scholarly journals Extracting statistically significant eddy signals from large Lagrangian datasets using wavelet ridge analysis, with application to the Gulf of Mexico

2021 ◽  
Vol 28 (2) ◽  
pp. 181-212
Author(s):  
Jonathan M. Lilly ◽  
Paula Pérez-Brunius

Abstract. A method for objectively extracting the displacement signals associated with coherent eddies from Lagrangian trajectories is presented, refined, and applied to a large dataset of 3770 surface drifters from the Gulf of Mexico. The method, wavelet ridge analysis, is a general method for the analysis of modulated oscillations, here modified to be more suitable to the eddy-detection problem. A means for formally assessing statistical significance is introduced, addressing the issue of false positives arising by chance from an unstructured turbulent background and opening the door to confident application of the method to very large datasets. Significance is measured through a frequency-dependent comparison with a stochastic dataset having statistical and spectral properties that match the original, but lacking organized oscillations due to eddies or waves. The application to the Gulf of Mexico reveals major asymmetries between cyclones and anticyclones, with anticyclones dominating at radii larger than about 50 km, but an unexpectedly rich population of highly nonlinear cyclones dominating at smaller radii. Both the method and the Gulf of Mexico eddy dataset are made freely available to the community for noncommercial use in future research.

2020 ◽  
Author(s):  
Jonathan M. Lilly ◽  
Paula Perez-Brunius

Abstract. A method for objectively extracting the displacement signals associated with coherent eddies from Lagrangian trajectories is presented, refined, and applied to a large dataset of 3761 surface drifters from the Gulf of Mexico. The method, wavelet ridge analysis, is modified to exclude the possibility of features changing from rotating in the cyclonic sense to rotating in the anticyclonic sense or vice-versa, transitions that would be physically unrealistic for a coherent eddy. A means for formally assessing statistical significance is introduced, addressing the issue of "false positives" arising by chance from an unstructured turbulent background, and opening the door to confident application of the method to very large datasets. Significance is measured in a two-dimensional parameter space by comparison with a stochastic dataset having statistical and spectral properties that match the original, but lacking organized oscillations due to eddies or waves. The application to the Gulf of Mexico reveals massive asymmetries between cyclones and anticyclones, with anticyclones dominating at radii larger than about 50 km, but an unexpectedly rich population of highly nonlinear cyclones dominating at smaller radii. Both the method and the Gulf of Mexico eddy dataset are made freely available to the community for use in future research.


2016 ◽  
Vol 46 (7) ◽  
pp. 2183-2199 ◽  
Author(s):  
Francisco J. Beron-Vera ◽  
J. H. LaCasce

AbstractPair-separation statistics of in situ and synthetic surface drifters deployed near the Deepwater Horizon site in the Gulf of Mexico are investigated. The synthetic trajectories derive from a 1-km-resolution data-assimilative Navy Coastal Ocean Model (NCOM) simulation. The in situ drifters were launched in the Grand Lagrangian Deployment (GLAD). Diverse measures of the dispersion are calculated and compared to theoretical predictions. For the NCOM pairs, the measures indicate nonlocal pair dispersion (in which pair separations grow exponentially in time) at the smallest sampled scales. At separations exceeding 100 km, pair motion is uncorrelated, indicating absolute rather than relative dispersion. With the GLAD drifters, however, the statistics are ambiguous, with some indicating local dispersion (in which pair separations exhibit power-law growth) and others suggesting nonlocal dispersion. The difference between the two datasets stems in part from inertial oscillations, which affect the energy levels at small scales without greatly altering pair dispersion. These were significant in GLAD but much weaker in the NCOM simulation. In addition, the GLAD drifters were launched over a limited geographical area, producing few independent realizations and hence lower statistical significance. Restricting the NCOM set to pairs launched at the same locations yields very similar results, suggesting the model is for the most part capturing the observed dispersion.


2013 ◽  
Vol 1 (2) ◽  
pp. 239-259 ◽  
Author(s):  
Wolfgang Tschacher ◽  
Fabian Ramseyer ◽  
Claudia Bergomi

