Academic literature on the topic 'Weak local residuals'
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Journal articles on the topic "Weak local residuals"
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Mungkasi, Sudi, and Stephen Gwyn Roberts. "Weak Local Residuals as Smoothness Indicators in Adaptive Mesh Methods for Shallow Water Flows." Symmetry 12, no. 3 (March 1, 2020): 345. http://dx.doi.org/10.3390/sym12030345.
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This paper proposes some formulations of weak local residuals of shallow-water-type equations, namely, one-, one-and-a-half-, and two-dimensional shallow water equations. Smooth parts of numerical solutions have small absolute values of weak local residuals. Rougher parts of numerical solutions have larger absolute values of weak local residuals. This behaviour enables the weak local residuals to detect parts of numerical solutions which are smooth and rough (non-smooth). Weak local residuals that we formulate are implemented successfully as refinement or coarsening indicators for adaptive mesh finite volume methods used to solve shallow water equations.
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Mungkasi, Sudi, Zhenquan Li, and Stephen Gwyn Roberts. "Weak local residuals as smoothness indicators for the shallow water equations." Applied Mathematics Letters 30 (April 2014): 51–55. http://dx.doi.org/10.1016/j.aml.2013.12.007.
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Roberts, Stephen Gwyn, and Sudi Mungkasi. "Well-balanced computations of weak local residuals for the shallow water equations." ANZIAM Journal 55 (December 9, 2015): 128. http://dx.doi.org/10.21914/anziamj.v56i0.9369.
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Jia, Zhuo, Sixin Liu, Ling Zhang, Bin Hu, and Jianmin Zhang. "Weak Signal Extraction from Lunar Penetrating Radar Channel 1 Data Based on Local Correlation." Electronics 8, no. 5 (May 23, 2019): 573. http://dx.doi.org/10.3390/electronics8050573.
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Knowledge of the subsurface structure not only provides useful information on lunar geology, but it also can quantify the potential lunar resources for human beings. The dual-frequency lunar penetrating radar (LPR) aboard the Yutu rover offers a Special opportunity to understand the subsurface structure to a depth of several hundreds of meters using a low-frequency channel (channel 1), as well as layer near-surface stratigraphic structure of the regolith using high-frequency observations (channel 2). The channel 1 data of the LPR has a very low signal-to-noise ratio. However, the extraction of weak signals from the data represents a problem worth exploring. In this article, we propose a weak signal extraction method in view of local correlation to analyze the LPR CH-1 data, to facilitate a study of the lunar regolith structure. First, we build a pre-processing workflow to increase the signal-to-noise ratio (SNR). Second, we apply the K-L transform to separate the horizontal signal and then use the seislet transform (ST) to reserve the continuous signal. Then, the local correlation map is calculated using the two denoising results and a time–space dependent weighting operator is constructed to suppress the noise residuals. The weak signal after noise suppression may provide a new reference for subsequent data interpretation. Finally, in combination with the regional geology and previous research, we provide some speculative interpretations of the LPR CH-1 data.
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Alcantara, C. A., J. D. Escoto, A. C. Blanco, A. B. Baloloy, J. A. Santos, and R. R. Sta. Ana. "GEOSPATIAL ASSESSMENT AND MODELING OF URBAN HEAT ISLANDS IN QUEZON CITY, PHILIPPINES USING OLS AND GEOGRAPHICALLY WEIGHTED REGRESSION." ISPRS - International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences XLII-4/W16 (October 1, 2019): 85–92. http://dx.doi.org/10.5194/isprs-archives-xlii-4-w16-85-2019.
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Abstract. Urbanization has played an important part in the development of the society, yet it is accompanied by environmental concerns including the increase of local temperature compared to its immediate surroundings. The latter is known as Urban Heat Islands (UHI). This research aims to model UHI in Quezon City based on Land Surface Temperature (LST) estimated from Landsat 8 data. Geospatial processing and analyses were performed using Google Earth Engine, ArcGIS, GeoDa, and SAGA GIS. Based on Urban Thermal Field Variance Index (UTFVI) and the normalized mean per barangay (village), areas with strong UHI intensities were mapped and characterized. high intensity UHIs are observed mostly in areas with high Normalized Difference Built-up Index (NDBI) like the residential regions while the weak intensity UHIs are noticed in areas with high Normalized Difference Vegetation Index (NDVI) near the La Mesa Reservoir. In the OLS regression model, around 69% of LST variability is explained by Surface Albedo (SA), Sky View Factor (SVF), Surface Area to Volume Ratio (SVR), Solar Radiation (SR), NDBI and NDVI. OLS yield relatively high residuals (RMSE = 1.67) and the residuals are not normally distributed. Since LST is non-stationary, Geographically Weighted Regression (GWR) regression was conducted, proving normally and randomly distributed residuals (average RMSE = 0.26).
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Mircheva, Biliana, Milen Tsekov, Ulrich Meyer, and Guergana Guerova. "Analysis of the 2014 Wet Extreme in Bulgaria: Anomalies of Temperature, Precipitation and Terrestrial Water Storage." Hydrology 7, no. 3 (September 9, 2020): 66. http://dx.doi.org/10.3390/hydrology7030066.
