Long-term performance interactions

The ET cover cannot be tested at every landfill site so it is necessary to extrapolate the results from sites of known performance to specific landfill sites. The factors that affect the hydrologic design of ET covers encompass several scientific disciplines and there are numerous interactions between factors. As a consequence, a comprehensive computer model is needed to evaluate the ET cover for a site.48 The model should effectively incorporate soil, plant, and climate variables, and include their interactions and the resultant effect on hydrology and water balance. An important function of the model is to simulate the variability of performance in response to climate variability and to evaluate cover response to extreme events. Because the expected life of the cover is decades, possibly centuries, the model should be capable of estimating long-term performance. In addition to a complete water balance, the model should be capable of estimating long-term plant biomass production, need for fertilizer, wind and water erosion, and possible loss of primary plant nutrients from the ecosystem. 

Changes in the fiber and fiber/cement interfacial region due to environmental interactions can affect the long-term performance of cement-based composites reinforced with natural fibers. A significant mechanism of changes in composite properties is pulp fiber degradation... 

So as to predict precisely the near-field behaviour for long-term performance analysis by inclusion of the near-field chemical evolution, we think it important to take into account the interactive model from thermal, hydrological and mechanical processes to chemical process as the first step of this research. After this step, we can really introduce the interactive model from chemical process to other processes, and then we can realize the fully coupled T-H-M-C model. 

The fourth reason is even more compelling, especially when considering biomaterials used in devices for tissue reconstruction. If a device is made from materials which are inert and which do not interact with the body in any way, then it is unlikely that it can be truly incorporated into the body. For effective long term performance in the dynamic tissue environment, it is far more preferable for there to be functional incorporation, which implies that the device should be stimulating the tissues to be reactive to it positively rather than negatively. Thus biocompatibility should not be concerned with avoiding reactions but selecting those which are the most beneficial to device performance. 

Like a bulk responsive material, surface of a substrate can be responsive upon electrochemical, photo, temperature, pH, mechanical, or electrical stimuli (Lahann Langer, 2005). Researchers are developing different ways to make these smart surfaces such as self-assembled monolayers (SAMs), polymer brushes, or copolymer coatings. A classic example is a switchable SAM surface in responsive to electric potential, which achieve hydrophobic-hydrophilic transition on a gold substrate. The switchable surfaces provide an idea platform to smdy surface-biological system interactions (Lahann et al., 2003). Polymer brushes and copolymers are more practical avenues to be applied with long-term performance. 

During operation at high temperatures, materials are subjected to complex interactions of temperature changes, oxidative and corrosive environmental attacks and mechanical stresses. These interactions determine whether components exhibit premature failure or show reliable and safe, long-term performance, and also limit the upper service temperature, which determines the degree of efficiency and, hence, the economical and ecological performance of materials. 

Geotextile containment applications are employed close to beaches where they provide safe solutions to the problems of erosion while interacting with humans. Major improvements in hydraulic stability behaviour and durability have enabled these geotextile units to be used for long-term solutions in exposed conditions. It is expected that the uses for these applications will continue to grow as long-term performance data become more readily available. 

---