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  • Cambridge University Press
  • Essen : Verl. Glückauf
  • Krefeld : Geologischer Dienst Nordhein-Westfalen
  • 2005-2009  (7,387)
  • 1935-1939  (1,368)
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  • 1
    Publication Date: 2017-04-04
    Description: Twenty eruptive events from the Northeast Crater of Stromboli volcano recorded by a thermal monitoring camera in early 2004 were analysed in order to understand the eruptive dynamics. Selected eventswere chosen to be typical of explosions that characterize the steady activity of Stromboli in terms of jet height and duration. Most of the explosions consisted of clast-rich single bursts, originating from the same vent inside the Northeast Crater. Conspicuous ash emission was scarce. Eruptions were preceded by the flashing of a perturbation wave characterized by low temperatures and an average propagation velocity of about 35–100 m s−1. This perturbation was thought to be caused by the bursting of the gas slug at the bottom of the crater and is interpreted as an air wave. This was immediately followed by the expansion of a jet of ‘hot’ gas and particles, at a velocity of 35–75 m s−1. Ejecta coarser than 138 cm appeared ∼1.6–2 s after the onset of the explosion, moving at a variable velocity (30–60 m s−1). Eruptive events were either vertical or inclined 7–13◦ towards the NNW. This inclination is thought to be a consequence either of the morphology of the conduit, following modest rock falls that partially obstructed the uppermost part of the crater, or of the displacement of the internal conduit due to the explosive activity of the volcano. The instability of the summit area is a further possible cause of the deformation of the conduit.
    Description: This work was partially funded by the Istituto Nazionale di Geofisica e Vulcanologia and the Dipartimento della Protezione Civile, Italy, project INGVDPC V2
    Description: Published
    Description: 591–601
    Description: 1.5. TTC - Sorveglianza dell'attività eruttiva dei vulcani
    Description: 1.10. TTC - Telerilevamento
    Description: 3.6. Fisica del vulcanismo
    Description: JCR Journal
    Description: reserved
    Keywords: explosive dynamic ; thermal video monitoring ; volcano-tectonic structures ; volcano collapses ; Stromboli ; 04. Solid Earth::04.04. Geology::04.04.99. General or miscellaneous ; 04. Solid Earth::04.04. Geology::04.04.11. Instruments and techniques ; 04. Solid Earth::04.07. Tectonophysics::04.07.99. General or miscellaneous ; 04. Solid Earth::04.07. Tectonophysics::04.07.05. Stress ; 04. Solid Earth::04.07. Tectonophysics::04.07.07. Tectonics ; 04. Solid Earth::04.07. Tectonophysics::04.07.08. Volcanic arcs ; 04. Solid Earth::04.08. Volcanology::04.08.99. General or miscellaneous ; 04. Solid Earth::04.08. Volcanology::04.08.01. Gases ; 04. Solid Earth::04.08. Volcanology::04.08.02. Experimental volcanism ; 04. Solid Earth::04.08. Volcanology::04.08.03. Magmas ; 04. Solid Earth::04.08. Volcanology::04.08.04. Thermodynamics ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring ; 04. Solid Earth::04.08. Volcanology::04.08.07. Instruments and techniques ; 04. Solid Earth::04.08. Volcanology::04.08.08. Volcanic risk ; 05. General::05.02. Data dissemination::05.02.99. General or miscellaneous ; 05. General::05.02. Data dissemination::05.02.03. Volcanic eruptions ; 05. General::05.08. Risk::05.08.99. General or miscellaneous
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 2
    Publication Date: 2022-05-25
    Description: Author Posting. © Cambridge University Press, 2005. This article is posted here by permission of Cambridge University Press for personal use, not for redistribution. The definitive version was published in Journal of Fluid Mechanics 540 (2005): 49-73, doi:10.1017/S002211200500577X.
    Description: Circulation driven by horizontal differential heating is studied, using a double-walled Plexiglas tank (20×15×2.5 cm3) filled with salt water. For instances of heating/cooling from above and below, results indicate that there is always quasi-equilibrium circulation. In contrast to most previous results from experimental/ numerical studies, circulation in our experiments appears in the form of a shallow cell adjacent to the boundary of thermal forcing. The non-dimensional stream-function maximum confirms the 1/5-power law of Rossby, Ψ ∼Ra1/5 L . Dissipation rate measured in the experiments appears to be consistent with theory. For cases of heating/cooling from a sloping bottom, circulation is similar to cases with a flat bottom; circulation is strong if heating is below cooling, but it is rather weak if heating is above cooling. Nevertheless, circulation in all cases is visible to the naked eye.
    Description: W. W. was supported by The National Natural Science Foundation of China through grant 40476010 and the Research Fund for the Doctoral Program of Higher Education through grant 20030423011. R. X. H. was supported by the National Science Foundation through grant OCE-0094807 and the National Aero- Space Administration through Contract 1229833 (NRA-00-OES-05) to the Woods Hole Oceanographic Institution.
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 3
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    Cambridge University Press
    Publication Date: 2022-05-25
    Description: Author Posting. © Cambridge University Press, 2008. This article is posted here by permission of Cambridge University Press for personal use, not for redistribution. The definitive version was published in Journal of Fluid Mechanics 602 (2008): 241-266, doi:10.1017/S0022112008000827.
    Description: The stability of a hydraulically driven sill flow in a rotating channel with smoothly varying cross-section is considered. The smooth topography forces the thickness of the moving layer to vanish at its two edges. The basic flow is assumed to have zero potential vorticity, as is the case in elementary models of the hydraulic behaviour of deep ocean straits. Such flows are found to always satisfy Ripa's necessary condition for instability. Direct calculation of the linear growth rates and numerical simulation of finite-amplitude behaviour suggests that the flows are, in fact, always unstable. The growth rates and nonlinear evolution depend largely on the dimensionless channel curvature κ=2αg′/f2, where 2α is the dimensional curvature, g′ is the reduced gravity, and f is the Coriolis parameter. Very small positive (or negative) values of κ correspond to dynamically wide channels and are associated with strong instability and the breakup of the basic flow into a train of eddies. For moderate or large values of κ, the instability widens the flow and increases its potential vorticity but does not destroy its character as a coherent stream. Ripa's condition for stability suggests a theory for the final width and potential vorticity that works moderately well. The observed and predicted growth in these quantities are minimal for κ≥1, suggesting that the zero-potential-vorticity approximation holds when the channel is narrower than a Rossby radius based on the initial maximum depth. The instability results from a resonant interaction between two waves trapped on opposite edges of the stream. Interactions can occur between two Kelvin-like frontal waves, between two inertia–gravity waves, or between one wave of each type. The growing disturbance has zero energy and extracts zero energy from the mean. At the same time, there is an overall conversion of kinetic energy to potential energy for κ〉0, with the reverse occurring for κ〈0. When it acts on a hydraulically controlled basic state, the instability tends to eliminate the band of counterflow that is predicted by hydraulic theory and that confounds hydraulic-based estimates of volume fluxes in the field. Eddy generation downstream of the controlling sill occurs if the downstream value of κ is sufficiently small.
    Description: This work was supported by the National Science Foundation (Grant OCE- 0525729).
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 4
    Publication Date: 2022-05-25
    Description: Author Posting. © Cambridge University Press, 2008. This article is posted here by permission of Cambridge University Press for personal use, not for redistribution. The definitive version was published in Journal of Fluid Mechanics 604 (2008): 369-388, doi:10.1017/S0022112008001237.
    Description: We discuss laboratory experiments investigating mixing in a density-driven current flowing down a sloping bottom, in a rotating homogenous fluid. A systematic study spanning a wide range of Froude, 0.8 〈 Fr 〈 10, and Reynolds, 10 〈 Re 〈 1400, numbers was conducted by varying three parameters: the bottom slope; the flow rate; and the density of the dense fluid. Different flow regimes were observed, i.e. waves (non-breaking and breaking) and turbulent regimes, while changing the above parameters. Mixing in the density-driven current has been quantified within the observed regimes, and at different locations on the slope. The dependence of mixing on the relevant non-dimensional numbers, i.e. slope, Fr and Re, is discussed. The entrainment parameter, E, was found to be dependent not only on Fr, as assumed in previous studies, but also on Re. In particular, mixing increased with increasing Fr and Re. For low Fr and Re, the magnitude of the mixing was comparable to mixing in the ocean. For large Fr and Re, mixing was comparable to that observed in previous laboratory experiments that exhibited the classic turbulent entrainment behaviour.
    Description: Support was given by the National Science Foundation project number OCE-0350891.
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 5
    Publication Date: 2022-05-25
    Description: Author Posting. © Cambridge University Press, 2008. This article is posted here by permission of Cambridge University Press for personal use, not for redistribution. The definitive version was published in Journal of Fluid Mechanics 605 (2008): 281-291, doi:10.1017/S002211200800150X.
    Description: A condition is derived for the hydraulic criticality of a 2-layer flow with transverse variations in both layer velocities and thicknesses. The condition can be expressed in terms of a generalized composite Froude number. The derivation can be extended in order to obtain a critical condition for an N-layer system. The results apply to inviscid flows subject to the usual hydraulic approximation of gradual variations along the channel and is restricted to flows in which the velocity remains single-signed within any given layer. For an intermediate layer with a partial segment of sluggish flow, the long-wave dynamics of the overlying and underlying layers become decoupled.
    Description: The work described herein was supported by the Office of Naval Research (N00014- 07-1-0590) and the National Science Foundation (OCE-0525729).
    Repository Name: Woods Hole Open Access Server
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  • 6
    Publication Date: 2022-05-25
    Description: Author Posting. © Cambridge University Press, 2008. This article is posted here by permission of Cambridge University Press for personal use, not for redistribution. The definitive version was published in Journal of Fluid Mechanics 616 (2008): 327-356, doi:10.1017/S0022112008003984.
    Description: A steady theory is presented for gravity currents propagating with constant speed into a stratified fluid with a general density profile. Solution curves for front speed versus height have an energy-conserving upper bound (the conjugate state) and a lower bound marked by the onset of upstream influence. The conjugate state is the largest-amplitude nonlinear internal wave supported by the ambient stratification, and in the limit of weak stratification approaches Benjamin's energy-conserving gravity current solution. When the front speed becomes critical with respect to linear long waves generated above the current, steady solutions cannot be calculated, implying upstream influence. For non-uniform stratification, the critical long-wave speed exceeds the ambient long-wave speed, and the critical-Froude-number condition appropriate for uniform stratification must be generalized. The theoretical results demonstrate a clear connection between internal waves and gravity currents. The steady theory is also compared with non-hydrostatic numerical solutions of the full lock release initial-value problem. Some solutions resemble classic gravity currents with no upstream disturbance, but others show long internal waves propagating ahead of the gravity current. Wave generation generally occurs when the stratification and current speed are such that the steady gravity current theory fails. Thus the steady theory is consistent with the occurrence of either wave-generating or steady gravity solutions to the dam-break problem. When the available potential energy of the dam is large enough, the numerical simulations approach the energy-conserving conjugate state. Existing laboratory experiments for intrusions and gravity currents produced by full-depth lock exchange flows over a range of stratification profiles show excellent agreement with the conjugate state solutions.
    Description: K. R. H. was supported by ONR grant N000140610798
    Repository Name: Woods Hole Open Access Server
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  • 7
    Publication Date: 2009-01-01
    Description: We review developments in radiocarbon measuring techniques from the Libby counter through proportional gas counters and liquid scintillation spectrometers to the more recent developments of accelerator mass spectrometry (AMS), followed by a coupling of gas chromatography with AMS for compound-specific 14C analyses. While during the first 60 yr of 14C measurements beta counting, specifically gas counting, was the dominant technique, in the future of 14C science AMS will be the dominant technology.