Time is a basic dimension in psychology, underlying behavior and experience. Timing and time perception constitute implicit processes that are often inaccessible to the individual person. Research in this field has shown that timing is involved in many areas of clinical significance. In the projects presented here, we combine timing with seemingly different fields of research, such as psychopathology, perceptual grouping, and embodied cognition. Focusing on the time scale of the subjective present, we report findings from three different clinical studies: (1) We studied perceived causality in schizophrenia patients, finding that perceptual grouping (‘binding’, ‘Gestalt formation’), which leads to visual causality perceptions, did not distinguish between patients and healthy controls. Patients however did integrate context (provided by the temporal distribution of auditory context stimuli) less into perceptions, in significant contrast to controls. This is consistent with reports of higher inaccuracy in schizophrenia patients’ temporal processing. (2) In a project on auditory Gestalt perception we investigated auditory perceptual grouping in schizophrenia patients. The mean dwell time was positively related to how much patients were prone to auditory hallucinations. Dwell times of auditory Gestalts may be regarded as operationalizations of the subjective present; findings thus suggested that patients with hallucinations had a shorter present. (3) The movement correlations of interacting individuals were used to study the non-verbal synchrony between therapist and patient in psychotherapy sessions. We operationalized the duration of an embodied ‘social present’ by the statistical significance of such associations, finding a window of roughly 5.7 seconds in conversing dyads. We discuss that temporal scales of nowness may be modifiable, e.g., by mindfulness. This yields promising goals for future research on timing in the clinical context: psychotherapeutic techniques may alter binding processes, hence the subjective present of individuals, and may affect the social present in therapeutic interactions.


2011 ◽  
Vol 6 (4) ◽  
pp. 152
Author(s):  
Carol D. Howe

Objective – To evaluate the usefulness of three point-of-care healthcare databases (BMJ Point-of-Care, Clin-eguide, and Nursing Reference Centre) in clinical practice. Design – A descriptive study analyzing questionnaire results. Setting – Hospitals within Alberta, Canada’s two largest health regions (at the time of this study), with a third health region submitting a small number of responses. Subjects – A total of 46 Alberta hospital personnel answered the questionnaire, including 19 clinicians, 7 administrators, 6 nurses, 1 librarian, 1 preceptor, and “some” project coordinators. Subjects were chosen using a non-probability sampling method. Methods – The researchers developed an online questionnaire consisting of 17 questions and posted it on the University of Calgary’s Health Sciences Library and the Health Knowledge Network websites. The questions, in general, asked respondents how easy the databases were to search and use, whether the database content answered their clinical questions, and whether they would recommend the databases for future purchase. Most questions required a response for each of the three databases. The researchers collected quantitative data by using a Likert scale from 1 to 5, with 5 being the most positive answer and 1 being the most negative. They collected qualitative data by asking open-ended questions. Main Results – With regard to ease of searching, BMJ Point-of-Care (BMJ) received the greatest number of responses (71%) at level 5. A smaller number of respondents (56%) rated Nursing Reference Centre (NRC) at level 5. Clin-eguide received 59% of the responses at level 5, but it also received the greatest number of responses at the next highest level (level 4). Respondents rated all three databases similarly with regard to levels 1 and 2. Regarding how easy the resources were to learn, most respondents rated all three databases as easy to learn (BMJ, 77%; Clin-eguide, 72%; and NRC, 68%). Very few respondents thought any of the databases were difficult to learn. The researchers gleaned from open-ended questions that the respondents generally thought all three databases were faster and easier to use than the conventional databases they had used. Respondents did not always agree with one another, however, about which features they liked or why. With regard to content, most respondents agreed that the information in all three databases was relevant to their needs (94.6% for Clin-eguide and 87.9% for BMJ and NRC). Respondents also generally agreed that all three databases answered their questions to a high degree. Clin-eguide had the highest percentage of answers at levels 4 and 5 and the lowest percentage of answers at level 2. NRC was the reverse, with the lowest percentage of answers at levels 4 and 5 and the highest percentage of answers at level 2. Still, the researchers felt that all three databases answered respondents’ questions to a similar degree. In the open-ended questions, respondents voiced additional likes and dislikes about content, but again, answers among respondents were not consistent with one another. Respondents were asked how often they would use the resource if it were available though their library. The majority of BMJ users reported that they would use it extensively or moderately. About 36% and 39% of NRC users reported they would use it extensively or moderately, respectively; while 43.5% and 34.8% of Clin-eguide users reported they would use it extensively or moderately, respectively. When asked if they would recommend the resource for the library, 84.8% would recommend Clin-eguide, 75% would recommend BMJ, and 67.6% would recommend NRC. The open-ended questions generally indicated that respondents would recommend all three databases. Regarding how respondents preferred training on these resources, users preferred online tutorials to learn Clin-eguide and NRC. Users preferred website tips and instruction to learn BMJ. The least preferred methods of training for all three databases were live demonstration and classroom training. Conclusion – None of the databases particularly stood out with regard to usability and content. The respondents generally liked all three databases. It is important to note, however, that detailed comparisons among the databases were difficult to make. First, respondents did not always give an answer for all three databases for a given question. Because of this, and to present a more meaningful analysis, the researchers often reported the number of respondents who answered a certain way as a percentage rather than a number. Second, although the respondents generally liked all three databases, opinions about likes and dislikes were not consistent among respondents. For example, one respondent thought the NRC and Clin-eguide interfaces were more difficult to navigate than BMJ, while another respondent thought BMJ had the harder-to-navigate interface. The researchers felt that respondents’ prior experience with the databases may have influenced their preferences. They were unable to determine if the respondents’ professional interests had any influence on their preferences. Inconsistent responses made it difficult for researchers to assign an overall value to a given database. Therefore, this survey did not help to make definitive purchasing decisions. The researchers felt they would have to look at each resource much more carefully to make such a decision. The researchers noted several ideas for future research of this sort. They acknowledged that the sample size was not big enough to determine statistical significance and thought that better marketing of the questionnaire may have increased the numbers. They also thought that it would be interesting to observe the respondents using the databases in real-time to find out such things as: what information they require in their daily work, how long it takes them to find it, and what they do with it once they find it.


