油桃缓冲包装的研究

研究了在不同运输振动频率下2种缓冲包装结构对油桃采后生理品质(失重率、呼吸强度、感官)变化的影响.结果表明,缓冲结构A和在平整路面(振动频率在10～20Hz)运输可以有效地抑制油桃的呼吸速率,减少营养成份的损失,延长油桃的货架寿命.但是在崎岖的道路上(振动频率在30～40Hz)运输时会加快油桃的呼吸速率,使其品质下降.     

基于递推估计的保鲜环境信息感知系统设计

目的 为降低鸡蛋在流通过程中的破损率,利用有限元法分析鸡蛋在振动条件下缓冲包装系统的响应特性,以选择其缓冲包装结构。方法 通过鸡蛋压缩实验,测试鸡蛋的破损强度,并分析鸡蛋的流通环境,确定振动的类型、频率和幅值;以聚苯乙烯泡沫(Expanded Polystyrene,EPS)为缓冲材料,选用2种缓冲结构,建立基于流-固耦合特性的鸡蛋缓冲包装系统有限元模型,分析不同缓冲厚度下2种结构的振动特性。结果 通过压缩试验测定鸡蛋破损强度极限值为5.3 MPa,为有限元分析提供评价条件。有限元仿真结果表明,结构?应力普遍大于10 MPa,不利于鸡蛋的保护,同等厚度下结构Ⅱ的应力明显减小;采用结构Ⅱ且缓冲厚度δ＞3 mm时可避免鸡蛋在振动过程中发生破损。结论 有限元仿真可快速、有效评估鸡蛋缓冲包装,选取较为有益的缓冲结构,提升鸡蛋流通中的安全性。     

框架式灯具缓冲包装结构设计

目的 在绿色包装设计的新要求下,改进传统塑料包装方案,以框架式灯具的安全运输为例,设计一种面向框架类产品的全瓦楞纸板的绿色缓冲包装.方法 以缓冲包装六步法为依据,利用平面材料立体化造型设计方法,设计全瓦楞纸板缓冲包装结构,并利用E和B型瓦楞纸板分别制作出2套结构尺寸相等的缓冲包装.根据ISTA-1A标准对2组包装件进行跌落试验,通过安装在灯具上的传感器测试的数据及包装件的变形,研究瓦楞板厚度对包装件缓冲性能的影响,综合评价包装件的缓冲性能.结果 对2套不同厚度的瓦楞纸板缓冲包装结构,分别进行一角、三棱、六面的跌落测试,得出了相应加速度-时间曲线和包装件变形图.结果 表明,跌落过程中灯具系统的最大加速度为684.17 m/s2,小于灯泡脆值(784 m/s2),并且灯架未变形,灯泡及配件均未损坏,B型瓦楞板制作缓冲包装结构在试验后相对于E型瓦楞板制作的变形更小.结论 2套全瓦楞缓冲包装具有良好的缓冲性能,厚度大的纸板具有更好的缓冲效果,能有效缓冲框架灯具在物流运输过程中所受到的冲击,适用于装卡在其他框架类产品的两端,具有较好的使用价值和应用前景.     

箱装苹果振动特性及损伤的试验研究

振动损伤是引起果品采后损耗的主要因素之一,研究振动强度、缓冲包装结构等因素对果品振动损伤的影响对控制和降低果品运输损伤具有重要意义.以正交试验为基础,研究了振动强度、缓冲包装结构和包装箱内果品放置层数这3个因素对苹果损伤率与果品振动传递率的影响,并用新的试验手段得到了振动工况下箱内各层果品的加速度变化情况.结果表明,3个因素对苹果损伤率和果品振动传递率均有影响,其中振动强度对其影响最为显著,缓冲包装结构、箱内果品放置层数的重要性依次减小;振动试验条件下,箱内各层苹果的加速度由下向上逐渐增加;不同试验条件下果品振动传递率不同,振动传递率越小,苹果损伤率越低.     

