Width Of Transition Zone Research Articles

Study of the Influence of Desert Sand-Mineral Admixture on the Abrasion Resistance of Concrete.

The incorporation of desert sand-mineral admixture improves the abrasion resistance of concrete. To prolong the service life of assembled concrete channels and mitigate the depletion of river sand resources, the effects of fly ash (FA), silica fume (SF), desert sand (DS), and basalt fiber (BF) on the mechanical properties and the abrasion resistance of concrete were examined, alongside an analysis of their microstructures to elucidate the underlying mechanisms of influence. The results indicated that the abrasion resistance strength of concrete mixed with 10% FA and 0.05% BF alone increased by 80.19% and 81.59%, respectively, compared with ordinary concrete (OC). When SF was added to the concrete at a dosage of 10%, it improved the mechanical properties and the abrasion resistance of the concrete. Furthermore, adding SF resulted in a 12.50% increase in compressive strength and a 12.27% increase in abrasion resistance strength compared to OC. The addition of DS did not significantly enhance the concrete's abrasion resistance. The combination of ingredients for desert sand concrete (DSC) that provides excellent abrasion resistance was determined using an orthogonal experiment. The optimal mixture consisted of 10% FA content, 10% SF content, 40% DS content, and 0.05% BF content, which increased the abrasion resistance strength by 112.95% compared to OC. Through microscopic analysis, it is found that the width of the interfacial transition zone (ITZ) is an important factor in determining the abrasion resistance of concrete, and a narrower ITZ enhances the concrete's abrasion resistance. The study's findings could function as a theoretical reference for the engineering design of DSC.

New strategy for fusion infiltration processed Cu/MoCu/Cu composites

Existing thermal management materials suffer from high thermal resistance, low strength and many interfacial defects. To solve these problems, in this study, Cu/Mo70Cu30/Cu (or CPC) composite was prepared by using fusion infiltration technology with Cu wrapped Mo (Cu@Mo) composite powder as the raw material, and CPC samples with a thickness of 1.8 mm and three layer thickness ratio of 1:4:1 were further processed using a jacket rolling process. Results showed that using the Cu@Mo composite powders and following melting and infiltration processes not only changed the interfacial homogeneous structures of composites from mechanical bonding to metallurgical bonding, but also created good thermal conductivity channels of Cu in the MoCu core structure. The large rolling rate of plastic deformation created a 0.7 μm wide transition zone at the Cu/MoCu interface, resulting in efficient heat and stress transfer between two phases of molybdenum and copper. The composites showed a high densification rate larger than 98 %, a thermal conductivity of 270.8 W/(m·K), a coefficient of thermal expansion of 7.96 × 10−6/K at 30 °C, and a tensile strength of up to 542.5 MPa.

Impact of calcium formate and anhydrous sodium sulfate on the flowability, mechanical properties, and hydration characteristics of UHPC

Ultra-high performance concrete (UHPC) is not an ideal material for rapid repairs of bridge expansion joints due to its slow early strength development. To mitigate this early strength limitation, this study investigated the use of calcium formate (CF) and anhydrous sodium sulfate (SS) as early strength agents to enhance the early strength of UHPC. The findings indicate that a composite addition of 0.25 % SS and 0.25 % CF significantly improves both strength and workability, resulting in a 28-day compressive strength of 141.3 MPa, a 28-day flexural strength of 12.6 MPa, and a flowability of 227 mm. SS facilitates the formation of ettringite (AFt) and calcium hydroxide (C-H), while CF promotes the generation of smaller gismondine particles. This substantial increase in hydration products reduces the porosity of UHPC, thereby densifying the matrix and enhancing its mechanical strength. The synergistic effect of both additives leads to a higher concentration of calcium ions (Ca2+) around the smaller gismondine particles, which generates additional hydration products, optimizes the pore structure of UHPC, and narrows the width of the interfacial transition zone (ITZ). Consequently, this combination significantly improves the early strength of UHPC, achieving a 45.6 % enhancement in the early hydration rate with the use of 0.25 % CF and 0.25 % SS.

