Auto-parametric resonance of a continuous-beam-bridge model under two-point periodic excitation:an experimental investigation and stability analysis

The auto-parametric resonance of a continuous-beam bridge model subjected to a two-point periodic excitation is experimentally and numerically investigated in this study.An auto-parametric resonance experiment of the test model is conducted to observe and measure the auto-parametric resonance of a continuous beam under a two-point excitation on columns.The parametric vibration equation is established for the test model using the finite-element method.The auto-parametric resonance stability of the structure is analyzed by using Newmark's method and the energy-growth exponent method.The effects of the phase difference of the two-point excitation on the stability boundaries of auto-parametric resonance are studied for the test model.Compared with the experiment,the numerical instability predictions of auto-parametric resonance are consistent with the test phenomena,and the numerical stability boundaries of auto-parametric resonance agree with the experimental ones.For a continuous beam bridge,when the ratio of multipoint excitation frequency(applied to the columns)to natural frequency of the continuous girder is approximately equal to 2,the continuous beam may undergo a strong auto-parametric resonance.Combined with the present experiment and analysis,a hypothesis of Volgograd Bridge's serpentine vibration is discussed.

Stochastic Programming for Hub Energy Management Considering Uncertainty Using Two-Point Estimate Method and Optimization Algorithm

To maximize energy profit with the participation of electricity,natural gas,and district heating networks in the day-ahead market,stochastic scheduling of energy hubs taking into account the uncertainty of photovoltaic and wind resources,has been carried out.This has been done using a new meta-heuristic algorithm,improved artificial rabbits optimization(IARO).In this study,the uncertainty of solar and wind energy sources is modeled using Hang’s two-point estimating method(TPEM).The IARO algorithm is applied to calculate the best capacity of hub energy equipment,such as solar and wind renewable energy sources,combined heat and power(CHP)systems,steamboilers,energy storage,and electric cars in the day-aheadmarket.The standard ARO algorithmis developed to mimic the foraging behavior of rabbits,and in this work,the algorithm’s effectiveness in avoiding premature convergence is improved by using the dystudynamic inertia weight technique.The proposed IARO-based scheduling framework’s performance is evaluated against that of traditional ARO,particle swarm optimization(PSO),and salp swarm algorithm(SSA).The findings show that,in comparison to previous approaches,the suggested meta-heuristic scheduling framework based on the IARO has increased energy profit in day-ahead electricity,gas,and heating markets by satisfying the operational and energy hub limitations.Additionally,the results show that TPEM approach dependability consideration decreased hub energy’s profit by 8.995%as compared to deterministic planning.

进水分配比对分段进水PN/A工艺脱氮性能影响

以预脱碳污水和市政污水作为目标污水,建立了好氧段分段进水的新模式,通过调整进水分配比来优化好氧段C/N,以期实现短程硝化-厌氧氨氧化(PN/A)工艺在实际工况下的稳定运行.采用4组以好氧/缺氧/好氧/缺氧(O/A/O/A)模式运行的序批式反应器(SBR),R1、R2、R3及R4以进水分配比(预脱碳污水:市政污水)分别为1:0、2:1、1:1及1:2的分段进水模式运行.结果表明,R1未能实现PN/A工艺,总氮去除率(NRE)仅为60.2%.随着进水分配比不断下降,R2、R3、R4分别在第34,30及36d实现PN/A工艺,NRE分别达到71.8%、80.3%及74.1%.其中R3系统处理性能最好且最稳定,厌氧氨氧化贡献率达到83.9%.污泥沉降性与粒径最佳.此外,高通量结果显示氨氧化菌(Nitrosomonas)和厌氧氨氧化菌(Candidatus_Kuenenia)丰度分别为2.74%和12.17%,且与好氧异养菌(AHB)形成了良好的协同作用.因此,分段进水模式在进水分配比为1:1时有利于实现稳定的PN/A工艺,此时各功能微生物可得到较好富集与平衡.

