High-speed Propagation Research Articles

Study of crack dynamic propagation behavior of fine-grained concrete under static loading

Under static loading, crack propagation processes are a dynamic process due to very high propagation speeds. For fine-grained concrete material under static loading, the crack propagation speed can reach 723.7 m/s, thus the crack propagation process under static loading actually can be considered as a dynamic issue, not a static issue. Crack propagations with a rapid speed are extremely unfavorable to the stability of concrete structures. Therefore, it is of significance to study the dynamic fracturing of concrete structure under static loading. Three-point bending (TPB) tests were conducted by using concrete specimens. A novel test system coupled with crack propagation gauges (CPGs) and strain gauges (SGs) was utilized to measure the crack speed and the initiation loads. The experimental results show that crack propagation velocities are not a constant and the propagation toughness of fine-grained concrete varies with the crack tip displacement. The initiation toughness is higher than the propagation toughness.

Numerical and experimental study of route choice behaviour using an impatience-determined model

ABSTRACTIn this paper, we present a dynamic impatience-determined route choice model that comprehensively considers the distance and density around exits. We apply this model into three scenarios (i.e. initially pedestrians are in centre, random and non-uniform distributions) and conduct a sensitivity analysis of the self-growth rate and propagation speed of impatience. We find that the centre and random distributions are insensitive to changes in two parameters. Under the non-uniform distribution, the high self-growth rate and small propagation speed of impatience lead to the quickest evacuation process. Moreover, the model enables the simultaneous observation of the pedestrian position and the impatience distribution from the dynamic impatience map. In addition, we conduct a series of experiments to evaluate the model. The experimental and numerical results demonstrate that the impatience level should be limited to an appropriate range because no impatience or excessive impatience leads to increased evacuation times.Highlights:A novel emotion-determined route choice model considering both the self-growth and the propagation of impatience is proposedThe update scheme is determined by the impatience levelA series of practical cases is executed to test the feasibility of this modelImpatience map over time can intuitively reflect the evacuation process and emotional state of pedestriansExperimental results indicate this model is applicable to the simulation of pedestrian behaviours

Research on the fatigue properties of S135 drill pipe steel under a variety of conditions

Through rotating bending fatigue test, the fatigue properties of S135 drill pipe steel were investigated under various conditions (a): the smooth specimens; (b): the notched specimens; (c): the notched specimens with H2S corrosion). The experimental results show that the fatigue life of smooth specimens is about 107 cycles at fatigue limit (540 MPa); the fatigue life of notched specimens is about 3 × 105 cycles at fatigue limit (320 MPa); and the fatigue life of notched specimens with H2S corrosion is about 5 × 104 cycles at fatigue limit (300 MPa). By analyzing the surface of fracture, it can be shown that the propagation direction of fatigue crack in the notched specimens is changed little and the propagation speed is faster than the smooth specimens. The cracks of notched specimens with H2S corrosion occur at the high-speed propagation earlier stage, and the initiation and propagation of crack are caused by hydrogen embrittlement and fatigue stress. Compared with H2S corrosion affect S135 drill pipe steel, the effect of the notch is greater on the fatigue life.

Intramonth oscillations of Atlantic ITCZ observed in SMAP satellite salinity

ABSTRACTThe time variability of wind and rainfall in the Atlantic Intertropical Convergence Zone (ITCZ) has a wide oscillation spectrum that includes strong intra-month periodicities. These latter short-period oscillations span from individual convection lifecycle events of a few hours to longer pentad and multi-week convective cluster periods. This study reports on measured ITCZ rain variability at periods of a few weeks and its imprint on sea surface salinity (SSS) observed using satellite remote sensing. Despite small amplitude of variations of only psu, these changes are shown to be detectable in radiometer SSS estimates collected by the Soil Moisture Active Passive (SMAP) satellite. They are shown to develop in the mid-Atlantic ITCZ latitude band and to follow its seasonal meridional progression. These rain-correlated sea surface signatures appear quasi-synchronously across a wide range of longitude. Both the ITCZ-related seasonal migration and high zonal propagation speeds distinguish these intra-month SSS oscillations from that of tropical instability waves (TIW), with TIWs having periods greater than month and slower westward propagation. While detection of tropical Atlantic TIW salinity signatures using satellite data has received significant attention, it appears that atmospheric freshwater forcing impacts on the upper ocean at these shorter periods represents an additional process resolvable from space using SMAP. Correlation analyses of precipitation and winds indicate that low latitude convection clusters are accompanied by an upward Ekman pumping anomaly, which uplifts saltier water to surface layers diluted by enhanced precipitation. These vertical processes modify the salt balance and change the phase relationship between the oceanic SSS response and the atmospheric freshwater forcing.

