Central Orifice Research Articles

Fe and S-isotope compositions of hydrothermal deposits from Kings Triple Junction, Lau Basin, southwest Pacific Ocean

We analyzed iron and sulfur isotopic compositions of polymetallic sulfides from an extinct hydrothermal mound near the Kings Triple Junction of the northern Lau basin belonging to a back-arc basin for understanding the origin and mineral zoning processes in this study. Sulfides from the hydrothermal mound's pedestal slab consisting of chalcopyrite and pyrite show enrichment of heavy S-isotope (δ34SV-CDT = +8.3 to +9.6‰). Sphalerite-dominated chimney on the mound's slope also has variable δ34S values between +5.5 and + 8.3‰ from central orifice to outer wall. These isotopic ratios indicate the substantial contribution of heavy isotope rich sulfate-S in seawater circulating within the mound. Low Δ33S values in these sulfides also indicate that the sulfate reduction is of thermal origin, with minimal or no role for microbes. Circulating seawater induced changes in fluid composition and post-depositional zone refinement of certain minerals can explain the variation in δ34S in different layers within the chimney and pedestal slab. The Fe-isotopic compositions (δ56FeIRMM-014) show a range from −1.1 to −0.3‰ in the pedestal slab while they vary between −1.7 and − 0.6‰ at different parts of the peripheral chimney section. We explain such changes are mostly due to redox processes and mineral zoning development during these sulfide deposit formation. The tree-like FeMn oxide growth structures in the vicinity of the hydrothermal mound having a thin birnessite top layer and amorphous iron oxide bottom part show distinct δ56Fe values of −3.0 and − 0.8‰, respectively.

Possible Early Generation of Physiological Helical Flow Could Benefit the Triflo Trileaflet Heart Valve Prosthesis Compared to Bileaflet Valves.

Background—Physiological helical flow in the ascending aorta has been well documented in the last two decades, accompanied by discussions on possible physiological benefits of such axial swirl. Recent 4D-MRI studies on healthy volunteers have found indications of early generation of helical flow, early in the systole and close to the valve plane. Objectives—Firstly, the aim of the study is to investigate the hypothesis of premature swirl existence in the ventricular outflow tract leading to helical flow in the valve plane, and second to investigate the possible impact of two different mechanical valve designs on the preservation of this early helical flow and its subsequent hemodynamic consequences. Methods—We use a pulse duplicator with an aortic arch and High-Speed Particle Image Velocimetry to document the flow evolution in the systolic cycle. The pulse-duplicator is modified with a swirl-generating insert to generate early helical flow in the valve plane. Special focus is paid to the interaction of such helical flow with different designs of mechanical prosthetic heart valves, comparing a classical bileaflet mechanical heart valve, the St. Jude Medical Regent valve (SJM Regent BMHV), with the Triflo trileaflet mechanical heart valve T2B version (Triflo TMHV). Results—When the swirl-generator is inserted, a vortex is generated in the core flow, demonstrating early helical flow in the valve plane, similar to the observations reported in the recent 4D-MRI study taken for comparison. For the Triflo trileaflet valve, the early helical flow is not obstructed in the central orifice, similar as in the case of the natural valve. Conservation of angular momentum leads to radial expansion of the core flow and flattening of the axial flow profile downstream in the arch. Furthermore, the early helical flow helps to overcome separation at the outer and inner curvature. In contrast, the two parallel leaflets for the bileaflet valve impose a flow straightener effect, annihilating the angular momentum, which has a negative impact on kinetic energy of the flow. Conclusion—The results imply better hemodynamics for the Triflo trileaflet valve based on hydrodynamic arguments under the discussed hypothesis. In addition, it makes the Triflo valve a better candidate for valve replacements in patients with a pathological generation of nonaxial velocity in the ventricle outflow tract.

Using Mie Scattering to Determine the Wavelength-Dependent Refractive Index of Polystyrene Beads with Changing Temperature.

