A high-efficiency nonlinear frequency converter with a built-in amplitude modulator

We report simultaneous frequency conversion and amplitude modulation in an optical second-harmonic generator by electrooptically controlling the relative phase between the 1064-nm fundamental and the 532-nm second-harmonic fields in a dispersion crystal section between two periodically poled lithium niobate (PPLN) sections. Theoretical derivation and experimental demonstration were carried out for two novel crystal configurations, including a linear cascaded configuration in which a 1-cm dispersion section is sandwiched between two 2-cm PPLN sections, and a folding-crystal high-efficiency configuration in which the mixing waves traverse twice in a 2-cm PPLN section through total internal reflections in a 1.5-cm dispersion section. Due to the coherence enhancement in the constructive phase between the two second-harmonic generation (SHG) fields in the two PPLN sections, we measured a 30% increase in conversion efficiency compared to a 4-cm continuous-grating PPLN under the same condition. The measured half-wave voltage for the amplitude modulation is 1.1 V /spl times/ d (/spl mu/m)/l/sub d/ (cm), where d is the separation of the electrodes and l/sub d/ is the length of the electrodes.     

Analytical thermal model for multilevel VLSI interconnectsincorporating via effect

The authors present compact analytical thermal models for estimating the temperature rise of multilevel VLSI interconnect lines incorporating via effect. The impact of vias has been modeled using (1) a characteristic thermal length and (2) an effective thermal conductivity of ILD (interlayer dielectric), k_ILD,eff, with k _ILD,_eff=k_ILDη/, where η is a physical correction factor, with 0<η<1. Both the spatial temperature profile along the metal lines and their average temperature rise can be easily obtained using these models. The predicted temperature profiles are shown to be in excellent agreement with the three-dimensional (3-D) finite element thermal simulation results. The model is then applied to estimate the temperature rise of densely packed multilevel interconnects. It is shown that for multilevel interconnect arrays, via density along the lines can significantly affect the temperature rise of such interconnect structures     

The effects of synoptical weather pattern and complex terrain on the formation of aerosol events in the Greater Taipei area

The aerosol in the Taipei basin is difficult to transport outward under specific weather patterns owing to complex terrain blocking. In this study, seven weather patterns are identified from synoptic weather maps for aerosol events, which occurred from March 2002 to February 2005. Among the identified weather patterns, High Pressure Peripheral Circulation (HPPC), Warm area Ahead of a cold Front (WAF), TYPhoon (TYP), Pacific High Pressure system stretching westerly (PHP), Weak High Pressure system (WHP), and Weak Southern Wind (WSW) are related to terrain blocking. The remaining pattern is High Pressure system Pushing (HPP). The classification of the pollution origin of the air masses shows that 15% of event days were contributed by long-range transport (LRT), 20% by local pollution (LP), and 65% by LRT/LP mix. Terrain blocking causes aerosol accumulation from high atmospheric stability and weak winds occurring under HPPC, TYP, and PHP weather patterns when the Taipei basin is situated on the lee side of the Snow Mountains Chain (SMC). Terrain blocking also occurs when the Taipei basin is situated on the upwind of SMC and Mt. Da-Twen under WAF and WSW patterns. To study the variation of aerosol properties under the mixed influence of terrain and pollution origin, we conducted a field observation simultaneously at the urban, suburban, and background sites in the Greater Taipei area from April 14 to 23, 2004. Terrain blocking plays an important role in aerosol accumulation in the stagnant environment when the Taipei basin is on the lee side of SMC. On the other hand, the PM(2.5) sulfate level is stable with a fraction of 30% in PM(2.5) during the observation period at the urban (25%-33%) and background (25%-41%) sites. It indicates that background PM(2.5) sulfate is high on the West Pacific in winter.     

诺梅克斯材料和诺梅克斯蜂窝结构的力学特性

介绍了对诺梅克斯纸和诺梅克斯蜂窝的线弹性力学特性的大量测试结果。诺梅克斯纸的基本力学特性被应用于有限元模型和诺梅克斯蜂窝结构分析。有限元计算结果与试验结果以及人们熟知的Gibson和Ashby公式计算结果进行对比,观测了诺梅克斯蜂窝模数的尺寸效应。     

Temperature control scheme using hot-gas bypass for a machine tool oil cooler

Journal of Mechanical Science and Technology - Accurate temperature control that addresses heat generation is crucial given the development of high-accuracy high-speed machining process. Heat...     

