scholarly journals Internal seiches in a karstic mesotrophic lake (Prošće, Plitvice Lakes, Croatia)

Geofizika ◽  
2020 ◽  
Vol 37 (2) ◽  
pp. 157-179
Author(s):  
Zvjezdana B. Klaić ◽  
Karmen Babić ◽  
Tomislav Mareković
Keyword(s):  
Observational Period ◽  
Vertical Temperature ◽  
Power Spectral ◽  
Power Spectral Densities ◽  
Second Mode ◽  
Temperature Experiment ◽  
Lake Temperature ◽  
Internal Seiches ◽  
Insight Into ◽  
Plitvice Lakes

A lake temperature experiment was performed at the Prošće, Plitvice Lakes, Croatia during a 4-month observational period (6 July–4 November, 2019) to investigate the occurrence and characteristics of internal seiches in the lake. Two-minute mean lake temperatures were measured at a single lake point at fifteen depths ranging from 0.2 to 27 m. Analysis of these data provided insight into the previously unknown and rather complex Prošće Lake seiching. Power spectral densities (PSDs) and magnitude-squared coherences (γ2), together with corresponding cross-spectrum phases that were obtained from the hourly mean lake temperature, air pressure and wind speed data, suggested the presence of three vertical modes of an internal seiche. The first mode (V1H1, period of 6.09 h) corresponds to free baroclinic oscillations; the second mode (V2H1, period of 11.64 h) and the third mode (V3H1, period of 25.60 h) are associated with forced baroclinic oscillations of the lake interior. Excitation of the higher vertical modes is attributed to the influence of dense tributary water. Due to this water influence, vertical temperature gradients in the lake interior were relatively weak; consequently, a single thick metalimnion and/or two metalimnetic layers were established, which resulted in the presence of the V2H1 and V3H1 modes, respectively. Additionally, due to the influence of tributary water, the lake did not attain the typical stratification that is characterized by hypolimnetic temperatures of ≈ 4°C. Instead, during the entire observational period, the hypolimnetic temperatures were consistently above 7.6 °C.

Modal Analysis of a Utility Bicycle From the Perspective of Riding Comfort

2019 ◽  
Author(s):  
Alberto Doria ◽  
Edoardo Marconi ◽  
Pierluca Cialoni
Keyword(s):  
Modal Testing ◽  
Vibration Modes ◽  
Response Functions ◽  
The Road ◽  
Power Spectral ◽  
Vehicle Structure ◽  
Power Spectral Densities ◽  
On The Road ◽  
The Relationship ◽  
Insight Into

Abstract The correlation between the modal properties and the comfort characteristics of a utility, step-through frame bicycle are investigated. In-plane modal testing of the vehicle is carried out both without and with the rider, and the major differences between the results obtained with the two conditions are highlighted. In order to have an insight into the contribution of the various bicycle components to the transmission of vibrations, the frequency response functions (FRFs) between the main interface points in the vehicle structure are measured and studied. Finally, the modal characteristics are compared with road tests data, emphasizing the relationship between the in-plane vibration modes and the main peaks in the acceleration power spectral densities (PSDs) measured on the road.

scholarly journals Evolution and dynamics of the vertical temperature profile in an oligotrophic lake

2020 ◽  
Author(s):  
Zvjezdana B. Klaić ◽  
Karmen Babić ◽  
Mirko Orlić
Keyword(s):  
Air Temperature ◽  
Heat Fluxes ◽  
Temperature Pattern ◽  
Lake Surface ◽  
Observational Period ◽  
Vertical Temperature Profile ◽  
Near Surface ◽  
Lake Temperature ◽  
Internal Seiches ◽  
Continuous Heat

