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Every day social multimedia applications generate millions of images. To handle such huge amount of images, an optimal solution is using the public cloud, since it has powerful storage capability. Images usually contain a wealth of sensitive information, therefore social service providers need not only to provide services such as retrieval and sharing but also to protect the privacies of the images. In this paper, we propose a privacy-preserving scheme for content-based image retrieval and sharing in social multimedia applications. First, the users extract visual features from the images, and perform locality-sensitive hashing functions on visual features to generate image profile vectors. We then model the retrieval on the images as the equality search on the image profile vectors. To enable accurate and efficient retrieval, we design the secure index structure based on cuckoo hashing, which has constant lookup time. To meet the requirements of dynamic image updating, we enrich our service with image insertion and deletion. In order to reduce the key management overhead and the access control overhead in social applications, we process keys using secret sharing techniques to enable the users holding similar images to query and decrypt images independently. Finally we implement the prototype of the proposed scheme, and perform experiments over encrypted image databases.

While moving ahead with science and technology., the service conditions of microelectronic devices are becoming more and more complicated., and the performance requirements of packaging materials are also increasing especially for hash applications. The dependability of solder joints in electronic chips under high temperatures and high strain rates have attracted much attention. In this paper., experimental studies are carried out on the dynamic behavior of Sn-3.0Ag-0.5Cu (SAC305) materials. The dynamic compression experiments are operated by using the Split-Hopkinson Pressure Bar (SHPB) with a heating furnace to achieve the target temperature condition. The true stress- strain curves are received by this system at a temperature of 343K and the strain rates from 959 ${\mathrm{s}^{-1}}$ to ${1961\ {\mathrm{s}^{-1}}}$ . Additionally., in order to investigate the deformation mechanism under impact scenarios., an optical microscopy is utilized to characterize the microstructure of the SAC305 lead-free solder specimen at high temperatures and high strain rates.

To overcome the problems of human skeleton loss and body occlusion in a person following system, this paper proposes a real-time and reliable control method for mobile service robots, which combines human skeleton tracker and the discriminative correlation filter with channel and spatial reliability (CSR-DCF) visual tracker. In particular, the CSR-DCF visual tracker is responsible for correcting and locking the special person when the human skeleton tracker provided by Orbbec SDK becomes unstable under the moving mobile service robot. While the skeleton tracker is responsible for taking over the tracking task when the CSR-DCF visual tracker drifts to non-skeleton regions. Experiment results show that the total accuracy has risen to 84.3%, which verifies the effectiveness of the proposed method.

In this study, the effect of current density on tensile performance of Cu/Sn-58Bi/Cu joints under electrothermo-mechanical (ETM) coupled loads was researched. The results indicate that the tensile strength of the joint under ETM coupled loads was much lower than that under tensile stress without electric current stressing at 25 °C. Moreover, the joint’s stiffness and tensile strength continuously decreases with increasing current density. Furthermore, the fracture position is transferred from solder matrix to the solder/IMC layer interface with a fracture mechanism transition from ductile fracture to ductile-brittle mixed one.

In this study, the ball grid array (BGA) structure microscale lead-free Cu/Sn-3.0Ag-0.5Cu/Cu (Cu/SAC305/Cu) joints with different heights (i.e., 100 and 200 μm) were used to investigate the shear deformation and fracture behavior after soaking treatment with liquid nitrogen for different time. The experimental results indicated that the ultimate strength of the joint under shear loading generally decreases slightly with the increase in time of liquid nitrogen soaking, while it increases obviously with the decrease in joint height. Moreover, the fracture locations of all tested solder joints are inside the solder matrix. At the same time, it can be deduced from the stress- strain curve and fracture morphology that the fracture behavior remains ductile.

We have improved the detection efficiency of Ti-based superconducting transition edge sensor(TES) with the integration of dielectric mirror at the operation wavelength of 1550 nm. The TES fabricated on the dielectric mirror is coupled to the optical fiber using back-side through-chip imaging. The measured effective response time is several μs and the detection efficiency is improved to 30%.