    Print ISSN: 0033-8222
    Electronic ISSN: 1945-5755
    Topics: Archaeology , Energy, Environment Protection, Nuclear Power Engineering , Geosciences
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  • 8
    Publication Date: 2009-08-01
    Description: How do multilateral institutions influence the strategic choices and actions of international managers? This paper addresses the question by exploring the impact of the World Trade Organization's (WTO) decision-making process on multinational enterprises (MNEs). We discuss the three phases of the WTO decision-making lifecycle - the formulation of trade rules, the implementation of those rules, and the enforcement of the rules – and propose a strategic adjustment framework for understanding how companies alter their strategies and structures in response to the WTO's rules and operations. We argue that the increased relevance of multilateral rules and enforcement mechanisms – embodied in the WTO - is an important influence on MNE strategies and structures because of the increasing embeddedness of the WTO in national levels of regulation. We illustrate this through examples taken from the pharmaceutical, textiles and sugar industries sectors that have witnessed substantial multilateral regulation.
    Print ISSN: 1369-5258
    Electronic ISSN: 1469-3569
    Topics: Political Science , Economics
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  • 9
    Publication Date: 2009-10-01
    Description: Although the global economy has flourished in the current global economic governance regime, the foundations of this order are starting to crumble. Both in trade and in finance, the existing institutions are under severe stress. In trade, more and more countries undermine the WTO by implementing preferential trade agreements. In finance, the IMF has been weak for most of this decade, although it experienced a revival in the current crisis. First and foremost, this weakness of the institutions of global economic governance is the result of policies implemented by the transatlantic powers. Both the European Union and the United States are actively pursuing policies that weaken the existing institutions. In trade, there is a large gap between the official rhetoric, which highlights the importance of the multilateral regime, and the trade policy practice, which is weakening the WTO. In finance, the transatlantic powers have until very recently blocked any progress in the IMF with regard to lending policies. In addition, the EU continues to defend its unjustified overrepresentation in the IMF's governance structures. The article suggests that one of the key explanations for this development is the weak support for globalization in most OECD-countries. Confronted with no enthusiasm for globalization in their domestic constituencies, policy makers in Europe and the United States are increasingly opting for policies that will, over time, erode the existing regimes of global economic governance.
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  • 10
    Publication Date: 2009-08-01
    Description: This essay explores the relationship between commerce and culture in the context of the recent debate over the social effect of Wal-Mart. In spite of much public debate, little is known about how Wal-Mart affects values. Using data collected from multiple sources, we show there is little evidence that Wal-Mart makes communities more conservative or more progressive.
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  • 11
    Publication Date: 2009-08-01
    Description: Seeking to build on related successes in other information technology sectors, the government of India has signaled its intent to transform the country's performance in microelectronics. Facing a young and expanding population, India needs to create manufacturing jobs in promising industries, and it needs to build out from its limited high-technology base. Semiconductors are foundational in this regard. Today, there is much discussion within India about the link between semiconductors and innovation in bio-electronics, alternative energy production and storage, and various micro- and nano-devices. The government's contemporary attempt to promote the building of infrastructure for manufacturing and applied research in semiconductors highlights reasons for hope. So too does the remarkable talent now available in the Indian diaspora. But significant impediments, especially in postsecondary and graduate-level education, must still be overcome if the necessary human capital is to be developed, equipped, and deployed effectively.
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  • 12
    Publication Date: 2009-10-01
    Description: The U.S. is no longer providing leadership in trade policy. In recent years, we have seen a sharp turn toward a rapid proliferation of bilateral preferential trade agreements, accords that are likely to undermine the World Trade Organization (WTO). By pursuing a strategy of ‘competitive liberalization’ both on a sectoral basis under the Bill Clinton administration, and then a policy of seeking bilateral arrangements under the George W. Bush administration, this article argues that American administrations have undermined the coalition for free trade in the United States. Consequently, protectionist industries including textiles, steel, and agriculture have made further liberalization more difficult and thus the prospects for promoting continued trade liberalization have grown dimmer.
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  • 13
    Publication Date: 2009-04-01
    Description: How and to what effect do firms coordinate their actions to deal with the negative external effects of productive activity? Under which conditions do associations engage in self-regulation and how do they tackle the specific regulatory challenges at stake? When developing hypotheses, we first vary attributes of the information environment in which private actors interact; and, secondly, actors' preferences as a function of the problem type at hand. With respect to the environmental conditions, our findings show that a regulatory threat matters when developing associative action, whilst the evidence is less clear as regards NGO campaigns. In terms of the problem type, we find that redistributive issues and prisoner's dilemma situations are much more conflict prone than coordination/win-win type of problems. Industry actors recur to various governance devices such as flexible contract design and compensation mechanisms to solve redistributive problems. Prisoner's dilemma (PD) problems may only partially be addressed by governance devices to the extent that free-riding is controlled and sanctioned within an association. We conclude that private actors engaging in self-regulation will not successfully manage all types of conflicts. They lack powerful sanctioning tools to deal with PD situations, but prove to be able to flexibly handle redistributive problems.
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  • 14
    Publication Date: 2009-04-01
    Description: For many, transnational capital is one of the most important driving forces of economic globalization; yet, we know little about what determines cross-border portfolio investments. In addition to recent economic literature's focus on information asymmetries as one key determinant of cross-border investment, this study brings in a political aspect to the field of international trade in assets. The –race to the bottom’ thesis connects domestic economic policies to investment decisions and argues that capital is more likely to move towards economies characterized by economic liberalism; political institutions are also relevant for portfolio investments, because democratic institutions often provide more credible protection against predatory practices. In this study, I model bilateral portfolio investments as a function of economic policies, political institutions, and levels of transparency of sending and receiving countries as well as important international connections. Empirical findings indicate the importance of transparency to attract portfolio investments. Moreover, transnational portfolio investments are only sensitive to some fiscal policy indictors and only within the OECD countries. Therefore, for non-OECD countries, there is still ‘room to move’ in maneuvering different aspects of fiscal policies. Finally, I find that investors care about the nature of political institutions as democratic institutions tend to be associated with higher levels of portfolio investment inflows. This is good news for developing countries that have undergone or are in the process of democratization. In addition to democratizing for peace, increased foreign capital further incentivizes a progression towards democratization.
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  • 15
    Publication Date: 2009-08-01
    Description: Is it possible to generate more efficient outcomes with respect to public procurement in general and defense acquisition in particular? Or are cost overruns inevitable when it comes to major engineering projects, like the development of modern weaponry? In this article, we draw on a unique data set of nearly 50 French armaments contracts in order to examine how one government has reformed its defense acquisition process over the past twenty years. Beginning in the early 1990s, France embarked on a series of policy reforms that enabled the state to contain skyrocketing weapons costs. We emphasize three, inter-related aspects of the defense acquisition environment in France that favored cost containment: first, hard budget constraints; second, the great technical capacity that the French government brought to bear on the weapons acquisition process, coupled with its iterative relationship with a small number of suppliers; and third, the use of contracting techniques that empowered project managers.
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  • 16
    Publication Date: 2009-10-01
    Description: Drawing upon a comprehensive database of contemporary protectionism, this paper offers an initial assessment of the extent to which our understanding of protectionism may have to evolve. While some long-standing features of protectionism appear to have endured (such as the distribution of discriminatory measures across economic sectors), specific corporate needs arising from the global financial crisis and particular national attributes are more likely to have influenced the choice of beggar-thy-neighbor policy instruments than binding trade rules and other international accords.
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  • 17
    Publication Date: 2009-04-01
    Description: American political campaigns have become a multi-billion dollar industry. Rather than assume that only political factors affect the campaigns that voters see, scholars must assess the importance of the business incentives associated with political consulting. Economic competition does not match political competition; firms compete for clients within the two major parties, against their political allies. I argue that the supply of firms in each party, the revenue models in the industry, the diversification of client types, and the cooperative structure in each party all may affect political campaigns. The way the industry operates and the different patterns of behavior within each party create incentives and practices that may alter campaigns in response to economic factors having little to do with optimal political strategy. Using two original surveys and a network analysis, I analyze how the industry is changing and how consultants in each party cooperate and compete.
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  • 18
    Publication Date: 2009-12-01
    Description: Why do many States in transitional economies lack the regulative capacities to evenly distribute property rights among emerging private firms resulting in having public good devoured by particularistic interests? I argue that uneven distribution of property rights is deeply embedded within broader power relations permeating political regimes. This study attempts to develop the concept of politically-embedded cronyism where State incumbents generate and protract uneven distribution of property rights in favor of a few private actors as tactics of regime survival that go beyond the mere interest of self-enrichment as the capture thesis would argue. Politically-embedded cronyism is likely to emerge the more State incumbents retain their relative autonomy from their cronies through higher concentration of power in the executive, less role of societal groups in general and business in particular in the reproduction of the power of top incumbents and higher public asset retention in the post-liberalization period in addition to possessing channels of political incorporation to fledging business.
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  • 19
    Publication Date: 2009-01-01
    Description: When comparing dendrodates and radiocarbon dates, I advocate using the mean value for archaeologically defined data series, as in the usual case, the correct dating is always more precise than the calibrated areas. However, in the extreme gradient of the calibration curve, we must consider the errors. Based on the Corded Ware from the Tauber basin, I put forward a first example in which a contradiction between the archaeological and 14C dating occurs. If one cleanly separates the older measurements from Köln and the younger ones from Heidelberg, the contradiction towards the archaeological dating is canceled out when only the younger Heidelberg dates are taken into account. Regarding the Early Bronze Age, I shall first deal with the cemetery at Singen and will show, using the typology and the horizontal distribution of the graves, how outliers can be identified, thus narrowing the range for dating of the cemetery. The comparison of 2 archaeologically contemporaneous cemeteries in the Neckar basin (Rottenburg and Gäufelden) again results in contradictions between the archaeological and 14C dating. In this case, the contradictions cannot be solved without any new dating measurements. It is recommended that these should be carried out by at least 2 laboratories. Finally, some recommendations are given to archaeologists. In my opinion, 14C dates that are archaeologically unsuitable should be used to check the findings and the archaeological-typological classification. The contradictions should be reported immediately to the 14C laboratory, so that any possible experimental errors can be identified.
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    Topics: Archaeology , Energy, Environment Protection, Nuclear Power Engineering , Geosciences
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  • 20
    Publication Date: 2009-01-01
    Description: In September 2005, an accelerator mass spectrometry (AMS) system based on a 1MV Tandetron accelerator arrived at the Centro Nacional de Aceleradores (CNA). One of the main research programs for this AMS facility is based on radiocarbon. At the same time as the AMS facility was installed and tested, the 14C sample preparation laboratory was designed and set up. A graphitization line that allows the preparation of 5 samples in parallel was designed and built in October 2006. The first months were mainly dedicated to check and optimize all the sample processing. For such a task, several reference samples have been prepared and measured. Since the beginning of 2007, the laboratory has been fully operational and is currently performing as a service for the scientific community. During 2007, nearly 100 unknown samples were prepared and measured in our AMS system. Most of them were for dating purposes, but also other applications were investigated. The performance of the 14C laboratory and dating service will be shown, with some examples as illustration.
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  • 21
    Publication Date: 2009-01-01
    Description: The iron dating project Aikarauta has been launched in Finland. This paper presents the results of the preliminary investigations. The ability for radiocarbon measurement by accelerator mass spectrometry (AMS) of iron in Finland has been demonstrated by using coal-produced iron as reference material. An elemental analyzer has been harnessed to measure the carbon content of small iron samples. In addition, we have hypothesized that a fingerprint of the limestone usage in the smelting process is the high Ca content of iron and slag. This has been examined by performing an iron smelting experiment with limestone as flux, by making elemental analyses of ingredients and the resulting slag and iron, and by a 14C analysis of the produced iron. It is possible that limestone dilutes the 14C contents of the produced iron, making its age determination challenging.
