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.

Water mass transformation and overturning circulation in the Arabian Gulf

2021 ◽  
Author(s):  
Maryam R. Al-Shehhi ◽  
Hajoon Song ◽  
Jeffery Scott ◽  
John Marshall
Keyword(s):  
Water Mass ◽  
Arabian Gulf ◽  
Three Dimensional ◽  
Heat Fluxes ◽  
Transformation Rate ◽  
Overturning Circulation ◽  
Resolution Model ◽  
Meridional Overturning ◽  
High Resolution Model ◽  
Water Mass Transformation

AbstractWe diagnose the ocean’s residual overturning circulation of the Arabian Gulf in a high-resolution model and interpret it in terms ofwater-mass transformation processes mediated by air-sea buoyancy fluxes and interior mixing. We attempt to rationalise the complex three-dimensional flow in terms of the superposition of a zonal (roughly along-axis) and meridional (transverse) overturning pattern. Rates of overturning and the seasonal cycle of air-sea fluxes sustaining them are quantified and ranked in order of importance. Air-sea fluxes dominate the budget so that, at zero order, the magnitude and sense of the overturning circulation can be inferred from air-sea fluxes, with interior mixing playing a lesser role. We find that wintertime latent heat fluxes dominate the water-mass transformation rate in the interior waters of the Gulf leading to a diapycnal volume flux directed toward higher densities. In the zonal overturning cell, fluid is drawn in from the Sea of Oman through the Strait of Hormuz, transformed and exits the Strait near the southern and bottom boundaries. Along the southern margin of the Gulf, evaporation plays an important role in the meridional overturning pattern inducing sinking there.

scholarly journals Secondary currents induced mixing at channel confluences

2017 ◽  
Vol 44 (12) ◽  
pp. 1071-1083 ◽  
Author(s):  
Xue Chen ◽  
David Z. Zhu ◽  
Peter M. Steffler
Keyword(s):  
Three Dimensional ◽  
Flow Dynamics ◽  
Side Channel ◽  
Mixing Rate ◽  
Secondary Current ◽  
Secondary Currents ◽  
Secondary Circulations ◽  
Mixing Rates ◽  
Large Discharge ◽  
Channel Confluence

Channel confluence is a common feature in river systems. The flow dynamics associated with channel confluence are highly three-dimensional with strong flow circulations and secondary currents and can result in enhanced river mixing downstream. In this study, a three-dimensional numerical model was employed to estimate the secondary currents induced streamline curvatures and the resulting mixing rate at channel confluences with different junction angles and discharge ratios. The results show that while twin secondary circulations are found at channel confluence, their contribution to the mixing depends on their local positions with respect to the river streams. With the secondary current growing downstream, the mixing rate is accelerated, in particular for the cases with the side channel perpendicular to the main channel and having a relatively large discharge. Turbulent diffusion can contribute up to about half of the rapid mixing. The mixing rates for different simulation cases are examined.

scholarly journals Pico and nanoplankton abundance and carbon stocks along the Brazilian Bight

PeerJ ◽  
2016 ◽  
Vol 4 ◽  
pp. e2587 ◽  
Author(s):  
Catherine Gérikas Ribeiro ◽  
Adriana Lopes dos Santos ◽  
Dominique Marie ◽  
Vivian Helena Pellizari ◽  
Frederico Pereira Brandini ◽  
...  
Keyword(s):  
Surface Waters ◽  
Heterotrophic Bacteria ◽  
Vertical Mixing ◽  
Water Masses ◽  
Variable Properties ◽  
Southwest Atlantic ◽  
Tropical Water ◽  
Light Levels ◽  
Lower Light ◽  
Marine Areas

Pico and nanoplankton communities from the Southwest Atlantic Ocean along the Brazilian Bight are poorly described. The hydrography in this region is dominated by a complex system of layered water masses, which includes the warm and oligotrophic Tropical Water (TW), the cold and nutrient rich South Atlantic Central Water (SACW) and the Coastal Water (CW), which have highly variable properties. In order to assess how pico- and nanoplankton communities are distributed in these different water masses, we determined by flow cytometry the abundance of heterotrophic bacteria,Prochlorococcus,Synechococcusand autotrophic pico and nanoeukaryotes along three transects, extending from 23°S to 31°S and 39°W to 49°W. Heterotrophic bacteria (including archaea, maximum of 1.5 × 106cells mL−1) were most abundant in Coastal and Tropical Water whereasProchlorococcuswas most abundant in open-ocean oligotrophic waters (maximum of 300 × 103cells mL−1).Synechococcus(up to 81 × 103cells mL−1), as well as autotrophic pico and nanoeukaryotes seemed to benefit from the influx of nutrient-rich waters near the continental slope. Autotrophic pico and nanoeukaryotes were also abundant in deep chlorophyll maximum (DCM) layers from offshore waters, and their highest abundances were 20 × 103cells mL−1and 5 × 103cells mL−1, respectively. These data are consistent with previous observations in other marine areas whereSynechococcusand autotrophic eukaryotes dominate mesotrophic waters, whereasProchlorococcusdominate in more oligotrophic areas. Regardless of the microbial community structure near the surface, the carbon stock dominance by autotrophic picoeukaryotes near the DCM is possibly linked to vertical mixing of oligotrophic surface waters with the nutrient-rich SACW and their tolerance to lower light levels.

