Compression Expansion Research Articles

Effects of deep soil mixing on existing shield tunnels in soft soil ground

To mitigate the impact of adjacent construction on existing shield tunnels, deep soil mixing (DSM) has been widely used to reinforce the soft soil ground around shield tunnels. However, the construction of DSM may cause the movement of existing shield tunnels under soft soil and sensitive ground conditions, and reasonable installation parameters will reduce the impact of DSM construction on the existing shield tunnels. Based on the field tests of DSM installation parameters and a program of field measurements of existing shield tunnels during the DSM construction in Suzhou, the reasonable installation parameters of DSM were selected, and the movement of soil behind the soil mixing walls (SMWs) during multirow DSM installation was investigated. The movement of the shield tunnels caused by DSM construction were discussed in detail. The field test results showed that the DSM columns installed at a higher speed and a lower water-cement ratio enlarged the movement of the surrounding soil. The DSM should be installed at a lower speed and a higher water-cement ratio to reduce the movement of the shield tunnels. The field measurement results showed that the displacement of the tunnel lining was primarily caused by the construction of DSM zones beside the shield tunnels, which led to vertical compression and horizontal expansion of the tunnel lining. The construction of DSM immediately above the shield tunnels caused uplift to the tunnels. In addition, the deformed shapes of the two shield tunnels were asymmetric, and the displacement of the spring lining was larger than that of the crown. By taking the reasonable installation parameters of DSM and under the protection of the SMWs, the deformation of the shield tunnels caused by the construction of DSM was effectively controlled, and the maximum displacement was within the control value of the shield tunnels in this study.

Dynamic Support Network for Few-Shot Class Incremental Learning.

Few-shot class-incremental learning (FSCIL) is challenged by catastrophically forgetting old classes and over-fitting new classes. Revealed by our analyses, the problems are caused by feature distribution crumbling, which leads to class confusion when continuously embedding few samples to a fixed feature space. In this study, we propose a Dynamic Support Network (DSN), which refers to an adaptively updating network with compressive node expansion to "support" the feature space. In each training session, DSN tentatively expands network nodes to enlarge feature representation capacity for incremental classes. It then dynamically compresses the expanded network by node self-activation to pursue compact feature representation, which alleviates over-fitting. Simultaneously, DSN selectively recalls old class distributions during incremental learning to support feature distributions and avoid confusion between classes. DSN with compressive node expansion and class distribution recalling provides a systematic solution for the problems of catastrophic forgetting and overfitting. Experiments on CUB, CIFAR-100, and miniImage datasets show that DSN significantly improves upon the baseline approach, achieving new state-of-the-arts.

Development and Field Application of Phosphogypsum-Based Soil Subgrade Stabilizers

A phosphogypsum-based subgrade stabilizer (PBSS) was formulated using industrial by-product phosphogypsum (PG), mixed with slag and calcium-silicon-rich active material (GSR). The active powder (AP) was used to modify PBSS, and PBSS-AP was obtained. PBSS and PBSS-AP were each mixed with 10% silty soil, and cement and lime (CAL: 5% lime + 2% cement) were used as the traditional material for comparative experiments. Samples were cured under standard conditions, and tested for unconfined compressive strength (UCS), water stability, volume expansion, and leachate, to explore the stabilization effect of the three solidified materials on silty soil. The results showed that the comprehensive performance of sility soil mixed with 12% PBSS-AP was the best. The CaO, SiO2 and Al2O3 provided by PG, Slag and GSR will react with water to form a stable C-S-H gel, which is conducive to stabilizing the soil. Field application results showed that the compaction exceeded 95%, the deflection was 144.9 mm, and UCS was 2.5 MPa after 28 days. These findings indicated that PBSS-AP is an effective stabilizer for subgrade soils.

Balanced change in crystal unit cell volume and strain leads to stable halide perovskite with high guanidinium content.