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Impact on the hydrology cycle is projected to be one of the most noticeable consequences of climate change. An increase in regional dry and wet extremes has already been observed, resulting in large socioeconomic losses. The 2014 wet conditions in Bulgaria present a valuable case study for analyzing the interaction between multiple drivers that are essential for early forecasting and warning of flood events. In this paper, time series analysis of temperature, precipitation and Terrestrial Water Storage Anomaly (TWSA) is performed and cross-correlations between observations and climate variability indices are computed for a 12-year period. In Bulgaria, a positive linear temperature trend was found with precipitation and TWSA exhibiting negative trends for the period 2003–2014. The year 2014 started with a drier and warmer than usual winter followed by five consecutive wet months from March to July. We found the following long-term variations: (1) temperature showing a local minimum in November 2014, (2) precipitation peaks in July 2014 and (3) a local TWSA maximum in December 2014. Over a 12-year period, weak to moderate negative correlations were observed between the long-term components of temperature, precipitation and TWSA. Moderate positive correlations with a 3 to 6-month lag were obtained between precipitation and TWSA long-term components. The long-term trends of temperature and precipitation from surface observations and atmospheric reanalysis showed very good alignment. Very large subseasonal precipitation residuals from observations and atmospheric reanalysis were obtained for April and September 2014. Two oscillation indices showed: (1) weak correlations with precipitation and (2) weak to moderate correlations with TWSA.
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Ren, Zhiming, and Yang Liu. "A hierarchical elastic full-waveform inversion scheme based on wavefield separation and the multistep-length approach." GEOPHYSICS 81, no. 3 (May 2016): R99—R123. http://dx.doi.org/10.1190/geo2015-0431.1.
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Elastic full-waveform inversion (FWI) updates model parameters by minimizing the residuals of the P- and S-wavefields, resulting in more local minima and serious nonlinearity. In addition, the coupling of different parameters degrades the inversion results. To address these problems, we have developed a hierarchical elastic FWI scheme based on wavefield separation and a multistep-length gradient approach. First, we have derived the gradients expressed by different wave modes; analyzed the crosstalk between various parameters; and evaluated the sensitivity of separated P-wave, separated S-wave, and P- and S-wave misfit functions. Then, a practical four-stage inversion workflow was developed. In the first stage, conventional FWI is used to achieve rough estimates of the P- and S-wave velocities. In the second stage, we only invert the P-wave velocity applying the separated P-wavefields when strong S-wave energy is involved, or we merely update the S-wave velocity by matching the separated S-wavefields for the weak S-wave case. The PP and PS gradient formulas are used in these two cases, respectively. Therefore, the nonlinearity of inversion and the crosstalk between parameters are greatly reduced. In the third stage, the multistep-length gradient scheme is adopted. The density structure can be improved owing to the use of individual step lengths for different parameters. In the fourth stage, we make minor adjustments to the recovered P- and S-wave velocities and density by implementing conventional FWI again. Synthetic examples have determined that our hierarchical FWI scheme with the aforementioned steps obtains more plausible models than the conventional method. Inversion results of each stage and any three stages reveal that wavefield decomposition and the multistep-length approach are helpful to improve the accuracy of velocities and density, respectively, and all the stages of our hierarchical FWI method are necessary to give a good recovery of P- and S-wave velocities and density.
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Musialkowska, Ida, Agata Kliber, Katarzyna Świerczyńska, and Paweł Marszałek. "Looking for a safe-haven in a crisis-driven Venezuela." Transforming Government: People, Process and Policy 14, no. 3 (April 20, 2020): 475–94. http://dx.doi.org/10.1108/tg-01-2020-0009.
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Purpose This paper aims to find, which of the assets: gold, oil or bitcoin can be considered a safe-haven for investors in a crisis-driven Venezuela. The authors look also at the governmental change of approach towards the use and mining of cryptocurrencies being one of the assets and potential applications of bitcoin as (quasi) money. Design/methodology/approach The authors collected the daily data (a period from 01 May 2014 to 31 July 2018) on the development of the following magnitudes: Caracas Stock Exchange main index: Índice Bursátil de Capitalisación (IBC) index; gold price in US dollars, the oil price in US dollars and Bitcoin price in bolivar fuerte (VEF) (LocalBitcoins). The authors estimated a threshold VAR model between IBC and each of the possible safe-haven assets, where the trigger variable was the IBC; then the authors modelled the residuals from the TVAR model using MGARCH model with dynamic conditional correlation. Findings The results show that that gold is a better safe-haven than oil for Venezuelan investors, while bitcoin can be considered a weak safe haven. Still, bitcoin can perform (to a certain extent) money functions in a crisis-driven country. Research limitations/implications Further research after the change of local currency from VEF into bolivar soberano might be looked at on the later stage. Practical implications The authors provide evidence on which of analysed asset is the best safe-haven for the investors acting in the time of the crisis. The evidence goes in line with other authors’ findings, thus, the results might bring implications for investors of more universal character. Additionally, the result might be helpful for governments and/or monetary authorities while projecting institutional frameworks and conducting monetary policy. Social implications The unprecedented economic crisis in Venezuela was one of the factors that fuelled the mining and use of cryptocurrencies in the daily life of its citizens. Nowadays, the country is a leader in terms of the use of bitcoin and other cryptocurrencies in Latin America. The results show a potential application of bitcoin as a store of value or even means of payments in Venezuelan (or in other countries affected by the crisis). Originality/value The paper builds on the original data set collected by the authors and brings evidence from the models the authors constructed to verify, which asset is the best option for investors in hard times of the crisis. The authors add to the existing literature on financial assets, cryptocurrencies and behaviour of investors under different economic conditions.
