木材斜角切削时垂直分力的研究

根据试验结果研究了在木材斜角切削时,垂直于切削方向上的分力与刃倾角及法面前角的关系。试验分为斜角纵向切削和斜角横向切削两部分,采用两种试材和两种切屑厚度。通过试验,找出了刃倾角和法面前角对垂直分力的影响规律;通过数学分析,对垂直分力的计算方法进行了研究。     

厚胶合板弹性模量预测模型

为了预测厚胶合板弹性模量,通过简化层合板理论,该文建立了胶合板弹性模量预测模型,并以单板条、经过涂胶热压处理的单板条和相同工艺条件下的单板层积材的弹性模量,采用4种不同铺层方式的19层桉树胶合板对模型进行了验证。结果表明:3种预测值与实测值的趋势一致,相关系数R2顺纹在0.86以上,横纹在0.88以上,但是精度不同。采用单板条弹性模量预测的胶合板弹性模量比实测值偏低;采用经过涂胶热压处理后的单板条弹性模量预测的胶合板弹性模量比实测值偏高;采用相同工艺条件下的单板层积材弹性模量预测的胶合板弹性模量与实测值偏差较小,顺纹平均误差为4.64%,横纹平均误差10.94%。因此,采用相同工艺条件下的单板层积材的弹性模量来预测胶合板的弹性模量是可行的。      

琵琶共鸣面板的振动模态分析

为研究琵琶共鸣面板的声学振动性能，采用快速傅里叶变换频谱分析仪测定了共鸣面板在0～1 000 Hz频率范围内的各阶振动频率，并分析了各阶振动频率对应的振动模态。结果表明:共鸣面板的振动可以分成顺纹理方向弯曲振动、横纹理方向弯曲振动、顺纹理与横纹理方向弯曲振动叠加而成的扭转振动3种，但扭转振动的振型并不是简单地由2个方向的弯曲振动叠加而成；各阶振动振型基本呈y轴（顺纹理方向）对称，但并不完全呈x轴（横纹理方向）对称，这主要是由琵琶共鸣面板的仿梨形结构决定的；对于（0,n）、（1,n）、（2,n）、（3,n）的各阶频率，当n值由0逐步增大时，共振频率的变化具有相似的增长趋势。      

风向对温室内气流分布模式影响的CFD分析

以自然通风的Venlo型两连栋玻璃温室为研究对象,基于CFD数值方法,以流体控制方程和标准湍流模型为理论依据,结合DO辐射模型对室外风向垂直屋脊和平行屋脊两种工况下室内气流分布模式进行了3-D数值模拟。结果发现风向垂直屋脊时侧窗外侧存在两个对称涡流,侧窗是主要进风口;室内气流速度随高度呈上升趋势;室内东侧流速较西侧低。风向平行屋脊时,侧窗气流流动复杂,天窗是主要进风口;气流速度随高度呈下降趋势;室内东侧流速较西侧高。两种风向下南北向流速分布相对均匀一致。室外风向对室内气流分布模式有明显影响。     

Large-scale, low-amplitude bedforms (chevrons) in the selima sand sheet, egypt

Landsat images of the Selima sand sheet in southwestern Egypt display alternating light and dark chevron-shaped patterns that occur downwind from low scarps and major dune fields. Images acquired between 1972 and 1988 indicate that these features move as discrete bedforms at a rate of up to 500 meters per year. Extremely long-wavelength (130 to 1200 meters), low-amplitude (10 to 30 centimeters) bedforms were measured in the field; the light chevrons seen in the orbital data may be thin accumulations of active sand sheet deposits in the lee of these bedforms. Dark chevrons contain an admixture of coarse-granule lag deposits that are continually winnowed by aeolian erosion on the windward sides of the large bedforms. Sediment transport budgets derived from orbital and field analyses suggest net movement of up to 83,000 cubic meters per year for a single light chevron; such measurements can be used as a check on similar calculations from dunes and other smaller scale features to determine sand transport budgets for large areas of the eastern Sahara.     

