Stages Of Collapse Research Articles

The population genomics of multiple tsetse fly (Glossina fuscipes fuscipes) admixture zones in Uganda.

Understanding the mechanisms that enforce, maintain or reverse the process of speciation is an important challenge in evolutionary biology. This study investigates the patterns of divergence and discusses the processes that form and maintain divergent lineages of the tsetse fly Glossina fuscipes fuscipes in Uganda. We sampled 251 flies from 18 sites spanning known genetic lineages and the four admixture zones between them. We apply population genomics, hybrid zone and approximate Bayesian computation to the analysis of three types of genetic markers: 55,267 double-digest restriction site-associated DNA (ddRAD) SNPs to assess genome-wide admixture, 16 microsatellites to provide continuity with published data and accurate biogeographic modelling, and a 491-bp fragment of mitochondrial cytochrome oxidase I and II to infer maternal inheritance patterns. Admixture zones correspond with regions impacted by the reorganization of Uganda's river networks that occurred during the formation of the West African Rift system over the last several hundred thousand years. Because tsetse fly population distributions are defined by rivers, admixture zones likely represent both old and new regions of secondary contact. Our results indicate that older hybrid zones contain mostly parental types, while younger zones contain variable hybrid types resulting from multiple generations of interbreeding. These findings suggest that reproductive barriers are nearly complete in the older admixture zones, while nearly absent in the younger admixture zones. Findings are consistent with predictions of hybrid zone theory: Populations in zones of secondary contact transition rapidly from early to late stages of speciation or collapse all together.

Experimental study on the effect of a deformable boundary on the collapse characteristics of a cavitation bubble

Cavitation phenomena widely exist in many fields such as medical treatment, chemical engineering, and hydraulic engineering. The boundary properties have a great influence on the collapse characteristics of a cavitation bubble. The interaction between a cavitation bubble and a boundary of different properties is an important part in the cavitation erosion mechanism. In this paper, cavitation bubbles under in-water pulse discharge and cavitation erosion under ultrasonic vibration were used to study the effect of a deformable boundary on the collapse characteristics of a cavitation bubble, which reveals the cavitation-resistance performance of different materials on the macroscopic scale. The main experimental results showed that on a deformable boundary, the cavitation bubble does not collapse toward the boundary in the later collapse stage compared with on the rigid boundary. The collapse process of the cavitation bubble is aggravated on the deformable boundary. In the condition of same cavitation strength, the cavitation?s erosion loss amount on the rigid boundary material is much higher than that on the deformable boundary material. The experimental conclusions have an important reference value for the development of cavitation erosion prevention and the exploration of cavitation-resistance materials.

Numerical simulation of single vapor bubble dynamics in a liquid in an intense acoustic field

The possibility of increasing the calculation efficiency by the joint use of two models of the dynamics of a single weakly-nonspherical vapor bubble under its strong collapse in liquid is studied. In both models the motion of liquid and vapor is split into a spherical component and its small nonspherical perturbation. The models differ in the description of the spherical component. In the first (simplified) model, it is described by a system of ODE together with partial differential equations in temperature, derived under the assumption of weak compressibility of liquid and bubble homobaricity. In the second model, one-dimensional gas dynamics equations are applied. The advantage of the simplified model consists in determining a numerical solution with much-less computer time costs in comparison with what is required for the numerical integration of gas dynamics equations. The assumptions used in the simplified model in the final stage of collapse become incorrect, and, as a result, the numerical solution errors increase. Therefore, the simplified model is applied at the beginning of bubble collapse, whereas the gas dynamics equations are used at its end. Within this approach, the numerical solution in the final stage of collapse is dependent on the moment of transition to the gas dynamics equations. It is shown that satisfactory description of evolution of bubble sphericity distortion is achieved when the transition is made under the condition that the Mach number M of vapor in the vicinity of the bubble surface is less than 0.4. Satisfactory resolution of the shock wave in the bubble is attained when the transition is performed at M<0.2.

