scholarly journals DEPTH OF DISTURBANCE OF SAND IN SURF ZONES

1978 ◽  
Vol 1 (16) ◽  
pp. 89
Author(s):  
Michael K. Gaughan
Keyword(s):  
Maximum Concentration ◽  
Surf Zone ◽  
Vertical Mixing ◽  
Sampling Interval ◽  
Sediment Surface ◽  
Tracer Concentration ◽  
Cross Sectional ◽  
Tidal Period ◽  
Contour Maps ◽  
In Parenthesis

A coring technique employed during wave action allowed accurate measurement of the depth of vertical mixing bm of fluorescent sand tracer grains within the surf zone of a gently sloping Pacific Ocean beach (beach slope tangent s = 0.012). The depth bm is the distance from the sediment surface to the lower limit of observed tracer grains within the inner portion of the core. Although this definition is only strictly applicable to a rectangular distribution of tracer concentration with depth, the bm results were quite similar to those using concentration-weighted depth averages of Crickmore (1967). For one winter regime experiment, vertical cross-sectional contour maps of tracer concentration normalized by the local core maximum were drawn with concentrations computed for each 0.4cm slice. Trends present are (1) in the onshore-offshore direction the maximum concentration is at the bed surface shorewards of the mid-surf position and 0.4 cm to 1.2 cm below the bed seaward of the mid-surf position, and (2) in the longshore direction (at the mid-surf position) the maximum concentration lies 0.4 cm to 1.6 cm below the bed surface. For spilling breaker heights Hb between 75 cm and 150 cm, histograms of bm were clearly different for spring/summer and fall/winter experiments: the mean and standard deviation (in parenthesis) are 0.5 cm (0.5 cm) and 1.1 cm (0.5 cm), respectively. These results are substantially less than both the 3.0 cm and the 20 cm to 40 cm disturbance depths per 100 cm of Hb reported by King (1951) and by Otvos (1965) and Williams (1970). The discrepancy with Otvos and Williams is due to the much different breaking process; in their experiments small breakers (Hb = 5 cm to 30 cm) plunged directly onto steep beach slopes (s = 0.1) causing large bm- The tracer grain's longer exposure to bottom stresses of passing surf bores may explain King's greater disturbance depths. Her sampling interval was one semi-diurnal tidal period T versus the span 0.02 T to 0.32 T in this study.

The Response of Buoyant Coastal Plumes to Upwelling-Favorable Winds*

2004 ◽  
Vol 34 (11) ◽  
pp. 2458-2469 ◽  
Author(s):  
Steven Lentz
Keyword(s):  
Wind Stress ◽  
Vertical Mixing ◽  
Wind Forcing ◽  
Ekman Transport ◽  
Entrainment Rate ◽  
Buoyant Plume ◽  
Cross Sectional ◽  
Buoyancy Forcing ◽  
Density Anomaly ◽  
Variable Wind

Abstract To better understand the response of a buoyant coastal plume to wind-induced upwelling, a two-dimensional theory is developed that includes entrainment. The primary assumption is that competition between wind-driven vertical mixing and lateral buoyancy forcing in the region where the isopycnals slope upward to intersect the surface results in continual entrainment at the offshore edge of the plume. The theory provides estimates of the buoyant plume characteristics and offshore displacement as a function of time t, given the wind stress, the characteristics of the buoyant plume prior to the onset of the wind forcing, and a critical value for the bulk Richardson number (Ric). The theory predicts that, for t̂ ≡ t/ts, the plume density anomaly decreases as (1 + t̂)−1, the thickness increases as (1 + t̂)1/3, the width increases as (1 + t̂)2/3, and the plume average entrainment rate decreases as (1 + t̂)−2/3. Here ts = 2Ao/(RicUE) is the time for entrainment to double the cross-sectional area of the plume Ao at the onset of the wind forcing, where UE is the Ekman transport. The theory reproduces results from 20 numerical model runs by Fong and Geyer, including their estimates of the plume-average entrainment rate (correlations greater than 0.98 and regression coefficients approximately 1 for plume characteristics and 1.7 for the entrainment rate). The theory, modified to allow for time-variable wind stress, also reproduces the observed response of the buoyant coastal plume from Chesapeake Bay during an 11-day period of upwelling winds in August 1994.

