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451.
目的 抑制压电薄膜体声波谐振器(FBAR)寄生振动模态干扰,提出一种异形电极调控的谐振器新结构,并进行力–电多物理场耦合有限元建模分析与参数优化。方法 基于压电薄膜体声波谐振器的力–电耦合方程,运用有限元方法进行参数影响仿真分析,获得不同电极结构形状与敏感几何参数对应的谐振器阻抗特性及寄生振动模态干扰的影响规律,并对提出的异形电极调控谐振器几何参数进行优化。结果 新型电极结构使得薄膜体声波谐振器的导纳特性曲线更加平滑,相位波纹减少,无明显寄生谐振峰。参数优化所得框状电极宽度为6 μm、厚度为0.1 μm,谐振频率为1.727 GHz。结论 通过异形电极结构形状设计,可以实现对谐振器寄生振动模态的有效抑制,提升谐振器的性能。 相似文献
452.
目的 研究7050铝合金硬质阳极氧化膜在热带海洋大气环境下的耐蚀性能变化规律。方法 在7050铝合金表面制备硬质阳极氧化膜,然后采用不封闭、沸水封闭与铬酸盐封闭3种后处理方式进行处理。采用实验室多因素组合循环模拟试验方式与热带海洋大气环境户外直接暴露对试样开展耐蚀性能试验。通过外观、极化曲线、电化学阻抗谱方法,分析其耐蚀性能变化规律。结果 硬质阳极氧化膜不封闭处理的耐蚀性较差,实验室多因素组合循环试验第1循环后表面就出现白色腐蚀产物,评级为5/2xA。户外暴露试验12个月后,不封闭处理膜层的自腐蚀电位为?814.88 mV,自腐蚀电流密度为0.307µA/cm2;沸水封闭膜层的自腐蚀电位为?717.86 mV,自腐蚀电流密度为0.177 µA/cm2;重铬酸盐封闭膜层的自腐蚀电位为?703.33 mV,自腐蚀电流密度为3.82×10?2 µA/cm2。户外暴露12个月后,不封闭处理、沸水封闭处理与重铬酸盐封闭处理膜层在0.01 Hz的阻抗模值分别为1.04×105、1.51×105、4.76×105 Ω.cm2。结论 封闭处理能提升7050铝合金硬质阳极氧化膜的耐蚀性能,且重铬酸盐封闭后的耐蚀性能优于沸水封闭后的耐蚀性能。 相似文献
453.
目的 研究弹头构型对水下射弹表面气泡的影响,提高射弹微气泡减阻的效果。方法 基于高速摄像系统,针对不同弹头构型的水下射弹展开水洞试验研究。对比分析不同速度和通气压力情况下,平台锥形弹头产生的微气泡形态变化规律,以及相同速度和通气压力下,不同弹头构型产生的微气泡形态变化规律。结果 相较椭圆尖弹头,平台锥形弹头更容易在微孔材料的前缘区域形成大气泡,对弹体具有更好的包裹效果。对于不同的弹头构型,在相同流速和通气压力下,弹头锥度为43.6°时的空泡包裹效果最好。结论 存在一个最佳的锥度使气膜的覆盖面积达到最大。 相似文献
454.
Zein has been studied for its potential as a biobased polymeric material. Due to the fact that films made exclusively from zein are brittle, composites of zein and oleic acid were prepared in our lab and formed into flexible films. Film properties were believed related to their structure. X-ray scattering measurements on zein films suggested the formation of layers along the plane of the film. Oleic acid seemed to play an important role in layer formation. However, X-ray measurements could not yield information on the nature of the interface between oleic acid and zein. Surface plasmon resonance (SPR) was used to further investigate interaction between zein and oleic acid. Dynamic adsorption of zein from alcoholic solutions onto hydrophilic and hydrophobic surfaces generated by self-assembled monolayers of 11-mercaptoundecanoic acid or 1-octanethiol was monitored by SPR. It was observed that zein had a greater affinity for hydrophilic than for hydrophobic surfaces under the prevalent experimental conditions. A mechanism for structure development of zein-oleate films was proposed based on these results and previous X-ray measurements. It is suggested that the structure development involves hydrophilic adsorption of fatty acids onto the zein surface followed by hydrophobic associations leading to a layered film structure organization. 相似文献
455.
