Photoionization Mass Spectrometric and Kinetic Modeling of Low-pressure Pyrolysis of Benzene

Pyrolysis of benzene at 30 Torr was studied from 1360 K to 1820 K in this work. Synchrotron vacuum ultraviolet photoionization mass spectrometry was employed to detect the pyroly- sis products such as radicals, isomers and polycyclic aromatic hydrocarbons, and measure their mole fraction profiles versus temperature. A low-pressure pyrolysis model of benzene was developed and validated by the experimental results. Rate of production analysis was performed to reveal the major reaction networks in both fuel decomposition and aromatic growth processes. It is concluded that benzene is mainly decomposed via H-abstraction reaction to produce phenyl and partly decomposed via unimolecular decomposition reac- tions to produce propargyl or phenyl. The decomposition process stops at the formation of acetylene and polyyne species like diacetylene and 1,3,5-hexatriyne due to their high thermal stabilities. Besides, the aromatic growth process in the low-pressure pyrolysis of benzene is concluded to initiate from benzene and phenyl, and is controlled by the even carbon growth mechanism due to the inhibited formation of C5 and C7 species which play important roles in the odd carbon growth mechanism.

Low-pressure pneumoperitoneum with abdominal wall lift in laparoscopic total mesorectal excision for rectal cancer:initial experience

AIM To evaluate the safety and feasibility of a new technology combining low-pressure pneumoperitoneum(LPP) and abdominal wall lift(AWL) in laparoscopic total mesorectal excision(TME) for rectal cancer.METHODS From November 2015 to July 2017,26 patients underwent laparoscopic TME for rectal cancer using LPP(6-8 mm Hg) with subcutaneous AWL in Qilu Hospital of Shandong University,Jinan,China.Clinical data regarding patients' demographics,intraoperative monitoring indices,operation-related indices andpathological outcomes were prospectively collected.RESULTS Laparoscopic TME was performed in 26 cases(14 anterior resection and 12 abdominoperineal resection) successfully,without conversion to open or laparoscopic surgery with standard-pressure pneumoperitoneum.Intraoperative monitoring showed stable heart rate,blood pressure and paw airway pressure.The mean operative time was 194.29 ± 41.27 min(range:125-270 min) and 200.41 ± 20.56 min(range:170-230 min) for anterior resection and abdominoperineal resection,respectively.The mean number of lymph nodes harvested was 16.71 ± 5.06(range:7-27).There was no positive circumferential or distal resection margin.No local recurrence was observed during a median follow-up period of 11.96 ± 5.55 mo(range:5-23 mo).CONCLUSION LPP combined with AWL is safe and feasible for laparoscopic TME.The technique can provide satisfactory exposure of the operative field and stable operative monitoring indices.

Process Optimization for AZ91 Mg-alloy Low-pressure EPC Process

The influence of a key process variable on the mold filling characteristics of AZ91 Mg-alloy was studied in the low pressure EPC process.The applied flow quantity of insert gas from 1 to 5 m~3/h associated with the pressurizing rate in the low pressure EPC casting process was considered for rectangle and L-shape plate casting. The experimental results show that there is an optimal flow quantity of insert gas for good mold filling characteristics in AZ91 Mg-alloy low-pressure EPC process. The optimal flow quantity of insert gas for the specimens is 3 to 4 m~3/h. Either less or higher than the optimal flow quantity of insert gas would lead to misrun defects or folds, blisters and porosity defects. The practice of hub casting confirmed that the low-pressure EPC process with an optimal processing variable exemplified as 4 m~3/h gas flow quantity was capable of producing complicated magnesium castings without misrun defects.

Numerical simulation and analysis of lithium plasma during low-pressure DC arc discharge

Alkali metal DC arc discharge has the characteristics of easy ionization,low power consumption,high plasma temperature and ionization degree,etc,which can be applied in aerospace vehicles in various ways.In this paper,we calculate the physical property parameters of lithium vapor,one of the major alkali metals,and analyze the discharge characteristics of lithium plasma with the magnetohydrodynamic(MHD)model.The discharge effects between constant current and voltage sources are also compared.It is shown that the lithium plasma of DC arc discharge has relatively high temperature and current density.The peak temperature can reach tens of thousands of K,and the current density reaches 6 x 107 A m 2.Under the same rated power,the plasma parameters of the constant voltage source discharge are much higher than those of the constant current source discharge,which can be used as the preferred discharge mode for aerospace applications.