Up-to-date studies propose that strain in halide perovskites is one of the key factors that determine a device's efficiency and stability. Here, we show a systematic approach to characterize the phenomenon in the standard methylammonium lead iodine (MAPbI3) perovskite system by: (i) the substitution of some MA by guanidinium (Gu); (ii) the incorporation of PbS quantum dot (QD) additives and (iii) addition of both Gu and PbS at the same time. We studied the effect of these incorporations on the film strain and crystal cell unit volume, and on the solar cell device efficiency and stability. Gu cations and PbS QDs affect the strain, the former due to the relatively large dimensions of Gu, and the latter due to the lattice matching parameters. With the control of Gu and PbS QD content, higher performance and longer solar cell stability are obtained. We demonstrated that the presence of Gu and PbS QDs alters the structure of perovskite, in terms of modification of the unit cell volume and strain. The greater size of Gu cations produces a MAPbI3 unit cell volume expansion as Gu is incorporated, modifying the strain from compressive to tensile. PbS QDs aid Gu incorporation, producing a unit cell volume expansion. In the case of 15% mol Gu incorporation, the addition of PbS QDs modifies strain from compressive to tensile, limiting the deleterious effect. At the same time the unit cell volume is less affected, increasing the solar cell stability. Our work shows that the control of compressive strain and the unit cell volume expansion lead to a 50% increase in T 80, the time in which the PCE decreases to 80% of its original value, increasing the T 80 value from 120 to 187 days under air conditions. Moreover it highlights the importance of exploiting not only the control of the strain induced by internal component, the cation, but also the strain induced by the external component, the QD, associated instead with critical volume variation of metastable perovskite unit cell volume.

Development of Thermodynamic Model of a Rapid Compression Expansion Machine Applied for the Estimation of the Flame Front Speed of Air/Hydrogen Mixtures

Development of Thermodynamic Model of a Rapid Compression Expansion Machine Applied for the Estimation of the Flame Front Speed of Air/Hydrogen Mixtures

Herriott cell enhanced SMF-coupled multi-scalar combustion diagnostics in a rapid compression expansion machine by supercontinuum laser absorption spectroscopy

A novel supercontinuum laser absorption spectroscopy (SCLAS) approach combining a planar external Herriott multi-pass cell (HMPC) with fully single-mode fiber (SMF) coupling is presented for broadband multi-scalar combustion measurements in a rapid compression expansion machine (RCEM). For the HMPC, 1-dimensional refractive index gradients occurring in the RCEM combustion chamber are analyzed via ray-tracing with respect to axial and vertical beam steering. The impact of beam steering on the SCLAS signal is compared with the ray-tracing analysis and high-speed flame luminosity images. SCLAS based measurements are presented during compression, auto-ignition and combustion in the RCEM for n-heptane/methane mixtures at varied AFR (air-fuel ratio) and n-heptane/EGR (exhaust gas recirculation) mixtures at temperatures exceeding 1800 K and pressures up to 80 bar. Simultaneous temperature and mole fraction courses of H2O, CH4, and CO2 are inferred from NIR (near-infrared) broadband absorbance spectra detected by a Czerny Turner spectrometer (CTS) in a spectral range of 1374 nm to 1669 nm. The multi-pass approach with SMF coupling, which avoids multi-mode fiber induced noise, allows for high-speed multi-species SCLAS measurements with low standard deviations; for temperature this amounts to about 5 K and partially below at a temporal resolution of 25 µs.

Effect of heat source on statistics and scaling in compressible homogeneous shear turbulence

The effects of heat sources on the velocity and pressure spectra, Mach number scaling of one-point statistics, and small-scale structures of compressible homogeneous shear turbulence are numerically studied. The dilatational components of flow fields are significantly enhanced by a strong heat source at low turbulent Mach numbers Mt and are dominated by an acoustic mode, leading to a strong acoustic equilibrium between the dilatational velocity and pressure. As the magnitude of the heat source increases, the scaling behaviors of the dilatational components of kinetic energy and dissipation rate change from Mt4 and approach a state that is nearly independent of the turbulent Mach number. Furthermore, a strong heat source has a significant effect on small-scale structures at low turbulent Mach numbers. The conditional probability density functions of the normalized eigenvalues of a strain rate tensor become more dependent on the dilatation owing to the effect of the heat source. For low turbulent Mach numbers with strong heat sources, the ratio of the normalized eigenvalues of the strain rate tensor tends to −1:0:0 and −0.2:0.25:1 in the strong compression and strong expansion regions, respectively, and the dilatational vortex stretching term can significantly enhance the enstrophy production.

