The surface seiches of Lake of Lugano

A computational analysis of the periods and structure of surface seiches of the southern basin of Lake of Lugano and its experimental verification from three simultaneous water gauge recordings, mounted along the shores in Agno, Morcote and Riva S. Vitale, is given. The first five theoretical modes are calculated with a finite element code of the tidal equations; it yields the eigenperiods and co-range and co-tidal lines, which are graphically displayed and discussed in detail. Experimental verification is from recordings taken during February/March 1982. Inspection by eye allows identification of the five lowest order modes, partly including interstation phase shift. Power spectral analysis of three-time series and interstation phase difference and coherence spectra allow identification of higher order modes, probably up to order 13. Agreement between the theoretically predicted and the experimentally determined periods is excellent for all calculated modes. Computational results for the four lowest modes and their structure of the northern basin of Lake of Lugano are also presented and experimentally verified with records taken from an event in August 1979. Agreement is again excellent.     

Movement patterns of an endemic South African sparid,the black musselcracker Cymatoceps nasutus,determined using mark-recapture methods

This study made use of data from three long-term fish tagging projects along the South African coastline to investigate the movement behaviour of the endemic black musselcracker Cymatoceps nasutus (Sparidae). From 1984 to 2016, a total of 3 430 C. nasutus (178–980 mm fork length) were tagged (with small plastic dart tags) throughout the species’ distributional range, with an overall reported recapture rate of 7.2%. Recaptured individuals displayed high levels of residency, moving an average of 14.8 km, with time-at-liberty ranging from 0 to 6 809 days. The majority of recaptures (84.6%) were made within 1 km of the tagging sites; however, some large-scale movements, of up to 528 km, were recorded. Although C. nasutus individuals moving greater distances were characterised by greater mean sizes (mm fork length) at time of recapture, the distances moved by juveniles were not significantly different from those of adults (p > 0.05). Low levels of connectivity among coastal regions were therefore expected due to the high degree of residency displayed by this species. Combining traditional management approaches together with a well-designed network of no-take marine protected areas is likely to be the most effective way to protect this vulnerable species. A lack of data on the movements of adults remains a challenge, but this could be overcome by tracking large individuals tagged with long-life acoustic transmitters.     

Wucherungen von Cyanophyceen an den Ufern des Zürichsees und deren Ursachen

Ohne Zusammenfassung Nach einem Referat, gehalten am I. Internationalen Cyanophyceen-Symposium in Luzern, Kastanienbaum, 29.8.-3.9. 60.     

Wavelet-based response spectrum compatible synthesis of accelerograms—Eurocode application (EC8)

An integrated approach for addressing the problem of synthesizing artificial seismic accelerograms compatible with a given displacement design/target spectrum is presented in conjunction with aseismic design applications. Initially, a stochastic dynamics solution is used to obtain a family of simulated non-stationary earthquake records whose response spectrum is on the average in good agreement with the target spectrum. The degree of the agreement depends significantly on the adoption of an appropriate parametric evolutionary power spectral form, which is related to the target spectrum in an approximate manner. The performance of two commonly used spectral forms along with a newly proposed one is assessed with respect to the elastic displacement design spectrum defined by the European code regulations (EC8). Subsequently, the computational versatility of the family of harmonic wavelets is employed to modify iteratively the simulated records to satisfy the compatibility criteria for artificial accelerograms prescribed by EC8. In the process, baseline correction steps, ordinarily taken to ensure that the obtained accelerograms are characterized by physically meaningful velocity and displacement traces, are elucidated. Obviously, the presented approach can be used not only in the case of the EC8, for which extensive numerical results/examples are included, but also for any code provisions mandated by regulatory agencies. In any case, the presented numerical results can be quite useful in any aseismic design process dominated by the EC8 specifications.     

Reflection on the first five years of South Africa’s Acoustic Tracking Array Platform (ATAP): status,challenges and opportunities

The Acoustic Tracking Array Platform (ATAP) is a marine science programme that monitors the movements and migrations of inshore marine animals along the South African coastline. Acoustically tagged animals are monitored by an expanded network of approximately 100 automated data-logging acoustic receivers moored at strategic node sites, from Cape Point in the west to the South Africa–Mozambique border in the east. During five years since its inception, in 2011, the ATAP has achieved outstanding progress in terms of the numbers of animals and the variety of species tagged. To date, the ATAP has yielded over 2.6 million detections from more than 700 acoustically tagged animals, representing 27 different species from 20 families, including the African penguin Spheniscus demersus, fishery-at-risk species (e.g. dusky kob Argyrosomus japonicus) and iconic elasmobranchs (e.g. white shark Carcharodon carcharias). Following a period of considerable equipment loss in 2014, refinement of the receiver network was required and the deeper receivers at each site were decommissioned without influencing the integrity of the nationwide array. The platform, managed by the South African Institute for Aquatic Biodiversity, ultimately represents a low-cost method of collecting long-term data that currently benefits approximately 25 researchers from 14 organisations. Case studies are presented to expose the opportunities provided by the ATAP, which will undoubtedly yield new discoveries and provide a greater understanding of the movement patterns and migrations of a wide variety of inshore marine and estuary-associated species.     