Polystyrene beads are often used as test particles in aerosol science. Here, a contact-less technique is reported for determining the refractive index of a solid aerosol particle as a function of wavelength and temperature (20-234 °C) simultaneously. Polystyrene beads with a diameter of 2 μm were optically trapped in air in the central orifice of a ceramic heating element, and Mie spectroscopy was used to determine the radius and refractive index (to precisions of 0.8 nm and 0.0014) of eight beads as a function of heating and cooling. Refractive index, n, as a function of wavelength, λ (0.480-0.650 μm), and temperature, T, in centigrade, was found to be n = 1.5753 - (1.7336 × 10-4)T + (9.733 × 10-3)λ-2 in the temperature range 20 < T < 100 °C and n = 1.5877 - (2.9739 × 10-4)T + (9.733 × 10-3)λ-2 in the temperature range 100 < T < 234 °C. The technique represents a step change in measuring the refractive index of materials across an extended range of temperature and wavelength in an absolute manner and with high precision.

Morphological Study of The Pancreas and Duodenum in Adult Guinea Pigs (Cavia porcellus)

The present study aimed to investigate the morphological features of the pancreas and duodenum of the adult males and females guinea pigs. Eight animals of each sex were collected to conduct this project. The selected organs were photographed in situ and macro morphometric measurements were conducted on them. Gross findings revealed that the pancreas of guinea pig was of compact type, of two lobes (right and left) connected by large central part (body). The organ drains the pancreatic secretion toward the last part of the ascending duodenum via minor pancreatic duct with absence of major pancreatic duct. The duodenum of the guinea pig was very short and V-shaped. The beginning of the duodenum contains duodenal papilla in which found central orifice for the exit of bile secretions of the common bile duct. In conclusions, the present findings showed the presence of only one minor pancreatic duct and such result was significantly different than most rodents by having major pancreatic duct. The duodenum in the studied guinea pigs was characteristically very short and V-shaped differently to other animals that have U-shaped and long duodenum.

Broadband Acoustic Ventilation Barriers

Conventional sound barriers impede airflow at the same time. Recent advances in acoustic metasurfaces provide a solution for air-permeable barriers utilizing the Fano-like interference. While the mechanism of Fano-like interference implies that such a realized device serves a narrow working frequency range around every destructive-interference frequency. Considering the fact that noise usually covers a wide frequency range, designing a broadband acoustic barrier is still a challenge. Here, we theoretically design a planar-profile and subwavelength-thickness (approximately $\ensuremath{\lambda}/8$) acoustic ventilation barrier prohibitive for sound in a broad range. Our design is a metasurface consisting of a central hollow orifice and two surrounding helical pathways with varying pitch. Thanks to the hornlike helical pathways, the response strength from the monopolar and dipolar modes of the system almost keeps balance in the frequency range of interest, leading to an effective blocking of more than $90\mathrm{%}$ of incident energy in the range of 900--1418 Hz. Experiments are conducted to validate the proposed design, whose results are consistent with the analytical predictions and simulations. The underlying working mechanism ensures the metasurface is capable of handling broadband sound coming from various directions. Our design has potential in air-permeable yet sound-proofing applications, such as simultaneously natural ventilation and noise reduction in green buildings.

Flow structure and mechanism of heat transfer in a Ranque–Hilsch vortex tube

Flow structure of incompressible fluid in a Ranque–Hilsch vortex tube was studied experimentally. A pattern of streamlines in the whole volume of the vortex tube was constructed from the velocity distributions measured using laser Doppler anemometry. The radial distributions of the azimuthal velocity in the Ranque–Hilsch vortex tube are shown to be different from those in a vortex tube with a tangential inlet and a single central exit orifice. Based on the obtained structure of the flow, a simple qualitative model is proposed to explain the physical mechanism of the temperature separation effect.

