闽江河口互花米草残体异位分解及磷养分释放特征

潮汐涨落导致的植物残体异位分解是河口湿地最常见的分解方式,研究分解环境变化下残体的分解及其养分释放对深入了解河口湿地养分循环具有重要意义。为此,2021年3–12月,在闽江河口互花米草(Spartina alterniflora)分布区,以自然环境梯度作为分解环境变化研究的替代系统,由陆向海方向布设入侵7年的互花米草湿地(M7,残体记为L7)、新近入侵1年的互花米草湿地(M1,残体记为L1)以及入侵前的光滩(BF)3个分解样地,采用分解袋法模拟研究了分解环境变化对不同入侵年限互花米草残体(L7和L1)分解及磷养分释放的影响。结果表明,分解环境变化可对残体分解速率产生显著影响。L7在M1和BF环境中的分解相比其在原来环境中(M7)更快,而L1在M7和BF环境中的分解相比其在原来环境中(M1)更慢。分解环境变化导致的L7或L1分解速率的改变一方面取决于分解环境中关键环境因子(温度和p H)的变化,另一方面与分解环境变化导致的残体质量(碳氮比和氮磷比)发生改变有关。相较于原分解环境,分解环境的变化导致L7的总磷(TP)含量整体增加,而L1的TP含量降低,但二者TP含量均在M1分解环境中最高。残留率是影响不同分解环境下残体TP含量变化的共性因素,而分解环境变化引起的主要环境因子(电导率)和残体质量改变是导致TP含量存在差异的重要原因。不同分解环境下L7和L1的磷养分在分解期间均表现为不同程度的净释放。研究发现,L7和L1的分解速率及磷养分释放量均在M1分解环境中较高,说明残体在该分解环境中的磷养分归还速率可能更快,而这有利于提高对新近入侵互花米草的磷养分的供给能力。

Detection and correction of level echo based on generalized S-transform and singular value decomposition

The echo of the material level is non-stationary and contains many singularities.The echo contains false echoes and noise,which affects the detection of the material level signals,resulting in low accuracy of material level measurement.A new method for detecting and correcting the material level signal is proposed,which is based on the generalized S-transform and singular value decomposition(GST-SVD).In this project,the change of material level is regarded as the low speed moving target.First,the generalized S-transform is performed on the echo signals.During the transformation process,the variation trend of window of the generalized S-transform is adjusted according to the frequency distribution characteristics of the material level echo signal,achieving the purpose of detecting the signal.Secondly,the SVD is used to reconstruct the time-frequency coefficient matrix.At last,the reconstructed time-frequency matrix performs an inverse transform.The experimental results show that the method can accurately detect the material level echo signal,and it can reserve the detailed characteristics of the signal while suppressing the noise,and reduce the false echo interference.Compared with other methods,the material level measurement error does not exceed 4.01%,and the material level measurement accuracy can reach 0.40%F.S.

Matched Field Localization Based on CS-MUSIC Algorithm

The problem caused by shortness or excessiveness of snapshots and by coherent sources in underwater acoustic positioning is considered.A matched field localization algorithm based on CS-MUSIC(Compressive Sensing Multiple Signal Classification) is proposed based on the sparse mathematical model of the underwater positioning.The signal matrix is calculated through the SVD(Singular Value Decomposition) of the observation matrix.The observation matrix in the sparse mathematical model is replaced by the signal matrix,and a new concise sparse mathematical model is obtained,which means not only the scale of the localization problem but also the noise level is reduced;then the new sparse mathematical model is solved by the CS-MUSIC algorithm which is a combination of CS(Compressive Sensing) method and MUSIC(Multiple Signal Classification) method.The algorithm proposed in this paper can overcome effectively the difficulties caused by correlated sources and shortness of snapshots,and it can also reduce the time complexity and noise level of the localization problem by using the SVD of the observation matrix when the number of snapshots is large,which will be proved in this paper.

