Second-order wave maker theory using force-feedback control. Part I: A new theory for regular wave generation     

Johannes Spinneken  Chris Swan 《Ocean Engineering》2009,36(8):539-548

Second-order wave maker theory has long been established; the most extensive and detailed approach given by Schäffer [1996. Second-order wave maker theory for irregular waves. Ocean Engineering 23, 47–88]. However, all existing theories assume the wave paddle is driven by a position-feedback motion controller. Early research in the wave power field led to the design of a force-controlled absorbing wave machine [Salter, S., 1982. Absorbing wave-makers and wide tanks. In: Directional Wave Spectra Applications, pp. 185–200]. In addition to operating as an excellent absorber, this machine seemed to introduce very little spurious harmonic content when driven with a first-order command signal. The present paper provides a mathematical model for the operation of wave makers using force-feedback control and seeks to explain this apparent advantage. The model is developed to second-order so that a command signal compensating for the remaining spurious wave is also provided. Due to the complexity of the problem, the model has been limited to flap-type wave machines and the generation of regular waves. A variety of numerical tests in force-control mode have been conducted, indicating that the spurious wave content is greatly reduced when compared to the position-control mode. A separate experimental study validating the theory is presented in a part II paper by the same authors.  相似文献   

Evaluating the effects of catch-and-release angling on Cape stumpnose Rhabdosargus holubi in a South African estuary     

NK Arkert  A-R Childs  MC Parkinson  AC Winkler  E Butler  S Mannheim 《African Journal of Marine Science》2018,40(3):235-244

Fisheries managers are increasingly promoting catch-and-release (C&R) to manage recreationally angled fish stocks. Despite this, there is a scarcity of information on the effects of C&R on estuarine-dependent species. Cape stumpnose Rhabdosargus holubi dominates the recreational fisheries catch and provides an important source of food for subsistence fishers in some temperate South African estuaries. The health and survival of R. holubi exposed to a C&R event was investigated by examining their physiological stress response (blood glucose and lactate), reflex impairment (reflex action mortality predictors [RAMP]) and short-term (12-hour) survival. Fish were captured and exposed to one of three air-exposure treatments: 0 s, 30 s or 90 s. Stress and health were measured either immediately (immediate) or one hour after (delayed) the C&R event. There was no significant difference in blood glucose between air-exposure treatments, but there was a significant difference between the mean immediate and delayed glucose levels within each treatment (F_(2,143) = 81.8, p < 0.01). In contrast, blood lactate level was significantly higher in the 90-s treatment (p < 0.05). Immediate blood lactate levels were significantly lower than the delayed samples for each treatment (F = 4.29, p = 0.02; n = 169). Although all fish exhibited at least one reflex impairment, the RAMP score was significantly higher in the 90-s air-exposure treatment (H_(2,86) = 9.73, p = 0.007). Also, RAMP scores were significantly lower in the delayed samples (p < 0.01). Although short-term mortality was relatively low (2.3%) for this species, it was highest in the 90-s treatment (7%). These results suggest that physiological stress is higher when R. holubi are exposed to longer periods of air exposure and that the physiological stress of fish subject to a C&R event is best measured after a delay.  相似文献   

Cosmic‐ray exposure ages of six chondritic Almahata Sitta fragments          下载免费PDF全文

M. E. I. Riebe  K. C. Welten  M. M. M. Meier  R. Wieler  M. I. F. Barth  D. Ward  M. Laubenstein  A. Bischoff  M. W. Caffee  K. Nishiizumi  H. Busemann 《Meteoritics & planetary science》2017,52(11):2353-2374

The Almahata Sitta strewn field is dominated by ureilites, but contains a large fraction of chondritic fragments of various types. We analyzed stable isotopes of He, Ne, Ar, Kr, and Xe, and the cosmogenic radionuclides ¹⁰Be, ²⁶Al, and ³⁶Cl in six chondritic Almahata Sitta fragments (EL6 breccia, EL6, EL3‐5, CB, LL4/5, R‐like). The cosmic‐ray exposure (CRE) ages of five of the six samples have an average of 19.2 ± 3.3 Ma, close to the average of 19.5 ± 2.5 Ma for four ureilites. The cosmogenic radionuclide concentrations in the chondrites indicate a preatmospheric size consistent with Almahata Sitta. This corroborates that Almahata Sitta chondrite samples were part of the same asteroid as the ureilites. However, MS‐179 has a lower CRE age of 11.0 ± 1.4 Ma. Further analysis of short‐lived radionuclides in fragment MS‐179 showed that it fell around the same time, and from an object of similar size as Almahata Sitta, making it almost certain that MS‐179 is an Almahata Sitta fragment. Instead, its low CRE age could be due to gas loss, chemical heterogeneity that may have led to an erroneous ²¹Ne production‐rate, or, perhaps most likely, MS‐179 could represent the true 4π exposure age of Almahata Sitta (or an upper limit thereof), while all other samples analyzed so far experienced exposure on the parent body of similar lengths. Finally, MS‐179 had an extraordinarily high activity of neutron‐capture ³⁶Cl, ~600 dpm kg^?1, the highest activity observed in any meteorite to date, related to a high abundance of the Cl‐bearing mineral lawrencite.  相似文献   

