瓦楞辊有限元模态分析

采用有限元方法，建立了瓦楞辊的有限元动力学模型，用ANSYS5．7软件研究了瓦楞辊的固有特性。所得结果既反映了瓦楞辊的动力学性能，又为瓦楞辊的动态响应计算和分析奠定了基础．     

Structural Analyses and Assessment of Historical Kamanl? Mosque in Izmir, Turkey

Historical structures are one of the most precious pieces of cultural accumulation. In this study, an interdisciplinary work was conducted to assess the structural condition of a historical masonry structure, Urla Kamanl? Mosque in ?zmir, Turkey. The structure is a member of group of structures, Yah?i Bey Complex, which includes a Turkish bath, a tomb, two fountains, and a primary school. The structure dates back to early 14th century to mid-15th century. History investigation, measurement survey, long-term settlement, and moisture observations were conducted. Nondestructive and destructive material tests were performed on stone, brick, and mortar. 3D finite-element model of the structure was used to investigate the critical locations of the structure under its self-weight, seismic load, and settlement load. Linear elastic and nonlinear settlement analyses were conducted to investigate the reason for massive cracks challenging the structural integrity.     

Dynamic and geometric error assessment of an XYC axis subset on five-axis high-speed machine tools using programmed end point constraint measurements

This paper presents a technique for assessing the volumetric errors on a five-axis machine tool for motion involving two linear axes and one rotary axis at selected feed rates using data from two sources. The first source of data is obtained through a programmed end point constraint procedure with measurement of the 3D volumetric positioning errors between a point on the tool holder and another fixed to the machine table reference frame. The tests involve maintaining the nominal coincidence of these two points whilst exercising the three axes. The second source of data is the position feedback signal from the encoder provided by the machine controller. Tests were carried out at low and high feed rates to evaluate the effect of geometric and dynamic errors. Polynomial functions are used to represent and then predict the geometric errors. The predicted geometric errors are then added to the dynamic errors provided by the servo errors from position feedback signals and propagated to the tool centre point and are compared with the measured volumetric errors. It shows that the influence of the geometric errors are dominant at low feed, whereas the effects of the servo errors of the linear axes become dominant as the feed increases, reaching 80% of the total error at a feed of 10,000 mm/min.     

Interaction of cell culture with composition effects on the mechanical properties of polycaprolactone-hydroxyapatite scaffolds fabricated via selective laser sintering (SLS)

In the current study PCL/HA composites were fabricated using SLS as two- and three-dimensional lattice structures and exposed to a cellular component (MC 3T3 osteoblast-like cells). The main aims were to determine the mechanical differences due to powder composition and to observe the physical and mechanical changes pertaining to cell presence. These structures were characterized by compressive mechanical testing, and the effects of cell culturing and degradation on mechanical properties of the scaffolds with different PCL/HA compositions were determined. Moreover, changes in the scaffold morphology due to the cell culture conditions were determined by μ-CT analysis.Cells steadily grew on the scaffolds for 21 days with preferential distribution around the macropores and initially PCL/HA(15%) composites had higher cell numbers. Removal of loosely sintered parts was observable during the culturing period. Cell culture conditions did not change the compressive moduli significantly but had a distinct effect on compressive strength. For PCL/HA(15%) composites, an initial loss in strength caused by cell culture was reversed by longer cell exposure, with compressive strength of the structures restored to the initial properties (p ≤ 0.05). μ-CT measurements showed widespread morphological changes in the scaffolds, such as a decrease in the roughness of the struts. In general, in the initial period composites with lower HA content (15 wt.%) showed better metabolic activity compared to the higher HA content, however by day 14 the performance of the two compositions was equal. These results suggest that changes in sintering due to the differences in powder composition can have profound effects on the short and long term mechanical properties of the scaffold particularly under cell culture conditions, and this should be closely considered for SLS processing of scaffolds.     

Attenuated total reflection-infrared nanofluidic chip with 71 nL detection volume for in situ spectroscopic analysis of chemical reaction intermediates

We present a micromachined silicon attenuated total reflection-infrared (ATR-IR) crystal with integrated nanofluidic glass channels which enables infrared spectroscopic studies with only 71 nL sample volume. Because of the short path length through silicon, the system allows IR spectroscopy down to 1200 cm(-1), which covers the typical fingerprint region of most organic compounds. To demonstrate proof-of-principle, the chip was used to study a Knoevenagel condensation reaction between malononitrile and p-anisaldehyde catalyzed by different concentrations of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) in solvent acetonitrile. By in situ measurement, it was demonstrated for the first time that at certain concentrations of DBU, reaction intermediates become stabilized, an effect that slows down or even stops the reaction. This is thought to be caused by increased ionic character of the solvent, in which protonated DBU stabilizes the intermediates. This clearly demonstrates that infrared mechanistic studies of chemical reactions are feasible in volumes as little as 71 nL.     

Selective and Sustainable Production of Sub-terminal Hydroxy Fatty Acids by a Self-Sufficient CYP102 Enzyme from Bacillus Amyloliquefaciens

Enzymatic hydroxylation of fatty acids by Cytochrome P450s (CYPs) offers an eco-friendly route to hydroxy fatty acids (HFAs), high-value oleochemicals with various applications in materials industry and with potential as bioactive compounds. However, instability and poor regioselectivity of CYPs are their main drawbacks. A newly discovered self-sufficient CYP102 enzyme, BAMF0695 from Bacillus amyloliquefaciens DSM 7, exhibits preference for hydroxylation of sub-terminal positions (ω-1, ω-2, and ω-3) of fatty acids. Our studies show that BAMF0695 has a broad temperature optimum (over 70 % of maximal enzymatic activity retained between 20 to 50 °C) and is highly thermostable (T₅₀ >50 °C), affording excellent adaptive compatibility for bioprocesses. We further demonstrate that BAMF0695 can utilize renewable microalgae lipid as a substrate feedstock for HFA production. Moreover, through extensive site-directed and site-saturation mutagenesis, we isolated variants with high regioselectivity, a rare property for CYPs that usually generate complex regioisomer mixtures. BAMF0695 mutants were able to generate a single HFA regiosiomer (ω-1 or ω-2) with selectivities from 75 % up to 91 %, using C12 to C18 fatty acids. Overall, our results demonstrate the potential of a recent CYP and its variants for sustainable and green production of high-value HFAs.     

Statistical investigation of wave power potential in the North Aegean Sea

Clean Technologies and Environmental Policy - Wave energy is recognized as a significant renewable energy source with a high energy density and very low environmental impact. Today, in parallel...     

Effects of sintering and zirconmullite doping on nanostructural vacancies of bovine hydroxyapatite by positron techniques

In this study, the nanostructural vacancy behavior of bovine derived hydroxyapatite (BHA) doped with powder zirconmullite (ZM) contents of 5, 7.5, 10 and 12.5 wt.% were presented at sintering temperatures of 1000, 1100, 1200 and 1300°C. ZM-doped BHA (ZM-BHA) was characterized by X-ray diffraction and positron annihilation lifetime spectroscopy (PALS). Density and hardness behavior were measured with respect to increasing sintering temperature. PALS results indicate that the longest lifetime component τ₃ of ortho-positronium (o-Ps) localized at open spaces is attributed to the vacancy site and almost constant with the ZM contents and the sintering temperatures to have a mean value of 0.680 ns (corresponding to the radius of 0.997 nm). This average value is ascribed to the OH group defects along the main crystalline line. On the other hand, the o-Ps intensity attributed to the number of vacancy sites increases almost linearly with ZM additives and sintering temperatures. The intensity is also related to the density and hardness of ZM-BHA in terms of ZM contents.