An Experimental and Numerical Study on the Cleaning of Pleated Bag Filters Using Low-Pressure Pulsed-Jets

Pulsed-jet cleaning is recognized as the most efficient method to regenerate bag dust collectors traditionally used in industrial processes to control the emission of particulates.In this study,non-woven needle felt filter bags with and without a film coating material have been analyzed considering different geometries(different number N of pairs of pleated filter bag sides)in the frame of dedicated low-pressure pulsed-jet cleaning experiments.The flow structure inside the bag and the response characteristics of its wall have also been analyzed numerically through a computational fluid-dynamics/structural-dynamics(CFD-CSD)unidirectional fluid-solid coupling method.As shown by the experiments,the peak pressure(P_(0))on the wall of the filter bag with N=8 and 12 is higher,which indicates dust can be removed more effectively in these cases.The peak pressure on the wall increases first and then decreases along the direction of the bag length,while the peak pressure of the pleated filter bag with nonwoven needled felt film coating is greater than that without film coating.A comprehensive analysis of the time variation of acceleration,deformation,strain,stress and other factors,has led to the conclusion that the pleated filter bag with N=12 would be the optimal choice.

The mechanism study of low-pressure air plasma cleaning on large-aperture optical surface unraveled by experiment and reactive molecular dynamics simulation

Low-pressure air plasma cleaning is an effective method for removing organic contaminants on large-aperture optical components in situ in the inertial confinement fusion facility.Chemical reactions play a significant role in plasma cleaning,which is a complex process involving abundant bond cleavage and species generation.In this work,experiments and reactive molecular dynamics simulations were carried out to unravel the reaction mechanism between the benchmark organic contaminants of dibutyl phthalate and air plasma.The optical emission spectroscopy was used to study the overall evolution behaviors of excited molecular species and radical signals from air plasma as a reference to simulations.Detailed reaction pathways were revealed and characterized,and specific intermediate radicals and products were analyzed during experiments and simulation.The reactive species in the air plasma,such as O,HO_(2)and O_(3)radicals,played a crucial role in cleaving organic molecular structures.Together,our findings provide an atomic-level understanding of complex reaction processes of low-pressure air plasma cleaning mechanisms and are essential for its application in industrial plasma cleaning.

Effect of Low-pressure Carbonation on the Heat Inactivation and Cytoplasmic Acidification of Saccharomyces cerevisiae

Effect of low-pressure carbonation （LPC） on heat inactivation of Saccharomyces cerevisiae was investigated. The cell suspension was carbonated at 1 MPa and 4℃ for 15 min and subsequently heated from 51 to 61 ℃ and 5 s to 5 min （heating with LPC）. As a control experiment, cell suspension was heat-treated under atmospheric pressure without LPC （heating）. The inactivation ratio of heating at 53℃ and 55℃ for l rain with LPC was approximately 1 log order higher than heating alone. Extending heating time to 5 min did not widen the difference in the inactivation ratio between heating with LPC and heating alone at both heating temperatures. At 57℃, the difference in inactivation ratio increased from 1 to 2.5 log order with extending treatment time from 5 to 15 s. The results suggested that the enhanced inactivation effect by LPC was obtained at the higher temperature with short time treatment than the lower temperature with longer time treatment. Under fluorescence microscope observation of LPC-treated cell stained with LysoSensor probe, it seemed that LPC was hardly able to acidify the cytoplasm ofS. cerevisiae. It is considered that the ability orS. cerevisiae ceils to keep their cytoplasmic pH during LPC resulted in the inferior increase in heat inactivation ratio by LPC as compared with bacteria in the previous studies.

Neutrons in a nanosecond low-pressure discharge in deuterium

Stable neutron generation with a yield of ~1.2×10^(4) neutrons per pulse was obtained during d(d,n)^(3)He reaction initiated by the high-voltage nanosecond discharge in a gap with a potential tungsten cylinder(anode)and a grounded deuterated zirconium plate(cathode)filled with deuterium at a pressure of ~10^(2) Pa.Estimated duration of the neutron pulse was ~1.5 ns.Less intensive neutron emission was registered without deuterated plate.Splashing of material of the tungsten electrode was observed during the high-voltage nanosecond discharge in the deuterium,hydrogen,helium and argon at pressures of 10^(2)-10^(4) Pa.