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  • 22
    Publication Date: 2009-01-01
    Description: Archaeological excavations performed for many years in Łekno, central Poland, have exposed relicts of wooden fortified settlements, and in its enclosure also basements of stone buildings, consisting of Romanesque rotunda and a Cistercian monastery, including an oratory, church, and abbot's house. Earlier archaeological, structural, and stratigraphical studies have shown that these buildings were constructed in a sequence and represented several phases of development.In this paper, we present results of radiocarbon dating of stone buildings of the rotunda and the monastery. For 14C dating, we used tiny pieces of charcoal retrieved from calcareous and gypsum mortar binding stone elements from the buildings. These pieces were incorporated in mortar during the firing process, where the fuel used for firing was wood. Most of the obtained 14C dates formed clear groups, confirming that individual buildings were constructed in separate periods. Calibrated 14C dates of these phases agree well with the constraints provided by historical sources, and enable us to set their ages with accuracy better than previously available. In particular, we have learned that the oldest rotunda was built at the boundary of the 10/11th centuries, and the church and the abbot's house, before AD 1250. However, some samples gave much too old 14C ages, clearly reflecting the use of old wood for firing. These problems were revealed only for samples from the rotunda and for the gypsum stone ornamental details.
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  • 23
    Publication Date: 2009-01-01
    Description: Understanding of processes that determined the expansion of farming and animal husbandry in south-western Europe is hampered by poor chronologies of the early Neolithic in this region. This paper presents new radiocarbon dates, which are used to construct such a chronological frame for a regional group of the most important culture of the early Neolithic in the western Mediterranean: the Cardial culture.
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  • 24
    Publication Date: 2009-01-01
    Description: The field of dendrochronology had a developmental “head start” of at least several decades relative to the inception of radiocarbon dating in the late 1940s, but that evolution was sufficiently advanced so that unique capabilities of tree-ring science could assure success of the 14C enterprise. The Laboratory of Tree-Ring Research (LTRR) at the University of Arizona played a central role in the cross-pollination of these disciplines by providing the first wood samples of exactly known age for the early testing and establishment of the “Curve of Knowns” by Willard Libby. From the 1950s into the early 1980s, LTRR continued to contribute dated wood samples (bristlecone pine and other wood species) to 14C research and development, including the discovery and characterization of de Vries/Suess “wiggles,” calibration of the 14C timescale, and a variety of tests to understand the natural variability of 14C and to refine sample treatment for maximum accuracy. The long and varied relationship of LTRR with 14C initiatives has continued with LTRR contributions to high-resolution studies through the 1990s and systematic efforts now underway that may eventually extend the bristlecone pine chronology back beyond its beginning 8836 yr ago as of 2009. This relationship has been mutualistic such that a half-century ago the visibility and stature of LTRR and dendrochronology were also elevated through their association with 14C-allied “hard sciences.”
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  • 25
    Publication Date: 2009-01-01
    Description: Newly available radiocarbon dates show the early signs of pottery-making in the North Caspian area, the Middle-Lower Volga, and the Lower Don at 8–7 kyr cal BC. Stable settlements, as indicated by “coeval subsamples,” are recognized in the Middle-Lower Volga (Yelshanian) at 6.8 kyr cal BC and the Caspian Lowland at about 6 kyr cal BC. The ages of the Strumel-Gostyatin, Surskian, and Bug-Dniesterian sites are in the range of 6.6–4.5 kyr BC, overlapping with early farming entities (Starčevo-Körös-Criş and Linear Pottery), whose influence is perceptible in archaeological materials. Likewise, the 14C-dated pollen data show that the spread of early pottery-making coincided with increased precipitation throughout the forest-steppe area.
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  • 26
    Publication Date: 2009-01-01
    Description: The direct measurement of organic matter included in archaeological pottery may yield a reliable assessment of age. The main problem consists in the identification of possible origins and assessment of distortion for the age of organic inclusions. Our experiments show that shells included in pottery fabrics are strongly influenced by the reservoir effect, which may reach 500 yr or more. Other organic inclusions, such as lake ooze, do not visibly distort the age. The obtained series of radiocarbon dates have been used for the assessing the age of the early stages of pottery manufacture in southern Russia.
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  • 27
    Publication Date: 2009-01-01
    Description: The subject of this article is the radiocarbon dating on bones in the western European Neolithic. By gathering 14C dates for 2 examples, one chosen in the middle Neolithic of the Rhine region and the other in the end of the early Neolithic in the same region and in the Paris Basin, a significant gap appears between the sum probabilities of dates on charcoals and the ones obtained with bones. A comparison between these results with the few available dendrochronological dates shows that dates on bones seem too young, while the sequence based on charcoals fits. The existence of too-young 14C dates of bones is not new: this phenomenon was already indicated in previous studies. Most explanations agree that there was a source of contamination, during the sample's burial or its treatment in laboratory. These examples illustrate that consequences can be heavy on a chronology built, partly or entirely, on 14C dates of bones.
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  • 28
    Publication Date: 2009-01-01
    Description: In the Monastery of Our Saviour and St. Andronicus in Moscow, skeletal remains of clerics and of (possibly) famous icon painters were discovered. The bones were radiocarbon dated, and concentrations of trace elements in bone tissues were measured. From tombs 1–4, the 14C dates obtained from human bones (likely monks) and from associated wood date to the 14th–15th centuries AD, as expected. Trace element concentrations indicate signs of fasting. Tomb 5 contained 2 burials; these could belong to the famous icon painters Rublev and Chernyi. Indeed, the bones show high concentrations of lead, zinc, and copper, which is typical for remains of artists and metallurgists. The 14C dates of the 2 skeletons, however, differ by 200 yr, and seem to be too old for Rublev and Chernyi. At this stage, it is not clear if the burials can be assigned to these painters.
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  • 29
    Publication Date: 2009-01-01
    Description: An attempt was made to trace the antiquity of custard apple in India on the basis of accelerator mass spectrometry (AMS) and liquid scintillation counting (LSC) radiocarbon dates. Recently, seed remains of custard apple (Annona squamosa L.) in association with wood charcoals were encountered from the Neolithic archaeological site of Tokwa at the confluence of the Belan and Adwa rivers, Mirzapur District, in the Vidhyan Plateau region of north-central India. The wood charcoal sample was dated at the 14C laboratory of the Birbal Sahni Institute of Palaeobotany (BSIP), Lucknow, by conventional LSC 14C dating. The sample dated to 1740 cal BC (BS-2054). A seed sample of custard apple was dated by AMS at the Institute of Physics 14C laboratory, Bhubaneswar, India (3MV tandem Pelletron accelerator). Interestingly, the AMS date was given as 1520 cal BC (IOPAMS-10), showing a reasonable agreement with the LSC date carried out at BSIP. On botanical grounds, the custard apple is native to South America and the West Indies and was supposed to have been introduced in India by the Portuguese in the 16th century. The present 14C dates of the samples pushes back the antiquity of custard apple on Indian soil to the 2nd millennium BC, favoring a group of specialists proposing diverse arguments for Asian-American transoceanic contacts before the discovery of America by Columbus in AD 1492.
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  • 30
    Publication Date: 2009-01-01
    Description: Exploratory work was performed to investigate the feasibility of using a simplified radiometric analytical approach for determining the bioethanol content of US automotive fuels. The method involves mixing fuel samples directly with a suitable fluor. Sample preparation is extremely rapid since all conventional sample preparation steps are essentially eliminated. Results are based on the background-corrected DPM values obtained when using 10 mL of sample mixed with 10 mL of Permafluor E+. Results are also reported in terms of conventional pMC for some of the samples. Bioethanol from a dry-mill ethanol plant served as the analytical reference sample that represented a 100% bioethanol content. Using current-day bioethanol as a reference sample eliminates the need to correct for “bomb carbon.” For 1:1 mixtures of sample and fluor, the background-corrected DPM showed a linear relationship with the bioethanol concentration, indicating that the quench correction approach was effective for the variable-quench samples. Based on the analysis of E0 (pure gasoline), E10, and “E85” from local gas stations, it appears that the method has good potential for determining the bioethanol content in commercial ethanol/gasoline blends. However, a variety of potential sources of error still require investigation in order to refine the method.
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  • 31
    Publication Date: 2009-01-01
    Description: Santa Lucía is a pottery production site dating to the Formative period (about 1600 BC to AD 200). It is located in the Cochabamba valleys of the eastern Bolivian Andes. The settlement consists of a residential area and a separate workshop area. A peripheral sector of ash mounds was used as refuse sites and burial grounds. The excavations yielded a total of 16 radiocarbon samples from all 3 sectors, which were dated at the Gliwice Radiocarbon Laboratory (Gliwice, Poland). The results from the deepest trench in the workshop sector (Trench 5) provide information for the stratigraphic sequence and help to define spatial and socioeconomic changes at around 600–500 BC with the beginning of the Late Formative or Santa Lucía III phase. The 14C dates from Santa Lucía, therefore, contribute to a better definition of the existing regional Formative period phases and finally to a better understanding of the processes during the Formative period in the south-central Andes.
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  • 32
    Publication Date: 2009-01-01
    Description: Complex interdisciplinary studies carried out in the territory of the Vilnius Lower Castle, E Lithuania, were used to construct a chronological framework based on radiocarbon data and archaeological information. Bulk samples (wood and sediment) were collected from an approximately 3-m core that crossed cultural layers and underlying strata. 14C dates indicate that the underlying bed possibly formed during the 6th century AD, although no archaeological finds were discovered there. Paleobotanical (pollen and plant macrofossil) investigations reveal evidence of agriculture that points to the existence of a permanent settlement in the area at that time. The chronological data indicates a sedimentation hiatus before the onset of the deposition of the cultural layer in the studied area. The 14C dates showed that the formation of the cultural bed began during the late 13th–early 14th centuries AD, that is, earlier than expected according to the archaeological record. The ongoing deposition of the cultural beds continued throughout the middle to latter half of the 14th century AD as revealed by the archaeological records and confirmed by well-correlated 14C results. After some decline in human activity in the middle of the 14th century AD, a subsequent ongoing development of the open landscape, along with intensive agriculture, points to an increase in human activity during the second half of the 14th century AD. The first half of the 15th century AD was marked by intensive exploitation of the territory, indicating a period of economic and cultural prosperity. The chronological framework indicates that the investigated cultural beds continued forming until the first half of the 16th century AD.
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  • 33
    Publication Date: 2009-01-01
    Description: The archaeological site of Populonia-Baratti, in the southern part of Tuscany (Italy), was one of the most important centers in ancient Etruria, as seen in the evidence of metallurgical activities carried out at that time. During recent archaeological excavations (2005) in the ancient industrial area of Populonia, along the Baratti beach, 2 interesting tombs were found. The 2 graves were unusually located in an area dedicated to metallurgical activity and showed a particular structure of the burial chambers and an extreme richness in the grave goods. The unique character of the 2 tombs prompted many questions: who were these 2 individuals (a woman wearing many jewels and a tall, vigorous man) and when did they die? In order to obtain useful information about the chronology of the 2 tombs, accelerator mass spectrometry (AMS) radiocarbon analyses were performed on samples taken from the ribs of the 2 skeletons. Measured 14C ages were converted to calibrated ages using additional information derived from stable isotope ratios measured in the extracted collagen. Actually, the 13C data provided useful hints about the diet of the 2 individuals, thus allowing us to estimate the percentage of marine food consumed (about 30%) and exploit a combined marine-terrestrial calibration curve. As a result, the age of the 2 individuals can be dated to the 2nd century AD, during Roman times, which is in good agreement with the information obtained from archaeological, anthropological, and stylistic studies of the 2 tombs.
