scholarly journals Investigation of the Relationship Between the Yucatan Channel Transport and the Loop Current Area in a Multidecadal Numerical Simulation

2014 ◽  
Vol 48 (4) ◽  
pp. 15-26 ◽  
Author(s):  
Robert Nedbor-Gross ◽  
Dmitry S. Dukhovskoy ◽  
Mark A. Bourassa ◽  
Steven L. Morey ◽  
Eric P. Chassignet
Keyword(s):  
High Frequency ◽  
Time Derivative ◽  
Low Frequency ◽  
Strong Relationship ◽  
Ocean Model ◽  
Rate Of Change ◽  
Loop Current ◽  
Data Set ◽  
Florida Straits ◽  
Yucatan Channel

Abstract A hypothesis by Maul (1977), stating the rate of change of loop current (LC) volume is related to deep Yucatan Channel (YC) transport, is tested with a continuous 54-year simulation of the Gulf of Mexico (GoM) using a regional 1/25° resolution Hybrid Coordinate Ocean Model (HYCOM) configuration. The hypothesis states that the imbalance of transport between the upper YC and the Florida Straits controls the rate of change of the LC volume and that the imbalance is compensated by transport through the deep YC. Bunge et al. (2002) found a strong relationship between the deep YC transport and the LC area using 7.5 months of data from a mooring array in the YC, but the observational record length was relatively short compared to the time scale of LC variability. The 54-year HYCOM simulation provides a much longer and spatially complete data set to study the LC variability. Results show that the time evolution of the LC between two shedding events can be viewed as a combination of relatively high-frequency fluctuations superimposed on a low-frequency trend. The high-frequency variability of the LC area time derivative and the deep YC transport are related. The low-frequency variability is examined by comparing the LC area time series with time-integrated transport in the deep YC, and statistically similar trends are identified, supporting the Maul (1977) theory.

scholarly journals Intrinsic variability of the Antarctic Circumpolar Current system: low- and high-frequency fluctuations of the Argentine Basin flow

Ocean Science ◽  
2014 ◽  
Vol 10 (2) ◽  
pp. 201-213 ◽  
Author(s):  
G. Sgubin ◽  
S. Pierini ◽  
H. A. Dijkstra
Keyword(s):  
High Frequency ◽  
Antarctic Circumpolar Current ◽  
Current System ◽  
Low Frequency ◽  
Drake Passage ◽  
Ocean Model ◽  
Intrinsic Variability ◽  
Circumpolar Current ◽  
The Antarctic ◽  
Argentine Basin

Abstract. In this paper, the variability of the Antarctic Circumpolar Current system produced by purely intrinsic nonlinear oceanic mechanisms is studied through a sigma-coordinate ocean model, implemented in a large portion of the Southern Ocean at an eddy-permitting resolution under steady surface heat and momentum fluxes. The mean transport through the Drake Passage and the structure of the main Antarctic Circumpolar Current fronts are well reproduced by the model. Intrinsic variability is found to be particularly intense in the Subantarctic Front and in the Argentine Basin, on which further analysis is focused. The low-frequency variability at interannual timescales is related to bimodal behavior of the Zapiola Anticyclone, with transitions between a strong and collapsed anticyclonic circulation in substantial agreement with altimeter observations. Variability on smaller timescales shows clear evidence of topographic Rossby-wave propagation along the eastern and southern flanks of the Zapiola Rise and of mesoscale eddies, also in agreement with altimeter observations. The analysis of the relationship between the low- and high-frequency variability suggests possible mechanisms of mutual interaction.

scholarly journals Alternating (AC) Loop Current Attacks Against the KLJN Secure Key Exchange Scheme

2021 ◽  
pp. 2150050
Author(s):  
Mutaz Y. Melhem ◽  
Christiana Chamon ◽  
Shahriar Ferdous ◽  
Laszlo B. Kish
Keyword(s):  
Electromagnetic Interference ◽  
High Frequency ◽  
Practical Importance ◽  
Low Frequency ◽  
Key Exchange ◽  
Power Density Spectrum ◽  
Voltage Source ◽  
Loop Current ◽  
Johnson Noise ◽  
Density Spectrum

Recently, several passive and active attack methods have been proposed against the Kirchhoff–Law–Johnson–Noise (KLJN) secure key exchange scheme by utilizing direct (DC) loop currents. The DC current attacks are relatively easy, but their practical importance is low. On the other hand, parasitic alternating (AC) currents are virtually omnipresent in wire-based systems. Such situations exist due to AC ground loops and electromagnetic interference (EMI). However, utilizing AC currents for attacks is a harder problem. Here, we introduce and demonstrate AC current attacks in various frequency ranges. The attacks exploit a parasitic/periodic AC voltage-source at either Alice’s or Bob’s end. In the low-frequency case, the procedure is the generalized form of the former DC ground-loop-based attack. In the high-frequency case, the power density spectrum of the wire voltage is utilized. The attack is demonstrated in both the low and the high-frequency situations. Defense protocols against the attack are also discussed.

