基于低场核磁共振的热风干燥猕猴桃切片含水率预测模型

为研究猕猴桃切片热风干燥过程中水分迁移规律,该试验通过对猕猴桃切片进行热风干燥,考察不同干燥温度(70、80、90℃)、切片厚度(3、4、5 mm)下的干燥特性。试验采用直接干燥法测定含水率,运用低场核磁共振技术(Low-Field Nuclear Magnetic Resonance,LF-NMR)分析热风干燥过程中猕猴桃切片内部水分分布状态与变化规律,建立动力学模型,验证并预测。结果表明:猕猴桃切片热风干燥开始为外部控制,随后属于内部扩散控制,水分有效扩散系数范围为1.58×10-7～4.18×10-7 m2/s,扩散效率随温度升高而增大。升高温度能显著提高猕猴桃干燥速率,可加快结合水、不易流动水以及自由水的迁移。自由水和结合水先于不易流动水发生变化,自由水含量在干燥前期逐渐下降,此过程中不易流动水和结合水含量均表现为先升高后降低的趋势。当自由水被脱除后,不易流动水和结合水含量依次达到最大值;此后,随着干燥的进行,不易流动水逐渐被脱除,此时结合水含量开始下降直至干燥结束。整个干燥过程中,猕猴桃切片部分自由水先转化为不易流动水和结合水,结合水与不易流动水相互转化,循环往复伴随整个干燥过程。以干燥过程中的自由水、结合水、不易流动水的核磁峰值总和、切片厚度和干燥温度为自变量,猕猴桃切片含水率为因变量,进行多元线性回归分析,建立含水率预测模型,模型的拟合优度为0.982。结果表明,低场核磁共振技术结合数学模型可用于描述猕猴桃切片热风干燥过程,可实现对猕猴桃切片干燥过程中含水率的快速、无损检测,研究结果可为猕猴桃热风干燥工艺和过程设计提供理论依据。     

箱式通风干燥机小麦干燥试验研究

为了解小麦平床通风干燥特性,该文以某型号箱式通风干燥机为试验设备,开展小麦收获后干燥试验研究,测试分析了干燥床风场分布、干燥床层含水率分布、温度分布及耗能等特性。研究表明,该设备在水平面和垂直面均存在较明显的干燥速度差异;在干燥6h结束时整个小麦床层的最大含水率差异超过3%,影响整批物料的干燥效率和干燥成本;干燥5h后整批物料含水率达到小麦贮藏要求,每1kg物料含水率下降5%的能耗成本为0.09元。根据试验研究结果,提出在入风口增加导风栅格、干燥仓体4个角采用圆弧过渡处理、采用气流换向机构和交替换向通风干燥工艺等改进措施来改善该设备干燥均匀性。研究结果为该类型干燥机的小麦干燥工艺优化及设备改进设计提供了依据。     

红枣片冷冻-红外分段组合干燥工艺优化

为开发一种提质增效的红枣片干燥工艺,比较了单一干燥（冷冻干燥、红外干燥、热风干燥和微波真空干燥）对红枣片干燥特性及品质的影响,选用冷冻与红外干燥分段组合的方法干制红枣片,以干燥时间和维生素C保留率为评价指标,采用三元二次通用旋转组合设计优化红枣片冷冻-红外组合干燥工艺参数,并与红外干燥（64℃,6.75 W/g）、冷冻干燥（-40℃,12 Pa,64℃）产品的干燥时间和品质进行对比分析。结果表明：1）冷冻与热风干燥的干燥时间最长,微波真空干燥最短,红外干燥次之;2）冷冻干燥产品品质较好,但酥脆性一般,红外干燥产品在色泽、质构（硬/脆度）、微观结构方面均好于热风和微波真空干燥产品,且酥脆性较好;3）转换含水率、红外温度和切片厚度对红枣片冷冻-红外组合干燥过程有显著影响（P<0.05）,对干燥时间影响主次顺序依次为转换含水率、红外温度、切片厚度,对维生素C保留率影响主次顺序依次为红外温度、转换含水率、切片厚度;4）采用响应曲面法优化与试验验证确定出较佳工艺参数为：转换含水率34 %、红外温度64℃、切片厚度5 mm,此时,干燥时间3.62 h,维生素C保留率68.92%;5）冷冻-红外组合干燥产品品质优于红外干燥,干燥时间比冷冻干燥缩短57.6%,维生素C保留率比红外干燥提高了34.6%。结果表明冷冻-红外组合干燥缩短了干燥时间同时保证了干燥品质,可为红枣片干制加工提供一种新的组合干燥技术和理论依据。     