Effects of K+ solutions on swelling behavior of compacted GMZ bentonite

During the long-term operation of a deep geological repository, the buffer/backfill properties of compacted bentonite could be affected by the chemistry of the infiltrated porewater. In this study, swelling tests and microstructural analyses were conducted on the compacted GMZ bentonite specimens with an initial dry density of 1.5 or 1.7 Mg/m3 with infiltration of distilled water, as well as, KCl and KOH solutions (0.1 and 1.0 M). Influences of K+ solutions on the swelling behavior of compacted GMZ bentonite were investigated. Results show that swelling properties of compacted GMZ bentonite specimens could be significantly influenced by concentration of K+ solutions and dry density of specimens. Swelling pressure of compacted GMZ bentonite specimens was significantly attenuated by infiltration of K+ salt/alkaline solutions. For swelling strain tests with infiltration of KCl or KOH solutions, instead of a secondary swelling stage, a volumetric collapse stage was observed. Micro-structural test results demonstrate that the attenuation of swelling behavior could be attributed to the K+ exchange or silica dissolution.

A 1D nonlinear finite element model for analysis of composite foam-insulated concrete sandwich panels

A simple 1D nonlinear finite element model is presented for the analysis of composite foam-insulated concrete sandwich panel (FICSP) structures. The material nonlinearities of concrete wythes, steel rebar and insulation layer are considered. By employing a sinus shear deformation beam theory, the effects of transverse shear stress in concrete wythes and insulation layer are incorporated in the presented finite element formulation. The present formulation takes into account the partially composite action of FICSP structures by using the concept of distributed spring layer model. Full-scale experimental data and 3D finite element results are used to validate the developed finite element formulation. The obtained numerical results demonstrate that the presented finite element model of this study is an efficient tool to predict the detailed structural response of FICSPs till collapse stage.

Optimum seismic design of multi-story buildings for increasing collapse resistant capacity

The distribution patterns of equivalent static seismic lateral forces used in current structural design codes are mostly derived from elastic vibration modes. Such force patterns may not be consistent with actual conditions when structures behave into the inelastic range or even into the collapse stage. In this study, a new design method for multi-story buildings that uses an optimum lateral force pattern is proposed based on the concept of uniform damage distribution at the collapse state of these buildings. To reduce the computational cost of statistical analyses for deriving the optimum lateral force pattern, the non-linear story behaviors are represented by a story shear-deformation model with tri-linear relationships. Systematic parametric analyses are performed to study the influences of various ground motion parameters (site condition, magnitude, distance to rupture, and near-fault effect) and structural parameters (number of stories, fundamental period, damping ratio, post-yielding stiffness, ductility, and degrading stiffness) on the optimum lateral force pattern. Formulas for the optimum lateral force pattern that are applicable for practical seismic designs are provided. The collapse resistant capacities of structures designed using the proposed and conventional methods are compared by fragility analyses. Results show that the proposed method increases the seismic collapse resistant capacity of structures under the same construction cost.

Zooming in on supermassive black holes: how resolving their gas cloud host renders their accretion episodic

Born in rapidly evolving mini-halos during the first billion years of the Universe, super- massive black holes (SMBH) feed from gas flows spanning many orders of magnitude, from the cosmic web in which they are embedded to their event horizon. As such, accretion onto SMBHs constitutes a formidable challenge to tackle numerically, and currently requires the use of sub-grid models to handle the flow on small, unresolved scales. In this paper, we study the impact of resolution on the accretion pattern of SMBHs initially inserted at the heart of dense galactic gas clouds, using a custom super-Lagrangian refinement scheme to resolve the black hole (BH) gravitational zone of influence. We find that once the self-gravitating gas cloud host is sufficiently well re- solved, accretion onto the BH is driven by the cloud internal structure, independently of the BH seed mass, provided dynamical friction is present during the early stages of cloud collapse. For a pristine gas mix of hydrogen and helium, a slim disc develops around the BH on sub-parsec scales, turning the otherwise chaotic BH accretion duty cycle into an episodic one, with potentially important consequences for BH feedback. In the presence of such a nuclear disc, BH mass growth predominantly occurs when infalling dense clumps trigger disc instabilities, fuelling intense albeit short-lived gas accretion episodes.