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Baryshnikov, Sergei O., Alla B. Krasiuk, and Valentin B. Chistov. "THE INFLUENCE OF LOCAL RESIDUAL DEFORMATIONS ON THE SHIPS HULLS RELIABILITY." Vestnik Gosudarstvennogo universiteta morskogo i rechnogo flota imeni admirala S. O. Makarova 14, no. 3 (September 2, 2022): 403–16. http://dx.doi.org/10.21821/2309-5180-2022-14-3-403-416.
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The changes in the bearing capacity of the hull sheets and beams of the ship’s set under the action of compressive and tensile forces are studied in the paper. The inf luence of local residual deformations on the permissible wear of the deformed element, which allows assessing its reliability, is established. Since the longitudinal forces (compressive and tensile) are significant only for the deck or bottom in the middle part of the hull, the effect of local residual deformations on the bearing capacity of sheets and beams of the longitudinal set is estimated only for these elements. It is assumed that the retained local residual deformations of the housing elements do not change with the time of ship operation. Corrections for permissible wear in the cross-section equal to a decrease in the average thickness of the sheets in the cross-section are calculated (for a section of the body equal to the length of the sheet, from joint to joint). The wear rate of all cross-section sheets is assumed to be the same, and the probability of its occurrence corresponds to the law of normal distribution with the characteristics specified in the Rules of the Russian River Register established for a given group of elements. According to the assumptions made above, it is possible to calculate the probability of failure in the cross-section of a group of elements with local residual deformations depending on the number of years of the vessel operation. The probability of failures in a given group of elements is estimated by the multiplication of the failures probability in several sections after a given number of years of operation. The probability of failures in the hull of the vessel is calculated as the multiplication of the failures probabilities in all groups of elements. Formulas for calculating the loss of the bearing area of the sheathing plates and beams of the longitudinal set due to the local residual deformations have been obtained. The loss of the working area of the sheets and longitudinal beams is represented as additional wear of the sheets. After dividing the mentioned loss of the cross-section area by the cross-section width, the value of the permissible reduction in the residual thickness of the sheets, weighted average for the section under consideration, is obtained.
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Lam, William, Kalev Kask, Javier Larrosa, and Rina Dechter. "Residual-Guided Look-Ahead in AND/OR Search for Graphical Models." Journal of Artificial Intelligence Research 60 (October 20, 2017): 287–346. http://dx.doi.org/10.1613/jair.5475.
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We introduce the concept of local bucket error for the mini-bucket heuristics and show how it can be used to improve the power of AND/OR search for combinatorial optimization tasks in graphical models (e.g. MAP/MPE or weighted CSPs). The local bucket error illuminates how the heuristic errors are distributed in the search space, guided by the mini-bucket heuristic. We present and analyze methods for compiling the local bucket-errors (exactly and approximately) and show that they can be used to yield an effective tool for balancing look-ahead overhead during search. This can be especially instrumental when memory is restricted, accommodating the generation of only weak compiled heuristics. We illustrate the impact of the proposed schemes in an extensive empirical evaluation for both finding exact solutions and anytime suboptimal solutions.
Dissertations / Theses on the topic "Weak local residuals"
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Ferré, Romain. "Etude expérimentale et modélisation de la durabilité d'un contact représentatif de l'interface aube / disque de soufflante grenaillé soumis à des chargements de fretting / fatigue / usure." Thesis, Ecully, Ecole centrale de Lyon, 2013. http://www.theses.fr/2013ECDL0012.
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Ce travail porte sur l’étude du risque d’amorçage de fissure en fretting/fatigue du contact aubes/disque de soufflante en alliage de titane Ti-6Al-4V d’un turboréacteur civil. De part les vibrations du moteur et le passage du flux d’air, le contact aube/disque est sujet à de microdéplacements: le fretting. Ce problème complexe concerne des zones en contact de faibles dimensions subissant des pressions de contact importantes et des micro-déplacements associées à des structures soumises à des chargements eux-mêmes complexes. Des essais de fretting simple, fretting précontraint et fretting fatigue sont réalisés en vue d’identifier les conditions d’amorçage de fissure pour plusieurs géométries présentant des gradients de contraintes différents. Les résultats expérimentaux mettent en évidence l’effet du gradient de contrainte sur l’amorçage. Ainsi, via des essais présentant une gamme étendue de gradient, il a été confirmé que les gradients de contraintes retardent l’initiation de fissure. Une approche non-locale couplée à un critère de fatigue multiaxiale et identifiée sur une unique condition expérimentale de fretting simple a permis la prédiction de l’ensemble des résultats expérimentaux. Ainsi, une méthodologie prédictive des durées de vie à amorçage a été proposée. Cette approche numérique intègre la multiaxialité du chargement, l’effet du gradient des contraintes, la réponse élastoplastique de l’interface et les limites de fatigue en traction/compression et torsion alternée du matériau. L’interface aube/disque grenaillée du moteur subit une alternance de sollicitations de faibles amplitudes générant l’amorçage de fissure, et de grandes amplitudes favorisant l’usure des zones en contact. Le phénomène de compétition usure/fissure a alors été étudié via les courbes en cloches (durée de vie en fonction de l’amplitude de déplacement) ainsi que l’influence des contraintes résiduelles de grenaillage. Une première conclusion sur l’effet bénéfique de l’usure a pu être apportée dans le cas d’un matériau sans traitement de surface. Si les contraintes résiduelles de grenaillage permettent d’apporter un gain notable sur les durées de vie pour des sollicitations de glissement partiel, à l’inverse, il