不同回潮处理法对饲料初水分测定效果的影响

本研究旨在探索测定饲料初水分时采用烘干后回潮法和不回潮法对测定结果有无显著影响。试验选用草坪草、苜蓿、莲花菜、白菜、马铃薯植株、胡萝卜、红薯、南瓜、西瓜皮、玉米青贮10种样品,通过配对试验,同时采用烘干回潮法(从烘箱取出后在室温下放置24 h后称重)和烘干不回潮法(从烘箱取出后在室温下放置30 min后称重)测定各饲料样品的初水分含量。试验结果表明5种饲料的初水分值均为烘干不回潮法显著或极显著高于烘干回潮法(P<0.05,P<0.01)。因此,实验室中测定饲料初水分时不能使用不回潮法。

四种豆科牧草初水分与营养成分关系的研究

分析 4种豆科牧草 9个不同半月龄的初水分含量和营养成分含量关系表明 ,4种豆科牧草的粗蛋白质含量与初水分含量间呈极显著正相关 (P <0 .0 1) ;粗纤维、酸性洗涤纤维、中性洗涤纤维、木质素含量与初水分含量间呈极显著负相关 ;粗脂肪含量与初水分含量间的相关程度则因牧草种类而异 ,分别表现出强正相关和中等程度正相关 ;而无氮浸出物含量与初水分含量的变数间则明显的表现出缺乏线性函数关系 ,两种变数的总变异中可以相互以线性关系说明的部分所占的比率较接近于 0 (0≤r2 ≤ 0 .4 4)。

华北北部奶牛鲜粪便燃烧值变化规律的研究

本试验的目的是探讨华北北部奶牛鲜粪便燃烧值的变化情况及其影响因素和影响程度,并揭示其内在规律。本研究采用多因素再裂裂区组试验设计,对华北北部奶牛鲜粪便样品进行采样、测定、化验分析以及多重比较。结果显示,奶牛鲜粪便燃烧值变动范围为2.161～4.221MJ/kg,与水分含量呈负相关,与海拔、季节、养殖模式三因素无显著相关,而奶牛组别对其有一定影响。

四川凉山州牛肉和猪肉主要营养成分比较研究

本次实验采用烘箱干燥法、凯氏定氮法、直接测热法,分析测定了四川凉山州牛肉和猪肉中初水分、吸附水、粗蛋白质、能值等主要营养成分的含量。初水分含量,牛肉为69.41%,猪肉为69.02%,牛肉比猪肉多0.39%;吸附水含量,牛肉为7.19%,猪肉为11.59%,牛肉比猪肉少4.4%;粗蛋白质含量,牛肉为22.57%,猪肉为19.96%,牛肉比猪肉多2.61%;畜肉干物质中能值含量,全干样测定时,牛肉为24591.53J/克,猪肉为25169.38J/克,牛肉比猪肉少577.85J/克。结果表明,牛肉除初水分含量、粗蛋白质含量比猪肉高外,其余都比猪肉少。

粮食干燥机性能指标折算系数的研究

粮食干燥机的性能试验受粮食条件和气候条件的影响,试验条件不同,干燥机性能指标的测试值也不同.大型干燥讥的试验是很难选择统一的试验条件的,所以难以比较不同干燥机的性能优劣.本文提出了一种不同试验条件下干燥机性能指标的折算方法,该方法较好地解决了干燥机性能比较评价问题,并为干燥机在各种操作条件下的运行提供了指导性的科学依据.

Isothermal diffusion of water vapor in unsaturated soils based on Fick’s second law

In arid regions, water vapor diffusion predominates the total water migration in unsaturated soil, which significantly influences agriculture and engineering applications. With the aim of revealing the diffusion mechanism of water vapor in unsaturated soil, a water vapor migration test device was developed to conduct the water vapor migration indoor test. The test results demonstrate that the characteristics of water vapor diffusion in unsaturated soil conformed to Fick’s second law. A mathematical model for water vapor diffusion under isothermal conditions in unsaturated soil was established based on Fick’s law. Factors including the initial moisture content gradient, initial moisture content distribution, soil type and temperature that affect the water vapor diffusion coefficient were analyzed. The results show that there was good agreement between the moisture content calculated by the mathematical model and obtained by the indoor experiment. The vapor diffusion coefficient increased with increasing initial moisture content gradient and temperature. When the initial moisture content gradient is constant, the vapor diffusion coefficient increases with the increase of matrix suction ratio in dry and wet soil section. The effect of soil type on the water vapor diffusion coefficient was complex, as both the moisture content and soil particle sizes affected the water vapor diffusion.

Drying of Fish Sardines in Oman Using Solar Tunnel Dryers

This paper deals with the design, construction and performance evaluation procedure of a solar tunnel dryer in drying fish. A 12 meter long and 2 meter width half-circled tunnel was designed and constructed to dry about 50-100 kg of freshly harvested fishes per batch. The half of the tunnel base was used as the flat plate air heating solar collector and the remaining half as a dryer. The drying air was forced from the collector region （north side） to the drying region （south side） of the half circled tunnel where the product is to be dried. The drying temperature could be easily raised by some 5-30 ℃ above the ambient temperature inside the tunnel at an air velocity of approximately 0.2 m/sec. The test was conducted with 51.5 kg freshly harvested sardines （hall-load） with initial moisture content of 66.5% （wet-basis） to analyze the performance of the dryer. The fishes were dried to a final average moisture content of 15.5% （wet-basis） within three days （30 hours）. It was possible to reach the moisture content level for safe storage within less than three days （30 hrs） with solar tunnel dryer and 7 days in open air natural sun drying. The improvement in the quality of fishes in terms of color, brightness, flavor, and taste and food value was distinctly recognized.