Effects of Scalloping on the Mixing Mechanisms of Forced Mixers With Highly Swirling Core Flow

2013 ◽  
Vol 135 (7) ◽  
Author(s):  
Alex Wright ◽  
Zhijun Lei ◽  
Ali Mahallati ◽  
Mark Cunningham ◽  
Julio Militzer
Keyword(s):  
Separation Bubble ◽  
Three Dimensional ◽  
Navier Stokes ◽  
Suction Surface ◽  
Mixing Rate ◽  
Reduced Pressure ◽  
Core Flow ◽  
Flow Swirl ◽  
Swirl Angle ◽  
Mixing Rates

This paper presents a detailed experimental and computational investigation of the effects of scalloping on the mixing mechanisms of a scaled 12-lobe turbofan mixer. Scalloping was achieved by eliminating approximately 70% of the lobe sidewall area. Measurements were made downstream of the mixer in a co-annular wind tunnel, and the simulations were carried out using an unstructured Reynolds averaged Navier–Stokes (RANS) solver, Numeca FINE/Hexa, with k-ω SST model. In the core flow, the swirl angle was varied from 0 deg to 30 deg. At high swirl angles, a three-dimensional separation bubble was formed on the lobe's suction surface penetration region and resulted in the generation of a vortex at the lobe valley. The valley vortex quickly dissipated downstream. The mixer lobes removed most of the swirl, but scalloped lobes removed less swirl in the region of the scalloped notch. The residual swirl downstream of the scalloped mixer interacted with the vortices and improved mixing rates compared to the unscalloped mixer. Core flow swirl up to 10 deg provided improved mixing rates and reduced pressure and thrust losses for both mixers. As core flow swirl increased beyond 10 deg, the mixing rate continued to improve, but pressure and thrust losses declined compared to the zero swirl case. Lobe scalloping, in high swirl conditions, resulted in better mixing and improved pressure loss over the unscalloped mixer but at the expense of reduced thrust.

Methods for Enhanced Turbulence Mixing in Supersonic Shear Flows

1994 ◽  
Vol 47 (6S) ◽  
pp. S188-S192 ◽  
Author(s):  
E. J. Gutmark ◽  
K. C. Schadow ◽  
K. H. Yu
Keyword(s):  
Compressible Flows ◽  
Three Dimensional ◽  
Shear Layers ◽  
Mixing Rate ◽  
Planar Shear ◽  
Wide Range ◽  
Turbulence Mixing ◽  
Mixing Rates ◽  
Performance Penalty ◽  
Supersonic Shear Layers

Supersonic shear layers have inherent low mixing rates due to compressibility effects. Their mixing rate relative to subsonic shear layers can be up to 5 times lower. Several important technological applications which require intense mixing of supersonic flows gave impetus to research aimed to develop methods to enhance mixing in compressible flows with minimal performance penalty. This paper reviews some of these methods applied to both planar shear layers and jets. The methods are arranged in several categories: passive and active control of shear layer instabilities, three dimensional jets, generation of axial vorticity and shock interaction with shear layers. The paper concludes by discussing the importance of the wide range of length-scales in which turbulent mixing occurs.

PERIODONTAL DISEASE STATUS, KNOWLEDGE, ATTITUDE, PRACTICE AND TREATMENT NEEDS OF PREGNANT WOMEN

2018 ◽  
Vol 8 (6) ◽  
pp. 138-144
Author(s):  
Thien Nguyen Duc ◽  
Tai Tran Tan
Keyword(s):  
Periodontal Disease ◽  
Pregnant Women ◽  
Oral Hygiene ◽  
Disease Status ◽  
Incidence Rates ◽  
Gestation Period ◽  
Treatment Needs ◽  
Cross Sectional ◽  
Mean Values ◽  
The Mean