a été observé que le matériau avec le traitement de surface de grenaillage présente des durées de vie plus faibles pour des sollicitations favorisant l’usure. À travers d’essais inédits avec un dispositif expérimental à trois vérins, le chargement complexe de l’interface aube/disque du moteur a pu être reproduit à l’échelle du laboratoire. Ainsi, la durabilité globale du contact représentatif de l’interface aube/disque de soufflante a été étudiée. Une synergie des sollicitations oligocycliques et polycycliques à l’interface a été constatée provoquant des phénomènes de réorganisation de contraintes résiduelles et l’accélération des cinétiques d’usure. Cette étude a montré l’importance de prendre en compte les sollicitations polycycliques dans le dimensionnement des structures aubes/disque. Ces sollicitations couplent les aspects de fatigue « fissuration » aux phénomènes de cumul de dommage et de cinétique d’usure des interfacesThis work aims at studying the crack initiation risk of a blade/disk contact under fretting/fatigue loading. The fan stage of a civil engine is studied and the material used is a titanium alloy: Ti-6Al-4V. This complex issue concerns small contacts which are subjected to high contact pressures and micro-displacements. Thus, a complex multiaxial loading occurs on the structure. Fretting, static stressed fretting and fretting fatigue testing are performed in order to quantify the crack nucleation thresholds. In addition, several geometries which present different stress gradient values are used. The experimental results show a stress gradient effect on the crack initiation. Thus, using a wide range of stress gradient, it has been confirmed that stress gradient delays crack nucleation. A multiaxial fatigue criterion is used to determine the equivalent stress field under the contact. Then, a non-local approach, identified thanks to one fretting experimental condition, is employed in order to consider the stress gradient effect. This approach provides the prediction of the whole experimental results. In this way, a predictive method of the initiation fatigue life has been introduced. This numerical approach takes into account the multiaxial loading, the stress gradient effect, the plastic-elastic behavior of the interface and the fatigue strength limits of the material. The blade/disk contacts of the engine are shot-peened. During the flight, interfaces are subjected to low displacement amplitudes leading to crack initiation. On the other hand, during landing and take-off, contacts are submitted to high displacement amplitudes leading to the interface wear. As a consequence, competition between wear kinetic and nucleation one is studied and “bell curves” are plotted (i.e. fatigue life time versus displacement amplitude).Moreover, the effect of the shot-peening residual stresses on fatigue life time is observed. In case of un-treated material, a beneficial impact on the fatigue life time is observed due to wear process. Compressive residual stresses of shot-peening increase the fatigue life when fretting/fatigue on partial slip regime occurs. Nevertheless, a decrease of the fatigue life time is observed when wear process is activated by the gross slip condition. Finally, the complex loading of the engine blade/disk contact has been reproduced in the laboratory. To achieve this, a new testing, using an experimental machine composed of three hydraulic actuators is developed. Thus, the global life time of the representative interface of the fan stage is studied. Oligocyclic (low frequency) and polycyclic (high frequency) solicitations interact themselves and lead, firstly, to a rearrangement of the residual stresses, and secondly, to an increase of the wear kinetics. This research work highlights the interest to consider the polycyclic loadings to design the blade/disk structure. These solicitations reproduce the “cracking” fatigue phenomenon, the cumulative damages and the wear kinetics of the interface
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Mungkasi, Sudi. "A study of well-balanced finite volume methods and refinement indicators for the shallow water equations." Phd thesis, 2012. http://hdl.handle.net/1885/10301.
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This thesis studies solutions to the shallow water equations analytically and numerically. The study is separated into three parts. The first part is about well-balanced finite volume methods to solve steady and unsteady state problems. A method is said to be well-balanced if it preserves an unperturbed steady state at the discrete level. We implement hydrostatic reconstructions for the well-balanced methods with respect to the steady state of a lake at rest. Four combinations of quantity reconstructions are tested. Our results indicate an appropriate combination of quantity reconstructions for dealing with steady and unsteady state problems.
The second part presents some new analytical solutions to debris avalanche problems and reviews the implicit Carrier-Greenspan periodic solution for flows on a sloping beach. The analytical solutions to debris avalanche problems are derived using characteristics and a variable transformation technique. The analytical solutions are used as benchmarks to test the performance of numerical solutions. For the Carrier-Greenspan periodic solution, we show that the linear approximation of the Carrier-Greenspan periodic solution may result in large errors in some cases. If an explicit approximation of the Carrier-Greenspan periodic solution is needed, higher order approximations should be considered. We propose second order approximations of the Carrier-Greenspan periodic solution and present a way to get higher order approximations. The third part discusses refinement indicators used in adaptive finite volume methods to detect smooth and nonsmooth regions. In the adaptive finite volume methods, smooth regions are coarsened to reduce the computational costs and nonsmooth regions are refined to get more accurate solutions. We consider the numerical entropy production and weak local residuals as refinement indicators. Regarding the numerical entropy production, our work is the first to implement the numerical entropy production as a refinement indicator into adaptive finite volume methods used to solve the shallow water equations. Regarding weak local residuals, we propose formulations to compute weak local residuals on nonuniform meshes. Our numerical experiments show that both the numerical entropy production and weak local residuals are successful as refinement indicators.