南丰蜜桔果实纵横径增长差异研究

在阐述南丰蜜桔果实生长动态基础上，分析不同品系、不同生长期、不同方位果实纵横径增长率差异后指出：虽然果实大小不等主要体现在横径大小值不等上，但造成同株果实大小不匀的直接主要内因，是单果间纵横径增长快慢不同，特别是纵径的日平均增长率与果实大小的相关性尤为显著。７月上旬是直接关系到小果系果实成熟时大小的关键时期。其采前“发泡”现象较其它柑桔品种不明显。     

香梨果实生长与气象因子的关系

在香梨果实生长发育期,通过定期测定果实横、纵径,对香梨果实生长发育规律及其与气象因子的关系进行了初步探索。结果表明,香梨果实横、纵径均呈持续增长趋势,横、纵径每10 d增长量呈现出2个相互重叠的增长高峰。通过灰色关联度分析法得出,60 cm地温是影响香梨果实膨大的主导气象因素。利用逐步回归分析法,建立了香梨果实日增长量与气象因子的回归模型,通过检验,模型效果较好,可为果园科学管理提供理论参考。     

辣椒果实螺旋性状的组织学与转录组学分析

为初步揭示螺丝椒(Capsicum annuum L.)果实螺旋生长的机理，以螺丝椒与牛角椒自交系为试材，利用徒手切片、石蜡切片和转录组测序等技术，对试材果形、子房壁、果肉细胞分裂与膨大情况以及花期子房转录组差异进行了解析。结果表明:果实螺旋生长的起始可能发生在子房发育早期；螺丝椒的螺旋生长由果肉细胞倾斜排列所导致；两试材果肉在纵、横向细胞数与细胞大小方面存在差异，推测两试材果形差异是由细胞分裂与膨大综合调控的。转录组分析发现:螺丝椒果实可能通过改变KIN、NPH3和IQ67通路相关基因的表达使子房细胞分裂方向发生改变并最终导致果实呈现螺旋状生长，同时该试材果实还可能通过调控OFP8、IQ67通路相关基因以及细胞分裂素相关基因的表达来增加纵向与横向细胞数目并影响细胞形状，最终使果实伸长。综上，本研究可为揭示辣椒果形形成机理以及植物形态建成机理提供科学依据。     

重组木微观力学模型及刚度参数分析方法探讨

以复合材料力学的微观力学分析方法为基础，在横观各向同性假设下，建立了重组木的材料力学与弹性力学分析的力学模型。由该模型，综合复合材料力学的理论，预测重组木的纵、横向弹性模量，泊松比，纵横向剪切弹性模量，给出材料力学分析的具体公式。     

1971—2010年茶陵县大风气候特征分析

基于1971—2010年茶陵县地面气象观测资料,使用线性倾向估计法、Mann-Kendall突变检验等方法分析茶陵县近40年大风天气的气候变化特征。结果表明:近40年茶陵县年大风日数呈减少趋势,减少率为-0.967 d/10 a,近10年转为非活跃期。主导风向季节性差异明显,春、秋、冬季盛行WNW风和NW风,夏季SSW风加强,具有明显的季风特性。茶陵县大风日数月变化呈多波动型,第1峰出现在3月,第2峰出现在7月,第3峰出现在10月,最少月为9、11月,大风主要集中在3—5月。     

南带产区不同立地类型间的杉木木材解剖

为了解不同立地类型杉木木材解剖上的差异,为杉木速生材的定向培育及材质改良提供更为充分的理论依据,该文采用宏观、微观的方法,以广西国营高峰林场12～13年生的杉木木材为试材,于2001—2003年研究了南带产区不同立地类型(南坡、山谷、山脊、山顶)间杉木木材解剖上的差异. 结果表明:①生长轮宽度及晚材率差异显著. 生长轮宽度径向变异随着年龄的增加呈先增加后减小的趋势,纵向变异随着高度的增加呈先增大后减小的趋势. 而晚材率的径向、纵向变异规律均不明显. ②管胞双壁厚及壁腔比差异显著,而长度、宽度、长宽比差异不显著. 各解剖因子径向变异模式相似,而纵向变异规律较为复杂.③微纤丝角差异不显著. 径向变异均为随着年龄的增加而减小,纵向变异呈“大—小—大”的模式. ④组织比量差异不显著. ⑤气干密度差异显著.      

