ead-free Sn3.5Ag and Sn3.5Ag0.5Cu solder balls were reflowed by laser to form solder bumps. Shear test was performed on the solder bumps, and SEM/EDX （scanning electron microscopy/energy dispersive X-ray spectrometer...ead-free Sn3.5Ag and Sn3.5Ag0.5Cu solder balls were reflowed by laser to form solder bumps. Shear test was performed on the solder bumps, and SEM/EDX （scanning electron microscopy/energy dispersive X-ray spectrometer） was used to analyze the formation of intermetallic compounds （IMCs） at interface region. A finite element modeling on the temperature gradient and distribution at the interface of solder bump during laser reflow process was conducted to elucidate the mechanism of the IMCs growth direction. The results show that the parameters window for laser reflow bumping of Sn3.5Ag0.5Cu was wider than that of Sn3.5Ag. The shear strength of Sn3.5Ag0.5Cu solder bump was comparable to that of Sn3.5Ag solder bump, and was not affected obviously by laser power and irradiation time when appropriate parameters were used. Both laser power and heating time had a significant effect on the formation of IMCs. A continuous AuSn4 intermetallic compound layer and some needle-like AuSn4 were observed at the interface of solder and Au/Ni/Cu metallization layer when the laser power is small. The formation of needle-like AuSn4 was due to temperature gradient at the interface, and the direction of temperature gradient was the preferred growth direction of AuSn4. With increasing the laser power and heating time, the needle-like AuSn4 IMCs dissolved into the bulk solder, and precipitated out once again during solidification along the grain boundary of the solder bump.展开更多
Rock mass dynamics disasters caused by excavations and mining occur frequently in deep mines.In order to establish a theoretical system and control technologies for such disasters,we first classify and define dynamic ...Rock mass dynamics disasters caused by excavations and mining occur frequently in deep mines.In order to establish a theoretical system and control technologies for such disasters,we first classify and define dynamic disasters,such as rock bursts,coal bursts,mine pressure bumps,and mine earthquakes.According to the occurrence mechanism of different types of dynamic disasters,we establish a compensation control theory based on excavation and mining effects.On the basis,we propose three key technologies:high prestress compensation technology for the roadway,pressure relief technology using directional roof cutting,and the goaf filling technology using broken rock dilation.These three technologies constitute the compensation control method for dynamic disasters in deep mines.Finally,this method was successfully applied in a deep coal mine with high stress,with monitored results suggesting its rationality.This work provides a new concept and control method for the prevention of rock dynamic disasters in deep mines.展开更多
The way in which persistent firing activity and synaptic plasticity are orchestrated to underlie working memory in recurrent neural networks is not fully understood. Here, we build a continuous attractor network of py...The way in which persistent firing activity and synaptic plasticity are orchestrated to underlie working memory in recurrent neural networks is not fully understood. Here, we build a continuous attractor network of pyramidal cells and interneurons to simulate an oculomotor delayed response task. Both short-term facilitation(STF) and short-term depression(STD) manifest at synapses between pyramidal cells. The efficacy of individual synapses depends on the time constants of STF and STD as well as the presynaptic firing rate. Self-sustained firing activity(i.e., a bump attractor) during the delay period encodes the cue position. The bump attractor becomes more robust against random drifts and distractions with enhancing STF or reducing STD. Keeping STF and STD at appropriate levels is crucial for optimizing network performance. Our results suggest that, besides slow recurrent excitation and strong global inhibition, short-term plasticity plays a prominent role in facilitating mnemonic behavior.展开更多