scholarly journals Pattern of anti-malarial drugs and artemether combination therapy adherence in an institution based medical centre, Nigeria

2020 ◽  
Vol 8 (3) ◽  
pp. 162-170
Author(s):  
Ujuamala Uloma Ezeani ◽  
Penaere Theresa Osahon ◽  
Michael Chukwudi Ezeani
Keyword(s):  
Combination Therapy ◽  
Antimalarial Drug ◽  
Medical Center ◽  
Drug Prescription ◽  
Treatment Guideline ◽  
Sampling Interval ◽  
Systematic Sampling ◽  
Cross Sectional ◽  
Who Guideline ◽  
Sulphadoxine Pyrimethamine

The change in policy guidelines for treating uncomplicated malaria became necessary because the therapeutic efficacy of chloroquine and SP had deteriorated. Hence compliance is a necessity to enable effective check on malaria. This work was carried out to evaluate antimalaria drug prescription and to update its usage in line with WHO guideline on Artemeter Combination therapy in a university based medical center. We utilized descriptive, cross-sectional, retrospective study of antimalaria prescriptions purposely carried out among male and female outpatients with mean age of 22.4±2.8 at a University health facility. This comprised all outpatients prescriptions that contained at least one antimalarial drug filed from October 2018 to September 2019. Systematic sampling was used to select the prescriptions. Based on the total number of 1250 prescriptions containing at least one antimalarial drug, a sampling interval of 5 was calculated and simple balloting was used for the first pick. A total number of two hundred and fifty (250) prescriptions containing at least one antimalarial drug were selected for the study. Out of 250 antimalaria prescriptions, usage of ACT class of Artemeter lumefantrine, Artemeter Amodiaquine and Artemeter Piparaqiune were recorded at 45.6%, 10.4% and 9.6% respectively. Triple combination Artemeter lumefantrine and Sulphadoxine-Pyrimethamine was recorded at 20.4% while Sulphadoxine-Pyrimethamine was recorded at 4%. Combination of antimalarial drugs with antibiotics was recorded at 31.2%. This study showed compliance with National Antimalarial Treatment Guideline for the treatment of malaria infection as it regards the use of artemisinin-based combination therapy. The frequency usage of artemeter lumefantrine was proceeding among other ACTs. The frequency in co-prescription of antibiotics with anti-malaria should be guarded to comply with WHO recommendation.

scholarly journals Shoreline recovery from storms on the east coast of Southern Africa

2012 ◽  
Vol 12 (1) ◽  
pp. 11-22 ◽  
Author(s):  
S. Corbella ◽  
D. D. Stretch
Keyword(s):  
East Coast ◽  
Surf Zone ◽  
Recovery Period ◽  
Management Tool ◽  
Negative Effects ◽  
Cross Sectional ◽  
Rock Outcrops ◽  
Sediment Loss ◽  
Recovery Times

Abstract. Episodic extreme waves due to sea storms can cause severe coastal erosion. The recovery times of such events are important for the analysis of risk and coastal vulnerability. The recovery period of a storm damaged coastline represents a time when the coastline is most vulnerable and nearby infrastructure is at the greatest risk. We propose that identification of the beach recovery period can be used as a coastal management tool when determining beach usage. As a case study, we analyse 37 yr of beach profile data on the east coast of South Africa. Considering beach length and cross-sectional area, we establish a global recovery period and rate and identify the physical characteristics of the coastlines that either accelerate or retard recovery. The beaches in the case study were found to take an average of two years to recover at a rate of approximately 90 m3 m−1 yr−1. Beach profiles with vegetated dunes recovered faster than urbanized beaches. Perpendicular beach structures have both positive and negative effects on beach recovery. Coastlines with rock outcrops in the surf zone tend to recover slowly and long-term sediment loss was identified in cases where storm damaged beaches have not recovered to pre-erosion levels.