Falls prevention in China: time for action

Falls prevention in China: time for action

Numerical investigation of the effect of injection strategy on a high-pressure isobaric combustion engine

High-pressure isobaric combustion adopted in the double compression expansion engine (DCEE) has the prospect to achieve higher thermal efficiency compared to conventional diesel combustion. This work numerically explored the effects of various injection strategies on the combustion and emission characteristics of isobaric combustion. The study developed a mathematical model to predict the injection rate profile. After validations, extensive simulations were conducted with a peak pressure of up to 300 bar – mimicking the high-pressure unit of DCEE. Several major engine design parameters such as the exhaust recirculation gas (EGR) rate, engine speed, injection strategy, and intake pressure were varied and evaluated. The results demonstrated that a higher EGR rate resulted in a higher exhaust loss but a lower heat transfer loss owing to the lower combustion temperature, so the thermal efficiency exhibited a firstly growing and then declining trend. Besides, a higher engine speed generated a higher thermal efficiency due to the shorter combustion duration and thus lower heat transfer loss. Consequently, a peak thermal efficiency of 47.5% was achieved at EGR = 50% and 1800 rpm. The high-pressure cylinder performance can also be improved with an appropriate introduction of the isochoric combustion, but its impact on the whole DCEE setup needs further investigation.

Combustion characteristics of hydrogen in a noble gas compression ignition engine

Hydrogen eliminates carbon emissions from compression ignition (CI) engines, while noble gases eliminate nitrogen oxide (NOx) emissions by replacing nitrogen. Noble gases can increase the in-cylinder temperature during the compression stroke due to their high specific heat ratio. This paper aims to find the optimum parameters for hydrogen combustion in an argon–oxygen atmosphere and to study hydrogen combustion in all noble gases, providing hydrogen combustion data with suitable engine parameters to predict hydrogen ignitability under different conditions. Simulations are performed with Converge CFD software based on the Yanmar NF19SK direct injection CI (DICI) engine parameters. The results are validated with the experimental results of hydrogen combustion in an argon–oxygen atmosphere with a rapid compression expansion machine (RCEM), and modifications of the hydrogen injection timing and initial temperature are proposed. Hydrogen ignition in an argon atmosphere is dependent on a minimum initial temperature of 340 K, but the combustion is slightly unstable. Helium and neon are found to be suitable for hydrogen combustion in low compression ratio (CR) engines. However, krypton and xenon require temperature modification and a high CR for stable ignition. Detailed parameter recommendations are needed to improve hydrogen ignitability in conventional diesel engines with the least engine modification.

Behaviour of Concentrically Braced Steel Frames under Fire Loading

Knowing how a steel structure behaves under fire loading is of vital importance, given a large number of events in recent years have proved the vulnerability of steel structures under this type of hazard. Older concentrically braced frames have been widely used in buildings without observing seismic provisions and details. Although the vulnerability of this type of structural system, here referred to as non-seismic braced frames, has been studied under earthquake loading before, its behaviour under fire loading has not been investigated yet. This paper investigated the behaviour of global and local responses of the mentioned structural system under various uniform fire scenarios. The heating and cooling phases of fire were taken into account for different building stories using the finite element method. The results of analyses showed that the braces buckled at high temperatures due to the large compressive axial forces and expansion of lateral constraints. This phenomenon led to the early loss of lateral resistance of stories, which, in turn, resulted in the failure of columns. Consequently, the underlying floor collapsed under fire. The analysis results contribute to a better understanding of the behaviour of steel braced frames under fire conditions and the corresponding local and global responses.

