Sill Height Research Articles

Sensitivity of Late Permian climate to bathymetric features and implications for the mass extinction

Evidence from stratigraphic sections of the Panthalassa, Paleo-Tethys and Neo-Tethys suggests that the oceans experienced widespread anoxia during the Late Permian, which likely contributed to the extinction of ~90% of marine and ~70% of terrestrial species. The Late Permian and Early Triassic were also characterized by significant carbon isotope excursions implying that considerable perturbations in the carbon cycle occurred. Bathymetric features of the Panthalassa during this period are not well known since most of the ocean floor has been subducted; however, tectonic reconstructions suggest that active marine subduction zones surrounded Pangea. Thus, it is reasonable to assume that there was an active mid-ocean ridge system located in Panthalassa during the Late Permian. In this study, the impact of such a spreading center within Panthalassa on the climate and carbon cycle is investigated using a comprehensive climate system model for the end-Permian. This is a novel approach because a majority of previous simulations assumed a flat bottom for the Panthalassa deep-sea. The mid-ocean ridge (MOR) simulation enhanced vertical mixing and topographic steering of the currents near the ridge-axis but in comparison with the simulation using a flat bottom, changes in the global distribution of water masses and circulation in the Panthalassa were insignificant. Dissolved oxygen concentrations were not considerably affected by the implementation of the mid-ocean ridge. Thus the approximation of using a flat-bottom topography in ocean models for the Late Permian remains valid.In a second sensitivity study, the effect of a sill between the deep Paleo-Tethys and Panthalassa on water mass distribution and oxygen content has been investigated. Model results suggest that the introduction of a sill led to enhanced stratification, as well as an increase in salinity and temperature in the Paleo-Tethys. An associated reduction of the dissolved oxygen concentration to dysoxic to near-anoxic conditions below 1800m suggests that the changes in sill height between the Paleo-Tethys and Panthalassa may have been a contributing factor of regional importance to the Permian-Triassic mass extinction.

Primary correction of nasal deformity in unilateral incomplete cleft lip: A comparative study between three techniques

Nasal deformities secondary to incomplete cleft lip are often underestimated in terms of their severity with resultant sub-optimal treatment. Constant refinements have led to the evolution of different surgical techniques in our institution for the treatment of these deformities. This study compared three different techniques in achieving nasal asymmetry for patients with unilateral incomplete cleft lip. Sixty-six patients who had primary correction of incomplete cleft lip nasal deformities at the age of 3 months were reviewed later at the age of 5 or 6. The patients were divided into three groups as according to the surgical treatment received: Group I (n=21) underwent a closed rhinoplasty with cartilage dissection and repositioning through lip incisions; Group II (n=25) underwent a semi-open rhinoplasty technique with cartilage dissection through bilateral rim incisions; and Group III (n=20) received a semi-open rhinoplasty technique through a Tajima incision on the cleft side and a rim incision on the contralateral side. Using photo-analysis, a total of seven measurements were obtained comparing the cleft side with the non-cleft sides, including bilateral nostril height, nostril width, height-to-width ratio, medial dome height, nasal sill height, nostril area, nasolabial angle and nostril axis. All the patients benefitted from primary correction of their incomplete cleft lip and nasal deformities. In addition, Group III patients achieved superior results over Groups I and II in terms of nostril height ratio and nostril axis (p<0.005). Primary correction of the nasal deformity is an important component of surgery at the time of lip correction. Our results indicated that a semi-open rhinoplasty technique accompanied by the Tajima incision provides the best overall nasal symmetry.

Reduction of stilling basin length with tall end sill

Experiments were conducted to characterize forced hydraulic jumps in stilling basins for enforced cases due to tail water level or dam site arrangement and construction. The case with a single tall sill was simulated in a horizontal flume downstream of a sluice gate. Results of experiments are compared with the classical hydraulic jump, and significant effect of tall sill on dissipation of energy in shorter distance was confirmed. Furthermore, the generated jumps were classified based on the ratio of sill height to basin length, and a simple design criterion was proposed to estimate the basin length for a desired jump and particular inflow.

