Top Of Wall Research Articles

Dynamic behavior of liquid water transport in a tapered channel of a proton exchange membrane fuel cell cathode

A numerical model of a proton exchange membrane fuel cell (PEMFC) cathode with a tapered channel design has been developed in order to examine the dynamic behavior of liquid water transport. Three-dimensional, transient simulations employing the level-set method (available in COMSOL 3.5a, a commercial finite element method software) have been used to explicitly track the liquid–gas interface. A liquid water droplet suspended in the center of the channel, 2 mm from the channel entrance, is subjected to airflow in the bulk of the channel. Three different cases have been studied: 1) hydrophobic bottom wall representing the gas diffusion layer and hydrophilic channel top and side walls, 2) all walls are partially wetted i.e. having a contact angle of 90°, 3) a hydrophilic bottom wall and hydrophobic top and side walls. The results show that tapering the channel downstream helps in water exhaust due to increased airflow velocity. A bottom wall, although hydrophilic, results in fast removal of water droplet as compared to partially wetted and hydrophobic bottom surfaces.

Mitral annular disjunction in myxomatous mitral valve disease: a relevant abnormality recognizable by transthoracic echocardiography

BackgroundMitral annular disjunction (MAD) consists of an altered spatial relation between the left atrial wall, the attachment of the mitral leaflets, and the top of the left ventricular (LV) free wall, manifested as a wide separation between the atrial wall-mitral valve junction and the top of the LV free wall. Originally described in association with myxomatous mitral valve disease, this abnormality was recently revisited by a surgical group that pointed its relevance for mitral valve reparability. The aims of this study were to investigate the echocardiographic prevalence of mitral annular disjunction in patients with myxomatous mitral valve disease, and to characterize the clinical profile and echocardiographic features of these patients.MethodsWe evaluated 38 patients with myxomatous mitral valve disease (mean age 57 ± 15 years; 18 females) and used standard transthoracic echocardiography for measuring the MAD. Mitral annular function, assessed by end-diastolic and end-systolic annular diameters, was compared between patients with and without MAD. We compared the incidence of arrhythmias in a subset of 21 patients studied with 24-hour Holter monitoring.ResultsMAD was present in 21 (55%) patients (mean length: 7.4 ± 8.7 mm), and was more common in women (61% vs 38% in men; p = 0.047). MAD patients more frequently presented chest pain (43% vs 12% in the absence of MAD; p = 0.07). Mitral annular function was significantly impaired in patients with MAD in whom the mitral annular diameter was paradoxically larger in systole than in diastole: the diastolic-to-systolic mitral annular diameter difference was -4,6 ± 4,7 mm in these patients vs 3,4 ± 1,1 mm in those without MAD (p < 0.001). The severity of MAD significantly correlated with the occurrence of non-sustained ventricular tachycardia (NSVT) on Holter monitoring: MAD›8.5 mm was a strong predictor for (NSVT), (area under ROC curve = 0.74 (95% CI, 0.5-0.9); sensitivity 67%, specificity 83%). There were no differences between groups regarding functional class, severity of mitral regurgitation, LV volumes, and LV systolic function.ConclusionsMAD is a common finding in myxomatous mitral valve disease patients, easily recognizable by transthoracic echocardiography. It is more prevalent in women and often associated with chest pain. MAD significantly disturbs mitral annular function and when severe predicts the occurrence of NSVT.

Performance characteristics of light gage steel stud partition walls

This paper presents results from quasi-static racking tests on gypsum wallboard sheathed light gage metal stud partition walls used in buildings. Eight nearly identical pairs of specimens were constructed following common United States practice. Each specimen consisted of a 4.88m long and 2.44m tall web wall and two return walls each 1.2m long and 2.44m tall. The main variables were (i) the configuration of the specimen, (ii) the spacing of wallboard-light gage stud self-tapping screws, (iii) the stud thickness and spacing, (iv) the presence of a vertically slotted track at the top of the partition wall, and (v) the wallboard thickness.

