Nucleation and growth kinetics of tin and tin -silver alloy during initial stages of electrodeposition

Electrodeposition has played an essential role in electronics packaging because it gives superior thickness control for chip interconnects. Pure tin, tin-silver and tin-silver-based solders have been identified as leading candidates for lead-free solders due to the desirable melting point, good creep resistance and thermo-mechanical behavior. The initial stage of electrodeposition, or the formation of small clusters of atoms (nuclei), is significant in the overall electrodeposition kinetics, as well as the appearance, structure, and properties of the resulting coatings. In this work, nucleation and growth kinetics of tin and tin-silver electrodeposition on copper and nickel substrates were investigated by electrochemical methods and surface analysis techniques (SEM and AFM). The nucleation rate, number density of active sites, critical nucleus size and free energy of critical nucleus formation were extracted under various electrolyte solutions. Based on chronoamperometric studies, in acid tin solution without additives, tin electrodeposition is instantaneous nucleation with three-dimensional diffusion controlled growth. Addition of thiourea to the solution changes the nucleation process from instantaneous to progressive, which was confirmed by SEM and AFM analysis. In the acid tin solution containing thiourea-silver, the process of nucleation is unclassified. In all cases, the number density of active sites increases exponentially as the deposition potential changes to more negative values, and it is the highest in the solution with thiourea-silver. According to classical and atomistic theories, in all cases, tin electrodeposition proceeds with three-dimensional phase formation and growth. The number of atoms forming the critical nucleus (Ncrit) consists of 0--2 atoms. The critical Gibbs free energy (DeltaGcrit) follows the sequence Cu-S \u3e Ni-P \u3e Cu-P, which is consistent with the number density of active sites on the substrate surface. The number density of nuclei in the AFM images was measured by AFM. In comparison with calculated nucleus densities, the measured values are much higher. At -550 mV, the measured density is about 2 times as great as the calculated value in acid tin solution without additive. In the presence of thiourea-silver, the measured density is about 6 times as great as the calculated one

Vital Sign Monitoring in Dynamic Environment via mmWave Radar and Camera Fusion

Contact-free vital sign monitoring, which uses wireless signals for recognizing human vital signs (i.e, breath and heartbeat), is an attractive solution to health and security. However, the subject's body movement and the change in actual environments can result in inaccurate frequency estimation of heartbeat and respiratory. In this paper, we propose a robust mmWave radar and camera fusion system for monitoring vital signs, which can perform consistently well in dynamic scenarios, e.g., when some people move around the subject to be tracked, or a subject waves his/her arms and marches on the spot. Three major processing modules are developed in the system, to enable robust sensing. Firstly, we utilize a camera to assist a mmWave radar to accurately localize the subjects of interest. Secondly, we exploit the calculated subject position to form transmitting and receiving beamformers, which can improve the reflected power from the targets and weaken the impact of dynamic interference. Thirdly, we propose a weighted multi-channel Variational Mode Decomposition (WMC-VMD) algorithm to separate the weak vital sign signals from the dynamic ones due to subject's body movement. Experimental results show that, the 90${^{th}}$ percentile errors in respiration rate (RR) and heartbeat rate (HR) are less than 0.5 RPM (respirations per minute) and 6 BPM (beats per minute), respectively

Genetic architecture of lodging resistance revealed by genome- wide association study in maize (Zea mays L)

Lodging is one of key factors influencing biomass yield, restricting planting density and reducing mechanical harvesting productivity in maize. Targeted cultivating lodging resistance varieties with screened lines is an eco- nomical and effective approach to improve ability of maize lodging resistance. To accomplish this objective, we performed phenotypic assessment of seven lodging-related traits in a diverse maize population consisting of 290 inbred lines and conducted a genome-wide association study with 201 SSR markers to detected marker-trait as- sociations. Seven lodging-related traits all showed broad phenotypic variations. Through evaluation of stalk push- ing resistance in the field for two years, a number of 32 inbred lines featured with strong lodging resistance were selected out. Correlation analysis indicated that stalk pushing resistance had a significantly positive correlation with third internode diameter and fourth internode diameter and a significantly negative correlation with ear height. Furthermore, a total of 27 and 13 significant associations for lodging-related traits were identified in year 2012 and 2013, respectively. Interestingly, three associations on chromosome 4, 5, and 6 were discovered in both years. Thus, this study provides useful information for understanding genetic architecture of lodging resistance in maize and will benefit maize marker-assistant breeding program with improving lodging resistance

Sea Level Pressure Variability Over the Southern Indian Ocean Inferred from a Glaciochemical Record in Princess Elizabeth Land, East Antarctica

A 250-year, high-resolution, multivariate ice core record from LGB65 (70degrees50\u2707 S, 77degrees04\u2729 E; 1850 m asl), Princess Elizabeth Land (PEL), is used to investigate sea level pressure (SLP) variability over the southern Indian Ocean (SIO). Empirical orthogonal function (EOF) analysis reveals that the first EOF (EOF1) of the glaciochemical record from LGB65 represents most of the variability in sea salt throughout the 250-year record. EOF1 is negatively correlated (95% confidence level and higher) to instrumental mean sea level pressure (MSLP) at Kerguelen and New Amsterdam islands, SIO. On the basis of comparison with NCEP/NCAR reanalysis, strong correlations were found between sea-salt variations and a quasi-stationary low that lies to the north of Prydz Bay, SIO. Comparison with a 250-year-long summer transpolar index (STPI) inferred from sub-Antarctic tree ring records reveals strong coherency. Decadal-scale SLP variability over SIO suggests shifting of the polar vortex. Prominent decadal-scale deepening of the southern Indian Ocean low (SIOL) exists circa 1790, 1810, 1835, 1860, 1880, 1900, and 1940 A. D., continuously after the 1970s, and prominent weakening circa 1750, 1795, 1825, 1850, 1870, 1890, 1910, and 1955 A. D. The LGB65 sea-salt record is characterized by significant decadal-scale variability with a strong similar to21-year periodic structure (99.9% confidence level). The relationship between LGB65 sea salt and solar irradiance changes shows that this periodicity is possibly the solar Hale cycle ( 22 years)