1,590 research outputs found
Distribution of nitrogenous nutrients and denitrifiers strains in estuarine sediment profiles of the Tanshui River, northern Taiwan
No full textRemoving Love waves from shallow seismic SH-wave data
No full textGeophysical exploration measurements are used to obtain an image of the geological structures of the subsurface, as detailed as possible. To this end, a wavefield is generated by a seismic source. This wavefield propagates through the subsurface, and will partly reflect on boundaries between layers with contrasting properties, and it will partly propagate further into the subsurface. De wavefields that have propagated back to the surface are measured with receivers. When this experiment is repeated several times on different locations, the measured data can be used to obtain the desired image. There are two kinds of seismic waves that can propagate through the subsurface. The ones that are generally used are the pressure waves, or P-waves, where the movement of the particles is parallel to the propagation direction of the wave. The other ones are the shear waves, or S-waves, where the movement of the particles is perpendicular to the propagation direction of the wave. When the particle movement is horizontally polarized (perpendicular to the plane of propagation), this wave type is often decoupled, or in other words, it propagates independently of other wave types. These waves are also called SH-waves. The surface of the Earth behaves as a perfect reflector for SH-waves. This means that all SH-waves that reach the surface will be completely reflected back into the subsurface. When the top layer of the subsurface is thin (smaller than the wavelength of the SH-wave), and when this top layer has a lower wave velocity than deeper layers, then the presence of the surface leads to a kind of surface waves, which were first described by A.E.H. Love, and are therefore called 'Love waves'. Love wave characteristics are: their group velocity is almost equal to the shear wave velocity; since they propagate solely along the surface, they attenuate slowly and are thus often stronger than reflected waves; and they are dispersive. The presence of Love waves deteriorates the quality of the final picture (or seismogram), because they obscure the desired reflections. Existing techniques to remove Love waves from seismic data often perform insufficient, or require certain knowledge about the subsurface. This knowledge is generally not available. Therefore, the ideal method should be one where the measured data alone is sufficient to separate the Love waves from the desired reflection information. The method we describe in this thesis uses the Betti-Rayleigh reciprocity theorem for elastic media. Reciprocity is a mathematical tool to relate two different states to each other. Here, one state is the actual situation, where the medium is bounded by a stress-free surface. The other state is an ideal situation, where there is no surface, and the top layer is extended to infinity. When there is no surface, there are also no surface waves. By applying the reciprocity theorem, we derive an integral equation, from which the Love wave free wavefield can be solved as a function of the data that do contain these surface waves. Other input parameters are the (shear-) wave velocity and the mass density of the top layer, and the source wavelet. When the data are discrete, the integral equation becomes a matrix equation. This can be solved using conventional numerical methods, such as matrix inversion. When the medium is horizontally layered (a so called 1-D medium), the kernel of the matrix equation becomes diagonal in the wave-number domain. Then the matrix equation reduces to a scalar expression. We tested the method on several synthetic datasets. In all cases, the Love waves were completely removed. Even other noise in the form of scattered Love waves was removed, in the cases where it was present. The method also had no problems when the input parameters were chosen wrongly. And when distortions were introduced into the data (distortions like random noise, or the effects of anelastic attenuation), the method still performed well. To test the method on field data, we performed a seismic experiment on the site of the Sofia tunnel (before it was drilled) near Hendrik Ido Ambacht in the Netherlands. The dataset that was the result seemed all right at first. Strong Love waves were indeed present in the data. However, we could not succeed in removing these Love waves with the method. Even worse, the method added noise to the data, to such an extent, that it completely obscured the original data. Although we searched extensively for possible reasons, we were not able to find the exact cause of the bad results. In the final chapter, we made a start to remove the surface waves from coupled P- and SV-wave systems, using the same method as we did for SH-waves. Because P- and SV-waves are coupled, the resulting equations are also coupled. This means that we need all possible source and receiver combinations to remove the surface waves. But it appeared that the equations could be solved independently with regard to the source direction. We validated the theory with an example where we removed the Rayleigh wave from the response of a homogeneousCivil Engineering and Geoscience