Effect of chloride ion corrosion on the microstructure of multiple interfaces of alkali-activated GGBS/FA based recycled concrete

In this paper, the resistance to chloride ion permeability of multiple interfaces in alkali-activated slag/fly ash (GGBS/FA) based full recycled concrete was investigated using the immersion method. In order to objectively and accurately reflect the microhardness and width of the interface transition zone (ITZ), box plots were used to process the measured point data. The results indicated that the microhardness of the interface was significantly lower than that of the matrix. The microhardness of the old aggregate interface (ITZOA-OM), the new aggregate interface (ITZOA-NM) and the new mortar interface (ITZOM-NM) all decreased to varying degrees with the extension of the immersion ages, but remained higher than that of the uneroded specimens. Chloride ions penetrated into ITZOA-OM and reacted with a large amount of enriched Ca (OH)2 to form an expansive composite salt (CaCl2.Ca(OH)2.H2O), which improved the microstructure of the ITZ, increased the microhardness and decreased the width of the ITZ. The dense structure of ITZOA-NM and ITZOM-NM inhibited the migration of chloride ions to a certain extent. leading to minimal changes in the width and microhardness of the ITZ. The micro mechanisms of chloride ion penetration resistance at the interfaces of alkali-activated GGBS/FA-based recycled concrete were investigated using BSE and EDS. More reaction products were generated at the interfaces after chloride ion erosion, and the newly generated substances continuously filled the microcracks, resulting in a more uniform bond at the interfaces. This contributed to the improvement of the microstructure and the resistance to chloride ion penetration of alkali-activated GGBS/FA based recycled concrete.

Enhancement of the tensile properties of cement mortar composites with nanoadditives produced by chemical vapor deposition

While graphene effectively enhances the performance of cement-based materials, its current production methods are characterized by environmental unfriendliness and high energy consumption. To investigate a large-scale and eco-friendly graphene preparation approach, Carbon Nano Sheets (CNS) were synthesized via chemical vapor deposition (CVD). The influence of CNS content on the tensile strength of cement mortar was assessed through the Brazilian splitting test. Concurrently, the mechanism of CNS was examined using acoustic emission monitoring and scanning electron microscope. The experimental results revealed that methane can be effectively decomposed into high-quality CNS at 1080 ℃ when using fly ash, silica fume, and sand as substrates. The Brazilian splitting test revealed that CNS effectively enhances the tensile strength of cement mortar, with improvements ranging from 9 % to 58.7 %. Acoustic emission results indicated that the inclusion of CNS reduces the occurrence of micro-fractures during the failure of cement mortar specimens. Furthermore, nano-mechanical testing and microstructural characterization demonstrate that CNS can reduce micro-cracks and pores in the interface transition zone and hydration products, playing a role in dense hydration products. Furthermore, it can decrease the width of the interface transition zone and enhance the micro-mechanical properties of cement pastes. This study offers a novel approach for the eco-friendly production of cement nano additives.

Species distribution ranges of Ilyocryptus Sars, 1862 (Cladocera: Ilyocryptidae) fit the transitional zone between Boreal and Tropical Provinces in the Far East.

In previous papers, it was shown that the Far East is a territory where moving south, Boreal fauna is fluently changed to Tropical fauna. Kotov (2016) proposed to place all taxa from the northern portion of Far East in several faunistic complexes according to the area of their differentiation in the past, i.e. in Pleistocene refugia. But many daphniids and chydorids were placed in an artificial group of non-revised taxa rather than a certain faunistic complex. Ilyocryptids are less numerous and better studied, and they could be used as a model group to test such an approach. Totally, 10 species were found in the Far East: from the very common I. spinifer group, the relatively common I. acutifrons, I agilis, I. yooni, I. raridentatus and I. cuneatus to the very rare I. cf. bhardwaji, I. isanensis, I. thailandensis and I. uenoi. Note that four species are found in Vietnam for the first time, namely, I. isanensis, I. cf. raridentatus, I. thailandensis and I. yooni. In contrast to the aforementioned daphniids and chydorids, ten Far Eastern ilyocryptid taxa accurately fit three faunistic complexes: WE-widely distributed in North Eurasia; ST-southern tropical; EN-Far Eastern endemic. Ilyocryptid distribution fits well with the "wide transitional zone concept" between "Palaearctic" (in reality, we have found that its separation within the Holarctic does not work well for the cladocerans) and Oriental zones, and such our conclusion is made based on the analysis of the adequately known group.

