SnPb钎料熔滴与Au/Ni/Cu焊盘的反应过程

研究了熔融的SnPb钎料由固定高度滴落到Au/Ni/Cu焊盘上的温度变化过程和界面反应情况。结果表明:对钎料熔滴到达焊盘瞬时的接触温度,熔滴初始温度是其主要影响因素,而高度变化对其影响不大。钎料与焊盘界面产生的金属间化合物形态受钎料熔滴初始温度影响很大。随着滴落钎料初始温度的提高,界面层由Au层基本不反应,变为形成了连续层状AuSn2及针状AuSn4。当初始温度升高到450℃时,AuSn2完全转化为AuSn4,棒状AuSn4生长极为明显,在离界面不远的钎料里发现细小的AuSn4。由计算推出界面反应的时间约为6～7ms,在如此短的时间内,发生Au的溶解和Au Sn化合物的形成,其原因在于Au在熔融钎料中溶解速度随温度变化的特殊性。

EFFECT OF COLD WORKING ON THE AGING PROPERTIES OF Cu-Cr-Zr-Mg ALLOY BY ARTIFICIAL NEURAL NETWORK

A developmental research has been carried out to deal with the high performance of Cu-Cr-Zr-Mg lead frame alloy by artificial neural network (ANN). Using the cold working to assist in the aging hardening can improve the the hardness and electrical conductivity properties of Cu-Cr-Zr-Mg lead frame alloy. This paper studies the effect of different extent of cold working on the aging properties by a supervised ANN to model the non-linear relationship between processing parameters and the properties. The back-propagation (BP) training algorithm is improved by Levenberg-Marquardt algorithm. A basic repository on the domain knowledge of cold worked aging processes is established via sufficient data mining by the network. The predicted values of the ANN coincide well with the tested data. So an important foundation has been laid for prediction and optimum controlling the rolling and aging properties of Cu-Cr-Zr-Mg alloy.

Semiconducting single-walled carbon nanotubes synthesized by S-doping

An approach was presented for synthesis of semiconducting single-walled carbon nanotubes(SWNTs) by sulfur(S) doping with the method of graphite arc discharge. Raman spectroscopy, UV-vis-NIR absorption spectroscopy and electronic properties measurements indicated the semconducting properties of the SWNTs samples. Simulant calculation indicated that S doping could induce convertion of metallic SWNTs into semiconducting ones. This strategy may pave a way for the direct synthesis of pure semiconducting SWNTs.

Methods for a blind analysis of isobar data collected by the STAR collaboration

In 2018,the STAR collaboration collected data from^(96)_(44)Ru+^(96)_(44)Ru and^(96)_(40)Zr+^(96)_(40)Zr at√^(S)NN=200 Ge V to search for the presence of the chiral magnetic effect in collisions of nuclei.The isobar collision species alternated frequently between 9644 Ru+^(96)_(44)Ru and^(96)_(40)Zr+^(96)_(40)Zr.In order to conduct blind analyses of studies related to the chiral magnetic effect in these isobar data,STAR developed a three-step blind analysis procedure.Analysts are initially provided a"reference sample"of data,comprised of a mix of events from the two species,the order of which respects time-dependent changes in run conditions.After tuning analysis codes and performing time-dependent quality assurance on the reference sample,analysts are provided a species-blind sample suitable for calculating efficiencies and corrections for individual≈30-min data-taking runs.For this sample,species-specific information is disguised,but individual output files contain data from a single isobar species.Only run-by-run corrections and code alteration subsequent to these corrections are allowed at this stage.Following these modifications,the"frozen"code is passed over the fully un-blind data,completing the blind analysis.As a check of the feasibility of the blind analysis procedure,analysts completed a"mock data challenge,"analyzing data from Au+Au collisions at√^(S)NN=27 Ge V,collected in 2018.The Au+Au data were prepared in the same manner intended for the isobar blind data.The details of the blind analysis procedure and results from the mock data challenge are presented.

Synthesis of Ni nanowires via a hydrazine reduction route in aqueous ethanol solutions assisted by external magnetic fields

One-dimensional Ni nanostructures were synthesized via a hydrazine reduction route under external magnetic fields. The mixture of de-ionized water and ethanol was used as the reaction solvent and hydrazine hydrate as reducing agents. The morphology and properties of Ni nanostructures were characterized by X-ray diffractometer(XRD), scanning electron microscopy(SEM), and vibrating sample magnetometer(VSM). It was found that the magnetic field strength, concentration of Ni ions,reaction time and temperature as well as p H values played key roles on formation, microstructures and magnetic properties of Ni nanowires. The optimal wires have diameter of ~200 nm and length up to ~200 μm. And their coercivity is ~260 Oe, which is much larger than the commercial Ni powders of 31 Oe. This work presents a simple, low-cost, environment-friendly and large-scale production approach to fabricate one-dimensional magnetic materials. The resulting materials may have potential applications in conductive filters, magnetic sensors and catalytic agents.