Electromagnetic effects in anti-Hermitian media with gain and loss
No full textFunding Information: L.F. was partly supported by DoinQTech, Jane and Aatos Erkko Foundation. L.F. and M.S.M. thank X. Wang, M. Nyman, and B. Zerulla for their invaluable help with numerical simulations. Also, L.F. wishes to acknowledge the support of Carsten Rockstuhl. Publisher Copyright: © 2024 authors. Published by the American Physical Society. Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.Incorporating both gain and loss into electromagnetic systems provides possibilities to engineer effects in unprecedented ways. Concerning electromagnetic effects in isotropic media that have concurrently electric and magnetic responses, there is, in fact, a degree of freedom to distribute the gain and loss in different effective material parameters. In this paper, we analytically scrutinize wave interactions with those media, and, most importantly, we contemplate the extreme scenario where such media are anti-Hermitian. Considering various conditions for excitation, polarization, and geometry, we uncover important effects and functionalities such as lasing into both surface waves and propagating waves, conversion of evanescent source fields to transmitted propagating waves, full absorption, and enhancing backward to forward scattering ratio. We hope that these findings explicitly show the potential of anti-Hermiticity to be used in optical physics as well as microwave engineering for creating and using unconventional wave phenomena.Peer reviewe
Exposé Landwinningsvraagstukken
No full textAls algemeen richtslijn is er aangegeven dat bij de opzet van landwinningswerken rekening gehouden moet worden met een tijdperk van ongeveer 40 jaren. Ten einde een nader inzicht in de voor te bereiden werkzaamheden te bekomen, werd er onderzoek verricht en gedeeltelijk in een viertal nota's vastgelegd. De onderzoeken gaan in specifiek over de 'Beplatingsmethode', waarbij slibvangen en beplanting der slikken een voorname rol spelen en de 'Bekleiingsmethode', waarbij getracht wordt sneller tot het doel te komen door inpoldering van een wadgebied en bekleiing ervan met specie uit de ondergrond. Bij het nagaan der mogelijkheden voor de eerstvolgende 40 jaar wordt gestuit op de volgende 7 hoofdvragen van landbouwkundige aard: 1. Is een proefpolder op de Wadden nodig ten einde te onderzoeken welke mening van slib en wadzand de meest wenselijke is? 2. Kan misschien met goedkopere middelen (proefbakken) worden volstaan? Hoe moeten deze worden ingericht? 3. Is het wadzand geschikt om als weidegrond te kunnen dien? Wat is dan de opbrengst per ha.? 4. Kunnen bossen op het Wadzand worden aangelegd? Welke opbrengst? 5. Wat kan met de zogenaamde woelmachine worden bereikt? Deze machine kan vruchtbare klei tot 4 meter diepte beneden maaiveld ophalen en over de oppervlakte spreiden. Kosten per laag van 4 cm dikte bedragen 300 à 400 gulden. 6. Welke resultaten zijn verkregen bij slibbemseting in Westerwolde en Drente? Een ter plaatse gehouden navraag wees uit dat een laag slib van eenige milimeter dikte na 30 jaar nog steeds opmerkelijk resultaten gaf. 7. Welk kavelgrootte is het meest wenselijk? De viertal nota's betreffen: - Verslag werkzaamheden in 1942 op Hollandsch Diep en Maartensgat (door opzichter Molendijk) - Verslag werkzaamheden in 1942 op de Hellegatplaten (door opzcihter Van Eyk) - Programma van onderzoek betreffende plantenonderzoek (door Dr. L.F. Kamps) - Verslag werkzaamheden proefvelden en plantenonderzoek in 1942 (door assisten Van Eerde)Landwinningswerken 194
Topology Optimization Method Research on Hollow Wide-chord Fan Blade of a High-bypass Turbofan Engine
No full textAbstractIn order to realize lightweight design of a high-bypass turbofan engine, topology optimization of vacuum structure on a wide-chord fan blade was carried out regarding mixed loading conditions as static strength, vibration and bird-strike. Without changing the leaf shape, relationship of performance indices on vacuum structure was analyzed with simplified mechanical model of loading conditions. Topology optimization designs were carried out according to the highly sensitive conditions. Vacuum structure layout of fan blade was constructed integrating the major load transfer paths in each design proposal. Performance indices of different fan blade structures were compared. Result shown that optimized fan blade can realize lightweight as well as meeting the strength design requirement
Columbia P.2
No full text2663 Columbia Coal Mine-Machine shop, Check House, with Fan House in background. Located near top of tramway. Gift of L.F. Rains
Author contributions: L.F
