基于可调谐式RS-POTDR实现已安装光纤累积PMD分布的测量

本文描述了一种新的偏振敏感OTDR方法,其非常适用于对已安装的光纤链路(可包含多种不同单模光纤类型)的累积PMD进行定量分布测量.通过这种方法,可以确定PMD较高的光纤区域,并且可以在必要的情况下替换该区域光纤,从而以经济有效的方法降低链路PMD.     

Eruptive history of Dubbi volcano,northeast Afar (Eritrea), revealed by optical and SAR image interpretation

A study of the remote Dubbi volcano, located in the northeastern part of the Afar triangle, Eritrea, was carried out using JERS-1 Synthetic Aperture Radar (SAR) and Landsat Thematic Mapper (TM) imagery. It investigated the last known eruption of Dubbi volcano in 1861, the only volcano in Afar for which historical reports indicate a major explosive eruption. Various image processing techniques were tested and compared in order to map different volcanic units, including effusive and explosive products. Principal component analysis and optical-SAR fusion were found to be useful to determine the extent of the 1861 pumice deposits surrounding the volcano. SAR imagery revealed old lava flows buried below tephra deposits, emphasizing the ground penetrating property of the L-band (HH polarization). The interpretation obtained from satellite imagery was cross-checked with sparse historical testimonies and available ground-truth data. Two scenarios are proposed for the 1861 eruptive sequences in order to estimate the volumes of lava flows erupted and the timing of explosive and effusive activity. Identified as a bimodal basaltic-trachytic eruption, with a minimum volume of 1.2 km³ of hawaiite lava and a minimum area of 70 km² of trachytic pumice, it represents the largest known historic eruption in the Afar triangle. This paper raises the issue of the potential volcanic hazards posed by Dubbi, which concern both the local population and the maritime traffic using the strategic route of the Red Sea.     

An analytical method to evaluate facility management services for residential buildings

Besides constructed quality and environmental quality, the quality of facilities in residential buildings is influential to the living quality of numerous residents there. The functional quality of the facilities, in turn, is dependent on the quality of their operation and management. A review of the relevant literature and a focus group discussion with Facility Management (FM) practitioners, which were parts of the study reported here, unveiled that prior performance evaluation studies focussed on assessing the outcome of FM services whereas an analytical method suitable for holistic evaluation of the services is lacking. An interview survey with 297 users of a typical residential estate in Hong Kong was carried out to solicit their perceived levels of importance and performance of FM services. The responses were tested using the Analytical Hierarchy Process (AHP) to isolate those with inconsistent judgments, followed by computing the weightings for various aspects of FM services based on the consistent responses. The calculation of a weighted performance score for benchmarking purposes and a critical evaluation of the cost-effectiveness of FM services, which are crucial for achieving a quality and sustainable built environment, are illustrated.     

Influence of the Cooling Temperature on the Mechanical Behavior of an Oxidized Self-Healing Ceramic Matrix Composite

Composites made of ceramic for both fibers and matrix are aimed at being used in aerospace applications, which means being submitted to mechanical stresses at high temperatures in oxidizing and corrosive environments for long durations. The oxidation/corrosion resistance of these materials is linked to their ability to self-heal by creating an oxide phase which can restrict the access of the oxygen into the bulk of the material. During thermomechanical cycles, the distribution of O₂ inside the material as well as the distribution and the state of the liquid oxides will undergo some modifications. A specific test has been conceived and performed in order to evidence the influence of the viscosity of this oxide on the mechanical properties of the material. Results have shown that the stiffening which is observed seems to be proportional to the increase in the viscosity of the sealing oxide, in conjunction with the decrease in the temperature.     

Reduction of ASR-expansion using powders ground from various sources of reactive aggregates

This study assesses the potential of ground reactive aggregates to reduce or suppress expansion associated with ASR. Particular attention is paid to fine admixtures (<80 μm) added to mortars, which contain the reactive aggregates from which the fines were ground. Many varieties of aggregate (quarried and natural, igneous, metamorphic and sedimentary rocks) from different geological settings were subjected to an autoclave test. The replacement of 10–20% of the sand by reactive aggregate powder (RAP) of different surface areas from 11 different reactive aggregates led to the reduction of ASR-expansion by up to 78% compared with control mortars. Increasing the amount of fines led to better performance. No clear relationship was observed between the reactivity degree of the aggregates and the efficiency of their ground powder to reduce expansion. A general trend was found regarding the fineness of ground aggregates: finer particles were more effective in reducing expansion. The reduction of the expansion due to RAP is discussed in terms of parameters affecting its efficiency and of the mechanisms responsible for the reduction.     