Book chapters on the topic "Weak local residuals"
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Miller, D. Gary. "The nominal system." In The Oxford Gothic Grammar, 58–101. Oxford University Press, 2019. http://dx.doi.org/10.1093/oso/9780198813590.003.0003.
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Nouns are inflected for gender (masculine, feminine, neuter), number (singular and plural), and case: nominative, accusative, genitive, dative. Except in -u- stems, the vocative has the form of the accusative and/or is syncretized with the nominative. Demonstratives and pronominals have a residual instrumental, e.g. þe (by this), and ablative, e.g. jáinþro (from there). Adjectives are similarly inflected but also have strong and weak forms. Comparatives and nonpast participles are weak. The precise syntactic status of D-words (demonstratives, determiners, and articles) is impossible to test. Personal pronouns of the first and second person are inflected for singular, plural, and dual, and have no gender distinction. The third person pronoun has all three genders but only singular and plural number. Interrogative and indefinite pronouns are morphologically identical. Gothic has a rich negative polarity system. Numerals are partly inflected and partly indeclinable. Deictic adverbs belong to an old local case system.
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Kompanets, Eduard, and Viktoria Lavrynenko. "ECOSYSTEM CONNECTIONS AND FISH HEALTH." In Priority areas for development of scientific research: domestic and foreign experience. Publishing House “Baltija Publishing”, 2021. http://dx.doi.org/10.30525/978-9934-26-049-0-40.
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Ecosystems are subject to many human influences. The balance between species is disturbed due to interference with the aquatic environment. Due to environmental pollution, its impact on fish and other aquatic organisms changes. This affects ecosystem connections. Changes in the environment also change the adaptive capacity of fish, leading to impaired health. Also, there is a need to study the protective capabilities of fish from the naturally occurring opportunistic species Aeromonas hydrophila, which causes infections in them. In natural hydrobiocenoses, fish, as well as pathogens of its diseases (aeromonads) are components of food chains formed by evolution. Literature sources prove that aeromonads are normally present in microbial associations of benthic microflora as a normal saprophytic component of hydroecosystems. These bacteria feed on organic residues that are concentrated at the bottom of water bodies and perform a sanitary function, like other similar types of microorganisms. The health of fish depends on their ability to adapt to the environment. Usually in the wild, fish are rarely susceptible to disease. Local populations for a long time of coexistence have formed a certain balance with other species, including parasitic. The balance is reflected by a certain rate of abundance between species. Imbalance due to fishing from the reservoir, or, conversely, with an artificial increase in numbers, leads to changes in the aquatic environment. Changes in the habitat of fish affect themselves. Fish health is changing. In nature, such a disease as aeromonosis is an ecological concept. Violation of the ecological conditions of the species leads to stress, and reduced immunity in fish, leads to fish disease. In aeromonad infections with weak symptoms in carp, a decrease in biological parameters was observed: growth, body weight, fatness and survival (57.1%). The number of blood cells in diseased fish decreased, especially leukocytes and lymphocytes. The percentage of T- and B-lymphocytes in the blood of carp-infected carp increased. The introduction of the bacterium stimulated the immune response – an increase in the percentage of T-lymphocytes. The percentage of B cells did not increase significantly. In diseased fish, the percentage and number of low-activity T-lymphocytes increased, which corresponded to the presence of an immune response to the bacterium. The values of antibacterial activity of blood serum (BASC) in both groups of fish did not change.
Conference papers on the topic "Weak local residuals"
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Moliere, Michel. "Benefiting From the Wide Fuel Capability of Gas Turbines: A Review of Application Opportunities." In ASME Turbo Expo 2002: Power for Land, Sea, and Air. ASMEDC, 2002. http://dx.doi.org/10.1115/gt2002-30017.
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Gas Turbines accept a wide range of alternative fuels in connection with the most diverse economy branches, including industry (coal; oil and gas; refining; petrochemistry; steel and mining activities) and, more recently, agriculture (biofuels). This fuel flexibility enhances the other qualities demonstrated by Gas Turbines among which the prominent ones are: energy effectiveness, operational reliability and emission compliance. Therefore, Gas Turbines using local fuel resources and deployed in simple or combined cycles or in cogeneration plants, enable the concept of cost-effective and environmentally-conscious power projects and can make a valuable contribution to the sustainable, regional development. However, in order to benefit from the fuel flexibility of Gas Turbines, some basic technical considerations are necessary. The paper intends to provide the power community with comprehensive information about alternative GT fuels. It offers a review of the main alternative fuel candidates and sets out the primary technical/engineering considerations that underlie their safe and reliable utilization. Special emphasis is placed on: (i) volatile fuels (naphtha, NLG, condensates); (iii) weak gas fuels from the coal/iron industry (coal-bed; coke-oven, blast furnace gas); (iv) paraffin-rich and hydrogen-rich by-products from refineries (‘fuel gas’; LPG) and (iv) ash-forming oils (residuals; heavy crude’s).
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Irmisch, Stefan. "Adaptive Finite-Volume Solution of the Two-Dimensional Euler Equations on Unstructured Meshes." In ASME 1994 International Gas Turbine and Aeroengine Congress and Exposition. American Society of Mechanical Engineers, 1994. http://dx.doi.org/10.1115/94-gt-087.
