Meniscus Formation Research Articles

Modeling of Thermochemomechanical Couplings of Concrete at Early Ages

This paper explores the theory of reactive porous media in the modeling of thermochemomechanical couplings of concrete at early ages. The formulation is based upon thermodynamics of open porous media composed of a skeleton and several fluid phases saturating the porous space. It accounts explicitly for the hydration of cement by considering the thermodynamic imbalance between the chemical constitutents in the constitutive modeling at the macrolevel of material description. In particular, the diffusion of water through the layers of hydrates is considered as the dominant mechanism of the hydration with respect to the kinetics of two apparent phenomena: aging and autogeneous shrinkage—the first related to the formation of hardened cement gel, the latter induced by capillary effects related to the formation of menisci due to water consumption through hydration. The intrinsic relations concerning heat generation, aging, and autogeneous shrinkage are so derived. Furthermore, it allows to make precise the decoupling hypothesis in order to clarify the linkages between different aging models: solidification theory and maturity models. In particular, it is shown that hydration degree, autogeneous shrinkage, and maturity are equivalent state variables, provided that stress and temperature evolutions do not effect the thermodynamic imbalance of hydration.

Stick-Slip Motion in Boundary Lubrication

Using dynamical analysis for a pin-on-disk sliding system and the consideration of meniscus formation at the sliding interface, a wide range of experimental observations on stick-slip motion can be explained. It is shown that when the initial growth rate of the static friction force is larger than about half the product of the substrate speed and the spring constant, slick-slip motion occurs in that sliding system. The critical substrate speed or the critical spring constant, above which stick-slip motion ceases, can thus be determined. It is also shown that the saturation substrate speed, below which stick-slip motion retains its maximum stick-slip amplitude, is inversely proportional to the total growth time of the static friction force. The maximum stick-slip amplitude is proportional to the final difference between the static and kinetic friction force. For a thicker surface liquid-film, the initial growth rate and the final static friction force are larger but the total growth time is shorter, result...

Proposed healing and consolidation mechanisms of rock salt revealed by ESEM.

The grain boundary healing behavior of crushed rock salt was mainly studied by employing the environmental scanning electron microscope (ESEM) to study the consolidation mechanism of rock salt backfill. Dedicated miniature round rock salt specimens were prepared for observation of the water trapping effect by using a cold stage in the ESEM to reach saturation conditions. Comparable high pressure pellets were prepared for measuring the crystal growth. Consolidation tests using materials made at different pressures and containing different moisture levels were conducted in order to construct the proposed mechanism. Direct observation of specimens in the ESEM resulted in viewing water trapped on the surface and the formation of a water meniscus between two particles. The concentration of brine at the grain boundary was observed as contributing to the amount of recrystallization. From aforementioned observations, a schematic drawing of the dissolution and recrystallization process may be redrawn. The amount of water therefore has a great effect on the consolidation of rock salt and is possibly due to the sliding, rotation, or crushing of the contact zone of the granular material. From such a study, tentative healing and consolidation mechanisms can be deduced.

Nature of static friction time dependence

Magnetic storage systems, like disk-head and tap-head interfaces, machine tool guideways, and many other friction pairs, are vulnerable to so-called 'stiction'. Stiction is a contact phenomenon whereby static friction increases relative to kinetic friction. As a rule, this effect increases dramatically with time of stationary contact. Thus, the time dependence of static friction is an important subject of tribological studies. The motivation of this work is to understand the static friction mechanism at both extremes of the rest time or dwell range: short-term dwell is in the order of seconds or minutes, and long-term dwell is in the order of days or months. The stiction models reviewed cover a wide spectrum of static friction processes related to material deformation, meniscus formation and viscous lubricant flow.

