Sulfate- and pH-driven metabolic flexibility in sugarcane vinasse dark fermentation stimulates biohydrogen evolution,sulfidogenesis or homoacetogenesis

Dark fermentation of sugarcane vinasse can be used as a “cleaning” step to remove sulfate prior to methanogenesis because sulfidogenic conditions can be successfully established in parallel with biohydrogen production. Using a 2² central composite rotational design (CCRD) and response surface methodology (RSM), this study assessed the impacts of bicarbonate and sulfate availability on the establishment of sulfidogenesis in the thermophilic (55 °C) fermentation of vinasse in batch reactors, equally assessing the impacts on biohydrogen evolution. CCRD-RSM results indicated the favoring of biohydrogen production at the lowest sulfate and bicarbonate concentrations, whilst the opposite was observed for sulfidogenesis. Glycerol, lactate, and hydrogen were the preferential electron donors utilized by sulfate-reducing bacteria (SRB), whilst ethanol was markedly consumed only at high sulfate concentrations. SRB were inhibited by sodium when dosing excess NaHCO₃ and Na₂SO₄. Complementary tests revealed maximum biohydrogen production (2.40 mmol) out of the CCRD, at pH exceeding 7.5 with no interference of sulfidogenesis. Non-efficient biohydrogen production was observed at low pH (<5.0; ～1.90 mmol) because the uptake of lactate was inhibited. Meanwhile, homoacetogenesis was established under intermediate pH range (5.5–6.5), as revealed by the accumulation of acetate (up to 2.5 g L^?1). 16S rRNA gene amplicon sequencing further revealed the genera Thermoanaerobacterium/Pseudoclostridium, Desulfotomaculum/Desulfohalotomaculum and Sporomusaceae/Moorella as the main biohydrogen-producing, sulfate-removing and biohydrogen-consuming (homoacetogens) microbial groups, respectively. Hence, using a single inoculum source, vinasse may provide a butyrate-rich (along with biohydrogen-rich biogas) or a sulfate-free and acetate-rich fermented effluent, depending mainly on proper pH control.     

一种重载汽车轮毂总成自动点焊机器人的研制

针对手工焊接汽车轮毂总成效率低下、焊接质量不稳定等问题及一种重载汽车轮毂总成的结构特点及焊接要求，设计了一种直角坐标型自动点焊机器人。阐述了自动点焊机器人本体的方案设计、控制系统应用等过程，并利用现场试验与工业性试验对自动点焊机器人的性能等进行了验证，为重载汽车轮毂总成的自动焊接提供了一种可供借鉴的方法。      

Spectroscopic investigations on high efficiency deep red-emitting Ca2SiO4:Eu3+ phosphors synthesized from agricultural waste

Europium doped calcium orthosilicate (Ca₂SiO₄) phosphors have been synthesized by the conventional high temperature solid-state reaction method in various concentrations from agricultural waste (egg shell as a CaO and rice husk as a SiO₂). These phosphors structure from X-ray diffraction and morphology from scanning electron microscopy have been examined. Concentration dependent Eu³⁺ ions luminescent properties in Ca₂SiO₄ phosphors have been studied from the excitation, emission and decay curves analysis. The ⁵D₀ → ⁷F_J transitions observed in luminescence spectrum allows to determine the site symmetry of the Eu³⁺ ion. A charge transfer band (CTB) at around 260?nm which is due to the Eu–O interaction in the host along with the 4f – 4f excitation bands due to Eu³⁺ ions in UV and blue regions are observed. The color co-ordinates determined from emission spectra varies with concentrations of Eu³⁺ ions and are found to fall in the red region. The decay curves show single exponential behavior for all concentrations of Eu³⁺ ions (0.01–0.4?mol%) and the lifetimes varied from 2.67 to 2.78?ms. It is worth noting that the present material is found to be far better than many red phosphors synthesized by using agricultural waste as raw materials.     