On Flare-CME Characteristics from Sun to Earth Combining Remote-Sensing Image Data with <Emphasis Type="Italic">In Situ</Emphasis> Measurements Supported by Modeling     

Manuela Temmer  Julia K. Thalmann  Karin Dissauer  Astrid M. Veronig  Johannes Tschernitz  Jürgen Hinterreiter  Luciano Rodriguez 《Solar physics》2017,292(7):93

We analyze the well-observed flare and coronal mass ejection (CME) from 1 October 2011 (SOL2011-10-01T09:18) covering the complete chain of effects – from Sun to Earth – to better understand the dynamic evolution of the CME and its embedded magnetic field. We study in detail the solar surface and atmosphere associated with the flare and CME using the Solar Dynamics Observatory (SDO) and ground-based instruments. We also track the CME signature off-limb with combined extreme ultraviolet (EUV) and white-light data from the Solar Terrestrial Relations Observatory (STEREO). By applying the graduated cylindrical shell (GCS) reconstruction method and total mass to stereoscopic STEREO-SOHO (Solar and Heliospheric Observatory) coronagraph data, we track the temporal and spatial evolution of the CME in the interplanetary space and derive its geometry and 3D mass. We combine the GCS and Lundquist model results to derive the axial flux and helicity of the magnetic cloud (MC) from in situ measurements from Wind. This is compared to nonlinear force-free (NLFF) model results, as well as to the reconnected magnetic flux derived from the flare ribbons (flare reconnection flux) and the magnetic flux encompassed by the associated dimming (dimming flux). We find that magnetic reconnection processes were already ongoing before the start of the impulsive flare phase, adding magnetic flux to the flux rope before its final eruption. The dimming flux increases by more than 25% after the end of the flare, indicating that magnetic flux is still added to the flux rope after eruption. Hence, the derived flare reconnection flux is most probably a lower limit for estimating the magnetic flux within the flux rope. We find that the magnetic helicity and axial magnetic flux are lower in the interplanetary space by ～?50% and 75%, respectively, possibly indicating an erosion process. A CME mass increase of 10% is observed over a range of \({\sim}\,4\,\mbox{--}\,20~\mathrm{R}_{\odot }\). The temporal evolution of the CME-associated core-dimming regions supports the scenario that fast outflows might supply additional mass to the rear part of the CME.  相似文献   

The multiple chronological techniques applied to the Lake Suigetsu SG06 sediment core,central Japan     

Richard A. Staff  Takeshi Nakagawa  Gordon Schlolaut  Michael H. Marshall  Achim Brauer  Henry F. Lamb  Christopher Bronk Ramsey  Charlotte L. Bryant  Fiona Brock  Hiroyuki Kitagawa  Johannes van der Plicht  Rebecca L. Payne  Victoria C. Smith  Darren F. Mark  Alison Macleod  Simon P. E. Blockley  Jean‐Luc Schwenninger  Pavel E. Tarasov  Tsuyoshi Haraguchi  Katsuya Gotanda  Hitoshi Yonenobu  Yusuke Yokoyama  Suigetsu Project Members 《Boreas: An International Journal of Quaternary Research》2013,42(2):259-266

The varved sediment of Lake Suigetsu (central Japan) provides a valuable opportunity to obtain high‐resolution, multi‐proxy palaeoenvironmental data across the last glacial/interglacial cycle. In order to maximize the potential of this archive, a well‐constrained chronology is required. This paper outlines the multiple geochronological techniques being applied – namely varve counting, radiocarbon dating, tephrochronology (including argon–argon dating) and optically stimulated luminescence (OSL) – and the approaches by which these techniques are being integrated to form a single, coherent, robust chronology. Importantly, we also describe here the linkage of the floating Lake Suigetsu (SG06) varve chronology and the absolute (IntCal09 tree‐ring) time scale, as derived using radiocarbon data from the uppermost (non‐varved) portion of the core. This tie‐point, defined as a distinct (flood) marker horizon in SG06 (event layer B‐07–08 at 1397.4 cm composite depth), is thus derived to be 11 255 to 11 222 IntCal09 cal. years BP (68.2% probability range).  相似文献   

Holocene peatland development and hydrological variability inferred from bog‐pine dendrochronology and peat stratigraphy – a case study from southern Sweden     

Johannes Edvardsson  Hans Linderson  Mats Rundgren  Dan Hammarlund 《第四纪科学杂志》2012,27(6):553-563