Abstract. Abstract. In this study, the fine-scale responses of a stratified oligotrophic karstic lake (Kozjak, Plitvice Lakes, Croatia; lake fetch is 2.3 km and maximum depth is 46 m) to atmospheric forcings on the lake surface are investigated. Lake temperatures measured at a resolution of 2 min at 15 depths ranging from 0.2 to 43 m, which were observed during the 6 July–5 November 2018 period were analyzed. The results show thermocline deepening from 10 m at the beginning, to 16 m at the end of the observational period, where the latter corresponds to approximately one third of the lake depth. The pycnocline followed the same pattern, except that the deepening occurred throughout the entire period approximately 1 m above the thermocline. On average, thermocline deepening was 3–4 cm per day, while the maximum deepening (12.5 cm per day) coincided with the occurrence of internal seiches. Furthermore, the results indicate three different types of forcings on the lake surface, and two of these forcings have diurnal periodicity: (1) continuous heat fluxes and (2) occasional periodic stronger winds, while the (3) forcing corresponds to occasional nonperiodic stronger winds with along the basin-steady directions. Continuous heat fluxes (1) produced forced diurnal oscillations in the lake temperature within the first 5 meters of the lake throughout the entire observational period. Noncontinuous periodic stronger winds (2) resulted in occasional forced diurnal oscillations in the lake temperatures at depths from approximately 7 to 20 m. Occasional steady along-the-basin stronger winds (3) triggered both, baroclinic internal seiches with a principal period of 8.0 h, and, barotropic surface seiches with a principal period of 9 min. Lake currents produced by the surface seiches under realistic-topography conditions generated baroclinic oscillations of the thermocline region (at depths of 9–17 m) with periods corresponding to the period of surface seiches (≈ 9 min), which to our knowledge, has not been reported in previous lake studies. Finally, a simple multiple linear regression model of the near-surface temperature (0.2 m), which depends on the air temperature and wind speed, can only be used as a rough estimate of the daily mean lake temperature under weak wind and undisturbed air temperature pattern conditions.

scholarly journals Evolution and dynamics of the vertical temperature profile in an oligotrophic lake

2020 ◽  
Vol 24 (7) ◽  
pp. 3399-3416
Author(s):  
Zvjezdana B. Klaić ◽  
Karmen Babić ◽  
Mirko Orlić
Keyword(s):  
Heat Fluxes ◽  
Lake Surface ◽  
Vertical Temperature ◽  
Vertical Temperature Profile ◽  
Different Types ◽  
Lake Temperature ◽  
Realistic Topography ◽  
Internal Seiches ◽  
Continuous Heat ◽  
Observation Period

Abstract. In this study, the fine-scale responses of a stratified oligotrophic karstic lake (Kozjak Lake, Plitvice Lakes, Croatia; the lake fetch is 2.3 km, and the maximum depth is 46 m) to atmospheric forcing on the lake surface are investigated. Lake temperatures measured at a resolution of 2 min at 15 depths ranging from 0.2 to 43 m, which were observed during the 6 July–5 November 2018 period, were analyzed. The results show thermocline deepening from 10 m at the beginning of the observation period to 16 m at the end of the observation period, where the latter depth corresponds to approximately one-third of the lake depth. The pycnocline followed the same pattern, except that the deepening occurred throughout the entire period approximately 1 m above the thermocline. On average, thermocline deepening was 3–4 cm d−1, while the maximum deepening (12.5 cm d−1) coincided with the occurrence of internal seiches. Furthermore, the results indicate three different types of forcings on the lake surface; two of these forcings have diurnal periodicity – (1) continuous heat fluxes and (2) occasional periodic stronger winds – whereas forcing (3) corresponds to occasional nonperiodic stronger winds with steady along-basin directions. Continuous heat fluxes (1) produced forced diurnal oscillations in the lake temperature within the first 5 m of the lake throughout the entire observation period. Noncontinuous periodic stronger winds (2) resulted in occasional forced diurnal oscillations in the lake temperatures at depths from approximately 7 to 20 m. Occasional strong and steady along-basin winds (3) triggered both baroclinic internal seiches with a principal period of 8.0 h and barotropic surface seiches with a principal period of 9 min. Lake currents produced by the surface seiches under realistic-topography conditions generated baroclinic oscillations of the thermocline region (at depths from 9 to 17 m) with periods corresponding to the period of surface seiches (≈ 9 min), which, to the best of our knowledge, has not been reported in previous lake studies.

Analysis of power spectral densities of electrocardiograms

1971 ◽  
Vol 12 (1-2) ◽  
pp. 41-51 ◽  
Author(s):  
Vrudhula K. Murthy ◽  
L. Julian Haywood ◽  
John Richardson ◽  
Robert Kalaba ◽  
Steven Salzberg ◽  
...  
Keyword(s):  
Spectral Densities ◽  
Power Spectral ◽  
Power Spectral Densities

scholarly journals Delta and Theta waves in Super Consciousness Meditation.