The Influence of Slag Content on the Structure and Properties of the Interfacial Transition Zone of Ceramisite Lightweight Aggregate Concrete.

Ceramisite lightweight concrete has excellent performance and relatively light self-weight characteristics. At the same time, the recent development of green high-performance concrete and prefabricated components has also brought the abundant utilization of these mineral mixture. An interfacial transition zone exists between the hardened cement paste and the aggregate, which is the weakest part of the concrete, characterized by high porosity and low strength. In order to study the effect of slag content on the interfacial transition zone in lightweight high-strength concrete, experiments were designed to replace cement with slag at different contents (0%, 5%, 10%, 15%). A series of studies was conducted on its macro-strength, microstructure, and composition. The results indicated that the addition of slag improved the porosity and width of the interfacial transition zone. Adding slag did not reduce the thickness of the concrete interfacial transition zone significantly at 3 d, but it led to significant improvement in the thickness of the interfacial transition zone at 28 d, and the thickness of the interfacial zone at 28 d was reduced from 19 μm to 8.5 μm, a reduction of 55%. The minimum value of microhardness in the slurry region of the interfacial specimens also increased from 19 MPa to 26 MPa, an increase of 36%. In addition, the structural density of the interfacial region was further increased, resulting in varying degrees of improvement in the macroscopic anti-splitting strength. One of the important reasons for this phenomenon is that the addition of slag optimizes the chemical composition of the interface and promotes the continuation of the pozzolanic reactivity, which further enhances the hydration at the interface edge.

The Upper Crustal Deformation Field of Greece Inferred From GPS Data and Its Correlation With Earthquake Occurrence

AbstractWe present a new geodetic strain rate and rotation rate model for Greece that has been derived using a highly dense GPS velocity field. The spatial distribution and the resolved rates of the various velocity gradient tensor quantities provided updated constraints on the present‐day upper crustal deformation in the region and revealed new details not reported previously. The spatial distribution of the second invariant demonstrated that the overall magnitude of strain rates is highest across two well‐defined provinces. The first follows the North Anatolian Fault and its two branches within the north Aegean, crosses central Greece and through the Gulf of Corinth it terminates in western Greece, while the second encompasses the extensional province of western Turkey and the eastern Aegean Sea islands. Our estimates revealed that shearing affects some of the fault‐bounded grabens of central Greece that lie to the SW of the North Aegean Basin implying considerable oblique extension. We identified a narrow region of counterclockwise rotation whose location and kinematics have been induced by the net effect across the intersection of the clockwise rotating domains of western and central Greece. The Aegean microplate and the Anatolian plate are separated by a wide transition zone which accommodates the curved stretching of the entire plate system. In both edges of the Hellenic forearc the dominant mode of crustal strain is E‐W extension. We found that earthquakes of M ≥ 5.6 are spatially well‐correlated with high‐strain areas, indicating that strain rate mapping could be used to inform future probabilistic seismic hazard analyses.

Mineral chemistry and alteration patterns of Cr-spinel in serpentinized peridotites from NW Iran

The Late Cretaceous ophiolite mélange in the Salmas area of NW Iran is a part of the Neotethys ophiolites. The mélange includes serpentinized harzburgite, serpentinites, mafic rocks, radiolarite, layered red pelagic limestones and grey and white marbles. Harzburgite main primary mineral phases are olivine, orthopyroxene, clinopyroxene and Cr-spinel. Cr-spinel has Cr2O3 contents of 21.13 to 30.18 wt% and high Al2O3 (38.67–48.52 wt%), FeO (15.18–18.13 wt%) and MgO (15.18–17.51 wt%) contents. The 100 × Cr/(Cr + Al) ratios of 23 to 34 indicate 9 to 13 % partial melting in the Mid Ocean Ridge (MOR) environment for the origin of the peridotites. An alteration zone is developed around the altered Cr-spinel. Fine-grained minerals assemblage at the spinel crystals’ margin includes Cr-rich chlorite, Cr-rich garnet and spinel-silicate mixture. A 2–5 μm wide transitional zone is developed between the chromite-silicate assemblage and the Cr-rich garnet zone. The chemical variations of major oxides across the alteration zone are mainly diffusion controlled. Al, Cr and Mg have diffused out from the primary spinel and Fe and Mn have diffused into the spinel. Cr-spinel is altered in two stages due to serpentinization. During the first stage and following hydration, spinel reacted with olivine and orthopyroxene to form Cr-rich chlorite and ferrian chromite. Silica formed at this stage. At the second stage, the reaction between the chromite-silicate assemblage and Cr-rich chlorite plus silica form the first stage and Ca2+ in the fluid (released from clinopyroxene alteration) produced Cr-rich garnet and H2O-rich fluid, at temperature between 400 and 600 °C.