Preparation and growth mechanism of nickel nanowires under applied magnetic field

Nickel nanowires with large aspect ratio of up to 300 have been prepared by a hydrazine hydrate reduction method under applied magnetic field. The diameter of nickel nanowires is about 200 nm and length up to 60 μm. The role of magnetic field on the growth of magnetic nanowires is discussed and a magnetic nanowire growth mechanism has been proposed. Nickel ions are firstly reduced to nickel atoms by hydrazine hydrates in a strong alkaline solution and grow into tiny spherical nanoparticles. Then, these magnetic particles will align under a magnetic force and form linear chains. Furthermore, the as-formed chains can enhance the local magnetic field and attract other magnetic particles nearby, resulting finally as linear nanowires. The formation and the size of nanowires depend strongly on the magnitude of applied magnetic field.

Synthesis of morphology-controlled silver nanostructures by electrodeposition

Nanostructured silver was obtained by potentiostatic electrolysis.The effects of ionized surfactant(sodium dodecanesulphonate)and the substrate(Cu and Ti)on the morphology of depositions were investigated.It is found that morphologies of silver nanostructures can be simply controlled via change of the substrate.Spherical Ag nanoparticles with narrow size distribution were obtained by electrodeposition in Ag NO3-SDS aqueous solution on copper substrate.In the case of titanium substrate,silver dendrite structures were obtained.Despite of different morphologies,XRD and TEM results showed that the as-prepared samples belong to face-centered cubic silver structure with good crystallinity.The formation mechanism of different silver nanostructures was discussed.

Ordering-induced Elinvar effect over a wide temperature range in a spinodal decomposition titanium alloy

Temperature-independent elastic modulus is termed as Elinvar effect,which is available by tuning the continuous spin transition of ferromagnetic alloys via composition optimization and the first-order martensitic transformation of shape memory alloys via plastic deformation.However,these reversible mechanisms are restricted generally in a narrow temperature range of less than 300 K.Here reports,by tuning a spinodal decomposition in a Ti-Nb-based titanium alloy via aging treatment,both the Elinvar effect in a wide temperature range of about 500 K and a high strength-to-modulus ratio of about 1.5%can be obtained by a continuous and reversible crystal ordering mechanism.The results demonstrate that the alloy aged at 723 K for 4 h has a nanoscale plate-like modulatedβ+α"two-phase microstructure and its elastic modulus keeps almost constant from 100 to 600 K.Synchrotron and in-situ X-ray diffraction measurements reveal that the crystal ordering parameter of theα"phase increases linearly with temper-ature from 0.88 at 133 K to 0.97 at 523 K but its volume fraction keeps a constant of about 33.8%.This suggests that the continuous ordering of theα"phase toward the high modulusαphase induces a posi-tive modulus-temperature relation to balance the negative relation of the elastically stableβphase.The aged alloy exhibits a high yield strength of 1200 MPa,good ductility of 16%and a high elastic admissible strain of 1.5%.Our results provide a novel strategy to extend the Elinvar temperature range and enhance the strength by tuning the crystal ordering of decomposition alloys.

Development of a 750-mm-long stripline kicker for HEPS

Purpose The superfast kickers are required for the HEPS storage ring on-axis injection system due to its very small dynamic aperture.A 750-mm-long stripline pair type of kicker prototype was researched and developed to demonstrate achieved performance of bandwidth,impedance,kicker strength,field uniformity and beam power loss.Methods The cross sections of the kicker main body and the end of taper part are optimized for a good impedance matching and field uniformity.3D simulation further optimizes the taper part to minimize the beam power loss and maintain a lower reflection.The high-voltage feedthrough is also designed and optimized by 3D CST.RF and high-voltage measurements are taken to verify the design of kicker assembly.Results The testing transmission odd-mode impedance is 50±0.5Ω,the even-mode impedance is 60±0.5Ω,and return loss is less than−13 dB.The peak voltage and the rise time of pulse width inserting kicker assembly just decrease 3%of 20 kV and slow down 80 ps,respectively.Conclusions RF testing results agree well with the simulation ones,which meet the design specification.The kicker assembly works well at±20 kV pulse.

Measurement of away-side broadening with self-subtraction of flow in Au+Au collisions at √sNN=200 GeV

High transverse momentum(pT)particle production is suppressed owing to the parton(jet)energy loss in the hot dense medium created in relativistic heavy-ion collisions.Redistribution of energy at low-to-modest pT has been difficult to measure,owing to large anisotropic backgrounds.We report a data-driven method for background evaluation and subtraction,exploiting the away-side pseudorapidity gaps,to measure the jetlike correlation shape in Au+Au collisions at √sNN=200 GeV in the STAR experiment.The correlation shapes,for trigger particles pT>3GeV/c and various associated particle pT ranges within 0.5<pT<10GeV/c,are consistent with Gaussians,and their widths increase with centrality.The results indicate jet broadening in the medium created in central heavy-ion collisions.