以丝瓜络为碳源的固相反硝化系统性能

构建以丝瓜络为碳源的固相反硝化系统,探究不同水力停留时间(HRT)和进水硝酸盐浓度(INC)下该系统的反硝化性能,为丝瓜络作为水产养殖尾水反硝化碳源的工艺优化提供理论依据。以丝瓜络(LS)为一维反硝化反应器(denitrification reactor,DR)外加碳源,在流场环境下,测定不同HRT(16、20、24和28 h)和INC(50、75、100和125 mg/L)下反硝化系统对硝酸盐氮(NO_(3)^(-)-N)、亚硝酸盐氮(NO_(2)^(-)-N)、氨氮(NH_(4)^(+)-N)、总氮(TN)、总磷(TP)和化学需氧量(CODcr)的去除效果。并采用高通量测序技术对丝瓜络反硝化反应器(LS-DR)在运行初期和末期时的细菌群落结构进行分析。当INC为50 mg/L,HRT为24h时,LS-DR对NO_(3)^(-)-N和TN均有较好的去除效果,去除率分别为98.97%±0.52%和97.84%±0.94%,此时出水NO_(2)^(-)-N浓度也达到较低水平(小于0.5 mg/L);在HRT为24 h的基础上,当INC增加至75、100和125 mg/L时,其NO_(3)^(-)-N去除率和NO_(3)^(-)-N去除速率(NRR)均随INC的增加而显著增加,出水COD则随INC的增加而降低,但均未实现完全反硝化,然而,LS-DR在整个实验期间均能完全去除NH_(4)^(+)-N;扫描电镜结果显示,丝瓜络表面结构有利于微生物附着生长;高通量测序结果显示,LS-DR的优势菌门包括变形菌门、拟杆菌门、弯曲杆菌门、厚壁菌门和疣微菌门;被鉴定的优势菌属中热单胞菌属(1.46%)、陶厄氏菌属(0.55%)、固氮螺菌属(3.32%)、Simplicispira(1.01%)、假黄色单胞菌属(0.39%)、草螺菌属(3.02%)和Uliginosibacterium(0.9%)主要参与反硝化的进行,Cytophaga xylanolytica(1.61%)和Cloacibacterium(2.69%)主要参与了丝瓜络的降解,黄杆菌属(1.17%)和Diaphorobacter(0.64%)既能进行反硝化,也能降解丝瓜络。LS-DR的最佳HRT为24 h,最适宜的INC为50 mg/L。本研究为丝瓜络固相反硝化工艺的优化提供了理论基础,为开发新型缓释碳源在养殖尾水处理中的应用提供参考。

A^(2)/O+反硝化深床滤池在城镇污水处理厂深度经济脱氮的运行优化

脱氮是当前城镇污水处理的重点,其中A^(2)/O+反硝化滤池工艺是生活污水处理主流工艺,四川省岷江流域某城镇污水处理厂通过优化进水流量分配比、调节溶解氧和内回流比、碳源筛选等工艺试验,综合考察了工艺调控措施对系统脱氮效能的提升以及脱氮成本的经济化控制。结果表明,A^(2)/O池进水100%进入厌氧区、内回流比200%、A^(2)/O池末端溶解氧控制在1.5 mg/L、反硝化深床滤池投加液体复合碳源,在有效深度脱氮的同时节约运行费用,总氮指标满足岷沱江标准,脱氮费用降低0.37元/m^(3)。

反硝化颗粒污泥系统和反硝化生物膜系统深度脱氮对比研究

对比分析了反硝化颗粒污泥系统和反硝化生物膜系统在不同进水条件和不同水力停留时间(HRT)下的脱氮效果。结果表明,当进水COD较高即外部碳源较为充足时,反硝化颗粒污泥系统和反硝化生物膜系统脱氮效果接近;而当进水总氮浓度较高即外部碳源受限时,生物膜系统的脱氮效果优于颗粒污泥系统。在不同的HRT条件下(3~6 h),反硝化生物膜系统的深度脱氮效果均优于反硝化颗粒污泥系统,且当HRT=5 h时,两系统的脱氮性能均达到最高。实验结果表明反硝化生物膜系统在脱氮性能方面略胜一筹。但是,结合经济性和去除性能进一步分析可知,与生物膜系统相比,颗粒污泥系统具有占地面积小、无载体成本等低成本的显著优势,在既有工艺出水深度脱氮的工程实践中,可优先选择反硝化颗粒污泥工艺,并可通过控制颗粒粒径和系统运行参数等措施强化脱氮性能。

关于两个两点Witten-Kontsevich关联子公式等价的一个注记

We prove the equivalence between two explicit expressions for two-point Witten-Kontsevich correlators obtained by Bertola-Dubrovin-Yang and by Zograf, respectively.

提质增效下河网地区典型城镇污水厂污泥产率变化趋势研究

近年来,我国大力推进城镇污水系统提质增效,污水厂进水浓度、进水量大幅度提升,污泥产量也随之提升。通过对广州市河网地区N污水厂调研研究,分析污泥产率在提质增效前后的变化规律,深入研究进水COD、BOD、SS浓度和进水量等因素在提质增效前后对污泥产率的具体影响,结果表明:污水厂污泥产率在提质增效前后具有明显差异,提质增效后污泥产率大幅度上升,后逐步降低并趋于稳定;提质增效强化了污泥产率与进水COD、SS浓度的正相关性关系,强化了污泥产率与进水量的负相关关系;污泥产率与进水BOD浓度在提质增效前呈弱的负相关关系,提质增效后呈弱的正相关关系。