Dendrochronological analysis was applied to subfossil remains of Scots pine (Pinus sylvestris L.) buried in a South Swedish peat deposit. In combination with peat stratigraphy, this approach was explored for its potential to provide information on the local hydrological and depositional history at the site, forming the basis for a regional palaeohydrological analysis. A 726‐year ring‐width chronology was developed and assigned an absolute age of 7233–6508 cal a BP (5284–4559 BC) through cross‐dating with German bog‐pine chronologies, whereas two short additional records of older ages were radiocarbon dated. Registration of growth positions of individual trees allowed assessment of the spatial dynamics of the pine population in response to hydrological changes and peatland ontogeny. Annually resolved growth variability patterns in the pine population reveal several establishment and degeneration phases, probably reflecting fluctuations in bog‐surface wetness. A major establishment phase at 7200–6900 cal a BP reflects the onset of a period of lowered groundwater level, also indicated by increased peat humification, and a development consistent with regional temperature and lake level reconstructions revealed from other proxies. This study demonstrates that subfossil bog‐pine populations may provide annually to decadally resolved reconstructions of local groundwater variability, which are highly relevant in a long‐term palaeoclimatic context. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

A projection of future sea level   总被引：1，自引：0，他引：1  

Johannes Oerlemans 《Climatic change》1989,15(1-2):151-174

Evidence is reviewed that suggests faster sea-level rise when climate gets warmer. Four processes appear as dominating on a time scale of decades to centuries: melting of mountain glaciers and small ice caps, changes in the mass balance of the large polar ice sheets (Greenland, Antarctica), possible ice-flow instabilities (in particular on the West Antarctic Ice Sheet), and thermal expansion of ocean water.For a given temperature scenario, an attempt is made to estimate the different contributions. The calculation yields a figure of 9.5 cm of sea-level rise since 1850 AD, which is within the uncertainty range of estimates of the observed rise.A further 33 cm rise is found as most likely for the year 2050, but the uncertainty is very large ( = 32 cm). The contribution from melting of land ice is of the same order of magnitude as thermal expansion. The mass-balance effects of the major ice sheets tend to cancel to some extent (increasing accumulation on Antarctica, increasing ablation on Greenland). For the year 2100 a value of 66 cm above the present-day stand is found ( = 57 cm). The estimates of the standard deviation include uncertainty in the temperature scenario, as presented elsewhere in this volume.  相似文献   

Reply to discussion of “The Azuara impact structure (Spain): new insights from geophysical and geological investigations” by K. Ernstson and J. Fiebag     

Kord Ernstson  Johannes Fiebag 《International Journal of Earth Sciences》1993,82(4):756-759

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Blockage of regional seismic waves by the Teisseyre-Tornquist zone   总被引：1，自引：0，他引：1  

Johannes Schweitzer 《Geophysical Journal International》1995,123(1):260-276

During the Group of Scientific Experts Technical Test (GSETT, second experiment, 22 April-2 June 1991), several hundred seismic events were located in Europe. Associating these events with the detecting stations-altogether 28 European stations including seven arrays participated in the GSETT-2 experiment-clearly shows that the Teisseyre-Tornquist Zone (TTZ) influences the propagation of regional seismic phases. Large explosions in the Bay of Gdańsk, for example, were observed by the well-established Scandinavian arrays'NORSAR (Δ 830km) and ARCESS (Δ 1650km), but not by the Polish station KSP (Δ 470km) nor by the new highly sensitive GERESS array (Δ 750km), both situated south-west of the TTZ. For events in central Europe with comparable magnitudes, we observe a similar increase of the detection threshold at stations located north-east of the TTZ in Scandinavia. to explain these observations, the wave propagation of P_n and P_g perpendicular to the TTZ was modelled for a profile from the Estonian/Russian border region to GERESS with Gaussian-beam seismograms. Published crustal and uppermost mantle models for Poland and for Europe were used as a starting point for developing a model of the TTZ. the observations cannot be explained only by a graben-like crustal structure with a jump in Moho depth from 30km to 50km. to defocus the seismic energy, the TTZ as a structural anomaly between eastern and western Europe must reach down into the upper mantle to a depth of at least about 200 km. the proposed model has such a deep-reaching root of the TTZ.  相似文献   

Hydrophobic and electrostatic parameters in bacterial adhesion   总被引：5，自引：0，他引：5  

Mark C. M. van Loosdrecht  Willem Norde  Johannes Lyklema  Alexander J. B. Zehnder 《Aquatic Sciences - Research Across Boundaries》1990,52(1):103-114

Recently it has been shown that the initial stages of bacterial adhesion to a model-surface of sulphated polystyrene can best be described using hydrophobic and electrostatic parameters. In the present study it is tested whether these parameters can generally be applied to predict bacterial adhesion by using (i) glass, as a model for hydrophilic and natural surfaces of silicates and oxides, (ii) polystyrene coated with proteins, as a model for a surface coated with an organic layer, and (iii) river Rhine sediment, as an example of a natural surface. Adhesion to glass was dominated by electrostatic interaction, whereas adhesion to polystyrene coated with various types of proteins depended on the surface characteristics of the bacteria and the type of protein. By relating Van der Waals interactions to hydrophobicity of the interacting species, the adhesion of bacteria to the various surfaces including the river Rhine sediments could be interpreted in terms of the DLVO-theory. It is therefore concluded that the conceptual principles of the DLVO-theory (interplay of Van der Waals and electrostatic interactions) are suitable to describe, at least qualitatively, the initial processes of bacterial adhesion to a wide range of surfaces.  相似文献