Forced Hydraulic Jumps below Abrupt Expansions

A new approach for studying forced hydraulic jumps below abrupt symmetric and asymmetric expansions is introduced. Intensive experiments for two expansion ratios, one asymmetry ratio, and different solid sill heights and locations were conducted specifically for the spatial jump case as a critical design case. A new parameter correlating sill height and sill location is presented and found to play an important role in the basin’s design, scour, and flow patterns. Using this parameter gives distinguished relationships for predicting sequent depth, energy dissipation, and basin length for the preliminary or operating design in expected or unexpected flow conditions. Empirical equations and experimental regression curves are introduced to predict the sequent depth and the basin length at any sill height and sill location. Scour and flow patterns are intensively studied experimentally and qualitatively described for the symmetric and asymmetric basins with or without sills for the spatial jump. A numerical ex...

Choke-free flow in trapezoidal channels

is very suitable to design a channel transition from the point of view of a no-choke condition. In this study, the condition of choke-free flow for two types of transitions in trapezoidal channels subject to a rise in bed elevation is considered. Based on the critical flow occurring downstream of the transition zone, the energy equation is solved with the aid of numerical methods to determine explicit equations for the maximum permitted bed rise under a given approaching regime. The presented procedure herein can also be used to determine end sill height in triangular and trapezoidal channel sections to assure hydraulic jump occurrence in stilling basins. Moreover, to determine the limits of upstream-flow depths (the choke-free regions) a suitable dimensionless specific energy equation is presented. This equation can be utilised to choose the operating ranges of upstream flow depths for choke-free flow in subcritical and supercritical upstream flow conditions. Finally energy loss in the transition zone is considered by applying it in the proposed equations.

Long-Term Comparison of Four Techniques for Obtaining Nasal Symmetry in Unilateral Complete Cleft Lip Patients: A Single Surgeonʼs Experience

This study was the result of a constant evaluation of surgical techniques and results to obtain excellence in primary cleft rhinoplasty. This was a retrospective study from 1992 to 2003 comparing the long-term outcomes of four techniques of nasal reconstruction. There were 76 patients divided into four groups: group I (n = 23 patients), primary rhinoplasty alone; group II (n = 16 patients), nasoalveolar molding alone; group III (n = 14 patients), nasoalveolar molding plus primary rhinoplasty; and group IV (n = 23 patients), nasoalveolar molding plus primary rhinoplasty plus overcorrection. The surgical results were analyzed using photographic records obtained at 5 years of age. A ratio of six measurements was obtained comparing the cleft and noncleft sides. A panel assessment was obtained to grade the appearance of the surgical results. All surgery was performed by the senior author (P.K.T.C.). The results are given for groups I to IV, respectively. The nostril height ratio was 0.73, 0.77, 0.81, and 0.95. The nostril width ratio was 1.23, 1.36, 1.23, and 1.21. The one-fourth medial part of nostril height ratio was 0.70, 0.87, 0.92, and 1.00. The nasal sill height ratio was 0.75, 1.02, 1.07, and 1.07. The nostril area ratio was 0.86, 0.89, 0.95, and 1.08. The nostril height-to-width ratio was 0.58, 0.58, 0.71, and 0.92. Finally, group IV had the best panel assessment. The results revealed that group IV had the best overall result. Overcorrection of 20 percent was necessary to maintain the nostril height. Further technical modifications are necessary to minimize widening of the nostril width.