An experimental study of a multi-orifice synthetic jet with application to cooling of compact devices

In the present work, the flow characteristics of free and impinging synthetic jets formed from a single cavity but with a different number of orifices are investigated using the particle image velocimetry technique. A synthetic jet is a zero-net mass-flux device that formed by periodic ejection and suction of fluid through a small opening. The flow characteristics are used to explain the heat transfer results in the literature. The number of satellite orifices, distance between orifices, and location of the surface from orifices are varied to observe the phenomenon of jet interaction and its influence on flow recirculation. The results show that interaction between adjacent jets causes the diversified flow characteristics of the multiorifice jet with respect to a single orifice jet. The multiorifice jet exhibits significantly higher entrainment and mixing compared to its equivalent diameter of a single orifice jet. Moreover, results from the impinging jet corroborate that the impingement of vortex pairs, their breakdown, and formation of a strong wall jet are responsible for a high heat transfer coefficient for the case of larger surface spacing (z/d ≥ 8; normalized distance between orifice and surface). However, for impingement at small surface spacing (z/d ≤ 2), change in recirculation behavior with different orifice configurations can lead to a variation in the heat transfer coefficient. For the large and medium surface spacing (2 &amp;lt; z/d &amp;lt; 8), the center orifice gets sufficient time to develop, which draws the satellite and impingement jets as a single orifice jet. In the case of large surface spacing, the wall jet vortices are not attracted during the suction stroke. While for medium surface spacing, wall jet vortices are closer to the orifice and easily entrained during the suction stroke and form a recirculating region. In the case of small surface spacing, the center jet does not get sufficient time, and hence both center and satellite jets impinge separately. It was found that the center jet having higher ejection velocity impinges earlier than the satellite jet and the wall jet vortex formed from the center orifice drives along a wall jet. Therefore, recirculation is absent for smaller surface spacing, and fresh fluid is sucked and impinges on the surface in each cycle. This study expands the current knowledge of multiorifice free and impinging jets and establishes a relationship between heat transfer and fluid flow, which eventually facilitates an efficient and effective heat transfer system for compact devices.

Regimes of jetting and bubbling in a fluidized bed studied using real-time magnetic resonance imaging

Real-time magnetic resonance imaging was used to study the different flow regimes which occur in a fluidized bed containing a gas injection system. The gas flow rates through the main distributor and a central orifice were varied independently. We identified six different regimes of bubbling and jetting behavior: (1) freely bubbling, (2) permanent jet, (3) spouting, (4) pulsating jet, (5) pulsating jet with bubble collapse and (6) pulsating jet and freely bubbling. While regimes (1–4) have been described previously in the literature, regimes (5) and (6) are described here for the first time. To construct a regime map, the Froude number (Fr) and the ratio of the superficial gas velocity to the minimum fluidization velocity (U/Umf) were used to describe the system. We observed that bubbles formed predominantly, when U/Umf > 1. Further, we propose an empirical model that predicts the length of jets in the permanent jet regime as a function of Fr and background gas flow as ljetdor=0.12Fr0.381+UbgUmf0.81. The proposed model is in good agreement with tomographic measurements in smaller 3D systems reported in the literature, indicating that the non-dimensionalized description of jet length using a Fr number is valid throughout a large range of system diameters. Moreover, the bubble breakoff frequency of the pulsating jet regime was assessed by Fourier analysis, demonstrating that the frequency increases with increasing Fr before plateauing.

P4381Improvement of the PISA method in the setting of mitral regurgitation of complex geometry

Abstract Background Doppler echocardiographic methods, such as proximal isovelocity surface area (PISA) are used to quantify mitral regurgitations. However, their accuracy and reproducibility are still discussed, especially in case of mitral regurgitations of complex geometry. Purpose The aim of this study was to test in-vitro the accuracy of the PISA method depending on the shape and number of regurgitant flows. Methods Several regurgitant volumes (RV) were produced through various regurgitation severities and shapes in a left heart double activation simulator. Circular mitral regurgitation (MR) was performed with a circular orifice in a rigid plate. Triangular and oblong MR were performed by suturing the extremity of a bioprosthesis leaflet to the annulus. Multiple jets regurgitation was performed by suturing centrally the two leaflets of an anatomically shaped mitral valve made of hydrogel. A transesophageal echocardiography probe was used to acquire the data. The RV was calculated with the classical PISA method (hemispheric assumption), or by considering the PISA as a hemicylinder or a double hemisphere. It was then compared to a reference value obtained from an electromagnetic flowmeter measurement (accuracy ± 2 ml/min). Results A central and circular orifice was correctly quantified, as expected, with the hemispheric assumption (bias 0.2±1.9 ml, p=0.46). For a triangular central jet, the hemispheric assumption best estimated the RV (−3.5±14.8 ml, p=0.10). An oblong MR was underestimated with the hemispheric assumption (−18.3±14.9 ml, p&lt;0.01) whereas the hemicylindrical assumption was more accurate (−0.2±5.8 ml, p=0.85). In case of 2 regurgitant jets, considering only the largest jet led to an important underestimation (−10.9±5.6 ml, p&lt;0.01), whereas adding the two RV was more accurate (−1.2±8.2 ml, p=0.50). Conclusions In case of a single central orifice, the hemispheric assumption correctly quantified the MR. In case of an oblong orifice, the hemicylindrical assumption provided a good quantification with simple measurements. In case of multiple jets of different sizes, it was more accurate to consider both jets for RV calculation. Acknowledgement/Funding Képhalios part of Affluent Medical