红锥和西南桦人工林木材力学性质的研究

为了研究树木南北向与径向位置的变化对人工林木材力学性质与气干密度的影响,该文通过对红锥、西南桦人工林木材南北向、近髓心和近树皮2个不同径向位置的力学性质以及气干密度进行测定,分析了南北向和不同径向位置2个因素对两种木材力学性质和气干密度的影响,以及木材密度与抗弯强度、抗弯弹性模量、顺纹抗压强度的相关性.结果表明:南北向的不同对红锥和西南桦人工林木材的大多数力学性质测定项目和气干密度无显著影响,仅有红锥的弦面顺纹抗剪强度、径向握钉力和西南桦3个面的表面硬度表现为南北向差异显著.近髓心和近树皮径向位置的不同对红锥的抗弯强度、抗弯弹性模量、顺纹抗压强度和气干密度无显著影响,但对西南桦的影响则全部达到差异显著水平.两个树种木材的气干密度与木材力学性质均表现为显著的正相关关系.      

风沙环境下防风挡沙墙复变作用规律的风洞模拟

【目的】风沙防护是干旱环境下人类基础设施建设和维护的关键工程问题之一,为探明不透风防风阻沙措施风沙运移的变化规律,筛选特殊风沙区域防护体系构建合适设置参数。【方法】采用风洞模拟对不同风向夹角条件下防风挡沙墙的气流速度场、风沙流结构以及沙粒阻截率/输导率的变化规律进行研究。【结果】(1)迎风侧模型4倍障高处始终为气流急剧变化的拐点,且不随着指示风速的变化而变化;当指示风速小于10 m/s,背风侧弱风区或静风区的范围随着指示风速的增大而增大,大于12 m/s则呈相反规律;同一指示风速作用下,随风向夹角的增大有效防护范围逐渐增加。(2)迎风侧积沙主要集中于近地表0～10 cm,平均占总输沙量的85.31%;45°、60°、75°与90°4种风向夹角条件下背风侧输沙量主要集中在20～30 cm高度范围内,分别占总输沙量的71.25%、88.75%、85.25%、86.00%。(3)背风侧0～10 cm高度层沙粒截留随指示风速的增加而增加,75°夹角时最大,平均为95.64%;10～30 cm高度层沙粒输导随着指示风速的增加有增大趋势,45°夹角时最大,平均为81.09%。【结论】指示风速的变化...     

基于BP神经网络番茄果实横纵径生长的建模研究

[目的]准确快速地预测果实的大小,提高温室番茄种植的经济效益。[方法]以2002和2003年果实横纵径部分试验资料为样本,根据BP神经网络的建模原理建立果实横纵径生长的模型,通过仿真试验检验了网络的仿真性能。[结果]以MATLAB6.5作为系统仿真平台,对果实横纵径进行了建模仿真。利用神经网络工具箱命令:[m,b,r]=postreg(A,T)对系统的仿真输出与目标输出作了线性回归分析,分析结果为:m=0.9987,b=0.0051,r=1.0000;m=1.0000,b=-1.7724e-004,r=1.0000。[结论]基于BP神经网络的果实横纵径模型具有较好的仿真效果,在果实横纵径的预测中具有很好的应用前景。     