优化污泥回流方式对多级AO-MBR工艺的影响

采用处理水量为0.15 m^(3)/h的中试装置,开展多级AO-MBR工艺处理低C/N城市污水试验研究,通过优化污泥回流方式、溶解氧及污泥浓度控制等措施,降低高溶解氧污泥回流对前端生化池的影响,实现出水水质达到地表水准Ⅳ类标准(TN除外)。结果表明,在耦合MBR工艺的形式下,经过生化池多级回流能显著保证各反应区的溶解氧环境,保持各反应区的污泥浓度平衡,进一步提高出水水质。在水温低于12℃、进水TN质量浓度为23~33 mg/L时,采用回流方式4能稳定保证TN去除率达到60%以上,实现出水TN质量浓度达到10 mg/L左右;进水TP质量浓度为2~4 mg/L时,TP去除率达到85%以上,实现出水TP质量浓度低于0.3 mg/L的要求。

The Reality of Baryonic Acoustic Oscillations

The initial idea for baryonic acoustic oscillations (BAO) came about during early efforts to understand the origin of galaxies by studying perturbed versions of the Friedmann-Robertson-Walker (FRW) model. In more recent times, the emphasis has shifted to the idea that 2-point galaxy correlations embedded in the distribution of matter by the BAO could be used as a standard ruler to fix the parameters of cosmological models. In this paper, we first consider the actual business of extracting the correlation length from large data sets of measured galaxy locations. To facilitate this process, we introduce a much-improved method for extracting the correlation peak from the data set. Fundamental to this process in any model is the use of a fiducial cosmological model to transition from redshift space to comoving coordinate space where the correlations actually exist. The belief is that the correlation length so determined can then be reverted to redshift space to fix the parameters of cosmological models. We show, however, that this process is circular and hence of no value whatsoever for fixing model parameters. All one obtains are the parameters of the model used to transition to comoving space in the first place. Finally, we present simple arguments that show that the idea of BAO being responsible for the structure of the universe, i.e. the cosmic web, is unworkable.

排水系统提质增效的外水定量分析及剥离措施研究

污水处理厂进水COD低是制约活性污泥工艺降解污染物效果提升的瓶颈。针对污水处理厂进水COD低的问题,建立了一种联用基于污水管网简化的水质水量模型逆向分析和正向摸查的外水入侵评估方法。通过污水管网简化的水质水量模型的逆向分析,确定了各级管网外水入渗量,并准确找出外水入侵的重点区域为主城区东北和西南侧。通过正向摸查发现,地下水入渗、雨水错接混入和河水倒灌为外水入侵主要原因,且外水侵入重灾区与定量分析结果一致。针对外水入侵的重点区域和外水入侵主要途径,实施了外水剥离措施,释放了管道内外水、增加污水收集量、提高旱天污水处理厂的进水COD浓度和保证旱天无溢流,最终达到污水处理厂进水COD浓度显著提升的目标。

污水处理厂纳污片区排水污染源调查与进水浓度关联分析

住建等四部委要求到2025年进水BOD_(5)浓度高于100 mg/L的城市生活污水处理厂规模占比达90%以上。本文以截至2023年的城市污水厂进水浓度距国家考核目标还存在较大差距的南方某城市为例,了解该市主城区污水处理厂纳污范围排水单元污染物浓度情况,选取有代表性的污水处理厂内约40家典型排水单元,以BOD_(5)为监测对象,分不同时期对水质调查监测,分析与污水厂进水浓度的关联性,得出排水单元BOD_(5)平均浓度总体能达到100 mg/L的考核要求;不同类型排水单元污染物浓度差距不明显;冬季污水中污染物浓度较高;纳污范围内排水管网对污染物浓度削减作用明显等主要结论。同时针对问题,提出推进污水处理“源头减量”、“提质增效”;加强运维管护“清淤疏浚”、“低位运行”;加强后续监测,精准分析等管理建议,以期为相关行业主管部门后续工作提供数据支撑。

清水池水力效率影响因素研究

清水池具有水力调节和消毒接触的双重作用,提高t_(10)/T是提高消毒效率而减少消毒剂投加量和副产物生成量的有效方法。针对清水池实例,进行整体建模,以数值模拟方法,研究主要尺寸对清水池t_(10)/T的影响程度,并验证设计方案的合理性。结果表明:长宽比是t_(10)/T影响最为明显的因素,但变大的趋势放缓。减少弯道数量及宽度和增大进水管管径,均可使t_(10)/T有所增加。清水池实例的长宽比为38,水力效率为0.54,可以满足不少于0.5的设计要求。

长江中下游典型污水系统提质增效案例研究

以长江中下游某城市南部污水系统为例,对污水系统外水入侵、高水位运行、进厂水质浓度低等问题进行分析,针对性的提出分片、分区、分阶段提质增效的思路,并给出降水位排查污水管网、市政管网系统整治、排水单元整治、污水管网优化运行等技术措施.先期实施的1#泵站片区通过上述措施,已挤出外水量约为12 708 m3/d,污水厂进水BOD5浓度由69.6 mg/L提升至78.3 mg/L,较整治前提升12.5%,城市污水集中收集率由61.6%提升至69.3%,基本实现了提质增效的阶段目标.