Objective climatology of 500-hPa cyclones in central and east mediterranean region during warm-dry period of the year

Summary ¶An Objective 500-hPa cyclone detection and analysis is performed during the warm-dry period (16 April to 15 October) of the year for the Central and Eastern Mediterranean Region (30°N–50°N, 5°E–35°E). The 40-year NCEP/NCAR reanalyzes gridded data of geopotential height and temperature employed in the study, enable a climatic approach with a spatial (2.5°×2.5°) and a 6-hour temporal (00, 06, 12, 18 UTC) resolution. The occurrence frequency for the entire region shows a high interannual variability without significant trends. The frequency maximization over land in the middle of the warm period indicates a possible relationship with land-air temperature difference. Three primary activity centers (Turkey, Black Sea and Genoa) are objectively determined in the frequency domain as local maxima and their intensity is assessed in terms of average geopotential height and temperature values. The Turkey center, though the most frequent, consists of shallow lows in contrast to the Black Sea center, which is second in frequency, but on average, contains the deepest lows amongst the three. The Genoa center, which comes third in frequency, shows the highest variability in the intensity of the lows. Frequency distributions in the area, during the three sub periods (Early, Middle and Late Warm Period) and during the four synoptic hours, provide insight in to the origins of these systems at the three locations and reveal secondary centers, such as the centers in the Adriatic (at 18 UTC), Northern Greece (during Middle Warm Period) and the South Aegean Sea (during Late Warm Period).Received February 20, 2002; revised November 4, 2002; accepted January 16, 2003 Published online July 30, 2003     

Deterministic and stochastic analyses of a nonlinear system with a Biot visco‐elastic element

In the paper the Biot hysteretic model involving an infinite collection of elements whose dynamic characteristics are specified through a probability density‐like function is re‐examined; in the limit case, the Biot model yields a dynamic system with ideal hysteretic damping which is known to be problematic for random vibration analysis. It is shown that bona fide Monte Carlo simulations can be conducted for the Biot model by treating, cautiously, the integrodifferential equation which is involved; this is based on recursive calculations of double integrals encountered in the representation of the system dynamics. The numerical results which pertain to the Monte Carlo studies are further used to assess the accuracy of a statistical linearization procedure adopted in determining the response of the hysteretically damped system to white noise. Published in 2001 by John Wiley & Sons, Ltd.     

Optimality in the estimation of a MA system from a long AR model for simulation studies

The determination of moving average (MA) models from a prior autoregressive (AR) approximation of a specified (target) spectral matrix is addressed; this is done in context with the need to simulate ground shaking and other natural phenomena as multivariate random processes. First, an existing technique based on a direct modeling of the target expression is revisited. In this regard, the influence of the order of the prior AR approximation, and the number of its harmonics used in the determination of the MA model, is described. Further, a simple selection technique of these parameters is presented that leads to an optimum MA approximation. Next, the relationship between a method based on the Cholesky factorization of the coveriance matrix and the present technique is investigated to derive additional insight into its convergence properties. Finally, an alternative modeling technique based on an AR representation of the inverse of the target spectral matrix is presented.     

Synthesis of accelerograms compatible with the Chinese GB 50011-2001 design spectrum via harmonic wavelets： artificial and historic records

A versatile approach is employed to generate artificial accelerograms which satisfy the compatibility criteria prescribed by the Chinese aseismic code provisions GB 50011-2001. In particular, a frequency dependent peak factor derived by means of appropriate Monte Carlo analyses is introduced to relate the GB 50011 -2001 design spectrum to a parametrically defined evolutionary power spectrum (EPS). Special attention is given to the definition of the frequency content of the EPS in order to accommodate the mathematical form of the aforementioned design spectrum. Further, a one-to-one relationship is established between the parameter controlling the time-varying intensity of the EPS and the effective strong ground motion duration. Subsequently, an efficient auto-regressive moving-average (ARMA) filtering technique is utilized to generate ensembles of non-stationary artificial accelerograms whose average response spectrum is in a close agreement with the considered design spectrum. Furthermore, a harmonic wavelet based iterative scheme is adopted to modify these artificial signals so that a close matching of the signals' response spectra with the GB 50011-2001 design spectrum is achieved on an individual basis. This is also done for field recorded accelerograms pertaining to the May, 2008 Wenchuan seismic event. In the process, zero-phase high-pass filtering is performed to accomplish proper baseline correction of the acquired spectrum compatible artificial and field accelerograms. Numerical results are given in a tabulated format to expedite their use in practice.