We summarize the latest results on the rapid changes that are occurring to Arctic sea ice thickness and extent, the reasons
for them, and the methods being used to monitor the changing ice thickness. Arctic sea ice extent had been shrinking at a
relatively modest rate of 3–4% per decade (annually averaged) but after 1996 this speeded up to 10% per decade and in summer
2007 there was a massive collapse of ice extent to a new record minimum of only 4.1 million km2. Thickness has been falling at a more rapid rate (43% in the 25 years from the early 1970s to late 1990s) with a specially
rapid loss of mass from pressure ridges. The summer 2007 event may have arisen from an interaction between the long-term retreat
and more rapid thinning rates. We review thickness monitoring techniques that show the greatest promise on different spatial
and temporal scales, and for different purposes. We show results from some recent work from submarines, and speculate that
the trends towards retreat and thinning will inevitably lead to an eventual loss of all ice in summer, which can be described
as a ‘tipping point’ in that the former situation, of an Arctic covered with mainly multi-year ice, cannot be retrieved. 相似文献
456.
M. R. Timmins D. F. Gilmore N. Lotti M. Scandola R. C. Fuller R. W. Lenz 《Journal of Polymers and the Environment》1997,5(1):1-15
An assay method has been developed for monitoring the enzymatic degradation of thin films of translucent polymers. The method
was based on the observation that when a solution-cast film of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) was exposed
to a solution of a depolymerase fromPseudomonas lemoignei, the surface of the film roughened and the film became visibly turbid. This increase in turbidity could be measured spectrophotometrically
and was reproducible during the initial stage of degradation. Turbidity correlated very closely with film weight loss early
in the degradation but reached a maximum value before extensive degradation had taken place. For a given set of films, this
correlation was independent of the concentration of the enzyme used, although it did vary with the mode of enzyme exposure.
The turbidity was associated with the exposure of crystalline domains due to the removal of amorphous material from the film
surface. The increase in crystallinity at the surface was verified by attenuated total reflectance infrared spectroscopy (ATRIR).
In conjunction with SEM, weight loss, and ATRIR, the film turbidity assay provided much semiquantitative insight into the
mechanism of the enzymatic degradation reaction. This assay was used to study the enzymatic degradation of films of PHBV solution
blended with cellulose acetate esters (CAE). The presence of only 25% of CAE of degree of substitution 2.9 severely hampered
the enzymatic degradability of PHBV, a result which is consistent with the environmental degradation of these same samples
exposed to activated sludge. 相似文献
457.
458.
生物膜法A/O工艺A段脱氮动力学研究 总被引:2,自引:0,他引:2
研究了生物膜法A/O工艺A段的动力学模式,根据在碳源充足时,反硝化速率和硝酸盐浓度呈零级动力学反应,从理论得出A段Vmax、变化不大,膜单位面积传质速率(dF/dt)与基质浓度无关,与生物膜厚度(δ)成正比,dF/dt=k1A√C0-Ce,动力学参数k1=√CmaxX表明A段NO3^--N去除率与进出水浓度差的平方根和填料表面积成正比,并通过试验求出动力学系数,K1=0.016。 相似文献
459.
D.P. Ryckman D.V. Weseloh P. Hamr G.A. Fox B. Collins P.J. Ewins R.J. Norstrom 《Environmental monitoring and assessment》1998,53(1):169-195
The levels of organochlorine contaminants (OCs) in the eggs of double-crested cormorants (Phalacrocorax auritus) from the Canadian Great Lakes, Lake Nipigon and Lake-of-the-Woods were monitored between 1970 and 1995. PCBs and p,p-DDE were present at the highest concentrations. Significant declines in OC concentrations on the Great Lakes were observed over this period for Lake Ontario, Lake Superior, Georgian Bay and North Channel but not Lake Erie where levels remained relatively stable. In the early 1970s, the greatest OC levels were generally observed in cormorant eggs from nesting sites in Georgian Bay and North Channel of Lake Huron. Between 1984 and 1995 mirex and PCB levels were consistently highest in samples from Lakes Ontario and Erie, respectively. Similar levels of PCDDs and PCDFs were observed from all regions of the Canadian Great Lakes in 1989. In general, OC levels in cormorant eggs between 1984-95 were ranked as follows: Lake Erie>Lake Ontario Lake Superior>Lake Huron. In 1995, eggshell thickness in Canadian Great Lakes cormorants, ranged from 0.423 to 0.440 mm and was on average only 2.3% thinner than pre-DDT era values. Between 1988 and 1996, 31 cormorant chicks with bill defects were observed at 16 different colonies (21% of all colonies surveyed) in Lakes Ontario and Superior, Georgian Bay and North Channel, and the main body of Lake Huron. No bill deformities were observed at reference sites in northwestern Ontario (Lake Nipigon and Lake-of-the-Woods). For the period 1988-96, the prevalence of bill defects in cormorant chicks (0.0 to 2.8/10,000 chicks) did not differ significantly (P > 0.05) among most regions in the Canadian Great Lakes. Georgian Bay was the only region to show a significant decrease in the prevalence of bill defects between the periods 1979-87 and 1988-95. 相似文献
460.