The mechanical properties of the interface between concrete–epoxy mortar: Splitting tensile vs. direct shear testing

This study investigated the effects of low-temperature curing environment, moisture content of concrete, and surface roughness of concrete on the interfacial bond performance of concrete–epoxy mortar composite specimens. The mechanical and microstructural properties of concrete–epoxy mortar composite specimens were studied systematically via splitting tensile strength test, direct shear strength test, and scanning electron microscopy test, and the failure modes were observed. Further, the factors that remarkably affect the mechanical properties of the concrete–epoxy mortar composite specimen were investigated by analysing the images obtained using grey correlation analysis. The results indicated that the compressive strength of epoxy mortar, interfacial splitting tensile strength, and shear strength of composite specimens decreased gradually with the decrease in curing temperature. The splitting tensile strength and shear strength at the interface of the composite specimens first increased and then decreased with increasing surface roughness of the concrete. However, these parameters gradually decreased with the increase in moisture content. Moreover, based on the results of grey correlation analysis the three factors, the curing temperature had the most influence on these two strengths, followed by surface roughness and then moisture content. In this case, the surface roughness and moisture content have a comparable degree of influence. The relationship between shear strength and splitting tensile strength was investigated and a good linear relationship was found between these two parameters. The microstructure performance analysis show that as the curing temperature decreased, pores appeared around the foundation concrete. Consequently, the aggregate structure became loose, and the overall denseness was remarkably reduced. As the moisture content of the concrete increased, the pores and cracks at the interface increased, and the width of the interface transition zone became larger.

Gradient Transformation of the Double Gyroid to the Double Diamond in Soft Matter.

Transitions between gyroid and diamond intercatenated double network phases occur in many types of soft matter, but to date, the structural pathway and the crystallographic relationships remain unclear. Slice and view scanning electron microscopy tomography of a diblock copolymer affords monitoring of the evolving shape of the intermaterial dividing surface, allowing structural characterization of both the majority and minority domains. Two trihedral malleable mesoatoms combine to form a single tetrahedral mesoatom in a volume additive manner while preserving network topology, as the types of loops, the number of mesoatoms in a loop, minority domain strut lengths, and directions that connect a given mesoatom to its neighbors evolve across a 150 nm wide transition zone (TZ). The [111]DD direction is coincident with the [110]DG direction so that the (111)DD and (110)DG planes define the boundaries of the TZ. Selection of the particular crystal orientations and direction and width of the transition zone is to minimize the cost of morphing the mesoatoms from one structure to the other, by maximizing like-block continuity and minimizing the variation of the surface curvature and thickness of the domains across the TZ. Such coherent continuity of the independent, intercatenated networks across the transition zone is critical for applications such as graded mechanical trusses where the pair of different networks are joined to provide different mechanical properties for adjacent grains or could serve as a nanoscale anode/cathode allowing super charging and discharging provided the networks are continuous and rigorously separate.

Microstructural damage and durability of plateau concrete: Insights into freeze-thaw resistance and improvement strategies

Extreme environmental conditions and inferior building materials in plateau regions present significant challenges to the durability of concrete structures, particularly in resisting freeze-thaw cycles. This study employs an actual mix ratio from a concrete mixing station in the Qinghai-Tibet Plateau for a comparative analysis against conventional mixes in plain terrains. Utilizing a fast-freezing test with controlled variables, the study explores the microstructural evolution of plateau concrete. Results reveal that although the adapted mix ratio meets strength criteria, it falls short in frost resistance compared to standard concrete used in plain regions. Further, the plateau-specific curing conditions were shown to increase both the width and porosity of the interface transition zone (ITZ). High clay content in building materials for plateau construction also impacts the cement paste's microstructure. The study offers engineering recommendations aimed at enhancing the quality and performance of concrete in plateau conditions to address the unique challenges posed by extreme environmental factors.

