Influences of wake-effects on bubble dynamics by utilizing micro-pin-finned surfaces under microgravity

The influences of wake on bubble dynamics under various heat fluxes have been studied in microgravity. Nucleate pool boiling experiments of FC-72 on silicon chips fabricated with micro-pin-fins were conducted in 10(-3) gravitational acceleration for 3.6 s. Experimental results indicated that wake field had little influence on bubble dynamics at low heat flux, q = 12.53 W/cm(2), but its effects on bubble dynamics became very great at moderate heat flux, q = 27.89 W/cm(2), and high heat flux, q = 39.54 W/cm(2). More importantly, wake-effects appeared even more significant in microgravity. In the wake field, the horizontal flow of the liquid on micro-pin-finned silicon chips promoted the collision, coalescence and movement of bubbles, and the vertical flow of liquid phase exerted an upward force on bubbles, which can effectively shorten the growth cycle and decrease the departure radius of bubbles. Furthermore, fresh liquid could easily be inhaled into the micro-pin-finned structure owning to the negative pressure in wake region, which can supply sufficient liquid for the growth of bubble, avoiding film boiling. The interaction between the micro-pin-finned structure and the wake effect promoted the process of bubble coalescence and departure effectively, so the process of heat transfer was significantly improved on micro-pin-finned surface. In addition, the flow field and bubble behavior in wake region were also briefly analyzed based on some reasonable simplifications and hypotheses. The theoretical analyses showed that the durations of wake-effects lasted longer than the time periods of the bubble in next generation, and the bubble diameters were also smaller than the thickness of Wake region. Therefore, the dominant bubble of next generation was influenced by the wake field during its ebullition cycle, which is consistent with the experimental phenomenon. (C) 2016 Elsevier Ltd. All rights reserved

Mechanical behavior and properties of hydrogen bonded graphene/polymer nano-interfaces

There is increasing evidence in literature for significant improvements in both toughness and strength of graphene-based nanocomposites through engineering their nano-interfaces with hydrogen bonds (H-bonds). However, the underlying mechanical behaviors and properties of these H-bonded interfaces at the microscopic level were still not experimentally clarified and evaluated. Herein, this work reports a study on the interfacial stress transfer between a monolayer graphene and a commonly used poly(-methyl methacrylate) (PMMA) matrix under pristine vdW and modified H-bonding interactions. A nonlinear shear-lag model considering friction beyond linear bonding was proposed to understand evolution of interfacial stresses and further identify key interfacial parameters (such as interfacial stiffness, strength, frictional stress and adhesion energy) with the aid of in situ Raman spectroscopy and atomic force microscopy. The present study can provide fundamental insight into the reinforcing mechanism and unique mechanical behavior of chemically modified graphene nano-interfaces and develop further a basis for interfacial optimal design of graphene-based high-performance nanocomposites. (C) 2016 Published by Elsevier Ltd