A LOW-PRESSURE AND ONE-STEP METHOD FOR THE SYNTHESIS OF ALKYLIDYNETRICOBALT NONACARBONYL CLUSTERS:RCCo_8(CO)_9

Metal clusters RCCo_3(CO)_9(R-H,C1,Br,CH_3,Ph) were prepared in 18.8-57.3% yields from the reaction of cobalt(Ⅱ)salt and RCX_a under mild PTC conditions(latm CO,25℃).The cobalt salt was reduced to Co(CO)_4 in the presence of Na_3S_2O_4.

Simulation of propagation of the HPM in the low-pressure argon plasma

The propagation of the high-power microwave（HPM） with a frequency of 6 GHz in the lowpressure argon plasma was studied by the method of fluid approximation.The two-dimensional transmission model was built based on the wave equation,the electron drift-diffusion equations and the heavy species transport equations,which were solved by means of COMSOL Multiphysics software.The simulation results showed that the propagation characteristic of the HPM was closely related to the average electron density of the plasma.The attenuation of the transmitted wave increased nonlinearly with the electron density.Specifically,the growth of the attenuation slowed down as the electron density increased uniformly.In addition,the concrete transmission process of the HPM wave in the low-pressure argon plasma was given.

Microstructure and Properties of Low-pressure Cold Sprayed Al-based Composite Coatings on Magnesium Alloy Surface

Pure Al and Al-30%Al_(2)O_(3)composite coatings are prepared on the surface of AZ31B magnesium alloy by low-pressure cold spraying.The morphology and structure of the coatings are analyzed by scanning electron microscope (SEM),energy dispersive spectroscopy (EDS),and X-ray diffraction (XRD),and the effects of the addition of Al_(2)O_(3)on the microstructure of the Al-based coatings are discussed.The mechanical properties and corrosion resistance of the coatings are fully evaluated by the micro-hardness tester,electronic tensile machine,and electrochemical workstation.The results show that the coating structure is more uniform and denser,and the porosity is significantly reduced after the addition of Al_(2)O_(3).The interfaces between the coatings and the magnesium alloy substrate are distinct,and the coatings and the substrate are mechanically combined.Compared with the pure Al coating,the microhardness of the Al-Al_(2)O_(3)composite coating is increased to 61.1 HV_(0.2),and the bonding strength reaches above 53.1 MPa.The self-corrosion potential of the two coatings is higher than that of the magnesium alloy,and the self-corrosion current density is significantly lower than that of the magnesium alloy substrate.The Al-based coatings prepared by low-pressure cold spraying have high hardness,good bonding strength,and good corrosion resistance,which can be used for the repair and protection of magnesium alloy structural parts.

基于计算机网络控制的智能喷灌系统应用研究

为了实现植株根部含水率的精确控制,基于ZigBee技术建立了智能喷灌系统。计算表层含水率变化量、平均温度、日照长度与根部含水率变化量的相对关联系数,选定表层含水率变化量为自变量参数,采用线性拟合的方法,建立根部含水率变化量模型;探究喷灌阀控制信号和喷灌流量之间的关系,进而建立喷灌阀控制信号与表层含水率变化量之间的模型;设计系统工作流程,实现根部含水率精确控制。对网络系统监测表层含水率的精度和根部含水率恒定控制进行测试,表明系统具有良好的工作性能。

拉萨河谷喷灌双季饲草作物系数与土壤蒸发研究

【目的】探究作物指标与作物系数、土壤蒸发之间的关系,为提高拉萨河谷喷灌蒸散发计算精度,制定适时适量的双季饲草灌溉制度提供理论支撑。【方法】通过微型蒸渗仪实测蒸散量与PM法计算参考作物的比值实测作物系数对PM法修正的单作物系数进行评价,分析误差水平及原因;基于自制株间土壤蒸发仪,获得株间土壤蒸发(E)与蒸散量(ET)的分摊比例(E/ET),建立实测Kc及E/ET与LAI、SPAD之间的关系。【结果】采用FAO-56推荐单作物系数修正法,对拉萨河谷小黑麦、燕麦单作物系数进行修正,小黑麦和燕麦初始生长期、生长中期和生长后期的作物系数分别为0.45和0.94,1.22和1.16,0.49和0.31。小黑麦全生育期土壤蒸发占蒸散量的44.8%,苗期-越冬期、越冬-返青期、返青-拔节期、拔节-抽穗期、抽穗-刈割期土壤蒸发占蒸散量比例分别为93.4%、94.8%、61.8%、22.2%和13.8%;燕麦苗期-分蘖期、分蘖-拔节期、拔节-抽穗期、抽穗-刈割期土壤蒸发占蒸散量比例分别为98.9%、79.1%、31.7%和16.8%。土壤蒸发在双季饲草种植过程中占蒸散量比例超过44%,减少土壤蒸发以提高水分利用效率的潜力较大。【结论】双季饲草实测作物系数、土壤蒸发占蒸散量比例与叶面积指数、叶绿素显著相关且呈线性或非线性函数关系。在单作物系数法基础上增加作物指标可以修正双季饲草蒸散的计算精度,通过构建数学模型使作物指标能直接模拟该地区作物土壤蒸发、间接模拟蒸散发全过程。