Study of the effects of structural uncertainties on a fractional system of the first kind – application in vibration isolation with the CRONE suspension

In this paper, we deal with the effects of the uncertainties on a fractional system of the first kind, mainly on the frequency-domain and the time-domain responses. For the structural uncertainties, two main aspects are studied: the nonlinearities of the physical components used to realize the fractional system and the consideration of the previously neglected dynamics of the system. Both uncertainties are introduced for the hydropneumatic CRONE suspension, previously synthesized and realized without taking into consideration these uncertainties. So, the novel approach treated in this work is to find whether the uncertainties, which were previously neglected in the synthesis and the realization phases, alter the behaviour of the system or not. The results show that the fractional order system behaviour is not affected.     

Lipid oxidation products of heated soybeans as a possible cause of protection from ruminal biohydrogenation

Heating oilseeds has been shown to improve the milk fatty acid profile when given to dairy cows, compared to raw oilseeds. However, results from published studies are conflicting. The conditions of heating and storage of the oilseeds could be responsible for these differences, probably partly through their effects on lipid oxidation, the products of which could act on ruminal biohydrogenation (BH). Thus, 15 different treatments were applied to ground soybeans: three levels of heating (no heating, 30 min at 110 or 150°C) × 5 ambient storage durations (0, 1, 2, 4, or 6 months). Soybeans were incubated in vitro with ruminal fluid for 6 h. Triacylglycerol (TAG) polymers, hydroperoxides and hydroxyacids (HOA), aldehydes, and fatty acids were assayed in soybeans and ruminal culture. No TAG polymer was detected in any treatment. Soybeans stored for a long time had a high content of HOA, whereas those heated at 150°C, whatever the storage duration, had high aldehyde contents. The percentage disappearance of cis‐9,cis‐12 18:2 and cis‐9,cis‐12,cis‐15 18:3 in incubates decreased significantly in cultures with heated soybeans, especially at 150°C, suggesting that this partial protection of polyunsaturated fatty acids (PUFA) from BH was at least in part linked to the aldehyde content of the heated soybeans. Practical applications: Oilseeds given to ruminants are often heated, and heat treatment is known to generate oxidation products. Knowing what oxidation products influence ruminal biohydrogenation of unsaturated fatty acids could result in technological processes allowing a better transfer of unsaturated fatty acids from oilseeds to ruminant products.     

An orthotropic variant of the equilibrium gap method applied to the analysis of a biaxial test on a composite material

In this paper, it is proposed to apply the equilibrium gap method to orthotropic composite materials to retrieve damage laws from measured displacement fields. A finite difference implementation method is first proposed. A linear system is formed, for which the unknowns are piecewise constant orthotropic rigidities, while the measured displacements are input (known) data. In this example, a cruciform specimen is considered for biaxial test. It is shown that, by referring to FE computed displacement fields a prescribed contrast map can be identified. Corrupted artificial displacement fields obtained through non-linear simulations are also used. When considering shear damage, a procedure using estimated contrast maps to identify a damage law is validated. An experimental biaxial test on a 2.5 C/C composite is finally analysed following the proposed approach. For each unloading step, a contrast map for all moduli is obtained from full-field measurements. By assuming that the shear moduli contrasts result from a damage mechanism, one subsequently obtains damage maps, and therefore, a growth law. The results are first validated by comparing measured and FE reconstructed displacement fields, and by comparing the identified damage fields with post-processed ones.     

Analysis for a two-dissimilar-component cold standby repairable system with repair priority

In this paper, a cold standby repairable system consisting of two dissimilar components and one repairman is studied. Assume that working time distributions and repair time distributions of the two components are both exponential, and Component 1 has repair priority when both components are broken down. After repair, Component 1 follows a geometric process repair while Component 2 obeys a perfect repair. Under these assumptions, using the perfect repair model, the geometric process repair model and the supplementary variable technique, we not only study some important reliability indices, but also consider a replacement policy T, under which the system is replaced when the working age of Component 1 reaches T. Our problem is to determine an optimal policy T^? such that the long-run average loss per unit time (i.e. average loss rate) of the system is minimized. The explicit expression for the average loss rate of the system is derived, and the corresponding optimal replacement policy T^? can be found numerically. Finally, a numerical example for replacement policy T is given to illustrate some theoretical results and the model's applicability.