On the Distinction Between Plasticity- and Roughness-Induced Fatigue Crack Closure

A series of experiments has been carried out to determine why some alloys display plasticity-induced fatigue crack closure (PIFCC), whereas other alloys display roughness-induced crack closure (RIFCC). Two alloys were studied, the aluminum alloy 6061-T6 (PIFCC) and a steel of comparable yield strength, S25C (RIFCC). The experiments included the determination of the crack-opening levels as a function of ??K, da/dN as a function of ??K _eff ?C ??K _effth, removal of the specimen surface layers, removal of the crack wake, the determination of crack front shapes, crack surface roughness profiles, and the degree of lateral contraction in the plastic zone at a crack tip. Based on crack tip opening displacement (CTOD) considerations, it is concluded that PIFCC is favored in alloys of low modulus and relatively low yield strength. In addition, a low strain-hardening rate such as for the 6061 alloy will favor PIFCC. Steels with a higher modulus and a higher strain-hardening rate than 6061 will, in general, exhibit RIFCC, even at comparable yield strength levels. In ferritic steels, the fracture surface roughness and consequently the crack-opening level will increase as the coarseness of the microstructure increases.     

Control system for automatic search and transportation of an object by a mobile robot with obstacle avoidance function

Artificial Life and Robotics - In this paper, using image processing and distance measurement, we develop a control system for automatic grasping and obstacle avoidance by a mobile robot. First,...     

Durability of the adhesive bond between continuous fibre sheet reinforcements and concrete in an outdoor environment

The authors set out to investigate the durability of the bond between carbon fibre (CF) sheet reinforcement and concrete. They conducted an outdoor exposure test in a moderate climate for 14 years and an immersion test for 6 months on CF sheet bonded to concrete, and then evaluated the adhesive bond properties using the pull-off and peel methods.The pull-off strength slightly decreased after 14 years of exposure, but residual values still indicate quite good adhesive properties. The failure modes for both the initial specimens and the specimens after 14 years of exposure consisted of concrete substrate failures in all cases. This result suggests that the slight decrease in pull-off strength does not necessarily indicate a change in the properties of the bond between CF sheet and concrete. On the other hand, results of the peel tests showed different types of failure modes and seemed more discriminant than those of the pull-off method.As regards specimens immersed in water, pull-off results were in few cases consistent with the peel characterizations, showing significant evolutions in the strength and failure mode. But for most specimens, the two methods provided divergent trends. In the end, this study suggested that the peel test could be relevant for evaluating the durability of the bond between CF sheet and concrete, while the representativeness of the pull-off test remains a matter of discussion.     

A One-Dimensional Propagation of Shock Wave Supported by Atmospheric Millimeter-Wave Plasma

A shock wave supported by an atmospheric breakdown plasma caused by a high-power millimeter-wave beam was studied. The shadow graph image in a shock tube visualized the one-dimensional shock-wave generated by the millimeter-wave breakdown in atmosphere for the first time. It was revealed that a normal shock wave propagated through the tube at the constant velocity while it was detached from the ionization front of the plasma whenever the propagation velocity of the ionization front was supersonic or subsonic. And it was visually clarified that the atmospheric millimeter-wave breakdown had the combined structure of the normal shock wave and the heating region of the millimeter-wave plasma. The measured pressure of the shock front was as equal as the normal shock which propagated at measured Mach number.     

Simultaneous Formation of Ni/Al Ohmic Contacts to Both n- and p-Type 4H-SiC

The fabrication procedure for silicon carbide power metal oxide semiconductor field-effect transistors can be improved through simultaneous formation (i.e., using the same contact materials and a one-step annealing process) of ohmic contacts on both the n-source and p-well regions. We have succeeded in the simultaneous formation of Ni/Al ohmic contacts to n- and p-type SiC after annealing at 1000°C for 5 min in an ultrahigh vacuum. Ohmic contacts to n-type SiC were found when the Al-layer thickness was less than about 6 nm, while ohmic contacts to p-type SiC were observed for an Al-layer thickness greater than about 5 nm. Only the contacts with an Al-layer thickness in the range of 5 nm to 6 nm exhibited ohmic behavior to both n- and p-type SiC, with a specific contact resistance of 1.8 × 10⁻⁴ Ω cm² and 1.2 × 10⁻² Ω cm² for n- and p-type SiC, respectively. An about 100-nm-thick contact layer was uniformly formed on the SiC substrate, and polycrystalline δ-Ni₂Si(Al) grains were formed at the contact/SiC interface. In the samples that exhibited ohmic behavior to both n- and p-type SiC, the distribution of the Al/Ni ratios in the δ-Ni₂Si(Al) grains was larger than that observed for any of the samples that showed ohmic behavior to either n- or p-type SiC. Furthermore, the grain size of the δ-Ni₂Si(Al) grains in the samples showing ohmic behavior to both n- and p-type SiC was smaller than the grains in any of the samples that showed ohmic behavior to either n- or p-type SiC. Thus, the large distribution in the Al/Ni ratios and a fine microstructure were found to be characteristic of the ohmic contacts to both n- and p-type SiC. Grains with a low Al concentration correspond to ohmic contacts to n-type SiC, while grains with a high Al concentration correspond to ohmic contacts to p-type SiC.     