基于变量灌溉动态分区管理的冬小麦产量与节水效果

喷灌机机载式红外温度传感器系统是动态监测农田作物水分亏缺状况、构建变量灌溉(variable rate irrigation,VRI)决策支持系统的重要工具。为了评估圆形喷灌机机载式红外温度传感器系统在变量灌溉动态分区管理中的应用效果,该研究以气象参数和土壤水分传感器网络构建的均一灌溉(uniform rate irrigation, URI)决策方法为对照,评估了基于气象参数、土壤水分传感器网络和作物冠层温度的变量灌溉决策方法对华北平原冬小麦灌溉制度、土壤含水率空间分布均匀性和节水增产效果的影响。在河北省邢台市大曹庄中国水利水电科学研究院智慧灌溉技术与装备创新示范推广基地开展试验,试验区为三跨加悬臂圆形喷灌机控制灌溉面积7.07 hm^(2),2021年试验区等分为2个子区,布置URI和VRI处理,2022年试验区等分为4个子区,布置URI处理、基于等间隔法进行管理区聚类划分的VRI(T1)处理、基于“Jenks”自然断点法进行管理区聚类划分的VRI(T2)处理和基于几何间隔断点法进行管理区聚类划分的VRI(T3)处理。结果表明,在冬小麦生育期内,URI和VRI处理灌水7~10次,2 a平均灌水量分别为201和173 mm。开展VRI管理后,冬小麦主根区的土壤含水率空间分布均匀性和产量均匀性提高。2021年URI和VRI处理的冬小麦产量分别为9 470和9 574 kg/hm^(2),2022年的冬小麦产量较2021年分别降低6.7%和6.0%。变量灌溉处理的管理区聚类划分方法未对灌溉制度和产量产生显著影响。与URI处理相比,VRI处理能够减少灌溉水量,且对产量和水分利用效率无显著影响。研究结果可为基于喷灌机机载式红外温度传感器系统的变量灌溉动态分区管理方法的建立提供指导,为变量灌溉决策支持系统的开发升级提供技术支持。

养殖肥水喷灌条件下摇臂式喷头水力性能研究

【目的】研究不同喷灌介质对喷头水力性能的影响。【方法】以20PY2H摇臂式喷头为研究对象,在不同工作压力下测定了清水和养殖肥水2种喷灌介质对喷头压力-流量、喷头水量分布的影响。通过模拟计算和田间喷灌试验分析相结合的方法,探查喷灌介质、工作压力、组合间距、田间气象条件与喷灌均匀性之间的关系。【结果】(1)与清水灌溉相比,养殖肥水运行下喷头流量降低了2.06%~5.38%,射程前中段径向水量分布差异较大;(2)工作压力为200~300k Pa、组合间距为1.0R~1.4R条件下,MATLAB拟合出的CU模拟值为0.74~0.88,CU试验值为0.66~0.79。复杂的大田气象条件导致喷灌均匀系数下降了6.28%~12.78%。工作压力、喷头组合间距对清水运行喷灌均匀性的影响大于养殖肥水运行。【结论】养殖肥水喷灌更利于喷灌系统降低工作压力和增加喷头布置间距以降低设计成本。

掺气摇臂喷头喷灌的综合性能评价与配置优化

掺气摇臂喷头具备气液两相射流、低压喷灌性能好等特性。为得到20PY2型该喷头的最优参数配置,基于组合喷灌试验,通过主成分分析法进行综合评价与配置优化。配置参数为工作压力、掺气管伸缩量和组合间距倍数,评价指标为平均喷灌强度、组合喷灌均匀度、喷洒能耗等。结果表明:平均喷灌强度与组合喷灌均匀度、喷洒能耗呈正相关,与有效喷灌面积和水利用系数呈负相关,其中,相关性最强的指标为平均喷灌强度和组合喷灌均匀度;选择特征根分别为2.534、1.322的两个主成分,第一主成分受平均喷灌强度、组合喷灌均匀度和有效喷洒面积影响大,第二主成分受喷洒能耗影响大;掺气摇臂喷头应选择相对较高的工作压力;最优的参数配置方案:工作压力250 kPa、掺气管伸缩量2 cm和组合间距倍数1.1,为掺气摇臂喷头的田间应用提供指导。