2021 ◽  
Vol 10 (21) ◽  
pp. 5176
Author(s):  
Jennifer Wang ◽  
Zyg Chapman ◽  
Emma Cole ◽  
Satomi Koide ◽  
Eldon Mah ◽  
...  

Background: Closed incision negative pressure therapy (ciNPT) may reduce the rate of wound complications and promote healing of the incisional site. We report our experience with this dressing in breast reconstruction patients with abdominal free flap donor sites. Methods: A retrospective cohort study was conducted of all patients who underwent breast reconstruction using abdominal free flaps (DIEP, MS-TRAM) at a single institution (Royal Melbourne Hospital, Victoria) between 2016 and 2021. Results: 126 female patients (mean age: 50 ± 10 years) were analysed, with 41 and 85 patients in the ciNPT (Prevena) and non-ciNPT (Comfeel) groups, respectively. There were reduced wound complications in almost all outcomes measured in the ciNPT group compared with the non-ciNPT group; however, none reached statistical significance. The ciNPT group demonstrated a lower prevalence of surgical site infections (9.8% vs. 11.8%), wound dehiscence (4.9% vs. 12.9%), wound necrosis (0% vs. 2.4%), and major complication requiring readmission (2.4% vs. 7.1%). Conclusion: The use of ciNPT for abdominal donor sites in breast reconstruction patients with risk factors for poor wound healing may reduce wound complications compared with standard adhesive dressings; however, large scale, randomised controlled trials are needed to confirm these observations. Investigation of the impact of ciNPT patients in comparison with conventional dressings, in cohorts with equivocal risk profiles, remains a focus for future research.


2019 ◽  
Vol 12 (7) ◽  
pp. 75
Author(s):  
Charinwit Seedanont ◽  
Suphawat Pookcharoen

EFL readers tend to experience a number of challenges while learning, due to a number of factors that affect how these readers achieve their learning goals. Metacognitive strategies, referring to one’s deliberate, goal-directed control over cognitive enterprises, are considered crucial for assisting EFL learners to be able to accomplish comprehension while reading. Previous studies have enriched the knowledge of metacognitive reading strategies in EFL settings. However, only few investigations yielded statistically significant effects on learners’ reading performance. This present study hence foresees an opportunity to shed new light on this issue by focusing on EFL learners’ proficiency. The objectives of this research are twofold: exploring the effects of the metacognitive strategy instruction on the strategy awareness, and perceiving the effects of the instruction on the reading performance in taking a standardized test. Forty-three students enrolling in a private male school in Bangkok, Thailand participated in the study, lasting ten weeks. A wide range of research tools were administered: SORS, IELTS reading test, and lesson plans. The findings suggested that the students’ awareness of reading strategies used in terms of sub-categories and IELTS reading test score improved with statistical significance. Pedagogical implications and suggestions for future research studies are discussed based on the findings.


2021 ◽  
Vol 850 (1) ◽  
pp. 012037
Author(s):  
J ShanthaSheela ◽  
A David Maxim Gururaj ◽  
Mohammed Ismail ◽  
S Dhanasekar

Abstract Nanofluids are the fluids containing nano materials, with interesting properties, and the distinctive features have shown unprecedented potential for many Industrial applications. Nano fluids have been receiving great attention in recent years for heat transfer applications in industrial processes. In literature, the highly nonlinear governing equations involved in the study of MHD nanofluids flow with thermal radiation past a vertical plate under varying physical nature are solved using numerical and analytical schemes. It is noted that due to the complexity of the governing equations, numerical schemes are more preferable than analytical schemes. The authors have taken effort in registering various forms of governing equations involved in the above studies, its impact on velocity and temperature field. This paper also tries to identify the research gaps and pave way for future research.


