Search Results (221)

We developed a self-consistent double-null description of an evaporating white-hole spacetime by embedding the outgoing Vaidya solution in a coordinate system that remains regular across the future horizon. Starting from the radiation-coordinate form, we specialize in retarded time so that a monotonically decreasing mass function $M\left(u\right)$ encodes outgoing positive-energy flux. Expressing the metric in null coordinates $(u,v)$, Einstein’s equations for a single-directional null-dust stress–energy tensor, $T_{uu}=\rho \left(u\right)$, then reduce to one first-order PDE for the areal radius: ${\mathsf{\partial }}_{v}r=B\left(u\right)\left(1-2M\left(u\right)/r\right)$. Its integral, $r+2M\left(u\right)ln|r-2M(u\left)\right|=v-C\left(u\right)$, defines an implicit foliation of outgoing null cones. The metric coefficient follows algebraically as $f(u,v)=1-2M\left(u\right)/r$. Residual gauge freedom in $B\left(u\right)$ and $C\left(u\right)$ is fixed so that u matches the Bondi retarded time at null infinity, while v remains analytic at the apparent horizon, generalizing the Kruskal prescription to dynamical mass loss. In the limit $M\left(u\right)\to M$, the construction reduces to the familiar Eddington–Finkelstein and Kruskal forms. Our solution, therefore, provides a compact analytic framework for studying white-hole evaporation, Hawking-like energy fluxes, and back-reaction in spherically symmetric settings without encountering coordinate singularities. Full article

Foundry slag has different characteristics from blast furnace slag, such as its high SiO₂ content and low basicity (CaO/SiO₂ < 1), which prevent it from being used as a cementitious component. Lime slurry is a waste product with a high CaO content and can be used to increase the basicity of the mixture. The aim of this study is to obtain new supplementary, eco-cementitious material composed of foundry slag and lime sludge. The compositions were designed with binary basicity (molar ratio of CaO/SiO₂) ranging from 1.0 to 1.4. Clinker was replaced with the proposed material in the range of 6–34 wt% and the performance of the different cement compositions was tested. The results showed that replacing 20 wt% of clinker with the new eco-cementitious material with binary basicity of 1.2 resulted in cement with the same mechanical strength as the reference cement. The new material reacted with free CaO to generate additional calcium silicate hydrate. The initial setting time of the cement containing the new eco-cementitious material was 240 min, acting as hydration reaction retardant. The technical feature of the new eco-cementitious material allows the use of both wastes in cement composition, contributing to the requirements of circular economy. Full article

This work investigates the influence of CaO as a partial substitute for fly ash in alkali-activated fly ash mortars (AAFM), aiming to reduce reliance on conventional thermal curing. Mortars containing 0%, 2%, and 4% CaO were prepared and subjected to two curing regimes: thermal curing at 70 °C for 24 h and ambient curing at 21 °C for 24 h. The materials were thoroughly characterised by XRD, XRF, TGA/DTA, SEM, and particle size distribution, while compressive and flexural strength, density, and porosity were evaluated at 7, 14, and 28 days. The results demonstrated that CaO addition improved mechanical performance in both curing environments, particularly at a 4% substitution level, where compressive strength increased by up to 13.8% under thermal curing conditions. These improvements were associated with the formation of C-S-H and C-A-S-H gels, especially margarite, which contributed to accelerated setting and earlier demoulding. Nonetheless, while CaO incorporation improved mechanical performance and allowed earlier demoulding, it could not fully replicate the effects of heat curing at the studied percentages. Ambient-cured mortars exhibited higher porosity and less compact microstructures than thermally cured samples, which displayed denser, layered morphologies. The study confirms that CaO can act as a partial substitute or reducer for conventional curing, but is not sufficient to enable in situ applications without heat treatment. Future research should explore higher CaO contents in combination with set retarders, intermediate curing regimes, or alternative strategies to balance mechanical performance with energy efficiency. Full article