新闻非线性编辑制作播出网络系统的升级改造

本文通过珠海广播电视台新闻非编系统的升级改造项目,对从采集、制作到合成等环节实现的新技术特点做了阐述,以求最大限度地利用原有设备,降低投入成本。希望对其他广播电视台类似项目的实施有一定的借鉴意义。     

Three-terminal capacitance–voltage measurements of pentacene field-effect transistors during operation

We propose a modified measurement technique of capacitance for three-terminal devices and apply this method for the evaluation of the channel formation in pentacene field-effect transistors. An additional structure in the capacitance–voltage curves clearly shows the channel formation from the saturation to the linear region in an operating transistor which has not been directly observed in conventional methods. Based on the amount of accumulated charge in the channel region, the validity of the gradual channel approximation model and the usability of a buffer layer are discussed. This method enables the detailed investigation of carrier behaviors in organic transistors through appropriate evaluation of the channel formation process during operation.     

Nanomanipulation of biological samples using a compact atomic force microscope under scanning electron microscope observation

We introduce a compact nanomanipulator that can be operated inside the sample chamber of a scanning electron microscope (SEM) for biological sample manipulation. The design of the nanomanipulator is based on that of an atomic force microscope (AFM). A self-sensitive cantilever is used to realize the compact body and thus it is possible to put a pair of the standalone AFM units on the sample stage in the SEM chamber. Using this system, we accomplished nanodissection of biological samples as well as AFM imaging under SEM observation. We then fabricated the surface of a rat renal glomerulus by scan-scratching and succeeded in making a small hole on the wall of a blood capillary. As a result, it was possible to observe the internal structure of the capillary, which had been hidden beneath the surface wall. Furthermore, using two AFM units on the sample stage of the SEM, we successfully dissected the lens fiber cells taken from a rat eye in a multi-probe operation using the two cantilevers. This system is expected to become a very useful tool for micro- and nanometer-scale anatomy and engineering applications.     

Using acknowledgement data to characterize funding organizations by the types of research sponsored: the case of robotics research

Funded research has been linked to academic production and performance. While the presence of funding acknowledgements may serve as an indicator of quality to some extent, we still lack tools to evaluate whether funding agencies allocate resources to novel and innovative research rather than mature fields. We address this issue in the present study by using bibliometrics. In particular, we exploit the citation network properties of academic articles to classify specific research fields into four categories: change maker, breakthrough, incremental, and matured. We then use funding acknowledgement information to identify the sponsors involved in each research type to characterize funding agencies. We focus our analysis on the robotics field in order to reveal international trends of financial acknowledgements. We find that the incremental and matured research areas show the highest counts of funding acknowledgements. Moreover, although research funded by some agencies is mostly recognized as incremental-type research, those in other categories may perform better in terms of the number of citations. Additionally, we analyze the interest of selected funding agencies in granular subject categories. The characterization of funding agencies in this study may help policymakers and funding organizations assess or adjust their strategies, benchmark with other key players, and obtain an overview of local and global acknowledgement trends.     

In situ high-temperature scanning tunneling microscopy study of bilayer graphene growth on 6H-SiC(0001)

Using in situ high-temperature (1395 K), ultra-high vacuum, scanning tunneling microscopy (STM), we investigated the growth of bilayer graphene on 6H-SiC(0001). From the STM images, we measured areal coverages of SiC and graphene as a function of annealing time and found that graphene grows at the expense of SiC. Graphene domains were observed to grow, at comparable rates, at (I) graphene-free SiC step edges, (II) graphene-SiC interfaces, and (III) the existing graphene domain edges. Based upon our results, we suggest that the rate-limiting step controlling bilayer graphene growth is the desorption of Si from the substrate.