The interface between polymer-modified cement paste and aggregates

The effects of polymer dispersions on the structure of the interfacial zone between portland cement paste and aggregates (limestone and granite) have been investigated. EDAX analyses of the polymer modified composites showed that a relatively high polymer content is present at the paste-aggregate interface. Scanning electron microscope (SEM) observations of fractured surfaces of the plain cement paste-aggregate interface revealed large calcium hydroxide crystals which are orientated with their c-axes perpendicular to the interface. With increasing polymer content cement hydration products become indistinct, and microcracks appeared to be bridged-up by the polymer film.     

Analytical form for a Bayesian wavelet estimator of images using the Bessel K form densities.

A novel Bayesian nonparametric estimator in the Wavelet domain is presented. In this approach, a prior model is imposed on the wavelet coefficients designed to capture the sparseness of the wavelet expansion. Seeking probability models for the marginal densities of the wavelet coefficients, the new family of Bessel K forms (BKF) densities are shown to fit very well to the observed histograms. Exploiting this prior, we designed a Bayesian nonlinear denoiser and we derived a closed form for its expression. We then compared it to other priors that have been introduced in the literature, such as the generalized Gaussian density (GGD) or the alpha-stable models, where no analytical form is available for the corresponding Bayesian denoisers. Specifically, the BKF model turns out to be a good compromise between these two extreme cases (hyperbolic tails for the alpha-stable and exponential tails for the GGD). Moreover, we demonstrate a high degree of match between observed and estimated prior densities using the BKF model. Finally, a comparative study is carried out to show the effectiveness of our denoiser which clearly outperforms the classical shrinkage or thresholding wavelet-based techniques.     

Computation of surface radiation and natural convection in a heated horticultural greenhouse

This study analyses the effects of the radiation exchange inside a horticultural greenhouse, under winter climatic conditions, according to the number of squared heating tubes used. These ones, hot and isothermal, are equidistant inside the greenhouse volume. The governing differential equations are discretized using a finite volume method and the coupling pressure–velocity problem is carried out by the SIMPLER algorithm. The algebraic systems obtained are solved by a conjugate gradient method. Results are reported in terms of isotherms, streamlines and average Nusselt number for Rayleigh number of 10³–10⁶. The contour lines show that the radiative effects are noted near the solid surfaces, and become increasingly important when the Rayleigh number increases. As a result, the rise in the value of Rayleigh number leads to an increase of the overall heat transfer within the greenhouse.     

A new modeling procedure for circuit design and performance prediction of evaporator coils using CO2 as refrigerant

The replacement of environmentally damaging synthetic refrigerants due to their ODP or GWI potential by natural refrigerants such as CO₂ is now up in the research agenda. Moreover, current energy supply concerns make of efficiency another first priority issue to dictate new stringent design criteria for industrial and commercial equipment. Heat exchangers are the most important components in refrigeration systems where they are used as evaporators or condensers and their design and operation have a considerable impact on overall system performance. Hence, it is important to better understand their thermal and hydrodynamic behaviour in order to improve their design and operation. Numerical simulation represents a very efficient tool for achieving this objective. In this paper, a new modeling approach, accounting for the heat transfer the hydrodynamics of the problem and intended to predict the dynamic behaviour of a refrigeration coil under dry conditions is proposed. A related FORTRAN program was developed, allowing the study of a large range of complex refrigerant circuit configurations. The equations describing these aspects are strongly coupled, and their decoupling is reached by using an original method of resolution. Circuits may have several inlets, outlets, bifurcations and feed one or several other tubes inlets. The coil was subdivided into several elementary control volumes and its analysis provided detailed information in X, Y and Z directions. Validation was performed with data from a CO₂ secondary refrigeration loop test bench built in CanmetENERGY Laboratories. These data were predicted satisfactorily over the operating range corresponding to refrigeration applications. Exemplary simulations were then performed on an evaporator typically employed in supermarkets, showing the effect of circuiting on operation and performance. Even though circuiting is common practice in refrigeration this simulation shows that care must be exercised in making the selection. A two-circuit configuration was chosen for analysis in this investigation. In terms of capacity and heat transfer, it was shown that the two circuits were well balanced in terms of pressure drop and heat transfer capacity. Low CO₂ pressure drop resulted in reduced temperature glide as compared to a single circuit.     

Antibacterial activity and chemical composition of 20 Eucalyptus species’ essential oils

The essential oils of twenty Eucalyptus species harvested from Zerniza and Souinet arboreta (North West and North of Tunisia), were screened for their antibacterial activities by the agar disc diffusion method. Eighteen major compounds, identified by GC and GC/MS, have been retained for the study of the chemical and biological activity variability. The main ones were 1,8-cineole followed by α-pinene, p-cymene, borneol, cryptone, spathulenol, viridiflorol and limonene. The chemical principal components analysis identified 10 chemotypes, however that of the inhibition zone diameter (izd) of growth bacteria separated 5 groups of Eucalyptus oils, characterised by their antibacterial inhibition ability. The most sensitive strain was the Gram positive Staphylococcus aureus with that of E. odorata oil (16.0 ± 1.0 mm izd), while the most resistant bacteria was Pseudomonas aeruginosa. Some correlation between the amount of 1,8-cineole, p-cymene, α-pinene, or of cryptone and the antibacterial activity were observed.     

