A postprocessor for table-tilting type five-axis machine tool based on generalized kinematics with variable feedrate implementation

Improvements in the machine tool and the machining process technologies increased the need for generic postprocessors in order to exploit the capabilities of the machine tools. Contrary to conventional machining approach, next-generation machining technologies such as force-based feedrate scheduling and toolpath optimization requires the implementation of the variable feedrate during toolpath which constitutes the aim of this article. Therefore, this paper introduces a postprocessor for table-tilting type five-axis machine tool based on generalized kinematics with variable feedrate implementation. Furthermore, a practical yet effective method for avoiding kinematic singularities by spherical interpolation and NC data correction is presented as well. Proposed approach is validated for various five-axis machine tools with different kinematic configurations via virtual machine simulation module. Results of the verification tests show that presented postprocessing approach can accurately convert the cutter location information into NC codes and it is demonstrated that integrated virtual simulation module can simulate toolpaths with large number of blocks.     

Knowledge-acquisitions and post-acquisition innovation performance: a comparative hazards model

Do acquisitions lead to instrumental innovations related to the acquired knowledge? Past arguments on vertical integration espouse how a quest for knowledge drives acquisitions culminating in innovation performance. Using Google and Yahoo as cases-in-point, we examine how facets of acquired innovation knowledge impact post-innovation performance. In particular, the apparently opposing fortunes of Google and Yahoo allow us to investigate the pace of their innovation performance as a hazards model. Results from our investigation highlight Google’s ambidexterity over Yahoo with a swifter, systematic pace of innovation performance – from hastening time to patenting new ideas to the time to releasing new applications from acquisitions.     

High-Order Multiderivative Time Integrators for Hyperbolic Conservation Laws

Multiderivative time integrators have a long history of development for ordinary differential equations, and yet to date, only a small subset of these methods have been explored as a tool for solving partial differential equations (PDEs). This large class of time integrators include all popular (multistage) Runge–Kutta as well as single-step (multiderivative) Taylor methods. (The latter are commonly referred to as Lax–Wendroff methods when applied to PDEs). In this work, we offer explicit multistage multiderivative time integrators for hyperbolic conservation laws. Like Lax–Wendroff methods, multiderivative integrators permit the evaluation of higher derivatives of the unknown in order to decrease the memory footprint and communication overhead. Like traditional Runge–Kutta methods, multiderivative integrators admit the addition of extra stages, which introduce extra degrees of freedom that can be used to increase the order of accuracy or modify the region of absolute stability. We describe a general framework for how these methods can be applied to two separate spatial discretizations: the discontinuous Galerkin (DG) method and the finite difference essentially non-oscillatory (FD-WENO) method. The two proposed implementations are substantially different: for DG we leverage techniques that are closely related to generalized Riemann solvers; for FD-WENO we construct higher spatial derivatives with central differences. Among multiderivative time integrators, we argue that multistage two-derivative methods have the greatest potential for multidimensional applications, because they only require the flux function and its Jacobian, which is readily available. Numerical results indicate that multiderivative methods are indeed competitive with popular strong stability preserving time integrators.     

The Usability of Boric Acid as an Alternative Foaming Agent on the Fabrication of Al/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Composite Foams

Pure Al and alumina (2, 5, 10 wt.% Al₂O₃)-added Al composite foams were fabricated through powder metallurgy technique, where boric acid (H₃BO₃) is employed as a new alternative foaming agent. It is aimed to determine the effects of boric acid on the foaming behavior and cellular structure and also purposed to develop the mechanical properties of Al foams by addition of Al₂O₃. Al and Al composite foams with porosity fraction in the range of 46-53% were achieved by sintering at 620 °C for 2 h. Cell morphology was characterized using a combination of stereomicroscope equipped with image analyzer and scanning electron microscopy. Microhardness values were measured via using Vickers indentation technique. Quasi-static compression tests were performed at strain rate of 10^?3 s^?1. Compressive strength and energy absorption of the composite foams enhanced not only by the increasing weight fraction of alumina, but also by the usage of boric acid which leads to formation of boron oxide (B₂O₃) acting as a binder in obtaining dense cell walls. The results revealed that the boric acid has outstanding potential as foaming agent in the fabrication of Al and Al composite foams by providing improved mechanical properties.     

Spatial control of a smart beam

This study presents the design and implementation of a spatial $ {\text{H}}_{\infty } $ controller for the active vibration control of a smart beam. The smart beam was modeled by assumed-modes method that results in a model including large number of resonant modes. The order of the model was reduced by direct model truncation and the model correction technique was applied to compensate the effect of the contribution of the out of range modes to the dynamics of the system. Additionally, spatial identification of the beam was performed, by comparing the analytical and experimental system models, in order to determine the modal damping ratios of the smart beam. Then, the spatial $ {\text{H}}_{\infty } $ controller was designed and implemented to suppress the first two flexural vibrations of the smart beam.     