On the Origin of Perpendicular Ion Anisotropy Inside Dipolarizing Flux Bundles

AbstractPerpendicular anisotropy of suprathermal ions, observed inside some of the dipolarizing flux bundles (DFBs) in the magnetotail plasma sheet, have been attributed to successive, betatron‐type accelerations during the DFB entry of ambient ions. It has been unclear, however, where and how these ions enter the DFBs. The proposed locations include the DFB flanks where cross‐tail drifting ions are picked up, and the DFB leading edge with sharp magnetic field gradient (the dipolarization front, DF). Here we examine the latter scenario, based on a simplistic, test particle approach, to predict the preferred conditions for the appearance of the DFB ion anisotropy. Our model predicts that the ion anisotropy would be stronger at locations closer to the neutral sheet and would appear preferentially in the DFB dawnside and central sectors rather than the duskside sector. We also predict that the ion anisotropy would more likely be observed in DFBs with higher propagation speeds. These properties can be understood in our model by the dawnward drift of ions during their DF penetration (attributed to the large magnetic gradient). To examine these predictions, we carry out a statistical survey based on observations from the THEMIS (Time History of Events and Macroscale Interactions during Substorms) mission, to show a clear dependence of the ion anisotropy on spacecraft location and the DFB propagation speed. These findings, therefore, are consistent with the scenario that the perpendicular ion anisotropy originates from the ion acceleration and penetration across sharp DFs.

Hydrodynamic processes in fused quartz under the action of laser radiation

The paper analyzes numerically the hydrodynamic processes developing inside the fused quartz under the action of intense laser impulses. Depending on laser intensity two basic regimes are obtained and described in details. At low intensities, the slow regime driven by the heat transfer is observed. Herewith, the fracture took place in the heated region before the phase transition. At higher intensities, the high-speed propagation regime is established characterized by the fracture events exactly at the interfacial boundary between the hot plasma and condensed phase. The propagation of absorption wave coupled with the fracture wave is limited by the value of sound speed in the hot plasma, which determines the expansion of plasma into the spallation region ahead of the absorption front. The proposed model of the process agrees well with the recent experimental data, in particular with the characteristic velocity scales.

Development of planar meso­scale combustor with double narrow slit flame holder and various aspect ratios for micropower generator

We have investigated the effects of the aspect ratio of the rectangular mesoscale combustor with a narrow slit flame holder on the flame stability limit, flame behavior and uniformity of combustor wall temperature. The combustor was made of copper with a cross-section area of 6 mm2. The combustor aspect ratio (AR) was varied as 1, 1.5, 2.67, and 6. LPG and pure oxygen were premixed and the experiment was conducted at a limited flow rate. Pure oxygen is selected as an oxidizing agent with the intention of revealing in detail the range of flame stability within a very narrow quenching distance. All observed flames were inside the combustion chamber, not outside the channel. This research used a new type of flame holder namely double narrow slit flame holder as a flame stabilizer. The flame holder with double slit and a kind of bluff body in the center helps recirculate the flow and prolong the residence time to make the flame more stable. The use of double narrow slit flame holder successfully extended the stability map to a very lean equivalence ratio (f). However, there was a dead zone near stoichiometry condition due to very high flame propagation speed. Aspect ratio had an important role for the non-circular combustor. The aspect ratio gave a great effect to determine the limit of the stability map that can be achieved at the rich mixture. The combustor with AR=1.5 had the widest range of flammability limit, while AR=6 hadthe narrowestflame stability limits. However, the latter reached the most uniform wall temperature, which is important to obtain high efficiency thermal to electric energy conversion. The results of this study can be used to determine the right fuel mixture on the mesoscale combustor as a heat source on the micro power generator/thermal electric system

Pancake joints in Utica gas shale: Mechanisms for lifting overburden during exhumation