哈密瓜变温压差膨化干燥工艺优化研究

为了对哈密瓜变温压差膨化干燥工艺进行优化,采用三因子二次回归正交旋转组合设计,分析预干燥后含水率、膨化温度和抽空时间3个变量对产品含水率、脆度、膨化度和色泽的影响,在此基础上由试验数据推导出描述4个指标的二次回归模型,并对变量进行响应面分析,得出优化膨化干燥工艺条件为:预干燥后原料含水率为30%,膨化温度为88～95℃,抽空时间为1.7～2.2 h.     

罗非鱼片热泵-微波联合干燥工艺

采用响应面分析法优化罗非鱼片热泵-微波联合干燥工艺参数。分别以干燥能耗和产品复水率为试验指标,以热泵干燥温度、转换点含水率、微波功率3因素为自变量,设计3因素3水平组合响应面分析试验,得出干燥能耗和产品复水率随热泵干燥温度、联合干燥转换点含水率和微波干燥功率变化的回归模型。三组验证试验的试验值与相应模型预测值的误差绝对值均小于5%。基于能耗最小的优化参数为:热泵干燥温度为34.34℃,转换点含水率为42.12%,微波功率为131.69 W;基于复水率最大的优化参数为:热泵干燥温度为33.87℃,转换点含水率为30%,微波功率为201.43 W。以热泵-微波联合干燥工艺参数组合(干燥温度为35℃,转换点含水率为39%,微波干燥功率取微波炉功率档252 W)进行试验,并与相同工况(温度和风速)热泵干燥试验值进行比较,结果表明,热泵-微波联合干燥时间比热泵干燥时间缩短了2/3;热泵-微波联合干燥罗非鱼片复水40 min,复水率达到57.40%,比热泵干燥的复水率(39.16%)增加46.5%。该文为热泵—微波联合干燥罗非鱼提供参考。     

鸡粪中低温干燥动力学特性与参数优化

为了研究鸡粪的中低温干燥特性,利用恒温鼓风干燥箱,以干燥温度、粪层厚度、风速为因素研究了鸡粪含水率和干燥速率随时间变化的规律,用常见的薄层干燥模型对鸡粪的干燥曲线进行了拟合分析,并用正交试验优化了鸡粪干燥工艺参数。结果表明:鸡粪的中低温干燥过程由2个降速阶段组成,第2降速阶段的干燥速率相对于第1降速阶段下降更快。干燥温度越高,粪层厚度越小,风速越大,干燥速率曲线出现拐点的时间越早,达到干燥平衡所用时间越短;Exponential模型能较好的模拟鸡粪的干燥过程;在中低温条件下,根据Fick定律得到2~6 cm粪层厚度鸡粪的有效扩散系数在2.25×10–7~2.35×10–6 m2/h间;用正交试验得到鸡粪中低温干燥时效率最高的工艺为:干燥温度55℃,粪层厚度6 cm,风速1.2 m/s,该工艺下鸡粪的干燥效率为0.47 h/g。     

固定床上下换向通风小麦干燥模拟与工艺优化

为了研究固定床上下换向通风干燥机理,确定合理烘干工艺参数,根据通风加热干燥过程中小麦和介质空气之间热质传递关系,采用经典PDE模型为理论基础,建立了适用于小麦固定床换向通风干燥计算机模拟的离散化模型。此模型可计算出小麦实时干燥状态、批次小麦干燥耗时、能耗经济成本等,并能依此推算出最优作业参数。经实际验证,模型模拟计算结果与试验结果基本相符,整床层小麦平均含水率模拟值和试验值的相关系数r达0.995,模型模拟可用于不同环境温度和相对湿度下的最优通风温度和风量分析。论文分析了换向通风干燥过程床层小麦含水率和温度变化规律;根据小麦收获时天气状况,选择环境温度20~35℃,环境相对湿度20%~85%范围,以批次烘干单位质量湿小麦能耗成本最低为优化判据,确定通风温度、风量及对应单位质量小麦烘干能耗成本,为实际小麦烘干工艺参数设定提供参考。     