断奶仔猪日粮中添加酵母培养物对生长性能、肠道健康和免疫的影响

选择216头断奶仔猪来研究口粮中添加不同水平的酵母培养物（YC）对生长性能、养分消化率、小肠形态、肠道微生物区系和免疫的影响并探讨酵母培养物是否可以替代抗生素生长促进剂（AGP）。共设2个试验：试验1，192头28d断奶仔猪（7．5±0．2kg）随机分为6个处理组：①对照组；②AGP（金霉素，80mg／kg）；③2．5g／kg酵母培养物；④5g／kg酵母培养物；⑤10g／kg酵母培养物；⑥20g／kg酵母培养物。每个处理8个重复，每个重复4头猪。试验期21d。饲喂5g／kg酵母培养物组仔猪平均日增重显著高于（P〈0．05）对照组和其他酵母培养物组。

Design of precision acquisition system for precision power supply of photon source

Purpose Photon source has developed to the fourth generation.The requirements for beam stability and power supply output current stability have been greatly improved.In this paper,a precision acquisition system is designed for improving the stability for power supply output current.Method The acquisition system consists of two parts,the analog to digital converter(ADC)system and the temperature control system.The composition and software simulation analysis are given in this paper.Results A prototype is made and tested.The test results showed that the acquisition system has an effective resolution of 15.5 bits,signal-to-noise ratio(SNR)of 98 dB,and integral nonlinearity(INL)of 86 ppm.The internal temperature stable range is±0.06℃.Conclusions The acquisition system can fully meet the requirements of the developed photon source.

Development of high-precision DC power supply prototype for HEPS-TF

Purpose This power supply prototype is developed for the quadrupole magnets in the storage ring of HEPS.The project requires a high current stability of these power supplies,in order to master the key technology of this type of power supply in advance,a prototype is made in the project of HEPS test facility.Methods Modularization is used in the prototype’s topology and a combination of digital and analog control is adopted in the closed-loop control.Three control loops are used to improve the output current’s quality.In order to improve the current stability,the key devices in the circuit are under thermostatical controlled.Results The acceptance test results for the NDRC are given in details,which show that all the parameters are better than the design indexes.Conclusions After a lot of experiments and tests,all the parameters of this prototype passed the acceptance test.Among the results,the stability of this prototype achieved 5.2 ppm,the repeatability is 3.2 ppm,and the low-frequency voltage ripples are lower than the requirements of Physicists.The success of this prototype means that the requirements of power supplies in physical design can be met.

Research on high bandwidth power supply

Background Fourth-generation photon sources like Free Electron Lasers(FEL)and Diffraction-Limited Storage Rings(DLSR)have high requirements for beam emittance.In the case of DLSR sources,a set of high-performance fast orbit feedback system(FOFB)is needed to correct the beam orbit quickly and accurately.Purpose FOFB system has four key components,which is BPM,orbit feedback calculation,fast correction magnet and fast corrector power supply.The FOFB gives the correction command and controls the fast corrector power supply to drive the fast correction magnet to correct the beam quickly and accurately.The corrector power supply has an important impact on the performance of FOFB.The corrector power supply needs to have high bandwidth and low output current ripple.Methods The new GaN power device is used to solve the restriction of the high-speed switching.The switching frequency of the power supply is increased to 300 kHz.The control system is designed to improve the bandwidth and optimize the output current ripple.The modeling analysis of the key parts of the system is given and the simulation experiments are carried out with MATLAB.Results and conclusion The test results showed that bandwidth of the designed power supply is 20 kHz.The step response time is 18us and output current ripple is lower than 1 mA.

A high-power and high-stability power supply design

Objective BEPCII is a high-performance collider with a design energy of 2.1 GeV. In order to obtain more physical experimentsand synchrotron radiation applications, BEPCII decided to carry out energy upgrading to 2.5 GeV. Insufficient energyof special magnet power supplies in collision zone is a key factor restricting BEPCII’s operation under 2.5 GeV energy.Therefore, three high-power and high-stability power supplies are designed for BEPCII energy upgrading.Methods The designed power supplies output part adopts high-frequency chopper modules parallel connected and adoptsdigital-analog hybrid control methods. The voltage loop regulator uses high-speed analog control, and current loop regulatoruses digital control which is based on FPGA.Conclusion The experimental data show that the output current stability of the developed power supplies is lower than50 ppm. The output current resolution is lower than 70 ppm. The developed power supplies can well meet the design requirementsof BEPCII energy upgrading.