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Search Results: 1 - 10 of 625446 matches for " S. J. Liu "
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Effect of thermal aging on the interfacial reactions of tin-based solder alloys and copper substrates and kinetics of formation and growth of intermetallic compounds
Madeni, J. C.;Liu, S.;
Soldagem & Inspe??o , 2011, DOI: 10.1590/S0104-92242011000100011
Abstract: the formation and growth of intermetallic compounds at the interface between four solder alloys, sn-3.5ag, sn-0.7cu, sn-3.2ag0.8cu and sn-9zn, and cu-plated substrates have been studied. thermal aging tests for 20, 100, 200, 500 hours at 70, 100 and 150 oc were carried out. as expected, results indicate that the formation of the intermetallic layer is a diffusion-controlled process. nevertheless, migration and dissolution of cu into the solder was observed, especially at lower temperatures. the thickness of the layer of intermetallic compound increased with increasing aging temperature and time. the sn-3.5ag alloy showed the smallest intermetallic growth and the sn-9zn alloy the highest, compared to the other alloys. the results also show definite morphological differences between the cu/cu3sn, the cu3sn/cu6sn5 and the cu6sn5/solder-matrix interfaces.
Multi-channel Observations of Plasma Outflows and the Associated Small-Scale Magnetic Field Cacellations on the Edges of an Active Region
S. Liu,J. T. Su
Physics , 2014, DOI: 10.1007/s10509-014-1853-7
Abstract: With the SDO/AIA instrument, continuous and intermittent plasma outflows are observed on the boundaries of an active region along two distinct open coronal loops. %with the speed of 30$\sim$200 km s$^{-1}$. By investigating the temporal sequence magnetograms obtained from HMI/SDO, it is found that small-scale magnetic reconnection probably plays an important role in the generation of the plasma outflows in the coronal loops. It is found that the origin of the plasma outflows coincides with the locations of the small-scale magnetic fields with mixed polarities, which suggests that the plasma outflows along coronal loops probably results from the magnetic reconnection between the small-scale close emerging loops and the large-scale open active region coronal loops.
Multiobjective Optimal Design of Underwater Acoustic Projector with Porous Piezocomposite Active Elements  [PDF]
A. V. Nasedkin, M. S. Shevtsova, J.-C. Liu, S.-H. Chang, J.-K. Wu
Journal of Applied Mathematics and Physics (JAMP) , 2013, DOI: 10.4236/jamp.2013.16017
Abstract: This paper concerns the optimization problem for multilayered ultrasonic transducer with active porous piezoelectric layer. The dependences of the effective moduli for porous piezoelectric material on porosity have been previously obtained and allowed to decrease the number of design variables. The multiobjective optimization problem based on the Pareto-frontier calculation has been solved using the live-link of finite-element (FE) package Comsol Multiphysics with MATLAB.
Responses of soil respiration to elevated carbon dioxide and nitrogen addition in subtropical forest ecosystems in China
Q. Deng,G. Zhou,J. Liu,S. Liu
Biogeosciences Discussions , 2009,
Abstract: Global climate change in the real world always exhibited simultaneous changes in multiple factors. Prediction of ecosystem responses to multi-factor global changes in a future world strongly relies on our understanding of their interactions. However, it is still unclear how nitrogen (N) deposition and elevated atmospheric carbon dioxide concentration [CO2] would interactively influence forest floor soil respiration in the subtropical China. We assessed the main and interactive effects of elevated [CO2] and nitrogen addition on soil respiration by growing tree seedlings in ten large open-top chambers under CO2 [ambient CO2 and 700 μmol mol 1] and nitrogen (ambient and 100 kg N ha 1 yr 1) treatments. Soil respiration, soil temperature and soil moisture were measured for 30 months, as well as root biomass and soil organic matter. Results showed that soil respiration displayed strong seasonal patterns with higher values observed in the wet season (April–September) and lower values in the dry season (October–March) in all treatments. Significant exponential relationships between soil respiration rates and soil temperatures, as well as significant linear relationships between soil respiration rates and soil moistures (below 15%) were found. Both CO2 and N treatments significantly affected soil respiration, and there was significant interaction between elevated [CO2] and N addition (p<0.001, p=0.003, and p=0.006, respectively). We also observed that the stimulatory effect of individual elevated [CO2] (about 28% increased) was maintained throughout the experimental period. The positive effect of N addition was found only in 2006 (9.91% increased), and then had been weakened over time. The combined effect of them on soil respiration (about 50% increased) was greater than the impact of either one alone. Mean value of annual soil respiration was 5.24±0.10, 4.47±0.06, 3.62±0.05 and 3.51±0.03 kg CO2 m 2 yr 1 in the chambers exposed to elevated [CO2] and high N deposition (CN), elevated [CO2] and ambient N deposition (CC), ambient [CO2] and high N deposition (NN), and ambient [CO2] and ambient N deposition (CK as a control), respectively. The greater root biomass was obtained in the CN, CC and NN treatments, and higher soil organic matter was observed only in the CN treatment. In conclusion, the combined effect of elevated [CO2] and N addition on soil respiration was apparent interaction. They should be evaluated in combination in subtropical forest ecosystems in China where the atmospheric CO2 and N deposition have been increasing simultaneously and remarkably.