干切牛肉冷冻干燥中解析干燥过程的动态模拟及优化

该文通过对干切牛肉冷冻干燥中解析阶段含水率、物料温度的动态模拟及干燥速率与耗能分析,确立干切牛肉冷冻干燥中解析干燥的优化操作条件。通过建立解析阶段中脱除水分所需干燥时间以及相应的物料表面温度、物料中心温度的数学模型,并假设解析干燥过程中物料含水率由升华结束时的10.0%下降到干燥结束的0,以含水率变化为自变量,模拟了物料厚度为6、8、12、15 mm的干切牛肉在干燥室压强10 Pa,加热板温度80℃的操作条件下含水率、物料温度随时间的动态变化。以所建模型预测厚度7、9、10、11、12、13、14 mm的干切牛肉在该操作条件下含水率、物料温度的动态值及解析干燥周期。验证试验表明：预测与实测含水率相对误差小于10%,物料中心温度计算值与实测值的绝对误差小于5℃,说明所建模型可用于模拟、预测6～15 mm干切牛肉冷冻干燥中解析干燥阶段的参数变化。比较不同厚度干切牛肉冷冻干燥中解析干燥阶段的干燥比耗时、干燥效率,结果是采用6 mm厚度切片进行干燥,生产单位产品耗能最低,且生产率最大。     

稻谷干燥温度对稻米食味品质影响规律的研究

研究了干燥条件对稻米理化成分的影响。试验结果表明,干燥温度是导致稻米食味下降的主要因素。高温干燥后稻米脂肪酸和直链淀粉含量升高,蛋白质含量变化不显著,内部结构由有序排列变得杂乱无序,并提出了稻谷临界干燥温度与初始含水率关系式T=e^{(5.021-0.058M)},这对保证稻米干燥后食味品质有很大意义     

高水分稻谷干燥工艺试验研究

针对中国南方地区稻谷收获季节需及时干燥高水分稻谷的市场要求,采用试验方法,在分批循环式稻谷干燥机上试验了低恒温干燥、变温干燥和变温干燥过程中增加缓苏时间的三种干燥工艺。依据试验结果,分析稻谷含水率、干燥介质温度、稻谷温度、缓苏烘干时间比等参数之间的联系与相互作用。试验表明：稻谷含水率高于21%时,降水速率可大于每小时1%,可采用60～70℃的介质。当稻谷含水率小于18%时,介质温度应小于60℃,降水速率小于每小时1%。当高水分稻谷进行了3～4次烘干缓苏后,利用中间缓苏仓增加缓苏时间,使稻谷内部与表层的温度、水分趋于平衡,有利于改善烘后品质和后续工艺的干燥降水。该结论对高水分稻谷干燥工艺设计和设备研制具有实用参考价值。     

低氮和干旱胁迫对富士和秦冠生长及氮素利用的影响

【目的】以富士（Fuji）、 秦冠（Qinguan）嫁接在平邑甜茶（Malus hupehensis Rehd.）上的当年生盆栽苗为试验材料,采用砂培方法,研究了缺氮胁迫和干旱对富士和秦冠生长情况、 光合参数、 植株各部位氮磷钾含量及氮素利用效率的影响,分析比较了低氮干旱条件下富士和秦冠生长及氮素利用的差异,以期为果树生产高效肥水利用提供理论指导。【方法】试验共设四个处理: 正常氮正常水（ZZ）、 低氮正常水（DZ）、 正常氮干旱（ZG）、 低氮干旱（DG）。氮素和水分均设置两个水平,分别为正常氮（6 mmol/L NO-3-N）、 低氮（0.3 mmol/LNO-3-N）、 正常供水（保持盆中砂子相对含水量为饱和含水量的80%~85%）、 干旱处理（保持盆中砂子相对含水量为饱和含水量的60%~65%）。【结果】富士和秦冠的生物量（茎和叶）、 株高茎粗等生长指标以及光合速率、 气孔导度、 蒸腾速率均为正常氮正常水（ZZ）＞低氮正常水（DZ）＞正常氮干旱（ZG）＞低氮干旱（DG）,并且相对应处理下秦冠的以上指标均高于富士;正常供水下,缺氮处理使富士、 秦冠的根冠比比正常氮处理均有所增加,富士提高了2.05%,秦冠提高了22.40%。富士和秦冠的氮、 磷、 钾含量均表现出正常氮正常水（ZZ）＞低氮正常水（DZ）＞正常氮干旱（ZG）＞低氮干旱（DG）; 氮、 钾元素含量在植株各部位的分布顺序依次是叶＞根＞茎,磷元素则是根＞叶＞茎;光合氮素利用效率（PNUE）和氮素利用效率表现为秦冠处理之间差异极显著,富士处理之间差异不显著;秦冠的PNUE和NUE明显高于富士,在低氮正常水（DZ）处理下,秦冠氮肥利用率比富士高42.07%,在低氮干旱（DG）处理下高64.14%;低氮胁迫下富士和秦冠的NUE显著提高,并且秦冠提高的幅度高于富士。【结论】施用氮肥能够显著提高富士与秦冠的干物质量,同等水肥条件下,秦冠生长优于富士;水分亏缺会减少叶片对氮的吸收,干旱条件下适度增施氮肥,可提高果树的抗旱能力;低氮干旱胁迫下秦冠的生长指标、 光合指标及氮素利用效率指标均优于富士,表现出较强的抗低氮干旱胁迫的能力。     