Full text linkIt is well-known that financial asset returns exhibit fat-tailed distributions and long-term memory. These empirical features are the main objectives of modeling efforts using (i) stochastic processes to quantitatively reproduce these features and (ii) agent-based simulations to understand the underlying microscopic interactions. After reviewing selected empirical and theoretical evidence documenting the behavior of traders, we construct an agent-based model to quantitatively demonstrate that "fat" tails in return distributions arise when traders share similar technical trading strategies and decisions. Extending our behavioral model to a stochastic model, we derive and explain a set of quantitative scaling relations of long-term memory from the empirical behavior of individual market participants. Our analysis provides a behavioral interpretation of the long-term memory of absolute and squared price returns: They are directly linked to the way investors evaluate their investments by applying technical strategies at different investment horizons, and this quantitative relationship is in agreement with empirical findings. Our approach provides a possible behavioral explanation for stochastic models for financial systems in general and provides a method to parameterize such models from market data rather than from statistical fitting. complex systems | power law | scaling laws M odeling price returns has become a central topic in the study of financial markets due to its key role in financial theory and its practical utility. Following models by Engle and Bollerslev (1, 2), many stochastic models have been proposed based on statistical studies of financial data to accurately reproduce price dynamics. In contrast to this stochastic approach, economists and physicists using the tools of statistical mechanics have adopted a bottom-up approach to simulate the same macroscopic regularity of price changes, with a focus on the behavior of individual market participants (3-10). Although the second socalled agent-based approach has provided a qualitative understanding of price mechanisms, it has not yet achieved sufficient quantitative accuracy to be widely accepted by practitioners. Here, we combine the agent-based approach with the stochastic process approach and propose a model based on the empirically proven behavior of individual market participants that quantitatively reproduces fat-tailed return distributions and long-term memory properties (11-14). Empirical and Theoretical Market Behaviors We start by arguing that technical traders (usually agents seeking arbitrage opportunities and make their trading decisions based on price patterns) contribute much more to the dynamics of daily stock prices S t (or log price s t ≡ lnðS t Þ) than fundamentalists (who attempt to determine the fundamental values of stocks). Although fundamentalists hold a majority of the stocks, they trade infrequently (see SI Appendix, Market surveys (16-18) also provide clear evidence of the prevalence of technical analysis. We consider here only technical traders, assuming that fundamentalists contribute only to market noise. Our study is of the empirical data recorded prior to 2006 and ignores the effect of high frequency trading (HFT) that has become significant only in the past 5 y. We propose a behavioral agent-based model that is in agreement with the following empirical evidence: i. Random trading decisions made by agents on a daily basis. n 0 technical traders use different trading strategies, hence their decisions to buy, sell, or hold a position appear to be random. A trading decision is made daily because empirical studies report the lack of intraday trading persistence in empirical trading data (19). Market survey (16) also shows that fund managers put very little emphasis on intraday tradings. We estimate the probability p of having daily trade empirically from trading volumes. ii. Price returns. The price return r t ≡ s t − s t−1 is controlled by the imbalance d t between the demand and the supply of stocks-the difference in the number of buy and sell trades each day. The excess in total demand or supply moves the price up or down, where the largest r t occurs when all traders act in unison, when they all either buy or sell their stocks. We assume this relationship between price change r t and d t to be linear each day, as supported by empirical findings (20, 21). iii. Centralized interaction mechanism of returns on technical strategies. For technical traders, an important input parameter in their strategies is past price movement (22, 23). Consequently, prices and orders reflect a main interaction mechanism between agents. In many agent-based models, the interaction strength between agents need to be adjusted with agent population size (5, 24, 25) or interaction structure (26) to sustain "fat" tails in return distributions. Here we propose a centralized interaction mechanism (price change) among agents so that the strength of interaction grows with agent population and is unaffected by interaction structure. iv. Opinion convergence due to price changes. This is the unique mechanism that distinguishes our model from other models. It specifies the collective behavior of technical traders. Duffy et al. (27) found that agents learn from each other and tend to adopt the strategy that gives the most payoff. Given the price patterns at any point in time, a few most profitable technical strategies dominate the market because every technical trade
In Search of Lost Meaning. Review of the Monograph by Kharayeva L.F., Kuchukova Z.A. “Gender and Ethnogender (on the Material of Kabardian Women’s Prose)”
