Reproduction,planula development,and substratum selection in three species of Stylactaria (Cnidaria: Hydrozoa) from Hokkaido,Japan

Modes of reproduction, morphology and behaviour of planulae, and substratum specificity were studied and compared in three species of the hydrozoan genus Stylactaria from Hokkaido, S. conchicola, S. uchidai, and S. multigranosi. Observed differences in these attributes provide additional characters for discrimination of the three species. Stylactaria conchicola is oviparous, its planulae are sedentary, and its hydroid is substratum specific (living only on shells of the gastropod Homalopoma amussitatum). Stylactaria uchidai differs in being ovoviviparous, in having crawling planulae, and in being a substratum generalist. Stylactaria multigranosi is parthenogenetic, its planulae are sedentary, and it is substratum specific (occurring exclusively on the gastropod Nassarius multigranosus). Only female colonies of S. multigranosi are known, and gonophores of this species differ from those of S. conchicola and S. uchidai in being eumedusoid rather than styloid. Correlations were noted between attributes of the planula larva and substratum specificity in the three species. The cnidome differences between the species suggest that penetrant nematocysts are particularly important for sedentary planulae colonizing moving substrata. These characters are also considered useful in the taxonomy of species of Stylactaria. The phylogenetic significance of different gonophore types in the genus is considered.     

Coexistence of species of two amphipod genera: Niphargus timavi (Niphargidae) and Gammarus fossarum (Gammaridae)

The co‐occurrence of amphipods Niphargus timavi and Gammarus fossarum was studied. A small brook in SW Slovenia was sampled monthly for one year. Below the primary spring the brook sinks, flows for about 150 m below the surface and springs again. Gammarus fossarum never reached the stretch above the sink. Both species were found at all sampling sites below the secondary spring throughout the year, but the abundance of the two varied along the stream spatially and temporarily. Differences in life cycles between G. fossarum and N. timavi were not informative; however, the estimated reproductive potential of G. fossarum was much higher than of N. timavi. A result of the higher reproductive potential may be the dominance of gammarids in permanent waters, while N. timavi may invade a surrounding fissure system where it survives gammarid competition and summer desiccations when the gammarid population becomes extinct.     

Decadal-scale variability of warm season temperature in Beijing over the past 2650 years

A continuous record of surface temperature for the past 2650 years was obtained in an earlier study from a Beijing stalagmite based on sedimentary layer counting and thickness measurements.Singular spectrum analysis,multi-taper and wavelet spectral analyses are used in this study to identify decadal-scale signals and their origins in this record.Besides long-term cycles of solar origin identified in earlier studies,this record contains cycles that dominate temperature with periods of 102-70,66-50,31,25-22,19,15,12 and 9 years.The 102-70,25-22,12 and 9 year cycles are attributable to solar variation,while the others are likely to be related to low-latitude ocean forcing.These results suggest that century-scale changes in the Beijing summer temperature over the past 2650 years are primarily controlled by solar variation,while ocean-atmospheric interactions play a prominent role in modu-lating decadal-scale variability.     

罗布泊地区天然盐渍土多次冻融循环试验研究

选取罗布泊地区亚硫酸盐渍土在开放系统中进行多次冻融循环试验,研究罗布泊地区亚硫酸盐渍土温度变化规律,盐冻胀特性。结果表明：罗布泊地区亚硫酸盐渍土的温度变化随时间呈抛物线型,同一深度的土体降温速率与升温速率相接近。在前六次冻融循环中,盐冻胀量与盐冻胀平均速度逐渐增大,且盐胀量具有较好累加性。并在第六次冻融循环时盐冻胀量达到最大值。土体在第七次冻融循环时盐冻胀量小于回落量,盐冻胀趋于稳定。     

故障3-元n-立方体的哈密顿圈嵌入

哈密顿圈嵌入问题是研究互连网络并行计算中最重要问题之一.在文章中,我们考虑带故障点的3-元n-立方网络Qn3的哈密顿圈嵌入问题并得到如下结果.给定一个具有至多2n-2个故障点的集合F,对Qn3-F中任意边,除一种特殊情况外,Qn3-F中都有一个哈密顿圈包含这条边,即Qn3-F是几乎-边哈密顿的.     