The Flat Creek Member of the Utica Formation along Canajoharie Creek south of Canajoharie, NY, is populated with unmineralized pancake joints, a term for horizontal, bed-parallel partings. Each pancake joint propagated outward from a central initiation point with radial growth in excess of 0.5 m in some instances. Propagation arrests with out-of-plane growth displaying either a tilt characteristic of an arrest line or bifurcation into a complex set of cylindrical splays or hackles. A rough surface morphology relative to vertical fractures (i.e., joints and veins) in the Flat Creek coupled with bifurcation at arrest are the manifestation of an accelerating crack tip reaching critical growth at the shear-wave velocity of the shale. The lack of mineralization and containment between vertical fractures are consistent with propagation during exhumation. One driving mechanism for a late propagation event could be axial splitting which places pancake joints in a class of brittle fracture that includes sheeting joints. The high-speed propagation is a manifestation of the rapid release of fracture energy characteristic of sheeting joints. However, we also consider a second driving mechanism, natural hydraulic fracturing. In the Appalachian Basin, high pore pressure is maintained in gas shale at depths less than 50% of the original overburden. If abnormal pore pressure is maintained for 300 my or more, it is present when exhumation carries the shale upward through the crossover depth where the least stress becomes vertical. If pore pressure exceeds the vertical stress, then pore pressure will lift overburden. A possible mechanism for maintaining pore pressure during exhumation to shallow depths is a poroelastic phenomenon known as Skemption's behavior. We posit that pancake joints differ from common sheeting joints because of the additional contribution from abnormal pore pressure as a driving mechanism that allows for deeper propagation depth.

Quench Propagation in Nb<inline-formula> <tex-math notation="LaTeX">$_\text{3}$</tex-math> </inline-formula>Sn Cos-Theta 11 T Dipole Model Magnets in High Stress Areas

A large number of training quenches at various currents, temperatures, and ramp rates, have been performed on six 11 T dipole model magnets. Quenches in the midplane of these magnets were of special interest, since the quench current in the last three models measured in 2016 was limited to between 84% and 92% of the magnets short sample limit. Measurements of quench propagation velocity, based on both voltage taps and quench antennas, yield a high propagation velocity of 50 to 80 m/s. Due to the high magnetic field gradient over the width of the midplane turn such a high propagation speed cannot be explained by propagation in longitudinal direction of the strand following the twist pitch. In these cases, current and heat sharing at the thin cable edge (where the field, stress, and cable compaction are high) are likely to provoke strand-to-strand quench propagation at higher velocities than along the strands. This investigation is focused on analyzing the quench propagation along the strands and strand-to-strand of various measured cases.

Research Progress of Low Dielectric Benzoxazine Resin

Benzoxazine resin, a new type of phenolic resin, has many advantages, such as a strong molecular design, no small molecular release in the curing process, excellent thermal stability and mechanical properties, and a high residual carbon ratio. Thus, it is important for electronic communication industry matrix material. To meet the needs of high-frequency and high-speed communication technology for low-dielectric polymer resin, the low-dielectric modification of benzoxazine resin is of great significance to the high frequency and high-speed propagation of the signal, which attracts a wide range of materials researchers’ attention. In this paper, we review a series of studies on the low dielectric modification of benzoxazine resin in recent years, including the synthesis of new monomers, inorganic - organic hybridization, copolymerization with other resins, and low molecular weight benzoxazine resin research trends.

Visualized localization and tracking of debris flow movement based on infrasound monitoring

During the initiation and movement of debris flow, low frequency infrasound is generated and emitted with characteristics such as strong penetration, low attenuation, and a high propagation speed that is faster than the debris flow. Monitoring infrasound has been used in debris flow detection and early warning systems; however, although the current infrasound-based warning system of debris flow can provide an alarm when debris flow occurs, it cannot locate and track the movement of debris flow in real time, and cannot determine the arrival time of debris flow to its potential victims. Thus, the potential applications of low frequency infrasound in debris flow disaster prevention and reduction have not yet been fully explored. In this study, we constructed an optimal triangular monitoring array based on factors such as the terrain of the monitoring area and characteristics of infrasound propagation. Combined with the time-delay estimation method, we determined and established an acoustic source localization model based on the time difference of arrival. Furthermore, with the help of a GIS platform, a visualized localization and tracking system for debris flow movement was developed to achieve real-time monitoring of debris flow. The performance of the system on acoustic source localization was validated using a simulation test and long-term field monitoring of debris flow at Jiangjia gully in Dongchuan, Yunnan province, China. Both the simulation and field test results showed that the system has high localization accuracy and strong real-time response. The results of the monitoring system could provide more accurate warning information of debris flow to local government and residents, allowing them to take appropriate mitigation measures well in advance to reduce the loss of life and property caused by debris flows.

