在简单随机抽样中样本容量的确定

在简单随机抽样中,用下列关系式(Freese 1962)估算样本容量。n=(t~2s~2/E~2)(1)或者 n=(Nt~2s~2/NE~2 t~2s~2)(2)式中:N 总体容量n 估计的样本容量E 样本平均数和未知总体平均数之间的最大允许误差s 总体标准差的估计值     

统计估计与检验中样本容量的近似计算法

本文给出了林业科研及生产上常用的估计与检验中样本容量的近似计算公式。利用公式算出的n值是使试验达到指定要求的样本容量最低限度。因此,可最大限度地缩短试验时间,减少试验费用。关于平均数的公式,既适用大样本,也适用小样本。     

大麻体细胞的染色体数目及其核型分析

以"云麻1号"的大麻芽株为试材,对大麻体细胞染色体的数目及其核型进行了研究,结果表明:大麻体细胞染色体的数目为2n=20,染色体核型公式为2n=20=2x=14 m 6 sm,属于2A型染色体,其N.F值为40,着丝点端化值(T.C.%)为56.35 %.     

叶艺兰辐射突变体的气孔特征与染色体核型分析

为阐明辐射诱发的叶艺兰植株与未经诱变植株的差异,以经辐射诱发的叶艺兰植株(TRIR-2)与未经诱变的全绿植株(TRIR-1)为试材,运用显微镜观察植物叶片的气孔及根尖细胞的染色体并使用Photoshop软件对染色体进行分析。结果表明,(1)TRIR-2的气孔数量、面积、密度值均小于TRIR-1;(2)TRIR-1植株的染色体核型公式为2n=2x=10m+24sm+6st,属较为对称的"2B"型;TRIR-2植株的染色体核型公式为2n=2x=10m+28sm+2st,属不对称的"2C"型。说明辐射诱变产生的叶艺兰突变体气孔特征和染色体结构发生了变化。     

DTOPSIS法在柠条品系综合评价中的应用

应用DTOPSIS法对21个供试的柠条材料的10个性状进行了综合评价,结果表明：Tun-3和Tun-2的Ci值排在第1位和第2位,是综合性状较好的2个柠条品系。     

接触角法测量马来海松酸改性双组分水性聚氨酯的表面能

将亲水改性的多异氰酸酯分别与马来海松酸改性聚酯多元醇(MPP)、聚酯多元醇(PP)和Bayhydrol D270聚酯多元醇水分散体进行复合交联制得MPP-2K-WPU、PP-2K-WPU和D270-2K-WPU,并采用FT-IR和DSC对产物进行表征。利用接触角法研究了n(—NCO)∶n(—OH)及多元醇组分种类对2K-WPU涂膜接触角、表面能和耐水性的影响,并采用Equation of State法和Owens-Wendt-Rabel-Kaelble法对试验数据进行分析。结果表明,与甲酰胺系列(甲酰胺、甲酰胺-二碘甲烷)检测液体相比,水系列(水、水-二碘甲烷)检测液体能更好地对2K-WPU涂膜表面性能进行描述;随着n(—NCO)∶n(—OH)的增加,MPP-2K-WPU的表面能先减小后增大,耐水性呈现先增强后减弱的趋势,当n(—NCO)∶n(—OH)为1.5∶1时其表面能最小、耐水性最强;与2种对照样(PP-2KWPU和D270-2K-WPU)相比,MPP-2K-WPU的表面能最小且耐水性最强。     

脱水蓖麻油聚酰胺-环氧树脂体系的固化反应动力学研究

由脱水蓖麻油制得聚酰胺固化剂,并用差示扫描量热法(DSC)研究了该固化剂与环氧树脂体系(DCOPA-EP)的固化反应动力学.综合采用Kissinger、Crane和Malek等方法探讨DCOPA-EP固化体系的固化动力学模型参数.由Kissinger方法算得表观活化能( E a)55.94kJ/mol,频率因子( A )1.61×107s-1;并经过分析验证,Malek法所得自催化反应模型(反应级数 m ＝0.135, n ＝0.766)比Crane法的 n 级反应模型(反应级数 n =0.90)更适合DCOPA-EP固化体系.     

