Heat and mass transfer flow over a stretching surface with Ohmic heating and chemical reaction

The present study analyzes the effect of chemical reaction on an unsteady magnetohydrodynamic boundary layer viscous fluid over a stretching surface embedded in a porous medium with a uniform transverse magnetic field. A Darcy‐Forchheimer drag force model is employed to simulate the effect of second‐order porous resistance. Dissipative heat energy based on both viscous and Joule dissipation along with a heat source/sink is considered to enhance the energy equation. Similarity analysis is imposed to transform the governing differential equations into a set of nonlinear coupled ordinary differential equations. These sets of equations are solved numerically using the Runge‐Kutta fourth‐order scheme followed by the shooting algorithm. The effects of physical parameters such as magnetic field, Prandtl number, Eckert number, Schmidt number, unsteadiness parameter, and chemical reaction parameters have been discussed on velocity, temperature, and concentration fields. Computation for the coefficient of skin friction, rate of heat and mass transfer is done and presented in a table for validation of the present outcomes.     

Effect of processing method on vitamin profile,antioxidant properties and total phenolic content of coconut (Cocos nucifera L.) sugar syrup

Coconut (Cocos nucifera L.) sugar is a more nutritious alternative sugar source as compared to sugar palm (Borassus flabellifer) and sugarcane (Saccharum officinarum L.). This work was aimed to investigate the browning index (BI), vitamin profile and antioxidant properties of coconut sap sugar syrups, which were produced by different processing methods: rotary evaporation (RE), microwave evaporation (ME) and open-heat evaporation (OHE). The results obtained showed that coconut sugar syrup produced by RE-60 contained high antioxidant activities [DPPH (36.71%) and ABTS (34.84%), TPC (299.87 mg per 100 g sample) and FRAP (3.74 mm )]. These values were slightly lower than those of ME and OHE. Coconut sugar syrup (RE-60) also contained higher amounts of vitamin C (1587.27 mg L⁻¹), vitamin B1 (97.44 mg L⁻¹) and vitamin B3 (19.84 mg L⁻¹) compared with those of ME and OHE coconut sugar syrups. RE-60 was the best method to produce coconut sugar syrup in a shorter time with lower browning index and higher vitamin contents.     

Policy reforms and productivity change in the judiciary system: a cost function approach applied to time series of the Dutch judiciary system between 1980 and 2016

The judiciary is constantly undergoing change in order to respond to a wide range of social developments that have brought the sector under increasing pressure. In order to deal with the constant call for enhancing budgets, different policy measures have been taken to downsize the appeal to the judiciary and to improve productivity. One of the central questions hereby is whether these measures have actually contributed to a more productive sector. This paper focuses on the development of productivity in the judiciary and how policy measures have affected productivity. In this empirical analysis, we apply a cost function model to time series data of the Dutch judiciary between 1980 and 2016. The results show a dramatic decline of productivity over the entire period (?50%), in spite of various policy measures. The year 2001 can be regarded as a turning point, as since then productivity has remained more or less stable. It seems that this is largely due to the establishment of the Council for the Judiciary and the associated increase in (financial and operational) autonomy for the judiciary. Another striking result is that technical change is biased toward using more personnel through time.     

Fourier Analysis of Serial Dependence Measures

Classical spectral analysis is based on the discrete Fourier transform of the autocovariances. In this article we investigate the asymptotic properties of new frequency‐domain methods where the autocovariances in the spectral density are replaced by alternative dependence measures that can be estimated by U‐statistics. An interesting example is given by Kendall's τ, for which the limiting variance exhibits a surprising behavior.     

Scheduling distributed flowshops with flexible assembly and set-up time to minimise makespan

The scheduling problems under distributed production or flexible assembly settings have achieved increasing attention in recent years. This paper considers scheduling the integration of these two environments and proposes an original distributed flowshop scheduling problem with flexible assembly and set-up time. Distributed production stage is deployed several homogeneous flowshop factories that process the jobs to be assembled into final products in the flexible assembly stage. The objective is to find a schedule, including a production subschedule for jobs and an assembly subschedule for products, to minimise the makespan. Such a scheduling problem involves four successive decisions: assigning jobs to production factories, sequencing jobs at every factory, designating an assembly machine for each product and sequencing products on each assembly machine. The computational model is first established, and then a constructive heuristic (TPHS) and two hybrid metaheuristics (HVNS and HPSO) are proposed. Numerical experiments have been carried out and results validate the algorithmic feasibility and effectiveness. TPHS can obtain reasonable solutions in a shorter time, while metaheuristics can report better solutions using more yet acceptable time. HPSO is statistically comparable yet less robust compared with HVNS for small-scale instances. For the large-scale case, HPSO outperforms HVNS on both effectiveness and robustness.     