A diffraction-limited storage ring with a multi-bend achromat lattice suffers from a small dynamic aperture for conventional off-axis injection.Thus,a longitudinal on-axis injection scheme based on a new type of crab ...A diffraction-limited storage ring with a multi-bend achromat lattice suffers from a small dynamic aperture for conventional off-axis injection.Thus,a longitudinal on-axis injection scheme based on a new type of crab cavity is proposed in this paper.Particle tracking simulations were performed to study the disturbance of the stored beam and the motion of the injected beam during the injection process.The possibility of multi-bunch injections was discussed.In addition,the effect of the long-range wake field induced by the stored beam was analyzed.A C-band standing-wave crab cavity was designed and produced as requested,and its field distribution was measured.The corresponding results are consistent with the simulation results.展开更多
The thermally induced cyclic loading on integral bridge abutments causes soil deformation and lateral stress ratcheting behind the abutment wall due to the expansion and contraction of the bridge deck.The forward and ...The thermally induced cyclic loading on integral bridge abutments causes soil deformation and lateral stress ratcheting behind the abutment wall due to the expansion and contraction of the bridge deck.The forward and backward movements of the abutment in response to the expansion/contraction of the bridge deck lead to the formation of settlement trough and surface heaving,frequently creating a bump at the bridge approach and increasing the lateral earth pressure behind the abutment.Measures to reduce the bump at the bridge approach,including several treatment methods,such as compaction of selected backfill materials,grout injection,installation of approach slab,and using a layer of compressible inclusion material behind the abutment were proposed.However,these guidelines still lack sufficient design details and there are limited experimental findings to validate design assumptions.In this paper,the use of engineered compressible materials to alleviate the lateral earth pressure ratcheting and settlement at the bridge approach is investigated.The comparative study is presented for the soil-inclusion,material-structure and soil-structure interactions for an integral bridge under three different backfill conditions,i.e.(a)sand,(b)sand and EPS geofoam,and(c)sand and Infinergy®.The study was conducted in a special large-scale test chamber with a semi-scale abutment to gain better insights into the soil-structure interaction(SSI).The kinematics and rearrangement of the soil during the cyclic loading have been investigated to identify the mitigating effects of compressible inclusions.The comparative study indicates that both compressible inclusions perform comparatively well,however,Infinergy®is a better alternative than the medium-density EPS geofoam,as it works more effectively to reduce the backfill settlement and heaving as well as soil ratcheting effects under cyclic translational movement.展开更多
基金supported by the National Natural Science Foundation of China under grant No.50475031/E052104.
文摘ead-free Sn3.5Ag and Sn3.5Ag0.5Cu solder balls were reflowed by laser to form solder bumps. Shear test was performed on the solder bumps, and SEM/EDX （scanning electron microscopy/energy dispersive X-ray spectrometer） was used to analyze the formation of intermetallic compounds （IMCs） at interface region. A finite element modeling on the temperature gradient and distribution at the interface of solder bump during laser reflow process was conducted to elucidate the mechanism of the IMCs growth direction. The results show that the parameters window for laser reflow bumping of Sn3.5Ag0.5Cu was wider than that of Sn3.5Ag. The shear strength of Sn3.5Ag0.5Cu solder bump was comparable to that of Sn3.5Ag solder bump, and was not affected obviously by laser power and irradiation time when appropriate parameters were used. Both laser power and heating time had a significant effect on the formation of IMCs. A continuous AuSn4 intermetallic compound layer and some needle-like AuSn4 were observed at the interface of solder and Au/Ni/Cu metallization layer when the laser power is small. The formation of needle-like AuSn4 was due to temperature gradient at the interface, and the direction of temperature gradient was the preferred growth direction of AuSn4. With increasing the laser power and heating time, the needle-like AuSn4 IMCs dissolved into the bulk solder, and precipitated out once again during solidification along the grain boundary of the solder bump.
基金supported by the Natural Science Foundation of China(Nos.41941018,52074164,42077267,42277174,and 52204260)the Fundamental Research Funds for the Central Universities,China(No.2022JCCXSB03).
