994 resultados para Mountain View
Resumo:
Sediments from the Black Sea, a region historically dominated by forests and steppe landscapes, are a valuable source of detailed information on the changes in regional terrestrial and aquatic environments at decadal to millennial scales. Here we present multi-proxy environmental records (pollen, dinoflagellate cysts, Ca, Ti and oxygen isotope data) from the uppermost 305 cm of the core 22-GC3 (42°13.53′N, 36°29.55′E) collected from a water depth of 838 m in the southern part of the Black Sea in 2007. The records span the last ~ 18 kyr (all ages are given in cal kyr BP). The pollen data reveal the dominance of the Artemisia-steppe in the region, suggesting rather dry/cold environments ~ 18–14.5 kyr BP. Warming/humidity increase during melt-water pulses (~ 16.1–14.5 kyr BP), indicated by δ18O records from the 22-GC3 core sediment and from the Sofular Cave stalagmite, is expressed in more negative δ13C values from the Sofular Cave, usually interpreted as the spreading of C3 plants. The records representing the interstadial complex (~ 14.5–12.9 kyr BP) show an increase in temperature and moisture, indicated by forest development, increased primary productivity and reduced surface run-off, whereas the switch from primary terrigenous to primary authigenic Ca origin occurs ~ 500 yr later. The Younger Dryas cooling is clearly demonstrated by more negative δ13C values from the Sofular Cave and a reduction of pines. The early Holocene (11.7–8.5 kyr BP) interval reveals relatively dry conditions compared to the mostly moist and warm middle Holocene (8.5–5 kyr BP), which is characterized by the establishment of the species-rich warm mixed and temperate deciduous forests in the low elevation belt, temperate deciduous beech-hornbeam forests in the middle and cool conifer forest in upper mountain belt. The border between the early and middle Holocene in the vegetation records coincides with the opening of the Mediterranean corridor at ~ 8.3 kyr BP, as indicated by a marked change in the dinocyst assemblages and in the sediment lithology. Changes in the pollen assemblages indicate a reduction in forest cover after ~ 5 kyr BP, which was likely caused by increased anthropogenic pressure on the regional vegetation.
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This paper offers an integrated analysis of out-sourcing, off-shoring and foreign direct investment within a systems view of international business. This view takes the supply chain rather than the firm as the basic unit of analysis. It argues that competition in the global economy selects supply chains that maximise the joint profit of all the firms in the chain. The systems view is compared with the firm-centred view commonly used in strategy literature. The paper shows that a firm’s strategy must be embedded within an efficient supply chain strategy, and that this strategy must be negotiated with, rather than imposed upon, other firms. The paper analyses the conditions under which various supply chain strategies - and by implication various firm-level strategies - are efficient. Only by adopting a systems view of supply chains is it possible to determine which firm-level strategies will succeed in a volatile global economy.
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Leaders across companies initiate and implement change and thus are crucial for successful organizations. This study takes a competency perspective on leaders and investigates the competencies leaders show to facilitate effective change. The article explores the content of the construct of leaders’ change competency and examines its antecedents and effects. We conducted a case study in a German tourism company undergoing a major change process. The study identified (a) distinct content facets regarding the construct of leaders’ change competency along its two dimensions of leaders’ readiness for change and leaders’ change ability; (b) the construct’s antecedents, specifically contextual factors, leaders’ competency potentials, and attitudes toward change; and (c) beneficial effects of leaders’ change competency. The study ends with implications for research and leadership practice as well as suggestions for future studies on leaders’ change competency.
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Data quality is a difficult notion to define precisely, and different communities have different views and understandings of the subject. This causes confusion, a lack of harmonization of data across communities and omission of vital quality information. For some existing data infrastructures, data quality standards cannot address the problem adequately and cannot fulfil all user needs or cover all concepts of data quality. In this study, we discuss some philosophical issues on data quality. We identify actual user needs on data quality, review existing standards and specifications on data quality, and propose an integrated model for data quality in the field of Earth observation (EO). We also propose a practical mechanism for applying the integrated quality information model to a large number of datasets through metadata inheritance. While our data quality management approach is in the domain of EO, we believe that the ideas and methodologies for data quality management can be applied to wider domains and disciplines to facilitate quality-enabled scientific research.