Application of SCIAMACHY and MOPITT CO total column measurements to evaluate model results over biomass burning regions and Eastern China
C. Liu,S. Beirle,T. Butler,J. Liu
Atmospheric Chemistry and Physics (ACP) & Discussions (ACPD) , 2011, DOI: 10.5194/acp-11-6083-2011
Abstract: We developed a new CO vertical column density product from near IR observations of the SCIAMACHY instrument onboard ENVISAT. For the correction of a temporally and spatially variable offset of the CO vertical column densities we apply a normalisation procedure based on coincident MOPITT (version 4) observations over the oceans. The resulting normalised SCIAMACHY CO data is well suited for the investigation of the CO distribution over continents, where important emission sources are located. We use only SCIAMACHY observations for effective cloud fractions below 20 %. Since the remaining effects of clouds can still be large (up to 100 %), we applied a cloud correction scheme which explicitly considers the cloud fraction, cloud top height and surface albedo of individual observations. The normalisation procedure using MOPITT data and the cloud correction substantially improve the agreement with independent data sets. We compared our new SCIAMACHY CO data set, and also observations from the MOPITT instrument, to the results from three global atmospheric chemistry models (MATCH, EMAC at low and high resolution, and GEOS-Chem); the focus of this comparison is on regions with strong CO emissions (from biomass burning or anthropogenic sources). The comparison indicates that over most of these regions the seasonal cycle is generally captured well but the simulated CO vertical column densities are systematically smaller than those from the satellite observations, in particular with respect to SCIAMACHY observations. Because SCIAMACHY is more sensitive to the lowest part of the atmosphere compared to MOPITT, this indicates that especially close to the surface the model simulations systematically underestimate the true atmospheric CO concentrations, probably caused by an underestimation of CO emissions by current emission inventories. For some biomass burning regions, however, such as Central Africa in July–August, model results are also found to be higher than the satellite observations.
Assessment of Long Term UV Radiation Measured by the Brewer Spectrophotometer in Hong Kong during 1995-2005  [PDF]
T.J. Wang, K.S. Lam, Q. Liu, X.M. Wang
Atmospheric and Climate Sciences (ACS) , 2011, DOI: 10.4236/acs.2011.11002
Abstract: Time series of daily UV radiation measured by the ground-based Brewer spectrophotometer #115 in Hong Kong during 1995-2005 were studied through statistics analysis, with focus on the variability and long term changes in relation to total ozone, clouds and AOD (Aerosol Optical Depth). The 11-year mean UV daily dose is 2644±262 J/m2, with maxima(3311 J/m2) in 2000 and minima (2415 J/m2) in 2002. The data were compared with that from TOMS (Total Ozone Mapping Spectrometer) Version 8 and show general agreement between the two. However, the Brewer UV measurement is about 10% lower compared to TOMS data. Apart from the common-known strong seasonal cycle, 26 month periodical was resolved by use of wavelet analysis, which was believed to be associated with quasi-biennial oscillation (QBO) of general circulation. In cloudy days, the annual mean UV daily dose decrease 3.5% to 44.5% compared to clear days. It was also found that surface UV irradiance has close relation to air pollution. Under clear sky condition, 1% AOD increase will lead to 0.2% UV decrease. While global UV radiation increase due to the worldwide observed ozone depletion, investigations indicate that this trend is not significant in Hong Kong during the last 11 years. The possible causes can be attributed to the compensative effect from two aspects. One is the increase of UV resulting from the reduction of clouds with rate of 0.56/10 yr. The other is the decrease of UV due to the enhancement of total ozone and AOD with a rate of 4.23 DU/10 yr and 0.33/10 yr, respectively.
Magnetic Properties Hard-Soft SmCo5-FeNi and SmCo5-FeCo Composites Prepared by Electroless Coating Technique  [PDF]
M. Lamichanne, B. K. Rai, S. R. Mishra, V. V. Nguyen, J. P. Liu
Open Journal of Composite Materials (OJCM) , 2012, DOI: 10.4236/ojcm.2012.24014
Abstract: Composites of SmCo5-FeNi and SmCo5-FeCo, hard-soft magnetic materials, have been synthesized via electroless plating of magnetically hard SmCo5 powder particles with magnetically soft FeNi and FeCo, respectively. The influence of coating thickness of soft magnetic layers on the structure and magnetic properties of the composite has been studied. Overall FeNi coating was found to be less dense compared to FeCo for the same plating duration. Structurally the coat ing was found to be nodular in morphology. These coating have dramatic effect on the overall magnetic property of the composite. As compared to FeNi coated SmCo5 composite, two-fold increase in the saturation magnetization has been observed upon coating SmCo5 (Ms~28 emu/g) with FeCo to a value 56 emu/g. The coercivity of composite powder was found to decrease with increasing the coating layer thickness. The absence of exchange spring behavior in the hard-soft composite is attributed to magnetically soft layer thickness exceeding the theoretical length limit for exchange-spring coupling.
