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51.
Trace elements in coal 总被引:1,自引:0,他引:1
Finkelman RB 《Biological trace element research》1999,67(3):197-204
Trace elements can have profound adverse effects on the health of people burning coal in homes or living near coal deposits,
coal mines, and coal-burning power plants. Trace elements such as arsenic emitted from coal-burning power plants in Europe
and Asia have been shown to cause severe health problems. Perhaps the most widespread health problems are caused by domestic
coal combustion in developing countries where millions of people suffer from fluorosis and thousands from arsenism. Better
knowledge of coal quality characteristics may help to reduce some of these health problems. For example, information on concentrations
and distributions of potentially toxic elements in coal may help delineate areas of a coal deposit to be avoided. Information
on the modes of occurrence of these elements and the textural relations of the minerals in coal may help to predict the behavior
of the potentially toxic trace metals during coal cleaning, combustion, weathering, and leaching. 相似文献
52.
53.
Stuart?RossEmail author David?Evans Michael?Webber 《The International Journal of Life Cycle Assessment》2002,7(1):47-52
In recent years many workers have examined the implications of various sources of uncertainty for the reliability of Life
Cycle Assessment (LCA). Indeed, the International Standardization Organization (ISO) has recognised the relevance of this
work by including several cautionary statements in the ISO 14040 series of standards. However, in practice, there is a risk
that the significance of these uncertainties for the results of an LCA could be overlooked as practitioners strive to complete
studies on time and within budget. This paper presents the findings of a survey of LCA studies we made to determine the extent
to which the problem of uncertainty had been dealt with in practice. This survey revealed that the significance of the limitations
on the reliability of LCA results given in the standards has not been fully appreciated by practitioners. We conclude that
the standards need to be revised to ensure that LCA studies include at least a qualitative discussion on all relevant aspects
of uncertainty. 相似文献
54.
The compliance score in randomized trials is a measure of the effect of randomization on treatment received. It is in principle a group-level pretreatment variable and so can be used where individual-level measures of treatment received can produce misleading inferences. The interpretation of models with the compliance score as a regressor of interest depends on the link function. Using the identity link can lead to valid inference about the effects of treatment received even in the presence of nonrandom noncompliance; such inference is more problematic for nonlinear links. We illustrate these points with data from two randomized trials. 相似文献
55.
Stefanie?HellwegEmail author Thomas?B.?Hofstetter Konrad?Hungerbuhler 《The International Journal of Life Cycle Assessment》2003,8(1):8-18
Background In Life-Cycle Assessment (LCA), decision makers are often faced with tradeoffs between current and future impacts. One typical
example is waste incineration, where immediate emissions to the air from the incineration process have to be weighted against
future emissions of slag landfills. Long-term impacts are either completely taken into account or they are entirely disregarded
in case of a temporal cut-off. Temporal cutoffs are a special case of discounting.
Objective In this paper, discounting is defined as valuing damages differently at different points of time using a positive or negative
discount rate. Apart from temporal cut-offs, discounting has rarely been applied in LCA so far. It is the goal of this paper
to discuss the concept of discounting and its applicability in the context of LCA.
Methods For this purpose, we first review the arguments for discounting and its principles in economic sciences. Discounting in economics
can be motivated by pure time preference, productivity of capital, diminishing marginal utility of consumption, and uncertainties.
The nominal discount rate additionally includes changes in the price level. These arguments and their justification are discussed
in the context of environmental impacts harming future generations.
Results and Discussion It is concluded that discounting across generations because of pure time preference contradicts fundamental ethical values
and should therefore not be applied in LCA. However, it has to be acknowledged that in practice decision makers often use
positive discount rates because of pure time preference — either because they might profit from imposing environmental damage
on others instead of themselves or because people in the far future are not of immediate concern to them. Discounting because
of the productivity of capital assumes a relationship between monetary values and environmental impact. If such a relationship
is accepted, discounting could be applied. However, future generations should be compensated for the environmental damage.
It is likely that they would demand a higher compensation if the real per capita income increases. As both the compensation
and the discount rate are related to economic growth, the overall discount rate might be close to zero. It is shown that the
overall discount rate might even be negative considering that the required compensation could increase (even to infinite)
if natural assets remain scarce, whereas the utility of consumption diminishes with increasing income. Uncertainties could
justify both positive and negative discount rates. Since the relationship between uncertainties and the magnitude of damage
is generally not exponential, we recommend to model changes in the magnitude of damage in scenario analysis instead of considering
it in discounting (which requires an exponential function of time in the case of a constant discount rate). We investigated
the influence of discounting in a case study of heavy metal emissions from slag landfills. It could be shown that even small
discount rates of less than 1 % lead to a significant reduction of the impact score, whereas negative discount rates inflate
the results.