scholarly journals Vertical Mixing and Heat Fluxes Conditioned by a Seismically Imaged Oceanic Front

2021 ◽  
Vol 8 ◽  
Author(s):  
Kathryn L. Gunn ◽  
Alex Dickinson ◽  
Nicky J. White ◽  
Colm-cille P. Caulfield
Keyword(s):  
Water Mass ◽  
Vertical Mixing ◽  
Three Dimensional ◽  
Heat Fluxes ◽  
Water Masses ◽  
Mixing Rate ◽  
Southwest Atlantic ◽  
Cross Sectional ◽  
Mean Values ◽  
Mixing Rates

The southwest Atlantic gyre connects several distinct water masses, which means that this oceanic region is characterized by a complex frontal system and enhanced water mass modification. Despite its significance, the distribution and variability of vertical mixing rates have yet to be determined for this system. Specifically, potential conditioning of mixing rates by frontal structures, in this location and elsewhere, is poorly understood. Here, we analyze vertical seismic (i.e., acoustic) sections from a three-dimensional survey that straddles a major front along the northern portion of the Brazil-Falkland Confluence. Hydrographic analyses constrain the structure and properties of water masses. By spectrally analyzing seismic reflectivity, we calculate spatial and temporal distributions of the dissipation rate of turbulent kinetic energy, ε, of diapycnal mixing rate, K, and of vertical diffusive heat flux, FH. We show that estimates of ε, K, and FH are elevated compared to regional and global mean values. Notably, cross-sectional mean estimates vary little over a 6 week period whilst smaller scale thermohaline structures appear to have a spatially localized effect upon ε, K, and FH. In contrast, a mesoscale front modifies ε and K to a depth of 1 km, across a region of O(100) km. This front clearly enhances mixing rates, both adjacent to its surface outcrop and beneath the mixed layer, whilst also locally suppressing ε and K to a depth of 1 km. As a result, estimates of FH increase by a factor of two in the vicinity of the surface outcrop of the front. Our results yield estimates of ε, K and FH that can be attributed to identifiable thermohaline structures and they show that fronts can play a significant role in water mass modification to depths of 1 km.

scholarly journals Spatiotemporal distributions of icebergs in a temperate fjord: Columbia Fjord, Alaska

2019 ◽  
Vol 13 (7) ◽  
pp. 1785-1799 ◽  
Author(s):  
Sarah U. Neuhaus ◽  
Slawek M. Tulaczyk ◽  
Carolyn Branecky Begeman
Keyword(s):  
Surface Area ◽  
Power Law ◽  
Vertical Mixing ◽  
Heat Content ◽  
Back Stress ◽  
Late Winter ◽  
Power Law Distribution ◽  
Cross Sectional ◽  
Power Law Exponent ◽  
Pixel Brightness

Abstract. Much of the world's ice enters the ocean via outlet glaciers terminating in fjords. Inside fjords, icebergs may affect glacier–ocean interactions by cooling incoming ocean waters, enhancing vertical mixing, or providing back stress on the terminus. However, relatively few studies have been performed on iceberg dynamics inside fjords, particularly outside of Greenland. We examine icebergs calved from Columbia Glacier, Alaska, over 8 months spanning late winter to mid-fall using 0.5 m resolution satellite imagery, identifying icebergs based on pixel brightness. Iceberg sizes fit a power-law distribution with an overall power-law exponent, m, of -1.26±0.05. Seasonal variations in the power-law exponent indicate that brittle fracture of icebergs is more prevalent in the summer months. Combining our results with those from previous studies of iceberg distributions, we find that iceberg calving rate, rather than water temperature, appears to be the major control on the exponent value. We also analyze icebergs' spatial distribution inside the fjord and find that large icebergs (10 000–100 000 m2 cross-sectional area) have low spatial correlation with icebergs of smaller sizes due to their tendency to ground on shallow regions. We estimate the surface area of icebergs in contact with incoming seawater to be 3.0±0.63×104 m2. Given the much larger surface area of the terminus, 9.7±3.7×105 m2, ocean interactions with the terminus may have a larger impact on ocean heat content than interactions with icebergs.