2020 ◽  
Author(s):  
Anil Kumar Bheemaiah
Keyword(s):  
Average Power ◽  
Spectral Densities ◽  
Theta Wave ◽  
Convolutional Networks ◽  
Theta Waves ◽  
Power Spectral ◽  
Power Spectral Densities ◽  
Lyapunov Coefficient ◽  
Fmri Time Series ◽  
Power Densities

Study on Kundalini Meditation of Super-conscious Meditation of the Himalayan Tradition and Sahaja Meditation, to determine the average power spectral densities and power ratios of TP9, AF7, AF8, and TP10, electrodes and two ear electrodes on a Muse Headset.These parameters are used to create quantitative criteria to indicate degree of meditation and to create a trigger for bird chirp events.We find an increase in Delta and Theta wave power densities, in the deep meditation state as compared to the initiation and restful states. keywords: Kundalini, super consciousness, neurosky, muse, chakra based meditation, alpha to beta ratio, delta to beta ratio, power spectral densities, differential power spectral densities, fMRi, time series, iD convolutional networks. Lyapunov coefficient

scholarly journals Differences Amplitude Based Improvement of Minimum Variance Distortionless Response Filter

2020 ◽  
Vol 8 (5) ◽  
pp. 1635-1637
Keyword(s):  
A Priori ◽  
Minimum Variance ◽  
Coherent Noise ◽  
Noise Interference ◽  
Power Spectral ◽  
Minimum Variance Distortionless Response ◽  
Power Spectral Densities ◽  
Noisy Signals ◽  
A New Technique ◽  
Priori Information

In this work, the author introduces a new technique for improving the performance of minimum variance distortionless response filter in condition of coherent noise. The proposal algorithm exploits a priori information of differences amplitude to balance power spectral densities of observed noisy signals. The output signal of MVDR filter is then processed by an additional post-filtering, which based speech presence probability to suppress more noise interference and increase quality speech. In experiments using two noisy signal recordings in anechoeic room, the modified MVDR-filter results provides that the suggested algorithm increases speech quality compared to the conventional MVDR filter.

Analysis of earth motions and seismic sources by power spectral density

1969 ◽  
Vol 59 (3) ◽  
pp. 1071-1091
Author(s):  
Dean V. Power
Keyword(s):  
Spectral Density ◽  
Power Spectral Density ◽  
High Explosive ◽  
Peak Velocity ◽  
Test Site ◽  
Nevada Test Site ◽  
Spectral Densities ◽  
Power Spectral ◽  
Power Spectral Densities ◽  
Velocity Spectra

abstract Ground motion records from six high-explosive cratering events in northeastern Montana, ten contained nuclear explosive events at the Nevada Test Site, and motions of an earth-fill dam during the Gasbuggy underground nuclear explosion in New Mexico were analyzed for power spectral density, peak velocity and velocity spectra. The high-explosive events included four 20-ton single charges at depths of burst which varied between 42 to 57 feet, a 140-ton row charge consisting of three 20-ton and two 40-ton charges at optimum cratering depths of burst, and a 0.5-ton charge at the optimum depth of burst. It was found that at these depths and charge weights an increase in depth of burst resulted in an increase in peak velocities and power-spectral densities as measured at distant points (> 5 km). Power spectral density was found to be approximately proportional to the first power of yield. For this region it was determined that power spectral density varied inversely as radial distance to the 3.55 power. Three analysis techniques—peak velocity, velocity spectra and power spectral density—are compared, and it is shown that power spectral density is the most consistent method when comparing records from different measuring stations. An analysis of power-spectral density measured at one station for the ten events at the Nevada Test Site shows that a significant shift in the frequency of the energy in the seismogram occurs when the source location changes. For events in the Yucca Flat area the peak energy at Mercury was consistently at 1.0 Hz, while for events in the Pahute Mesa area this peak occurs at 2.5 Hz. A comparison of the power spectral densities on and near the Navajo Dam revealed that the natural frequencies and first harmonics of the dam are 1.4, 2.0 and 2.5 Hz in the mode where motion is parallel to the canyon axis. A simple model makes use of these frequencies to calculate a shear-wave velocity of 1130 ft/sec. A method of using power spectral density to measure earthquake magnitudes and measure the yield of underground explosions is proposed.