Mixing layer dynamics in separated flow over an estuarine sill with variable stratification

We investigate the generation of a mixing layer in the separated flow behind an estuarine sill (height H ∼ 4 m) in the Snohomish River, Washington as part of a larger investigation of coherent structures using remote and in situ sensing. During increasing ebb flows the depth d and stratification decrease and a region of sheared flow characterized by elevated production of turbulent kinetic energy develops. Profiles of velocity and acoustic backscatter exhibit coherent fluctuations of order 0.1 Hz and are used to define the boundaries of the mixing layer. Variations in the mixing layer width and its embedded coherent structures are caused by changes to both the normalized sill height H/d and to a bulk Richardson number Rih defined using the depth of flow over the sill. Entrainment ET and the mixing layer expansion angle increase as stratification and the bulk Richardson number decrease; this relationship is parameterized as ET = 0.07Rih−0.5 and is valid for approximately 0.1 &lt; Rih &lt; 2.8. Available comparisons with literature for inertially dominated conditions (Rih &lt; 0.1) are consistent with our data and validate our approach, though lateral gradients may introduce an upwards bias of approximately 20%. As the ratio H/d increases over the ebb, the free surface boundary pushes the mixing layer trajectory downward, reduces its expansion angle, and produces asymmetry in the acoustic backscatter (coherent structures). Three‐dimensional divergence, as imaged by infrared video and transecting data, becomes more prominent for H/d &gt; 0.8 due to blocking of flow by the sill.

Effect of water depth and the bottom boundary layer upon internal wave generation over abrupt topography

The role of water depth and bottom boundary layer turbulence upon lee-wave generation in sill regions is examined. Their effect upon vertical mixing is also considered. Calculations are performed using a non-hydrostatic model in cross-section form with a specified tidal forcing. Initial calculations in deeper water and a sill height such that the sill top is well removed from the surrounding bed region showed that downstream lee-wave generation and associated mixing increased as bottom friction coefficient k increased. This was associated with an increase in current shear across the sill. However, for a given k, increasing vertical eddy viscosity A v reduced vertical shear in the across sill velocity, leading to a reduction in lee-wave amplitude and associated mixing. Subsequent calculations using shallower water showed that for a given k and A v, lee-wave generation was reduced due to the shallower water depth and changes in the bottom boundary layer. However, in this case (unlike in the deepwater case), there is an appreciable bottom current. This gives rise to bottom mixing which in shallow water extends to mid-depth and enhances the mid-water mixing that is found on the lee side of the sill. Final calculations with deeper water but small sill height showed that lee waves could propagate over the sill, thereby reducing their contribution to mixing. In this case, bottom mixing was the major source of mixing which was mainly confined to the near bed region, with little mid-water mixing.

Hydraulic jump in stilling basin with vertical end sill

Stilling basins with dentiated or continuous sills are frequently used as energy dissipaters downstream of hydraulic structures. In this study, experiments are conducted to evaluate effects of a single vertical continuous sill and its position on control of depth and length of a forced jump in stilling basin without considering tailwater depth which is variable and totally controlled by downstream river conditions. A sill with five different heights was placed at three different longitudinal distances along a scaled model of a stilling basin. The hydraulic characteristics of the jump were measured and compared with the classical hydraulic jump under variable discharges. Results of experiments confirmed significant effect of the sill on dissipation of energy. A new relationship was developed between sill height and position, sequent depth ratio, and length of stilling basin. The advantage of the proposed relationship in practice is its capability to design stilling basin where tailwater depth is unpredictable

Messinian sea level fall in the Dacic Basin (Eastern Paratethys): palaeogeographical implications from seismic sequence stratigraphy

The signature of the Mediterranean Messinian Salinity Crisis (MSC) in the Paratethys has received wide attention because of the inferred changes in connectivity and base level. In this article, we present sequence stratigraphic interpretations on a seismic transect across the western part of the semi-isolated Late Miocene–Pliocene Dacic Basin (Eastern Paratethys, Romania), chronologically constrained by biostratigraphic field observations and well data. They reveal significant sea level changes during the middle Pontian that are coeval with the MSC. These changes were most likely transmitted to the western Dacic Basin from the downstream Black Sea and controlled by the sill height of the interconnecting gateway. During the middle Pontian lowstand of the western Dacian Basin, sedimentation continued in a remnant 300 m deep lake with a positive water balance. Our observations show that the evolution of semi-isolated sedimentary basins is strongly dependent on the communication with other depositional realms through its control on base level and sediment supply.

