Mechanical properties of metastable glacial till before and after water‐induced compaction

The mechanical properties of metastable soils have been approached from different backgrounds by civil engineers and soil scientists, with the main focus being on water‐induced self‐compaction rates. This study was conducted to determine the rebound‐recompression properties of metastable soil before and after wetting and to study the effect of water‐induced compaction on the mechanical stability depending on the overburden pressure. Rebound and recompression properties were measured with oedometer tests using sieved sandy loam, taken from a nonweathered Saalian glacial till layer, as the metastable test soil. The mechanical stability (preconsolidation load) of the dry and wetted soil was derived mathematically from recompression data after the test soil was unloaded. Void‐ratio changes during unloading and reloading were on a low level (Δe = 0.03). Rebound and recompression rates of the dry samples increased with load, whereas the void‐ratio change was twofold higher during recompression. Rebound rates of the wetted samples tended to decrease with load, while the recompression rates remained constant. Preconsolidation load calculated for the dry samples overestimated the simulated overburden pressure, whereas the wetted samples showed a high congruence. In both cases, the point of greatest curvature estimated in the earlier step of deviation gave values that were more realistic to the loads from which the unloading started. Our results indicate that both dry compaction and water‐induced compaction induce primarily plastic deformation. Furthermore, we found that in both the dry and wetted state the mechanical stability of the soil reflecting the overburden pressure remained constant.     

Clinical signs of barotrauma in golden perch,Macquaria ambigua (Richardson), and associated effects on post‐release mortality and health

This study assessed the effects of different retrieval depths (2, 10 or 20 m), surface intervals (none or 15 min) and release methods (untreated, vented or recompressed) on the incidence of external and internal clinical signs of barotrauma (ECSB and ICSB) and post‐release mortality in golden perch, Macquaria ambigua (Richardson). Fish were assessed for ECSB before and after surface intervals and either monitored for mortality over 3 days in two deep cages or killed for internal examination. When all fish were left untreated, short‐term mortality increased with retrieval depth from 0% and 4.2% among 2 and 10‐m fish, respectively, to 19.2% among 20‐m fish; while surface interval only affected the incidence of two ECSB (excess buoyancy and a prolapsed cloaca). Mortality was also greater among 20‐m fish that were subjected to a 15‐min surface interval and left untreated (22.2%) or vented (22.2%) than those that were recompressed (5.6%). Of the ECSB, only exophthalmia was associated with increased mortality, with half of the affected fish dying. However, many fish retrieved from 10 and 20 m also sustained numerous ICSB, including compressed gonads or vital organs and ruptured or collapsed, haemorrhaging swimbladders that remained deflated for up to 3 days after release.     

Recovery potential of black rockfish,Sebastes melanops Girard,recompressed following barotrauma

Overfished species of rockfish, Sebastes spp., from the Northeast Pacific experience high bycatch mortality because of ‘barotrauma’, a condition induced from the rapid change in pressure during capture. Field experiments show that it may be possible for rockfish to recover from barotrauma if quickly recompressed; however, no work has followed the physiological recovery of rockfish after recompression or determined whether it is possible for rockfish to survive barotrauma in the long term. Barotrauma was induced in adult black rockfish, Sebastes melanops Girard, from a simulated depth of 35 m, followed by recompression. Blood and selected tissues (eye, heart ventricle, head kidney, liver, rete mirabile and gonad) were sampled at days 3, 15 and 31 post‐recompression to evaluate the tissue‐ and physiologic‐level response during recovery. No mortality from barotrauma occurred during the experiments, and feeding resumed in 80% of both treatment and control fish. The primary injury in treatment fish was the presence of a ruptured swimbladder and/or a ruptured tunica externa (outer layer of swimbladder), which was slow to heal. Blood plasma was analysed for glucose, sodium, chloride, potassium, calcium, phosphorus, insulin‐like growth factor‐1 and cortisol. Plasma analyses indicated no strong effects because of barotrauma, suggesting overall handling stress outweighed any effect from barotrauma. Rockfish with ruptured swimbladders may face compromised competency in the wild; however, it appears the majority of black rockfish decompressed from 35 m have a high potential for recovery if recompressed immediately after capture. This research suggests recompression could be a valuable bycatch mortality reduction tool for rockfish in recreational fisheries.     

酒精糟清液带热泵多效蒸发系统的优化研究

运用大系统优化理论“分解”、“协调”的思想，以酒精糟清液的蒸发浓缩为例，证明了“带喷射式热泵的多效蒸发若按等面积设计，在经济压缩比范围内无最佳解。”这一结论，对不等面积的寻优设计，给出了“分级决策求解法”和“两级平衡求解法”两种方法。     

不同含水率苜蓿干草的高密压缩成型特性的试验研究

为探究含水率对苜蓿干草高密压缩成型特性的影响,基于封闭状态下的干草压缩成型原理,利用压缩装置,以不同含水率8%~20%的苜蓿干草为研究对象,在相同的初始密度、压缩方向和压缩速度条件下进行二次高密压缩试验,获得了不同含水率苜蓿干草的高密压缩特性曲线,并将干草高密压缩过程分为压紧、成型和蠕变3个阶段。试验结果表明:对应相同压缩量的干草成型密度小于300kg/m³时,随着干草含水率的增加干草压力的增幅较小,最大干草压力为1.05MPa;当干草成型密度大于400kg/m³时,含水率对干草压力的影响非常显著,干草压力的最大增幅为120%。     

硫酸废液机械蒸汽再压缩减压膜蒸馏特性分析

为了高效回收处理工农业生产过程中产生的硫酸废液，该研究提出了一种机械蒸汽再压缩减压膜蒸馏系统。首先，基于质量和能量守恒定律建立数学模型，并设计搭建了系统试验装置，初步以自来水为测试对象开展了可行性验证试验；然后以硫酸溶液为研究对象，借助Matlab软件进行迭代求解计算，模拟分析操作参数对系统热力特性的影响规律。试验结果表明系统膜通量和电导率分别为1.6 kg/(m2·h)和48 μS/cm，单位加热能耗Shec和Cop分别为71.88 kWh/t和8.88，比常规蒸汽加热的减压膜蒸馏系统节能74.7%。模拟结果表明进料浓度增加，压缩机功耗增加，但性能系数Cop减小；进料温度、进料流速以及渗透侧压力增加，压缩机功耗减小，Cop增加。因此，该系统具有良好的节能性、经济性和环境效益，应用前景广阔。