Pasture Vegetation Elemental Analysis by Laser-Induced Breakdown Spectroscopy

Laser-induced breakdown spectroscopy (LIBS) is a new technique for the analysis of plant material. This study investigates the application of LIBS to pasture-based plant samples. The LIBS measurements were obtained from pelletized pasture samples (100 samples) that had been also analyzed by inductively coupled plasma–optical emission spectroscopy (ICP-OES) following microwave digestion for calibration and comparison purposes. Comparisons for elements sodium (Na), potassium (K), magnesium (Mg), calcium (Ca), manganese (Mn), iron (Fe), copper (Cu), zinc (Zn), boron (B), phosphorus (P), and sulfur (S) showed that LIBS could be used for almost all the standard profile total elements with concentrations down to low mg/kg levels (observed error of Na: 0.024 percent, K: 0.18 percent, Mg: 0.016 percent, Ca: 0.073 percent, P: 0.017 percent, Mn: 31 mg/kg, Fe: 150 mg/kg, Zn: 6.6 mg/kg, and B: 1.1 mg/kg). Elemental analysis at less than mg/kg levels was not possible using LIBS. The elements S and Cu were particularly difficult to analyze with reliability using LIBS at the concentration levels found in the plant samples. Replacing microwave digestion and subsequent ICP analysis with a direct analysis of dried plant samples using LIBS has the potential to improve the productivity and reduce the cost of testing.     

Faculty positions:Center for Agricultural Resources Research,Chinese Academy of Sciences

正The Center for Agricultural Resources Research(CARR),the Institute of Genetics and Developmental Biology(IGDB),Chinese Academy of Sciences,invites applicants for several research group leader positions.CARR is one of the research organizations in Chinese Academy of Sciences(CAS).We seek nominations and applications from individuals who have expertise and a record of accomplishment in research areas related to ecology,agro-hydrology,     

Macroinvertebrates in North American tallgrass prairie soils: effects of fire, mowing, and fertilization on density and biomass

The responses of tallgrass prairie plant communities and ecosystem processes to fire and grazing are well characterized. However, responses of invertebrate consumer groups, and particularly soil-dwelling organisms, to these disturbances are not well known. At Konza Prairie Biological Station, we sampled soil macroinvertebrates in 1994 and 1999 as part of a long-term experiment designed to examine the effects and interactions of annual fire, mowing, and fertilization (N and P) on prairie soil communities and processes. For nearly all taxa, in both years, responses were characterized by significant treatment interactions, but some general patterns were evident. Introduced European earthworms (Aporrectodea spp. and Octolasion spp.) were most abundant in plots where fire was excluded, and the proportion of the total earthworm community consisting of introduced earthworms was greater in unburned, unmowed, and fertilized plots. Nymphs of two Cicada genera were collected (Cicadetta spp. and Tibicen spp.). Cicadetta nymphs were more abundant in burned plots, but mowing reduced their abundance. Tibicen nymphs were collected almost exclusively from unburned plots. Treatment effects on herbivorous beetle larvae (Scarabaeidae, Elateridae, and Curculionidae) were variable, but nutrient additions (N or P) usually resulted in greater densities, whereas mowing usually resulted in lower densities. Our results suggest that departures from historical disturbance regimes (i.e. frequent fire and grazing) may render soils more susceptible to increased numbers of European earthworms, and that interactions between fire, aboveground biomass removal, and vegetation responses affect the structure and composition of invertebrate communities in tallgrass prairie soils.     