殷商羌族及岳神芻議

[[abstract]]中國古代羌族與先秦華夏民族之融合、形成有密切關係，而商、周之際，羌族之與周 ，實為商周與替之重要關鍵。然有關中國古代羌族之資料非夥，除金文、經籍、考古 發掘外，以甲骨文所載者為最早而可信，故本文乃以甲骨文資料為主，探討１．殷商 羌族與殷人之關係；２．羌、姜同源之歷史演變；３．古代羌族之岳神信仰等問題。 本文以嚴一萍先生「商周甲骨文總集」一書為基礎，分期整理「總集」中所見之全部 「羌」、「岳」字形，編為附錄，並製成「羌」、「岳」字形演化表，由此分期所得 進論上列諸問題，而文中引證卜辭，除原拓不清者外，亦悉描錄文後，以便參閱。 本文討論所得可歸納如下： １．甲骨文中「羌」字乃象羌人披髮而立之形，並非從羊從人會意。 ２．殷商羌人分布主要居殷西，並有少數羌人散居於殷北、殷東、殷南，由此可知甲 骨文中羌字已用為種族之稱。 ３．羌人之於殷，有敵之者，有臣之者。敵者殷人執而為牲，終殷之世不變；臣者殷 人使以田獵、征戰，並有服殷官職者。臣於殷者，自有其原，不必皆為戰爭之俘虜。 ４．殷商羌族、考古所見陝西商代「姜炎文化」、周代姜姓諸族三者間有其關聯，時 間、地望均可相合，若僅就此一歷史演變之情形而言，羌、姜同源之說仍可成立。然 甲骨文中末見「姜」字，「姜」字始見周金，均用稱女子之姓，所謂「羌姜一字」之 說法不可信。 ５．甲骨文中岳字，像山上復有疊峰之形，乃特稱山西一座神山，或即霍山，共非高 山之通稱。 ６．殷人視「岳」為一自然神，並未將之納入祖神系統，而古代羌族乃將岳神視為祖 神，二者有異。然甲骨文中之岳神羌族，除地望稍近外，尚末見有其他關係。

Contextual Refurbishing: Renovations of the Residential Building, Skopje, Macedonia

Skopje, in the last decades, underwent a dramatic spatial shift, due to transformation (traditional to modern), natural disasters (seismic destruction), and resurgence (re-plan and reconstruction). These changes have created a complex city, which over time became even more diverse through the creation of various cityscapes by both residents and architects. On the level of the building blocks wecan see some of the changes that have been made by residents in the form of building extensions. These adjustments reveal that a pure architect-driven project is incapable of reflecting the diversity of society.Architecture, Urbanism and Building Science

Simulation of the Flexural Response of Ultrahigh Performance Fiber-Reinforced Concrete with Lattice Fracture Model

The flexural response of ultrahigh performance fiber-reinforced concrete (UHPFRC) was simulated based on the lattice fracture model. Fiber was modelled as separated beam that was connected to the matrix with interface beams. The simulated results were compared with the experimental results. Deviations occurred at the late stage of the strain-softening period. But both the strain-hardening behavior and multicracking phenomenon were observed in the simulation. The effects of fiber orientation and fiber content were studied with the lattice fracture model. The flexural strength and toughness of UHPFRC improved as the fibers were aligned distributed or the fiber content increased. The proposed model has the potential to help with the materials design of UHPFRC, and the limitations of the model were also discussed in the paper.MicrolabMaterials and Environmen

Calibration and validation of cellular automaton traffic flow model with empirical and experimental data

For traffic flow models, calibration and validation are essential. Cellular automaton (CA) models are a special class of models, describing the movement of vehicles in discretised space and time. However, the previous work on calibration and validation does not discuss CA models systematically. This study calibrates and validates a stochastic CA model. The authors use a simple CA model, which only has two important parameters to be calibrated. The methodology for optimisation is to minimise the relative root mean square error between two properties: The averaged velocity and the variation of velocities in a platoon at a given density. Three different sites are used as cases to show the methodology, for which different types of data (video trajectories or GPS data) are available. The authors find that the best model parameters vary for the different locations. This may result from various driving strategies and potential tendencies. Thus, it is concluded that for CA models, various traffic flow phenomena need to be simulated by various parameters.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Transport and Plannin

Ground vibration induced by high speed trains on an embankment with pile-board foundation: Modelling and validation with in situ tests