组合瓦楞纸板缓冲衬垫的力学性能研究

本文研究了3A型、3B型、BAB型组合瓦楞纸板缓冲衬垫的抗弯性能和平压性能。抗弯试验结果表明,组合衬垫的载荷一挠度曲线可分为4个阶段,依次为瞬时弹性变形阶段、延迟弹性变形阶段、弹塑性变形阶段和屈服塑性变形阶段;从抗弯性能方面考虑,在对瓦楞纸板进行粘接使用时,可以将A型或B型瓦楞自行组合,但最好不要将B型或A型瓦楞与AB型瓦楞组合。平压试验结果表明,在3A型、3B型及BAB型组合瓦楞纸板缓冲衬垫的静态压缩曲线均存在三个峰值,且峰值与瓦楞纸板层数一一对应,各层按照屈服强度从小到大的顺序依次屈服、破坏;从静态压缩性能方面考虑,BAB结构的抗压性能最好,3B结构次之,3A结构最差。根据静态压缩试验绘制的瓦楞纸板缓冲系数-最大静应力曲线,为采用组合瓦楞纸板衬垫进行缓冲包装设计提供了依据。当采用该曲线进行缓冲包装时,应根据产品特性及流通环境特点,尤其是产品或包装件可能给予缓冲衬垫的静压力范围,合理选择衬垫的组合型式。     

疲劳振动对蜂窝纸板承载力和缓冲性能的影响

对蜂窝纸板进行疲劳振动实验,测定分析振动次数、加速度对蜂窝纸板承载力、缓冲性能的影响,并与未振动纸板进行比较.结果表明,随着振动次数和振动加速度的增加,蜂窝纸板剩余屈服应力减小,缓冲系数增大,蜂窝纸板的缓冲性能有所下降.缓冲包装设计时,应考虑疲劳振动对蜂窝纸板衬垫缓冲性能的影响,以确保实现预期缓冲包装的要求.     

基于缓冲材料选择的打印机防护包装设计

目的提高打印机包装的缓冲性能,避免打印机在流通过程中可能造成的外观性功能性损坏,从而造成不必要的损失。方法通过缓冲材料动态压缩实验,分析对比EPE和EPS的缓冲性能,从而设计缓冲结构,使整体包装包装具有优良的容装性、保护性和方便性。对包装件进行包装测试。结果经过分析对比厚度相同的EPE和EPS可知,EPE吸收的能量更多,缓冲性能更强。A瓦相较于B,E瓦的边压强度更高、缓冲强度更好。结论选择EPE作为缓冲材料,A型瓦楞纸板作为外包装材料设计打印机的整体运输包装。经震动测试加速度在许用范围之内时装载物并未受到损坏,跌落测试下包装件未受到严重损坏,因此打印机整体运输包装具有可行性。     

疲劳振动对瓦楞纸板承载能力与缓冲性能的影响

对瓦楞纸板进行疲劳振动试验,测定分析振动次数、加速度对瓦楞纸板承载能力、缓冲性能的影响,并与未经振动材料进行比较.结果表明,随着振动次数、振动加速度的增加,瓦楞纸板剩余屈服应力减小,缓冲系数增大,其中在小应力阶段缓冲系数变化不大,在大应力阶段,缓冲系数显著增大.进行频率20Hz、加速度为2.0g、80000次振动试验后,瓦楞纸板承载能力下降了38.88%,静态应力0.012MPa下的缓冲系数增大了46.37%.缓冲包装设计时,应考虑疲劳效应对瓦楞纸板衬垫缓冲性能的影响,以确保实现预期缓冲包装的要求.     

纸浆模制品结构参数与缓冲作用

纸浆模包装材料缓冲性能的研究表明纸浆模制品的缓冲性能与其结构形式、形状尺寸及原料组成密切相关,结构体的形状、侧壁斜度、厚度和高度等结构参数决定着纸浆模结构在包装应用中的抗压能力和缓和冲击与振动的保护性能,纸浆模缓冲结构参数的分析方法能够建立起模体结构形状特征与缓冲包装性能的对应关系,使缓冲包装设计有据可依,纸浆模结构缓冲数据库的建立将为计算机辅助设计与应用奠定基础。     

组合瓦楞纸板抗弯性能研究

采用瓦楞纸板及其组合衬垫代替非环保的泡沫塑料衬垫进行缓冲包装设计,是今后绿色缓冲包装设计的发展趋势.首先采用淀粉胶将瓦楞纸板试样进行黏结,构造不同结构的组合结构,然后研究环境湿度对组合结构抗弯性能的影响.研究结果表明.B型与AB型瓦楞纸板的黏结组合(B AB)的抗弯强度随湿度的增大显著降低;在A型瓦楞纸板的3层顺向粘结组合(AAA)中,瓦楞的走向与受压位置对纸板的抗弯性能起着决定性的作用,横向抗弯强度大于纵向.     