Active thrust fluid-film bearings: Theoretical and experimental studies

Research in the field of active fluid-film bearing has been recently getting more and more attention, integration of control systems becoming one of the most promising means of enhancement of rotor-bearing nodes' characteristics. It has been determined that the vast majority of papers published on active fluid-film bearing only consider radial bearings, and very few focus on thrust bearings. This lack of attention along with the obvious necessity to fill the said gap has triggered the present research. In cases of rotor machines that experience extensive axial loading due to various reasons, e.g. various turbine engines (aero and spacecraft) and hydraulic pumps (crude oil extraction facilities), such research could prove the feasibility of application of a control system to significantly increase the performance of the whole machine. Moreover, extensive wear during start up and shut down could be eliminated by means of rotor position control, thus life time of a rotor-bearing system could be significantly increased. The present paper features a complex mathematical model of an active thrust fluid-film bearing with a central feeding orifice, a developed test rig designed to verify the presented mathematical model allowing a series of numerical tests to be carried out. Numerical studies focus on the hypothesis of a possibility to use active control in thrust bearings to decrease power loss due to friction and extensive axial vibrations by means of identification of an energy efficient area of axial gaps based on the lubrication regime and its maintenance by means of application of controlled lubrication principles.

Fluid-Structure Interaction and In Vitro Analysis of a Real Bileaflet Mitral Prosthetic Valve to Gain Insight Into Doppler-Silent Thrombosis.

Prosthetic valve thrombosis (PVT) is a serious complication affecting prosthetic heart valves. The transvalvular mean pressure gradient (MPG) derived by Doppler echocardiography is a crucial index to diagnose PVT but may result in false negatives mainly in case of bileaflet mechanical valves (BMVs) in mitral position. This may happen because MPG estimation relies on simplifying assumptions on the transvalvular fluid dynamics or because Doppler examination is manual and operator dependent. A deeper understanding of these issues may allow for improving PVT diagnosis and management. To this aim, we used in vitro and fluid-structure interaction (FSI) modeling to simulate the function of a real mitral BMV in different configurations: normally functioning and stenotic with symmetric and completely asymmetric leaflet opening, respectively. In each condition, the MPG was measured in vitro, computed directly from FSI simulations and derived from the corresponding velocity field through a Doppler-like postprocessing approach. Following verification versus in vitro data, MPG computational data were analyzed to test their dependency on the severity of fluid-dynamic derangements and on the measurement site. Computed MPG clearly discriminated between normally functioning and stenotic configurations. They did not depend markedly on the site of measurement, yet differences below 3 mmHg were found between MPG values at the central and lateral orifices of the BMV. This evidence suggests a mild uncertainty of the Doppler-based evaluation of the MPG due to probe positioning, which yet may lead to false negatives when analyzing subjects with almost normal MPG.