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This paper presents a finite-volume method for solving the compressible, two-dimensional Euler equations using unstructured triangular meshes. The integration in time, to a steady-state solution, is performed using an explicit, multistage Runge-Kutta algorithm. A special treatment of the artificial viscosity along the boundaries reduces the production of numerical losses. Convergence acceleration is achieved by employing local time-stepping, implicit residual smoothing and a multigrid technique. The use of unstructured meshes, based on Delaunay triangulation, automatically adapted to the solution, allows arbitrary geometries and complex flow features to be treated easily. The employed refinement criterion does not only detect strong shocks, but also weak flow features. Solutions are presented for several subsonic and transonic standard test cases and cascade flows that illustrate the capability of the algorithm.
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Wilk, Andrzej B., Henryk M. Madej, and Bogusław E. Łazarz. "Vibration Processing Techniques for Fault Detection in Gearboxes." In ASME 2003 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. ASMEDC, 2003. http://dx.doi.org/10.1115/detc2003/ptg-48084.
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Vibration analysis is a very important tool in condition monitoring of operating machines. Many signal processing methods have been developed to extract information about incipient faults from externally measured vibration signals. The article presents the laboratory examinations of some faults in spur and helical gears. In case of spur gears two types of progressing local faults of cracked and chipped gear tooth were simulated and the smoothed pseudo Wigner-Ville distribution was used to demonstrate fault advancement via residual vibration signal analysis. Observing changes in the features of the WV distribution in the contour plots and changes of Kurtosis value monitored the progression of a fault. In case of helical gears some signal changes of transverse vibration velocity of shafts during the process of pitting growth in the tooth working surface have been investigated. Some new indices of pitting wear have been suggested and compared with other non-dimensional discriminants.
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Murata, Naokazu, Naoki Saito, Kinji Tamakawa, Ken Suzuki, and Hideo Miura. "Effect of Crystallographic Quality of Grain Boundaries on Both Mechanical and Electrical Properties of Electroplated Copper Thin Film Interconnections." In ASME 2011 Pacific Rim Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Systems. ASMEDC, 2011. http://dx.doi.org/10.1115/ipack2011-52048.
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Both mechanical and electronic properties of electroplated copper films used for interconnections were investigated experimentally considering the change of their micro texture caused by heat treatment. The fracture strain of the film annealed at 400°C increased from about 3% to 15% and their yield stress decreased from about 270 MPa to 90 MPa. In addition, it was found that two different fatigue fracture modes appeared in the film. One was a typical ductile fracture mode and the other was brittle one. When the brittle fracture occurred, a crack propagated along weak or porous grain boundaries which were formed during electroplating. The brittle fracture mode disappeared after the annealing at 300°C. These results clearly indicated that the mechanical properties of electroplated copper thin films vary drastically depending on their micro texture. The electrical reliability of the electroplated copper yjin film interconnections was also investigated. The interconnections used for electromigration tests were made using by a damascene process. An abrupt fracture mode due to local fusion appeared in the as-electroplated interconnections. Since the fracture rate increased almost linearly with the square of the applied current density, this fracture mode was dominated by local Joule heating. It seemed that the local current concentration occurred around the porous grain boundaries. The life of the interconnections was improved drastically after the annealing at 400°C. This was because of the increase of the average grain size and the improvement of the quality of grain boundaries in the annealed interconnections. However, the stress-induced migration occurred in the interconnections annealed at 400°C. This was because of the high tensile residual stress caused by the constraint of the densification of the films during annealing by the surrounding oxide film. Therefore, it is very important to control the crystallographic quality of electroplated copper films for improving the reliability of thin film interconnections. The quality of the grain boundaries can be evaluated by applying an EBSD (Electron Back Scatter Diffraction) analysis. New two experimentally determined parameters are proposed for evaluating the quality of grain boundaries quantitatively. It was confirmed that the crystallographic quality of grain boundaries can be evaluated quantitatively by using the two parameters, and it is possible to estimate both the strength and reliability of the interconnections.
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Verhaeghe, R., G. Wilms, P. Mombaerts, J. Vermylen, A. Baert, and M. Verstraete. "FEMORO-POPLITEAL ARTERY THROMBOLYSIS WITH INTRA-ARTERIAL INFUSION OF RECOMBINANT TISSUE-TYPE PLASMINOGEN ACTIVATOR (rt-PA)." In XIth International Congress on Thrombosis and Haemostasis. Schattauer GmbH, 1987. http://dx.doi.org/10.1055/s-0038-1643892.