Background: Periodontal disease is a prominent and important issue of public health, especially in pregnant women. The objective of this study is to describe the clinical characteristics; learn knowledge, attitudes, practice oral hygiene and assess the need for treatment of periodontal disease in pregnant women. Subjects and Methods: A cross-sectional study of 210 pregnant women who visited the Department of Obstetrics and Gynecology at the Hue University of Medicine and Pharmacy Hospital. Clinical examination and interview questions on knowledge, attitudes and practice of oral care for all subjects. Results: The incidence of gingivitis was 100%, with mild gingivitis of 4,3% and moderate gingivitis of 95.7%. There was a difference in incidence rates of gingivitis in the gestational period (p<0.001). The incidence of periodontitis is 17.6% and there is no difference in gestational age (p>0.05). The mean values of GI and BOP indices differed by gestation period (p<0.05) and PD, OHI-S, PlI have statistically significant relationship with gestation period (p>0.05). The incidence of periodontal disease is 80.5%; The percentage of pregnant women who abstain from brushing their teeth after birth is 61.4%. Prevalence of brushing once a day: 7.1%; Twice a day: 70.5% and 3 times daily: 22.4%; The mean values of GI, PD, BOP, OHI-S and PlI were inversely proportional to the number of brushing (p<0.001). The rate of dental hygiene is just 3.3%; The rate of oral hygiene, dental plaque and plaque removal was 94,3%; The proportion of subjects required for intensive treatment is 2.4%. Conclusion: Periodontal disease, especially for pregnant women, is high. It is necessary to educate the knowledge, attitudes and practice of proper oral hygiene and to better meet the demand for periodontal disease treatment for pregnant women. Key words: Periodontal disease, pregnant women, knowledge, attitude, practice for oral hygiene, treatment needs

scholarly journals Accuracy and Reproducibility of Facial Measurements of Digital Photographs and Wrapped Cone Beam Computed Tomography (CBCT) Photographs

Diagnostics ◽  
2021 ◽  
Vol 11 (5) ◽  
pp. 757
Author(s):  
Maged Sultan Alhammadi ◽  
Abeer Abdulkareem Al-mashraqi ◽  
Rayid Hussain Alnami ◽  
Nawaf Mohammad Ashqar ◽  
Omar Hassan Alamir ◽  
...  
Keyword(s):  
Computed Tomography ◽  
Soft Tissue ◽  
Cone Beam Computed Tomography ◽  
High Reliability ◽  
Three Dimensional ◽  
Cone Beam ◽  
Cross Sectional ◽  
Facial Profile ◽  
Digital Photographs ◽  
Gonial Angle

The study sought to assess whether the soft tissue facial profile measurements of direct Cone Beam Computed Tomography (CBCT) and wrapped CBCT images of non-standardized facial photographs are accurate compared to the standardized digital photographs. In this cross-sectional study, 60 patients with an age range of 18–30 years, who were indicated for CBCT, were enrolled. Two facial photographs were taken per patient: standardized and random (non-standardized). The non-standardized ones were wrapped with the CBCT images. The most used soft tissue facial profile landmarks/parameters (linear and angular) were measured on direct soft tissue three-dimensional (3D) images and on the photographs wrapped over the 3D-CBCT images, and then compared to the standardized photographs. The reliability analysis was performed using concordance correlation coefficients (CCC) and depicted graphically using Bland–Altman plots. Most of the linear and angular measurements showed high reliability (0.91 to 0.998). Nevertheless, four soft tissue measurements were unreliable; namely, posterior gonial angle (0.085 and 0.11 for wrapped and direct CBCT soft tissue, respectively), mandibular plane angle (0.006 and 0.0016 for wrapped and direct CBCT soft tissue, respectively), posterior facial height (0.63 and 0.62 for wrapped and direct CBCT soft tissue, respectively) and total soft tissue facial convexity (0.52 for both wrapped and direct CBCT soft tissue, respectively). The soft tissue facial profile measurements from either the direct 3D-CBCT images or the wrapped CBCT images of non-standardized frontal photographs were accurate, and can be used to analyze most of the soft tissue facial profile measurements.

scholarly journals A Numerical Study of Sub-Millisecond Integrated Mix-and-Inject Microfluidic Devices for Sample Delivery at Synchrotron and XFELs

2021 ◽  
Vol 11 (8) ◽  
pp. 3404
Author(s):  
Majid Hejazian ◽  
Eugeniu Balaur ◽  
Brian Abbey
Keyword(s):  
Molecular Dynamics ◽  
Flow Rate ◽  
Numerical Study ◽  
Three Dimensional ◽  
Microfluidic Devices ◽  
Liquid Jets ◽  
Mixing Efficiency ◽  
X Ray Diffraction ◽  
Cross Sectional ◽  
Time Required