Variation in quality parameters between and within 14 Nordic tree fruit and berry species

Abstract

A 3-year study was carried out to investigate quality parameters in 14 tree fruit and berry species grown in southern Norway. The species were blueberry, apple, aronia, sour cherry, sweet cherry, red raspberry, strawberry, blackcurrant, gooseberry, red currant and elderberry, harvested along with wild bilberry, cloudberry and lingonberry. Significant differences between species were identified for all quality parameters. The coefficient of variation between species was lowest for pH (12.5%), dry matter (18.9%) and soluble solids (25.3%), followed by titratable acids (59.3%), total phenolics (83.8%), antioxidant capacity FRAP (85.7%) and antiradical power by the DPPH-assay (97.8%), total monomeric anthocyanins (132%) and ascorbic acid (137%). Average coefficient of variation within species were lower and ranged from 4 (pH) to 62% (ascorbic acid). Only the FRAP values were significantly affected by harvesting year with lower levels in 2004 than in 2005 and 2006. There were significant interactions between species and harvesting year for dry matter, soluble solids, pH, ascorbic acid and FRAP. The results indicate generic ranges in composition within species independent upon growing location and climate, and the composition of the tree fruits and berries is not likely to deviate from these ranges. It is concluded that desirable composition of tree fruits and berries and their products should primarily be achieved by selection among species rather than searching fors broadened variation within individual species.     

Potassium Fixation and Release Characteristics in Rhizosphere and Nonrhizosphere Soils for a Rapeseed–Rice Cropping Sequence

Potassium (K) fixation and release in soil are important factors in the long-term sustainability of a cropping system. Changes in K concentration and characteristics of K fixation and release in rhizosphere and nonrhizosphere soils in the rapeseed (Brassica napus L.)–rice (Oryza sativa L.) rotation were investigated using a rhizobox system. The concentrations of different forms of K in both rhizosphere and nonrhizosphere soils decreased with plants compared to without plants, regardless of K fertilizer application. Potassium uptake by crops mainly came from the rhizosphere soil. In the treatment without K fertilizer (–K), the main form of K supplied by the soil to the crops was 1.0 mol L^?1 nitric acid (HNO₃) nonextractable K, followed by nonexchangeable K, and then exchangeable K. In the treatment with K fertilizer (+K), the main K forms supplied by the soil to the crops were exchangeable K and nonexchangeable K. The amount and rate of K fixation after one cycle of the rapeseed–rice rotation was greater in rhizosphere soil than in nonrhizosphere soil. The amount and rate of K fixation of soil in the +K treatment were significantly less than in the –K treatment. The cumulative amounts of K released with 1.0 mol L^?1 ammonium acetate (NH₄OAc) and 1.0 mol L^?1 HNO₃ extraction increased with the increasing numbers of extractions, but the K-releasing power of soil by successive extraction decreased gradually and finally became almost constant. The release of K was less in rhizosphere soil than in nonrhizosphere soil. The release of K in the +K treatment was similar to that in the –K treatment in rhizosphere soil, but the K release in nonrhizosphere soil was greater with the +K than the –K treatment. Overall, the information obtained in this study will be helpful in formulating more precise K fertilizer recommendations for certain soils.     

Electron donor and pH relationships for biologically enhanced dissolution of chlorinated solvent DNAPL in groundwater