Using COVID19 as an Opportunity to Measure Seismic Silences and Bring Geoscience Projects to Students

2021 ◽  
Author(s):  
Artash Nath
Keyword(s):  
Northwest Territories ◽  
World Health ◽  
Virtual Classrooms ◽  
Power Spectral ◽  
Essential Services ◽  
Power Spectral Densities ◽  
The World ◽  
Seismic Vibrations ◽  
Health Organization ◽  
Almost All

<p>On 11 March 2020, the World Health Organization declared Covid19 a pandemic. Countries around the world rushed to declare various states of emergencies. Canada also implemented emergency measures to restrict the movements of people including the closure of borders, non-essential services, and schools and offices to slow the spread of Covid19. I used this opportunity to measure changes in seismic vibrations registered in Canada before, during, and after the lockdown due to the slowdown in transportation, economic, and construction activities. I analyzed continuous seismic data for 6 Canadian cities: Calgary and Edmonton (Alberta), Montreal (Quebec), Ottawa, and Toronto (Ontario), and Yellowknife (Northwest Territories). These cities represented the wide geographical spread of Canada. The source of data was seismic stations run by the Canadian National Seismograph Network (CNSN). Python and ObSpy libraries were used to convert raw data into probabilistic power spectral densities. The seismic vibrations in the PPSDs that fell between 4 Hz and 20 Hz were extracted and averaged for every two weeks period to determine the trend of seismic vibrations. The lockdown had an impact on seismic vibrations in almost all the cities I analyzed. The seismic vibrations decreased between 14% - 44% with the biggest decrease in Yellowknife in the Northwest Territories. In the 3 densely populated cities with a population of over 1 million - Toronto, Montreal, and Calgary, the vibrations dropped by over 30%.</p><p>To enable other students to undertake similar projects for their cities, I created a comprehensive online training module using Jupyter notebooks available on Github. Students can learn about seismic vibrations, how to obtain datasets, and analyze and interpret them using Python. They can share their findings with local policymakers so that they become aware of the effectiveness of the lockdown imposed and are better prepared for lockdowns in the future. When we make data and technology accessible, then lockdowns because of pandemics can be an opportunity for students to take up practical geoscience projects from home or virtual classrooms.</p>

scholarly journals EOG feature relevance determination for microsleep detection

2017 ◽  
Vol 3 (2) ◽  
pp. 815-818
Author(s):  
Martin Golz ◽  
Sebastian Wollner ◽  
David Sommer ◽  
Sebastian Schnieder
Keyword(s):  
Cross Correlation ◽  
Feature Reduction ◽  
Support Vector ◽  
Spectral Bands ◽  
Automatic Relevance Determination ◽  
Signal Features ◽  
Power Spectral ◽  
Vector Machines ◽  
Power Spectral Densities ◽  
Feature Relevance

AbstractAutomatic relevance determination (ARD) was applied to two-channel EOG recordings for microsleep event (MSE) recognition. 10 s immediately before MSE and also before counterexamples of fatigued, but attentive driving were analysed. Two type of signal features were extracted: the maximum cross correlation (MaxCC) and logarithmic power spectral densities (PSD) averaged in spectral bands of 0.5 Hz width ranging between 0 and 8 Hz. Generalised learn-ing vector quantisation (GRLVQ) was used as ARD method to show the potential of feature reduction. This is compared to support-vector machines (SVM), in which the feature reduction plays a much smaller role. Cross validation yielded mean normalised relevancies of PSD features in the range of 1.6 - 4.9 % and 1.9 - 10.4 % for horizontal and vertical EOG, respectively. MaxCC relevancies were 0.002 - 0.006 % and 0.002 - 0.06 %, respectively. This shows that PSD features of vertical EOG are indispensable, whereas MaxCC can be neglected. Mean classification accuracies were estimated at 86.6±b 1.3 % and 92.3±b 0.2 % for GRLVQ and SVM, respec-tively. GRLVQ permits objective feature reduction by inclu-sion of all processing stages, but is not as accurate as SVM.

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