Water extraction out of mortar during brick laying: A NMR study

The water extraction out of mortar during brick laying was studied using nuclear magnetic resonance. The experiments show that using a fired-clay brick, the water is extracted out of the mortar within 3 minutes, whereas in the case of a sand-lime brick this takes about 10 minutes. Prewetting a fired-clay brick hardly affects the water extraction, whereas prewetting a sand-lime brick slows down the water extraction, although the effect is small. The extraction process is slowed down only if the bricks are almost fully saturated. These effects are explained with the help of computer simulations. The final moisture content of the mortar is shown to depend on the suction of the brick and thereby on the equilibrium moisture content of the brick. By adding a water retention agent to the mortar, the extraction process seems to slow down, although the final moisture content of the mortar is not changed. The water extraction experiments suggest that the suction of the mortar which is formed depends on the water extraction rate and thereby on the type of brick that is used in the extraction experiment. Petrographic analyses indicate that the extent of bonding between the brick and the mortar is different for fired-clay brick and sand-lime brick.

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Résumé L'extraction de l'eau du mortier par la brique a été étudiée par la méthode de résonance magnétique nucléaire. Les résultats montrent que les briques en terre cuite extraient l'eau du mortier en 3 minutes, alors que dans le cas de briques à base de chaux ce temps augmente à 10 minutes. L'humidification préalbble des briques en terre cuite a peu d'influence sur leur extraction de l'eau; dans le cas des briques à base de chaux, l'humidification préalable ralentit l'extraction, mais très légèrement. L'absorption de l'eau du mortier par la brique est sensiblement ralentie lorsque les briques sont préalablement saturées d'eau. Ces phénomènes sont expliqués grace à des simulations numériques. La teneur en eau finale du mortier dépend de l'aspiration de la brique et donc de la teneur en eau à l'équilibre de la brique. L'ajout d'un agent rétenteur d'eau au mortier semble ralentir l'extraction de l'eau par la brique sans pour autant changer la teneur en eau finale du mortier. Les résultats suggèrent que l'aspiration du mortier dépend du taux d'extraction d'eau par la brique et donc du type de brique utilisé. L'analyse pétrographique montre que l'adhérence mortier-brique est différente pour les briques en terre cuite et celles à base de chaux.

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Editorial note H.J.P. Brocken works at the Department of Architecture, Building and Planning, Eindhoven University of Technology, a RILEM Associate Member L. Pel and K. Kopinga also work at the Eindhoven University of Technology. M. E. Spiekman works at the Department of Civil Engineering, Delft University of Technology, a RILEM Associate Member, J. A. Larbi works at TNO Building and Construction Research, a RILEM Titular Member.     

Investigation of structural parameters and self-aggregation of Algerian asphaltenes in organic solvents

Elemental analysis, Fourier transform infrared (FTIR), 1H-NMR, fluorescence spectroscopy, and surface tension methods have been used to characterize the molecular structure and the aggregation behaviors of two asphaltenic fractions derived, respectively, from an Algerian petroleum well and a corresponding storage tank deposit. Elemental analysis, FTIR, 1H-NMR, and fluorescence spectroscopy were used to investigate the chemical composition and structural parameters of asphaltenes, while the surface tension method was used to measure the critical micelle concentration (CMC) in organic solvents with different solubility parameters and polarities in order to characterize the asphaltenes’ aggregation behaviors. Results show that the unstable asphaltenes fraction extracted from the storage tank deposit possesses a higher polarity (higher heteroatoms content) and a lower aromaticity than stable asphaltenes from the petroleum well. The CMC results indicate that asphaltenes with high polarity and low aromaticity have a high solubility in polar solvents such as nitrobenzene, whereas asphaltenes with low polarity and high aromaticity are more soluble in solvents with weak polarity, like toluene. It is concluded that the difference of structure of asphaltene samples and polarity of solvents can lead to difference of aggregation behaviors.     

Heuristic solutions for transshipment problems in a multiple door cross docking warehouse

Cross docking is a practice in logistics with the main operations of unloading products from an incoming truck, regrouping them with respect to their destinations and loading them directly into an outbound truck with minimum storage in between these operations. In this article, we study the transshipment scheduling problem in a multiple inbound and outbound dock configuration. The operations manager has several decisions to make: he can decide to transship products directly from inbound to an outbound truck, if an outbound truck is available; he can temporarily store certain products and have them loaded later on; or he can replace an outbound truck to facilitate direct loading. The objective is to find the best schedule of transshipment operations to minimize the sum of inventory holding and truck replacement costs. In this article, we present several heuristics to attain this objective. Numerical experiments are presented and the results are compared with the optimal solution to evaluate the performance of the heuristics.     

焊接连接的钢筋混凝土梁的静力性能

对高强混凝土组合梁桥梁中的钢和混凝土的连接件的静力和瞬时性能进行研究。在一系列条件下完成了拔出(Push-out)试验,并且依靠3D-F模型进行了分析。试验结果显示,平均最终剪切应力约为5·5MPa,而且结构响应主要依靠二维应力状态下的混凝土的行为。此外,粘合的连接件显示出很高的刚度和几乎与机械连接件一样的强度。对梁的模拟也表明,粘合的连接可以像梁一样被很精确地模拟。在混凝土桥面上开裂的风险也被显著减小,与那些采用机械连接相比的结构而言,这可能会增加粘合的钢-混凝土组合结构的耐久性。