Microfluidic devices which integrate both rapid mixing and liquid jetting for sample delivery are an emerging solution for studying molecular dynamics via X-ray diffraction. Here we use finite element modelling to investigate the efficiency and time-resolution achievable using microfluidic mixers within the parameter range required for producing stable liquid jets. Three-dimensional simulations, validated by experimental data, are used to determine the velocity and concentration distribution within these devices. The results show that by adopting a serpentine geometry, it is possible to induce chaotic mixing, which effectively reduces the time required to achieve a homogeneous mixture for sample delivery. Further, we investigate the effect of flow rate and the mixer microchannel size on the mixing efficiency and minimum time required for complete mixing of the two solutions whilst maintaining a stable jet. In general, we find that the smaller the cross-sectional area of the mixer microchannel, the shorter the time needed to achieve homogeneous mixing for a given flow rate. The results of these simulations will form the basis for optimised designs enabling the study of molecular dynamics occurring on millisecond timescales using integrated mix-and-inject microfluidic devices.

scholarly journals Pool Boiling Heat Transfer Coefficients in Mixtures of Water and Glycerin

Processes ◽  
2021 ◽  
Vol 9 (5) ◽  
pp. 830
Author(s):  
Viktor Vajc ◽  
Radek Šulc ◽  
Martin Dostál
Keyword(s):  
Heat Transfer ◽  
Dynamic Method ◽  
Water Mass ◽  
Heat Fluxes ◽  
Static Method ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Mean Relative Error ◽  
Mixture Effects ◽  
Mass Fractions

Heat transfer coefficients were investigated for saturated nucleate pool boiling of binary mixtures of water and glycerin at atmospheric pressure in a wide range of concentrations and heat fluxes. Mixtures with water mass fractions from 100% to 40% were boiled on a horizontal flat copper surface at heat fluxes from about 25 up to 270kWm−2. Experiments were carried out by static and dynamic method of measurement. Results of the static method show that the impact of mixture effects on heat transfer coefficient cannot be neglected and ideal heat transfer coefficient has to be corrected for all investigated concentrations and heat fluxes. Experimental data are correlated with the empirical correlation α=0.59q0.714+0.130ωw with mean relative error of 6%. Taking mixture effects into account, data are also successfully correlated with the combination of Stephan and Abdelsalam (1980) and Schlünder (1982) correlations with mean relative error of about 15%. Recommended coefficients of Schlünder correlation C0=1 and βL=2×10−4ms−1 were found to be acceptable for all investigated mixtures. The dynamic method was developed for fast measurement of heat transfer coefficients at continuous change of composition of boiling mixture. The dynamic method was tested for water–glycerin mixtures with water mass fractions from 70% down to 35%. Results of the dynamic method were found to be comparable with the static method. For water–glycerin mixtures with higher water mass fractions, precise temperature measurements are needed.

Effect of Medialization of the Trochlear Groove and Lateralization of the Tibial Tubercle on TT-TG Distance: A Cross-sectional Study of Dysplastic and Nondysplastic Knees

2021 ◽  
pp. 036354652098781
Author(s):  
Mathias Paiva ◽  
Lars Blønd ◽  
Per Hölmich ◽  
Kristoffer Weisskirchner Barfod
Keyword(s):  
Trochlear Dysplasia ◽  
Cross Sectional Study ◽  
Magnetic Resonance Images ◽  
Tibial Tubercle ◽  
Control Group ◽  
Trochlear Groove ◽  
Sectional Study ◽  
Cross Sectional ◽  
Mean Values ◽  
The Mean

Background: Tibial tubercle–trochlear groove (TT-TG) distance is often used as a measure of lateralization of the TT and is important for surgical planning. Purpose: To investigate if increased TT-TG distance measured on axial magnetic resonance images is due to lateralization of the TT or medialization of the TG. Study Design: Cross-sectional study; Level of evidence, 3. Methods: A total of 84 knees (28 normal [NK], 28 with trochlear dysplasia [TD], and 28 with patellar dislocation without TD [PD]) were examined. The medial border of the posterior cruciate ligament (PCL) was chosen as the central anatomic landmark. The distance from the TT to PCL (TT-PCL) was measured to examine the lateralization of the TT. The distance from the TG to the PCL (TG-PCL) was measured to examine the medialization of the TG. Between-group differences were investigated by use of 1-way analysis of variance. Results: The mean values for TT-TG distance were 8.7 ± 3.6 mm for NK, 12.1 ± 6.0 mm for PD, and 16.7 ± 4.3 mm in the TD group ( P < .01). The mean values for TT-PCL distance were 18.5 ± 3.6 mm for NK, 18.5 ± 4.5 mm for PD, and 21.2 ± 4.2 mm in the TD group ( P = .03). The mean values for TG-PCL distance were 9.6 ± 3.0 mm for NK, 7.1 ± 3.4 mm for PD, and 5.1 ± 3.3 mm in the dysplastic group ( P < .01). Conclusion: The present results indicate that increased TT-TG distance is due to medialization of the TG and not lateralization of the TT. Knees with TD had increased TT-TG distance compared with the knees of the control group and the knees with PD. The TT-PCL distance did not differ significantly between groups, whereas the TG-PCL distance declined with increased TT-TG.

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