scholarly journals SUSPENDED SAND TRANSPORT ON A DISSIPATIVE BEACH

1984 ◽  
Vol 1 (19) ◽  
pp. 119 ◽  
Author(s):  
John P. Downing
Keyword(s):  
Water Depth ◽  
Surf Zone ◽  
Vertical Mixing ◽  
Low Frequency ◽  
Field Studies ◽  
Sand Transport ◽  
Wave Band ◽  
Sediment Loads ◽  
Longshore Transport ◽  
Individual Wave

Field studies were conducted in November 1979 to measure suspended sand transport on Twin Harbor Beach, Washington U.S.A. This beach has an average slope of 0.02 and is composed of well-sorted sand with a mean diameter of 0.21mm. The significant height of breaking swells approaching the beach at small angles can be estimated from variance spectra of water level by 4.36 0^. In the surf zone significant wave heights are linearly related to the local mean water depth by Y = H /h » 0.45. Variance, a \, in the gravity wave band (0.048 to 1.0 Hz) is proportional to water depth squared. Low-frequency variance (less than 0.048 Hz) although not systematically related to water depth, is usually largest in the inner surf zone where breakers are small. Sand suspension is correlated with strong offshore flows that recur at about one-fifth the incident wave frequency. Vertical mixing of sand in the water column by these water motions rather than turbulence generated by shear at the bed associated with individual wave oscillations is a key mechanism in sand transport on dissipative beaches. The largest sediment loads occur in the inner surf zone where lowfrequency motions dominate the breakers. Maximum longshore transport rates, however, were measured in the middle of the surf zone because of the higher longshore current speeds there. The suspended load probably accounts for as much as 45 percent of the litoral drift on a dissipative beach exposed to moderately-high swells approaching the shore at small angles.

scholarly journals Tracer concentration profiles measured in central London as part of the REPARTEE campaign

2011 ◽  
Vol 11 (1) ◽  
pp. 227-239 ◽  
Author(s):  
D. Martin ◽  
K. F. Petersson ◽  
I. R. White ◽  
S. J. Henshaw ◽  
G. Nickless ◽  
...  
Keyword(s):  
Urban Areas ◽  
Dispersion Model ◽  
Vertical Mixing ◽  
Mixing Times ◽  
Empirical Correlations ◽  
Tracer Concentration ◽  
Vertical Dispersion ◽  
Regent's Park ◽  
Lateral Advection ◽  
Tracer Experiments

Abstract. There have been relatively few tracer experiments carried out that have looked at vertical plume spread in urban areas. In this paper we present results from two tracer (cyclic perfluorocarbon) experiments carried out in 2006 and 2007 in central London centred on the BT Tower as part of the REPARTEE (Regent's Park and Tower Environmental Experiment) campaign. The height of the tower gives a unique opportunity to study vertical dispersion profiles and transport times in central London. Vertical gradients are contrasted with the relevant Pasquill stability classes. Estimation of lateral advection and vertical mixing times are made and compared with previous measurements. Data are then compared with a simple operational dispersion model and contrasted with data taken in central London as part of the DAPPLE campaign. This correlates dosage with non-dimensionalised distance from source. Such analyses illustrate the feasibility of the use of these empirical correlations over these prescribed distances in central London.

scholarly journals Eating disorders among borderline patients: understanding the prevalence and psychopathology