文摘Rock mass dynamics disasters caused by excavations and mining occur frequently in deep mines.In order to establish a theoretical system and control technologies for such disasters,we first classify and define dynamic disasters,such as rock bursts,coal bursts,mine pressure bumps,and mine earthquakes.According to the occurrence mechanism of different types of dynamic disasters,we establish a compensation control theory based on excavation and mining effects.On the basis,we propose three key technologies:high prestress compensation technology for the roadway,pressure relief technology using directional roof cutting,and the goaf filling technology using broken rock dilation.These three technologies constitute the compensation control method for dynamic disasters in deep mines.Finally,this method was successfully applied in a deep coal mine with high stress,with monitored results suggesting its rationality.This work provides a new concept and control method for the prevention of rock dynamic disasters in deep mines.
基金supported by STI 2030-Major Projects 2021ZD0201300。
文摘The way in which persistent firing activity and synaptic plasticity are orchestrated to underlie working memory in recurrent neural networks is not fully understood. Here, we build a continuous attractor network of pyramidal cells and interneurons to simulate an oculomotor delayed response task. Both short-term facilitation(STF) and short-term depression(STD) manifest at synapses between pyramidal cells. The efficacy of individual synapses depends on the time constants of STF and STD as well as the presynaptic firing rate. Self-sustained firing activity(i.e., a bump attractor) during the delay period encodes the cue position. The bump attractor becomes more robust against random drifts and distractions with enhancing STF or reducing STD. Keeping STF and STD at appropriate levels is crucial for optimizing network performance. Our results suggest that, besides slow recurrent excitation and strong global inhibition, short-term plasticity plays a prominent role in facilitating mnemonic behavior.
基金the National Natural Science Foundation of China(Nos.11975298 and 12175292).
文摘A diffraction-limited storage ring with a multi-bend achromat lattice suffers from a small dynamic aperture for conventional off-axis injection.Thus,a longitudinal on-axis injection scheme based on a new type of crab cavity is proposed in this paper.Particle tracking simulations were performed to study the disturbance of the stored beam and the motion of the injected beam during the injection process.The possibility of multi-bunch injections was discussed.In addition,the effect of the long-range wake field induced by the stored beam was analyzed.A C-band standing-wave crab cavity was designed and produced as requested,and its field distribution was measured.The corresponding results are consistent with the simulation results.
基金The authors gratefully acknowledge and thank BASF for providing the Infinergymaterial used in this research.The continuous technical support provided by Mr.Van Doan and Advanced Materials Characterisation Facility(AMCF)at Western Sydney University(WSU)are also gratefully acknowledged.This research is supported by the Graduate student research fund of WSU.This research did not receive any specific grant from funding agencies in the public,commercial,or not-for-profit sectors.
文摘The thermally induced cyclic loading on integral bridge abutments causes soil deformation and lateral stress ratcheting behind the abutment wall due to the expansion and contraction of the bridge deck.The forward and backward movements of the abutment in response to the expansion/contraction of the bridge deck lead to the formation of settlement trough and surface heaving,frequently creating a bump at the bridge approach and increasing the lateral earth pressure behind the abutment.Measures to reduce the bump at the bridge approach,including several treatment methods,such as compaction of selected backfill materials,grout injection,installation of approach slab,and using a layer of compressible inclusion material behind the abutment were proposed.However,these guidelines still lack sufficient design details and there are limited experimental findings to validate design assumptions.In this paper,the use of engineered compressible materials to alleviate the lateral earth pressure ratcheting and settlement at the bridge approach is investigated.The comparative study is presented for the soil-inclusion,material-structure and soil-structure interactions for an integral bridge under three different backfill conditions,i.e.(a)sand,(b)sand and EPS geofoam,and(c)sand and Infinergy®.The study was conducted in a special large-scale test chamber with a semi-scale abutment to gain better insights into the soil-structure interaction(SSI).The kinematics and rearrangement of the soil during the cyclic loading have been investigated to identify the mitigating effects of compressible inclusions.The comparative study indicates that both compressible inclusions perform comparatively well,however,Infinergy®is a better alternative than the medium-density EPS geofoam,as it works more effectively to reduce the backfill settlement and heaving as well as soil ratcheting effects under cyclic translational movement.