Erosion Study of New Orleans Levee Materials Subjected to Plunging Water

During Hurricane Katrina, overtopping water caused erosion and subsequent failure of several sections of I-type flood walls in New Orleans. Erosion stemmed from the kinetic energy of water falling from the top of the flood wall, unlike the typical surface erosion caused by shear flow. This study evaluated the effects of important parameters of levee soils—fines content, degree of compaction (DOC), clay mineralogy, and water content in relation to the erosion behavior of New Orleans levees subjected to the plunging water. In general, test results showed that a higher fines content contributed to greater erosion resistance. The trend became unclear when fines content exceeded 20–25%. A higher degree of compaction did not necessarily contribute to greater erosion resistance. Underwater soaked soils showed much less erosion resistance than nonsoaked soils. Soils containing expansive clay minerals showed less erosion resistance than soils containing nonexpansive clay minerals.

A numerical study on the effect of a heated hollow cylinder on mixed convection in a ventilated cavity

The present work is aimed to study mixed convection heat transfer characteristics within a ventilated square cavity having a heated hollow cylinder. The heated hollow cylinder is placed at the center of the cavity. In addition, the wall of the cavity is assumed to be adiabatic. Flows are imposed through the inlet at the bottom of the left wall and exited at the top of the right wall of the cavity. The present study simulates a practical system such as air-cooled electronic equipment with a heat component or an oven with heater. Emphasis is sited on the influences of the cylinder diameter and the thermal conductivity of the cylinder in the cavity. The consequent mathematical model is governed by the coupled equations of mass, momentum and energy and solved by employing Galerkin weighted residual method of finite element formulation. A wide range of pertinent parameters such as Reynolds number, Richardson number, cylinder diameter and the solid-fluid thermal conductivity ratio are considered in the present study. Various results such as the streamlines, isotherms, heat transfer rates in terms of the average Nusselt number and average fluid temperature in the cavity are presented for different aforesaid parameters. It is observed that the cylinder diameter has significant effect on both the flow and thermal fields but the solid-fluid thermal conductivity ratio has significant effect only on the thermal field.

Crimpling and repairing of orbital septum in plasty of lower eyelid bags

Objective To discuss the implications of orbital septum repairing and crimpling in the plastic surgery of lower eyelid bags. Methods The ultimate results were analyzed in the patients (aged less than 40) who received three different operations from six months to five years and the effect of operation and recrudescence of lower eyelid sag were observed. The procedures included simple fat removal, fat removal plus orbicularis oculi hanging, and orbicularis oculi hanging plus orbital septum repairing and crimplling. Results Since 2002, 157 cases were treated, and the ultimate effects of patients were analyzed. 86 cases treated with orbicularis oculi hanging plus orbital septum repairing and crimplling reached the best results without recurrence. 71 cases treated with simple fat removal or fat removal plus orbicularis oculi hanging experienced recurrence in different degree within a short period. Conclusion The weakness and laxation of the former wall causes the formation of lower eyelid bag, the appearance and recrudescence mainly locate below the former wall. Orbital septum repairing and crimpling most effectively strengthen the underside of the former wall. Orbicularis oculi hanging strengthens the top of the former wall and prevents any complications. The effects of the last procedure are better than that of the other two in the near future or in the long term. Key words: Lower eyelid bag; Orbital septum repairing and crimpling

Anatomy Studies on Six Mosses in Kanas Nature Reserve

Paraffin sectioning technique and scanning electron microscopy methods were applied to observe six species of masses.The internal structure of stems,leaves and the stratum corneum surface ornamentation,warts growth and micro-hole were compared.The results indicated that the epidermal cells of Rhytidium rugosum(Hedw.) Kindb.have small verrucose on outer wall,while the tandem of the wall adjacent to the surface of the cuticle cell patterns long into parallel bundles;stem axis of the Abietinella abietina(hedw.) fleisch was not obvious,in the back of a rib-like thorns protruding warts,dorsal,ventral surfaces of the side wall warts,was covered like;the epidermal cells wall of Bartramia ithphylla Brid.uplift,holes was not sink,orifice was covered by the cuticle ornamentation;the back surface of leaf crude cell wall of Aulacomnium palustre(Hedw.) Schwagr.warts highlighted by the depression,cuticle ornamentation was banded,leaf faces big belly,and in many cell wall-like interface was open;the epidermal cells of back leave of Hylocommium splendens(Hedw.) B.S.G wart like thorns wide,dorsal,ventral warts rough high,the top of the cell wall with depression;Dorsal,ventral cells irregular depressions adjacent cell wall of Ceratodon purpureus(hedw.) Brid.was a small intensive wart.