不同固结度冻融软土动载下孔压模型试验研究

以冻结温度和融土初始固结度为影响因素,通过室内动三轴试验对地铁循环荷载作用下冻融软土的孔压发展规律进行研究.结合试验数据,建立了考虑冻结温度和融土初始固结度的影响因素的冻融土动孔压累积试验模型.研究表明,冻融作用改变土体内部颗粒联结形式和孔隙结构,导致在循环荷载作用下冻融土动孔压累积速率加快;冻结温度越低,冻融土孔压发展速率越快,且在振动后期的稳定孔压值越高;冻融土初始固结度对孔压发展有影响,初始固结度越高,孔压发展越缓慢,且稳定值越低;低温冻结和低初始固结度的耦合作用加剧了冻融土孔压的累积,使其结构进一步软化.     

干湿循环作用下贺兰山岩画载体砂岩风化特征研究

以宁夏岩质文物区域内的典型砂岩(记为A、B)为研究对象,针对其实际的赋存环境进行干湿循环试验,研究砂岩试样的力学特征,分析浸泡在真实水环境中砂岩试样经历不同循环次数后各力学参量的变化规律;并结合SEM观察岩样微观特性。研究结果表明:干湿循环结束后砂岩试样强度具有明显的"弱化"趋势,在干湿循环前期表现更为明显。砂岩A强度下降了74.67%,砂岩B强度下降了45.18%,A对干湿循环作用表现更为敏感。SEM试验结果发现岩石微观结构随着循环次数的增加,其微观结构越松散,颗粒空间排布越不均匀;与宏观试验强度变化结果相吻合,说明岩质文物受水的作用时,干湿循环作用是不可能忽视的影响因素。研究结果为具有宁夏区情的石质岩画文物劣化机理理论、后期保护和修复提供的理论基础。     

引气混凝土在冻融循环过程中的氯离子渗透与孔结构

C30和C50引气混凝土在3.5%NaCl溶液中自然浸泡或快速冻融循环,测试盐冻过程中混凝土表面和内部的超声声时,混凝土中的氯离子浓度分布及孔结构演变。研究结果表明:超声声时较好反映了混凝土在盐冻过程中的损伤演化,其表面和内部超声声时均先下降,后保持稳定,当混凝土剥落严重时迅速上升;冻融循环过程中的低温环境降低了混凝土表面氯离子浓度和氯离子扩散速度,但冻融损伤程度的增加将导致混凝土中氯离子扩散速度的提高;盐冻循环50,150和400次时,C50混凝土中孔径大于100 nm毛细孔数量由31.85%提高到42.70%和56.60%,孔径大于0.1 mm的微裂纹数量由12.80%降低为8.37%,并最终提高到25.29%。此外,混凝土经过150次冻融循环,相比于C30混凝土,C50混凝土中孔径大于100 nm的毛细孔数量降低20.10%,微裂纹数量降低43.44%。     

可控脉冲信号发生器的设计

数字信号由于具有抗干扰能力强、无噪声积累,便于存储、处理和交换等一系列优点,已经成为现代控制领域的主要处理信号.要求改变脉冲信号的周期、占空比和输出脉冲个数可控的电路模块在很多控制领域都有应用.本文介绍了一种基于FPGA芯片的可控输出信号周期、占空比和信号个数的设计方法.应用时钟管理模块对输入时钟进行倍频来提高输出信号的周期范围和精度;调用IP核来完成相应的数学运算;应用两个可控减计数器来控制每一周期内高低电平的持续时间;应用数量控制计数器对输出的脉冲进行计数,控制输出量.该设计运行在ALTERA公司的clcyone芯片上,取得良好的效果,具有灵活高效的优点.     

一种改进型防止策略性操纵的信道分配协议

针对认知无线电信道分配过程中作弊次用户（SU）对未作弊SU性能存在影响的问题，利用最适交易循环（TTC）匹配理论，提出一种名为改进TCC的信道分配协议（ITTC）。ITTC按照SU对于信道的喜好排序进行分配，将改变真实喜好列表排序的行为视为作弊。SU作弊只能获得更差的分配性能，未作弊者获得不低于原来性能的分配结果，从而有效解决因作弊造成的不公平性。为定量分析ITTC的分配性能，设计并使用了一种量化SU分配结果的评估方法（PEM-SU）。PEM-SU对PU网络以及SU数据包到达、分配、传输过程进行设置，将分配结果转化为统一形式进行性能量化。利用PEM-SU与二次申请延时接收协议（SPDA）和TTC协议的对比，结果表明，ITTC在平均吞吐量、时延、队长和拒绝率上均优于SPDA和TTC，且能够有效防止策略性操纵，保护未作弊SU的利益。