智慧农业灌溉控制系统的电路设计研究

文章设计了基于ZigBee技术、STM32F103微控制器的智慧农业灌溉控制系统,该系统主要由主控电路、土壤湿度传感器电路、喷灌电机的驱动电路及供电电路组成,可实现土壤湿度的精准控制及远程监测。通过灌溉系统精准控制试验,验证了本系统对土壤湿度的控制准确度、稳定性和灌溉效率都比较高,可为我国智能化节水灌溉装备的发展提供一定参考。

折射式微喷头水力性能试验及工作参数优选

为探究折射式微喷头水力性能并确定其适宜的工作参数,开展微喷头水力性能测试,明晰不同工况下单个微喷头水量分布特征,分析其流量、射程、喷灌强度随工作压力和喷嘴直径的变化趋势。探究在正方形和正三角形组合方式下,工作压力和组合间距变化对喷灌均匀系数CU的影响,基于主成分分析方法,统一相关评价指标,建立折射式微喷头工作参数综合评价模型。结果表明:单喷头的流量、喷灌强度均与工作压力呈正相关,而射程随压力的变化并不明显;正方形和正三角形两种组合方式下,组合间距变化对CU产生的影响明显大于工作压力和组合方式;依据各工况评分高低,对微喷头最优工况做出合理选择,实例应用的结果表明:折射式微喷头最优工况为正三角形组合,工作压力0.25 MPa,组合间距0.4 m。

间歇和连续喷灌下土壤水分运动特征COMSOL数值模拟与验证

为探明间歇喷灌和连续喷灌条件下的土壤水分运动规律,建立喷灌随时间变化的非均匀灌水边界下的土壤水分二维运动模型,借助COMSOL数值模拟软件,实现模型的求解,并通过土箱试验对模型进行验证,分析不同喷灌模式下土壤水分运动特征,评估喷灌均匀性和喷灌模式对土壤含水率均匀性的影响。结果表明,土壤含水率和土壤湿润峰模拟值与实测值之间的一致性较好。喷灌模式对土壤水分运动过程和含水率均匀度影响不大。随着间歇次数和间歇时长的增加,喷灌结束时表层土壤含水率减小、水分入渗深度增加。喷灌条件下,土壤含水率均匀度高于地表测得的喷灌均匀度。当喷灌均匀度为39.77%~80.15%时,土壤含水率均匀度为88.57%~94.47%。当喷灌均匀度较低、点喷灌强度较高、总灌水量较大时,采用间歇喷灌、增加间隙次数和总间歇时长,可以一定程度降低地表径流和深层渗漏风险、改善土壤含水率均匀性。研究可为喷灌系统设计均匀度合理取值和高效运行提供理论基础。

Controlling secondary flow in high-lift low-pressure turbine using boundary-layer slot suction

The design of high-lift Low-Pressure Turbines(LPTs)causes the separation of the boundary layer on the suction side of the blade and leads to a strong secondary flow.This present study aims to minimize secondary losses through endwall slot suction and incoming wakes in a front-loaded high-lift LPT cascade with Zweifel of 1.58 under low Reynolds number of 25000.Two slotted schemes for the boundary layer of the endwall were designed(Plan A and Plan B),and the effects of suction mass flow on secondary flow were studied.The underlying physics of the endwall boundary layer of the suction and secondary flow under unsteady wakes was discussed.The results show that slot suction at the endwall boundary layer can significantly suppress the secondary flow by removing low-momentum fluids.Plans A and B significantly reduced the secondary kinetic energy by 44.2%and 36.9%,respectively,compared with the baseline cascade at the suction mass flow ratios of 1%.With an increase in the mass flow ratio of suction,the secondary flow was gradually reduced in both Plans A and B.It is more beneficial to control the secondary flow to destroy the intersection of the pressure side and suction side of the horseshoe vortex before it develops into a passage vortex.Under unsteady wakes,the combined effects of incoming wakes and endwall boundary layer suction can further suppress the secondary flow at the suction mass flow ratios of 2%for Plan A,because the positive and negative vorticity inside upstream wakes accelerated the mixing of the main flow and secondary flow and thus increased the energy of secondary vortices.