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  • 34
    Publication Date: 2009-01-01
    Description: The results of a tentative oak tree-ring chronology built from charcoal samples found in Late Bronze to early Iron Age contexts (late 2nd millennium to early 1st millennium BCE) at the site of Tille Höyük in southeast Turkey, and its placement in time, was published in 1993 (Summers 1993). This represented one of the few publications about archaeological dendrochronology for this period and region. However, the dendrochronological sequence and its crossdating have been questioned, including in this journal (Keenan 2002). Here, we critically reassess and revise the dendrochronological positioning of the site's building phases and their place in time by absolutely dating 7 decadal tree-ring sequences via radiocarbon wiggle-matching.
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  • 35
    Publication Date: 2009-01-01
    Description: The inception of the radiocarbon dating method in 1949 was immediately supported by many archaeologists. In the following 2 decades, many important archaeological sites in the Old World were dated, marking the beginning of building a reliable chronological framework for prehistoric and early historic cultural complexes worldwide. The author presents an observation of some of the most important results in establishing a chronology for Old World archaeology, based on 14C dating performed in the last 50 yr. An extensive bibliography should help scholars to get acquainted with early summaries on archaeological chronologies based on 14C data and their evaluation, as well as with some recent examples of the application of 14C dating in Old World archaeology.
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  • 36
    Publication Date: 2009-01-01
    Description: Mortar as a mixture of binder and aggregate can be reliably dated with radiocarbon if the applied preparation method allows one to eliminate unburnt carbonate fragments, bearing 14C-depleted carbon and causing overestimation of 14C age. To avoid these problems, separation of specific grain-size fractions of mortar and 14C analysis of the CO2 portions collected in different time intervals of the acid-leaching reaction is usually helpful. In the present paper, we demonstrate that the rate of the leaching reaction of mortars with dense carbonate aggregate differs from that of mortars with crumbled limestone and scattered shells (e.g. of foraminifera). Verification of the obtained 14C dates against historical sources shows that for mortars rich in foraminiferous limestone, a reaction rate-based chemical elimination of “dead carbon” may appear impossible.
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  • 37
    Publication Date: 2009-01-01
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  • 38
    Publication Date: 2009-01-01
    Description: Preparation of bone material for radiocarbon dating is still a subject of investigation. In the past, the most problematic ages appeared to be the very old bones, i.e. those with ages close to the limit of the dating method. Development of preparative methods requires sufficient amounts of bone material as well as the possibility of verification of the ages. In the peat section at Niederweningen, ZH Switzerland, numerous bones of mammoth and other animals were found in the late 19th century. The first accelerator mass spectrometry (AMS) radiocarbon ages of those bones from 1890/1891 excavations placed the age between 33,000 and 35,000 BP. The excavations in 2003/2004 provided additional material for 14C dating. An age of 45,870 ± 1080 BP was obtained on base (NaOH step) cleaned gelatin from mammoth bone, which was very close to the age of 45,430 ± 1020 BP obtained for the peat layer that buried the mammoths. The 14C age of gelatin cleaned using the ultrafiltration method obtained in this study, 45,720 ± 710 BP, is in a very good agreement with the previously obtained results. Moreover, the study shows that 3 pretreatment methods (base+Longin, Longin+ultrafiltration, and base+Longin+ultrafiltration) give ages consistent with each other and with the age of the peat section.
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  • 39
    Publication Date: 2009-01-01
    Description: Radiocarbon measurements of hermatypic corals from 4 sites in the Gulf of Mexico (GOM) and Caribbean Sea were made to estimate the marine 14C reservoir age (R) and the marine regional correction (ΔR) for this region. Coral skeletal material from the Flower Garden Banks (northern GOM continental shelf), Veracruz, Mexico, and 2 reefs from the Cariaco Basin, Venezuela, were analyzed. Annual and subannual samples from 1945–1955 were milled and 14C composition was determined. In the Gulf of Mexico, average coral Δ14C is −52.6 ± 0.7‰ and average Δ14C for the Cariaco Basin corals is −53.4 ± 0.8‰. Average values for the marine reservoir age and ΔR are computed with this data and compared with results derived from previous measurements made in the same regions. These values are important in calibrating the 14C ages of carbonate samples from the area.
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  • 40
    Publication Date: 2009-01-01
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  • 41
    Publication Date: 2009-01-01
    Description: This article reports on 10 new accelerator mass spectrometry (AMS) radiocarbon dates from early phases of the Early Bronze Age at the long-lived settlement of Pella (modern Tabaqat Fahl) in the north Jordan Valley. The new AMS dates fall between 3400 and 2800 cal BC, and support a recent suggestion that all Chalcolithic period occupation had ceased by 3800/3700 cal BC at the latest (Bourke et al. 2004b). Other recently published Early Bronze Age14C data strongly supports this revisionist scenario, suggesting that the earliest phase of the Early Bronze Age (EBA I) occupied much of the 4th millennium cal BC (3800/3700 to 3100/3000 cal BC). As this EB I period in the Jordan Valley is generally viewed as the key precursor phase in the development of urbanism (Joffe 1993), this revisionist chronology has potentially radical significance for understanding both the nature and speed of the move from village settlement towards a complex urban lifeway.
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  • 42
    Publication Date: 2009-01-01
    Description: With the introduction of the radiocarbon method in 1949 and the calibration curve constantly improving since 1965, but especially due to the development of the more accurate accelerator mass spectrometry (AMS) dating some 30 yr ago, the application of the 14C method in prehistory revolutionized traditional chronological frameworks. Theories and models are adjusted to new 14C sequences, and such sequences even lead to the creation of new theories and models. In our contribution, we refer to 2 major issues that are still heavily debated, although their first absolute dating occurred some decades ago: 1) the transition from the Mesolithic to the Early Neolithic in the eastern and western Aegean. Very high 14C data for the beginning of the Neolithic in Greece around 7000 BC fueled debates around the Preceramic period in Thessaly (Argissa-Magoula, Sesklo) and the Early Neolithic in Macedonia (Nea Nikomedeia). A reinterpretation of these data shows that the Neolithic in Greece did not start prior to 6400/6300 BC; 2) the beginning and the end of the Chalcolithic period in SE Europe. Shifting from relative chronologies dating the Chalcolithic to the 3rd millennium BC to an absolute chronology assigning the Kodžadermen-Gumelniţa-Karanovo VI cultural complex to the 5th millennium BC, the exact beginning and the end of the period are still under research. New data from Varna (Bulgaria) and Pietrele (Romania) suggest that start and end of the SE European Chalcolithic have to be dated deeper into the 5th millennium BC.
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  • 43
    Publication Date: 2009-01-01
    Description: The present research is focused on the dating of the Oglakhty burial ground, the key site of stage I of the Tashtyk culture. Despite the numerous well-preserved burials of that type investigated at the Oglakhty complexes, their chronological position has remained unclear. From the early 20th century until the present, 2 different time periods had been identified for the Tashtyk burials: (1) from the 1st century BC until the 1st century AD and (2) from the 1st until the 2nd century AD. New data obtained in the 1990s suggested a different age for Tashtyk burials, namely the 3rd–4th centuries AD. This considerable shift in chronology needed to be checked with independent data. The chronological position of one of the Oglakhty burials, tomb 4, has been investigated with the use of wiggle-matching, applied to wooden logs used in the construction of tomb 4. The resulting dates for this burial strongly suggest its age as being limited to the 3rd–4th centuries AD, which is corroborated by the archaeological dates of the imported artifacts found in the grave and which is in agreement with the chronological position of the Oglakhty site, as proposed by previous investigations.
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  • 44
    Publication Date: 2009-01-01
    Description: Over the last 30 yr, there has been an ongoing debate on the dates and modes of the earliest colonization of East Polynesia, namely the Cook Islands, the 5 archipelagos of French Polynesia, the Hawai'i Islands, Easter Island, and New Zealand. At least 3 alternative models were proposed by Sinoto, Anderson, Kirch, and Conte, but interestingly all these models basically relied on the same set of roughly 200 radiocarbon dates on various organic materials from archaeological excavations as far back as the 1950s. Some of the models differed by 500–1000 yr—for a proposed initial colonization around the turn of the BC/AD eras, if not considerably later. By comparing the different approaches to this chronological issue, it becomes evident that almost all known problems in dealing with 14C dates from archaeological excavations are involved: stratigraphy and exact location of samples, sample material and quality, inbuilt ages and reservoir effects, lab errors in ancient dates, etc. More recently, research into landscape and vegetation history has produced alternative 14C dating for early human impact, adding to the confusion about the initial stages of island colonization, while archaeological 14C dates, becoming increasingly “young” as compared to former investigations, now advocate a rapid and late (post-AD 900) colonization of the archipelagos. As it appears, the Polynesian case is more than just another case study, it's a lesson on 14C-based archaeological chronology. The present paper does not pretend to solve the problems of early Polynesian colonization, but intends to contribute to the debate on how 14C specialists and archaeologists might cooperate in the future.
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  • 45
    Publication Date: 2009-01-01
    Description: Recent investigations devoted to the Eurasian loess formations have provided an integrated high-resolution climatic sequence well radiocarbon dated between 13.4 and 42.5 kyr BP on charcoal and wood remains. Here, we show that the reproducible climatic signature of this loess sequence can be compared by proxy-correlation with the Greenland ice climatic signals, taking into account the distribution of the aeolian components in both records. This correlation allows situating with precision the series of 14C dates obtained from loess with regard to the Greenland climatic sequence. In this way, comparing the atmospheric loess-derived 14C chronology with the chronologies of the marine sequences becomes possible.
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  • 46
    Publication Date: 2009-01-01
    Description: There are 2 fundamental assumptions in radiocarbon dating, which were known early in the method development to be approximations, and which lead directly to the need to calibrate 14C dates: 1.The rate of formation of 14C in the upper atmosphere has been constant over the entire applied 14C dating timescale (approximately the last 65,000 yr).2.The 14C activity of the atmosphere has been in equilibrium with the biosphere and ocean over the applied timescale.
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  • 47
    Publication Date: 2009-01-01
    Description: Human bones from 3 Mesolithic sites in the Upper Volga basin were analyzed for trace elements, and dated by accelerator mass spectrometry (AMS). The radiocarbon dates of the bones correspond to the Mesolithic era. However, some dates differ from those obtained for the enclosing deposits and for the worked wood fragments in the cultural layer. The elemental composition of the bones is interpreted in terms of increased concentrations of some elements and their impact on human health and behavior.
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  • 48
    Publication Date: 2009-01-01
    Description: Glacier fluctuations and paleoclimatic oscillations during the Late Quaternary in Val di Rabbi (Trentino, northern Italy) were reconstructed using a combination of absolute dating techniques (14C and 10Be) and soil chemical characterization. Extraction and dating of the stable fraction of soil organic matter (SOM) gave valuable information about the minimum age of soil formation and contributed to the deciphering of geomorphic surface dynamics. The comparison of 10Be surface exposure dating (SED) of rock surfaces with the 14C ages of resilient (resistant to H2O2 oxidation) soil organic matter gave a fairly good agreement, but with some questionable aspects. It is concluded that, applied with adequate carefulness, dating of SOM with 14C might be a useful tool in reconstructing landscape history in high Alpine areas with siliceous parent material. The combination of 14C dating of SOM with SED with cosmogenic 10Be (on moraines and erratic boulders) indicated that deglaciation processes in Val di Rabbi were already ongoing by around 14,000 cal BP at an altitude of 2300 m asl and that glacier oscillations might have affected the higher part of the region until about 9000 cal BP. 10Be and 14C ages correlate well with the altitude of the sampling sites and with the established Lateglacial chronology.