Improvement of the PISA method in the setting of mitral regurgitation of complex geometry

Doppler echocardiographic methods, such as proximal isovelocity surface area (PISA) are used to quantify mitral regurgitations (MR). However, their accuracy and reproducibility are still discussed, especially in case of MR of complex geometry. The aim of this study was to test in-vitro the accuracy of the PISA method depending on the shape and number of regurgitant flows. Several regurgitant volumes (RV) were produced through various regurgitation severities and shapes in a left heart double activation simulator. Central and oblong MR were performed by suturing the extremity of a bioprosthesis leaflet to the annulus. Multiple jets regurgitation was performed by suturing centrally the two leaflets of an anatomically shaped mitral valve made of hydrogel. A transesophageal echocardiography probe was used to acquire the data. The RV was calculated with the classical PISA method (hemispheric assumption), or by considering the PISA as a hemicylinder or a double hemisphere. It was then compared to a reference value obtained from an electromagnetic flowmeter measurement (accuracy ± 2 ml/min). For a central jet, the hemispheric assumption best estimated the RV (bias − 3.5 ± 14.8 ml, P = 0.10). Oblong MR was underestimated with hemispheric assumption (−18.3 ± 14.9 ml, P < 0.01) whereas hemicylindrical assumption was more accurate (−0.2 ± 5.8 ml, P = 0.85). In case of 2 regurgitant jets, considering only the largest jet led to an important underestimation (−10.9 ± 5.6 ml, P < 0.01), whereas adding the two RV was more accurate (−1.2 ± 8.2 ml, P = 0.50). In case of a single central orifice, the hemispheric assumption correctly quantified the MR. In case of an oblong orifice, the hemicylindrical assumption provided a good quantification with simple measurements. In case of multiple jets of different sizes, it was more accurate to consider both jets for RV calculation.

Proposed percutaneous aortic valve prosthesis made of cryogel.

Transcatheter heart valves are promising for high-risk patients. Generally, their leaflets are made of pericardium stented in a Nitinol basket. Despite their relative success, they are associated with significant complications such as valve migration, implantation risks, stroke, coronary obstruction, myocardial infraction, acute kidney injury (which all are due to the release of detached solid calcific pieces in to the blood stream) and expected issues existing with tissue valves such as leaflet calcification. This study is an attempt to fabricate the first ever polymeric percutaneous valves made of cryogel following the geometry and mechanical properties of porcine aortic valve to address some of the above-mentioned shortcomings. A novel, one-piece, tricuspid percutaneous valve, consisting of leaflets made entirely from the hydrogel, polyvinyl alcohol cryogel reinforced by bacterial cellulose natural nanocomposite, attached to a Nitinol basket was developed and demonstrated. Following the natural geometry of the valve, a novel approach was applied based on the revolution about an axis of a hyperboloid shape. The geometry was modified based on avoiding sharp warpage of leaflets and removal of the central opening orifice area of the valve when valve is fully closed using the finite element analysis. The modified geometry was replaced by a cloud of (control) points and was essentially converted to Bezier surfaces for further adjustment. A cavity mold was then designed and fabricated to form the valve. The fabricated valve was sewn into the Nitinol basket which is covered by Dacron cloth. The models presented in this study merit further development and revisions for both aortic and mitral positions.

Experimental investigation on thermal and flow characteristics of synthetic jet with multiple-orifice of different shapes

The impingement heat transfer characteristics of a multiple-orifice synthetic jet of circular, oval and diamond orifice shapes are investigated experimentally at different Stokes number, normalized axial distance and pitch ratio. In this study, particle image velocimetry (PIV) based measurements are also undertaken to better understand the underlying flow characteristics of multiple-orifice synthetic jet and to support the associated heat transfer data. The average Nusselt number (Nuavg) obtained with multiple-orifice synthetic jet is up to 75% higher than a single orifice synthetic jet using the same input power to synthetic jet actuator. For larger pitch ratio (R > 1.25), the maximum value of Nuavg is observed to be reduced and obtained closer to heated surface. Multiple-orifice configurations with diamond shape exhibited better thermal performance as compared to other shapes examined in the study. The multiple-orifice configurations with one and two satellite orifices demonstrated two local peaks in Nuavg and are observed only with smaller values of pitch ratio. The location of these local peaks illustrated very little or no dependence on Stokes number (S). Configurations with no center orifice exhibited significantly lower heat transfer as compared to the configurations with center orifice as well as the case with single center orifice. The secondary maxima in Nuavg are entirely missing in the configurations with no center orifice. The PIV data reveals interactions between the adjacent synthetic jets in multiple-orifice case to form a combined synthetic jet with better mixing characteristics as compared to a single orifice synthetic jet and therefore the former exhibits higher heat transfer rate. The PIV data further illustrated the individual behavior of synthetic jets resulting from satellite orifices in multiple-orifice configurations with no center orifice. In addition to heat and flow characteristics of multiple-orifice synthetic jet, the heat transfer correlations are also developed from the experimental data for different orifice shapes. The study of multiple-orifice synthetic jet presented here is expected to be useful in designing the cooling modules for electronic devices.