This study focused on the thermal stability and ablative behavior assessment of five newly developed composite TPS configurations. All ten test samples were 3D printed via FDM using various fire-retardant thermoplastic materials, with and without reinforcement. Eight samples integrated a new thermal management internal air chamber conceptualized architecture. A prompt feasible approach for the flame resistance preliminary assessment of ablative TPS samples was developed, using an in-house oxy-acetylene torch test bench. Experimental OTB ablation tests involved exposing the front surface samples to direct flame at 1450 ± 50 °C at 100 mm distance. For each configuration, two samples were tested: one subjected to 30 s of flame exposure and the other to 60 s. During testing, internal temperatures were measured at two backside sample contact points. Recorded temperatures remained below 46 °C, significantly under the maximum allowable back face temperature of 180 °C set for TPSs. The highest mass losses were measured for PC and PETG FR materials, achieving around 19% (30 s) and, respectively, 36% (60 s), while the reinforced configurations showed overall only a third of this reduction. The study’s major outcomes were the internal air chamber concept validation and identifying two reinforced configurations as strong candidates for the further development of 3D-printed ablative TPSs. Full article

Cementitious materials are susceptible to water ingress due to their hydrophilicity and porous microstructure, which can cause premature destruction and compromise long-term durability. Integral hydrophobic modification using alkyl silanes is an effective strategy for enhancing water resistance, while the influence of different silanes on early-age properties (within the first 7 d) of various binder systems remains unclear. This study investigates the rheology, flowability, setting behavior, reaction kinetics, compressive strength, and hydrophobicity of ordinary Portland cement (OPC) and alkali-activated fly ash–slag (AAFS) pastes incorporating alkyl silanes of varying alkyl chain lengths, i.e., methyl-(C1TMS), butyl-(C4TMS), octyl-(C8TMS), and dodecyl-trimethoxysilane (C12TMS). In OPC, C1TMS reduced yield stress and plastic viscosity by 33.6% and 21.0%, respectively, and improved flowability by 27.6%, whereas C4TMS, C8TMS, and C12TMS showed the opposite effects. In contrast, the effect of alkyl silanes on rheology and flowability of AAFS was less pronounced. Silanes delayed setting of OPC and AAFS by 5.6–164.4%, with shorter alkyl chains causing greater retardation. C1TMS and C4TMS inhibited early-age heat release and decreased the 1-day compressive strength by 14.8–35.7% in OPC and 82.0–84.5% in AAFS, whereas longer-chain silanes had comparatively minor effects. The hydrophobic performance in both binder systems was strongly correlated with alkyl chain length. C8TMS exhibited the best hydrophobicity in OPC, achieving a water contact angle of 145° and a 75.7% reduction in water sorptivity, while C4TMS demonstrated the highest hydrophobicity in AAFS. This study provides fundamental guidance for the rational selection of alkyl silanes in OPC and AAFS systems, offering insights into the design of multifunctional water-resistant cementitious composites for marine structures, building facades, and other applications with waterproofing requirements. Full article

The electric energy metering box serves as a crucial node in power grid operations, offering essential protection for key components in the distribution network, such as smart meters, data acquisition terminals, and circuit breakers, thereby ensuring their safe and reliable operation. However, the non-metallic housings of these boxes are susceptible to aging under environmental stress, which can result in diminished flame-retardant properties and an increased risk of fire. Currently, there is a lack of rapid and accurate methods for assessing the fire resistance of non-metallic metering box enclosures. In this study, laser-induced breakdown spectroscopy (LIBS), which enables fast, multi-element, and non-contact analysis, was utilized to develop an effective assessment approach. Thermal aging experiments were conducted to systematically investigate the degradation patterns and mechanisms underlying the reduced flame-retardant performance of sheet molding compound (SMC), a representative non-metallic material used in metering box enclosures. The results showed that the intensity ratio of aluminum ionic spectral lines is highly correlated with the flame-retardant grade, serving as an effective performance indicator. On this basis, a one-dimensional convolutional neural network (1D-CNN) model was developed utilizing LIBS data, which achieved over 92% prediction accuracy for different flame-retardant grades on the test set and demonstrated high recognition accuracy for previously unseen samples. This method offers significant potential for rapid, on-site evaluation of flame-retardant grades of non-metallic electric energy metering boxes, thereby supporting the safe and reliable operation of power systems. Full article