No full textThe review offered to our readers is devoted to the study of the phenomenon of Kabardian women’s prose, presented in the monograph “Gender and Ethnogender” by L.F. Kharaeva and Z.A. Kuchukova. The author analyzes the monograph from the point of view of its structure, sequence of presentation, relevance to the topic and corpus of chosen literary texts. The undoubted value of the monograph recognizes its theoretical and practical significance, as well as an indisputable novelty. The author recommends this scientific research to be read by all who are interested in issues of gender and its ethnospecificity, gender literature, and the latest Kabardian literature
Getijcentrale in de Brouwersdam: De proefcentrale Brouwerssluis
No full textDELTA NV heeft in december 2007 opdracht gegeven aan de TU Delft, Faculteit Civiele Techniek en Geowetenschappen, voor het verrichten van een verkennende studie naar de mogelijkheden van energiewinning bij introductie van een (gedempt) getij op het Grevelingenmeer. In het Eindrapport betreffende deze studie (dat in juni 2008 werd uitgebracht) wordt gesteld dat het mogelijk is om bij de Brouwersdam energie uit het getij te winnen met een jaarlijkse opbrengst van 143 to 392 GWh. De hoogte van de mogelijke opbrengst is direct afhankelijk van de maximaal toegestane peilvariatie op het Grevelingenmeer. Kort daarop is, vooruitlopend op een besluit t.a.v. een getijcentrale in de Brouwersdam, besloten op korte termijn stappen te ondernemen voor het plaatsen van een proefinstallatie in één van de kokers van de Brouwerssluis in de Brouwersdam. Vervolgens zijn er tijdens een bespreking in Middelburg afspraken gemaakt tussen Rijkswaterstaat, DELTA NV en de TU-Delft t.a.v een ‘Pilot getijde-energie in de Brouwerssluis’. In dit rapport presenteert de TU Delft zijn bevindingen t.a.v deze pilot. Omdat Rijkswaterstaat de Brouwerssluis zoveel tijd als mogelijk open wil laten staan heeft men de gedachte laten varen om de proefinstallatie in een bestaande koker te bouwen. Immers voor een dergelijke inbouw zou de betreffende sluiskoker zes maanden tot een jaar zijn afgesloten. Deze beperking leidt er toe om een turbinegenerator voor te stellen die kan worden ingebouwd in een caisson. De caisson wordt drijvend aangevoerd, vervolgens gepositioneerd en afgezonken tegen een kokerinlaat aan de meerzijde van de Brouwerssluis. Indien gewenst kan een dergelijke caisson na afloop van de proefperiode eventueel weer worden opgedreven en verwijderd. Een andere mogelijkheid zou zijn geweest om een z.g.n stroomturbine op te hangen in de inlaatopening van een koker aan de meerzijde. Met een dergelijke stroomturbine wordt echter niet voldaan aan de eis van DELTA NV ‘dat een dergelijk demonstratieprojekt alleen zinvol is als er ervaring mee kan worden opgedaan voor een toekomstige centrale als beschreven in het eerder genoemde rapport. Modelonderzoek heeft uitgewezen dat de netto jaarlijkse nergieopbrengst van de proefinstallatie bij een dubbelzijdig werkende bulb-turbine met een diameter van 3,5 m omstreeks 2,0 GWh kan zijn. De proefinstallatie kan hiermee de electriciteit leveren voor 550 tot 600 huishoudens. Het vermogen van de turbine zal 570 á 600 kW zijn. De kosten voor het bouwen van de caisson ( 33,6 (l) x 8,3(b) x 15 (h) m3), het vervoeren, plaatsen en afzinken, het leveren en inbouwen van de turbine-generator, enz. zal zo’n \u80 12 miljoen bedragen. Hoewel een afzonderlijke economische benadering voor een proefinstallatie hier in feite niet op zijn plaats is, zij vermeld dat men bij een bedrijfsperiode van 20 jaar uitkomt op een kWh-prijs van 52 eurocent, bij 40 jaar wordt dit 38 eurocent. Als men rekent met een voorbereidingstijd van een jaar en een bouwtijd van 1,5 jaar zou de proefinstallatie medio 2011 in bedrijf kunnen zijn.Hydraulic EngineeringCivil Engineering and Geoscience
Matrices, not seeds. Vallisneri's research on mines: between empiricism and philosophy
Full text linkSince the beginning of his scientific activity the physician and naturalist Antonio Vallisneri (1661-1730) devoted many studies to the Earth sciences. In those years his interest focused particularly on the features of mineral kingdom and its relationship with spring water. The first observations date back to the last decade of XVII century, when the author analysed the gypsum
and sulphur veins on the Monte Gesso, in the Duchy of Modena and Reggio.
Some years later, during one of his journeys across the northern Apennines in search for the origin of springs, Vallisneri reached the Este domain of Garfagnana. There he explored the iron caves of Fornovolasco: this experience allowed him to support his theory with many empirical
information, later exposed in the Lezione Accademica intorno all’Origine delle Fontane (1715).
The many data collected by Vallisneri encouraged him to outline a theoretical interpretation of mineral genesis. He supposed the mineral veins as developed by ‘seeds’ released in the Earth
by God. The successful growth of ore veins, therefore, depended on the more or less favourable environment they would have found by accident. These ‘seeds’, as the author clarified, were not intended to be the very same of ‘perfect germs of generation’ typical of animals or plants. Rather, they were ‘matrices’ that had to be detected in order to exploit the wealth of mines posed, in a proper Leibnizian conception, ‘by God for world’s use’
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