Effect of garbage collection in iterative algorithms on Spark: an experimental analysis

The Journal of Supercomputing - Spark is one of the most widely used systems for the distributed processing of big data. Its performance bottlenecks are mainly due to the network I/O, disk I/O, and...     

Boundary image matching supporting partial denoising using time-series matching techniques

Multimedia Tools and Applications - In this paper, we deal with the problem of boundary image matching which finds similar boundary images regardless of partial noise exploiting time-series...     

Precipitation behaviors of carbides and Cu during continuous heating for tempering in Cu-bearing medium C martensitic steel

The precipitation behaviors of carbides and Cu during continuous heating for tempering were investigated in Cu-bearing medium C martensitic steel by means of dilatometry, electrical resistivity, and transmission electron microscopy. The addition of 1.5 wt% Cu suppressed carbide precipitation during quenching from 900 °C, resulting in a large amount of solute C atoms in virgin martensite. The addition of Cu increased both the finish temperature of ε-carbide precipitation and the amount of ε-carbide precipitates during continuous heating. The precipitation of cementite was retarded and the amount of cementite precipitates increased by the addition of Cu. Retarded cementite precipitation in the Cu-bearing steel was attributed to sluggish Cu partitioning from cementite particles to the martensite matrix, the hindrance to the migration of cementite interfaces by Cu particles, and the slowed diffusions of C and Fe atoms. Cu precipitation was accelerated by cementite precipitation because cementite interfaces and the high Cu concentration near cementite particles provided nucleation sites for Cu precipitation. The hardness of the tempered Cu-bearing steel was higher than that of the tempered Cu-free steel at the temperatures of over 300 °C due to both Cu precipitation hardening and retarded cementite precipitation.     

The effects of N on the microstructures and tensile properties of Fe–15Mn–0.6C–2Cr–xN twinning-induced plasticity steels

Three Fe–15Mn–0.6C–2Cr–xN (wt.%) twinning-induced plasticity (TWIP) steels with N concentrations of 0.02%, 0.09% and 0.21% were fabricated using a pressure-induction furnace. The variations in tensile properties and deformed microstructure as a function of N concentration were investigated. The yield and tensile strengths of the steels increased without a loss of total elongation as the concentration of N increased. The strain hardening rates (SHR) of the TWIP steels with 0.02% and 0.09% N decreased gradually as the true strain increased until failure. The SHR of the TWIP steel with 0.21% N decreased sharply until a strain of approximately 0.07 and increased with further strain, exhibiting the highest value at a strain of over 0.15. The addition of N delayed the kinetics of mechanical twinning, particularly secondary twinning. The TWIP steel with 0.02% N had many intersections between primary and secondary twins, at which α′ martensite formed. The TWIP steel with 0.09% N possessed few intersections because primary twins obstructed the growth of secondary twins. The TWIP steel with 0.21% N had primary twins with few secondary twins and intersections. The addition of N increased the critical strain for triggering serrations on the tensile stress–strain curves, indicating a reduction in dynamic strain aging (DSA). The TWIP steel with 0.21% N exhibited the highest SHR at large strains, despite the reduced twinning and DSA, because of both the thinning of the mechanical twins and the hardening of the twin boundaries as the N concentration increased.     

Can Autonomous Vehicles Be Safe and Trustworthy? Effects of Appearance and Autonomy of Unmanned Driving Systems

Although autonomous vehicles are increasingly becoming a reality, eliminating human intervention from driving may imply significant safety and trust-related concerns. To address this issue from a psychological perspective, this study applies layers of anthropomorphic cues to an artificial driving agent and explicates the process in which these cues promote positive evaluations and perceptions of an unmanned driving system. In a between-subjects factorial experiment (N = 89) consisting of three unmanned driving scenarios, participants interacted with an artificial driving agent with different levels of anthropomorphic cues induced by the variations in appearance (human-like vs. gadget-like) and autonomy (high vs. low) of the agent. The results indicated that human-like appearance and high autonomy were more effective in eliciting positive perceptions of the agent. In addition, a mediation analysis revealed that the greater level of anthropomorphism induced by human-like appearance and high autonomy in the agent evoked the feelings of social presence, which in turn positively affected the perceived intelligence and safety of and trust in the agent, suggesting that the extent to which users perceive the driving agent as intelligent, safe, and trustworthy is largely determined by the feelings of social presence experienced during their interaction.     

Structural optimization of a full-text <Emphasis Type="Italic">n</Emphasis>-gram index using relational normalization

As the amount of text data grows explosively, an efficient index structure for large text databases becomes ever important. The n-gram inverted index (simply, the n-gram index) has been widely used in information retrieval or in approximate string matching due to its two major advantages: language-neutral and error-tolerant. Nevertheless, the n-gram index also has drawbacks: the size tends to be very large, and the performance of queries tends to be bad. In this paper, we propose the two-level n-gram inverted index (simply, the n-gram/2L index) that significantly reduces the size and improves the query performance by using the relational normalization theory. We first identify that, in the (full-text) n-gram index, there exists redundancy in the position information caused by a non-trivial multivalued dependency. The proposed index eliminates such redundancy by constructing the index in two levels: the front-end index and the back-end index. We formally prove that this two-level construction is identical to the relational normalization process. We call this process structural optimization of the n-gram index. The n-gram/2L index has excellent properties: (1) it significantly reduces the size and improves the performance compared with the n-gram index with these improvements becoming more marked as the database size gets larger; (2) the query processing time increases only very slightly as the query length gets longer. Experimental results using real databases of 1 GB show that the size of the n-gram/2L index is reduced by up to 1.9–2.4 times and, at the same time, the query performance is improved by up to 13.1 times compared with those of the n-gram index. We also compare the n-gram/2L index with Makinen’s compact suffix array (CSA) (Proc. 11th Annual Symposium on Combinatorial Pattern Matching pp. 305–319, 2000) stored in disk. Experimental results show that the n-gram/2L index outperforms the CSA when the query length is short (i.e., less than 15–20), and the CSA is similar to or better than the n-gram/2L index when the query length is long (i.e., more than 15–20).     