Self-organization of pure electron plasma in a partially toroidal magnetic-electrostatic trap: A 3D particle-in-cell simulation

The dynamics of a pure electron plasma magnetically confined in a partial toroidal trap is investigated using 3D3V PIC simulation. In particular, a toroid having a rectangular meridian, a tight aspect ratio of 1.6, and a 3π/2 toroidal domain is considered. Externally applied negative end-plug potentials electrostatically seal off the toroidal ends of the device for the confined electron cloud. A homogeneous square-toroidal segment of pure electron plasma is loaded in the middle of the trap. Strong non-uniform sheared poloidal flow reshapes the square cross section into 00an elliptical profile with symmetric closed contours of density peaking in the center. On the toroidal midplane, the plasma gets shaped into a crescent by the opposing dispersing and confining forces of the self-electric field and the end-plug fields, respectively. Density inside the crescent falls symmetrically from the middle to the two tapered ends. The self-reorganization of the loaded square-toroidal segment into an “elliptic-crescent” is completed within a time scale of ∼0.1μs. The cloud then starts to engage in poloidal orbits of the fundamental (toroidal) diocotron mode. The poloidal orbit’s time period is ∼2μs. The first orbit is turbulent and incurs significant electron losses (∼30%) to a particular segment of the poloidal boundary. Subsequent orbits are dynamically stable with a compression–expansion cycle of the cloud as it moves in an out of strong magnetic fields on the poloidal plane. The poloidal compression–expansion cycle is collisionlessly coupled with the toroidal cloud shaping through the self-electric fields and manifests as an elongation–contraction cycle of the crescent on the toroidal midplane. A radical improvement of the device’s confinement is observed when its volume is isotropically compressed keeping other parameters the same. The numerical design of the partial toroidal trap has several novel aspects such as the use of specialized numerical “pseudo-dielectric” layers for producing functional end-plug fields in the numerical device setup.

Effect of Sulphur-Containing Tailings Content and Curing Temperature on the Properties of M32.5 Cement Mortar.

The effect of the dosage of sulphur-containing tailings (STs) and curing temperature on the properties of M32.5 cement mortar was studied in this work. An experimental study was conducted to evaluate the effects of STs with different substitution ratios (0, 10%, 20%, 30%, 40%) on the compressive strength experiment, fluidity, expansion ratio, and pore structure of M32.5 cement mortar. The results showed that the addition of STs reduced the fluidity of mortar, and the fluidity decreased with the increase of the STs dosage. The compressive strength of mortars increased at a lower substitution rate (0~20%) but decreased at a higher substitution rate (>20%). Ettringite peaks and new sulfate peaks were found by X-ray diffraction (XRD) analysis. Scanning electron microscope (SEM) observation of the microstructure showed that a large number of hydrated products, such as ettringite, formed and filled in the interstitial space, which was conducive to the development of strength. The optimal STs replacement ratio of river sand was 10%. Then, the performance of mortar at curing temperatures of 23 ± 1, 40, 60, and 80 °C was further investigated under the optimal STs replacement ratio. Under high-temperature curing conditions, the early strength of M32.5 cement mortar with STs increased greatly, but the late strength decreased gradually with the increase in curing temperature. The early strength development of the mortar mainly depended on the high speed of hydration reaction, and the late strength variation was mainly affected by hydration products and the pore size distribution. After comprehensive consideration, the optimal curing temperature of M32.5 cement mortar with STs was 40 °C.

A Study on Diesel Spray Flame by Time-Resolved PIV with Chemiluminescence of OH*

<div class="section abstract"><div class="htmlview paragraph">To clarify the relationship between the local heat release and the velocity distribution inside the diesel spray flame, simultaneous optical diagnostics of OH* chemiluminescence and particle image velocimetry (PIV) have been applied to the diesel spray flame under the elevated in-cylinder pressure and temperature conditions formed in a rapid compression expansion machine (RCEM). The cranking speed of the RCEM was 900 rpm, and the in-cylinder pressure and temperature were 8 MPa and 800 K at the start of injection, respectively. The amount of fuel was 10.2 mg. The injection pressure was 120, 90, and 60 MPa. To minimize the disturbance of luminous flame on optical diagnostics, a solvent, with comparable combustion characteristics to diesel fuel was used as fuel. The oxygen concentration was set to 15%. Results clearly show that PIV can successfully analyze the velocity distribution in diesel spray flames. The local velocity fluctuation inside the diesel spray flame represents the peak value slightly inside of the high-temperature region. In addition, the intensity of local velocity fluctuation increases as the injection pressure increases.</div></div>