1997 ◽  
Vol 1997 (1) ◽  
pp. 916-919
Author(s):  
Debra A. Simecek-Beatty ◽  
William J. Lehr ◽  
Walter R. Johnson ◽  
James M. Price

ABSTRACT As part of a joint program to use satellite-tracked drifters at accidental oil spills, the National Oceanic and Atmospheric Administration deployed three drifters supplied by the Minerals Management Service during the barge Buffalo 292 spill in the Gulf of Mexico. The deployments complemented visual observations of the oil spill and provided data for calibrating the on-scene spill model. The data-rich environment of this particular spill response made it possible to calculate the vector correlation between the drifters and a hindcast of the oil movement and to estimate the wind-drift factors for the oil-tracking drifters.


2020 ◽  
Vol 7 (1) ◽  
Author(s):  
Kristin Yeoman ◽  
Mary B. O’Connor ◽  
Sara Sochor ◽  
Gerald Poplin

Abstract Background Transportation events are the most common cause of offshore fatalities in the oil and gas industry, of which helicopter accidents comprise the majority. Little is known about injury distributions in civilian helicopter crashes, and knowledge of injury distributions could focus research and recommendations for enhanced injury prevention and post-crash survival. This study describes the distribution of injuries among fatalities in Gulf of Mexico oil and gas industry-related helicopter accidents, provides a detailed injury classification to identify potential areas of enhanced safety design, and describes relevant safety features for mitigation of common injuries. Methods Decedents of accidents during 2004–2014 were identified, and autopsy reports were requested from responsible jurisdictions. Documented injuries were coded using the Abbreviated Injury Scale (AIS), and frequency and proportion of injuries by AIS body region and severity were calculated. Injuries were categorized into detailed body regions to target areas for prevention. Results A total of 35 autopsies were coded, with 568 injuries documented. Of these, 23.4% were lower extremity, 22.0% were thorax, 13.6% were upper extremity, and 13.4% were face injuries. Minor injuries were most prevalent in the face, neck, upper and lower extremities, and abdomen. Serious or worse injuries were most prevalent in the thorax (53.6%), spine (50.0%), head (41.7%), and external/other regions (75.0%). The most frequent injuries by detailed body regions were thoracic organ (23.0%), thoracic skeletal (13.3%), abdominal organ (9.6%), and leg injuries (7.4%). Drowning occurred in 13 (37.1%) of victims, and drowning victims had a higher proportion of moderate brain injuries (7.8%) and lower number of documented injuries (3.8) compared with non-drowning victims (2.9 and 9.4%, respectively). Conclusions Knowledge of injury distributions focuses and prioritizes the need for additional safety features not routinely used in helicopters. The most frequent injuries occurred in the thorax and lower extremity regions. Future research requires improved and expanded data, including collection of detailed data to allow characterization of both injury mechanism and distribution. Improved safety systems including airbags and helmets should be implemented and evaluated for their impact on injuries and fatalities.


2011 ◽  
Vol 3 (4) ◽  
pp. 481-486 ◽  
Author(s):  
Craig I. Schranz ◽  
Robert J. Sobehart ◽  
Kiva Fallgatter ◽  
Robert H. Riffenburgh ◽  
Michael J. Matteucci

Abstract Background Due to increasing time constraints, the use of bedside presentations in resident education has declined. We examined whether patient satisfaction in the emergency department is affected when first-year residents present at the bedside with attendings. Methods We performed an observational, prospective, nonblinded study in the emergency department of a military teaching hospital. We alternately assigned first-year residents to present a convenience sample of 248 patients to the attending physician at the patient's bedside or away from the patient. We measured patient satisfaction by using the Patient Satisfaction Questionaire-18 (PSQ-18), a validated survey instrument that utilizes a Likert scale, and additional nonvalidated survey questions involving Likert and visual analog scales. Results While the median PSQ-18 score of 74 (95% confidence interval [CI], 72–76) was higher for patient satisfaction when residents made bedside presentations than that for standard presentations, 72 (95% CI, 70–74), the difference did not reach statistical significance (P  =  .33). Conclusion There was no significant difference in overall patient satisfaction between residents' bedside presentations and presentations to attendings away from the patient. Although not significant, the differences noted in PSQ-18 subscales of communication, general satisfaction, and interpersonal manner warrant further investigation. Patients did not appear to be uncomfortable with having their care discussed and with having subsequent resident education at the bedside. Future research on patient satisfaction after implementation of standardized bedside teaching techniques may help further elucidate this relationship.


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