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The recession of mountain glaciers around the world has been linked to anthropogenic climate change and small glaciers (e.g. < 2 km2) are thought to be particularly vulnerable, with reports of their disappearance from several regions. However, the response of small glaciers to climate change can be modulated by non-climatic factors such as topography and debris cover and there remain a number of regions where their recent change has evaded scrutiny. This paper presents results of the first multi-year remote sensing survey of glaciers in the Kodar Mountains, the only glaciers in SE Siberia, which we compare to previous glacier inventories from this continental setting that reported total glacier areas of 18.8 km2 in ca. 1963 (12.6 km2 of exposed ice) and 15.5 km2 in 1974 (12 km2 of exposed ice). Mapping their debris-covered termini is difficult but delineation of debris-free ice on Landsat imagery reveals 34 glaciers with a total area of 11.72 ± 0.72 km2 in 1995, followed by a reduction to 9.53 ± 0.29 km2 in 2001 and 7.01 ± 0.23 km2 in 2010. This represents a ~ 44% decrease in exposed glacier ice between ca. 1963 and 2010, but with 40% lost since 1995 and with individual glaciers losing as much as 93% of their exposed ice. Thus, although continental glaciers are generally thought to be less sensitive than their maritime counterparts, a recent acceleration in shrinkage of exposed ice has taken place and we note its coincidence with a strong summer warming trend in the region initiated at the start of the 1980s. Whilst smaller and shorter glaciers have, proportionally, tended to shrink more rapidly, we find no statistically significant relationship between shrinkage and elevation characteristics, aspect or solar radiation. This is probably due to the small sample size, limited elevation range, and topographic setting of the glaciers in deep valleys-heads. Furthermore, many of the glaciers possess debris-covered termini and it is likely that the ablation of buried ice is lagging the shrinkage of exposed ice, such that a growth in the proportion of debris cover is occurring, as observed elsewhere. If recent trends continue, we hypothesise that glaciers could evolve into a type of rock glacier within the next few decades, introducing additional complexity in their response and delaying their potential demise.
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Surface-based GPS measurements of zenith path delay (ZPD) can be used to derive vertically integrated water vapor (IWV) of the atmosphere. ZPD data are collected in a global network presently consisting of 160 stations as part of the International GPS Service. In the present study, ZPD data from this network are converted into IWV using observed surface pressure and mean atmospheric water vapor column temperature obtained from the European Centre for Medium-Range Weather Forecasts' (ECMWF) operational analyses (OA). For the 4 months of January/July 2000/2001, the GPS-derived IWV values are compared to the IWV from the ECMWF OA, with a special focus on the monthly averaged difference (bias) and the standard deviation of daily differences. This comparison shows that the GPS-derived IWV values are well suited for the validation of OA of IWV. For most GPS stations, the IWV data agree quite well with the analyzed data indicating that they are both correct at these locations. Larger differences for individual days are interpreted as errors in the analyses. A dry bias in the winter is found over central United States, Canada, and central Siberia, suggesting a systematic analysis error. Larger differences were mainly found in mountain areas. These were related to representation problems and interpolation difficulties between model height and station height. In addition, the IWV comparison can be used to identify errors or problems in the observations of ZPD. This includes errors in the data itself, e.g., erroneous outlier in the measured time series, as well as systematic errors that affect all IWV values at a specific station. Such stations were excluded from the intercomparison. Finally, long-term requirements for a GPS-based water vapor monitoring system are discussed.