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  • 49
    Publication Date: 2009-01-01
    Description: Ultrafiltration of bone collagen, dissolved as gelatin (M ~100,000 D), has received considerable attention as a means to remove small contaminants and thus produce more reliable dates (Brown et al. 1988; Bronk Ramsey et al. 2004; Higham et al. 2006; Mellars 2006). However, comparative dating studies have raised the question whether this cleaning step itself may introduce contamination with carbon from the filters used (Bronk Ramsey et al. 2004; Brock et al. 2007; Hüls et al. 2007).Here, we present results of further ultrafiltration experiments with modern and fossil collagen samples using Vivaspin 20™ and Vivaspin 15R™ ultrafilters. Evidently, the Vivaspin 20 (VS 20) ultrafilter with a polyethersulfone (PES) membrane retains more material in the 〉30 kD fraction than the Vivaspin 15R (VS 15R) filter with a regenerated cellulose membrane (Hydrosat), which may be related to increased retention of proteins due to suboptimal electrostatic conditions during ultrafiltration with the PES membrane. In addition, this filter type shows clear evidence for contamination with fossil carbon, presumably from membrane fibers, in the
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  • 50
    Publication Date: 2009-01-01
    Description: A celebration is in order: the journal Radiocarbon is now a mature 50 years without drastic changes in its identity. There have been, of course, additions in terms of specific isotopes (it is now an international journal of cosmogenic isotope research), but the 14C content is still very extensive. The triannual offshoots, conference proceedings (started in 1980), and calibration issues (the first in 1986) testify to the strength of the 14C component.
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  • 51
    Publication Date: 2009-01-01
    Description: While kept at the Rockefeller Museum in East Jerusalem, many Dead Sea Scroll fragments were exposed to castor oil by the original team of editors in the course of cleaning the parchments. Castor oil must be regarded as a serious contaminant in relation to radiocarbon dating. If modern castor oil is present and is not removed prior to dating, the 14C dates will be skewed artificially towards modern values. In Rasmussen et al. (2001), it was shown that the standard AAA pretreatment procedure used in the 2 previous studies dating Dead Sea Scroll samples (Bonani et al. 1992; Jull et al. 1995) is not capable of removing castor oil from parchment samples. In the present work, we show that it is unlikely that castor oil reacts with the amino acids of the parchment proteins, a finding which leaves open the possibility of devising a cleaning method that can effectively remove castor oil. We then present 3 different pretreatment protocols designed to effectively remove castor oil from parchment samples. These involve 3 different cleaning techniques: extraction with supercritical CO2, ultrasound cleaning, and Soxhlet extraction—each with their own advantages and disadvantages. Our data show that the protocol involving Soxhlet extraction is the best suited for the purpose of decontaminating the Dead Sea Scrolls, and we recommend that this protocol be used in further attempts to 14C date the Dead Sea Scrolls. If such an attempt is decided on by the proper authorities, we propose a list of Scroll texts, which we suggest be redated in order to validate the 14C dates done earlier by Bonani et al. (1992) and Jull et al. (1995).
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  • 52
    Publication Date: 2009-01-01
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    Topics: Archaeology , Energy, Environment Protection, Nuclear Power Engineering , Geosciences
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  • 53
    Publication Date: 2009-01-01
    Description: The 5th International Radiocarbon and Archaeology Symposium was held at the ETH Zurich between March 26th and 28th, 2008. A total of 164 participants (including 47 students) from 28 countries attended the symposium. We had presentations of 13 invited speakers who opened 6 thematic/topic sessions that included 31 oral presentations and 49 posters.
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  • 54
    Publication Date: 2009-01-01
    Print ISSN: 0033-8222
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    Topics: Archaeology , Energy, Environment Protection, Nuclear Power Engineering , Geosciences
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  • 55
    Publication Date: 2009-01-01
    Description: The most extensive chronometric study ever undertaken on Egyptian Dynastic sites was published in Radiocarbon by Bonani et al. (2001). It comprised 269 radiocarbon measurements on monuments ranging from the 1st–12th dynasties. However, many of the calibrated dates obtained were significantly offset from historical estimates. The greatest discrepancies occurred in the 4th Dynasty where, paradoxically, the dating program had been most rigorous. For this period, 158 measurements were made at 12 sites, with the majority of the dates being 200–300 yr older than expected. The 4th Dynasty results were especially significant as they included some of the most important monuments in Egypt. In this paper, the raw data from that study have been reanalyzed using the OxCal calibration program, making particular use of its new outlier detection functionality. This Bayesian approach has resulted in a new series of calibrations that show much closer agreement with conventional chronological records.
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  • 56
    Publication Date: 2009-01-01
    Description: Since the publication of the first article (Lanting and van der Plicht 2001/2002) about the possibilities of dating cremated bones, the number of dated cremation remains has grown exponentially. The success of this dating technique lies in the fact that an absolute date now can be attributed to archaeological phenomena that previously were only datable indirectly. When archaeological artifacts where present, the cremation burials were dated based on the typology of ceramics and metals. An absolute date could be attributed if charcoal from the pyre were present. Unfortunately, these items were not omnipresent at the burial sites. Consequently, a complete site was dated by means of the few datable burials present. This implies that the internal chronology of the site could not be studied. Furthermore, the typochronology of the ceramics and the metals remains questionable. A series of dating projects on urnfield cemeteries in the Low Countries (northern France, Belgium, and the Netherlands) have shown that the classical chronology of these sites must be revised.
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  • 57
    Publication Date: 2009-12-01
    Description: Until the 1990's, Switzerland could be classified as either a corporatist, cooperative or coordinated market economy where non-market mechanisms of coordination among economic and political actors were very important. In this respect, Business Interest Associations (BIAs) played a key role. The aim of this paper is to look at the historical evolution of the five main peak Swiss BIAs through network analysis for five assorted dates during the 20th century (1910, 1937, 1957, 1980 and 2000) while relying on a database that includes more than 12,000 people. First, we examine the logic of membership in these associations, which allows us to analyze their position and function within the network of the Swiss economic elite. Until the 1980's, BIAs took part in the emergence and consolidation of a closely meshed national network, which declined during the two last decades of the 20th century. Second, we investigate the logic of influence of these associations by looking at the links they maintained with the political and administrative worlds through their links to the political parties and Parliament, and to the administration via the extra-parliamentary commissions (corporatist bodies). In both cases, the recent dynamic of globalization called into question the traditional role of BIAs.
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  • 58
    Publication Date: 2009-12-01
    Description: With increasing fragmentation of worldwide production chains and the corresponding contracting relations between companies, the “firm as an inspector” has become a frequent phenomenon. Buyer firms deploy supervising activities over their suppliers' products and production processes in order to ensure their compliance with regulatory standards, thereby taking on tasks commonly performed by public authorities. Why would a firm engage in such activities? In this article we will analyze the conditions under which firms play the role of an inspector vis-à-vis their sub-contractor firms to guarantee compliance with quality and environmental regulations. We develop a theoretical argument based on transaction cost economics and institutionalism to offer hypothetical answers to this question and provide an empirical assessment of our hypotheses.
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  • 59
    Publication Date: 2009-12-01
    Description: This paper broadens the scope and depth of business alliance research by way of interdisciplinary enrichment. The paper draws on the political science literature on nation-state alliances to generate insights into the establishment, operations and performance of inter-firm alliances. Shared theory bases of game theory and transaction cost economics, as well as theories, variables and research findings indigenous to political science are posited as a platform from which propositions regarding inter-firm alliances are derived.
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  • 60
    Publication Date: 2009-10-01
    Description: This paper discusses the pros and cons of a Transatlantic Free Trade Area (TAFTA) in comparison with an informal trade-facilitating marketplace between Europe and the US. It finds considerably more cons, especially since TAFTA would be expected to produce larger, more detrimental discriminatory effects on dynamic non-member economies, mainly in Asia but also in food-exporting regions as well. Efficiency-enhancing effects are argued to be achievable under a marketplace concept which does not separate insiders from outsiders. It is also shown that in foreign direct investment (FDI) and FDI-related service trade, TAFTA seems redundant as in recent years bilateral capital and trade flows have proven to be buoyant without preferential treatment.
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  • 61
    Publication Date: 2009-10-01
    Description: Over the last 60 years, the multilateral management of trade through the GATT and subsequently through the WTO has been led by the United States and Europe. Since the turn of the new millennium, however, developing countries have increasingly used their leverage to insist that talks on agriculture receive priority attention, deny the inclusion of investment and competition policy on the negotiating agenda, and block agreement on negotiating modalities for agriculture and non-agricultural market access (NAMA). Cooperation between the United States and the European Union is still essential, but no longer sufficient, for successful multilateral negotiations. Specifically, the “BRICKs” (Brazil, Russia, India, China, and Korea) are likely to be pivotal in directing the course and contributing to the success or failure of the WTO.
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  • 62
    Publication Date: 2009-08-01
    Description: Most of the existing studies of the welfare state have dealt with OECD countries. Moreover, these studies have focused on government partisanship (left versus right), or institutional features under democracy, as primary causal variables. By providing four primary causal mechanisms (the power of popularly based parties, labor strength, democracy, and political instability) that are different from those of OECD countries, I answer the question of whether and why the efficiency or compensation hypothesis holds for developing countries. I show that either the efficiency or compensation thesis can hold for developing countries depending on the type of globalization with which popularly based governments interact.
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  • 63
    Publication Date: 2009-04-01
    Description: In this study we advance the current research on corporate political strategy by examining how firms decide on their level of engagement in political action. This study proposes a contingency approach that identifies conditions in which firms prefer individual action to collective action in their pursuit of political strategy and introduces a framework that addresses this preference. Our results show that even in concentrated industries, a firm's preference of individual action over collective action varies when government contracts or research and development intensity are important considerations.
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  • 64
    Publication Date: 2009-10-01
    Description: Reform of the multilateral trade regime is not simply a second order problem within a wider economic crisis. The completion of the Doha Round may be a second order question but the global trade regime faces a series of broader systemic challenges beyond the completion of the current negotiations. This paper identifies five challenges: (i) a marked reduction in popular support for open markets in major OECD countries; (ii) the stalling of a transition from one global economic equilibrium to another; (iii) a lack of clarity and agreement on the agenda and objectives for the WTO as we move deeper into the 21st century; (iv) the demand for fairness and justice in the governance of the WTO'the ‘legitimacy’ question and (v) the rise of regional preferentialism as a challenge to multilateralism. Failure to address these challenges will represent not only a fundamental question for the future of the WTO as the guarantor of the norms and rules of the global trade regime specifically, but also the ability to establish greater coherence in global economic governance overall when its need is arguably greater than at any time since the depression years of the 20th century inter-war period.
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  • 65
    Publication Date: 2009-12-11
    Description: There has been a longstanding debate as to whether the large scales in grid turbulence should be classified as of the Batchelor or Saffman type. In the former, the integral scales, u and l, satisfy u2l5 constant, while in Saffman turbulence we have u2l3 = constant. For strictly homogeneous turbulence the energy decay rates in these two types of turbulence differ, with u2 ̃ t10/7 in Batchelor turbulence and u2 ̃ t6/5 in Saffman turbulence. We present high-resolution measurements of grid turbulence taken in a large wind tunnel. The particularly large test section allows us to measure energy decay exponents with high accuracy. We find that the turbulence behind the grid is almost certainly of the Saffman type, with u2l 3 = constant. The measured energy decay exponent, however, is found to lie slightly below the theoretical prediction of u2 ̃ t 1.2. Rather we find u2 ̃ tn, with n = 1.130.02. This discrepancy is shown to arise from a weak temporal decay of the dimensionless energy dissipation coefficient, εl/u3, which is normally taken to be constant in strictly homogeneous turbulence, but which varies very slowly in grid turbulence. © 2010 Cambridge University Press.