不同保鲜袋包装对采后油桃果实贮藏品质的影响

目的研究常温环境下不同保鲜袋包装处理对油桃果实贮藏品质的影响。方法以黄心油桃为实验材料,比较相同厚度的聚丙烯(PP)、双向拉伸聚丙烯(BOPP)和聚乙烯(PE)薄膜包装袋对油桃果实贮藏品质的影响,筛选出合适的薄膜包装材料。结果采用3种保鲜袋包装对油桃果实的贮藏品质存在不同程度的影响,各处理组的油桃果实都发生了不同程度的腐烂褐变;未包装的油桃果实很快失去了食用价值,在贮藏12 d时褐变指数为4.5,腐烂率为65.33%;采用BOPP保鲜袋包装的油桃果实在贮藏12d时褐变指数仅为2.3,腐烂率仅为32.29%,果实出汁率保持在58%以上;BOPP保鲜袋包装处理的油桃果实在出汁率、TSS、TA、Vc、MDA等营养指标和衰老指标上均不同程度优于PP和PE保鲜袋包装的油桃果实。结论采用BOPP薄膜材料包装的油桃果实在常温贮藏下有较好的保鲜效果,有效地延长了油桃果实的货架期。     

1-MCP保鲜纸的制备及其在油桃保鲜中的应用

以吸水纸为芯纸,两侧覆上面纸,以热熔胶黏合,在芯纸上均匀打孔载入定量的1-MCP药剂,制得1-MCP保鲜纸,并采用GC-MS,对保鲜纸中1-MCP的释放规律进行研究。研究表明,实验条件下1-MCP处于气态,在第2 d保鲜纸中的1-MCP释放达到最大值,说明此时的湿度达到适合1-MCP释放的条件。以油桃为实验对象,研究保鲜纸中1-MCP用量对果实感官评价、失重率、呼吸强度及可溶性固形物含量等指标的影响。结果表明,质量浓度为4 mg/L的1-MCP保鲜纸对油桃感官评价的影响最小,对果实失重率、呼吸强度、可溶性固形物含量的抑制作用最明显,整体而言,对油桃的保鲜效果最好。     

On pseudorandom sequences of k symbols constructed using finite fields

A family of pseudorandom sequences of \(k\) symbols are constructed by using finite fields of prime-power order. The construction is an extension of certain construction of Sárközy and Winterhof on binary sequences using the quadratic character with polynomial arguments over any finite fields, and of certain construction of Ahlswede, Mauduit and Sárközy on sequences of \(k\) symbols using multiplicative characters with polynomial arguments over finite prime fields. Certain pseudorandom measures of the resulting sequences are considered.     

Have we reached the organisational ceiling? a review of applied accident causation models,methods and contributing factors in construction

Work-related fatalities continue to represent a significant issue within the construction industry. Contemporary accident causation models are underpinned by systems thinking, however, it is unclear whether these theories have translated into the construction domain. This article presents the findings of a review that was conducted to determine if the construction accident analysis literature has applied a systems thinking approach to understand accident causation. Specifically, the review examined two key aspects: first the types of models and methods that have been applied to analyse construction incidents, and second, the types of contributing factors identified as playing a role in construction incidents. The findings are summarised using Rasmussen’s Risk Management Framework. The review revealed that contemporary models of accident causation have not yet been applied in construction-related research. It is concluded that the models and methods applied in the construction literature predominantly identify contributing factors associated with the company, management, and frontline work levels of the system, rather than considering broader, system-wide factors. Further, the relationships between individuals and organisations operating at each level of the system have not been typically examined. Further research underpinned by systems thinking is required to better understand accident causation in the construction domain.

• Highlights

• The review revealed that contemporary models of accident causation have not yet been applied in construction-related research;

• The models and methods applied in the construction literature predominantly identify contributing factors associated with the company, management, and front line work levels of the system, rather than considering broader, system-wide factors;

• Relationships between individuals and organisations operating at each level of the system have not yet been examined;

• Despite the efforts of regulators and construction entities, the consistently high rate of fatal accidents in construction highlights the challenges surrounding the practical management of safe production within complex and dynamic working environments;

• Accident analysis methods used in this industry have not kept pace with advances in the field of safety science.

