吸声保温玉米秸秆穰板制备及性能研究

以疏解后的玉米秸秆穰丝为基材,异氰酸酯为胶黏剂,均匀组坯后经热压制备成吸声保温玉米秸秆穰板。通过单因素试验分别探究了施胶量、热压温度板材密度、厚度对玉米秸秆穰板吸声、导热和压缩性能的影响。结果表明:综合板材的性能和生产成本,优化工艺为施胶量2%、热压温度140℃、密度0.10 g/cm3,所得板材吸声性能达到GB/T 16731—1997的Ⅲ级标准,压缩强度满足GB/T 25975—2010中的要求,属高效保温材料。     

Development of thermal insulating and sound absorbing agro-sourced materials from auto linked flax-tows

The aim of this paper is to develop a green composite using only flax fiber material for thermal insulations and sound absorbing using flax-tows and thus enhance the less noble part of the flax plant. The Lin-K process is a simple patented manufacturing process used to develop these self-linked materials. Thermal conductivity, absorbing acoustic coefficient, hydric properties and the effect of several parameters on these performances are reviewed. The use of fine flax-tows leads to extract more organic substances of the inner fibers during the microwave treatment which improves the mechanical performances and reduces the thermal conductivities of these materials. The environment has very significant effects on thermal stability and durability of these materials.     

吸声材料的当量声阻率

在进行车辆乘座室声固耦合振动有限元分析时 ,得到一反映吸声材料对声波吸收作用的复阻尼矩阵。本文从能量守恒原理出发 ,提出了将吸声材料的声抗率转化到声阻率中去的当量声阻率 ,这样既能简化计算 ,又能保证具有较高的计算精度     

基于声强信号分析和组合神经网络的发动机故障诊断

建立了一个基于声强信号分析和组合神经网络的发动机故障诊断模型。该模型首先运用小波理论分析各类故障下发动机产生的声强信号,获取反映发动机工作状态的频带特征向量,然后将特征向量用于组合神经网络训练,进行故障模式识别。通过对3Y丰田2．0发动机的试验数据分析表明,这种模型可有效提高故障诊断的效率和准确率。     

蜂窝与微穿孔声学结构研究进展及其在木结构建筑中的应用

声学性能是衡量木结构建筑质量的重要指标之一,也是保障用户居住舒适度的关键因素。主要介绍了国内外蜂窝隔声结构、微穿孔吸声结构和蜂窝与微穿孔复合结构声学性能的相关研究成果,并对其在木结构建筑中的应用进行探讨,以期为今后蜂窝与微穿孔结构的深化研究与木结构建筑声学性能相关的基础应用研究提供理论借鉴。     

丛生竹地板与毛竹地板吸声性能比较

以国产毛竹地板和印度丛生竹为原料制造的丛生竹地板为主要材料,用驻波管法测试了两种竹地板的吸声系数,比较了它们的吸声性能.结果显示:丛生竹地板的吸声性能好于毛竹地板,丛生竹地板和毛竹地板的平均吸声系数分别为0.231和0.213.在低频段(f≤1 000 Hz),毛竹地板的低频吸声特性优于丛生竹地板;在中高频段(1 000 Hz相似文献   

超声波热萃取-紫外分光光度法测定蜂巢蜜中总黄酮的含量

[目的]为建立一种快速测定蜂巢蜜中总黄酮含量的方法.[方法]蜂巢蜜、蜂胶、蜂王浆、椴树蜜的超声波萃取液通过聚酰胺柱层析去除杂质,以紫外分光光度法在360 nm波长下测定总黄酮含量.[结果]该方法回收率在90％以上,变异系数小于2％,方法准确度好.具有试剂消耗少,操作简单等优点.[结论]蜂巢蜜中总黄酮的含量为14.97 mg,/100 g,虽然只有蜂胶产品总黄酮的含量的0.87％,但相对与其他种蜂蜜,总黄酮含量至少高出1倍.     

Pacific herring (Clupea pallasii) consumption by marine birds during winter in Prince William Sound,Alaska

Following the 1989 MV Exxon Valdez oil spill (EVOS) and subsequent herring population collapse in Alaska's Prince William Sound (PWS), the Pacific herring (Clupea pallasii) fishery was closed. In the 25 yr since EVOS, herring and several herring‐dependent marine bird species have failed to reach pre‐spill population levels. One hypothesis is that intense predation pressure may be inhibiting herring recovery. To inform herring modeling efforts, this study estimated marine bird consumption of juvenile and adult herring in PWS for 10 winters over an 18‐yr period (1989–90 through 2006–2007). Total estimated herring consumption by wintering marine birds averaged 2409 ± 950 t, indicating that avian consumption represents a substantial and inter‐annually variable source of herring mortality. Common murre (Uria aalge) consumed the greatest portion (16–80%) of herring in all years among marine bird species. Juvenile herring biomass consumed annually by common murre was greater than murre consumption of adult herring biomass. Time lag analyses showed that marine bird consumption of adult herring is negatively correlated with the amount of herring spawn observed in subsequent years, but such effects were not observed more than 2 yr. Our models indicate that during years in which herring recruitment is low or bird populations are particularly large, marine birds can consume up to 10% of the annual adult herring biomass. Our results highlight the importance of herring to wintering PWS birds. We propose that future management of herring stocks seeks to reduce negative impacts on marine birds that prey on herring.     

Fracture behaviour of bread crust: Effect of ingredient modification

The influence of the formulation on the crispness of bread crust was studied. Crispness is a relevant sensory attribute that depends on several factors particularly the plasticizer content (water), the mechanical properties of the solid matrix and the morphological architecture of the bread. Enzymes and additives were used to modify the bread formulation. This resulted in a modification of the bread characteristics. Crust and crumb had higher porosity than the control breads and a decreased water content of the bread crust was found. Instrumental crispness was evaluated by simultaneous analysis of the fracture behaviour and sound emission while breaking the crust. Addition of lipase, amylase, glucose oxidase and hydroxypropyl methylcellulose (HPMC) increased the number of force and sound events, indicative of higher crispness. The number of fracture and sound events correlated negatively with the water content and positively with the porosity of the crust. Both properties are affected by the use of enzymes/additives. Whether the observed positive effect of the enzymes and additives on the number of force and sound events is due to a direct effect on the flour components properties or interactions or to an indirect effect via structure-water migration properties is still open to discussion.