Conclusions and Recommendations Discounting is only applicable when temporally differentiated data is available. In some cases, such a temporal differentiation
is necessary to take sound decisions, especially when long emission periods are involved. An example is the disposal of nuclear
or heavy metal-containing waste. In these cases, the results might completely depend on the discount rate. This paper helps
to structure arguments and thus to support the decision about whether or not discounting should be applied in an LCA. 相似文献
56.
The quadrupole moment of formaldazine, H2C=N-N=CH2, has been studied for the trans structure (Ð(C-N-N-C) = = 180) and a series of gauche structures ( > 120). Restricted Hartree-Fock theory, second-order Møller-Plesset theory, and quadratic CI theory have been used in conjunction with the basis sets 6-31G*, 6-31G**, 6-311G** and 6-311++G**. Formaldazine is a quadrupolar molecule with primitive quadrupole moment tensor components of Q
xx
= -22.4, Q
yy
= -20.4 and Q
zz
= -25.6 DÅ at the theoretical level QCISD/6-311++G**. The examination of the theoretical level dependency shows that the reliable computation of a quadrupole moment requires the use of a flexible basis set. A large part of the component Q
zz
= -25.6 DÅ is due to the -system and compares, on a per electron basis, with the Q
zz
value of benzene. Conformational changes of the azines in the range 120° < < 180 have but a minute effect on the energy and are associated with only minor electronic relaxation. These conformational changes alter the quadrupole moment tensor components less than Q
xx
= +0.4, Q
yy
= +1.6 and Q
zz
= -1.0 DÅ at QCISD/6-311++G**//QCISD/6-31G*. The direction of these changes is explained by consideration of the rotation of the CN--systems and a small reduction of the CN bond polarity in the gauche structures. The Q
zz
component of formaldazine is representative of the quadrupole moment tensor component along the direction of the C
2
axis of the azine bridge as such. Hence, the results of this study suggest that azines can engage in strong quadrupole-quadrupole interactions and can be employed as lateral synthons in crystal engineering. Electronic Supplementary Material available. 相似文献
57.
Cells from metazoan organisms are eliminated in a variety of physiological and pathophysiological processes by apoptosis.
In this report, we describe the cloning and characterization of molecules from the marine sponges Geodia cydonium and Suberites domuncula, whose domains show a high similarity to those that are found in molecules of the vertebrate Bcl-2 superfamily and of the
death receptors. The Bcl-2 proteins contain up to four Bcl-2 homology regions (BH). Two Bcl-2-related molecules have been
identified from sponges that are provided with two of those regions, BH1 and BH2, and are termed Bcl-2 homology proteins (BHP).
The G. cydonium molecule, BHP1_GC, has a putative size of 28,164, while the related sequence from S. domuncula, BHP1_SD, has a M
r
of 24,187. Phylogenetic analyses of the entire two sponge BHPs revealed a high similarity to members of the mammalian Bcl-2
superfamilies and to the Caenorhabditis elegans Ced-9. When the two domains, BH1 and BH2, are analyzed separately, again the highest similarity was found to the members
of the Bcl-2 superfamily, but a clearly lower relationship to the C. elegans BH1 and BH2 domains in Ced-9. In unrooted phylogenetic trees the sponge BH1 and BH2 are grouped among the mammalian sequences
and are only distantly related to the C. elegans BH domains. The analysis of the gene structure of the G. cydonium BHP showed that the single intron present is located within the BH2 domain at the same position as in C. elegans and rat Bcl-xL. In addition, a sponge molecule comprising two death domains has been characterized from G. cydonium. The two death domains of the potential proapoptotic molecule GC_DD2, M
r
24,970, share a high similarity with the Fas-FADD/MORT1 domains. A death domain-containing molecule has not been identified
in the C. elegans genome. The phylogenetic analysis revealed that the sponge domain originated from an ankyrin building block from which the
mammalian Fas-FADD/MORT1 evolved. It is suggested that the apoptotic pathways that involve members of the Bcl-2 superfamily
and of the death receptors are already present in the lowest metazoan phylum, the Porifera.
Received: 27 July 1999 / Accepted: 28 December 1999 相似文献
58.