Effect of Preoperative Cardiac Anatomy and Surgical Approach on HVAD Inflow Position

Purpose We assessed the influence of preoperative cardiac anatomy and surgical approach on inflow cannula position in Heartware HVAD recipients. Methods We reviewed pre- and postoperative CT scans and echocardiography. Anatomic variables were chosen based on prior studies: LV end-diastolic dimension (LVEDD), axial plane midline-to-apex distance (ApexDist), and coronal-plane LV outflow tract angulation from horizontal (LVOT angle). Surgical technique was conventional sternotomy (CS) or lateral thoracotomy/hemisternotomy (LTHS). Inflow cannula angular deviation from a line intersecting the apex and mitral orifice center was measured in two planes. Anterior plane deviation is toward the superior or inferior free wall. Lateral plane deviation is toward the septum or lateral wall. Total deviation is the sum of the two. Cutoffs for malposition were deviation ≥ 20 deg in any direction or ≥ 40 deg total. Results 99 HVAD patients (43 CS, 56 LTHS) implanted since 2011 with pre- and postoperative CT were included. LVEDD was larger for LTHS (7.2 vs 6.7 cm, p=0.01). ApexDist and LVOT angle were similar between CS and LTHS. Figure shows inflow position by surgical technique. Inferior-wall deviation was common, while no patient had superior wall-directed malposition. Significantly more septal malposition occurred in CS patients (14% vs 2%; p=0.04). Shorter ApexDist predicted lateral wall malposition (p Conclusion Preoperative CT measurements and surgical approach were associated with different morphologies of HVAD inflow malposition. Surgical planning techniques to optimize inflow position are under study.

Relationship between Inflow Malposition and Clinical Outcomes in HVAD Recipients

Purpose We evaluated the effect of different inflow cannula malposition morphologies on readmission and selected complication rates in Heartware HVAD recipients. Methods Inflow malposition was defined as the angular deviation from a line intersecting the apex and mitral orifice center in two CT imaging planes. Anterior plane deviation is toward the superior or inferior free wall. Lateral plane deviation is toward the septum or lateral wall. Total deviation is the sum of the two. Cutoffs for malposition were deviation ≥ 20 deg in any direction and total deviation ≥ 40 deg. Clinical outcomes were: 30-day and total cardiovascular-related readmissions (CVR; excludes bleeding, infections, noncardiac procedures, transplants); persistent VT/VF (pVT; ≥ 2 episodes); combined pump thrombosis (PT) or embolic stroke (PT-eCVA); and 90-day mortality. Results 99 HVAD patients implanted since 2011 with postoperative CT scans were included. All were followed for complications. 87 were discharged and were assessed for CVR. Prevalence of each morphology of malposition is shown in Table. Deviation toward the inferior free wall occurred most frequently. Eighteen of 87 patients (21%) had 30-day CVR. Total deviation ≥ 40 deg was significantly associated with 30-day CVR (p=0.01). Median total CVR rate was 0.21/100 pt-days (IQR 0-0.68). Inferior wall deviation ≥ 20 deg was significantly associated with total CVR rate (p = 0.03). Eight of 99 patients (8.1%) had PT-eCVA (5 eCVA, 3 PT), 27% had pVT, and 90-day mortality occurred in 7%. No malposition measurement predicted any of these complications. Conclusion PT-eCVA, pVT, and early mortality were not associated with malposition. However, worse overall malposition was associated with 30-day CVR. Inferior wall malposition occurred in half of patients and was associated with overall CVR rate. Improved surgical planning techniques to mitigate malposition are warranted.