To investigate the train-induced ground vibration, an explicit time-domain, three dimensional (3D) finite element (FE) model is developed. The train, track, embankment, pile-board structure and nearby ground soils are all fully coupled in this model. The complex geometries involving the track components and pile-board structure are all modelled in detail, which makes the simulation of wave propagation more realistic from the train to the ground. The model is validated with in situ tests data collected in the Beijing-Shanghai high speed railway line. Good agreements have been achieved between the numerical results and experimental results both in time domain and frequency domain. The proposed model is thus capable of reproducing the dynamic ground response induced by a typical high speed train. Soil responses induced by different number of vehicles are compared. With more vehicles, the spectral peaks of soil responses are more prominent at the integral multiples of the vehicle passing frequency. Too few vehicles will not bring about such phenomenon, thus sufficient number of vehicles should be included in a train to properly model train-induced ground vibration. With the proposed model, the influence of the pile-board foundation on the ground vibration is investigated. It is found that the pile-board foundation can significantly attenuate the low frequency ground vibration. The attenuation of the ground vibration as a function of distance from the track is simulated and the influential factors to the local vibration amplification are investigated. It is found that soil Young's modulus and soil impedance contrast are the two main factors influential to the local vibration amplification. The softer the natural soil, the larger the amplification. The larger soil impedance contrast makes the amplification more obvious. The soil stratification and geometric discontinuity at ground surface are not the main cause of the local vibration amplification in this work.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Pavement EngineeringRailway Engineerin

Mechanical behaviour and energy evolution of polyurethane-mixed ballast under revised bonding constitutive model

The bonding contact presents complex modes in polyurethane-mixed ballast. The commonly used parallel bond model is revised and four different contact models are developed including Ballast-Ballast Contact Bonding, Ballast-Ballast Noncontact Bonding, Ballast-Sleeper Contact Bonding, and Ballast-Sleeper Noncontact Bonding. The mechanical behaviour and energy evolution of polyurethane-mixed ballast with various amounts of glue are studied from the macro and mesoscopic properties. Results show that the elastic strain energy has always been the main form in polyurethane-mixed bed, followed by viscous strain energy, frictional energy, and damping energy. Compared with the common ballast bed, there are more contacts in polyurethane-mixed ballast bed and, when more glue is used, the amount of contacts is further increased while the maximum contact force is reduced. After bonding, the amount of contacts is significantly increased and all forms of energy become more evenly distributed at different surfaces of the sleeper. The kinetic energy of polyurethane-mixed ballast fluctuates with smaller amplitude and convergences more quickly under cyclic loading, which is reflected in the macroscopic aspect that the settlement of polyurethane-mixed ballast bed is relatively small and can be fast completed.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Mechanics and Physics of Structure

The data and services analysis of Chinese NSDI based on Backx model

The data and services analysis are indispensable for the refined development of SDI. This paper, taking Chinese NSDI as a study case, analyzed the data and services advantages and shortcomings of Chinese NSDI and developed a recommendable data and services framework which could improve the Chinese NSDI better services for public and private sectors from known, attainable and usable aspects by using Backx model. And the recommendation framework can also be referenced by other national and local SDI for its better services and applications.OLD Geo-information and Land Developmen

Effect of reactive aggregate on the early age reaction of water-glass activated slag/fly ash mortars

Alkali activated materials (AAMs) have received worldwide attention due to its lower embodied energy and environmental impact than that of traditional cementitious materials. However, the activators with high alkalinity may raise the risk of alkali silica reaction (ASR) induced deterioration when reactive aggregates are used, which thereby limits the commercial use of AAMs. Not speaking the ASR induced long-term expansion, the early-age reaction of AAMs prepared with reactive aggregates is largely unknown. In this paper, isothermal calorimetry, thermogravimetry (TG) and mercury intrusion porosimetry (MIP) were adopted to study the heat evolution, mineralogical changes and pore structures of early-age ordinary Portland cement (OPC) mortar and water-glass activated slag/fly ash mortars. In each system, emphasis were made to understand the differences between mixtures prepared with standard inert quartz sands and reactive fine aggregates. The results show that the mortars prepared with reactive aggregates generated more heat in the wetting and dissolution stage. Particularly, the water-glass activated slag mortar presented the highest heat flow peak. Meanwhile, the results of TG illustrate that higher amount of reaction products were formed in water-glass activated mortars prepared with reactive aggregates than that with inert quartz sands. These findings suggest that the reactive aggregates are evidently involved in the early-age alkaline reaction of AAMs system