Quantitative evaluation of dynamic precipitation kinetics in a complex Nb-Ti-V microalloyed steel using electrical resistivity measurements

The kinetics of dynamic precipitation in austenite of a complex Nb-Ti-V microalloyed steel during hot compression at 900 °C with a strain rate of 6.7 s^?1 was quantitatively investigated through electrical resistivity measurements. The dynamic precipitation in the Nb-Ti-V microalloyed steel started at a strain of 0.15. The amount of tiny Nb-rich (Nb,Ti,V)C carbides, which were precipitated at crystal defects gradually increased up to 0.02 wt% at a maximum strain of 0.67. The electrical resistivity was successfully applied to the quantitative evaluation of dynamic precipitation kinetics in microalloyed steel by excluding the effects of crystal defects and interstitial atoms on the electrical resistivity.     

Quantitative analyses of dissolution and precipitation kinetics of θ-Al2Cu phase in an Al-6.2Si-2.9Cu alloy using electrical resistivity

The dissolution kinetics of the θ phase during solution treatment and isothermal precipitation kinetics during aging in an Al-6.2Si-2.9Cu alloy were quantitatively examined through electrical resistivity, hardness, and transmission electron microscopy (TEM). The electrical resistivity successfully predicted that pre-existing θ particles in the as-cast Al-Si-Cu alloy were fully dissolved after 4.5 h at 500 °C, which was in a good agreement with that directly observed by TEM. The electrical resistivity immediately decreased during aging at 250 °C due to the precipitation of θ′ phase and was saturated within 2 h. A maximum hardness peak appeared in 1 h at 250 °C due to the formation of a metastable θ′ phase, and then gradually decreased due to the coarsening of the θ′ phase as well as the annihilation of the θ″ phase. The θ′ phase was finally transformed to θ phase after 3.5 h at 250 °C.     

Influence of undissolved second-phase particles on dynamic recrystallization behavior of Mg-7Sn-1Al-1Zn alloy during low-and high-temperature extrusions

This study investigates the effects of fine and coarse undissolved particles in a billet of the Mg-7Sn-1Al-1Zn (TAZ711) alloy on the dynamic recrystallization (DRX) behavior during hot extrusion at low and high temperatures and the resultant microstructure and mechanical properties of the alloy.To this end,partially homogenized (PH) and fully homogenized (FH) billets are extruded at temperatures of 250 and 450 ℃.The PH billet contains fine and coarse undissolved Mg2Sn particles in the interdendritic region and along the grain boundaries,respectively.The fine particles (＜1 μm in size) retard DRX during extrusion at 250 ℃ via the Zener pinning effect,and this retardation causes a decrease in the area fraction of dynamically recrystallized (DRXed) grains of the extruded alloy.In addition,the inhomogeneous distribution of fine particles in the PH billet leads to the formation of a bimodal DRXed grain structure with excessively grown grains in particle-scarce regions.In contrast,in the FH billet,numerous nanosized Mg2Sn precipitates are formed throughout the material during extrusion at 250 ℃,which,in turn,leads to the formation of small,uniform DRXed grains by the grain-boundary pinning effect of the precipitates.When the PH billet is extruded at the high temperature of 450 ℃,the retardation effect of the fine particles on DRX is weakened by their dissolution in the α-Mg matrix and the increased extent of thermally activated grain-boundary migration.In contrast,the coarse Mg2Sn particles in the billet promote DRX during extrusion through the particle-stimulated nucleation phenomenon,which results in an increase in the area fraction of DRXed grains.At both low and high extrusion temperatures,the extruded material fabricated using the PH billet,which contains both fine and coarse undissolved particles,has a lower tensile strength than that fabricated using the FH billet,which is virtually devoid of second-phase particles.This lower strength of the former is attributed mainly to the larger grains and/or absence of nanosized M2Sn precipitates in it.     

Separate Evaluation of the Kinetics of Carbide Precipitation Occurring at the Interface of Preexisting Particles and Within the Austenitic Matrix in a Microalloyed Steel

The isothermal kinetics of carbide precipitation occurring at the interface of preexisting (Ti,Nb)(N,C) particles and within the deformed γ-austenite matrix were separately evaluated using a Nb-Ti-V microalloyed steel through small-angle neutron scattering and transmission electron microscopy. While the specimen was isothermally held after deformation at 1223 K (950 °C), (Nb,Ti)(C,N) particles were precipitated at the interface of coarse (Ti,Nb)(N,C) particles preexisting in the recrystallized γ matrix. This resulted in a single size distribution curve, which was converted from the measured magnetic scattering cross section. However, during isothermal holding after deformation at 1123 K (850 °C), fine (Nb,Ti,V)(C,N) particles formed mainly within the deformed γ matrix, although some of them were precipitated at the interface of preexisting coarse (Ti,Nb)(N,C) particles. Accordingly, the specimens held at 1123 K (850 °C) exhibited double size distribution curves. The separate evaluation between matrix and interface precipitation kinetics was successfully performed using the size distribution curves due to the difference in particle size according to the nucleation site. The reliability of carbide precipitation kinetics was confirmed by comparing the measured ratio between magnetic and nuclear scattering cross sections with the ratio calculated based on the measured chemical composition of precipitates.