A novel in vitro model of clinical cryoablation to investigate the transition zone for focal tumor ablation

Cryoablation (CA) of solid tumors is highly effective at reducing tumor burden and eliminating small, early stage tumors. However, complete ablation is difficult to achieve and cancer recurrence is a significant barrier to treatment of larger tumors compared to resection. In this study, we explored the relationship between temperature, ice growth, and cell death using a novel in vitro model of clinical CA with the Visual-ICE (Boston Scientific) system, a clinically approved and widely utilized device. We found that increasing the duration of freezing from 1 to 2 min increased ice radius from 3.44 ± 0.13 mm to 5.29 ± 0.16 mm, and decreased the minimum temperature achieved from −22.8 ± 1.3 °C to −45.5 ± 7.9 °C. Furthermore, an additional minute of freezing increased the amount of cell death within a 5 mm radius from 42.5 ± 8.9% to 84.8 ± 1.1%. Freezing at 100% intensity leads to faster temperature drops and a higher level of cell death in the TRAMP-C2 mouse prostate cancer cell line, while lower intensities are useful for slow freezing, but result in less cell death. The width of transition zone between live and dead cells decreased by 0.4 ± 0.2 mm, increasing from one to two cycles of freeze/thaw cycles at 100% intensity. HMGB-1 levels significantly increased with 3 cycles of freeze/thaw compared to the standard 2 cycles. Overall, a longer freezing duration, higher freezing intensity, and more freeze thaw cycles led to higher levels of cancer cell death and smaller transition zones. These results have the potential to inform future preclinical research and to improve therapeutic combinations with CA.

Correlation between mechanical properties and pore structure deterioration of recycled concrete under sulfate freeze-thaw cycles: an experimental study

Concrete is subject to the combined erosive effects of physical and chemical activities in cold, salty soil regions. In this work, durability tests of recycled concrete (RC) subjected to sulfate freeze-thaw cycles were conducted. The macroscopic performance deterioration law of RC under the influence of the replacement rate (0%, 50%, 100%) and the moisture content of coarse recycled concrete aggregate (CRCA) (0%, 50%, 100%) was investigated by analyzing the change characteristics of apparent damage, mass loss rate, and Relative dynamic modulus of elasticity (RDME) of RC during the erosion process. At the same time, nuclear magnetic resonance (NMR) and microhardness testing equipment were used to examine the multi-parameter evolution features such as porosity, pore distribution, interfacial transition zone (ITZ) width, and strength. The findings indicate that the main cause of the variation in the degree of damage to the RC surface layer is the variance in the effective water-cement (w/c) ratio of the mortar due to replacement rate and moisture content. The strength and area of erosion damage increase when the CRCA replacement rate rises due to the easier inward penetration of the sulfate solution. CRCA with a 50% moisture content could increase the strength of the mortar by decreasing the mortar's effective w/c ratio. The rate and effectiveness of salt solution replenishment inward were simultaneously slowed down by the improved ITZ performance. In erosive situations, the fractal dimension of RC reduces to varying degrees. This is due to the expansion of the pore structure. The porosity/fractal dimension is employed as the comprehensive pore parameter η in this research so as to take into account the integrity of the pore structure and the specificity of the pore distribution. The improved microstructure damage variables can reflect the erosive microstructure deterioration process of RC.