Learning to perform a new movement with robotic assistance: comparison of haptic guidance and visual demonstration
J Liu, S C Cramer, DJ Reinkensmeyer
Journal of NeuroEngineering and Rehabilitation , 2006, DOI: 10.1186/1743-0003-3-20
Abstract: Healthy subjects (n = 20) attempted to reproduce a novel three-dimensional path after practicing it with mechanical guidance from a robot. Subjects viewed their arm as the robot guided it, so this "haptic guidance" training condition provided both somatosensory and visual input. Learning was compared to reproducing the movement following only visual observation of the robot moving along the path, with the hand in the lap (the "visual demonstration" training condition). Retention was assessed periodically by instructing the subjects to reproduce the path without robotic demonstration.Subjects improved in ability to reproduce the path following practice in the haptic guidance or visual demonstration training conditions, as evidenced by a 30–40% decrease in spatial error across 126 movement attempts in each condition. Performance gains were not significantly different between the two techniques, but there was a nearly significant trend for the visual demonstration condition to be better than the haptic guidance condition (p = 0.09). The 95% confidence interval of the mean difference between the techniques was at most 25% of the absolute error in the last cycle. When asked to reproduce the path repeatedly following either training condition, the subjects' performance degraded significantly over the course of a few trials. The tracing errors were not random, but instead were consistent with a systematic evolution toward another path, as if being drawn to an "attractor path".These results indicate that both forms of robotic demonstration can improve short-term performance of a novel desired path. The availability of both haptic and visual input during the haptic guidance condition did not significantly improve performance compared to visual input alone in the visual demonstration condition. Further, the motor system is inclined to repeat its previous mistakes following just a few movements without robotic demonstration, but these systematic errors can be reduced with peri
Variability of aboveground litter inputs alters soil physicochemical and biological processes: a meta-analysis of litterfall-manipulation experiments
S. Xu,L. Liu,E. J. Sayer
Biogeosciences Discussions , 2013, DOI: 10.5194/bgd-10-5245-2013
Abstract: Global change has been shown to greatly alter the amount of aboveground litter inputs to soil, which could cause substantial cascading effects on belowground biogeochemical cyling. Although having been studied extensively, there is uncertainty about how changes in aboveground litter inputs affect soil carbon and nutrient turnover and transformation. Here, we conducted a comprehensive compilation of 68 studies on litter addition or removal experiments, and used meta-analysis to assess the responses of soil physicochemical properties and carbon and nutrient cycling under changed aboveground litter inputs. Our results suggested that litter addition or removal could significantly alter soil temperature and moisture, but not soil pH. Litter inputs were more crucial in buffering soil temperature and moisture fluctuations in grassland than in forest. Soil respiration, soil microbial biomass carbon and total carbon in the mineral soil increased with increasing litter inputs, suggesting that soil acted as a~net carbon sink although carbon loss and transformation increased with increasing litter inputs. Total nitrogen and the C : N ratio in the mineral soil increased with increased litter inputs. However, there was no correlation between litter inputs and extractable inorganic nitrogen in the mineral soil. Compared to other ecosystems, tropical and subtropical forests are more sensitive to variation in litter inputs. Increased or decreased litter inputs altered the turnover and accumulation of soil carbon and nutrient in tropical and subtropical forests more substantially over a shorter time period compared to other ecosystems. Overall, our study suggested that, although the magnitude of responses differed greatly among ecosystems, increased litter inputs generally accelerated the decomposition and accumulation of carbon and nutrients in soil, and decreased litter inputs reduced them.
Measurement of deforming mode of lattice truss structures under impact loading
Liu J.,Pattofatto S.,Zhao H.
EPJ Web of Conferences , 2012, DOI: 10.1051/epjconf/20122601029
Abstract: Lattice truss structures, which are used as a core material in sandwich panels, were widely investigated experimentally and theoretically. However, explanation of the deforming mechanism using reliable experimental results is almost rarely reported, particularly for the dynamic deforming mechanism. The present work aimed at the measurement of the deforming mode of lattice truss structures. Indeed, quasi-static and Split Hopkinson Pressure Bar (SHPB) tests have been performed on the tetrahedral truss cores structures made of Aluminum 3003-O. Global values such as crushing forces and displacements between the loading platens are obtained. However, in order to understand the deforming mechanism and to explain the observed impact strength enhancement observed in the experiments, images of the truss core element during the tests are recorded. A method based on the edge detection algorithm is developed and applied to these images. The deforming profiles of one beam are extracted and it allows for calculating the length of beam. It is found that these lengths diminish to a critical value (due to compression) and remain constant afterwards (because of significant bending). The comparison between quasi-static and impact tests shows that the beam were much more compressed under impact loading, which could be understood as the lateral inertia effect in dynamic bucking. Therefore, the impact strength enhancement of tetrahedral truss core sandwich panel can be explained by the delayed buckling of beam under impact (more compression reached), together with the strain hardening of base material.
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