Biologically enhanced dissolution offers a method to speed removal of chlorinated solvent dense non-aqueous-phase liquid (DNAPL) sources such as tetrachloroethene (PCE) and trichoroethene (TCE) from aquifers. Bioremediation is accomplished by adding an electron donor to the source zone where fermentation to intermediates leading to acetic acid and hydrogen results. The hydrogen and possibly acetic acid are used by dehalogenating bacteria to convert PCE and TCE to ethene and hydrochloric acid. Reductive dehalogenation is thus an acid forming process, and sufficient alkalinity must be present to maintain a near neutral pH. The bicarbonate alkalinity required to maintain pH above 6.5 is a function of the electron donor: 800 mg/L of bicarbonate alkalinity is sufficient to achieve about 1.2 mM TCE dechlorination with glucose, 1.7 mM with lactate, and a much higher 3.3 mM with formate. Laboratory studies indicate that in mixed culture, formate can be used as an electron donor for complete conversion to ethene, contrary to pure cultures studies indicating it cannot. Various strategies can be used to add electron donor to an aquifer for DNAPL dehalogenation while minimizing pH problems and excessive electron donor usage, including use of injection-extraction wells, dual recirculation wells, and nested injection-extraction wells.     

Biodiversity and ecogeography of wild Lactuca spp. in some European countries

Staff members of the Department of Botany of Palacký University in Olomouc and Gene Bank Department – Workplace Olomouc, Research Institute of Crop Production in Prague, Czech Republic, conducted an expedition in seven European countries (Austria, Czech Republic, France, Germany, Italy, the Netherlands, Switzerland) in August/September 1999 to collect wild Lactuca spp. germplasm and study its geographic distribution, ecology and biodiversity. During the mission, more than 600 locations were visited resulting in the collection of 602 seed samples (accessions) of wild Lactuca species and 13 seed samples of related genera (Chondrilla and Mycelis). Lactuca serriola f. serriola, L. serriola f. integrifolia, L. saligna and L. viminea subsp. chondrilliflora were prevalent in southern Europe (Italy, France), however, only L. serriola was common in central and western Europe (Austria, Czech Republic, Germany, Netherlands, Switzerland). The greatest diversity of Lactuca species was found in France, where also the most seed samples (165) were collected. The most characteristic habitats with a high density of Lactuca spp. populations were observed along roads and highways, grassy ditches, ruderal communities, and dust-heaps. Natural infections by powdery mildew (Erysiphe cichoracearum) and downy mildew (Bremia lactucae) on some wild Lactuca spp. were observed. Recent observations concerning the geographic distribution, population structure, habitats, and natural occurrence of diseases of Lactuca spp. are discussed. This assemblage of genetic resources of Lactuca spp. can serve as the basis of future studies of species diversification, spatial population structure, plant microevolution, domestication processes, and genetic variability of host-parasite interactions.     

Increase in auxiliary photoprotective photosynthetic pigments in wheat seedlings induced by Azospirillum brasilense

Inoculation of wheat seedlings with the plant growth-promoting bacterium Azospirillum brasilense Cd was immobilized in alginate microbeads and, without applying any stress, significantly increased the quantity of several photosynthetic pigments, such as chlorophyll a, chlorophyll b, and the auxiliary photoprotective pigments violaxanthin, zeaxanthin, antheroxanthin, lutein, neoxanthin, and β-carotene. This resulted in greener plants with no apparent visible stress. After monitoring the quantity of photosynthetic pigments for 4 weeks, we observed that inoculated plants had higher quantities of pigments in shoot and stem. The greatest difference in the quantity of all pigments between inoculated and noninoculated plants occurred in the first week of growth. Regardless of treatment, the quantity of pigments in stems was three to four times less than the quantity of these pigments in shoots. Application of Azospirillum, either as liquid inoculant or as alginate microbeads, did not alter the positive effect of the bacteria on pigment production or the positive response of the plants towards A. brasilense Cd inoculation.     

In-situ enrichment and analysis of atrazine-degrading microbial communities using atrazine-containing porous beads

We examined the community composition of microbes that colonized atrazine-containing beads buried in agricultural soils that differed in atrazine treatment history. Bacterial abundance was 5-40-fold greater in atrazine-fortified beads. In beads containing 20 mg atrazine kg⁻¹ buried in soil with a history of atrazine application (conditioned soil), the abundance of Actinobacteria increased approximately 80-fold whereas in control soil, Actinobacteria were enriched only 10-fold and the gamma-Proteobacteria and Planctomycetes increased by 60- and 25-fold, respectively. The gamma-Proteobacteria were enriched by 120- and 230-fold in beads containing 200 mg atrazine kg⁻¹ in conditioned and control soil, respectively. The results demonstrate that BioSep^® beads are a suitable matrix for recruiting a diverse subset of the bacterial community involved in atrazine degradation.