Influence of freeze–thaw cycles on mechanical properties of pervious concrete: From experimental studies to discrete element simulations

In this paper, pervious concrete (PC) was prepared using fly ash, granulated blast furnace slag, and rice husk ash as supplementary cementitious materials (SCMs), and the mechanical properties, water permeability, and freeze–thaw durability of permeable concrete were mainly investigated. Discrete elements (DEM) were used to mimic the freeze–thaw cycle process of pervious concrete to assess better how freeze–thaw cycles affect the mechanical properties of pervious concrete. To allow water particles of various sizes to fill the model pores, new algorithms were developed. However, since some connected pores release some of the pressure generated by water expansion when undergoing FTCs, two different water particles must be defined. Meanwhile, an elastoplastic parallel bond contact model (EPPBM) was created to account for any residual strain brought on by water freeze–thaw expansion at the aggregate bond. Through experiments, it was determined that adding SCMs increased the compressive strength of the pervious concrete by 1.22 %, 15.32 %, 32.34 %, and 35.20 % at 7, 28, 56, and 90 days compared to the control group. The microstructure of the hydrated calcium silicate (C-S-H) gel could be relatively dense by SEM. The width of the interfacial transition zone (ITZ) was found to have been effectively shortened by further scanning using EDS. As a result, in the tests of mechanical properties after freeze–thaw cycles (25, 50, 75, and 100 cycles), there was a significant improvement in the loss of strength compared to the control group, which was 2.13 %, 6.91 %, 10.04 %, and 17.40 %, respectively. Using numerical simulation to correct the functional correlation between FTCs and the mechanical characteristics of permeable concrete, the trend essentially aligns with the experiment's results, demonstrating the model's viability. Acoustic emission monitoring of model rupture location and strain energy loss after FTCs were utilized and the effect of different porosity and initial uniaxial compressive strength (UCS) on the attenuation constant of the freeze–thaw resistance of pervious concrete was analyzed. The decay constant of UCS increased with increasing porosity and elastic modulus while decreasing with increasing initial UCS. Therefore, the decay constant of UCS and elastic modulus after arbitrary FTCs can be easily estimated using the initial parameters of the pervious concrete.

Influence of B addition on the Mo diffusion-controlled eutectic dissolution process during homogenization of super austenitic stainless steel S31254

The influence of B addition on dissolution behavior of (σ + γ)e eutectics of a 6Mo super austenitic stainless steel S31254 during the homogenization process was investigated by SEM-BSE observations combined with EDS. The results showed that the addition of 0.005 wt% B accelerated the dissolution of the σ phase controlled by Mo diffusion, during homogenization from 30 to 90 min at 1180 °C. TOF-SIMS results showed that B segregated along the σ/γ interface in the as-cast samples. TEM observations combined with EDS investigated the phase interfaces in two as-cast samples in detail to correlate σ phase dissolution. Compared with the B-free sample, the wide transition zone (∼60 nm) with a composition gradient was more clearly observed at the σ/γ interface in the B-containing sample. The transition zone with B had two features: local segregation of B element and precipitation of R phases at the σ/γ interface. R phases owned larger contents of Mo, which was not almost observed in the as-cast S31254. The results indicated that B segregation changed the phase interface, accelerating Mo diffusion at the σ/γ interface. In addition, the results of nanoindentation indicated a more uniform distribution of hardness at the σ/γ interface after homogenization of the B-containing sample, which can be beneficial to improve the deformation compatibility of S31254 during hot working.

Research on macro-microscopic mechanical evolution mechanism of cement-stabilized steel slag

In this paper, the chemical composition, phase composition, physical properties and expansibility of steel slag in Xinjiang, China are analyzed, and the feasibility of steel slag as pavement base material is demonstrated. At the same time, through the tests of unconfined compressive strength, X-ray diffraction, scanning electron microscope and nuclear magnetic resonance, the relationship between macroscopic strength and microstructure of cement-stabilized steel slag at different ages is discussed and compared with that of cement-stabilized macadam. The results show that the mechanical properties of steel slag aged more than one year can fully meet the requirements of relevant specifications for all kinds of pavement base. Compared with cement-stabilized macadam, the compressive strength of cement-stabilized steel slag at the age of 7 d, 14 d and 28 d increased by 15.4%, 22.0% and 23.7%, respectively. Due to hydration and pozzolanic action, the C–S–H content in the interfacial transition zone of cement-stabilized steel slag is higher, while the contents of Ca(OH)2 and AFt are lower. Due to the internal curing effect of steel slag, the interfacial transition zone width of cement-stabilized steel slag at the age of 7 d and 28 d decreased by 9.4% and 31.0% respectively compared with cement-stabilized macadam; with the increase of curing time, the adsorption porosity of cement-stabilized steel slag increased, while the amount of seepage pore and migration pore decreased significantly, and the pore span and total porosity decreased by 47.7% and 7.29%, respectively.