Effect of heating location and size on mixed convection in lid-driven cavities

A numerical study is performed to analyze the mixed convection heat transfer and fluid flow in lid-driven cavities with different lengths of the heating portion and different locations of it. The left wall has been heated fully or partially to a higher temperature, whereas the right wall is maintained at a lower temperature. Three different lengths of the heating portion and three different locations of it are used along the hot wall. The remaining portions of the left wall, and the top and the bottom walls of the cavity are insulated. The finite volume method is used to discretize the governing equations which are then solved iteratively. The velocities and pressure are coupled by the SIMPLE algorithm. Results are presented graphically in the form of streamlines, isotherms and velocity profiles. It is concluded that the heat transfer rate is enhanced on reducing the heating portion and when the portion is at middle or top of the hot wall of the cavity.

Application of the similarity theory including variable property effects to a complex benchmark problem

An asymptotic method to account for variable property effects, recently described in this journal, is now applied to a complex benchmark geometry. It is a room which is ventilated by forced convection through inlet and outlet slit nozzles at the top and bottom of the side walls. Four heating elements standing on the ground floor add heat with constant heat flux density of varying strength. CFD solutions with the full coverage of all property temperature dependencies of air and SF6 are compared with asymptotic results (ACFD), applied for these fluids. ACFD results are given as systematic expansions with respect to a heat transfer parameter \({\varepsilon}\) which serves as perturbation parameter. First and second order asymptotic results of the Nuselt number at the surface of the heating elements are shown as well as temperature distributions along the adiabatic walls of the room. Special attention is given to the reference Nuselt numbers of zero order \({(\varepsilon=0)}\) which are those for constant properties only for pure forced convection.

Senojo ir vidurinio geležies amžiaus skydai Lietuvoje

Karyba – organizuoti agresyvūs veiksmai tarp dviejų nepriklausomų politinių vienetų – kaip socialinis reiskinys žinoma jau nuo seniausių laikų. Dar neseniai buvo manoma, kad kariniai konfliktai (pirmiausia reidai, o vėliau ir karai) atsirado kartu su žemdirbyste ir gyvulininkyste, taciau naujausi archeologiniai duomenys rodo, kad tai daug ankstesnis reiskinys – pirmosios jo užuomazgos pastebimos jau paleolite (Thorpe, 2003). [...]

Influence of exit opening location on mixed convection in a channel with volumetric heat sources

Mixed convection heat transfer in a channel with volumetric heat source and different opening ratio at the exit has been analyzed numerically. Steady, laminar, two-dimensional model based on the finite-volume method is used for solving the mass, momentum and energy transfer governing equations. The flow is injected to the duct with a uniform velocity distribution. The problem is studied in three aspect ratios ( A = 1, 3 and 5) and three opening cases as single opening near the ceiling, single opening near the bottom and double openings. The study is also tested for different Richardson numbers between 0.01 and 10. Streamlines, isotherms, Nusselt numbers and temperature profiles were obtained for indicated cases. It is found that both the Richardson number and the locations of exit openings have strong effects on flow and temperature distribution in the presence of volumetric heat sources. The highest heat transfer was formed when the outlet port is located onto top of vertical wall.

Effect of the Presence of a Heat Conducting Horizontal Square Block on Mixed Convection inside a Vented Square Cavity

Finite element method is used to solve two-dimensional governing mass, momentum and energy equations for steady state, mixed convection problem inside a vented square cavity. The cavity consists of adiabatic left, top and bottom walls and heated right vertical wall; but it also contains a heat conducting horizontal square block located somewhere inside the cavity. Forced flow conditions are imposed by providing an inlet at the bottom of the left wall and an exit at the top of the right wall, through which the working fluid escape out of the cavity. The aim of the study is to describe the effect of such block on the flow and thermal fields. The investigations are conducted for various values of geometric size, location and thermal conductivity of the block under constant Reynolds and Prandtl numbers. Various results such as the streamlines, isotherms, heat transfer rates in terms of the average Nusselt number, average fluid temperature in the cavity and the temperature at the center of solid block are presented for different parameters. It is observed that the block size and location have significant effect on both the flow and thermal fields but the solid-fluid thermal conductivity ratio has insignificant effect on the flow field. The results also indicate that the average Nusselt number at the heated surface, the average temperature of the fluid inside the cavity and the temperature at the center of solid block are strongly dependent on the configurations of the system studied under different geometrical and physical conditions.