Compression and Thermal Expansion Behaviors of Highly Crystalline Polyimide Particles Prepared from Poly(amic acid) and Monomer Salts

Compression and Thermal Expansion Behaviors of Highly Crystalline Polyimide Particles Prepared from Poly(amic acid) and Monomer Salts

Study on the Influence of Isolated Roughness on Hypersonic Flow over Blunt Wedge

To investigate the problem of the influence of the depth of the isolated D-type roughness element on the hypersonic flow around the blunt wedge boundary, the high-order accuracy finite difference method is used to carry out the direct numerical simulation, the influence of the depth of the isolated D-type roughness element on the interaction between the free flow and the wall is analysed, and the influence of the D-type roughness element on the wall pressure, the wall friction resistance and the wall heat flow is discussed. The results show that the strength of compression wave and expansion wave increases with the increase of the depth of D-type roughness element, but the position of compression wave and expansion wave does not change; With the increase of the depth of the D-type element, the change speed of the flow parameters will be accelerated, the peak value will increase and the trough value will decrease, and the position of the peak and trough will gradually move away from the center of the element with the increase of the depth of the element. When the depth of the D-type element is greater than or equal to 0.08, a vortex will form in the D-type element, and the length of the vortex increases with the deepening of the element. The D-type element will not change the flow state of the shear layer near it.

The Effect of Porosity Change in Bentonite Caused by Decay Heat on Radionuclide Transport through Buffer Material

Bentonite is used as a buffer material in most high-level radioactive waste (HLW) repository designs. Smectite clay is the main mineral component of bentonite and plays a key role in controlling the buffer’s physical and chemical behaviors. Moreover, the long-term functions of buffer clay could be lost through smectite dehydration under the prevailing temperature stemming from the heat of waste decay. Therefore, the influence of waste decay temperatures on bentonite performance needs to be studied. However, seldom addressed is the influence of the thermo-hydro-chemical (T-H-C) processes on buffer material degradation in the engineered barrier system (EBS) of HLW disposal repositories as related to smectite clay dehydration. Therefore, we adopted the chemical kinetic model of smectite dehydration to calculate the amount of water expelled from smectite clay minerals caused by the higher temperatures of waste decay heat. We determined that the temperature peak of about 91.3 °C occurred at the junction of the canister and buffer material in the sixth year. After approximately 20,000 years, the thermal caused by the release of the canister had dispersed and the temperature had reduced close to the geothermal background level. The modified porosity of bentonite due to the temperature evolution in the buffer zone between 0 and 0.01 m near the canister was 0.321 (1–2 years), 0.435 (3–10 years), and 0.321 (11–20,000 years). In the buffer zone of 0.01–0.35 m, the porosity was 0.321 (1–20,000 years). In the simulation results of near-field radionuclide transport, we determined that the concentration of radionuclides released from the buffer material for the porosity of 0.321 was higher than that for the unmodified porosity of 0.435. It occurs after 1, 1671, 63, and 172 years for the I-129, Ni-59, Sr-90, and Cs137 radionuclides, respectively. The porosity correction model proposed herein can afford a more conservative concentration and approach to the real release concentration of radionuclides, which can be used for the safety assessment of the repository. Smectite clay could cause volume shrinkage because of the interlayer water loss in smectite and cause bentonite buffer compression. Investigation of the expansion pressure of smectite and the confining stress of the surrounding host rock can further elucidate the compression and volume expansion of bentonite. Within 10,000 years, the proportion of smectite transformed to illite is less than 0.05%. The decay heat temperature in the buffer material should be lower than 100 °C, which is a very important EBS design condition for radioactive waste disposal. The results of this study may be used in advanced research on the evolution of bentonite degradation for both performance assessments and safety analyses of final HLW disposal.