Full textAbstract:
The efficacy and tolerance of intra-arterial rt-PA infusion was tested in 27 patients with a thrombotic occlusion of the femoro-popliteal artery. The mean length of the occluding thrombus was 10 cm (range : 2-25 cm). The occlusion was recent (<1 week old) in 7 patients; in 2 it existed for more than 6 months. The rt-PA solution was infused through an angiographic catheter embedded into the thrombus at a rate of 10 mg/hr in the first 11 patients, 5 mg/hr in the next 11 and 3 mg/hr in the last 5. The maximal dose foreseen in the protocol was 50 mg; the mean dose infused was 42 mg. Heparin (400 IU/hr) was infused concomitantly. Thrombolysis occurred in all 27 patients. Angiographic restoration of patency was obtained in 25 (93%); it first appeared after a mean dose of 27 mg rt-PA (range : 10 to 50 mg). In 21 patients, a percutaneous transluminal angioplasty was needed to dilate a residual stenotic lesion or remaining mural thrombi. This secondary procedure initiated reocclusion in 2 patients by causing a distal embolus and a subintimal dissection, respectively. Early rethrombosis occurred spontaneously in 3 other patients. Thus, 20 (74%) patients had a clinical improvement at discharge from the hospital.rt-PA infusion was complicated by bleeding in 10 (37%) patients: a groin hematoma at the catheter entry site occurred in 9 patients, a hematoma from a previous venous in 2 and gingival oozing in 3. None required blood transfusion. Premature interruption of the infusion because of local hematoma formation was the cause of failure in one patient.This pilot trial confirms the feasibility of thrombolysis with local infusion of rt-PA in peripheral arterial thrombosis. The early clinical results and the incidence of bleeding complications appear similar to those observed with local low-dose streptokinase, although initial patency seems easier to restore with rt-PA. A prospective trial comparing rt-PA to streptokinase in this condition is thus warranted
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Murata, Naokazu, Naoki Saito, Kinji Tamakawa, Ken Suzuki, and Hideo Miura. "Micro Texture Dependence of Both the Mechanical and Electrical Properties of Electroplated Copper Thin Films Used for Interconnection." In ASME 2010 International Mechanical Engineering Congress and Exposition. ASMEDC, 2010. http://dx.doi.org/10.1115/imece2010-37279.
Full textAbstract:
Both mechanical and electrical properties of electroplated copper thin films were investigated experimentally with respect to changes in their micro texture. Clear recrystallization was observed after the annealing even at low temperature of about 150°C. The fracture strain of the film annealed at 400°C increased from the initial value of about 3% to 15%, and at the same time, the yield stress of the annealed film decreased from about 270 MPa to 90 MPa. In addition, it was found that there were two fatigue fracture modes in the film annealed at the temperatures lower than 200°C. One was a typical ductile fracture mode with plastic deformation and the other was brittle one. When the brittle fracture occurred, the crack propagated along weak or porous grain boundaries which remained in the film after electroplating. The brittle fracture mode disappeared after the annealing at 400°C. These results clearly indicated that the mechanical properties of electroplated copper thin films vary drastically depending on their micro texture. Next, the electrical reliability of electroplated copper thin film interconnections was discussed. The interconnections used for electromigration (EM) tests were made by damascene process. The width of the interconnections was varied from 1 μm to 10 μm. An abrupt fracture mode due to local fusion appeared in the as-electroplated films within a few hours during the test. Since the fracture rate increased linearly with the increase of square of the applied current density, this fracture mode was dominated by local Joule heating. It seemed that the local resistance of the film increased due to the porous grain boundaries and thus, the local temperature around the porous grain boundaries increased drastically. On the other hand, the life of the interconnections annealed at 400°C was improved significantly. This was because of the increase of the average grain size and the improvement of the quality of grain boundaries in the annealed films. The electrical properties of the electroplated copper films were also dominated by their micro texture. However, the stress migration occurred in the interconnections after the annealing at 400°C. This was because of the high residual tensile stress caused by the constraint of the densification of the films by the surrounding oxide film in the interconnection structures during the annealing. Finally, electroplating condition was controlled to improve the electrical properties. Both the resistance of electromigration and electrical resistivity were improved significantly. However, electromigration of copper atoms still occurred at the interface between the electroplated copper and the thin tantalum (Ta) layer sputtered as base material. Therefore, it is very important to control the crystallographic quality of electroplated copper films and the interface between different materials for improving the reliability of thin film interconnections.
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Musil, J., V. Dolhof, and E. Dvorácek. "Repair of Water Turbine Blades by Wire Electric Arc Spraying." In ITSC 1996, edited by C. C. Berndt. ASM International, 1996. http://dx.doi.org/10.31399/asm.cp.itsc1996p0911.
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Abstract Water turbine parts damaged by cavitation erosion (CE) and/or slurry erosion (SE) may cause excessive operational costs for plants worldwide. The damages can be reduced by choosing more resistant materials and right technology in the first-production or at repair and overhaul. Thermal spray technologies have a great potential in the field of repairing works. Thick multilayered coatings deposited by wire electric arc spraying (WAS) has been developed and applied as CE and SE protection at the repair of stationary Francis turbine blades. Repair technology by WAS was performed on large eroded areas (1-3 m3) of preguide blades of Francis turbine: 1) local damaged depths 30-35 mm maximum were repaired by sprayed materials, 2) subsequently wire arc spraying of functional coating was applied. Three types of functional coatings with total thickness 10 mm a) duplex high - Cr stainless steel with NiAl bond coat, b) graded NiAl - Cr stainless steel coatings, and c) multilayered graded NiAl - Cr stainless steel coatings were compared by means of stress measurements and structural analysis. The coating structure influences very strongly the residual stress level and adhesive-cohesive strength. Multilayered graded NiAl - Cr stainless steel coatings showed the best results and were sprayed on water turbine blades in 4 Czech water power station during regular cut-off repair periods. After 30 - 36 months' continuous operation, Francis turbine blades repaired by WAS technology show better behaviour in comparison with original material from the point of wear resistance, reliability, cost-effect and life-time.
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Naboulsi, Sam. "A Crystallographic Approach to Life Prediction Analysis of a Turbine Engine Blade to Disk Attachment." In ASME 2014 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/imece2014-40208.
