Effect of calcium aluminate cement variety on the hydration of Portland cement in blended system

Two kinds of CACs with different monocalcium aluminate (CA) contents were used in the PC/CAC (PAC) mixtures. Effects of CA and CACs on the properties of PAC were analyzed by setting times and the compressive strength tests, and also by means of calorimetry, XRD, DTA-TG and ESEM. The experimental results show that the compressive strength of the PAC mortars decreases with increasing content of CAC while it declines sharply with a higher content of CA in CAC. Compared with neat PC paste, the content of calcium hydroxide in hydrates of PAC paste decreases significantly, and the hydration time of PC is prominently prolonged. Additionally, the higher the content of CA in CAC, the more obviously the hydration of PC is delayed, confirming that the CA phase in CAC plays an important role in the delay of PC hydration

Supported ITZ modification efficiencies via surface coating nanoparticles on aggregate and its influence on properties

In order to modify the porous interfacial transition zone (ITZ) microstructure of concrete more efficiently, a method of coating aggregate surfaces by using several nanoparticles was evaluated in this study. The compressive strength, chloride penetration of sound, and pre-loading samples were assessed in relation to the type of coating materials used (slag, nano-CaCO3, and nano-SiO2) and the designed coating thickness (5, 10, and 15 mu m). The ITZ microstructure was quantitatively determined via Backscattered electron (BSE) image analysis. Results showed that the overall performance of concrete is highly dependent on the coating materials and the designed coating thickness. Increasing the coating thickness of slag and nano-SiO2 could improve the chloride penetration resistance but decrease the compressive strength. Using nano-CaCO3 to coat the aggregate leads to a significant reduction in the properties of the so-prepared concrete. Though coating inert fine particles around aggregate could disturb the initial particle packing and modify the ITZ, it is not able to improve the overall concrete properties. Coating aggregate could determine the ITZ microstructure, especially within the region that is around 30 mu m away from aggregate surface

ブンカ カガク シュウ サクジン ノ ブンガク カクメイ ショキ ノ ブンガク シュチョウ カラ ミル シン ジュウブン ノ ブンガクカン

日中台共同研究「現代中国と東アジアの新環境」 ②21世紀の日中関係 : 青年研究者の思索と対

Evaluation of isolated DC/DC converter topologies for future HVDC aerospace microgrids

High performance power conversion equipment is currently gaining an increasing interest for aircraft applications. In particular, isolated bidirectional DC/DC converters are often proposed for modern HVDC aircraft distribution systems. For such reason an evaluation of several isolated DC/DC converter topology is carried out considering the proposed application, interfacing a 270V DC network with a 28V DC network. A trade off evaluation has been carried out for three different topologies and an experimental prototype has been manufactured for the selected conversion architecture. Simulation and experimental results are provided in order to validate the trade off and the design of the proposed converter

Enantioselective Total Synthesis of (+)-Psiguadial B

The first enantioselective total synthesis of the cytotoxic natural product (+)-psiguadial B is reported. Key features of the synthesis include (1) the enantioselective preparation of a key cyclobutane intermediate by a tandem Wolff rearrangement/asymmetric ketene addition, (2) a directed C(sp^3)–H alkenylation reaction to strategically forge the C1–C2 bond, and (3) a ring-closing metathesis to build the bridging bicyclo[4.3.1]decane terpene framework

Influence of the interfacial transition zone and interconnection on chloride migration of portland cement mortar

Available experimental studies on the effect of the interfacial transition zone (ITZ) on transport properties of cement-based composite materials appear to be ambiguous. The main objective of this work was to enhance the understanding of the relationship between ITZ and transport properties of Portland cement-based materials by using both a rapid chloride migration test and theoretical calculations. A densification factor which is related to aggregate volume content was introduced to further determine the transport of ITZ. Results indicate that the overall porosity decreased with increasing aggregate volume content due to the dilution effect by impermeable aggregates. The porosity was above the theoretical dilution line obtained from P0 x (1-Vagg) for mortars with more than 20 % of aggregate, which can be attributed to the presence of high porous ITZ. On the other hand, more porous ITZ was expected to be accompanied by a denser bulk cement matrix, which leaded to a decrease in the porosity of mortar with less than 35 % of aggregate. The ITZ effect would dominate the blocking aggregate, densification and tortuosity of bulk paste when aggregate volume content exceeded 0.35. The ratio between the migration coefficient of the ITZ and that of the matrix (DITZ/Dmatrix) increased with aggregate volume content and assumed ITZ thickness. In addition, the influence of ITZ increased with increasing the degree of interconnection slightly until 1.0. Beyond this value, a sudden increase in DITZ/Dmatrix ratio was observed indicating the negative percolation effect when the adjacent ITZ start to interconnect

Vnímání, kauzalita a pozornost Roger Bacon a Petr Olivi

[Sensation, Causality, and Attention: Roger Bacon and Peter Olivi] This paper investigates what conditions are to be met for sensory perception to occur. It introduces two diff erent theories of perception that were held by two medieval Franciscan thinkers — namely, Roger Bacon (1214/1220–1292) and Peter Olivi (ca. 1248–1298). Bacon analyses especially the causal relation between the object and the sensory organ in his doctrine of the multiplication of species. In his view, a necessary condition of perception is the reception of the species in a fully disposed sensory organ. On the contrary, Olivi stresses the active role of the sensory power. A necessary condition of sensation is the aspectus — i.e. the focus of our power’s attention on the object. Furthermore, the paper investigates whether and how each of the two thinkers can deal with the arguments proposed by his opponent — namely whether Bacon’s theory is able to explain attention and what the causal role of the object in Olivi’s theory is