Molecular gas dynamics analysis on condensation coefficient of vapour during gas–vapour bubble collapse

This study investigates the influence of the condensation coefficient of vapour on the collapse of a bubble composed of condensable gas (vapour) and non-condensable gas (NC gas). We simulated vapour and NC gas flow inside a bubble based on the molecular gas dynamics analysis in order to replicate the phase change (viz., evaporation and condensation) precisely, by changing the initial number density ratio of the NC gas and vapour, the initial bubble radius and the value of the condensation coefficient. The results show that the motion of the bubble is unaffected by the value of the condensation coefficient when that value is larger than approximately 0.4. We also discuss NC gas drift at the bubble wall during the final stage of the bubble collapse and its influence on the condensation coefficient. We conclude that vapour molecules can behave as NC gas molecules when the bubble collapses, owing to the large concentration of NC gas molecules at the gas–liquid interface. That is, the condensation coefficient reaches almost zero when the bubble collapses violently.

The Glycosaminoglycan Content of Hip Cartilage in Osteonecrosis of Femoral Head: Evaluation with Delayed Gadolinium-Enhanced Magnetic Resonance Imaging of Cartilage.

Hip cartilage quality is essential for the success of joint-preserving surgery for osteonecrosis. This study aimed to characterize cartilage changes in osteonecrosis of femoral head (ONFH) using delayed gadolinium-enhanced magnetic resonance imaging of cartilage (dGEMRIC). Fifteen asymptomatic (control) and 60 ONFH subjects were included in this study. The ONFH subjects were stratified in accordance with the Association Research Circulation Osseous (ARCO) classification (n = 15 hips per ARCO stage). All participant hips were investigated using dGEMRIC and theT1Gd data were collected and analyzed. T1Gd value was significantly lower in the ONFH group (365.1 ± 90.5 ms; range 200-498 ms) compared with the control group (546.1 ± 26.0 ms; range 504-580 ms) (P < 0.001). The T1Gd values of ARCO stage I-IV ONFH were 460.2 ± 17.3 ms (439-498 ms), 408.9 ± 43.4 ms (337-472 ms), 359.9 ± 34.5 ms (303-412 ms), 231.5 ± 15.1 ms (200-253 ms), respectively. Decreased T1Gd value was found to correlate significantly with increased ONFH severity (P < 0.001). T1Gd value in collapse stage was significantly lower than that of noncollapse stage (295.7 ± 70.3 ms [range 200-412 ms] vs. 434.6 ± 41.7 ms [range 337-498 ms]; P < 0.001). dGEMRIC identified hip cartilage as abnormal in ONFH, even at early-stage, as represented by decreased T1Gd, and this was further aggravated by ONFH collapse.

In situ X-ray micro-CT for investigation of damage evolution in black shale under uniaxial compression

Crack damage evolution of shale is crucial to the hydraulic fracturing treatment and engineering stability. Although many effects have been done on the macroscopic characteristics of shale, yet the microscopic failure mechanism is not well understood. A uniaxial compressive test on black shale was conducted under topographic monitoring using in situ X-ray micro-tomography (µCT). A series of high-resolution reconstruction images were obtained by carrying out CT scans at six key points throughout the test to obtain the internal structure of shale sample. In addition, the CT values for the purpose of crack damage evolution in shale were identified. Clear 2D/3D CT images, CT value analysis and image segmentation analysis reveal that the sample experiences compression, damage, cracking, crack propagation, and collapse stages. Crack geometry and distribution in the shale sample is visualized by rendered CT images, and a combined tension and shear failure mode is observed from the fracture rose diagram. This work suggests that formation and propagation of fractures are influenced by the stratified structure and weak cementation medium between layers.