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Rising sea level is perhaps the most severe consequence of climate warming, as much of the world’s population and infrastructure is located near current sea level (Lemke et al. 2007). A major rise of a metre or more would cause serious problems. Such possibilities have been suggested by Hansen and Sato (2011) who pointed out that sea level was several metres higher than now during the Holsteinian and Eemian interglacials (about 250,000 and 120,000 years ago, respectively), even though the global temperature was then only slightly higher than it is nowadays. It is consequently of the utmost importance to determine whether such a sea level rise could occur and, if so, how fast it might happen. Sea level undergoes considerable changes due to natural processes such as the wind, ocean currents and tidal motions. On longer time scales, the sea level is influenced by steric effects (sea water expansion caused by temperature and salinity changes of the ocean) and by eustatic effects caused by changes in ocean mass. Changes in the Earth’s cryosphere, such as the retreat or expansion of glaciers and land ice areas, have been the dominant cause of sea level change during the Earth’s recent history. During the glacial cycles of the last million years, the sea level varied by a large amount, of the order of 100 m. If the Earth’s cryosphere were to disappear completely, the sea level would rise by some 65 m. The scientific papers in the present volume address the different aspects of the Earth’s cryosphere and how the different changes in the cryosphere affect sea level change. It represents the outcome of the first workshop held within the new ISSI Earth Science Programme. The workshop took place from 22 to 26 March, 2010, in Bern, Switzerland, with the objective of providing an in-depth insight into the future of mountain glaciers and the large land ice areas of Antarctica and Greenland, which are exposed to natural and anthropogenic climate influences, and their effects on sea level change. The participants of the workshop are experts in different fields including meteorology, climatology, oceanography, glaciology and geodesy; they use advanced space-based observational studies and state-of-the-art numerical modelling.
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Khartoum like many cities in least developing countries (LDCs) still witnesses huge influx of people. Accommodation of the new comers leads to encroachment on the cultivation land leads to sprawl expansion of Greater Khartoum. The city expanded in diameter from 16.8 km in 1955 to 802.5 km in 1998. Most of this horizontal expansion was residential. In 2008 Khartoum accommodated 29% of the urban population of Sudan. Today Khartoum is considered as one of 43 major cities in Africa that accommodates more than 1 million inhabitants. Most of new comers live in the outskirts of the city e.g. Dar El-Salam and Mayo neighbourhoods. The majority of those new comers built their houses especially the walls from mud, wood, straw and sacks. Selection of building materials usually depends on its price regardless of the environmental impact, quality, thermal performance and life of the material. Most of the time, this results in increasing the cost with variables of impacts over the environment during the life of the building. Therefore, consideration of the environmental impacts, social impacts and economic impacts is crucial in the selection of any building material. Decreasing such impacts could lead to more sustainable housing. Comparing the sustainability of the available wall building materials for low cost housing in Khartoum is carried out through the life cycle assessment (LCA) technique. The purpose of this paper is to compare the most available local building materials for walls for the urban poor of Khartoum from a sustainability point of view by going through the manufacturing of the materials, the use of these materials and then the disposal of the materials after their life comes to an end. Findings reveal that traditional red bricks couldn’t be considered as a sustainable wall building material that will draw the future of the low cost housing in Greater Khartoum. On the other hand, results of the comparison lead to draw attention to the wide range of the soil techniques and to its potentials to be a promising sustainable wall material for urban low cost housing in Khartoum.
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Amid a worldwide increase in tree mortality, mountain pine beetles (Dendroctonus ponderosae Hopkins) have led to the death of billions of trees from Mexico to Alaska since 2000. This is predicted to have important carbon, water and energy balance feedbacks on the Earth system. Counter to current projections, we show that on a decadal scale, tree mortality causes no increase in ecosystem respiration from scales of several square metres up to an 84 km2 valley. Rather, we found comparable declines in both gross primary productivity and respiration suggesting little change in net flux, with a transitory recovery of respiration 6–7 years after mortality associated with increased incorporation of leaf litter C into soil organic matter, followed by further decline in years 8–10. The mechanism of the impact of tree mortality caused by these biotic disturbances is consistent with reduced input rather than increased output of carbon.