Three-dimensional ray-tracing simulation of fast magnetoacoustic waves in a stratified solar atmosphere

In the solar atmosphere, there exist two frequently-observed phenomena, Moreton waves and EIT (extreme-ultraviolet imaging telescope) waves, whose physical nature is still under debate. In this work, we perform a three-dimensional ray-tracing simulation for the propagation of fast magnetoacoustic waves. We build a stratified solar atmosphere model and take partial ionization into consideration to give an exact description of chromosphere and transition region. The calculated result is compared with a flare event observation in which both Moreton waves and EIT waves were present. In agreement with observations, the calculated wavefront show different kinematical characteristics in different propagation directions during different times. Moreton waves and EIT waves have higher propagation speeds near the active region where the magnetic field strength is strong. The result suggests that both Moreton waves and EIT waves of this event can be interpreted as the fast magnetoacoustic waves propagating at different heights in the solar atmosphere.

Specyfika, funkcje i mechanizmy stanów medytacyjnych na podstawie badań neuropsychologicznych nad uważnością

Neuropsychological findings suggest that mindfulness state (meditation state) can be shown as higher state of consciousness, which differs from relaxation state (requires much more energy) and alertness (domination of parasympathetic activation). At the higher level of meditation (low demand for energy), there occur increased activation of the anterior cingulate cortex (ACC), left insula and striatum, and reduction of activation of the lateral prefrontal cortex (LPFC) and parietal cortex. Meditation plays an important role in top-down switching (early noticing of the stimulus – 100 msec. after appearance of the stimulus) and maintenance of the attention (dealing with mind wandering). Crucial mechanisms occurring during meditation states are: vertical synchronization of brain steam, limbic system and neocortex (higher attention of stimuli), bilateral hemispheric activation (deeper insight on negative emotions and unconsciousness) and domination of gamma band fluctuations (high speed of information propagation). Specificity, functions and mechanisms occurring in meditative states have a positive influence on many aspects of the humane life (bodily regulation, attuned communication, emotional balance, fear extinction, response flexibility, insight, empathy, intuition and morality).

On the Dependence of Squall-Line Characteristics on Surface Conditions

Abstract The influence of surface conditions in the form of changing surface temperatures on fully developed mesoscale convective systems (MCSs) is investigated using a cloud-system-resolving setup of the Icosahedral Nonhydrostatic (ICON) model (1-km grid spacing). The simulated MCSs take the form of squall lines with trailing stratiform precipitation. After the squall lines have reached a quasi-steady state, secondary convection is triggered ahead of the squall line, resulting in an increase of squall-line propagation speed, also known as discrete propagation. The higher propagation speed is then maintained for the remainder of the simulations because secondary convection ahead of the squall line acts to reduce the environmental wind shear over the depth of the squall line’s cold pool. The surface conditions have only a marginal effect on the squall lines themselves. This is so because the surface fluxes cannot significantly affect the cold pool, which is continuously replenished by midtropospheric air. The midtroposphere remains similar given the use of identical initial profiles. The only effect of the surface fluxes consists in an earlier acceleration of the squall line due to earlier initiation of secondary convection with higher surface temperature. Finally, a conceptual model to estimate the change in surface temperature needed to achieve a change in onset time of prefrontal secondary convection and the associated discrete propagation events given the environmental conditions is presented.