Formation and Evolution of Transient Jets and Their Cavities in Black Hole X-Ray Binaries

We propose a model explaining the origin of transient/episodic jets in black hole X-ray binaries, in which they are caused by transitions from a collimated, strongly magnetized jet to a wide, uncollimated outflow. The change occurs when the accretion flow leaves the magnetically choked state due to an increase of the accretion rate for a weakly varying magnetic flux. The formed powerful jet then detaches from its base, and propagates as a discrete ejection. The uncollimated outflow then produces a relativistic plasma that fills the surroundings of the black hole, contributing to the formation of a low-density cavity. While the pressure in the cavity is in equilibrium with the surrounding interstellar medium (ISM), its inertia is orders of magnitude lower than that of the ISM. This implies that the plasma cannot efficiently decelerate the ejecta, explaining most of the observations. The modest deceleration within the cavities observed in some cases can then be due to the presence of clouds and/or filaments, forming a wide transition zone between the cavity and the ISM.

Strains of high-performance and ordinary concretes depending on the cement paste volume and the w/c ratio

The test results of 15 high performance concretes (HPCs) and ordinary concretes allowed to explain the influence of different volumes of cement paste on shaping the deformation properties of concrete under temporary compressive load. Increasing the volume of the paste by 100 dm3/m3 and reducing the volume of coarse aggregate at the same time reduces the modulus of elasticity and significantly increases the compressive strain at the peak stress. When increasing the volume of cement paste, smaller changes in properties were observed in ordinary concretes than in HPCs, modulus of ordinary concrete elasticity decreased by 4–9%, and compressive strains at the peak stress increased by 18–23%. However, in HPCs the changes are greater. Modulus changes are 7–28% and strains at the peak stress changes are from 19% to 41% at w/c = 0.25. It was found that the compressive strength of all concretes with the smallest volume of cement paste at each w/c ratio from 0.25 to 0.60 was the highest. Increasing the volume of cement paste in concretes for each w/c ratio causes a large increase in the compressive strains at peak stress.Hence, the likely causes of changes in the examined properties are the reduced adsorption of water on the smaller surface area of the aggregate, which dries less bulk cement paste, increasing the aggregate-cement paste interfacial transition zone (ITZ) width, which is visible on the scanning electron microscopy (SEM) images taken. When the volume of the aggregate is larger and the volume of the paste is smaller, as a result of water adsorption by the larger surface area of the aggregate grains, the actual (effective) w/c ratio in bulk paste decreases, resulting in improved strength and deformation properties.

Effect of Liquid-Solid Volume Ratio and Surface Treatment on Microstructure and Properties of Cu/Al Bimetallic Composite

Due to exceptional conductivity, lightweight nature, corrosion resistance, and various other advantages, Cu/Al bimetallic composites are extensively utilized in the fields of communication, new energy, electronics, and other industries. To solve the problem of poor metallurgical bonding of Cu/Al bimetallic composites caused by high-temperature oxidation of Cu, different coating thicknesses of Ni layer on Cu rods were used to fabricate the Cu/Al bimetallic composite by gravity casting. The effect of liquid–solid volume ratio and coating thickness on microstructure and properties of a Cu/Al bimetallic composite were investigated in this study. The results indicated that the transition zone width increased from 242.3 μm to 286.3 μm and shear strength increased from 17.8 MPa to 30.3 MPa with a liquid–solid volume ratio varying from 8.86 to 50. The thickness of the transition zone and shear strength increased with the coating thickness of the Ni layer varying from 1.5 μm to 3.8 μm, due to the Ni layer effectively preventing oxidation on the surface of the Cu rod and promoting the metallurgical bonding of the Cu/Al interface. The presence of a residual Ni layer in the casted material hinders the diffusion process of the Cu and Al atom. Therefore, the thickness of the transition zone and shear strength exhibited a decreasing trend as the coating thickness of the Ni layer increased from 3.8 μm to 5.9 μm. Shear fracture observation revealed that the initiation and propagation of shear cracks occurred within the transition zone of the Cu/Al bimetallic composite.