This field study describes the successful implementation and evaluation of a Polymer-free Delayed Acid System, a next-generation acid retarder system that is chemically superior to traditional emulsified acid systems with an amphoteric-based surfactant. It is a polymer-free system that stimulates ultra-tight carbonate reservoirs in extreme sour and high-temperature conditions. The candidate well, located in an onshore gulf region field, for a major oil and gas company demonstrated chronically unstable production behavior for over two years, with test volumes fluctuating unpredictably between 200 and 400 barrels of oil per day. This indicated severe near-wellbore damage, high skin, and limited matrix permeability (<0.3 mD). The well was chosen for a pilot trial of the Polymer-free Delayed Acid System technology after a thorough formation study, which included mineralogical characterization and capillary diagnostics. The innovative acid retarder formulation, designed for deep matrix penetration and controlled acid–rock reaction, uses intrinsic encapsulation kinetics to significantly increase the acid’s reactivity, allowing it to bypass damaged zones, minimize acid leak-off, and initiate dominant wormhole propagation into the tight formation. The stimulation procedure began with a custom pre-flush designed to change nanoscale wettability and interfacial tension, so increasing acid displacement and assuring effective contact with the formation rock. Real-time injectivity testing and operational data collecting were performed prior to, during, and following the acid job, with pre-stimulation injectivity peaking at 1.2 bpm, indicating poor formation conductivity. Treatment with the Polymer-free Delayed Acid System resulted in a 592% increase in post-stimulation injectivity, indicating significant increases in near-wellbore permeability and successful propagation. However, a substantial operational difficulty arose: the well remained shut down for more than two months following the acid stimulation work due to surface infrastructure delays, notably the scheduling and execution of a flowline cleanup campaign. This lengthy closure slowed immediate flowback analysis and impeded direct assessment of treatment performance because production could not be tracked in real time. Despite this, once the surface system was operational and the well was open to flow, a structured production testing program was carried out over four quarterly intervals. The well regularly produced at an average stable rate of 500 bbl/day, more than doubling pre-treatment performance and demonstrating the long-term effectiveness and mechanical durability of the acid-induced wormhole network. Despite the post-job shut-in, the Polymer-free Delayed Acid System maintained the stimulating impact even under non-ideal settings, demonstrating its robustness. The Polymer-free Delayed Acid System outperforms conventional emulsified acid systems, giving better control over acid placement and reactivity, especially under severe reservoir conditions with bottomhole temperatures reaching 200 °F. This project offers a field-proven methodology that combines advanced chemical engineering, formation-specific design, and live diagnostics, as well as a scalable blueprint for unlocking hydrocarbon potential in similarly complicated, low-permeability reservoirs. Full article

This study introduces xylitol, a natural compound, as a multifunctional additive to enhance the performance of alkali-activated slag/fly ash materials (AASFMs). A systematic investigation was conducted to elucidate xylitol’s mechanism in modifying AASFM properties, including fresh behavior, hydration kinetics, compressive strength, and autogenous shrinkage. The experimental findings demonstrated that xylitol significantly delayed early-age hydration while promoting more extensive hydration at later stages. Specifically, the initial and final setting times of AASFM pastes were extended by 640% and 370%, respectively, and paste flowability increased by 30%. At a 0.2% dosage, xylitol markedly reduced porosity and refined the microstructure of AASFMs, leading to improved mechanical properties. The 3-day and 28-day compressive strengths were enhanced by 39.8% and 39.7%, respectively, while autogenous shrinkage was suppressed by 61.4%. These results demonstrate the multifunctional potential of xylitol in AASFMs, serving as an effective retarder, plasticizer, strength enhancer, and shrinkage reducer. Notably, the refined pore structure induced by xylitol may also mitigate the risks of the alkali–silica reaction, though further durability validation is warranted. Full article

Organic acids could act as retarders in magnesium oxysulfide (MOS) systems, not only delaying setting and improving fluidity but also enhancing compressive strength and water resistance. These effects are generally attributed to both the presence of H⁺ ions and anion chelation. However, the enhancement efficiency of different organic acids in MOS systems varies significantly due to differences in their molecular structures. To determine the underlying mechanism, this study comparatively investigated the effects of amino trimethylene phosphonic acid (ATMP) and tartaric acid (TA) on the setting time, fluidity, compressive strength, and water resistance of the MOS system, with the two additives incorporated at mole ratios to MgO ranging from 0.002 to 0.006. The mechanism behind it was revealed by discussion on the hydration heat, hydrates, and pH value. Results showed that both ATMP and TA could effectively improve the fluidity, delay the setting process, and enhance the mechanical properties, including strength and water resistance. At a mole ratio of 0.006, the incorporation of ATMP increased the 28 d compressive strength and the softening coefficient by 214.12% and 37.29%, respectively, compared with the blank group. In contrast, under the same dosage, TA led to an increase of 55.13% in the 28 d strength and 22.03% in the softening coefficient. Furthermore, hydration heat, product analysis, and pH measurements indicated that both ATMP and TA inhibited hydration during the initial hours but promoted hydration at later stages. The potential reason could be divided into two aspects: (1) H⁺ ions from ATMP and TA suppressing the formation of Mg(OH)₂; (2) anion chelation with Mg²⁺ in the liquid phase, leading to a supersaturated solution with higher saturation, which further hindered Mg(OH)₂ formation and facilitated the later development of 5Mg(OH)₂·MgSO₄·7H₂O (517 phase). By contrast, under the same mole dosage of H⁺ or anions, the enhancement in compressive strength as well as the water resistance is superior when using ATMP. This was owing to its stronger chelating ability of ATMP, which more effectively inhibited Mg(OH)₂ formation and then promoted the formation of the 517 phase. These findings confirm that the chelating ability of anions exerts an important impact on the retarding effect as well as the enhancement of strength in MOS systems. Full article