Shear deformation and fracture behavior of microscale BGA structure Cu/Sn-3.0Ag-0.5Cu/Cu joints with a pad diameter 320 μm and a joint height 220 μm and different solder ball diameters 600, 500 and 400 μm (i.e., different solder volumes) were investigated at a temperature from 25 to -120 oC in this study. Results show that, when the solder ball diameter of the solder joint is 600 μm, the shear strength increases with the descending temperature; while, as the solder ball diameter of the solder joint decreases to 500 and 400 μm, a peak shear strength appeared at -100 and -80 oC, respectively. Moreover, the fracture behavior of all the joints is temperature dependent. Regardless of the solder ball diameter, the joint fracture position keeps in the solder matrix at a higher temperature, which shifts to the interface between the solder and the interfacial Cu 6 Sn 5 layer at a lower temperature, and the fracture mode shows a ductile-to-brittle transition with the descending temperature. Moreover, the temperature of the ductile-to-brittle transition is joint size dependent, which is lowered as the solder ball diameter decreases.

To reduce thermal shock on thinner devices and substrates during reflow process, low melting-point Sn–58Bi (SnBi) solder paste was studied to replace high melting-point Sn–3.0Ag–0.5Cu (SAC305) solder paste. In this study, SAC305 solder ball as integrated circuit (IC) pin was reflowed using SnBi solder paste on substrate board to form mixed assembled Cu/SAC305-ball/SnBi-paste/Cu BGA structure joints, then the microstructural evolution and shear properties of mixed assembled joints after thermal aging and current stressing were investigated. Results show that current stressing induces a polarity effect on growth of interfacial Cu6Sn5 layer of the mixed assembled joints during electromigration, and promotes the growth of Cu6Sn5 layer at the anodic Cu/SAC305-ball interface significantly, while reversely on the cathode side. Bi atoms migrate to the anode side to form the Bi-rich phase layer at anodic SnBi-paste/Cu interface. In addition, regardless of change in electron flow direction, difference in migration rate between Bi and Sn atoms leads to formation of voids near the SnBi-paste/Cu interface, and shear strength of mixed assembled joints decreases with prolonging current stressing time, the fracture occurs mainly at SnBi-paste/Cu interface. Fracture mode is mixed ductile-brittle fracture and brittle fracture when SnBi-paste/Cu interface is on cathode side and anode side, respectively.

In the process of implementing combat missions, depending on mission briefs, battlefield situation information and environment, aircraft swarms need to evolve its space configuration adaptively and provide the best spatial location for transducers and weapons to enhance operational effectiveness. In view of the above problem, the thesis proposes an evolution method of aircraft swarms space configuration. On the basis of Event Condition Action (ECA) rules and with the help of modified Statecharts, the method builds an aircraft swarms ECA model based on Statecharts. Finally, taking the space configuration evolution of three aircraft cooperating passive location for example, the feasibility of the model and the effectiveness of the method proposed in the thesis is validated.

Shear performance and fracture of BGA structured Cu/Sn–3.0Ag–0.5Cu(SAC305)/Cu joints under current stressing were characterized. Solder joints undergoing electric current stressing have lower shear strength, and fracture tends to take place near the interface between the solder and the intermetallic compound (IMC), and shear fracture strength of the joints decreases with increasing current density. In addition, under electric current stressing, fracture largely occurred mainly by mixed ductile-brittle mode. The temperature of the joints increases greatly upon applying electric current as confirmed by finite element simulation (FE simulation), which is induced by the Joule heating effect. Moreover, the phenomenon of local melting has been observed in solder joints with electric current stressing.

To reduce the cost of soldering materials and alleviate the thermal shock of temperature-sensitive electronic components during board-level packaging process, SnBi(Ag) solder pastes were explored to replace SnAgCu solder pastes due to the feature of low melting temperature of SnBi(Ag) solders. In this study, Sn3.0Ag0.5Cu (SAC305) solder balls as IC pins were assembled with SnBi(Ag) solder pastes in the substrate board, and the microstructures and shear properties of mixed assembly BGA structure SnAgCu/SnBi(Ag)/Cu joints were studied comprehensively. Results show that the thickness of the interfacial Cu 6 Sn 5 layer of the SAC305/SnBi(Ag)/Cu joint is thinner than that of the SAC305/SAC305/Cu joint, and the SAC305/SnBiAg/Cu joint has the lowest interfacial Cu 6 Sn 5 layer. The shear strength of SAC305/SnBi(Ag)/Cu joints is higher than that of SAC305/SAC305/Cu joints. Moreover, for BGA structure SAC305/SnBi/Cu and SAC305/SnBiAg/Cu joints, the shear strength of all the joints increases firstly and then decreases with increasing the loading rate in shear test, and the SAC305/SnBiAg/Cu joint has higher shear strength than SAC305/SnBi/Cu joint under a low loading rate, while being reverse at a high loading rate. Both SAC305/SnBi/Cu and SAC305/SnBiAg/Cu joints exhibit a mixed ductile and brittle fracture mode, and the fracture occurs mainly in the solder matrix and partially at the solder/IMC interface.