Influence of open boundary conditions and sill height upon seiche motion in a gulf

A cross-sectional model of an idealised constant depth gulf with a sill at its entrance, connected to a deep ocean, is used to examine the barotropic and baroclinic response of the region to wind forcing. The role of the oceanic boundary condition is also considered. Calculations show that in the case of a tall sill, where the pycnocline intersects the sill, the baroclinic response of the gulf is similar to that of a lake, and internal waves cannot radiate energy out of the gulf. The barotropic response shows free surface oscillations, with nodes located close to the centre of the oceanic basin and entrance to the gulf, with associated barotropic resonant periods. As the sill height is reduced, baroclinic wave energy is radiated from the gulf into the ocean, and the form of the baroclinic response changes from a standing wave (tall sill) as in a lake to a progressive wave (no sill). The location of sea surface elevation nodes and resonant periods changes as the sill height is reduced. Calculations of the barotropic resonant periods with and without stratification could not determine if they were influenced by the presence of stratification, although published analytical theory suggests that they should be able to when energy is lost from the gulf by internal wave radiation. This inability to detect changes in barotropic resonant period due to stratification effects is due to the small change in resonant frequency produced by baroclinic effects, as shown by analytical results, and the broad peak nature of the computed resonant frequency. In the case of a closed offshore boundary (an offshore island), there is a stronger and narrower energy peak at the resonant frequency than when a barotropic radiation condition is applied. However, the influence of stratification upon the resonant frequency could not be accurately determined. Although the offshore boundary was well removed from the gulf to such an extent that any baroclinic waves reflected from it could not reach the gulf within the integration period, it did, however, slightly influence the gulf baroclinic response due to its influence on the barotropic response.

Rule of Thumb for Daylighting of Rooms with External Obstructions

A daylighting rule of thumb or simplified formula for side-lit room with external obstruction has been presented by Littlefair. Based on Littlefair's formula and daylighting simulations generated by AGi-32, a modified rule of thumb for daylighting is proposed for a location in Sydney, New South Wales (Latitude −35° South and Longitude −150° East). Previous daylighting rules of thumb for Sydney based upon simulations using Lumen Micro 8 are revisited and revised. Lumen Micro 8 has been noted for its tendency of giving higher illuminance readings compared to other simulation software. In this research, AGi-32 is utilized in daylighting simulation of medium to large size rooms with external obstructions angles ranging from 5° to 80° from the window sill height (or work plane). The impacts of different surface reflectances (0% and 25%) of external obstructions on indoor illuminance are also examined.

A general formula for the prediction of vent flows

A new formula for fire-induced wall vent flow rate is developed based upon a theoretical derivation and mathematical fit to data. Previous research had developed a formula of mass flow rate for fire-induced doorway flows only. Here it is extended to include window flows. A theoretical model based on an ideal point source fire plume is used to guide the form of the empirical correlation. A thorough examination concerning the difference between the window and doorway flow modes is conducted. Both sill height and width of the windows pose key influence on the formula. The two vent configurations are merged into one equation. The results were compared to available flow data and shown to be within 15% accuracy for a wide range of fire conditions.

Characteristics of Shear Layer Structure in Skimming Flow over a Vertical Drop Pool

The characteristics of shear layer structure between the sliding jet and the pool for skimming flows over a vertical drop pool were investigated experimentally, using flow visualization technique and high speed particle image velocimetry. Four series of experiments having different end sill ratios (h/H=0.12, 0.43, 0.71 and 1.0, where h=end sill height and H=drop height) with various approaching flow discharges were performed to measure the detailed quantitative velocity fields of the shear layer. The mean velocities and turbulence properties were obtained by ensemble averaging the repeated measurements. From the velocity profiles, it is found that the growth of the shear layer in the downward direction as the jet slides down the pool represents the momentum exchange. Analyzing the distribution of measured velocity, the similarity profile of the mean velocity at different cross sections along the shear layer was obtained. The proposed characteristic scales provided unique similarity profiles having promising regression coefficient. The selection of these characteristic scales is also discussed. Further, the spatial variations of mean velocity profiles, turbulence intensities, in-plane turbulent kinetic energy, and Reynolds shear stress were also elucidated in detail. The imperative observation is that the Reynolds shear stress dominates the major part along the shear layer as compared to the viscous shear stress. The study also provides an insight into the flow phenomena through the velocity and turbulent characteristics.