Undercutting and interference for thread form grinding with a tilt angle

In the form grinding that is widely used to produce precision threads, screws, and gears, the grinding wheel profile is usually calculated from a given tooth profile and the so-called equation of meshing. However, in the presence of undercutting or secondary enveloping, the grinding wheel calculated cannot be guaranteed to produce the desired thread profile. Therefore, this paper proposes a geometric approach to determining the grinding wheel profile and the conditions to avoid undercutting by means of the tilt grinding wheel axis. Specifically, we calculate the thread’s profile based on its relationship to each transverse plane of the grinding wheel in the form grinding process. The grinding wheel profile on each transverse plane is then determined using the shortest distance from all the thread profile points to the grinding wheel revolution axis. Obtaining these distances allows derivation of a formula to calculate the minimum tilt angle that avoids undercutting. This proposed geometric approach is numerically more stable than the conventional equations of meshing, and the derivation of the undercutting equation is straightforward and easy to understand.     

Experimental implementation of complex path tracking control for large robotic hydraulic excavators

The experimental implementation of the path tracking control of a real hydraulic excavator with an operating weight of 4,500 kg for realising a large hydraulic servo robot with a high loading ability is described in this article. The three working arms are driven by hydraulic valve-controlled cylinders with boom structure systems to achieve rotational motion. Accordingly, the non-linearity of the boom mechanisms, large masses, large dimensions and low natural frequency of the working arms, as well as the coupling influence between the multi-body systems of the three working arms make it difficult to realise high accuracy path tracking control. The control strategy of the model reference adaptive control, which has a simple algorithm and on-line self-tuning ability, is used. Complex path profiles tracking can be achieved by the combination of the path tracking control of the three working arms. Consequently, the large hydraulic excavator can be used as large multi-purpose robots for high loading and high precision applications.     

Host-specific 16S rRNA gene markers of Bacteroidales for source tracking of fecal pollution in the subtropical coastal seawater of Hong Kong

This study investigated the diversity of Bacteroidales communities in the feces of eight host species in Hong Kong (subtropical Asia), including human (in the form of sewage), cow, pig, horse, cat, dog, rabbit and rat. The analysis of terminal restriction fragment length polymorphism (TRFLP) in the 16S rRNA genes revealed significant differences in Bacteroidales communities among all host species, with the exception of dog and cat. Manual examination of TRFLP profiles resulted in six terminal restriction fragments (TRFs) that were potentially specific to the sewage (one TRF), cow (three TRFs) or pig (two TRFs) samples. All six TRFs were (1) present in 100% of the samples of the respective target host, (2) absent in other hosts or present only in low frequency and low intensity, and (3) verified for sizes using in silico digestion of DNA sequences in clone libraries. The six TRFs could reliably indicate the source of fecal contaminations in natural seawater amended with sewage, cow or pig fecal samples. In field tests conducted for two polluted and one unpolluted coastal site, the sewage-specific TRF was detected in all seawater samples of the sites known to be impacted by raw and treated sewage. However, only two of three cow-specific TRFs were detected for the two polluted sites, which also received fecal input from feral cows. No pig-specific TRF was detected, although one of the coastal sites was chronically polluted by pig farm run-offs. Nevertheless, the total absence of the six potentially host-specific TRFs in the seawater of an unpolluted site demonstrated the specificity of the TRFs as gene markers in indicating actual pollution.     

Reducing PCDD/F formation by adding sulfur as inhibitor in waste incineration processes

The results obtained in this study indicate that addition of sulfur in incineration processes could effectively reduce PCDD/F formation. PCDD/F formation is reduced dramatically (54.1%) when S/Cl molar ratio is controlled at about 2 in a laboratory-scale system (LSS). The XRD analysis of the fly ash confirms the existence of vulcanized metals such as Cu2SO4, Cu2S, SnS and ZnS. The results suggest that the sulfur added would poison Cu-based metals and render the Deacon reaction catalyst less active, thereby reducing PCDD/F formation. In addition, the results obtained from the tests conducted in an industrial waste incinerator (IWI) indicate that the efficiency of reducing PCDD/F formation by adding sulfur was 51.6% at S/Cl mole ratio of 0.4. The results indicate that adding too much sulfur would actually increase particle concentration and also increase PCDD/F yield. This study demonstrates the effectiveness of adding sulfur as an alternative technology for reducing PCDD/F emissions from waste incineration processes. The efficiency of reducing PCDD/F formation by addition of sulfur is strongly influenced by S/Cl mole ratio.