Crushing and densification of rapid prototyping polylactide foam: Meso-structural effect and a statistical constitutive model

The deformation characteristics and mechanical behavior of closed-cell polylactide (PLA) foams under quasi-static uniaxial compression are investigated. The PLA foam specimens are constructed numerically with 3D Voronoi technique and prepared with fused deposition modeling (FDM). The effects of meso‑structure, layer deposition strategy and relative density on the crushing and densification behaviors of PLA foams are analyzed. The experimental results indicate that PLA foams with regular meso‑structures are more likely to induce local collapse during compression, and those with random meso‑structures show good performances, such as high specific energy absorption, low stress fluctuation and stable deformation process. The experimental results further reveal that random PLA foams with the deposition layers perpendicular to the loading direction have higher strength and smaller lateral expansion than those with other orientations. The quasi-static compression stress-strain curves of random PLA foams exhibit three typical stages, namely linear elastic stage, plastic collapse stage and densification stage. A stress drop after reaching the initial peak stress is observed. To characterize these features, we propose a statistical constitutive model which takes into account the meso‑structural characteristics and deformation mechanism at the cell scale. This constitutive model contains six parameters and fits the experimental results very well. In particular, it can capture the peak stress at the onset of plastic collapse and the subsequent stress drop of cellular materials. Finally, the dependence of the six parameters in the constitutive model on the relative density is analyzed and the corresponding quantitative statistical relationships are determined.

Quantitative evaluation of progressive collapse process of steel portal frames in fire

This paper presents quantitative investigations on the collapse behavior of steel portal frames exposed to standard fires. The complete collapse process is divided into safe, alert, dangerous and collapse stages. These four stages are to warn firefighters to make timely reactions to stay, ready to evacuate, and must evacuate, respectively. Numerical models are established and validated against fire tests on a full-scale steel portal frame. Based on the key displacements of the heated columns and rafters, the four stages are quantitatively determined in terms of visible phenomena and warning times. It is found that one should be ready to evacuate when the heated rafter shows large deflections, and must evacuate when the heated column moves back to its initial position. The 1 h, 2 h, 3 h fire rating of protected steel portal frames can be used to estimate the ready-evacuate, must-evacuate and collapse warning time, respectively. The findings from this preliminary study aim to provide references for firefighters to make wise decisions to evacuate timely and safety from the fire scene.

Micro-damage evolution and macro-mechanical property degradation of limestone due to chemical effects

Nuclear Magnetic Resonance (NMR) imaging in combination with mechanical tests are carried out to investigate the influence of chemical solutions on porosity change, micro damage and macro mechanical property degradation of limestone samples under external stress. The NMR images and T2 values for compression stage, micro damages emergence stage, micro damages development stage and fracture and collapse stage are obtained and analysed. The results of the corrosive influence of chemical solutions with different pH values and immersion periods on the mechanical property degradation of limestone samples are investigated. By choosing porosity as the damage variable, the micro damage of the samples during triaxial compression are calculated. It can be concluded that pH values of the chemical solutions change the porosity and micro damage evolution of the rock, which is the root reason for its mechanical properties degradation. The chemical erosion also has a significant influence on the micro crack propagation in the limestone samples under triaxial compression.

Effects of sclerotic changes on stress concentration in early-stage osteonecrosis: A patient-specific, 3D finite element analysis.

Stress distribution remains unclear in early-stage osteonecrosis of the femoral head (ONFH). To clarify this issue, we generated patient-specific finite element models (FEMs) from 51 patients with ONFH. Patients' hips were classified into three groups: ONFH without a sclerotic boundary (Stage 1, n = 6), ONFH with a sclerotic boundary (Stage 2, n = 10), and ONFH with both a sclerotic boundary and <2 mm collapse (Stage 3, n = 35). Four hips without ONFH were used as controls. Stress distribution in each FEM was compared with magnetic resonance imaging (MRI) and computed tomography (CT) results. Fifteen wholly resected femoral heads in Stage 3 hips were assessed by micro-CT. Furthermore, we histologically examined three Stage 2 femoral heads that subsequently developed subchondral fractures after FEM analyses. In all FEMs of both control and Stage 1 hip, stress was equally distributed on the femoral head surface. However, in all FEMs of both Stages 2 and 3 hips, stress was concentrated at the lateral boundary of the femoral head surface, corresponding to both a low-intensity band on T1-weighted MRI images and sclerotic changes on CT. On micro-CT, subchondral fractures consistently began at the lateral boundary with sclerotic changes, in which bone volume fraction was increased. Histology showed breakage of subchondral plates at the junction between necrotic and reparative zones. In early-stage ONFH, sclerotic changes caused stress concentration, which can trigger subchondral fractures at the lateral boundary. Clinical Significance: Our results will clarify the pathogenic mechanism of collapse in ONFH. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:3169-3177, 2018.

