The glial cell is the most numerous cell type in the central nervous system and is believed to play an important role in guiding brain development and in supporting adult brain function. One type of glial cell, the astrocyte also may be an integral computational element in the brain since it undergoes neurotransmitter-triggered signalling. Here we review the role of the astrocyte in the central nervous system, emphasizing receptor-mediated Ca2+ physiology. One focus is the recent discovery that the neurotransmitter glutamate induces a variety of intracellular Ca2+ changes in astrocytes. Simple Ca2+ spikes or intracellular Ca2+ oscillations often appear spatially uniform. However, in many instances, the Ca2+ rise has a significant spatial dimension, beginning in one part of the cell it spreads through the rest of the cell in the form of a wave. With high enough agonist concentration an astrocyte syncitium supports intercellular waves which propagate from cell to cell over relatively long distances. We present results of experiments using more specific pharmacological glutamate receptor agonists. In addition to describing the intercellular Ca2+ wave we present evidence for another form of intercellular signalling. Some possible functions of a long-range glial signalling system are also discussed. 相似文献
Summary Tracheal epithelial cells were grown on Nuclepore filters coated with human placental collagen. When grown immersed in medium
containing fetal bovine serum, cells displayed an undifferentiated ultrastructure (no cilia and a cell height of ∼ 10 μm).
Short-circuit current (Isc) was approximately 1/10 that of the native epithelium. By contrast, when grown in hormonally defined, serum-free medium with
an air interface, cells showed Isc equal to or greater than the original tissue, possessed cilia, and had a cell height of ∼ 50 μm. Responses in Isc to mediators were similar to those of the original tissue, but differed from those of dog or human tracheal epithelium. Given
the ready availability and low cost of the native tissues, bovine tracheal cultures grown in serum-free medium with an air
interface should prove useful in studies of airway epithelial physiology. 相似文献
Obsolescence, as premature end of use, increases the overall number of products produced and consumed, and thereby can increase the environmental impact. Measures to decrease the effects of obsolescence by altering the product or service design have the potential to increase use time (defined as the realized active service life) of devices, but can themselves have (environmental) drawbacks, for example, because the amount of material required for production increases. As such, paying special attention to methodological choices when assessing such measures and strategies using life cycle assessment (LCA) needs is crucial.
Methods
Open questions and key aspects of obsolescence, including the analysis of its effects and preventative measures, are discussed against the backdrop of the principles and framework for LCA given in ISO 14040/44, which includes guidance on how to define a useful functional unit and reference flow in the context of real-life use time.
Results and discussion
The open and foundational requirements of ISO 14040/14044 already form an excellent basis for analysis of the phenomenon obsolescence and its environmental impact in product comparisons. However, any analysis presumes clear definition of the goal and scope phase with special attention paid to aspects relevant to obsolescence: the target product and user group needs to be placed into context with the analysed “anti-obsolescence” measures. The reference flow needs to reflect a realized use time (and not solely a technical lifetime when not relevant for the product under study). System boundaries and types of data need to be chosen also in context of the anti-obsolescence measure to include, for example, the production of spare parts to reflect repairable design and/or manufacturer-specific yields to reflect high-quality manufacturing.
Conclusions
Understanding the relevant obsolescence conditions for the product system under study and how these may differ across the market segment or user types is crucial for a fair and useful comparison and the evaluation of anti-obsolescence measures.
The International Journal of Life Cycle Assessment - Since 2013, the European Commission (EC) is developing and testing the Product Environmental Footprint (PEF)—a product evaluation method,... 相似文献
The International Journal of Life Cycle Assessment - The main goal of this special issue is to further the understanding of how to integrate life cycle sustainability assessment (LCSA) methods and... 相似文献
The International Journal of Life Cycle Assessment - In the last years, India has taken a number of initiatives to boost small hydropower development based on the assumption of being a green energy... 相似文献
The International Journal of Life Cycle Assessment - Weighting as an optional step in life cycle impact assessment (LCIA) has recently gained momentum through increased policy requirements in the... 相似文献
Goal, Scope and Background The automotive industry has a long history in improving the environmental performance of vehicles - fuel economy and emission
improvements, introduction of recycled and renewable materials, etc. The European Union also aims at improving the environmental
performance of products by reducing, in particular, waste resulting from End-of-Life Vehicles (ELVs) for example. The European
Commission estimates that ELVs contribute to approximately 1 % of the total waste in Europe [9]. Other European Union strategies
are considering more life cycle aspects, as well as other impacts including resource or climate change. This article is summarizing
the results of a European Commission funded project (LIRECAR) that aims at identifying the environmental impacts and relevance
for combinations of recycling / recovery and lightweight vehicle design options over the whole life cycle of a vehicle - i.e.
manufacturing, use and recycling/recovery. Three, independent and scientific LCA experts reviewed the study according to ISO
14040. From the beginning, representatives of all Life Cycle Stakeholders have been involved (European materials & supplier
associations, an environmental Non-Governmental Organization, recycler’s association).
Model and System Definition The study compared 3 sets of theoretical vehicle weight scenarios: 1000 kg reference (material range of today’s end-of-life,
mid-sized vehicles produced in the early 1990’s) and 2 lightweight scenarios for 100 kg and 250 kg less weight based on reference
functions (in terms of comfort, safety, etc.) and a vehicle concept. The scenarios are represented by their material range
of a broad range of lightweight strategies of most European car manufacturers. In parallel, three End-of-Life (EOL) scenarios
are considered: EOL today and two theoretical extreme scenarios (100% recycling, respectively, 100% recovery of shredder residue
fractions that are disposed of today). The technical and economical feasibility of the studied scenarios is not taken into
consideration (e.g. 100% recycling is not possible).
Results and Discussion Significant differences between the various, studied weight scenarios were determined in several scenarios for the environmental
categories of global warming, ozone depletion, photochemical oxidant creation (summer smog), abiotic resource depletion, and
hazardous waste. However, these improvement potentials can be only realized under well defined conditions (e.g. material compositions,
specific fuel reduction values and EOL credits) based on case-by-case assessments for improvements over the course of the
life cycle. Looking at the studied scenarios, the relative contribution of the EOL phase represents 5% or less of the total
life cycle impact for most selected impact categories and scenarios. The EOL technology variations studied do not impact significantly
the considered environmental impacts. Exceptions include total waste, as long as stockpile goods (overburden, tailings and
ore/coal processing residues) and EOL credits are considered.
Conclusions and Recommendations LIRECAR focuses only on lightweight/recycling, questions whereas other measures (changes in safety or comfort standards, propulsion
improvements for CO2, user behavior) are beyond the scope of the study. The conclusions are also not necessarily transferable to other vehicle
concepts. However, for the question of end-of-life options, it can be concluded that LIRECAR cannot support any general recommendation
and/or mandatory actions to improve recycling if lightweight is affected. Also, looking at each vehicle, no justification
could be found for the general assumption that lightweight and recycling greatly influence the affected environmental dimension
(Global Warming Potential or resource depletion and waste, respectively). LIRECAR showed that this general assumption is not
true under all analyzed circumstances and not as significant as suggested. Further discussions and product development targets
shall not focus on generic targets that define the approach/technology concerned with how to achieve environmental improvement
(weight reduction [kg], recycling quota [%]), but on overall life cycle improvement). To enable this case-by-case assessment,
exchanges of necessary information with suppliers are especially relevant. 相似文献