Determination of the uncertainty of mass flow measurement using the orifice for different values of the Reynolds number

Standard orifice flowmeters are widely used in the chemical and energy industry. Therefore, it is essential to know how accurate the measurements made with these instruments are. The paper presents an estimation of measurement uncertainty of a liquid mass flow using the orifice plate. The authors will present the influence of ranges of the Reynolds number on the estimated uncertainty, obtained on the basis of simulation and laboratory experiments. The research was conducted for the central orifice in the Reynolds number 8,000 &lt; Re &lt; 21,000. The results of estimating the extended uncertainty of the measurement of water flow using simulation and experimental method, are convergent. The maximum difference in the extended uncertainty values of flow measurement for the simulation and experiment was 0.04.10-3 kg/s.

Topographical Changes of Rat's Colonic Mucosal After Chronic Arsenic Exposure - A Scanning Electron Microscopy Study

Introduction: Human are exposed to arsenic threats in several ways. Our drinking water for instance, can be hazardous due to the contamination of arsenic-based pesticide and herbicide into our water supply. The most vulnerable part of our body due to ingestion of arsenic is our gastrointestinal system. Thus, the aim of this study was to determine the effects of chronic exposure to organic arsenic (Monosodium methylarsonate, MSMA) on the surface topography of rat's colonic mucosa by using scanning electron microscope (SEM). Materials and Methods: 30 Sprague Dawley rats were given daily oral gavage of MSMA 42.13 mg/kg, which is 1/30 LD50, and 30 Sprague Dawley rats acted as control. 10 exposed rats and 10 control rats were sacrificed at regular intervals (2 months, 4 months and 6 months) and their colon specimens were examined by SEM. Results: In the control group, the colonic mucosa appeared normal with uniform size individual glandular units and has a central crypt orifice. The goblet cells were located in between the absorptive cells to produce mucous. In the exposed group, the rat's colonic mucosa showed increasing features of surface alterations such as haphazard shape of glandular units, slit-like crypt opening and less goblet cells with reduced number of microvilli. Conclusion: There were topographical changes of colonic mucosa of rats exposed to chronic low dose of organic arsenic.

Analysis of Pseudo-Turbulence Flow Induced by Bubble Periodic Formation in Non-Newtonian Fluids

Laser Doppler Velocimetry (LDV) has been employed to determine pseudo-turbulence characteristics of the flow field around bubble train forming in non-Newtonian caboxymethylcellulose (CMC) aqueous solution at low gas flow rate condition. The Reynolds stress and turbulent intensity of the liquid were investigated by means of Reynolds time-averaged method. The experimental results show that axial Reynolds stress rises greatly and then fluctuates slightly with the vertical height, whereas displays symmetrical Gaussian distribution in the horizontal direction; Radial Reynolds stress changes nonobviously in the vertical direction, but increases followed by a decrease in the horizontal direction. The axial turbulent intensity begins to wave to some degree with the height for near vertical axis passing through orifice center, but maintains constant within bubble channel in the horizontal direction; Radial turbulent intensity gets down with the vertical height, compared with the opposite trend of its variation with the horizontal distance.

Adverse Hemodynamic Conditions Associated with Mechanical Heart Valve Leaflet Immobility.

Artificial heart valves may dysfunction, leading to thrombus and/or pannus formations. Computational fluid dynamics is a promising tool for improved understanding of heart valve hemodynamics that quantify detailed flow velocities and turbulent stresses to complement Doppler measurements. This combined information can assist in choosing optimal prosthesis for individual patients, aiding in the development of improved valve designs, and illuminating subtle changes to help guide more timely early intervention of valve dysfunction. In this computational study, flow characteristics around a bileaflet mechanical heart valve were investigated. The study focused on the hemodynamic effects of leaflet immobility, specifically, where one leaflet does not fully open. Results showed that leaflet immobility increased the principal turbulent stresses (up to 400%), and increased forces and moments on both leaflets (up to 600% and 4000%, respectively). These unfavorable conditions elevate the risk of blood cell damage and platelet activation, which are known to cascade to more severe leaflet dysfunction. Leaflet immobility appeared to cause maximal velocity within the lateral orifices. This points to the possible importance of measuring maximal velocity at the lateral orifices by Doppler ultrasound (in addition to the central orifice, which is current practice) to determine accurate pressure gradients as markers of valve dysfunction.