scholarly journals Loop Current Variability as Trigger of Coherent Gulf Stream Transport Anomalies

2019 ◽  
Vol 49 (8) ◽  
pp. 2115-2132 ◽  
Author(s):  
Joël J.-M. Hirschi ◽  
Eleanor Frajka-Williams ◽  
Adam T. Blaker ◽  
Bablu Sinha ◽  
Andrew Coward ◽  
...  
Keyword(s):  
Gulf Of Mexico ◽  
Gulf Stream ◽  
Time Lag ◽  
Ocean Model ◽  
Surface Velocity ◽  
Loop Current ◽  
Intrinsic Variability ◽  
Cape Hatteras ◽  
Florida Straits ◽  
Stream Transport

AbstractSatellite observations and output from a high-resolution ocean model are used to investigate how the Loop Current in the Gulf of Mexico affects the Gulf Stream transport through the Florida Straits. We find that the expansion (contraction) of the Loop Current leads to lower (higher) transports through the Straits of Florida. The associated surface velocity anomalies are coherent from the southwestern tip of Florida to Cape Hatteras. A simple continuity-based argument can be used to explain the link between the Loop Current and the downstream Gulf Stream transport: as the Loop Current lengthens (shortens) its path in the Gulf of Mexico, the flow out of the Gulf decreases (increases). Anomalies in the surface velocity field are first seen to the southwest of Florida and within 4 weeks propagate through the Florida Straits up to Cape Hatteras and into the Gulf Stream Extension. In both the observations and the model this propagation can be seen as pulses in the surface velocities. We estimate that the Loop Current variability can be linked to a variability of several Sverdrups (1Sv = 106 m3 s−1) through the Florida Straits. The exact timing of the Loop Current variability is largely unpredictable beyond a few weeks and its variability is therefore likely a major contributor to the chaotic/intrinsic variability of the Gulf Stream. However, the time lag between the Loop Current and the flow downstream of the Gulf of Mexico means that if a lengthening/shortening of the Loop Current is observed this introduces some predictability in the downstream flow for a few weeks.

scholarly journals Postoperative seizure outcome-guided machine learning for interictal electrocorticography in neocortical epilepsy

2018 ◽  
Vol 119 (6) ◽  
pp. 2265-2275 ◽  
Author(s):  
Seong-Cheol Park ◽  
Chun Kee Chung
Keyword(s):  
Machine Learning ◽  
Free Group ◽  
High Frequency ◽  
Low Frequency ◽  
Outcome Data ◽  
Training Data ◽  
Seizure Outcome ◽  
Data Set ◽  
Neocortical Epilepsy ◽  
Postoperative Seizure

The objective of this study was to introduce a new machine learning guided by outcome of resective epilepsy surgery defined as the presence/absence of seizures to improve data mining for interictal pathological activities in neocortical epilepsy. Electrocorticographies for 39 patients with medically intractable neocortical epilepsy were analyzed. We separately analyzed 38 frequencies from 0.9 to 800 Hz including both high-frequency activities and low-frequency activities to select bands related to seizure outcome. An automatic detector using amplitude-duration-number thresholds was used. Interictal electrocorticography data sets of 8 min for each patient were selected. In the first training data set of 20 patients, the automatic detector was optimized to best differentiate the seizure-free group from not-seizure-free-group based on ranks of resection percentages of activities detected using a genetic algorithm. The optimization was validated in a different data set of 19 patients. There were 16 (41%) seizure-free patients. The mean follow-up duration was 21 ± 11 mo (range, 13–44 mo). After validation, frequencies significantly related to seizure outcome were 5.8, 8.4–25, 30, 36, 52, and 75 among low-frequency activities and 108 and 800 Hz among high-frequency activities. Resection for 5.8, 8.4–25, 108, and 800 Hz activities consistently improved seizure outcome. Resection effects of 17–36, 52, and 75 Hz activities on seizure outcome were variable according to thresholds. We developed and validated an automated detector for monitoring interictal pathological and inhibitory/physiological activities in neocortical epilepsy using a data-driven approach through outcome-guided machine learning. NEW & NOTEWORTHY Outcome-guided machine learning based on seizure outcome was used to improve detections for interictal electrocorticographic low- and high-frequency activities. This method resulted in better separation of seizure outcome groups than others reported in the literature. The automatic detector can be trained without human intervention and no prior information. It is based only on objective seizure outcome data without relying on an expert’s manual annotations. Using the method, we could find and characterize pathological and inhibitory activities.