Numerical investigation on freeze-drying of aqueous material frozen with pre-built pores

Freeze-drying of the initially porous frozen material with pre-built pores from liquid material was found experimentally to save drying time by over 30% with an initial saturation being 0.28 compared with the conventional operation with the initial saturation being 1, using mannitol as the solid material. In order to understand the mass and heat transfer phenomena of this novel process, a two-dimensional mathematical model of coupled mass and heat transfer was derived with reference to the cylindrical coordinate system. Three adsorption–desorption equilibrium relationships between the vapour pressure and saturation value namely, power-law, Redhead's style and Kelvin's style equation, were tested. Kelvin's style in exponential form of adsorption equilibrium relation gave an excellent agreement between the model prediction and experimental measurement when the equation parameter, γ, of 5000 was applied. Analyses of temperature and ice saturation profiles show that additional heat needs to be supplied to increase the sample temperature in order to promote the desorption process. Simulation also shows that there is a threshold initial porosity after which the drying time decreased with the increase in the initial porosity. Enhanced freeze-drying is expected to be achieved by simultaneously enhancing mass and heat transfer of the process.

Experimental Study on the Dam-Break Hydrographs at the Gate Location

When studying the dam-break flow phenomenon,the basic hydrodynamic features of the dam-break flow at the gate location should be verified primarily.In this study,laboratory experiments were performed in a rectangular and horizontal flume with the same initial water head setting on the dry and wet downstream bed conditions.Water surface elevation was extracted through image analysis and validated by comparing with the data measured using a wave gauge.Temporal variation of the water surface elevation at the gate location,quantified in terms of high-speed video recorded images,can be divided into three stages,the sharp decreasing stage,the relatively steady stage,and the gradually decreasing stage.Applicability of several classic analytical solutions of the dam-break problem at the gate location was validated using present experimental data.Ritter's solution is effective for the dry bed condition while Stoker's solution could be applied to the wet bed case,and both are only applicable during the steady stage.Lin' solution reproduces the gate-site hydrographs well during both the relatively steady and the gradually decreasing stages,especially for the condition under which the down-upstream water depth ratio is smaller than 0.138.

Recent leveling off of vegetation greenness and primary production reveals the increasing soil water limitations on the greening Earth

Global vegetation photosynthesis and productivity have increased substantially since the 1980s,but this trend is heterogeneous in both time and space.Here,we categorize the secular trend in global vegetation greenness into sustained greening,sustained browning and greening-to-browning.We found that by 2016,increased global vegetation greenness had begun to level off,with the area of browning increasing in the last decade,reaching 39.0 million km^(2)(35.9%of the world’s vegetated area).This area is larger than the area with sustained increasing growth(27.8 million km^(2),26.4%);thus,12.0%±3.1%(0.019±0.004 NDVI a^(-1))of the previous earlier increase has been offset since 2010(2010–2016,P<0.05).Global gross primary production also leveled off,following the trend in vegetation greenness in time and space.This leveling off was caused by increasing soil water limitations due to the spatial expansion of drought,whose impact dominated over the impacts of temperature and solar radiation.This response of global gross primary production to soil water limitation was not identified by land submodels within Earth system models.Our results provide empirical evidence that global vegetation greenness and primary production are offset by water stress and suggest that as global warming continues,land submodels may overestimate the world’s capacity to take up carbon with global vegetation greening.

Carbon-water coupling and its relationship with environmental and biological factors in a planted Caragana liouana shrub community in desert steppe,northwest China

The carbon and water cycle,an important biophysical process of terrestrial ecosystems,is changed by anthropogenic revegetation in arid and semiarid areas.However,there is still a lack of understanding of the mechanisms of carbon and water coupling in intrinsic ecosystems in the context of human activities.Based on the CO,and H,O flux measurements of the desert steppe with the planted shrub Caragana liouana,this study explored the carbon and water flux coupling of the ecosystem by analyzing the variations in gross primary productivity(GPP),evapotranspiration(ET)and water use efficiency(WUE)and discussing the driving mechanisms of biological factors.The seasonal variation in climate factors induced a periodic variation pattern of biophysical traits and carbon and water fluxes.The GPP and ET fluctuated in seasons,but the WUE was relatively stable in the growing season.The GP,ET and WUE were significantly driven by global radiation(R,),temperature(T,and T),water vapor pressure deficit,leaf area index and plant water stress index(PWSI).However,R,temperature and PWSI were the most important factors regulating WUE.R,and temperature directly affected WUE with a positive effect but indirectly inhibited WUE by rising PWSl.Plant water stress inhibited photosynthesis and transpiration of the planted shrub community in the desert steppe.When the plant water stress exceeded a threshold(PWSI>0.54),the WUE would decrease since the GPP responded more quickly to the plant water stress than ET.Our findings suggest that policies related to large-scale carbon sequestration initiatives under afforestation must first fully consider the status of water consumption and WUE.