Role of acute respiratory diseases in pathogenesis of distal limb infections in cattle

According to current concepts, ruminal and metabolic acidosis occur due to feeding cattle mainly with preserved acidic feeds such as silage and haylage. However, errors in feeding are not the only etiological factor leading to acidosis. In some cases, metabolic acidosis in cattle can develop along with respiratory infection caused by viral and bacterial agents. The main pathological processes resulting from acute respiratory diseases of cattle are bronchitises, tracheites and pneumonias. When the respiratory tract is affected in cattle, hypoxia occurs, causing intoxication and, thus, leading to ruminal acidosis. As a result, vasoactive substances (bacterial endotoxins, histamine, lactate) enter the bloodstream, the vascular endothelium is damaged due to the simultaneous expansion of arterioles and compression of venules, blood fluid is perfused from the vessels into the surrounding tissues, the blood flow in the microcirculatory bed is disrupted. An important role in the disturbance of blood circulation in small blood vessels is played by circulating immune complexes representing the «antigen-antibody» complex. Low molecular weight circulating immune complexes settle in various organs and tissues of the body, lead to inflammation and damage the normal tissue structure. Most frequently, immune complexes affect the endothelium of blood vessels, renal glomeruli and joints. Distal limb vessels are primarily affected in cattle, leading to disturbance of skin trophism of the limbs and hooves, development of laminitis, while the hoof horn is weakly keratinized and cannot resist aggressive mechanical and chemical environmental factors. Damaged hooves are the gateway of infection for the agents of necrobacteriosis (Fusobacterium necrophorum), staphylococcosis (Staphylococcus spp.), streptococcosis (Streptococcus spp.) and other pathogens. In addition, favorable conditions evolve for the development of mixed infection due to reduction in the overall organism resistance, which is observed for both respiratory and distal limb infections.

Numerical Simulation of the Volumetric Strain Distribution of a Protected Coal Seam

To investigate the deformation characteristics of protected coal seams, the numerical simulation of the mining of an upper protective coal seam was carried out in the present study. Based on the basic definition of strain, a method for the extraction of the strain data of the protected coal seam was proposed, and the strain distribution characteristics were obtained. It was found that the x -direction strain is mainly distributed near the coal pillars on both sides and inside the goaf, the y -direction strain is mainly distributed at the working face, the initial mining line, and inside the goaf, and the z -direction strain is mainly distributed at the working face, the initial mining line, the coal pillars on both sides, and inside the goaf. The distribution characteristics and the value of volumetric strain were found to be basically consistent with the z -direction strain. As the working face advances, the protected coal seam undergoes compression and damage expansion in turn. The turning point between compression and damage expansion is approximately 15 m in front of the working face. The variation law of gas drainage in the boreholes of the protected coal seam is closely related to the distribution characteristics of volumetric strain. The results of this research are of great significance for the comprehensive investigation of the effects of pressure relief and the permeability enhancement of protective coal seam mining.

Evaluation of Compressive Strength and Setting Expansion of GC and Adenta Dye Stones

Introduction: The aim of this study was the Evaluation of compressive strength and setting expansion of GC and Adenta dye stones. Materials & Methods: This study was an experimental study. The sample number was 21 for each group (n = 21). Compressive strength and setting expansion of GC and Adenta dye stones was tested based on ADA Standard 25 and Iranian Standard No. 2792. Data analysis was done with Independent-Sample t-test (p value = 0.05). Results: There was no significant difference between GC (47.61 ± 5.54) and Adenta groups (44.31 ± 7.71) in terms of compressive strength. Also, there was no significant difference in the setting expansion between GC (0.07 ± 0.008) and Adenta dye stones (0.08 ± 0.001). Conclusion: The results of this study showed that there is no statistically significant difference in setting expansion and compressive strength between GC and Adenta dye stones and both samples was under standard condition )p value < 0.05).