Cyclotron acceleration of energetic ions by plasma blobs

Due to their intrinsic vertical polarization induced by magnetic drifts, outward propagating plasma blobs (filaments), which arise at the nonlinear stage of the pedestal collapse, can serve as natural gaps for cyclotron acceleration of the fast ions having gyro-radius larger than the blob size transverse to magnetic field. Acceleration time is determined by the drift motion of the fast ion guiding center. For the electron temperature at the separatrix Tes ∼ 100 eV, even one blob encountered by the fast ion in the scrape-off layer can increase its energy by 50–60 keV above the injection energy. The possible relation of this result with observations in the ASDEX Upgrade tokamak is discussed.

Pressure and Velocity Fluctuation in the Numerical Simulation of Bubble Detachment in a Venturi-Type Bubble Generator

The Venturi-type bubble generator proposed by Oak Ridge National Laboratory is used to produce micro-sized bubbles. In this paper, a numerical simulation is carried out to study the process of the bubble formation and detachment from a wall orifice of a Venturi-type bubble generator in a cross-flowing liquid. The Volume-of-Fluid (VOF) method is applied to track the two-phase interface and study the evolution of the bubble formation. The result of the computation provides a visual three-dimensional bubble and shows the process of bubble formation and detachment. Three stages are identified during bubble formation (the expansion stage, the rising stage, and the collapse stage). Because of the compressibility of the gas, a fluctuation of the pressure and the mass flow rate in the gas chamber is observed, which is considered a significant effect on the bubble formation and detachment. The mechanism of the bubble detachment is clarified with the help of the mass flow rate fluctuation. The equivalent diameter is compared with that predicted by a previous model. A Coupled Level Set Volume-of-Fluid (CLSVOF) simulation is compared with the VOF simulation; the three stages and the fluctuation are also observed in the CLSVOF simulation.

Verification of the applicability of the Gaussian mixture modelling for damage identification in reinforced concrete structures using acoustic emission testing

This article presents an experimental study on verification of the applicability of Gaussian mixture modelling (GMM) algorithm of acoustic emissions for damage identification in reinforced concrete (RC) structures. Eight RC-flanged beam specimens with different properties were tested subjected to flexural loading. An incremental cyclic load was applied on RC-flanged beam specimens till failure, and simultaneously, the released acoustic emissions (AE) were recorded. It may be required to study crack classification in RC structures, because crack classification studies are useful to predict the structural performance and subsequently to implement the appropriate structural rehabilitation methods. AE belonging to tensile cracking and shear cracking can be studied by a probabilistic approach. It was observed that the line separating the AE clusters belonging to tensile and shear cracks was shifting towards a higher rise angle as the specimen is reaching collapse stage. This observation indicates dominance of shear cracks near the collapse stage. At the loading cycle where yielding occurred in the test specimen obtained by using GMM algorithm for AE, the load cycle entered into heavy damage zone is almost same as per NDIS-2421 damage assessment chart. The results obtained by both GMM algorithms for AE and NDIS-2421 criterion to evaluate the damage in the RC-flanged beams were compared and discussed.