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  • 66
    Publication Date: 2009-12-10
    Description: A second-order nonlinear frequency-domain model extending the linear complementary mild-slope equation (CMSE) is presented. The nonlinear model uses the same streamfunction formulation as the CMSE. This allows the vertical profile assumption to accurately satisfy the kinematic bottom boundary condition in the case of nonlinear triad interactions as well as for the linear refractiondiffraction part. The result is a model with higher accuracy of wavebottom interactions including wavewave interaction. The model's validity is confirmed by comparison with accurate numerical models, laboratory experiments over submerged obstacles and analytical perturbation solutions for class III Bragg resonance. © 2009 Cambridge University Press.
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  • 67
    Publication Date: 2009-12-10
    Description: The two-dimensional space spanned by the velocity gradient invariants Q and R is expanded to three dimensions by the decomposition of R into its strain production 1/3s ijs jks ki and enstrophy production 1/4ω iω js ij terms. The {Q; R} space is a planar projection of the new three-dimensional representation. In the {Q; sss; s} space the Lagrangian evolution of the velocity gradient tensor A ij is studied via conditional mean trajectories (CMTs) as introduced by Martn et al. (Phys. Fluids, vol. 10, 1998, p. 2012). From an analysis of a numerical data set for isotropic turbulence of Reλ ̃ 434, taken from the Johns Hopkins University (JHU) turbulence database, we observe a pronounced cyclic evolution that is almost perpendicular to the QR plane. The relatively weak cyclic evolution in the QR space is thus only a projection of a much stronger cycle in the {Q; sss;ωω s} space. Further, we find that the restricted Euler (RE) dynamics are primarily counteracted by the deviatoric non-local part of the pressure Hessian and not by the viscous term. The contribution of the Laplacian of A ij, on the other hand, seems the main responsible for intermittently alternating between low and high intensity A ij states. © 2009 Cambridge University Press.
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  • 68
    Publication Date: 2009-12-09
    Description: Planar Rayleigh scattering provides quantitative mixing measurements in the developing region of axisymmetric turbulent helium jets issuing into air. The measurements focus on the relatively near field, in which the jets are primarily momentum driven. The imaging parameters are specified to ensure high spatial resolution. The mean jet fluid concentration fields attain self-similarity within the measurement region, though the forms of the mole fraction profiles indicate a reduction in turbulent transport at the jet outer boundary, arising from the reduced jet fluid density. Nevertheless, jet-like scaling pertains for the concentration fields. Mass fraction fluctuations on the jet centreline attain the expected asymptotic value of ≈ 23% of the centreline mass fraction values. The scalar dissipation rates, however, show an axial decay rate that is slower than theoretical predictions. The two-dimensional extent of the measurements also allows spatial filtering similar to that inherent in large-eddy simulations (LESs). The results confirm that fluctuation levels and scalar dissipation rates determined for the filtered fields are reduced as the effective resolution is reduced, but while the fluctuation profiles for the filtered fields are similar for the different filter sizes, the forms of the scalar dissipation profiles are highly dependent on filter size. These latter results in particular are of a form that will be useful for grid-dependent assessments of LES results. © 2009 Cambridge University Press.
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  • 69
    Publication Date: 2009-12-08
    Description: It has been recently shown that the flow of a Bingham fluid in a channel is always linearly stable (Nouar et al., J. Fluid Mech., vol. 577, 2007, p. 211). To identify possible paths of transition we revisit the problem for the case in which the idealized base flow is slightly perturbed. No attempt is made to reproduce or model the perturbations arising in experimental environments which may be due to the improper alignment of the channel walls or to imperfect inflow conditions rather a general formulation is given which yields the transfer function (the sensitivity) for each eigenmode of the spectrum to arbitrary defects in the base flow. It is first established that such a function, for the case of the most sensitive eigenmode, displays a very weak selectivity to variations in the spanwise wavenumber of the disturbance mode. This justifies a further look into the class of spanwise homogeneous modes. A variational procedure is set up to identify the base flow defect of minimal norm capable of optimally destabilizing an otherwise stable flow; it is found that very weak defects are indeed capable to excite exponentially amplified streamwise travelling waves. The associated variations in viscosity are situated mostly near the critical layer of the inviscid problem. Neutrally stable conditions are found as function of the Reynolds number and the Bingham number, providing scalings of critical values with the amplitude of the defect consistent with previous experimental and numerical studies. Finally, a structured pseudospectrum analysis is performed; it is argued that such a class of pseudospectra provides information well suited to hydrodynamic stability purposes. © 2010 Cambridge University Press.
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  • 70
    Publication Date: 2009-12-04
    Description: The evolution and decay of a homogeneous flow over random topography in a rotating system is studied by means of numerical simulations and theoretical considerations. The analysis is based on a quasi-two-dimensional shallow-water approximation, in which the horizontal divergence is explicitly different from zero, and topographic variations are not restricted to be much smaller than the mean depth, as in quasi-geostrophic dynamics. The results are examined by comparing the evolution of a turbulent flow over different random bottom topographies characterized by a specific horizontal scale, or equivalently, a given mean slope. As in two-dimensional turbulence, the energy of the flow is transferred towards larger scales of motion; after some rotation periods, however, the process is halted as the flow pattern becomes aligned along the topographic contours with shallow water to the right. The quasi-steady state reached by the flow is characterized by a nearly linear relationship between potential vorticity and transport function in most parts of the domain, which is justified in terms of minimum-enstrophy arguments. It is found that global energy decays faster for topographies with shorter horizontal length scales due to more effective viscous dissipation. In addition, some comparisons between simulations based on the shallow-water and quasi-geostrophic formulations are carried out. The role of solid boundaries is also examined: it is shown that vorticity production at no-slip walls contributes for a slight disorganization of the flow. © 2010 Cambridge University Press.
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  • 71
    Publication Date: 2009-12-02
    Description: Defining and identifying the aeroacoustic sources in a turbulent flow is a great challenge especially for noise control strategy. The purpose of the present study consists in proposing a new methodology to localize regions associated with sound generation. These regions are associated, in the present work, with those of high sensitivity of the acoustic field, using the heuristic argument that modifying the flow in these regions would lead to a very significant change in the radiated noise. The proposed method relies on the efficient coupling between the time-reversal theory applied to the Euler equations and the complex differentiation method to compute the sensitivity variable. To the knowledge of the authors, this is the first time that the time-reversal technique is applied to vectorial hydrodynamic equations, in place of the classical scalar wave equation. Subsequently, regions associated with sound generation are related to spatiotemporal events which exhibit the maximum of sensitivity to acoustical disturbances measured in far field. The proposed methodology is then successively tested on three cases for which the nature of the source is different: injection of mass, vibrating surfaces and flow instabilities arising in a plane mixing layer flow. For each test case, the two-dimensional Euler equations are solved using a numerical solver based on a pseudo-characteristics formulation. During these computations flow, variables are stored only at the computational boundaries. These variables are time reversed and relevant information concerning the acoustical disturbances is tagged using complex differentiation in order to lead the sensitivity analysis. The same numerical solver is used to access the evolution of the time-reversed variables. In each test case, the proposed methodology allows to localize successfully zones associated with noise generation. © 2010 Cambridge University Press.
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  • 72
    Publication Date: 2009-12-02
    Description: We show that a triple-valued sliding law can be heuristically motivated by the transverse spatial structure of an ice-stream velocity field using a simple one-dimensional model. We then demonstrate that such a sliding law can lead to some interesting stream-like patterns and time-oscillatory solutions. We find a generation of rapid stream-like solutions within a slow ice-sheet flow, separated by narrow internal boundary layers (shear margins), and analyse numerical simulations in two horizontal dimensions over a homogeneous bed and including longitudinal shear stresses. Different qualitative behaviours are obtained by changing a single physical parameter, a mass source magnitude, leading to changes from a slow creeping flow to a relaxation oscillation of the stream pattern, and to steady ice-stream-like solution. We show that the adjustment of the ice-flow shear margins to changes in the driving stress in the one-dimensional approximation is governed by a form of the GinzburgLandau equation and use stability analysis to understand this adjustment. In the model analysed here, the width scale of the stream is not set spontaneously by the ice flow dynamics, but rather, it is related to the mass source intensity and spatial distribution. © 2009 Cambridge University Press.
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  • 73
    Publication Date: 2009-12-04
    Description: Direct numerical simulation is used to study the development of a single laminar vortex ring as it impinges on a free surface directly from below. We consider the limiting case in which the Froude number approaches zero and the surface can be modelled with a stress-free rigid and impermeable boundary. We find that as the ring expands in the radial direction close to the surface, the natural TsaiWidnallMooreSaffman (TWMS) instability is superseded by the development of the Crow instability. The Crow instability is able to further amplify the residual perturbations left by the TWMS instability despite being of differing radial structure and alignment. This occurs through realignment of the instability structure and shedding of a portion of its outer vorticity profile. As a result, the dominant wavenumber of the Crow instability reflects that of the TWMS instability, and is dependent upon the initial slenderness ratio of the ring. At higher Reynolds number a short-wavelength instability develops on the long-wavelength Crow instability. The wavelength of the short waves is found to vary around the ring dependent on the local displacement of the long waves. © 2010 Cambridge University Press.
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  • 74
    Publication Date: 2009-12-10
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  • 75
    Publication Date: 2009-12-02
    Description: Acoustic instabilities with frequencies roughly higher than 1 kHz remain among the most harmful instabilities, able to drastically affect the operation of engines and even leading to the destruction of the combustion chamber. By coupling with resonant transverse modes of the chamber, these pressure fluctuations can lead to a large increase of heat transfer fluctuations, as soon as fluctuations are in phase. To control engine stability, the mechanisms leading to the modulation of the local instantaneous rate of heat release must be understood. The commonly developed global approaches cannot identify the dominant mechanism(s) through which the acoustic oscillation modulates the local instantaneous rate of heat release. Local approaches are being developed based on processes that could be affected by acoustic perturbations. Liquid atomization is one of these processes. In the present paper, the effect of transverse acoustic perturbations on a coaxial air-assisted jet is studied experimentally. Here, five breakup regimes have been identified according to the flow conditions, in the absence of acoustics. The liquid jet is placed either at a pressure anti-node or at a velocity anti-node of an acoustic field. Acoustic levels up to 165 dB are produced. At a pressure anti-node, breakup of the liquid jet is affected by acoustics only if it is assisted by the coaxial gas flow. Effects on the liquid core are mainly due to the unsteady modulation of the annular gas flow induced by the acoustic waves when the mean dynamic pressure of the gas flow is lower than the acoustic pressure amplitude. At a velocity anti-node, local nonlinear radiation pressure effects lead to the flattening of the jet into a liquid sheet. A new criterion, based on an acoustic radiation Bond number, is proposed to predict jet flattening. Once the sheet is formed, it is rapidly atomized by three main phenomena: intrinsic sheet instabilities, Faraday instability and membrane breakup. Globally, this process promotes atomization. The spray is also spatially organized under these conditions: large liquid clusters and droplets with a low ejection velocity can be brought back to the velocity anti-node plane, under the action of the resulting radiation force. These results suggest that in rocket engines, because of the large number of injectors, a spatial redistribution of the spray could occur and lead to inhomogeneous combustion producing high-frequency combustion instabilities. © 2009 Cambridge University Press.
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  • 76
    Publication Date: 2009-12-02
    Description: Nonlinear shallow water equations are employed to model the inviscid slumping of fluid along an inclined plane and analytical solutions for the motion are derived using the hodograph transformation to reveal the run-up and the inception of a bore on the backwash. Starting from rest, the fluid slumps along the inclined plane, attaining a maximum run-up, before receding and forming a relatively thin and fast moving backwash. This interacts with the less rapidly moving fluid within the interior to form a bore. The evolution of the bore and the velocity and height fields either side of it are also calculated to reveal that it initially grows in magnitude before diminishing and intersecting with the shoreline. This analytical solution reveals features of the solution, such as the onset of the bore and its growth and decline, previously known only through numerical computation and the method presented here may be applied quite widely to the run-up of other initial distributions of fluid. © 2009 Cambridge University Press.