THERMOPLASTIC POLYMER MACHINE GUARDS – EXPLOITATION SAFETY

The machine construction sector uses from 2 to 5% of thermoplastic polymer produc-tion. This material is used to make small elements and big parts of equipment, includ-ing guards. The latter have mechanical vibration damping capacity, do not require any maintenance, are cheap and look attractive. Moreover, polymer guards are an essen-tial element of machines as they improve workplace safety. They are used in such ma-chines as lathes, milling machines, drills, extruding machines, presses and grinders. Pursuant to the Ordinance of the Minister of Labour and Social Policy on general provi-sions for safety and health at work, protective devices used in machines should be strong and durable so as to ensure the appropriate level of occupational safety. This is why the selection of the right material to make such devices is essential. Most fre-quently guards used in the market are steel frames with a polycarbonate screen or lam-inated safety glass. Other materials used to manufacture guards are poly(methyl methacrylate) (PMMA) and polystyrene (PS). Thermoplastics are characterised by high visual light transmittance (even up to 98% in the case of PMMA), easy treatment, pos-sibility to form any shape and resistance to atmospheric factors. However, they are also characterised by limited high temperature resistance, low fire resistance and high speed of fire propagation on their surface which may be dangerous for employees in case of fire. The article discusses the selection of appropriate material for the produc-tion of guards in the context of their exploitation in higher temperature conditions and examines threats posed by thermoplastics in fire conditions.

Reopening modes of a collapsed elasto-rigid channel

Motivated by the reopening mechanics of strongly collapsed airways, we study the steady propagation of an air finger through a collapsed oil-filled channel with a single compliant wall. In a previous study using fully compliant elastic tubes, a ‘pointed’ air finger was found to propagate at high speed and low pressure, which, if clinically accessible, offers the potential for rapid reopening of highly collapsed airways with minimal tissue damage (Heap & Juel Phys. Fluids, vol. 20 (8), 2008, 081702). The mechanism underlying the selection of that pointed finger, however, remained unexplained. In this paper, we identify the required selection mechanism by conducting an experimental study in a simpler geometry: a rigid rectangular Hele-Shaw channel with an elastic top boundary. The constitutive behaviour of this elasto-rigid channel is nonlinear and broadly similar to that of an elastic tube, but unlike the tube, the channel’s cross-section adopts self-similar shapes from the undeformed state to the point of first near wall contact. The ensuing simplification of the vessel geometry enables the systematic investigation of the reopening dynamics in terms of increasing initial collapse. We find that for low levels of initial collapse, a single centred symmetric finger propagates in the channel and its shape is set by the tip curvature. As the level of collapse increases, the channel cross-section develops a central region of near opposite wall contact, and the finger shape evolves smoothly towards a ‘flat-tipped’ finger whose geometry is set by the strong depth gradient near the channel walls. We show that the flat-tipped mode of reopening is analogous to the pointed finger observed in tubes. Its propagation is sustained by the vessel’s extreme cross-sectional profile at high collapse, while vessel compliance is necessary to stabilise it. A simple scaling argument based on the dissipated power reveals that this reopening mode is preferred at higher propagation speeds when it becomes favourable to displace the elastic channel wall rather than the viscous fluid.

Intermittent tremor migrations beneath Guerrero, Mexico, and implications for fault healing within the slow slip zone

AbstractSlow slip events exhibit significant complexity in slip evolution and variations in recurrence intervals. Behavior that varies systematically with recurrence interval is likely to reflect different extents of fault healing between these events. Here we use high‐resolution tremor catalogs beneath Guerrero, Mexico, to investigate the mechanics of slow slip. We observe complex tremor propagation styles, including rapid tremor migrations propagating either along the main tremor front or backward, reminiscent of those in northern Cascadia. We also find many migrations that originate well behind the front and repeatedly occupy the same source region during a tremor episode, similar to those previously reported from Shikoku, Japan. These migrations could be driven by slow slip in the surrounding regions, with recurrence intervals possibly modulated by tides. The propagation speed of these migrations decreases systematically with time since the previous migration over the same source area. Tremor amplitudes seem consistent with changes in the propagation speeds being controlled primarily by changes in the slip speeds. One interpretation is that the high propagation speeds and inferred high slip speeds during the migrations with short recurrence intervals are caused by incomplete healing within the host rock adjacent to the shear zone, which could lead to high permeability and reduced dilatant strengthening of the fault gouge. Similar processes may operate in other slow slip source regions such as Cascadia.