This study describes the spatial and temporal dynamics of several physical, chemical and biological variables in the Grussai
lagoon, and their relationship to ephemeral sand bar openings and to a constant in natura waste water input. The spatial variation
in pH, dissolved oxygen, electrical conductivity, total alkalinity and nutrients (e.g. soluble reactive silicate, soluble
reactive phosphate and ammonium) was associated to the anoxic and nutrient rich groundwater discharge, the development of
aquatic macrophytes, the biological activities of phytoplanktonic community and the marine influence. During the period when
the sand bar was closed (isolated), the lagoon water was supersaturated with dissolved oxygen and exhibited high values of
pH (8–10), total alkalinity (3.000–5.000 μeq l-1), and chlorophyll a contents (60-300 μg l-1), and had low values of dissolved nutrients (nearly undetectable). These suggest a biological processes dominance. When the
sand bar was opened, there was an enrichment with dissolved inorganic nutrients (e.g. ammonium and soluble reactive phosphorus
up to 120 and 5 μM, respectively) and a decrease in pH (below 8), total alkalinity (below 3.000 μeq l-1) and dissolved oxygen during the initial second to eight days. Subsequently there was a period when the physical and chemical
characteristics of seawater prevailed. The lagoon returned chemical to the pre-opening water conditions in a few days (∼ 10–20).
This quick return implies highly efficient biological mechanisms. The high levels of chlorophyll a, total nitrogen and phosphorus
in the water column indicate a high eutrophication stage in the Grussai lagoon during the sand bar closed periods.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
59.
Potential replacement vegetation: an approach to vegetation mapping of cultural landscapes 总被引:1,自引:0,他引:1
Milan Chytrý 《应用植被学》1998,1(2):177-188
Abstract. The concept of mapping potential replacement vegetation (PRV) is proposed as a parallel to potential natural vegetation (PNV). Potential replacement vegetation (PRV) is an abstract and hypothetical vegetation which is in balance with climatic and soil factors currently affecting a given habitat, with environmental factors influencing the habitat from outside such as air pollution, and with an abstract anthropogenic influence (management) of given type, frequency and intensity. For every habitat, there is a series of possible PRV-types corresponding to the different anthropogenic influences, e.g. grazing, mowing, trampling or growing cereals. The PRV-concept is especially useful in large-scale mapping (scales > 1 : 25 000) of small areas where replacement vegetation is the focus of attention for managers and land-use planners, for example in nature reserves where the aim is conservation of replacement vegetation managed in a traditional way, or in restoration ecology where the concept may be used for defining restoration goals and evaluating the success of restoration efforts. At smaller scales, PRV-mapping may be useful for revealing the biogeographical patterns of larger areas which may be different from the corresponding PNV patterns, because replacement vegetation and natural vegetation may respond to environmental gradients at different scales. An example of medium-scale PRV-mapping through the coincidence of diagnostic species of vegetation types, based on species distribution grid data, is presented. In cultural landscapes, the advantage of using the PRV-concept instead of PNV is its direct relationship to the replacement vegetation. In the habitat mapping with respect to the replacement vegetation, the PRV concept yields more valuable results than the mapping of actual vegetation, as the latter is strongly affected by spatially variable anthropogenic influences which may be largely independent from climatic and soil factors. 相似文献
60.
Mads S. Thomsen Thomas Wernberg Fernando Tuya Brian R. Silliman 《Journal of phycology》2009,45(4):812-819
Invasions by nonindigenous macroalgal species (NIMS) potentially cause severe impacts on native species. We conducted a meta‐analysis of 18 field‐based manipulative experiments to quantify the direction and magnitude of impacts (Hedges effect size d, hereafter ES). We found significant small‐to‐medium negative effects on “macrophyte abundance” (cover, biomass of native taxa; EScumulative = ?0.30) and medium‐to‐large negative effects on “macrophyte assemblages” (richness, diversity, total abundance; EScumulative = ?0.70). In contrast, EScumulative were not significant for “macrophyte processes” (growth, mortality; EScumulative = ?0.39), “animal abundance” (densities; EScumulative = ?0.13), or “animal assemblages” (richness, diversity; EScumulative = 0.75). The nonsignificant effect sizes were characterized by low sample sizes and should be interpreted with caution. Three study‐specific effect sizes were particularly large (2.0), showing that, in specific cases, impacts can be highly negative. From a conservation perspective, focus could be on such worst‐case scenarios. Still, the reported EScumulative are likely biased toward larger effects because only the most conspicuous NIMS have been tested and because nonsignificant results are less likely to be published. To better understand the impacts of NIMS, more manipulative experiments are needed, testing more species and under contrasting environmental conditions. Future studies should include procedural control treatments and report the abundance of the NIMS to avoid ambiguous interpretations. In conclusion, current experimental evidence shows that NIMS have, on average, small‐to‐large negative impacts on native plant species and assemblages. It is possible that these effects can result in severe consequences when accumulated over long time periods and large spatial scales. 相似文献