Where Opportunity knocked

For 683 Martian days–more than a full Martian year and almost two Earth years–NASA’s Mars Exploration Rover Opportunity explored Victoria Crater, both from its rim and from partway down the crater slope. The crater is about 730 meters wide and 6 kilometers from Opportunity’s landing site.This recent image of Victoria Crater, by the High Resolution Imaging Science Experiment aboard the Mars Reconnaissance Orbiter, is taken at an oblique angle that reveals the geologic strata of the crater’s walls. The camera was aimed 22° east of vertical, comparable to the angle at which one might look out of an airplane to see landscape below. East is at the top, and the Sun illuminates the scene from the west. The colors have been enhanced to highlight subtle differences. Opportunity’s investigations showed that the bright white band seen here at the top of the crater wall was formed by diagenesisl—chemical and physical changes in sediments after deposition. The band separates bedrock below from deposits of ejecta from the crater impact. Dunes of windblown sand and material eroded from the crater walls cover the crater floor.Some of Opportunity’s tracks are faintly visible to the north (left) of the crater.To submit candidate images for Back Scatter, visit http://www.physicstoday.org/backscatter.html.(Image courtesy of NASA/JPL–Caltech/University of Arizona.)PPT|High resolution© 2009 American Institute of Physics.

RANKL Links Arterial Calcification With Osteolysis

See related article, pages 1041–1048 Vascular calcification is a pathological sequence of events that has similarities to the normal physiological process of osteogenesis.1,2 It is thought to result from an imbalance in both local and systemic inhibitors and promoters,3,4 which occurs as a consequence of chronic inflammation, hyperleptinemia, and a deregulation of various bone-regulating proteins. It is common in patients with diabetes and renal failure and in the elderly.4,5 The fact that coronary artery calcification is such a major health problem and the recognition that it is highly correlative with mortality risk6 makes the understanding of vascular calcification a worthy and exciting area of study. In normal skeletal physiology, bone deposition by osteoblasts is in balance with bone resorption by osteoclasts. RANKL (receptor activator of nuclear factor [NF]-κB ligand) and its soluble decoy receptor, osteoprotegerin (OPG), are critical regulators of bone remodeling. Binding of RANKL to its cognate receptor RANK, expressed on osteoclasts and its precursors, induces NF-κB signaling, resulting in NF-κB translocation to the nucleus with a subsequent increase in RelB levels, in turn, stimulating osteoclastic differentiation (Figure, A). OPG, a decoy receptor, expressed by osteoblasts, binds with RANKL, preventing RANK (receptor activator of NF-κB) signaling and thus inhibiting osteoclastogenesis (Figure, B).7 Figure. Bone resorption in the skeleton often coexists with bone formation in the vasculature. A, Binding of RANKL to RANK stimulates osteoclast maturation and destruction of bone through loss of mineral. B, Osteoblasts express OPG the natural decoy receptor for RANKL, preventing RANK activation and inhibiting maturation of osteoclasts thus inhibiting bone resorption. An increased availability of OPG and the block on RANKL signaling supports osteoblast differentiation, maturation, and function allowing the deposition of bone. C, Elevated OPG in the vasculature and increased Ca/P products marks a commitment of …

RFID behavior study in enclosed marine container for real time temperature tracking

The performance of radio waves in open environments has been studied for years. In contrast, the behavior of Radio Frequency Identification (RFID) inside metal enclosed areas is not yet understood. This research project focuses on the 3-D mapping of RFID signal strength inside a 12 m refrigerated marine container instrumented with three different types of radio frequency (RF) emitters: 915 MHz reader; 2.45 GHz reader and 433 MHz RF transmitter. The main goal is to find a frequency/configuration that would allow real time reading of the temperature in a shipment of perishable products using RFID. Only one frequency and one antenna were used at a time. The RF transmitter antenna was mounted at two different places inside the container; at the top of the front wall (facing back) and on the ceiling in the middle of the container (facing down). The signal strength was acquired by a spectrum analyzer and its antenna was mounted on a small electric cart inside the container. The cart was programmed to move along the length of the container and stop repeatedly, allowing three automated measures per position. All data were analyzed in terms of power level and attenuation. The maps showed that the RFID antenna positioned at the front of the container delivered slightly better results than the one in the middle of the ceiling. The results showed a significantly higher performance at the 433 MHz level.