Laboratory study of maximum scour depth downstream of sills

Bed sills have been widely used as a sequence of grade-control structures in mountain streams where incision has to be prevented. Major local scouring downstream of these structures is, however, often observed. In order to investigate the characteristics of local scouring, a number of experiments have been carried out with 105 cases in different situations. The initial bed slopes were 0·176 and 0·268; sediments were coarse sand, fine gravel and medium gravel. The sill spacings were 0·4, 0·6, 0·8 and 0·9 m, and the sill heights above initial stream bed level were 0, 0·02, 0·04 and 0·06 m, respectively. Three stages of scour evolution could be classified. The size of scour hole depends on the bed slope, sediment diameter, sill height and sill spacing. The slope of the stream bed was found to be the most important parameter affecting the maximum scour depth. Using dimensional analysis, the relative maximum scour depth at the equilibrium stage was formulated as functions of the relative morphological jump to mobility of sediment and the relative energy loss to flow energy. Compared with the measured data at the Maso di Spinelle River in the Italian Alps, the proposed formulae showed satisfactory results.

Depth-dependent overtides from internal tide reflection in a glacial fjord

Observations of current velocity profiles and hydrography over and near a tall sill in a Chilean glacial fjord are used to illustrate the interactions between barotropic and baroclinic tides. The character of the barotropic tide in the glacial fjord is mixed with semidiurnal dominance. The ratio of sill height to water column depth at the study site is ca. 0.95. Water column stratification appeared only in the upper 5 m of the water column. Current velocity variations in the stratified surface layer were quite different to those underneath. Below the pycnocline, nonlinear interactions between semidiurnal M2 and diurnal K1 oscillations yielded a third-diurnal distortion MK3. Most interesting, surface layer currents were distorted by the superposition of semidiurnal M2 and sixthdiurnal M6 oscillations. The oscillations with M6 variability were identified, through wave superposition approaches, as reflected internal tides linked to M2 tidal variations. This was confirmed by theoretical results of stratified barotropic tidal flows interacting with abrupt bathymetry. Under the predominantly tidally mixed regime of the study area, the distortion to surface currents caused by the reflected wave was nearly symmetric during the large tidal ranges of the diurnal cycle. Nearly symmetric distortions resulted as the phase lag between incident and reflected wave- induced currents was small (reflected currents developing a few minutes after maximum tidal flows). During the small ranges of the diurnal cycle, distortions were asymmetrical because of the relatively larger phase lags of the reflected signal (reflected currents developing tens of minutes after maximum tidal flows).

Efficient algorithms for finding sills in digital topographic maps

In stratified geophysical flows, the energetically optimal exchange of dense fluid across a topographic barrier generally takes place at the deepest unblocked connection, which is typically a saddle point (sill). The flow at or near a sill is often hydraulically controlled, in which case the sill is called a controlling sill. Oceanographic examples include overflows of newly formed dense water at high latitudes as well as sills in channels connecting major ocean basins, such as the Strait of Gibraltar. Controlling sills are usually associated with strong flows, making them ideal sites for monitoring transport and hydrographic variability. The locations and depths of controlling sills also provide strong constraints for the downstream hydrographic properties below sill depth. Here, two algorithms for finding sills in digital topographic maps are presented. The first approximates the sill height to arbitrary precision in O ( k ) steps, where k is the number of data points in the map. The second algorithm, which requires O ( k log k ) steps, additionally returns the sill location. Several tests carried out with realistic problems from physical oceanography reveal that the second algorithm runs faster in practice, even though its worst case behavior is worse.

