1,721,343 research outputs found
Iron Corrosion: Scientific Heritage in Jeopardy
No full textResearch on the use of metallic iron (Fe0) for environmental remediation and water treatment has taken off during the past three decades. The results achieved have established filtration on Fe0 packed beds as an efficient technology for water remediation at several scales. However, the further development of Fe0-based filtration systems is impaired by the non-professional behavior of scientists who ignore available advances in knowledge. The confusion is overcome when due consideration is given to the fact that revealing state-of-the-art knowledge is a prerequisite to presenting individual achievements
Redirecting Research on Fe0 for Environmental Remediation: The Search for Synergy
No full textA survey of the literature on using metallic iron (Fe0) for environmental remediation suggests that the time is ripe to center research on the basic relationship between iron corrosion and contaminant removal. This communication identifies the main problem, which is based on the consideration that contaminant reductive transformation is the cathodic reaction of iron oxidative dissolution. Properly considering the inherent complexities of the Fe0/H2O system will favor an appropriate research design that will enable more efficient and sustainable remediation systems. Successful applications of Fe0/H2O systems require the collective consideration of progress achieved in understanding these systems. More efforts should be made to decipher the long-term kinetics of iron corrosion, so as to provide better approaches to accurately predict the performance of the next generation Fe0-based water treatment systems
Stability Analysis of Natural Circulation in BWRs at High Pressure Conditions
No full textAt rated conditions, a natural circulation boiling water reactor (NCBWR) depends
completely on buoyancy to remove heat from the reactor core. This raises the issue of
potential unstable flow oscillations. The objective of this work is to assess the
characteristics of stability in a NCBWR at rated conditions, and the sensitivity to design
and operating conditions in comparison to previous BWRs.
Two kinds of instabilities, namely Ledinegg flow excursion and Density Wave
Oscillations (DWO), have been studied. The DWO analyses were conducted for three
oscillation modes: Single Channel thermal-hydraulic stability, coupled neutronics regionwide
out-of-phase stability and core-wide in-phase stability. Using frequency domain
methods, the three types of DWO stability characteristics of the NCBWR and their
sensitivity to the operating parameters and design features have been determined. The
characteristic equations are constructed from linearized equations, which are derived for
small deviations around steady operating conditions.
The Economic Simplified Boiling Water Reactor (ESBWR) is used in our analysis as a
reference NCBWR design. It is found that the ESBWR can be stable with a large margin
around the operating conditions by proper choice of the core inlet orifice scheme, and for
appropriate power to flow ratios.
In single channel stability analysis, neutronic feedback is neglected. Design features of
the ESBWR, including shorter fuel bundle and use of part-length rods in the assemblies,
tend to improve the thermal-hydraulic stability performance. However, the thermalhydraulic
stability margin is still lower than that of a typical BWR at rated conditions. In
neutronic-coupled out-of-phase as well as in-phase stability analysis, the perturbation
decay ratios for ESBWR at our assumed conditions are higher than that of a typical BWR
(Peach Bottom 2) at rated conditions, due to its lower thermal-hydraulic stability margin
and higher neutronic feedback. Nevertheless, the stability criteria are satisfied.
To evaluate the NCBWR stability performance, comparison with BWR/Peach Bottom 2
at both the rated condition and maximum natural circulation condition has been
conducted. Sensitivity studies are performed on the effects of design features and
operating parameters, including chimney length, inlet orifice coefficient, power, flow
rate, and axial power distribution, reactivity coefficients, fuel pellet-clad gap
conductance. It can be concluded that the NCBWR and BWR stabilities are similarly
sensitive to operating parameters.Tokyo Electric Power CompanyU.S. Nuclear Regulatory Commissio
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Bestimmung von hydraulischen Parametern in Lockergesteinen: Ein Vergleich unterschiedlicher Feldmethoden
No full textISSN:1432-1165ISSN:1430-483XISSN:1430-483
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Least Squares Shadowing sensitivity analysis of chaotic limit cycle oscillations
No full textThe adjoint method, among other sensitivity analysis methods, can fail in chaotic dynamical systems. The result from these methods can be too large, often by orders of magnitude, when the result is the derivative of a long time averaged quantity. This failure is known to be caused by ill-conditioned initial value problems. This paper overcomes this failure by replacing the initial value problem with the well-conditioned “least squares shadowing (LSS) problem”. The LSS problem is then linearized in our sensitivity analysis algorithm, which computes a derivative that converges to the derivative of the infinitely long time average. We demonstrate our algorithm in several dynamical systems exhibiting both periodic and chaotic oscillations.United States. Air Force Office of Scientific Research (AFOSR Award F11B-T060007)United States. National Aeronautics and Space Administration (NASA Award NNH11ZEA001N, DOE PSAAP Program at Stanford University
Case Study of Heat Transfer during Artificial Ground Freezing with Groundwater Flow
No full textFor the artificial ground freezing (AGF) projects in highly permeable formations, the effect of groundwater flow cannot be neglected. Based on the heat transfer and seepage theory in porous media with the finite element method, a fully coupled numerical model was established to simulate the changes of temperature field and groundwater flow field. Firstly, based on the classic analytical solution for the frozen temperature field, the model’s ability to solve phase change problems has been validated. In order to analyze the influences of different parameters on the closure time of the freezing wall, we performed the sensitivity analysis for three parameters of this numerical model. The analysis showed that, besides the head difference, the thermal conductivity of soil grain and pipe spacing are also the key factors that control the closure time of the frozen wall. Finally, a strengthening project of a metro tunnel with AGF method in South China was chosen as a field example. With the finite element software COMSOL Multiphysics® (Stockholm, Sweden), a three-dimensional (3D) numerical model was set up to simulate the change of frozen temperature field and groundwater flow field in the project area as well as the freezing process within 50 days. The simulation results show that the freezing wall appears in an asymmetrical shape with horizontal groundwater flow normal to the axial of the tunnel. Along the groundwater flow direction, freezing wall forms slowly and on the upstream side the thickness of the frozen wall is thinner than that on the downstream side. The actual pipe spacing has an important influence on the temperature field and closure time of the frozen wall. The larger the actual pipe spacing is, the slower the closing process will be. Besides this, the calculation for the average temperature of freezing body (not yet in the form of a wall) shows that the average temperature change of the freezing body coincides with that of the main frozen pipes with the same trend
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