极差例释

利用样本极差W估算标准差б的优点是运算简便,且样本大小n很小时,估计效率也颇高(表1)。表1n 2 4 5 6 7 8 10 00效率% 100 98 96 93 91 89 85 0估算的依据是,W的数学期望与б成正比,所以可用W/dn作为标准差的一个无偏估计。这里的dn为W/б的均值,其值见表2的第二     

膦腈环核腰果酚环氧树脂的制备及表征

以腰果酚、六氯环三磷腈(HCCP)为原料,利用NaH作为缚酸剂制备了膦腈环核六取代腰果酚(HCPP),并采用H_2O_2/HCOOH体系对HCPP进行环氧化反应得到膦腈环核腰果酚环氧树脂(EHCPP),实验优化了EHCPP的合成条件,并采用FT-IR和~1H NMR对中间产物HCPP和最终产物EHCPP进行了分析和表征。实验结果表明:EHCPP较佳合成条件为以腰果酚的双键为基准,n(双键)∶n(甲酸)=1.0∶1.0,n(双键)∶n(H_2O_2)=1.0∶1.8,催化剂TsOH添加量为1%(以HCPP质量为基准),反应温度65℃,反应时间6 h;此条件下得到的产物EHCPP环氧值为4.1 mmol/g。FT-IR和~1H NMR分析结果表明:实验得到的HCPP和EHCPP的结构与预期结构基本相符。     

检测方法对混凝土强度值影响的差异探讨

阐述了回弹法和试块抗压强度法对混凝土的强度进行检测,回弹值与试块抗压强度值之间的关系,并运用数理统计方法,总结回弹值与试块抗压强度值之间关系的修正系数,对影响检测抗压强度的各种因素作了综合分析,提出了提高检测精度的应对措施。     

简支变连续小箱梁裸梁静载试验研究

简支转连续箱梁桥是现今公路与城市道路桥梁中一种常用的桥梁结构形式。在结构体系转换前单根小箱梁裸梁是处于简支状态。本文提出一种确定简支转连续小箱梁裸梁静荷载试验加载内力的计算方法,并采用加载块等效的方法对小箱梁裸梁进行静力荷载试验加载,对裸梁承载能力进行了评定测试与评估,结果表明,计算方法与试验满足评估要求。     

25种优良阔叶树种育苗技术研究

通过对吉安双江林场和南昌树木园3年生25个优良阔叶树种的育苗试验,表明采用常规育苗方法可培育出供生产用的合格苗木,但各树种在育苗时的种子催芽方法不尽相同,播种时间有所差异,同时对苗木的根系及苗木的产苗量进行了初步的探讨。     

用软X射线检验林木种子发芽率的研究

采用HY-35型软X-射线仪对杉木、柳杉,马尾松和香椿等15个树种的种子进行摄影,并进行定位发芽试验。根据各树种种子X光片的成像特征,得出各树种种子各等级的判定粒效(百分比)。将各等级种子进行合理累加,用差异最小的值估测发芽率,其结果与定位发芽试验所得发芽率基本相符。由此认定,此法可以作为测定林木种子发芽率的重要方法加以推广应用。     

大跨预应力混凝土连续刚构桥承载能力试验与评定

为了判定连续刚构桥梁在试验荷载作用下的实际工作性能和承载能力,评价桥梁的施工质量,本文以松原龙华松花江特大桥为实例,运用有限元法对该桥进行理论分析,以此为基础对该桥竣工阶段进行静载试验,对控制截面的挠度和应变进行测试分析。依据试验结果,运用交通部公路科学研究院颁布的《公路桥梁承载能力评定规程》中的承载力评定方法对该桥进行承载能力评定。评定结果说明该桥承载能力满足设计要求,主梁处于良好的弹性工作状态,可以正常使用。同时根据分析时发现的问题提出该种结构在设计和施工上应该注意的问题,为以后该种桥型的建设提供借鉴。     

江西九连山国家级自然保护区有效管理评价

采用《自然保护区经营管理评价技术规范》中的指标赋分值及"中国林业系统自然保护区管理能力与管理效果评价"项目的调查方法和因子筛选法确定评价因子,对江西九连山国家级自然保护区有效管理进行量化评价。     

Load sharing and weakest lamina effects on the compressive resistance of cross-laminated timber under in-plane loading

A new approach was developed to predict the compressive resistance of cross-laminated timber (CLT) using the compressive strength of small samples of different grade lamina from E12 and E8 larch, and E10 and E6 nut pine. CLT of three different thicknesses was manufactured using different grades of laminas from each species. To evaluate the compressive resistance of CLT, three different methods were employed. The first method was used to determine the compressive resistance, which was predicted by multiplying the compressive strength of lamina aligned with the loading direction, and the cross-sectional areas of the lamina. The second method is similar to the first method, but additionally considering the stiffness ratio of the laminas. The third method developed from the current study accounts for load sharing and weakest lamina effects in the prediction of compressive resistance. When the lower 5th percentile compressive resistance in a major direction was predicted using the first two methods, the difference between the experimental test and the predicted value ranged from 2.5 to 43.4%. However, when the compressive resistance in a major direction was predicted using the developed method from the current study, the difference between the experimental test and predicted value ranged from ??8.7 to 10.8%.     