Output Power Correlation Between Adjacent Wind Power Plants*

2003 ◽  
Vol 125 (4) ◽  
pp. 551-555 ◽  
Author(s):  
Yih-huei Wan ◽  
Michael Milligan ◽  
Brian Parsons
Keyword(s):  
Power Plant ◽  
Wind Power ◽  
High Frequency ◽  
Power Plants ◽  
Meteorological Data ◽  
Low Frequency ◽  
Spatial Separation ◽  
Rate Of Change ◽  
Wind Power Plant ◽  
Wind Power Plants

The National Renewable Energy Laboratory (NREL) started a project in 2000 to record long-term, high-frequency (1-Hz) wind power data from large commercial wind power plants in the Midwestern United States. Outputs from about 330 MW of installed wind generating capacity from wind power plants in Lake Benton, MN, and Storm Lake, Iowa, are being recorded. Analysis of the collected data shows that although very short-term wind power fluctuations are stochastic, the persistent nature of wind and the large number of turbines in a wind power plant tend to limit the magnitude of fluctuations and rate of change in wind power production. Analyses of power data confirms that spatial separation of turbines greatly reduces variations in their combined wind power output when compared to the output of a single wind power plant. Data show that high-frequency variations of wind power from two wind power plants 200 km apart are independent of each other, but low-frequency power changes can be highly correlated. This fact suggests that time-synchronized power data and meteorological data can aid in the development of statistical models for wind power forecasting.

scholarly journals An Analysis of Loop Current Frontal Eddies in a ⅙° Atlantic Ocean Model Simulation

2013 ◽  
Vol 43 (9) ◽  
pp. 1924-1939 ◽  
Author(s):  
Haosheng Huang ◽  
Nan D. Walker ◽  
Ya Hsueh ◽  
Yi Chao ◽  
Robert R. Leben
Keyword(s):  
Numerical Model ◽  
Atlantic Ocean ◽  
General Circulation ◽  
Model Simulation ◽  
Ocean Model ◽  
Anticyclonic Eddy ◽  
Loop Current ◽  
Particle Tracking Method ◽  
The Caribbean ◽  
Yucatan Channel

Abstract The Loop Current frontal eddies (LCFEs) refer to cyclonic cold eddies moving downstream along the outside edge of the Loop Current in the eastern Gulf of Mexico. They have been observed by in situ measurements and satellite imagery, mostly downstream of the Campeche Bank continental shelf. Their evolution, simulated by a primitive equation ⅙° and 37-level Atlantic Ocean general circulation numerical model, is described in detail in this study. Some of the simulated LCFEs arise, with the passage through the Yucatan Channel of a Caribbean anticyclonic eddy, as weak cyclones with diameters less than 100 km near the Yucatan Channel. They then grow to fully developed eddies with diameters on the order of 150–200 km while moving along the Loop Current edge. Modeled LCFEs have a very coherent vertical structure with isotherm doming seen from 50- to ~1000-m depth. The Caribbean anticyclone and LCFE are two predominant features in this numerical model simulation, which account for 22% and 10%, respectively, of the short-term (period less than 100 days) temperature variance at 104.5 m in the complex empirical orthogonal function (CEOF) analysis. The source water inside the LCFEs that are generated by Caribbean anticyclonic eddy impingement can be traced back, using a backward-in-time Lagrangian particle-tracking method, to the western edge of the Caribbean Current in the northwest Caribbean Sea and to coastal waters near the northern Yucatan Peninsula. The model results indicating a pairing of anticyclonic and cyclonic eddies within and north of the Yucatan Channel are supported by satellite altimetry measurements during February 2002 when several altimeters were operational.

A teleseism-specific detection algorithm for single short-period traces

1983 ◽  
Vol 73 (4) ◽  
pp. 1173-1186
Author(s):  
John R. Evans ◽  
Stephen S. Allen
Keyword(s):  
Frequency Band ◽  
High Frequency ◽  
Vertical Component ◽  
Low Frequency ◽  
Field Studies ◽  
Detection Algorithm ◽  
P Waves ◽  
Data Set ◽  
Short Period ◽  
Worldwide Network

abstract An algorithm for microprocessor-controlled seismographic recorders is described which reliably detects major phases from earthquakes more than 3° from the sensor but rejects noise events and most earthquakes closer than 3°. Unusually large earthquakes within 3° also are detected. The algorithm is applicable to field studies using triggered seismographs to record teleseismic P waves, to worldwide network automation, and to scanning records for teleseisms. It uses two band-pass filtered data streams evolved from a single short-period vertical-component seismometer to differentiate (low-frequency) teleseisms from other signals; the low-frequency band (0.5 to 2.0 Hz) declares “triggers” while the high-frequency band (3.0 to 8.0 Hz) inhibits any of these triggers generated by broadband signals such as local earthquakes. Locally generated noise is usually high frequency and does not excite the low-frequency band. A 16-bit fixed-word-length implementation of this algorithm detected 82 per cent of good P phases (readable to ±0.25 sec) occurring more than 20° from the seismograph, and 50 per cent of earthquakes between 3° and 20°, in a test data set comprising 23 hr of data in 93 segments. The same implementation of the algorithm rejected most noise and 91 per cent of earthquakes within 3° of the seismograph.