2020 ◽  
Author(s):  
Mohsen Khosravi
Keyword(s):  
Eating Behaviors ◽  
Demographic Data ◽  
Cross Sectional Study ◽  
Sampling Interval ◽  
Eating Attitudes ◽  
Cross Sectional ◽  
Borderline Patients ◽  
Eat 26 ◽  
The Relationship ◽  
Tas 20

Abstract Background: Common comorbidity and the shared psychopathology in borderline personality disorder (BPD) and feeding and eating disorder (FED) resulted in conceptualization of the relationship theory between disordered eating behaviors (DEB), alexithymia, depression, and anxiety. Therefore, the present study aims at investigating the FED prevalence in patients with BPD and evaluating the relationship between DEB, alexithymia, anxiety, and depression.Methods: This cross-sectional study was performed from August 2018 to November 2019; 110 patients with BPD and 110 healthy people were studied in this research. The participants were selected by systematic random sampling out of the patients referring to Baharan psychiatric hospital in Zahedan, Iran, with the sampling interval of 3. The subjects were evaluated by demographic data form, the 26-item eating attitudes test (EAT-26), 20-item Toronto alexithymia scale (TAS-20), Beck anxiety disorder (BAI), and Beck depression inventory-II (BDI-II).Results: The results show a 65.4% (n = 72) prevalence of FED in borderline patients; the highest and lowest prevalence rates are reported for avoidant/restrictive food intake disorder (ARFID) and bulimia nervosa, respectively. The highest mean score of TAS-20 is reported in anorexia nervosa. The regression analysis results show that anxiety and depression play a mediating role in the relationship between alexithymia and DEB.Conclusions: The results suggest that alexithymia should be paid clinical attention as a trait and distress-independent construct in the BPD and FED comorbidity.

scholarly journals Spatiotemporal Distributions of Icebergs in a Temperate Fjord: Columbia Fjord, Alaska

2019 ◽  
Author(s):  
Sarah U. Neuhaus ◽  
Slawek M. Tulaczyk ◽  
Carolyn Branecky Begeman
Keyword(s):  
Surface Area ◽  
Power Law ◽  
Vertical Mixing ◽  
Heat Content ◽  
Correlation Coefficients ◽  
Back Stress ◽  
Late Winter ◽  
Power Law Distribution ◽  
Cross Sectional ◽  
Pixel Brightness

Abstract. Fjord-terminating glaciers account for the majority of recent sea level rise. Inside fjords, icebergs may affect glacier-ocean interactions by cooling incoming ocean waters, enhancing vertical mixing, or by providing back stress on the terminus. However, relatively few studies have been performed on iceberg dynamics inside fjords, particularly outside of Greenland. We examine icebergs calved from Columbia Glacier, Alaska, over eight months spanning late winter to mid-fall using 0.5-meter resolution satellite imagery, identifying icebergs based on pixel brightness. Iceberg sizes fit a power-law distribution with an overall power-law exponent, m, of −1.26 ± 0.05. We find that iceberg calving rate, rather than water temperature, appears to be the major control on the exponent value. We also examine iceberg spatial distribution inside the fjord, and find that large icebergs (10,000 m2 − 100,000 m2 cross-sectional area) have low spatial correlation with icebergs of smaller sizes (correlation coefficients between 0.345 ± 0.132 and 0.490 ± 0.114, compared to 0.809 ± 0.052 − 0.989 ± 0.006 for the highly spatially-correlated smaller icebergs), due to their tendency to ground on the shallows. We estimate the surface area of icebergs in contact with incoming seawater to be 2.8 ± 0.58 × 104 m2. When compared with our estimated terminus surface area, 9.7 ± 3.7 × 105 m2, we expect iceberg impact on the heat content of the incoming seawater to be negligible in this fjord. Additionally, we find mechanical buttressing of the glacier to be negligible due to low iceberg density near the calving front and lack of winter sea ice in the fjord.

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