Effect of sill in the hydraulic jump in a triangular channel/ Effet du seuil sur le ressaut hydraulique dans un canal triangulaire

Hydraulic jumps are experimentally examined in a horizontal symmetrical triangular channel of 90° central angle. This study investigates the main features of both the minimum-B jump and the sill-controlled jump under various inflow conditions. The development of jumps was ensured using either a thin-crested or a broad-crested sill. Based on a large experimental program, the data were fitted to empirical relations to detect the effect of the inflow Froude number on the relative sill height, the sequent depths ratio and the non-dimensional toe position of the sill. The relations obtained are recommended for designing irrigation ditches.

Impacts of some parameters affecting the hydraulic performance of U-shaped side spillways

Side channel spillways are one type of outlet works at dams with wide applications in irrigation and drainage systems and in water and wastewater facilities. When the flow enters the side channel through the end and two side weirs of the spillway, it is called a three-sided spillway. Based on the results of laboratory experiments, the present study investigates the impacts of variation in end-sill elevation and location and the bed slope of the side channel for different inflow rates into a spillway. In these evaluations, variation in flow regime is taken as a qualitative index and the flow turbulence index is taken as a quantitative index. The values for the latter index were calculated from readings of momentary pressures using a datalogger system. The results showed that the sill elevation had the greatest effect on pressure fluctuations and on the hydraulic performance of the side channel in these spillways. Increasing the sill height decreased the quantitative value of the water turbulence index in the side channel. According to the findings of the present study, the location of the sill in relation to the side channel does not have a considerable effect on pressure fluctuations. It was also found that increasing the channel bed slope reduces pressure fluctuations by about 3%. Greater increases in the bed slope cause increased flow turbulence. Increasing the channel bed slope in the reverse (negative) direction had considerable effects on reducing the channel flow turbulence.Key words: hydraulic performance, pressure fluctuations, spatially varied flow, three-sided channel spillway, U-shaped spillway.

Morphological variation and airflow dynamics in the human nose

Airflow dynamics are recognized as being important to the functioning of the human nose in conditioning and filtering inspired air, yet these dynamics are poorly understood. Despite considerable research on airflow dynamics by otolaryngologists, respiratory physiologists, and toxicologists, major disagreements remain about the nature of airflow in the human nose. Specifically, there is little consensus about the character of nasal airflow regimes (laminar or turbulent) and about the major pathways of airflow through the internal chamber. Additionally, a number of features in the human nose have been argued to enhance airflow turbulence, thus increasing the exposure of moving air to the nasal mucosa and facilitating heat and moisture exchange in cold and/or dry climates. These features include: an inferior orientation of the nares; a nasal sill that is high relative to the floor of the internal nasal chamber; a nasal valve that is small in cross-sectional area relative to that of the internal chamber; and large, projecting conchae. The claim that these features affect airflow dynamics has never been tested. To clarify the nature of human nasal airflow and to test these claims of functional significance to nasal variation, we studied airflow across physiological flow rates using water and dye flowing through anatomically accurate acrylic models of human nasal air passageways (with adjustment of water flow rates to maintain dynamic similarity). The models were derived from direct casting of the nasal passageways of 10 Caucasian ("leptorrhine") cadavers (six male, four female). Measures of naris angle, nasal sill height, nasal valve area relative to internal chamber cross-sectional area, and relative projection of the inferior and middle turbinates were taken directly on the resulting casts. The relationships between aspects of nasal morphology and turbulent air flow were evaluated by examining the flow regimes (laminar, semiturbulent, or turbulent) at varying flow rates, with the expectation that the greater the development of the proposed turbulence-enhancing features the slower the flow rate at which flow would shift from one regime to another. Flow characteristics (both flow regimes and principal pathways) were highly variable within our sample. The relative projection of the inferior turbinate was the only variable that significantly affected the flow rate at which flow became turbulent. However, more projecting turbinates appear to laminate flow rather than to induce turbulence. Nostril orientation was moderately correlated with flow dynamics (with more inferiorly directed nares producing turbulence at slower flow rates), but this correlation was not statistically significant. Relative nasal valve area and nasal sill height were unrelated to turbulence in our models.