DWT Based Blind Watermark in Relational Database

2013 ◽  
Vol 760-762 ◽  
pp. 2123-2128
Author(s):  
Yi Liu ◽  
Juan Wang
Keyword(s):  
Wavelet Transform ◽  
Theoretical Analysis ◽  
Data Fusion ◽  
Relational Database ◽  
High Frequency ◽  
Low Frequency ◽  
Blind Watermarking ◽  
Watermark Image ◽  
Data Set ◽  
Strong Robustness

Aiming to balance the robustness and imperceptibility of database watermark, propose a wavelet transform (DWT) based blind watermarking algorithm. The algorithm screens candidate attributes that can be embedded watermark and conducts subset segmentation and rearrangement, and then performs DWT transformation to the data subsets and the scrambled watermark image respectively. Embed the compressed low-frequency part of the watermark into the High-frequency part of the data set to achieve data fusion. Theoretical analysis and experiments show that the algorithm enjoys strong robustness and good invisibility.

A new approach to health condition identification of rolling bearing using hierarchical dispersion entropy and improved Laplacian score

2020 ◽  
pp. 147592172094862 ◽  
Author(s):  
Xiaoan Yan ◽  
Ying Liu ◽  
Dongsheng Huang ◽  
Minping Jia
Keyword(s):  
High Frequency ◽  
Low Frequency ◽  
Rolling Bearing ◽  
Weight Coefficient ◽  
Fault Identification ◽  
Selection Strategy ◽  
Data Set ◽  
Softmax Classifier ◽  
Laplacian Score ◽  
Low Dimensional

Since bearing fault signal under complex running status is usually manifested as the characteristics of nonlinear and non-stationary, which implies it is difficult to extract accurate affluent features and achieve effective fault identification via conventional signal processing tools. In this article, a hybrid intelligent fault identification scheme, the combination of hierarchical dispersion entropy and improved Laplacian score, is proposed to address this problem, which is mainly composed of three procedures. First, the particle swarm optimization–based optimized hierarchical dispersion entropy is adopted to excavate multilevel fault symptoms from low-frequency and high-frequency components, which can both solve the shortcoming of missing of high-frequency feature information existing in the recently presented multiscale dispersion entropy and artificial parameter selection issue of hierarchical dispersion entropy. Second, an improved feature selection strategy based on improved Laplacian score is proposed to select the sensitive features to establish a low-dimensional feature data set by incorporating the weight coefficient into Laplacian score. Finally, the established low-dimensional feature data set is fed to a Softmax classifier to automatically identify different health conditions of rolling bearing. The efficacy of the proposed method is validated by two experimental cases. Results show that our approach is highly effective in recognizing different fault categories and severities of rolling bearing. Meanwhile, our approach exhibits higher accuracy and better identification performance than some similar entropy-based hybrid approaches and other identification methods reported in this article.

scholarly journals Frequency effects on the vowel length contrast merger in Seoul Korean

2015 ◽  
Vol 6 (3-4) ◽  
Author(s):  
Yoonjung Kang ◽  
Tae-Jin Yoon ◽  
Sungwoo Han
Keyword(s):  
High Frequency ◽  
Low Frequency ◽  
Sound Change ◽  
Rate Of Change ◽  
Frequency Effect ◽  
Vowel Duration ◽  
Speech Corpus ◽  
Vowel Length ◽  
On Line ◽  
High Frequency Words

AbstractThis paper presents an apparent-time study of the vowel length contrast merger in Seoul Korean based on duration measurements of over 370,000 vowels in word-initial syllables in a read-speech corpus. The effects of word frequency on vowel duration and the lexical diffusion of long-vowel shortening are also examined. The findings confirm the observation made in the previous literature that the vowel length contrast is on its way out in the language, and that this sound change is nearing completion. We also find a significant effect of frequency on long-vowel duration: other things being equal, these vowels are shorter in high-frequency words than in low-frequency words. The rate of change does not differ significantly depending on the frequency of words apart from the high-frequency words reaching the endpoint of change and bottoming out in the change earlier than mid- and low-frequency words. The observed frequency effect is compatible with a model in which the frequency effect on duration comes from on-line factors that affect phonetic implementation of speech sounds, along with an across-the-board lenition bias that drives the sound change, not from stored tokens of word-specific variants.

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