m/s by using a ...two-stage combustion light-gas gun. After the impact experiments, the crater diameter and depth as well as the crater volume were carefully measured. The concrete fragments were collected from the target chamber and the fragment mass was measured. The size of the crater (including the volume, diameter, and depth) and the fragment mass increased with increasing impact velocities, while the fragment distributions at different impact velocities were almost the same. Scaling laws for the crater volume impacted by the rod-shaped projectile were discussed and an empirical formula of crater volume was determined by the experimental data from the literature. Through the verification of the present experimental results, the predictive ability of the empirical formula proved to be reliable. Scaling laws for the size distribution of concrete fragments were also discussed. The normalized fragment mass distribution was proportional to the impact velocity raised to the power 1.5.
•A reactive material double-bumper shield which can effectively shield against centimeter-sized projectiles was presented.•The process of projectile impacting on the reactive material double-bumper ...shield was analyzed.•The ballistic limit curve of the reactive material double-bumper shield was obtained.
The hypervelocity impact of space debris will cause fatal damage to spacecraft. At present, most of the protective shield structures can only resist the impact of millimeter sized projectiles, and it is very difficult for the protective structure with the finite area density and overall spacing to be impacted by the projectile with the diameter ≥1cm without failure. In this paper, a PTFE (polytetrafluoroethylene)/Al (aluminum) reactive material double-bumper shield for centimeter sized space debris was presented, and the experiments of projectiles with hypervelocity impact on PTFE/Al reactive material double-bumper shields were carried out by using two-stage light-gas gun. The hypervelocity impact characteristics of Aluminum alloy double-bumper shield and PTFE/Al reactive material double-bumper shield were compared by numerical simulation. The ballistic limit curve of the PTFE/Al reactive material double-bumper shield was obtained by experiments and numerical simulations. The PTFE/Al reactive material double-bumper shield can resist the impact of the projectiles with the diameter ≥1cm at the low velocity range, intermediate velocity range, and the high velocity range. The PTFE/Al reactive material double-bumper shield can stop projectiles with 2∼4 times greater mass than the Aluminum alloy double-bumper shield at these impact conditions, and the PTFE/Al reactive material double-bumper shield can provide better protection than the Aluminum alloy double-bumper shield of equivalent weight. Compared with the Nextel/Kevlar Stuffed-Whipple shield, the impact resistance of PTFE/Al reactive materials is not lower than that of Nextel/Kevlar fiber materials.
lBallistic experiments of hypervelocity penetration of long-rod projectiles with aspect ratio of 10 on concrete targets were carried out.lThe depth of penetration was found to be greater than the ...hydrodynamic limit penetration depth.lIt was obtained that the head of the long-rod projectile eroded and deformed into a hemisphere during hypervelocity penetration.lThe penetration model of long-rod projectiles penetrating concrete targets at hypervelocity was constructed based on the Alekseevskii-Tate model.
Hypervelocity penetration experiments were performed on semi-infinite concrete targets with 7 mm-diameter 40CrNiMo steel long-rod projectiles at impact velocities ranging from 2117 m/s to 3086 m/s by using a two-stage combustion light-gas gun. After the experiments, the crater dimensions and penetration depth were carefully measured, also the residual projectiles were recovered. The depth of penetration was found to be greater than the hydrodynamic limit penetration depth. Numerical simulation was conducted to analyze the penetration process, and combined with the experimental results, it was obtained that the head of the long-rod projectile eroded and deformed into a hemisphere during hypervelocity penetration. According to the experimental and numerical simulation results, the penetration model of long-rod projectiles penetrating concrete targets at hypervelocity was constructed based on the Alekseevskii-Tate model. The penetration model was compared with the experimental depths of penetration, showing that the model had good applicability.
The cavitation phenomenon can seriously decrease the strike performance of military weapons. As military terminal-ballistic activities have turned to hypervelocity attacks, the cavitation effect ...existing in the hypervelocity penetration deserves more attention. In terms of long-rod hypervelocity penetration into concretes, this study presents an analytical cavity model for the prediction of the cavity diameter based on the two-stage cavitation mechanism and the u-v relationship. The two-stage mechanism involving mushrooming and radial momentum expansion is used to describe the cavitation modes and the penetration parameters for the projectiles used in the analytical model are determined by numerical simulations empirically. Besides, the three modes including rigidity, deformation and erosion are introduced into the cavity model to elucidate the projectile state. Moreover, the hypervelocity impact experiments on the long rods into semi-infinite concrete targets at velocities of 2117 ∼ 3086 m/s are carried out to observe the cavitation effect of concrete targets and for further validating the model through comparing with the experimental cavity profiles, where the cavity profile is quantified with silica gel, and the cavity diameter is found to be more than five times the projectile diameter. The cavitation effect is observed significantly and quantified from the experiment results. The cavity model is compared with the experimental cavity profiles, showing that the model has good applicability.
Streptococcus mutans is known as the crucial pathogen of human dental caries, owing to its contribution to the biofilm development via the capacity of synthesizing exopolysaccharide (EPS), which ...mainly compose of alpha-glycosidic bond and beta-glycosidic bond. beta-glycosidic bond is less flexible than alpha-glycosidic bond because of differences between their configurational properties. Previous studies have shown that the rnc gene is implicated in the EPS formation and the cariogenicity of S. mutans. However, the effects of rnc on the microstructure of EPS have been not well-understood yet. Here, we further investigated how the rnc gene worked to modulate microstructural properties of the extracellular polysaccharide of S. mutans using glycomics methods. The gas chromatography-mass spectrometer showed that the proportion of glucose was decreased in water-soluble EPS and galactose was absent in water-insoluble EPS from the S. mutans rnc-deficient strain (Smurnc), compared with the isogenic wild-type strain (UA159). The composition of functional groups and the displacement of hydrogen bond were analyzed by infrared radiation and sup.1H nuclear magnetic resonance, respectively. In addition, phenotypic modulation of the biofilm matrix was assessed by microscopy. We found that the EPS of UA159 and the rnc overexpression strain (Smurncsup.+) mainly consisted of beta-glycosidic bonds. Conversely, the EPS of Smurnc were made up of mostly alpha-glycosidic bonds, leading to the attenuation of biofilm biomass and bacterial adhesion. Furthermore, the existence of beta-glycosidic bond was verified by enzyme digestion. Collectively, the rnc gene modulates the conversion of beta-glycosidic bonds, which may play important roles in regulating the micromolecule structure of the EPS matrix, thus affecting the characteristics of S. mutans biofilm. These data illustrate that beta-glycosidic bonds mediated by rnc may be potential targets for the prevention and treatment of dental caries. Keywords: beta-Glycosidic bond, Exopolysaccharide, rnc gene, Streptococcus mutans, Dental caries
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