Search Results (4)

In response to the increasingly severe situation of main roadway shock in coal seams, with a focus on the strong-bump coal seam in main roadways under an asymmetric goaf in a certain mine, theoretical analysis, numerical simulation, and engineering practices were employed. This study investigated factors influencing main roadway roof shock damage, changes in roof stress, and characteristics of overlying strata movement. This research unveiled the mechanism and prevention of roof shock in main roadways of strong-bump coal seams in an asymmetric goaf. The research results indicate that the influencing factors of main roadway roof shock damage can be divided into two categories: “strata-support” structure strength and surrounding rock stress. For the determination of the “strata-support” structure, in the case of strong bumps in coal seam roadways influenced by the asymmetric goaf, the key factors contributing to shock damage are the side abutment pressure on the coal pillar in the goaf and the activity level of the roof strata. The distribution of roof stress in the main roadway undergoes continuous changes as district faces are sequentially mined. When the goaf area on the west side gradually increases towards the south, the roof stress in the main roadway consistently rises, and the stress increment follows a pattern of initial increase followed by a decrease. The strata structure of the main roadway roof gradually transforms from an “asymmetric T” shape to a “symmetric T” shape in the transverse profile, and with the evolution of the roof rock layer structure, the mutual feedback effect of strata activity on both sides of the roadway gradually strengthens. Affected by the asymmetric goaf, the main roadway in the district undergoes three different stages: one side of subcritical mining influence → both sides of subcritical mining influence → one side of subcritical mining and one side of critical mining influence. In addition, comprehensively considering the impact of various factors in different stages, the theoretical criteria for roof shock failure in the main roadway are determined. The formulation of an optimized position for the main roadway and a scheme for depressurization through deep-hole blasting in the roof reduce the stress level in the surrounding rock of the main roadway, effectively preventing the occurrence of roof shock in the asymmetric goaf of the coal seam main roadway. Full article

Lead frames have been widely used in the semiconductor package assembly industry; a lot of demand is still maintained in fields requiring high reliability, such as automobiles, although many fields are being replaced by laminated substrates according to the recent electronic package product trend that requires high I/O pin count. The purpose of this paper is to introduce two-layer Rt-QFN, one of the lead frame-based coreless substrates. (Rt-QFN is a trademark of Haesung DS, which means premold type lead frame substrate.) two-layer Rt-QFN can secure more advanced design freedom compared with the lead frame and thus has I/O pin count coverage intermediate between the lead frame and laminated substrate. In addition, Rt-QFN can exhibit excellent heat dissipation performance by replacing via holes of the laminated substrate with Cu bumps formed by etching. CAE analysis showed that the thermal resistance of the two-layer Rt-QFN substrate was about 23% lower than that of the laminate substrate. The excellent heat dissipation property of two-layer Rt-QFN allows it to replace the existing expensive ceramic substrate and can achieve cost savings. In addition, the sputtering technique, including the LIS (Linear Ion Source) module, was introduced as a method to sufficiently secure the interfacial adhesion between the resin/Cu interface, which is a key factor in producing a two-layer substrate. As a method to enhance the interfacial adhesion between the resin/Cu interface, the collimated mode of LIS was used in the Ar atmosphere inside the vacuum chamber to activate the resin surface. After plasma pretreatment on the surface of the resin, a Cu seed layer was continuously formed by sputtering. As a result, it was possible to secure the high reliability of the two-layer Rt-QFN substrate, and it was confirmed through the evaluation of interfacial adhesion of more than 1.2 kgƒ/cm during the peel-off tape test at the resin/Cu interface and further moisture absorption evaluation. Full article

The fabrication of conformal nanostructures on microarchitectures is of great significance for diverse applications. Here a facile and universal method was developed for conformal self-assembly of nanospheres on various substrates including convex bumps and concave holes. Hydrophobic microarchitectures could be transferred into superhydrophilic ones using plasma treatment due to the formation of numerous hydroxyl groups. Because of superhydrophilicity, the nanosphere suspension spread on the microarchitectures quickly and conformal self-assembly of nanospheres can be realized. Besides, the feature size of the conformal nanospheres on the substrates could be further regulated by plasma treatment. After transferring two-dimensional tungsten disulfide sheets onto the conformal nanospheres, the periodic nanosphere array was demonstrated to be able to enhance the light harvesting of WS₂. Based on this, a light-enhanced room-temperature gas sensor with a fast recovery speed (<35 s) and low detecting limit (500 ppb) was achieved. Moreover, the WS₂-covered nanospheres on the microarchitectures were very sensitive to the changes in air pressure due to the formation of suspended sheets on the convex bumps and concave holes. A sensitive photoelectronic pressure sensor that was capable of detecting the airtightness of vacuum devices was developed using the WS₂-decorated hierarchical architectures. This work provides a simple method for the fabrication of conformal nanospheres on arbitrary substrates, which is promising for three-dimensional microfabrication of multifunctional hierarchical microarchitectures for diverse applications, such as biomimetic compound eyes, smart wetting surfaces and photonic crystals. Full article

The forced Korteweg-de Vries equation is considered to investigate the impact of bottom configurations on the free surface waves in a two-dimensional channel flow. In the study of shallow water waves, the bottom topography plays a critical role, which can determine the characteristics of wave motions significantly. The interplay between solitary waves and the bottom topography can exhibit more interesting dynamics of the free surface waves when the bottom configuration is more complex. In the presence of two bumps, there are multiple trapped solitary wave solutions, which remain stable between two bumps up to a finite time when they evolve in time. In this work, various stationary trapped wave solutions of the forced KdV equation are explored as the bump sizes and the distance between two bumps are varied. Moreover, the semi-implicit finite difference method is employed to study their time evolutions in the presence of two-bump configurations. Our numerical results show that the interplay between trapped solitary waves and two bumps is the key determinant which influences the time evolution of those wave solutions. The trapped solitary waves tend to remain between two bumps for a longer time period as the distance between two bumps increases. Interestingly, there exists a nontrivial relationship between the bump size and the time until trapped solitary waves remain stable between two bumps. Full article