西藏林芝不同居群桃儿七表型多样性分析

[目的]分析西藏林芝不同居群桃儿七的表型多样性,为桃儿七种质资源鉴定、保护和利用研究提供参考.[方法]对西藏林芝4个不同居群桃儿七(DWZ、DJC、LZQ和NYG)的12个表型性状进行测定,计算其多样性指数,并对12个性状指标的平均值进行数理统计分析.[结果]4个不同居群桃儿七的叶、茎、果实、种子等表型性状多样性较高,Shannon-Wiener多样性指数在0.16~1.76,按其多样性指数排序为叶横径>叶纵径>叶横径/纵径>果横径>果纵径>茎色>种子数>果横径/纵径>种子千粒重>叶被毛=叶裂缺>叶裂深浅;不同居群桃儿七叶片大小变异较大,其次为果实大小和种子特性,叶被毛和叶裂缺变异最小.不同居群桃儿七的遗传多样性水平依次为DJC=LZQ>NYG>DWZ.主成分分析结果显示,第一主成分特征值为6.799,贡献率为56.662%,主要由果横径/果纵径、果横径、茎色、叶裂深浅、叶横径、叶纵径决定;第二主成分的特征值为3.024,贡献率为25.200%,主要由果横径、种子数、叶横径/叶纵径决定.相关性分析发现,桃儿七部分性状(叶横径与叶纵径、叶被毛与叶裂缺、果横径/纵径和茎色间)间表现出显著(P<0.05)或极显著(P<0.01)相关.聚类分析结果显示,4个居群可划分为两大类群,即在欧氏距离9处,DJC居群首先从4个种源中分离出来,归为一类,其余的3个居群归为第二类;在欧氏距离2处,第二类又分为两个亚类,LZQ居群自成一类,DWZ和NYG居群为一类.[结论]西藏林芝不同居群桃儿七具有较高的表型多样性,且表型性状的变异具有间断性.     

夏、冬季苏北近岸海域悬沙浓度垂直分布特征

通过将2012年8月、12月在苏北黄海海域野外调查获得的声学多普勒流速剖面仪(ADCP)后向散射强度数据与悬沙浓度进行拟合,得知两者的相关系数在0.8以上,反演结果较理想。并结合同步观测的温度、盐度等水文要素资料,对该区域夏、冬季两季悬浮泥沙的垂直分布特征、形成原因及输运进行了研究,结果表明苏北近岸海域悬浮泥沙分布的典型性季节变化明显,冬季悬沙浓度普遍高于夏季。悬浮泥沙分布及输运受苏北沿岸水、黄海西部沿岸流、长江冲淡水、黄海暖流、黄海冷水团等影响,其中黄海西部沿岸流的季节变化为主要的影响因素。苏北沿岸水携带废黄河口的再悬浮泥沙和近岸悬沙向东南外海扩散,冬季的搬运量和扩散范围显著大于夏季。黄海暖流阻碍悬沙向外海扩散,使其在近岸被大量捕集下来。夏季长江冲淡水的东北方向偏转,使得苏北南部海域悬沙分布出现层化现象。     

杉木木材管胞纵向弹性模量的研究

通过测定杉木木材薄片小试样的顺纹抗拉弹性模量和气干密度,计算管胞的纵向弹性模量,进而研究杉木管胞纵向弹性模量的株内变异规律及其与微纤丝角之间的关系。结果表明:杉木管胞的纵向弹性模量沿径向变异较大,靠近髓心处管胞的弹性模量较小;管胞的纵向弹性模量沿树干高度方向变化不大。杉木管胞的平均纵向弹性模量为44.06 GPa;随着微纤角的增大,管胞的纵向弹性模量显著降低;当微纤丝角大于24°后,管胞的纵向弹性模量降低的幅度明显减缓。      

Large wind shift on the great plains during the medieval warm period

Spring-summer winds from the south move moist air from the Gulf of Mexico to the Great Plains. Rainfall in the growing season sustains prairie grasses that keep large dunes in the Nebraska Sand Hills immobile. Longitudinal dunes built during the Medieval Warm Period (800 to 1000 years before the present) record the last major period of sand mobility. These dunes are oriented NW-SE and are composed of cross-strata with bipolar dip directions. The trend and structure of the dunes record a drought that was initiated and sustained by a historically unprecedented shift of spring-summer atmospheric circulation over the Plains: Moist southerly flow was replaced by dry southwesterly flow.     