Efficient promotion of methane hydrate formation and elimination of foam generation using fluorinated surfactants

Methane hydrate preparation is an effective method to store and transport methane. In promoters to facilitate methane hydrate formation, homogeneous surfactant solutions, sodium dodecyl sulfate (SDS) in particular, are more favorable than heterogeneous particles, thanks to their faster reaction rate, more storage capacity, and higher stability. Foaming, however, could not be avoided during hydrate dissociation with the presence of SDS. This paper investigated the ability of five fluorinated surfactants: potassium perfluorobutane sulfonate (PBS), potassium perfluorohexyl sulfonate (PHS), potassium perfluorooctane sulfonate (POS), ammonium perfluorooctane sulfonate (AOS), and tetraethylammonium perfluorooctyl sulfonate (TOS) to promote methane hydrate formation. It was found that both PBS and PHS achieve a storage capacity of 150 (V/V, the volume of methane that can be stored by one volume of water) within 30 min, more than that of SDS. Cationic ions and the carbon chain length were then discussed on their effects during the formation. It was concluded that PBS, PHS, and POS produced no foam during hydrate dissociation, making them promising promoters in large-scale application.     

Pre-stack elastic reverse time migration in tunnels based on cylindrical coordinates

Seismic forward-prospecting in tunnels is an important step to ensure excavation safety. Nowadays, most advanced imaging techniques in seismic exploration involve calculating the solution of elastic wave equation in a certain coordinate system. However, considering the cylindrical geometry of common tunnel body, Cartesian coordinate system seemingly has limited applicability in tunnel seismic forward-prospecting. To accurately simulate the seismic signal received in tunnels, previous imaging method using decoupled non-conversion elastic wave equation is extended from Cartesian coordinates to cylindrical coordinates. The proposed method preserves the general finite-difference time-domain (FDTD) scheme in Cartesian coordinates, except for a novel wavefield calculation strategy addressing the singularity issue inherited at the cylindrical axis. Moreover, the procedure of cylindrical elastic reverse time migration (CERTM) in tunnels is introduced based on the decoupled non-conversion elastic wavefield. Its imaging effect is further validated via numerical experiments on typical tunnel models. As indicated in the synthetic examples, both the PP- and SS-images could clearly show the geological structure in front of the tunnel face without obvious crosstalk artifacts. Migration imaging using PP-waves can present satisfactory results with higher resolution information supplemented by the SS-images. The potential of applying the proposed method in real-world cases is demonstrated in a water diversion tunnel. In the end, we share our insights regarding the singularity treatment and further improvement of the proposed method.     

双圆弧齿轮端面齿廓方程及其啮合过程

详尽而又简明地推导了分阶式双圆弧齿轮的端面齿廓方程。通过插图来展示各坐标系的相互关系 ,介绍如何具体的在计算机上绘出双圆弧齿轮端面图及模拟齿轮的啮合过程。     

超细Nb_20_5粉末的研制

对采用均匀沉淀法制备陶瓷电容器级(平均粒径为0.1-0.2μm的超细粉末)Nb2O5粉末的最佳工艺条件进行了探讨,研究了均匀沉淀过程中,反应温度、沉淀终点pH值、反应物浓度、脱水剂和添加剂以及焙烧温度对Nb(OH)5粉体粒度分布及粒径的影响。利用TG-DTA、SEM、XRD、比表面积测试仪(BET)和CILAS粒度测试仪进行了测定,结果表明:当H2NbOF5浓度在0.2~0.4M时,以NH3·H2O作沉淀剂,用乙醇、丙酮等作脱水剂,所获沉淀在80~100℃干燥后,制备的Nb(OH)5粉体粒度均匀且分布窄,其平均粒径为0.07 μm,经700℃焙烧后,可制得粒度分布窄、团聚少、比表面积为14.44 m2/g、平均粒径为0.1 μm,且纯度>99.95%的陶瓷电容器级Nb2O5微粉体。该方法具有设备简单、工艺流程短、污染小,产品纯度高等特点。     

用线性回归理论解决GPS大地坐标向地方坐标系坐标转换的新方法

本文根据不同空间直角坐标系的关系，提出了一种利用线性回归理论解决GPS大地坐标向地方坐标系坐标转换的新方法。实际应用检验证明，该方法具有理论严密、计算简便、转换精度高等多种优点。该法除可用于GPS大地坐标向地方坐标系坐标转换外，也适用于不同空间（或地方）坐标系间坐标的相互转换。     

数字化坐标的几何条件和插值

以角度型和面积型的条件方程为例，说明数字化坐标为观测值的条件平差法，给出了闭合差的限差公式。讨论了数字化曲线的拉格朗插值及其参数方程的建立。     

缓圆曲线上任意点的测量坐标计算

根据坐标的平移、旋转原理和正算、反算公式，推出缓圆曲线上任意点测量坐标的计算公式，以便在道路施工中采用坐标制放线。