Full textAbstract:
Fretting fatigue raises many challenges in modeling and predicting of a turbine engine blade disk attachment response. It occurs when the blade and disk are pressed together in contact and experience a small oscillating relative displacement due to variations in engine speed and vibratory loading. Fretting causes a very high local stress near the edge of contact resulting in wear, nucleation of cracks, and their growth, which can result in significant reduction in the life of the material. Fretting depends on geometry, loading conditions, residual stresses, nonlinear response, and surface roughness, among other factors. These complexities make fretting a significant driver of fatigue damage and failure risk of disks. That is, fretting is often the root cause of the nucleation of cracks at attachments of structural components, and the cyclic plastic cumulative deformation and damage occur within depths of only several grains. Hence, resolving the deformation at the scale of individual grains, in order to understand the crystallographic orientation dependence of plasticity driven fretting fatigue and its relation to surface contact conditions, is important. In this study, a finite strain computational crystal plasticity constitutive law will be implemented to simulate and investigate time dependent response of turbine engine blade to disk attachment. The present work leverages the computational model of early efforts, which focused on modeling damage initiation and propagation due to fretting fatigue using micro-thermo-mechanical model, and further enhances the capabilities of capturing the micro-scale nature of the fretting small oscillatory relative displacement at grain level. These efforts provided a high fidelity approach to capture the life of the material at the blade to disk attachment and to simulate the realistic mechanism associated with fretting.
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Vilarinho, Cândida, José Teixeira, Jorge Araújo, and Joana Carvalho. "Effect of Time and Acid Concentration on Metal Extraction From Galvanic Sludges." In ASME 2017 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2017. http://dx.doi.org/10.1115/imece2017-71370.
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Galvanic sludge is a solid waste produced by the surface treatment industry, classified as hazardous because of their high concentration of heavy metals, which in its final destination is disposed in waste disposal facilities, with economic costs to the holders. Through hydrometallurgical processing, it is possible to extract valuable metals, with low costs involved, while the hazardous level of the residue is reduced. In the present work, the heap leaching method was studied as a solution to the treatment of these residues, which in order to consist in a valuable option, processing and operation costs must be kept as low as possible. For the experimental testing, a closed loop lixiviation column for hydrometallurgical treatment of galvanic sludge with possibility of continuous flow of the leachate (and static process as well) was constructed, simulating the heap leaching process. The galvanic waste in study, delivered by a local surface treatment company, was both chemically and physically characterized, proving to be rich in valuable metals like Nickel, Chromium and Copper. The waste material was characterized both for physical parameters (grain size) and chemical composition. The lixiviation trials, with a maximum duration of 1 week, were conducted. The influence upon the extraction rate of metals such as Nickel, Chromium and Copper, of parameters such as the concentration of the leaching agent (sulfuric acid) and time were tested. In order to quantify the leachate circulation effect, a static trial was conducted as well. Extraction rates of 35.5 % of Nickel, 14% of Copper and 13.6 % of Chromium were obtained after 6 hours in a dynamic trial, with 100 g/L sulfuric acid solution concentration. The acid consumption rate was correlated with the metal extraction. Finally, the results were compared with others obtained in previous galvanic sludge agitation lixiviation and laterites heap leaching works.
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Lavagnoli, S., C. De Maesschalck, and V. Andreoli. "Design Considerations for Tip Clearance Control and Measurement on a Turbine Rainbow Rotor With Multiple Blade Tip Geometries." In ASME Turbo Expo 2016: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2016. http://dx.doi.org/10.1115/gt2016-56544.
Full textAbstract:
The accurate design, control and monitoring of the running gaps between static and moving components is vital to preserve the mechanical integrity and ensure the correct functioning of any compact rotating machinery. Throughout engine service, the rotor tip clearance undergoes large variations due to installation tolerances or as the result of different thermal expansion rates of the blades, rotor disk and casing during speed transients. Hence, active tip clearance control concepts and engine health monitoring systems rely on precise real-time gap measurements. Moreover, this tip gap information is crucial for engine development programs to verify the mechanical and aerothermal design, and validate numerical predictions. This paper presents an overview of the critical design requirements for testing engine-representative blade tip flows in a rotating turbine facility. The manuscript specifically focuses on the challenges related with the design, verification and monitoring of the running tip clearance during a turbine experiment. In the large-scale turbine facility of the von Karman Institute, a rainbow rotor was mounted for simultaneous aerothermal testing of multiple blade tip geometries. The tip shapes are a selection of high-performance squealer-like and contoured blade tip designs. On the rotor disc, the blades are arranged in seven sectors operating at different clearance levels from 0.5 up to 1.5% of the blade span. Prior to manufacturing, the blade geometry was modified to compensate for the radial deformation of the rotating assembly under centrifugal loads. A numerical procedure was implemented to minimize the residual unbalance of the rotor in rainbow configuration, and to optimize the placement of every single airfoil within each sector. Subsequently, the rotor was balanced in-situ to reduce the vibrations and satisfy the international standards for high balance quality. The single-blade tip clearance in rotation was measured by three fast-response capacitive probes located at three distinct circumferential locations around the rotor annulus. Additionally, the minimum running blade clearance is captured with wear gauges located at five axial positions along the blades chord. The capacitance probes are self-calibrated using a multi-test strategy at several rotational speeds. The in-situ calibration methodology and dedicated data reduction techniques allow the accurate measurement of the distance between the turbine casing and the local blade tip features (rims and cavities) for each rotating airfoil separately. General guidelines are given for the design and calibration of a tip clearance measurement system that meets the required measurement accuracy and resolution in function of the sensor uncertainty, nominal tip clearance levels and tip seal geometry.