     

Cement concrete and concrete–polymer composites: Two merging worlds: A report from 11th ICPIC Congress in Berlin, 2004

The search for durable and sustainable construction materials inspires the developments in the world of cement concrete, as well as in the world of concrete–polymer composites. Both worlds recognize, strive for and accept each other’s contribution to the synergetic effects that are realized by the combination of classical building materials and polymers. A better knowledge of materials behaviour, especially in the field of admixtures, and a better understanding of curing processes allowed the development of highly performing mineral or modified mineral concretes, mortars and grouts. CPC-science becomes an invaluable element in the development of sustainable construction materials. ICPIC brings together practitioners and scientists, dealing with concrete–polymer composites in all industrial fields, but with emphasis on construction industry. The 11th International ICPIC Congress took place in Berlin, 2–4th June 2004. New trends and evolutions have been presented and discussed. The highlights of the Congress, and the synergies for the construction world that emerge from this congress on polymers in concrete in combination with cement concrete, are presented.     

Enhanced Thermal Conductivity of 5A Molecular Sieve with BNs Segregated Structures

5A molecular sieves have been widely used as adsorbents in cryogenic distillation for hydrogen isotope separation in fusion reactor engineering, but its low thermal conductivity is detrimental to the process stability. Improving the thermal conductivity of 5A molecular sieves is one of the most important goals for high‐performance devices. Here, firm segregated structures with boron nitride sheets (BNs) are constructed around 5A molecular sieve particles. SEM results show 30 µm BNs tend to form the better networks in comparison with that of 0.12 µm BNs at 40 wt% loadings. It is further verified that BNs with the larger size promote the thermal conductivity. Meanwhile, the thermal conductivity increases with the increasing amounts of BNs. XRD and specific surface area results indicate that the sintering and the addition of BNs exert negligible effects on the structure of 5A molecular sieve. These results indirectly show 5A molecular sieve with BNs segregated structures is very likely to be used for the application of hydrogen isotopic separation. Besides, this work provides new insight into the construction of segregated structure in inorganic porous materials.

     

Study on System Coupling Interaction of Large-Scale Construction Companies Programme Contracting and Firm Growth

Constant changes in the construction market have resulted in individual projects being challenged to meet the long-term growth needs of large construction companies. Change should be based on the construction of this new model project group, to achieve better interaction, and to allow for a more rapid enterprise development. This paper is based on the system coupling analysis of large-scale construction enterprises and construction projects. A clear system presents itself and forms the basis of the system construction, institutional change and mechanism of the path between base construction projects and business growth.     

Nitrogen-rich carbon spheres made by a continuous spraying process for high-performance supercapacitors

Supercapacitors have high power densities, high efficiencies, and long cycling lifetimes; however, to enable their wider use, their energy densities must be significantly improved. The design and synthesis of improved carbon materials with better capacitance, rate performance, and cycling stability has emerged as the main theme of supercapacitor research. Herein, we report a facile synthetic method to prepare nitrogen-rich carbon particles based on a continuous aerosol-spraying process. The method yields particles that have high surface areas, a uniform microporous structure, and are highly N-doped, resulting in a synergism that enables the construction of supercapacitors with high energy and power density for use in both aqueous and commercial organic electrolytes. Furthermore, we have used density functional theory calculations to show that the improved performance is due to the enhanced wettability and ion adsorption interactions at the carbon/electrolyte interface that result from nitrogen doping. These findings provide new insights into the role of heteroatom doping in the capacitance enhancement of carbon materials; in addition, our method offers an efficient route for large-scale production of doped carbon.

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Review of nanostructured current collectors in lithium–sulfur batteries

Lithium–sulfur (Li–S) batteries are receiving increasing attention because of their high theoretical energy density and the natural abundance of S. However, their practical applications are impeded by the low areal S loading in the cathode and the fatal Li dendrites in the anode of the Li?S cells, which yield an inferior practical energy density and introduce safety concerns, respectively. In this review, we focus on an emerging approach—the nanostructured current collector—to overcome these two critical challenges for Li?S batteries. We describe the general attributes of nanostructured current collectors and examine how these attributes enhance the S utilization with a high S loading and suppress the Li dendrites by regulating the Li-deposition behavior. We present various assembly blocks that have been used for the construction of advanced nanostructured current collectors to build better S cathodes and Li anodes. Finally, we investigate the current challenges and possible solutions regarding the practical applications of nanostructured current collectors in Li?S batteries.

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