IGBT模块在激光电源中的应用及其对激光电源性能的改进

介绍一种典型的应用于激光电源的对IGBT功率开关器件进行PWM脉冲宽度控制的电路,它能满足对激光电源的大功率,高稳定性,以及高伍流性等要求．     

Stepwise demineralisation and chemical isolation of the mineral matter of Göynük lignite

The mineral matter of coal contains a number of inorganic constituents, which play an important role in almost all coal utilisation systems. Some techniques have been applied to coal to separate its mineral matter from its organic part. In this study, an alternative method was applied to separate the mineral matter content of a Turkish lignite. For this purpose, Göynük lignite was treated, in sequence, with acetic acid, ammonia, hydrochloric acid, hydrofluoric acid and nitric acid at 70°C for 60 min in order to remove individual mineral species. After each stage, the lignite was treated with performic acid, the product of reaction between hydrogen peroxide and formic acid, at 50°C. The organic coal matrix was decomposed as a result of performic acid oxidation, and consequently, the recovered mineral species were isolated. Ammonia, which has the potential of chemical comminution, was used to increase the effects of the subsequent reagents and enhance the extent of separation between the organic and inorganic phases. In each mineral matter removal stage, the lignite was treated with the reagents of the previous stage, and then, a new reagent was added to investigate whether the last stage has a different effect on the mineral species. FT-IR and X-ray diffractometry techniques were used to determine the constituents of the isolated mineral matter after each stage.     

Few-mode vertical-cavity surface-emitting lasers for space-division multiplexing

In order to choose the proper radius of oxide aperture for few-mode vertical-cavity surface-emitting lasers (VCSELs), the influences of oxide aperture size on the multi-transverse-mode behaviors are investigated in detail. By establishing the effective refractive index model to simulate VCSELs with different radii of oxide apertures, the wavelength and corresponding order of different modes are obtained. VCSELs with three kinds of oxide apertures are manufactured. Then the multi-transverse-mode spectra and near-field are measured. It is found that when the radius is between 1.5 and 4.5 μm, few-mode VCSELs can be implemented. The 2.5 μm VCSEL manufactured in this paper only emits LP01 mode and LP21 mode. Since the space distance between the two modes is 2 μm, it is expected to realize direct-modulation few-mode VCSELs by channel etching or ion implantation between the two modes.     

Cyber victim and bullying scale: A study of validity and reliability

The purpose of this study is to develop a reliable and valid scale, which determines cyber victimization and bullying behaviors of high school students. Research group consisted of 404 students (250 male, 154 male) in Sakarya, in 2009–2010 academic years. In the study sample, mean age is 16.68. Content validity and face validity of the scale was provided via field specialists’ judgment. Confirmatory and exploratory factor analyses were performed for investigation of the factor structure of the scale. As a result of principal component analysis of cyber victim subscale three factors emerged which accounted for the 46.38% of the total variance. Also for cyber bullying subscale, same three factors emerged accounting for the 49.18% of the total variance. Scales with 22 items under 3 factors were tested with confirmatory factor analysis for each victim and bullying variables. Three factors were named as cyber verbal bullying, hiding identity and cyber forgery. Three factors model of scales were found theoretically and statistically fitted after confirmatory factor analysis. For criterion related validity the correlation between cyber victim and bullying scale and Aggression Scale was calculated as .27 and .36, respectively. The internal consistency coefficients calculated for reliability. Cyber victim and bullying scales’ internal consistency coefficients were .89 and split-half coefficients were .79. for both scales. Test-retest reliability for cyber victim .85, for cyber bullying respectively .90 was found. These results demonstrate that the Cyber Victim and Bullying Scale’ is a valid and reliable instrument.     

Crack growth resistance in fibre reinforced alkali-activated fly ash concrete exposed to extreme temperatures

This paper examines the crack growth resistance of alkali-activated fly ash concrete under extreme temperatures. Plain and hybrid fibre reinforced alkali activated concrete prepared with fly ash were subjected to a range of temperatures from ? 30 to 300 °C, sustained for 2 h. The alkali activation was effected with a blend of sodium hydroxide and sodium silicate. A fibre blend of steel to polypropylene in the volume ratio of 4:1 and a total as high as 1% by volume fraction reinforced the mixtures. The resulting systems were examined for residual strength under compression and splitting tension. Further, notched prisms were loaded under 4-point flexure to evaluate the residual fracture toughness. Based on the results, four different stages for fracture behaviour were identified with superior fibre efficiency seen at sub-zero temperatures. Across the breadth of temperatures examined, adding fibres led to higher residual fracture toughness for those systems that displayed a narrow range of thermal conductivity.