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  • 77
    Publication Date: 2009-12-10
    Description: The motion of two immiscible liquids in a capillary tube is analysed, theoretically and numerically, for the case in which a residual film confines the displacing liquid to the core of this tube. The theoretical analysis has shown that the three flow regimes predicted by Taylor (J. Fluid Mech., vol. 10, 1961, pp. 161165), for the case of gas-displacement, can only be achieved when the ratio of the viscosity of the displaced fluid to that of the displacing one is greater than 2. An elliptic mesh generation technique, coupled with the Galerkin finite-element method, is used to compute the velocity field and the configuration of the interface between the two fluids. A map of cases in the Cartesian space defined by the capillary number (Ca) and the viscosity ratio (Nμ) is constructed in order to locate the different flow patterns the problem exhibits. The critical capillary number at which the flow enters the transition range between the bypass regime and the full-recirculating one is given. While a decrease of the fraction of mass attached to the wall is achieved by decreasing Ca or increasing Nμ, bypass flow patterns are formed as a consequence of high values of the capillary number and viscosity ratio. © 2009 Cambridge University Press.
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  • 78
    Publication Date: 2009-12-17
    Description: A freely rotating sphere in a solid-body rotating flow is experimentally investigated. When the sphere is buoyant, it reaches an equilibrium position from which drag and lift coefficients are determined over a wide range of particle Reynolds numbers (2 ≤ Re ≥ 1060). The wake behind the sphere is visualized and appears to deflect strongly when the sphere is close to the cylinder axis. The spin rate of the sphere is recorded. In fluids with low viscosity, spin rates more than twice as large as the angular velocity of the cylinder can be observed. By comparing numerical results for a fixed but freely spinning sphere with a fixed non-spinning sphere for Re ≤ 200, the effect of the sphere spin on the lift coefficient is determined. The experimentally and numerically determined lift and drag coefficients and particle spin rates all show excellent agreement for Re ≤ 200. The combination of the experimental and numerical results allows for a parameterization of the lift and drag coefficients of a freely rotating sphere as function of the Reynolds number, the particle spin and the location of the particle with respect to the cylinder axis. Although the effect of the flow rotation on the particle spin is different in shear flow and solid-body rotating flow, the effect of spin on lift is found to be comparable for both types of flow. © 2009 Cambridge University Press.
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  • 79
    Publication Date: 2009-12-23
    Description: An experimental investigation of the flow generated by a homogeneous population of bubbles rising in water is reported for three different bubble diameters (d = 1.6, 2.1 and 2.5 mm) and moderate gas volume fractions (0.005 ≤ α ≥0.1). The Reynolds numbers, Re = V0d/, based on the rise velocity V0 of a single bubble range between 500 and 800. Velocity statistics of both the bubbles and the liquid phase are determined within the homogeneous bubble swarm by means of optical probes and laser Doppler anemometry. Also, the decaying agitation that takes place in the liquid just after the passage of the bubble swarm is investigated from high-speed particle image velocimetry measurements. Concerning the bubbles, the average velocity is found to evolve as V0α0.1 whereas the velocity fluctuations are observed to be almost independent of. Concerning the liquid fluctuations, the probability density functions adopt a self-similar behaviour when the gas volume fraction is varied, the characteristic velocity scaling as V0α0.4. The spectra of horizontal and vertical liquid velocity fluctuations are obtained with a resolution of 0.6 mm. The integral length scale is found to be proportional to V02/g or equivalently to d/Cd0, where g is the gravity acceleration and Cd0 the drag coefficient of a single rising bubble. Normalized by using, the spectra are independent on both the bubble diameter and the volume fraction. At large scales, the spectral energy density evolves as the power 3 of the wavenumber. This range starts approximately from δ and is followed for scales smaller than δ/4 by a classic 5/3 power law. Although the Kolmogorov microscale is smaller than the measurement resolution, the dissipation rate is however obtained from the decay of the kinetic energy after the passage of the bubbles. It is found to scale as α0.9 V 03/δ. The major characteristics of the agitation are thus expressed as functions of the characteristics of a single rising bubble. Altogether, these results provide a rather complete description of the bubble-induced turbulence. © 2009 Cambridge University Press.
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  • 80
    Publication Date: 2009-12-17
    Description: Numerical investigation of the compressible flow past an 18% thick circular-arc aerofoil was carried out using detached-eddy simulation for a free-stream Mach number M∞ = 0.76 and a Reynolds number Re = 1.1×107. Results have been validated carefully against experimental data. Various fundamental mechanisms dictating the intricate flow phenomena, including moving shock wave behaviours, turbulent boundary layer characteristics, kinematics of coherent structures and dynamical processes in flow evolution, have been studied systematically. A feedback model is developed to predict the self-sustained shock wave motions repeated alternately along the upper and lower surfaces of the aerofoil, which is a key issue associated with the complex flow phenomena. Based on the moving shock wave characteristics, three typical flow regimes are classified as attached boundary layer, moving shock wave/turbulent boundary layer interaction and intermittent boundary layer separation. The turbulent statistical quantities have been analysed in detail, and different behaviours are found in the three flow regimes. Some quantities, e.g. pressure-dilatation correlation and dilatational dissipation, have exhibited that the compressibility effect is enhanced because of the shock wave/boundary layer interaction. Further, the kinematics of coherent vortical structures and the dynamical processes in flow evolution are analysed. The speed of downstream-propagating pressure waves in the separated boundary layer is consistent with the convection speed of the coherent vortical structures. The multi-layer structures of the separated shear layer and the moving shock wave are reasonably captured using the instantaneous Lamb vector divergence and curl, and the underlying dynamical processes are clarified. In addition, the proper orthogonal decomposition analysis of the fluctuating pressure field illustrates that the dominated modes are associated with the moving shock waves and the separated shear layers in the trailing-edge region. The results obtained in this study provide physical insight into the understanding of the mechanisms relevant to this complex flow. © 2009 Cambridge University Press.
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  • 81
    Publication Date: 2009-11-25
    Description: In the present study we investigate the dynamics of initially spherical capsules (made from elastic membranes obeying the strain-hardening Skalak or the strain-softening neo-Hookean law) in strong planar extensional flows via numerical computations. To achieve this, we develop a three-dimensional spectral boundary element algorithm for membranes with shearing and area-dilatation tensions in Stokes flow. The main attraction of this approach is that it exploits all the benefits of the spectral methods (i.e. high accuracy and numerical stability) but without creating denser systems. To achieve continuity of the interfacial geometry and its derivatives at the edges of the spectral elements during the interfacial deformation, a membrane-based interfacial smoothing is developed, via a Hermitian-like interpolation, for both the interfacial shape and the membrane elastic forces. Our numerical results show that no critical flow rate exists for both Skalak and neo-Hookean capsules in the moderate and strong planar extension flows considered in the present study. As the flow rate increases, both capsules reach elongated ellipsoidal steady-state configurations; the cross-section of the Skalak capsule preserves its elliptical shape, while the neo-Hookean capsule becomes more and more lamellar. The curvature at the pointed edges of these elongated steady-state shapes shows a very fast increase with the flow rate. The large interfacial deformations are accompanied with the development of strong membrane tensions especially for the strain-hardening Skalak capsule; the computed increase of the membrane tensions with the flow rate or the shape extension can be used to predict rupture of a specific membrane (with known lytic tension) due to excessive tensions. The type of the experiment imposed on the capsule as well as the applied flow rate affect dramatically the time evolution of the capsule edges owing to the interaction of the hydrodynamic forces with the membrane tensions; when a spherical Skalak capsule is let to deform in a strong flow, very large edge curvatures (with respect to the steady-state value) are developed during the transient evolution. © 2009 Cambridge University Press.
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  • 82
    Publication Date: 2009-11-23
    Description: Lighthill's analysis (J. Fluid Mech., vol. 60, 1973, p. 1) of the Weis-Fogh lift mechanism is extended to include the spreading phase of the cycle. Lighthill proposed a two-dimensional inviscid irrotational analytical model to compute the circulation around two flat plates (the wings) as they open out, in opposite directions, about a common centre of rotation taken to be at the point of contact of an edge of each plate (the opening phase). At a critical opening angle, the plates separate and move apart horizontally (the spreading phase). During this second phase, the fluid region becomes doubly connected and is not analysed by Lighthill. It can, however, also be studied analytically and the results are presented here. We also extend a similar analysis, in an application to turbomachinery, due to Furber & Ffowcs Williams (J. Fluid Mech., vol. 94, 1979, p. 519). © 2009 Cambridge University Press.
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  • 83
    Publication Date: 2009-11-16
    Description: The behaviour of an initially planar shock wave propagating into a linearly convergent wedge is investigated experimentally and numerically. In the experiment, a 25 internal wedge is mounted asymmetrically in a pressure-driven shock tube. Shock waves with incident Mach numbers in the ranges of 1.41.6 and 2.42.6 are generated in nitrogen and carbon dioxide. During each run, the full pressure history is recorded at fourteen locations along the wedge faces and schlieren images are produced. Numerical simulations performed based on the compressible Euler equations are validated against the experiment. The simulations are then used as an additional tool in the investigation. The linearly convergent geometry strengthens the incoming shock repeatedly, as waves reflected from the wedge faces cross the interior of the wedge. This investigation shows that aspects of this structure persist through multiple reflections and influence the nature of the shock-wave focusing. The shock focusing resulting from the distributed reflected waves of the Mach 1.5 case is distinctly different from the stepwise focusing at the higher incoming shock Mach number. Further experiments using CO2 instead of N2 elucidate some relevant real-gas effects and suggest that the presence or absence of a weak leading shock on the distributed reflections is not a controlling factor for focusing. © 2009 Cambridge University Press.
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  • 84
    Publication Date: 2009-11-13
    Description: In this article, we study the influence of solid-to-fluid density ratio m on the type of vortex-induced oscillation of a square section prism placed inside a two-dimensional channel. We assume that the solid body has neither structural damping nor spring restoring force. Accordingly, the prism equation of motion contains only inertia and aerodynamics forces. The problem is considered in the range of Reynolds numbers Re ε [50 200] (based on the prism cross-section height h) and channel widths H = H'/h ε [2.5 10]. We found that, for each Re and H, there is a critical mass ratio mc that separates two different oscillation regimes. For m 〉 mc, the prism oscillation is periodical and contains a single harmonic. For m 〈 mc, the prism oscillation changes completely and assumes an irregular pattern that is characterized by multiple harmonics that appear to belong to a uniform spectrum. The change from one regime to the other is abrupt and we were not able to observe a transitional regime in which the number of response harmonics grew by finite steps. The value of the critical mass ratio grows along with the Reynolds number and the channel width. © 2009 Cambridge University Press.
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  • 85
    Publication Date: 2009-12-04
    Description: Natural convection in calm near-shore waters induced by daytime heating or nighttime cooling plays a significant role in cross-shore exchanges with significant biological and environmental implications. Having previously reported an improved scaling analysis on the daytime radiation-induced natural convection, the authors present in this paper a detailed scaling analysis quantifying the flow properties at varying offshore distances induced by nighttime surface cooling. Two critical functions of offshore distance have been derived to identify the distinctness and the stability of the thermal boundary layer. Two flow scenarios are possible depending on the bottom slope. For the relatively large slope scenario, three flow regimes are possible, which are discussed in detail. For each flow regime, all the possible distinctive subregions are identified. Two different sets of scaling incorporating the offshore-distance dependency have been derived for the conduction-dominated region and stable-convection-dominated region respectively. It is found that the scaling for flow in the stable-convection-dominated region also applies to the time-averaged mean flow in the unstable region. The present scaling results are verified by numerical simulations. © 2010 Cambridge University Press.