This study focuses on developing a novel clinker-free cement, specifically comprising phosphorus slag-based cementitious materials (PSCMs), by utilizing lime and industrial byproducts, including granulated electric furnace phosphorus slag and fluidized bed combustion bottom ash. The optimal composition of PSCM was determined by investigating the effects of different proportions of activators (water glass and sodium sulfate) and retarder (potassium fluoride) on the setting time and the mechanical strength of PSCMs. Performance evaluations demonstrated that the compressive and flexural strengths of the optimal PSCM formulation at 28 days were 64.1 MPa and 7.5 MPa, respectively. Notably, concrete prepared with the optimal PSCM exhibited superior freeze–thaw resistance and sulfate resistance compared to Portland cement concrete of equivalent strength grades. The comprehensive characterization of selected PSCM compositions, conducted using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and scanning electron microscope–energy-dispersive spectrometry (SEM-EDS), provided in-depth insights into the interrelationship among mechanical properties, durability, and microstructural characteristics. SEM-EDS analysis confirmed that calcium aluminosilicate hydrate and sodium aluminosilicate hydrate are the predominant hydration products of PSCMs. FTIR and TG analyses elucidated the continuous hydration behavior of PSCMs during the curing process, while SEM observations revealed a densely compact microstructure in the hardened PSCM paste. Full article

Aiming at the problem of synergistic regulation of setting time and strength of brucite-based magnesium phosphate cement (BMPC), this study used ammonium chloride (AC) as a variable, and revealed the regulation mechanism of AC on the hydration behavior of BMPC through the tests of setting time, fluidity, and compressive strength, as well as the monitoring of pH-ion concentration, and the microanalysis of XRD-TG-MIP. The results showed that the optimal performance combination of BMPC (setting time of 16 min, fluidity of 120 mm, and compressive strength of 20.5/30.7/54.5 MPa at 3 h/1 d/28 d, respectively) was obtained when AC was doped at a dosage of 4%. The mechanism of retardation stems from the fact that the addition of AC inhibits the dissolution rate of ADP and retards the hydration reaction of Mg²⁺ and $\mathrm{P}{\mathrm{O}}_4^{3-}$. An appropriate amount of AC can optimize the pore structure of the BMPC matrix and improve the compressive strength of the matrix. The BMPC system based on complete replacement of magnesite by brucite not only significantly reduces carbon emission and cost, but also provides a new path for the development of low-carbon MPC. Full article

Achieving long downhill constant-speed driving of heavy vehicles is of great significance for improving vehicle transport safety. As a kind of auxiliary brake, the hydraulic retarder has the characteristics of large braking torque and compact structure. More importantly, the hydraulic retarder is capable of braking for a long period of time, which enables the vehicle to travel downhill at a constant speed with less or no use of mechanical brakes. However, due to the complexity of hydraulic retarder braking conditions, its output braking torque presents time-varying and non-linear characteristics, and the control of the hydraulic retarder filling rate in order to achieve the vehicle’s long downhill constant-speed braking is a challenging problem. This research proposes a constant-speed control strategy utilizing the robust control method to address the issue of prolonged downhill braking at constant speed for heavy-duty vehicles, which achieves constant-speed and stable driving downhill by controlling the filling rate of the hydraulic retarder. Initially, the dynamic model of the downhill process for heavy-duty vehicles and the physical model of the hydraulic retarder are established. Then, based on the concept of sliding mode control, the sliding mode controller with saturation function and the high-frequency robust controller are developed to modulate the filling rate of the hydraulic retarder in response to variations in vehicle speed. In order to verify the effectiveness of the algorithm, three different operating conditions were set according to the vehicle mass and road gradient, and simulation tests were carried out in the MATLAB/Simulink environment. Simulation results indicate that the high-frequency controller exhibits remarkable robustness against dynamic disturbances within the system. Additionally, when variations in vehicle mass and road gradient occur, the root mean square error of the high-frequency controller’s speed, in comparison to the fuzzy controller, decreases by 0.1157 km/h, while the maximum absolute error in vehicle speed diminishes by 0.248 km/h. Simultaneously, the high-frequency controller proficiently suppresses chatter, thereby meeting the demand for consistent speed braking in big trucks on prolonged downhill gradients. Full article