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In this paper a generalization of collectively compact operator theory in Banach spaces is developed. A feature of the new theory is that the operators involved are no longer required to be compact in the norm topology. Instead it is required that the image of a bounded set under the operator family is sequentially compact in a weaker topology. As an application, the theory developed is used to establish solvability results for a class of systems of second kind integral equations on unbounded domains, this class including in particular systems of Wiener-Hopf integral equations with L1 convolutions kernels
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We propose a Nystr¨om/product integration method for a class of second kind integral equations on the real line which arise in problems of two-dimensional scalar and elastic wave scattering by unbounded surfaces. Stability and convergence of the method is established with convergence rates dependent on the smoothness of components of the kernel. The method is applied to the problem of acoustic scattering by a sound soft one-dimensional surface which is the graph of a function f, and superalgebraic convergence is established in the case when f is infinitely smooth. Numerical results are presented illustrating this behavior for the case when f is periodic (the diffraction grating case). The Nystr¨om method for this problem is stable and convergent uniformly with respect to the period of the grating, in contrast to standard integral equation methods for diffraction gratings which fail at a countable set of grating periods.
Resumo:
We consider second kind integral equations of the form x(s) - (abbreviated x - K x = y ), in which Ω is some unbounded subset of Rn. Let Xp denote the weighted space of functions x continuous on Ω and satisfying x (s) = O(|s|-p ),s → ∞We show that if the kernel k(s,t) decays like |s — t|-q as |s — t| → ∞ for some sufficiently large q (and some other mild conditions on k are satisfied), then K ∈ B(XP) (the set of bounded linear operators on Xp), for 0 ≤ p ≤ q. If also (I - K)-1 ∈ B(X0) then (I - K)-1 ∈ B(XP) for 0 < p < q, and (I- K)-1∈ B(Xq) if further conditions on k hold. Thus, if k(s, t) = O(|s — t|-q). |s — t| → ∞, and y(s)=O(|s|-p), s → ∞, the asymptotic behaviour of the solution x may be estimated as x (s) = O(|s|-r), |s| → ∞, r := min(p, q). The case when k(s,t) = к(s — t), so that the equation is of Wiener-Hopf type, receives especial attention. Conditions, in terms of the symbol of I — K, for I — K to be invertible or Fredholm on Xp are established for certain cases (Ω a half-space or cone). A boundary integral equation, which models three-dimensional acoustic propaga-tion above flat ground, absorbing apart from an infinite rigid strip, illustrates the practical application and sharpness of the above results. This integral equation mod-els, in particular, road traffic noise propagation along an infinite road surface sur-rounded by absorbing ground. We prove that the sound propagating along the rigid road surface eventually decays with distance at the same rate as sound propagating above the absorbing ground.
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e consider integral equations on the half-line of the form and the finite section approximation to x obtained by replacing the infinite limit of integration by the finite limit β. We establish conditions under which, if the finite section method is stable for the original integral equation (i.e. exists and is uniformly bounded in the space of bounded continuous functions for all sufficiently large β), then it is stable also for a perturbed equation in which the kernel k is replaced by k + h. The class of perturbations allowed includes all compact and some non-compact perturbations of the integral operator. Using this result we study the stability and convergence of the finite section method in the space of continuous functions x for which ()()()=−∫∞dttxt,sk)s(x0()syβxβx()sxsp+1 is bounded. With the additional assumption that ()(tskt,sk−≤ where ()()(),qsomefor,sassOskandRLkq11>+∞→=∈− we show that the finite-section method is stable in the weighted space for ,qp≤≤0 provided it is stable on the space of bounded continuous functions. With these results we establish error bounds in weighted spaces for x - xβ and precise information on the asymptotic behaviour at infinity of x. We consider in particular the case when the integral operator is a perturbation of a Wiener-Hopf operator and illustrate this case with a Wiener-Hopf integral equation arising in acoustics.