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  • 86
    Publication Date: 2009-12-02
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  • 87
    Publication Date: 2009-12-10
    Description: This paper investigates the noise radiation produced by a rotor inside a duct, which is convected by a swirling-translating mean flow. The study is based on an extension of Gennaretti's and Morino's boundary element method to the frequency domain for scattering problems in conjunction with a spinning rotor source model in the presence of a swirl flow. The proposed formulation is validated against exact solutions and is further used to investigate the effects of the translating flow Mach number and swirling flow angular velocity on noise radiation to the far field. The scattered sound is highly affected by the convecting mean flow. The modal content of the scattered field increases when increasing the translating flow Mach number, while a swirling flow leads to a reduction of the mode propagation, if co-rotating with respect to the azimuthal order of the spinning source, or an increase of the modal content, if counter-rotating with respect to the source. In general, the mean translating flow moves the main lobes of the directivity patterns downstream, while in some cases the mean swirling flow neglects this effect and the downstream lobe is completely shifted. © 2009 Cambridge University Press.
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  • 88
    Publication Date: 2009-12-15
    Description: The free fall of a liquid mass through vertical tubes with a weakly increasing cross-section induces an acceleration of the upper liquid interface larger than gravity. The phenomenon is well described by a one-dimensional inviscid model. The super acceleration of the upper interface comes from the additional positive pressure gradient caused by the expanding geometry, which adds to the gravity body force. A perturbative expansion of this base solution further accounts for the interface shape and stability. In particular, the positive pressure gradient at the interface makes it unstable, forming a concentrated nipple on top of the essentially flat base solution. We discuss the possible connexion of these findings with the problem of wave breaking in free surface flows. © 2010 Cambridge University Press.
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  • 89
    Publication Date: 2009-12-10
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  • 90
    Publication Date: 2009-12-02
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  • 91
    Publication Date: 2009-11-30
    Description: A model is developed for a turbulent plume with heterogeneous chemical reaction rising in an unbounded environment. The chemical reaction, which may generate or deplete buoyancy in the plume, occurs at the interface between two phases, a continuous phase and a dispersed one. We study the case in which a buoyant reactant is released at the source and forms the dispersed phase, consisting of very small bubbles, droplets or particles. Once in contact with the ambient fluid, a first-order irreversible reaction takes place at the surface of the, for example, droplets. The behaviour of this plume in a uniform and stratified environment is examined. We show that the dynamics of a pure plume with such heterogeneous reaction is completely determined by the ratio of the environmental buoyancy frequency N and a frequency parameter associated with the chemical reaction, G. The group G is a measure of the ability of the reaction to generate buoyancy in the plume. In a uniform environment, the sign of parameter G fully determines the plume motion. When the reaction generates buoyancy (positive G) the motion is unbounded, whilst when reaction depletes buoyancy (negative G) the plume reaches a level of neutral buoyancy. A relation for this neutral buoyancy level as a function of the initial buoyancy flux of the plume and G is calculated. Our theoretical predictions compared well with experimental results using a plume of calcium carbonate particles descending in an acidic aqueous solution. In a stratified environment, the motion of the plume is always bounded, irrespective of the magnitude of G, and we determine the level of maximum buoyancy flux, as well as those of zero buoyancy and zero momentum as a function of N/G. Finally, our model is applied to study the dynamics of a localized release of carbon dioxide in the ocean. © 2010 Cambridge University Press.
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  • 92
    Publication Date: 2009-12-02
    Description: Direct numerical simulation (DNS) of the near field of a three-dimensional spatially developing turbulent lifted hydrogen jet flame in heated coflow is performed with a detailed mechanism to determine the stabilization mechanism and the flame structure. The DNS was performed at a jet Reynolds number of 11,000 with over 940 million grid points. The results show that auto-ignition in a fuel-lean mixture at the flame base is the main source of stabilization of the lifted jet flame. A chemical flux analysis shows the occurrence of near-isothermal chemical chain branching preceding thermal runaway upstream of the stabilization point, indicative of hydrogen auto-ignition in the second limit. The Damkhler number and key intermediate-species behaviour near the leading edge of the lifted flame also verify that auto-ignition occurs at the flame base. At the lifted-flame base, it is found that heat release occurs predominantly through ignition in which the gradients of reactants are opposed. Downstream of the flame base, both rich-premixed and non-premixed flames develop and coexist with auto-ignition. In addition to auto-ignition, Lagrangian tracking of the flame base reveals the passage of large-scale flow structures and their correlation with the fluctuations of the flame base. In particular, the relative position of the flame base and the coherent flow structure induces a cyclic motion of the flame base in the transverse and axial directions about a mean lift-off height. This is confirmed by Lagrangian tracking of key scalars, heat release rate and velocity at the stabilization point. © 2009 Cambridge University Press.
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  • 93
    Publication Date: 2009-11-10
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  • 94
    Publication Date: 2009-11-02
    Description: The deformation of a drop as it flows along the axis of a circular capillary in low Reynolds number pressure-driven flow is investigated numerically by means of boundary integral computations. If gravity effects are negligible, the drop motion is determined by three independent parameters: the size a of the undeformed drop relative to the radius R of the capillary, the viscosity ratio λ between the drop phase and the wetting phase and the capillary number Ca, which measures the relative importance of viscous and capillary forces. We investigate the drop behaviour in the parameter space (a/R,λ, Ca), at capillary numbers higher than those considered previously. If the fluid flow rate is maintained, the presence of the drop causes a change in the pressure difference between the ends of the capillary, and this too is investigated. Estimates for the drop deformation at high capillary number are based on a simple model for annular flow and, in most cases, agree well with full numerical results if λ ≥ 1/2, in which case the drop elongation increases without limit as Ca increases. If λ 〈 1/2, the drop elongates towards a limiting non-zero cylindrical radius. Low-viscosity drops (λ 〈 1) break up owing to a re-entrant jet at the rear, whereas a travelling capillary wave instability eventually develops on more viscous drops (〉 1). A companion paper (Lac & Sherwood, J. Fluid Mech., doi:10.1017/S002211200999156X) uses these results in order to predict the change in electrical streaming potential caused by the presence of the drop when the capillary wall is charged. © 2009 Cambridge University Press.
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  • 95
    Publication Date: 2009-10-29
    Description: The relaxation and breakup of an elongated droplet in a viscous and initially quiescent fluid is studied by solving the full NavierStokes equations using a three-dimensional finite volume method coupled with a moving mesh interface tracking (MMIT) scheme to locate the interface. The two fluids are assumed incompressible and immiscible. The interface is represented as a surface triangle mesh with zero thickness that moves with the fluid. Therefore, the jump and continuity conditions across the interface are implemented directly, without any smoothing of the fluid properties. Mesh adaptations on a tetrahedral mesh are employed to permit large deformation and to capture the changing curvature. Mesh separation is implemented to allow pinch-off. The detailed investigations of the relaxation and breakup process are presented in a more general flow regime compared to the previous works by Stone & Leal (J. Fluid Mech., vol. 198, 1989, p. 399) and Tong & Wang (Phys. Fluids, vol. 19, 2007, 092101), including the flow field of the both phases. The simulation results reveal that the vortex rings due to the interface motion and the conservation of mass play an important role in the relaxation and pinch-off process. The vortex rings are created and collapsed during the process. The effects of viscosity ratio, density ratio and length ratio on the relaxation and breakup are studied. The simulations indicate that the fluid velocity field and the neck shape are distinctly different for viscosity ratios larger and smaller than O(1), and thus a different end-pinching mechanism is observed for each regime. The length ratio also significantly affects the relaxation process and the velocity distributions, but not the neck shape. The influence of the density ratio on the relaxation and breakup process is minimal. However, the droplet evolution is retarded due to the large density of the suspending flow. The formation of a satellite droplet is observed, and the volume of the satellite droplet depends strongly on the length ratio and the viscosity ratio. © 2009 Cambridge University Press.
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  • 96
    Publication Date: 2009-10-29
    Description: A new method is introduced for estimating the convection velocity of individual modes in turbulent shear flows that, in contrast to most previous ones, only requires spectral information in the temporal or spatial direction over which a modal decomposition is desired, while only using local derivatives in other directions. If no spectral information is desired, the method provides a natural definition for the average convection velocity, as well as a way to estimate the accuracy of the frozen-turbulence approximation. Existing data from numerical turbulent channels at friction Reynolds numbers Reτ ≤ 1900 are used to validate the new method against classical ones, and to characterize the dependence of the convection velocity on the eddy wavelength and wall distance. The results indicate that the small scales in turbulent channels travel at the local mean velocity, while large global modes travel at a more uniform speed proportional to the bulk velocity. To estimate the systematic deviations introduced in experimental spectra by the use of Taylor's approximation with a wavelength-independent convection velocity, a semi-empirical fit to the computed convection velocities is provided. It represents well the data throughout the Reynolds number range of the simulations. It is shown that Taylor's approximation not only displaces the large scales near the wall to shorter apparent wavelengths but also modifies the shape of the spectrum, giving rise to spurious peaks similar to those observed in some experiments. To a lesser extent the opposite is true above the logarithmic layer. The effect increases with the Reynolds number, suggesting that some of the recent challenges to the kx1 energy spectrum may have to be reconsidered. © 2009 Cambridge University Press.
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  • 97
    Publication Date: 2009-10-20
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  • 98
    Publication Date: 2009-11-02
    Description: Explicit expressions for the added mass tensor of a bubble in strongly nonlinear deformation and motion near a plane wall are presented. Time evolutions and interconnections of added mass components are derived analytically and analysed. Interface dynamics have been predicted with two methods, assuming that the flow is irrotational, that the fluid is perfect and with the neglect of gravity. The assumptions that gravity and viscosity are negligible are verified by investigating their effects and by quantifying their impact in some cases of strong deformation, and criteria are presented to specify the conditions of their validity. The two methods are an analytical one and the boundary element method, and good agreement is found. It is explained why a strongly deforming bubble is decelerated. The classical RayleighPlesset equation is extended with terms to account for arbitrary, axisymmetric deformation and to account for the proximity of a wall. An expression for the corresponding cycle frequency that is valid in the vicinity of the wall is derived. An equation similar to the RayleighPlesset equation is presented for the most important anisotropic deformation mode. Well-known expressions for the angular frequencies of some periodic solutions without a wall follow easily from the equations presented. A periodically deforming bubble without initial velocity of the centroid and without a dominating isotropic deformation component is eventually always driven towards the wall. A simplified equation of motion of the centre of a deforming bubble is presented. If desired, full deformation computations can be speeded up by selecting an artificially low value of the polytropic constant Cp/Cv. © 2009 Cambridge University Press.
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  • 99
    Publication Date: 2009-10-30
    Description: In addition to being observable in laboratory experiments, internal wave beams are reported in geophysical settings, which are characterized by non-uniform density stratifications. Here, we perform a combined theoretical and experimental study of the propagation of internal wave beams in non-uniform density stratifications. Transmission and reflection coefficients, which can differ greatly for different physical quantities, are determined for sharp density-gradient interfaces and finite-width transition regions, accounting for viscous dissipation. Thereafter, we consider even more complex stratifications to model geophysical scenarios. We show that wave beam ducting can occur under conditions that do not necessitate evanescent layers, obtaining close agreement between theory and quantitative laboratory experiments. The results are also used to explain recent field observations of a vanishing wave beam at the Keana Ridge, Hawaii. © 2009 Cambridge University Press.
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  • 100
    Publication Date: 2009-10-20
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