Transport capacity models for unsteady and non-equilibrium sediment transport in alluvial channels

This study investigates transport capacity models based on different dominant variables-shear stress, stream power, unit stream power, flow discharge, flow velocity, and energy slope – in a model of unsteady and non-equilibrium sediment transport in alluvial channels. The model simulates fully coupled system of water flow, suspended sediment, and bed load sediment transport processes in two-layer system of water flow phase and movable bed. The model employs conservation of mass equation for the water in both the layers; suspended sediment in the water flow phase; sediment in the movable bed layer; and the momentum equation for the water flow in the flow phase. The system is closed by relating the sediment flux in the movable bed layer to the sediment concentration in the same layer by employing the kinematic wave theory. Using the sediment transport capacity expression with different dominant variables, a series of numerical experiments are carried out for unsteady and non-equilibrium sediment transport. The results seem theoretically reasonable for hypothetical cases. The model is calibrated and validated using different experimental data sets. The calibrated value for the transport capacity model’s exponent (k_i) is found to be 1.50, 1.65, 0.24, 0.56, 4.80, and 0.22 for shear stress, stream power, unit stream power, discharge, velocity, and slope approaches, respectively. The numerical investigation results show that transport capacity model based on any dominant variable can be employed for modelling unsteady and non-equilibrium sediment transport.     

Mechanism of polarized light perception

As background for a report on our current selective adaptation experiments in decapod crustaceans, the various facts and hypotheses generally relevant to intraretinal sensitivity to polarized light in arthropods as well as cephalopods have been marshaled. On the basis of this review, the following working hypotheses have been made. 1) One ommatidium in the compound eye is the functional unit in image perception but contains in its component retinular cells subunits which can work independently in detecting other visual parameters, such as polarization. 2) Single retinular cells do respond differentially to light polarized in various planes. 3) Light sensitivity, including e-vector detection, is localized in the rhab domeres, which comprise closely packed arrays of microvilli protruding axially from retinular cells; the dichroism of the photopigment molecules, which are contained within the microvilli, provides the molecular basis of e-vector detection. 4) The visual pigment molecules have their major dichroic axis aligned predominantly parallel to the long axis of the microvillus containing them; typically all microvilli in a single rhab domere are closely parallel to one another, thus comprising at the cellular level a unit dichroic analyzer with maximum optical density to photons vibrating in the direction parallel to these microvillous protrusions. 5) In most decapod crustaceans, in cephalopods, and in some insects the microvilli in all rhabdomeres of a retinula are oriented in only two directions, perpendicular. to each other. Therefore, e-vector perception must depend at the retinular level on a two channel system consisting of a pair of dichroic analyzers with their major transmitting axes fixed at a 90 degrees angle determined by the two directions of microvillus orientation. Our new results on selective adaptation in the eye of Cardisoma provide direct experimental evidence for such a two-channel analyzer in which the pair of functional units have their maximum sensitivity to polarization in the same retinal directions as the rhab dom microvilli observed in electron micrographs. In turn, these directions correspond with the vertical and horizontal axes of the animal's normal spatial orientation. In e-vector detection the seven retinular cells of a single decapod ommatidium thus form two operational subgroups of four and three cells, respectively (39). The correspondence of the electrophysiological evidence for a dual polarization analyzer with the perpendicular directions shown by the microvilli in a single rhabdom strengthens the idea that one ommatidium is enough for detecting e-vector orientation. On this evidence we may conclude that the model developed above for a two-channel polarization analyzer effectively accounts for the relevant spectrophotometric, fine-structural, electrophysiological, and behavioral data currently available for a considerable number of arthropods and cephalopods.