Size effect of solder balls on the interfacial reaction and microstructural evolution of BGA structure Cu/Sn3.0Ag0.5Cu-ball/Sn3.0Ag0.5Cu-paste/Cu joints during isothermal aging at 125 °C was systematically investigated. Results show that a large amount of bulk Cu 6 Sn 5 phase distributes in the solder matrix of joints with large solder ball size, resulting from larger outflux Cu atoms from the interface to the molten solder and the low solubility of Cu in the solder matrix. The solder ball size has a significant influence on the interfacial Cu 6 Sn 5 layer thickness at the Sn3.0Ag0.5Cu-ball/Cu interface, which increases with decreasing solder ball size, while showing less effect on that at the Sn3.0Ag0.5Cu-paste/Cu interface. The grain size of Ag 3 Sn phase in joints decreases with decreasing solder ball size. During isothermal aging, the growth of interfacial IMC layers at both Sn3.0Ag0.5Cu-ball/Cu and Sn3.0Ag0.5Cu-paste/Cu interfaces of joints is mainly controlled by bulk diffusion.

The dynamic wetting behavior and formation of solder ball spattering of Sn-58Bi solder paste on Cu substrate during reflow soldering process were studied by the soldering interrupt test method; meanwhile, the formation mechanism of solder ball spattering was analyzed. Further, the effect of reflow process parameters on the severity of solder ball spattering defect during reflow soldering process was investigated by a modified solder ball test. Results show that solder ball spattering mainly takes place during the second ramp-up stage of the reflow profile, in which the oxidation of solder alloy elements on the surface of molten solder pool is deoxidized into high Bi content liquid solder ball by redox reactions, then the liquid flux film breaks up and pushes the liquid Bi-rich solder balls to the edge of the solder pool, this finally results in the formation of solder ball spattering. The results of solder balling test show that a higher ramp-up rate significantly increases the severity of solder ball spattering, and a longer dwelling time can also increase the severity of solder ball spattering for the high volatility solder paste.

In order to reduce the cost of solder materials and retard the thermal shock of temperature-sensitive electronic components during packaging process, SnBi solder paste was explored to replace SnAgCu solder paste due to the low melting temperature. In this study, BGA structure Cu/solder-ball/solder-paste/Cu joints were designed and prepared to study the interfacial reactions and microstructural evolution of the mixed assembly joints, by using homogenous Sn3.0Ag0.5Cu (SAC305) and Sn-58Bi (SnBi) solders in the forms of both ball and paste, during isothermal aging. Results show that microstructural coarsening occurs in Cu/SAC305-ball/SnBi-paste/Cu, Cu/SAC305-ball/SAC305-paste/Cu and Cu/SnBi-ball/SnBi-paste/Cu joints and the thicknesses of interfacial IMCs increase with prolonging the isothermal aging time. Crack may form in the fusion region between the SnAgCu and SnBi-SnAgCu mixed solders in Cu/SAC305/SnBi/Cu joints after aging at 125 °C for 150 h due to the difference in coefficient of thermal expansion (CTE) between the SAC305 and SnBi solders, which may significantly weaken the reliability of mixed assembly joints. Moreover, in the solder matrix of Cu/SAC305/SnBi/Cu joints, a large amount of bulk Cu 6 Sn 5 phase exists due to the limited solubility of Cu in the SnBi matrix. In addition, the growth of interfacial IMC layer at both solder-ball/Cu and solder-paste/Cu interfaces of the joints is mainly controlled by bulk diffusion.

We reported on a progress toward a CPT-Ramsey clock based on a continuous cold cesium beam. The cesium beam has a high flux of 3 × 1010 atoms/s and a most probable velocity of 7 m/s. Two Raman laser beams are aligned to be orthogonal to the cold atomic beam. The two CPT zones are spatially separated. A CPT resonance is observed with a single interaction zone.

Characteristics of superconducting FeSe 0.5 Te 0.5 hot electron bolometer are reported. The superconducting FeSe 0.5 Te 0.5 film is grown by pulsed laser deposition on MgO substrate, and its transition temperature and complex conductivity indicate that the film quality is good enough for hot electron bolometer. We then fabricate hot electron bolometer based on the superconducting FeSe 0 . 5 Te 0 . 5 film, and study the resistive transition curve and its current-voltage characteristics.