An experimental approach to determine pull-out strength of single and multiple axially loaded steel rods bonded in glulam parallel to the grain

ABSTRACT

A glued-in rods' connection is generally constituted by a group of steel bars bonded by an adhesive into timber elements. In the past, most of the research focused on single-rod connections, in order to exploit the maximum resistance of the connection without accounting for interaction among bars or splitting failure in the timber member due to close edge distances or spacing between bars. Such interaction problems arise when dealing with multiple rods, thus requiring specific investigation to fully understand the behavior of the connection as a whole and to determine its capacity. In both cases, existing test procedures determine bond strength in specific geometrical configuration. The paper aims to determine the pull-out strength of single and multiple axially loaded steel rods bonded in glulam parallel to the grain differentiating the adhesive failure from the other failure modes. After an initial review of typical applications and existing design procedures, test results on single rod with confined or unconfined test setup on single rod at different embedment depths are presented and discussed, indicating that the confinement has a negligible influence on the pull-out capacity. Subsequently, interaction between bars is investigated by a specific unconfined configuration. The accounted parameters are the embedment depth of the bars, the dimensions of the timber section, and the spacing between bars. Results are discussed and compared with three-dimensional numerical simulations. Both experimental and numerical results suggest that the critical value at which the transition from pull-out to timber-related failure is observed depends on the mechanical properties of the timber and on the properties of the adhesive, such that a single value of spacing should not be provided in design standard if the full capacity of the adhesive is to be exploited.     

Der Nachweis winterlicher SO2-Immissionen an jungen Fichten Ein Vergleich dreier Methoden

The detection of winter SO₂ pollution effects on young spruce. A comparison of three methods. The suitability, sensitivity and tediousness of three methods (turbidity-test, peroxidase activity, buffering capacity) were compared for detecting the effect of SO₂ pollution in winter on spruce seedlings. Buffering capacity failed to detect a difference between controls and fumigated trees. Turbidity test and peroxidase activity yielded statistically significant differences. The turbidity test is less tedious but also less sensitive than peroxidase activity and its use is restricted to conifers.     

Storability measures of Norway spruce and Scots pine seedlings and assessment of post-storage vitality by measuring shoot electrolyte leakage

As indoor frozen storage is increasing in forest tree nurseries it is important to have accurate methods for assessing seedling storability in autumn and methods to determine post-storage vitality. Storability of spruce (Picea abies (L.) Karst.) and pine (Pinus sylvestris L.) seedlings can be based on determination of dry matter content (DMC) of seedling shoots or by freezing shoots at –25°C and thereafter measure electrolyte leakage (SEL_diff–25). To compare these two methods we stored 1-year-old spruce and pine seedlings at different occasions during the autumn. To test if leakage of electrolytes from shoots (SEL) could indicate deteriorated vitality, we measured SEL at the end of storage. After storage seedling viability was determined in a three-week growth test, measuring shoot and root growth capacity (RGC). Determination of freezing tolerance (SEL_diff–25) before storage had a better ability to predict the outcome of storage compared to the DMC test. Measuring SEL at the end of the frozen storage period accurately indicated seedling vitality. Seedlings with SEL of 0–5% had a high survival rate whereas SEL over 10% indicated low survival and growth capacity after storage. The SEL method has a potential to become a screening test for identifying batches of seedlings that have been damaged during storage in the nursery.     

不同干燥方式对黑果腺肋花楸果粉品质的影响

【目的】通过比较3种干燥方式所得黑果腺肋花楸果粉的物理特性、活性物质含量和体外抗氧化活性的差异,评价不同干燥方式对果粉品质的影响。【方法】以黑果腺肋花楸果为试材,分别采用热风干燥、真空冷冻干燥及喷雾干燥3种干燥方式对黑果腺肋花楸果进行干燥。通过Lab颜色模型评价果粉色泽,pH值示差法测定花色苷含量,比色法测定总酚、黄酮含量以及DPPH自由基能力、总抗氧化能力,并对果粉的溶解性、分散性、堆积密度、流动性等物理性质进行分析。【结果】不同的干燥方式对黑果腺肋花楸果粉的物理特性、生物活性物质含量及体外抗氧化能力具有显著的差异性影响。通过真空冷冻干燥方式制得的果粉具有最优的分散性能并且最大程度的保留了生物活性物质,总酚(42.29 mg/g)、黄酮(41.50 mg/g)、花色苷(2.21 mg/g)的含量最高,较其他干燥方式果粉呈现极显著差异(P <0.01),体外抗氧化能力最强,果粉的综合性能优越;通过喷雾干燥方式制得的果粉具有良好的物理性能,含水率最低,溶解性、流动性、色泽极显著优于其他果粉(P <0.01),但是高温致使生物活性物质失活导致黄酮含量、总酚含量、花色苷含量最低,体外抗氧化能力最差;热风干燥方式制得的果粉得率(15.98%)最高,但是果粉物理性质、生物活性物质含量及体外抗氧化的能力显著低于其他干燥方式(P <0.05)。【结论】综合评价黑果腺肋花楸果粉的品质和干燥效率,真空冷冻干燥适宜在黑果腺肋花楸果粉加工产业推广应用。