Evaluation of NALDN performance characteristics in the vicinity of the CN Tower based on tall-structure lightning

The North American Lightning Detection Network has been providing lightning data since 1998. Important applications, such as detection of lightning-caused forest fires, power line fault location and aviation safety procedures, have triggered a number of hardware and software upgrades for improvement of the network performance characteristics, including its detection efficiency and location accuracy. The performance characteristics of the network have been here evaluated by examining the reported North American Lightning Detection Network (NALDN) return-stroke data based on the lightning current measured at CN Tower during three major storms (2005, 2011 and 2014). Each of these three storms followed a substantial network upgrade in 2003–2004, 2010–2011 and 2013–2014, respectively. The objective of this investigation is to outline the evolution of the network and determine where there may be opportunities for additional improvements. (It is important to stress that the evaluation of NALDN in the vicinity of the tower is mainly based on tall-structure lightning, which is upward-initialed, due to the rarity of recording downward-initiated lightning at the extremely tall tower.) Since 1990, the CN Tower has been equipped to measure the lightning current derivative signals. Its 553-m height has allowed the recording of many hundreds of current derivative signals, mostly resulting from return strokes. Also, image recording systems have been used to capture images of strikes to the tower. The evaluation of the NALDN performance characteristics includes polarity, flash and stroke detection efficiency, location accuracy and peak current estimation. The 2013 deployment of LS7002 digital sensors with the enhanced embedded software has substantially improved the sensitivity of the sensors leading to greater flash and return-stroke detection efficiencies. Furthermore, the 2014 total lightning processor (TLP100), well designed with new algorithm and techniques, provides smaller time-of-arrival errors and better location accuracy. Based on this investigation, following the latest network upgrade, the polarities of the NALDN-detected return strokes were perfectly matched with the polarities of the corresponding return-stroke currents measured at the tower. In 2014, the NALDN detected every flash that contained at least one return stroke, as well as all recorded CN Tower return strokes, resulting in 100% flash- and stroke-detection efficiencies. The perfect stroke-detection efficiency in 2014 confirms a significant network improvement in comparison with the assessment in 2005 (55.3%) and 2011 (53.8%). In the 2014 evaluation, relative to the location of the tower, the NALDN is found to have a median absolute location error of 119m and an average absolute location error of 129m. The 2014 median absolute location error is found to be significantly lower than those for 2005 (289m) and 2011 (199m). Based on 2014 evaluation, the NALDN is found to overestimate the current peak measured at the tower by a factor of 3.89, which is due to field enhancement effect resulting from high speed propagation of the current within the tall tower. The presented analysis shows that the latest NALDN upgrade (2013–2014) following the 2003–2004 and 2010–2011 upgrades, has substantially improved the NALDN performance characteristics, especially in terms of stroke-detection efficiency and location accuracy.

Application of the final flotation waste for obtaining the glass-ceramic materials

This work describes the investigation of the final flotation waste (FFW), originating from the RTB Bor Company (Serbia), as the main component for the production of glass-ceramic materials. The glass-ceramics was synthesized by the sintering of FFW, mixtures of FFW with basalt (10%, 20%, and 40%), and mixtures of FFW with tuff (20% and 40%). The sintering was conducted at the different temperatures and with the different time duration in order to find the optimal composition and conditions for crystallization. The increase of temperature, from 1100 to 1480?C, and sintering time, from 4 to 6h resulted in a higher content of hematite crystal in the obtained glass-ceramic (up to 44%). The glass-ceramics sintered from pure FFW (1080?C/36h) has good mechanical properties, such as high propagation speed (4500 m/s) and hardness (10800 MPa), as well as very good thermal stability. The glass-ceramics obtained from mixtures shows weaker mechanical properties compared to that obtained from pure FFW. The mixtures of FFW with tuff have a significantly lower bulk density compared to other obtained glass-ceramics. Our results indicate that FFW can be applied as a basis for obtaining the construction materials.

Routing in FRET-Based Nanonetworks

Nanocommunications, understood as communications between nanoscale devices, is commonly regarded as a technology essential for cooperation of large groups of nanomachines and thus crucial for development of the whole area of nanotechnology. While solutions for point-to-point nanocommunications have been already proposed, larger networks cannot function properly without routing. In this article we focus on the nanocommunications via Forster Resonance Energy Transfer (FRET), which was found to be a technique with a very high signal propagation speed, and discuss how to route signals through nanonetworks. We introduce five new routing mechanisms, based on biological properties of specific molecules. We experimentally validate one of these mechanisms. Finally, we analyze open issues showing the technical challenges for signal transmission and routing in FRET-based nanocommunications.