An Analysis of the Causes of Decadal Variations of Rainfall in Shandong in Summer

The precipitation in Shandong in July, August as well as the whole summer (JJA) and the corresponding 500 hPa geopotential height fields are analyzed by means of the SVD (singular value decomposition) methodology. It is found that the general circulations in East Asia and the Western Pacific underwent decadal changes around 1979. The geopotential height, in particular over key areas like the South China Sea and the Philippines, increased after 1979. Corresponding to the changes in the geopotential height, the rainfall in Shandong started to decrease around 1979. The synthesized analysis shows that when the geopotential height at 500hPa level decreases in the key areas, the Western Pacific subtropical high shifts northward and an anticyclonic anomalous cell enforces the southerly flow over Shandong-Korea-Japan, Shandong could experience a wet period. A dry period is likely to occur when the geopotential height increases in these key areas, the subtropical high moves southward or expands westward to a great distance, and a cyclonic anomalous cell controls Shandong. Respective conceptual models for the causative mechanism are obtained for the cases of July, August and the whole summer (JJA) .

Forward Displacement Analysis of a Class of the 6-6 Stewart Platforms

A special form of the Stewart platform is presented in which the top platform and base platform are similar and corresponding vertices are connected by six prismatic joints.A closed-from solution for the forward displacement analysis of this mechanism is developed.When the six vertices of the top platform are in a quadratic curve,this mechanism becomes singular.This new theoretical result is confirmed with a numerical example.

In Situ Dissimilatory Nitrate Reduction to Ammonium in a Paddy Soil Fertilized with Liquid Cattle Waste

Most studies on dissimilatory nitrate reduction to ammonium （DNRA） in paddy soils were conducted in the laboratory and in situ studies are in need for better understanding of the DNRA process. In this study, in situ incubations of soil DNRA using ^15N tracer were carried out in paddy fields under conventional water （CW） and low water （LW） managements to explore the potential of soil DNRA after liquid cattle waste （LCW） application and to investigate the impacts of soil redox potential （Eh） and labile carbon on DNRA. DNRA rates ranged from 3.06 to 10.40 mg N kg 1 dry soil d-1, which accounted for 8.55%-12.36% and 3.88% 25.44% of consumption of added NO3-^15N when Eh at 5 cm soil depth ranged from 230 to 414 mV and -225 to -65 mV, respectively. DNRA rates showed no significant difference in paddy soils under two water managements although soil Eh and/or dissolved organic carbon （DOC） were more favorable for DNRA in the paddy soil under CW management 1 d before, or 5 and 7 d after LCW application. Soil DNRA rates were negatively correlated with soil Eh （P 〈 0.05, n = 5） but positively correlated with soil DOC （P 〈 0.05, n - 5） in the paddy soil under LW management, while no significant correlations were shown in the paddy soil under CW management. The potential of DNRA measured in situ was consistent with previous laboratory studies; and the controlling factors of DNRA in paddy soils might be different under different water managements, probably due to the presence of different microfioras of DNRA.

Cobalt(Ⅱ) coordination polymers built on isomeric dipyridyl triazole ligands with pyromellitic acid:Synthesis,characterization and their effects on the thermal decomposition of ammonium perchlorate

Three new cobalt（II） coordination compounds, [Co（3,3＇-Hbpt）2（H2pm）（H20）2]＇2H20 （1）, [Co（4,4＇-Hbpt）（pm）0.5（H20）]＇3H20 （2） and [Co（3,4＇-Hbpt）（pm）0.5（H20）3]＇2H20 （3） （3,3＇-Hbpt = 3,5-bis（3-pyridyl）-lH-1,2,4-triazole; 4,4＇-bpt = 3,5-bis（4-pyridyl）- 1H-1,2,4-triazole, 3,4＇-Hbpt = 3-（3-pyridyl）-5-（4＇-pyridyl）-lH-1,2,4-triazole and Hapm = pyromellitic acid） have been synthe- sized by hydrothermal reactions. Single-crystal X-ray diffraction reveals that compound 1 has a one-dimensional （1D） chain network, 2 exhibits a four-connected three-dimensional （3D） structure with 1D open channels encapsulated by water molecules, while 3 displays a regular two-dimensional （2D） architecture connected through 1D metal helical chains. In addition, the effi- cacy of compounds 1-3 as additives to promote the thermal decomposition of ammonium perchlorate （AP） is explored by dif- ferential scanning calorimetry （DSC）.