Predicted Loads in Steel Reinforced Soil Walls Using the AASHTO Simplified Method

The paper investigates the accuracy of the AASHTO simplified method by using load measurements reported in a large database of full-scale instrumented walls for bar mat, welded wire, and steel strip soil reinforced walls. The accuracy of the AASHTO simplified method is quantified by computing the mean and coefficient of variation of the ratio (bias) of measured loads under operational conditions to predicted loads. The paper shows that for steel strip walls, the AASHTO simplified method is reasonably accurate for granular backfill soils with friction angles less than 45°. For bar mat walls, the method is demonstrated to be slightly conservative. The simplified method underpredicts reinforcement loads at shallow overburden depths for steel strip walls with backfill friction angles greater than 45° due to compaction-related effects. It is concluded that these compaction-induced loads near the wall top do not contribute to internal instability due to pullout.

Vascular Plants from the Old Walls in Kystendil (Southwestern Bulgaria)

ABSTRACTThe aim of this study is to establish species diversity, the conformities and trends about the origin and variability of the wall flora in the central city part of Kystendil, The study area is National architectural reserve, located in the border of the old fortress wall on antique Pautalia and medieval Velbuzhd. The study is carried out for two periods 1998–2001 and 2007–2008. During the study are determined total 122 taxa (on walls and their neighboring area): Magnoliophyta (110), Polypodiophyta (5) and Bryophyta (7). With most participation are families Fabaceae (20), Poaceae (18), Asteraceae (10), Caryophyllaceae (6), Lamiaceae (5), Rosaceae (5), etc. Hemicriptophytes and therophytes are prevailed. The number of annual species is bigger on the wall surface, while perennials are typical for the wall base and neighbouring area. From the base to top of walls, the species diversity decrease and the percent of typical rock xerophytes arise. The northern exposure of the walls causes more rich flora and vegetation. New species for the floristic region are Petrorhagia glumacea, Eleusine indica, Bromus tectorum and Rumex crispus. The dominant floristic elements are Eur-Med-Orient, Eur-Med-Orient-Tur and Eur-Med- Orient-Cauc. As a result the wall flora shows characteristics similar to European and Mediterranean wall floras. Plants from old walls are additional ornamental element and contribute to the complete perceive of architectural and historical objects. Threes effect negatively wall's structure. On the base of present study are given estimation of contemporary wall's state as well as send recommendations about how to maintain old walls and their neighboring area.

An in situ sealing method for liquid-filled micro-cavities based on photoembossing

An in situ method for sealing an array of pre-filled micro-cavities, such as encountered in electrophoretic displays, is presented. The technique, which is based on photoembossing, forms a hermetic seal between the cover and the cavity walls. The seal locations are defined by ultraviolet exposure through a photolithographic mask, forming a latent image overlapping with the locations of the cavity walls. During a thermal development step, while the cover is mounted on top of the micro-cavities, the seal evolves and makes firm contact with the cavity walls. This technology is demonstrated to be insensitive to small deviations in cavity height, flatness of the cover and thin fluid films remaining between the cover and the top of the cavity walls. In the past, these aspects made it difficult to effectively seal large-area devices.

Wastage Rate of Water Walls in a Commercial Circulating Fluidized Bed Combustor

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Target reliability based design optimization of anchored cantilever sheet pile walls

In this study, the stability of anchored cantilever sheet pile wall in sandy soils is investigated using reliability analysis. Targeted stability is formulated as an optimization problem in the framework of an inverse first order reliability method. A sensitivity analysis is conducted to investigate the effect of parameters influencing the stability of sheet pile wall. Backfill soil properties, soil – steel pile interface friction angle, depth of the water table from the top of the sheet pile wall, total depth of embedment below the dredge line, yield strength of steel, section modulus of steel sheet pile, and anchor pull are all treated as random variables. The sheet pile wall system is modeled as a series of failure mode combination. Penetration depth, anchor pull, and section modulus are calculated for various target component and system reliability indices based on three limit states. These are: rotational failure about the position of the anchor rod, expressed in terms of moment ratio; sliding failure mode, expressed in terms of force ratio; and flexural failure of the steel sheet pile wall, expressed in terms of the section modulus ratio. An attempt is made to propose reliability based design charts considering the failure criteria as well as the variability in the parameters. The results of the study are compared with studies in the literature.