污水厂低浓度进水问题分析

随着《城镇污水处理提质增效三年行动方案(2019~2021)年》的印发,全国各地积极开展提质增效工作。工程实施后,部分城市污水处理厂进水浓度偏低的问题改善有限,成为提质增效的痛点。基于完成市政排水管网改造工程的情况,对某污水处理厂进水CODCr浓度仍不足100 mg/L的污水分区进行成效评估排查,通过水质水量平衡计算,分析出该新建区存在规划与现状不匹配、非生活用水占比高、雨污混接情况复杂等问题,得出通过工程手段难以彻底解决污水厂低浓度进水问题的结论。为该区域后续提质增效工作提出优化排水结构、强调建管结合、加强排水管理及合理制定提质增效目标的建议。

Simulation and control strategy for the variational influent of WWTP

With the development of activated sludge model, the simulation software for the design and operation of wastewater treatment plant （WWTP） was produced and has been widely used. The dynamic change of the quality and flow of influent are major factors causing the unstable operation of wastewater treatment process. As a basic model, ASMI model was used for the simulation of activated sludge process, and double exponential model was selected for the simulation of secondary sedimentation tank. The influences of influent change to the aeration tank and secondary sedimentation tank were investigated, and the relationship among influent change, the quality of effluent and the level of sludge blanket in secondary sedimentation tank was established. On the basis of the simulation results, the operation of the WWTP could be adjusted under the dynamic change of the influent. Furthermore, the controlling strategy combined the feed-forward on the influent flow and the feedback on the level of sludge blanket in the secondary sedimentation tank was studied.

Existence of solutions and positive solutions to a fourth-order two-point BVP with second derivative

Several existence theorems were established for a nonlinear fourth-order two-point boundary value problem with second derivative by using Leray-Schauder fixed point theorem, equivalent norm and technique on system of integral equations. The main conditions of our results are local. In other words, the existence of the solution can be determined by considering the height of the nonlinear term on a bounded set. This class of problems usually describes the equilibrium state of an elastic beam which is simply supported at both ends.

Existence and iteration of monotone positive solutions for a third-order two-point boundary value problem

The existence of nondecreasing positive solutions for the nonlinear third-order twopoint boundary value problem u′″（t） ＋ q（t）f（t,u（t）,u′（t）） = 0, 0 〈 t 〈 1, u（0） = u″（0） = u′（1） = 0 is studied. The iterative schemes for approximating the solutions are obtained by applying a monotone iterative method.

HIGH ACCURACY FINITE VOLUME ELEMENT METHOD FOR TWO-POINT BOUNDARY VALUE PROBLEM OF SECOND ORDER ORDINARY DIFFERENTIAL EQUATIONS

In this paper, a high accuracy finite volume element method is presented for two-point boundary value problem of second order ordinary differential equation, which differs from the high order generalized difference methods. It is proved that the method has optimal order error estimate O(h3) in H1 norm. Finally, two examples show that the method is effective.

Two-point compression ultrasonography: Enough to rule out lower extremity deep venous thrombosis?

BACKGROUND: Deep venous thrombosis(DVT) is a major cause of morbidity and is a common presenting complaint to the emergency department(ED). Point-of-care two-point compression ultrasonography has evolved as a quick and effective way of diagnosing DVT. The purpose of this study is to validate the prevalence and distribution of venous thrombi isolated to proximal lower extremity veins, other than common femoral and popliteal veins in patients with DVT.METHODS: This is a single-center retrospective study that looked at patients presenting to the ED of a tertiary care hospital between January 2014 and August 2018. The clinical presentation and laboratory and imaging results were obtained using the hospital's electronic medical record.RESULTS: A total of 2,507 patients underwent a lower extremity duplex ultrasound during the study period. Among them, 379(15%) were included in the study. The percentages of isolated thrombi to the femoral vein and deep femoral vein were 7.92% and 0.53%, respectively. When the patients were stratified into the two groups of isolated DVT and two-point compression DVT, there were no statistically significant differences in the laboratory results between both groups. However, immobilized patients and patients with recent surgeries were more likely to have an isolated DVT.CONCLUSIONS: Thrombi isolated to proximal lower extremity veins other than the common femoral and popliteal veins make up 8.45% of DVTs. Given this significant number of missed DVTs, the authors recommend the addition of the femoral and deep femoral veins to the two-point compression exam.