In water-rich strata, a traditional vertical barrier exhibits certain limitations when applied to deep foundation pit construction under complex geological conditions, such as it is difficult to completely cut off deep and thick aquifer, which may pose potential risks during pit dewatering. To address the above challenge, this study introduced a mixed barrier system in which the horizontal barrier (HB) was set at the bottom of the foundation pit and was combined with the enclosure wall to collectively retard groundwater seepage into the pit. Based on an actual project in Tianjin, this study established HB models with varying numbers of its layers using ABAQUS 6.14 software. It systematically investigated the effect of HB on groundwater drawdown, ground surface settlement, and enclosure deflection during foundation pit dewatering. The research shows that HB can significantly reduce the magnitude of external water level drawdown by altering groundwater seepage paths while effectively controlling soil settlement. Furthermore, it exhibits favorable overall restraining effects on wall deformation. Varying the number of horizontal barrier layers (L) exhibits an insignificant effect on water-blocking and subsidence-control performance. However, the constraint effect on the enclosure shows a correlation with L. Full article

In order to shorten the curing time of the cement-treated aggregate base, provide a stable paving base for an asphalt mixture, and finally, achieve rapid traffic reopening during the maintenance of the pavement (milling and resurfacing of the base layer), sulphoaluminate cement (SAC) was used to prepare cement-treated aggregate with high early strength. As a result, the SAC was first optimized by adding several cement admixtures (i.e., polycarboxylic water reducer, borax, lithium carbonate, and calcium formate) based on hydration kinetics, setting time, compressive strength, and morphology tests. Then, the optimized SAC was used to prepare the sulphoaluminate cement-treated aggregate (SACTA). The test results show that the addition of compound retarder and compound early strength agent in SAC could delay the hydration, reduce microcracks, and ensure required setting time and high early strength. Compared with ordinary Portland cement-treated aggregates (OPCTAs) with the same cement content, the 1 d unconfined compressive strength and indirect tension strength of SACTAs increased by 87.7–184.6% and 133.8–263.6% respectively. The SACTA had smaller total drying shrinkage strain and better anti-scouring performance than OPCTA when using the same cement content. Besides, the 1 d interfacial bonding strength between SACTA and OPCTA was 0.18 MPa, which was higher than the indirect tension strength of OPCTA. The findings in this study indicate that the prepared SACTA could be used for rapid traffic opening during road maintenance. Full article

This case study presents the long-term management of a 14-year-old male diagnosed with 18q deletion syndrome, also known as de Grouchy Syndrome, highlighting the challenges of treating rare chromosomal disorders in rural Romania. Background and Clinical Significance: 18q deletion syndrome, also known as de Grouchy syndrome, is a chromosomal disorder caused by the deletion of a part of the long arm of chromosome 18. This syndrome is seen in one out of 10,000 live births. The main features of the syndrome are short stature, hearing loss, hypotonia, mental retardation, endocrine disorders, and autoimmunity. Case Presentation: The patient’s condition was initially suspected at birth due to abnormal features and was later confirmed through genetic testing, revealing a 46,XY,del(18) karyotype. Key clinical features include craniofacial dysmorphism, delayed growth, congenital cardiac anomalies, developmental delay, severe neurological impairment, and multiple comorbidities such as endocrine dysfunction, dental anomalies, and orthopedic deformities. Despite early interventions such as cardiac surgery, the patient’s management has been challenged by limited access to specialized care. Conclusions: The case underscores the importance of timely genetic testing, early multidisciplinary care, and the role of family support in managing complex disorders. This report also addresses the gaps in healthcare accessibility in rural settings and emphasizes the need for improved infrastructure and genetic services. By comparing this case with the existing literature, the study explores the variability in clinical presentations of 18q deletion syndrome and advocates for more precise genetic testing to better understand its phenotypic spectrum. The patient’s ongoing challenges with medical and socio-economic factors emphasize the critical need for coordinated care and family support in managing rare genetic conditions. Full article