Relation between alternating open/closed-conduit conditions and deformation patterns: An example from the Somma-Vesuvius volcano (southern Italy)

We present the results of a meso-scale systematic structural analysis of fractures, faults and dykes exposed at the Somma-Vesuvius volcano (southern Italy). Observed fractures include: (i) radial and tangential (with respect the caldera axis), sub-metric to metric joints associated with the edifice load and volcano-tectonic activity (i.e. inflation, deflation and caldera collapse stages) and (ii) decameter-scale fractures related to volcano flank instabilities. For the Somma-Vesuvius volcano, preexisting radial joints were commonly reactivated as transfer faults during the caldera formation, allowing different blocks to move toward the center of the collapsing area. Dykes occur with different geometries, including en-echelon structures bounding structural depressions. The orientation analysis of all structures indicates that they are preferentially oriented. Furthermore, we provide a morphological lineament analysis using high-resolution Digital Terrain Models of Somma-Vesuvius. Azimuth and spatial distribution of dykes and morphological lineaments were analyzed for comparison with the old Somma Crater and Gran Cono axes, respectively. Results highlight the overprinting of radial and clustered strain patterns recorded in different volcano-tectonic evolution stages. We suggest a possible deformation evolution model in which structures develop along either radial or preferential trends, highlighting different volcanic conditions: (i) where radial patterns occur, the structures developed during volcanic inflation cycles with a closed magmatic conduit condition whereas (ii) clustered patterns are probably associated with a regional strain field that overcomes the local deformation field, a situation typical in the case of open-conduit activity.

Acoustic emission data analyses based on crumb rubber concrete beam bending tests

Acoustic emission (AE) is a vital analysis method used to explain the fracture properties of concrete specimens. Four representative analyses methods, including the b-value method, AE signal intensity, average frequency (AF) versus RA (RA means rise time divided by the amplitude) value, and cluster analyses, are utilised to characterise and analyse the damage mechanisms and failure modes of three-point and four-point crumb rubber concrete bending beams with different rubber contents, including, 0%, 5%, 10%, and 15%. Tests and analysed results show that the fracture magnitude in the crumb rubber concrete is larger than that in the normal concrete before the main collapse stage. The improved b-value (Ib-value) fluctuations in local regions are more closely clustered with increase of rubber content. Based on intensity analyses, the severity (Sr) and historical index (HI) boundaries of the safe regions of crumb rubber concrete are proposed. Three clusters that correspond to the three different stages of the fracture process are mainly observed. There is a very clear distinction between the different clusters based on RA and AF values for all specimens. Furthermore, the AE rise time, ring down counts, energy, duration, and amplitude, are indicators used in the cracking mode characterization of the tested specimens.

Investigation on the characteristics of overlying strata caving in the Chengchao Iron Mine, China

In this study, a comprehensive assessment of the overlying strata caving characteristics of mental mines is conducted for the non-pillar sublevel caving method, especially considering the geological features and rock mass characteristics. In general, the overlying strata caving process can be divided into four stages: the intermittent roof caving stage, the crack extension and surface subsidence stage, the karst collapse stage, and the mining-induced collapse stage. Roof caving is an intermittent process, with higher caving occurring in stronger rock masses, and occurs more easily in weaker rock masses. Due to gaps generated in the overlying rock mass, the bulking coefficient of the overlying strata is much greater than the laboratory-measured value; it also varies with the mining advance lines. During the crack extension and surface subsidence stage, the surface deformation is less extensive when the rock strength is greater, and the gradient of surface deformation is lower when the rock mass integrity is lower. Thus, higher mining height and lower rock mass quality result in greater surface deformation. Furthermore, weak planes, such as faults and joints, can help to generate fissures in weathered rock masses; these fissures create passageways for groundwater flow, which accelerates crack extension and connection in reverse. In addition, surface collapses can be divided into karst collapses and mining-induced collapses. Because a large number of fissures and a high karst rate create favorable conditions for karst collapse, significant variations in groundwater levels can induce karst collapse at the surface, with high negative pressure forming in the karst caves. Mining-induced collapses are mainly related to the mining depth, mining height, and the properties of the overlying rock mass. Underground mining is a major factor in surface collapse, and heavy rainfall can induce a delayed but sudden collapse.