高质量浓度曲拉通X-100对煤泥浮选的抑制效应及机理

表面活性剂在煤泥浮选领域中应用广泛,且表面活性剂常被用于煤泥浮选促进剂,本文从另一个方面探究了表面活性剂在过量的情况下对煤泥浮选的抑制效应及其机理。以低灰煤粒和表面活性剂曲拉通X-100为研究对象,采用X射线光电子能谱(XPS)表征曲拉通X-100在煤表面的吸附状态,静态接触角测定仪测定曲拉通X-100对煤表面疏水性的影响,并探究了不同质量浓度曲拉通X-100液滴在煤粒表面的润湿与铺展情况,采用诱导时间测量仪分析不同质量浓度曲拉通X-100水溶液中的气泡与煤粒的黏附情况,最后通过紫外分光光度计定量表征浮选槽中残留曲拉通X-100质量浓度与不同浮选时间下浮选结果的对应关系。结果表明:高质量浓度曲拉通X-100会抑制煤粒上浮,随着浮选试验的进行,曲拉通X-100质量浓度逐渐降低,低质量浓度曲拉通X-100会促进煤粒被上浮气泡黏附而浮出;高质量浓度曲拉通X-100能够在煤粒表面发生有效吸附,该吸附属于物理吸附,且在一定程度上提高了煤表面的疏水性;高质量浓度曲拉通X-100水溶液更容易润湿煤表面,从而减缓了气泡-煤粒黏附过程中的液膜薄化与破裂速率;在高质量浓度曲拉通X-100水溶液中,气泡表面因罩盖有曲拉通X-100分子,导致气泡表面发生改性,难以与煤粒发生有效黏附。高质量浓度曲拉通X-100主要通过对气泡改性,以及减缓气泡与煤粒碰撞-黏附过程中的液膜薄化-破裂速率来抑制煤粒的浮选。     

On the feasibility of on-farm biogas-to-electricity conversion: To what extent is solid oxide fuel cells durability a threat to break even the initial investment?

Despite their promising features, adverse economic feasibility still hamper SOFCs wide implementation and this effect is emphasized as long as the system size is reduced. According to previous investigations, the biogas pre-treatment section represents a burden for the economic viability. Aiming at reducing the extent of installation costs in SOFC-based configurations, biogas partial upgrading through CO₂ gas-separation membranes is put forth as innovative solution against reforming. This innovative system concept is expected to make SOFCs more cost-effective, yet resulting feeding gas might cause a quicker SOFC performance decay. Besides solving this trade-off, the economic viability results strongly sensitive to subsidiary electricity prices in force according to the regulatory framework.This paper presents a comparative economic assessment regarding biogas-to-electricity conversion via Solid Oxide fuel cells (SOFCs) and mature technologies as internal combustion engines (ICEs). Results highlighted that, the innovative SOFC system is far more viable than reforming-based one, exhibiting a reasonable payback time, with an adequate subsidized electricity sale price (4 and 5 years for small/medium and large-size plants respectively when subsidy is 0.28 €/kWh), up to 1%_1000h degradation rate. On the other hand, whilst considering a SOFC degradation rate of 0.03%_1000h, the reforming-based system appears feasible only on large-size plants, yet recovering the initial capital expenditure in 9 years. Moreover, once the break-even point is reached, the gain in the net revenue produced by the innovative system is amplified in the event of small-size installation. This allows the possibility to undertake the risk of higher degradation rates (up to 2%_1000h) without jeopardizing the economic profitability. Therefore, in the present regulatory framework and under current capital costs projections, the innovative SOFC system appears as much profitable as ICE mature technology. Such effort in the design of the fuel pre-treatment unit can lever SOFC broad spreading into the market of small biogas producers.     

一种改进的合成流量法及其在水文预报中的应用

合成流量法对下游站流量作出预报的关键是确定各上游站流量到达下游站的时间。在实际中常采用平均传播时间,然而不同水情下真实传播时间与平均传播时间存在一定的差距,影响预报精度。对此,提出时间窗口概念,以平均传播时间为中心,向前、后各开一个时间窗口,用上游各站时间窗口内流量的线性组合表示其到达下游站的流量,以提高模型对不同水情的适应能力和预报精度。以三峡水库2009~2015年流量数据率定参数,以2016~2018年流量数据作为预报对象,试验结果表明时间窗口法能够显著改善预报精度。     

基于广义二次互相关的低信噪比信号时延估计

针对时延估计精度受噪声影响,导致时延估计不准确的问题,在现有广义二次相关算法的基础上,提出了一种改进的广义二次相关算法,通过将二次相关函数先做指数运算,降低噪声干扰,再将傅里叶逆变换得到的相关函数做高次方运算,达到锐化峰值提高时延正确率的目的。仿真结果表明,信噪比(SNR)在0~10 dB时,改进算法的均方根误差明显优于广义二次相关算法,正确率相比于广义二次相关算法也显著提高,且在更低SNR的情况下仍然具有一定优势。