Moisture Effects Including Stiction Resulting From Adsorbed Water Films

Stiction resulting from moisture effects at small elastic contact spots has been identified and studied using bundles of fine, gold-plated copper fibers sliding on a gold-plated copper surface. The relevant measurements were made in the hoop apparatus which permits simultaneous monitoring of the momentary coefficient of friction and electrical contact resistance. Previous studies made with the hoop apparatus have shown that under the action of high local pressure, adsorbed moisture is expelled from between the contact spots leaving only one monomolecular layer of adsorbed water on each of the contacting surfaces. Additional details of the observations are varied and permit a refined analysis. Stiction results during periods of very slow motion or rest through local energy reduction at the spots as excess water is slowly drained in the course of molecular ordering of the two absorbed layers. Complex variations of kinetic friction with humidity and sliding speed are explained through the interplay of excess molecules between the contact spot surfaces, meniscus formation, fluid drag about the spots, and shear thinning in that flow.

Bond strength measurement in composites—Analysis of experimental techniques

Two of the most common techniques used to measure fiber-matrix interfacial shear strength, the single-fiber fragmentation test and the microbond, have been analyzed and compared. Photoelastic and finite element analyses were performed to obtain the stress distribution at the fiber-matrix interface and its dependence on the loading and geometrical parameters. The effect of a penny-shaped crack in the fiber, in the fiber fragmentation test is shown to be one of the parameters governing the interfacial failure mode. It is also shown that loading conditions, meniscus formation, and fiber free length have a large effect on the distribution of interfacial stresses in the case of the microbond, which may explain the large observed scatter of experimental results. Furthermore, it is shown that the effect of the stress distribution is highly non-uniform, thus making the calculation of shear stress very inaccurate when single averages are considered. It appears that the single-fiber fragmentation test is more reliable than the microbond test because of its simplicity and the smaller number of parameters involved in its analysis.

Some transparent immiscible liquid pairs

This report identifies 121 transparent immiscible liquid pairs that have properties compatible with optical instrumentation based on laser-induced fluorescence. Physical data such as specific gravity, index of refraction, viscosity, flash point, and toxicity were found in the literature. Compatibility with Plexiglas (PMMA), contact angles of the internal meniscus on glass and PMMA, meniscus formation times, and clearing times were measured. A useful noninvasive technique for determining interfacial tensions is explained and used. Some dependence of interfacial tension on molecular structure is found.

Interaction effects between a cylindrical hot-film anemometer probe and bubbles in air/water and oil/water flows

A theory is presented which describes the interaction between a cylindrical element and a bubble front and rear interface, and these results are used to interpret the heat transfer effects from a hot-film probe in contact with a bubble. Stepwise interface tests were carried out to test the main features of the developed theory, and a good agreement was demonstrated. However, bubbly two-phase flows are dynamic situations, and dynamic interface and single-bubble tests were also carried out to evaluate the additional dynamic effects. These results emphasised the main features of the static theory and tests, and confirmed that dynamic effects related to distortion of the menisci, meniscus formation and film stability must be included to describe correctly the response of a hot-film probe to the passage of a bubble. Tests were carried out for both air/water and kerosene/water mixtures and in both cases similar responses were obtained.

Comparison of Lung Sounds and Gas Trapping in the Study of Airway Mechanics

We have previously shown that gas is trapped in isolated animal lungs and have proposed that this gas-trapping process is related to meniscus formation in the small airways of the lung. The purpose of this investigation was to compare how the lung sound-generation process and the gas-trapping process are related to airway mechanics and each other. Rats were anesthetized, the heart and lungs were removed en bloc and placed in a liquid-filled plethysmograph. Lung sounds were recorded by using a microphone acoustically coupled to the tracheal cannula. The results show that discontinuous lung sounds in the form of crackles occur during lung inflation at the same time gas trapping takes place.

Mechanisms of gas loss from normal and hyperinflated excised guinea pig lungs

Increased pulmonary gas trapping was produced by in vivo inhalation exposures of guinea pigs to bronchoconstrictive aerosols. Both normal (filtered air-exposed) and hyperinflated excised lungs lost about 20% of their initial volume by 4h; gas loss was more rapid during the first 60 min (early period) than the following 180 min (late period). During both periods, absolute rates of gas loss were positively correlated ( P < 0.001) with initial excised lung gas volumes (ELGVs). Tracheal foam movement was observed in most of the hyperinflated lungs, but only during the early period. Occlusion of the trachea reduced gas loss during the early period, but not the late. Gas volumes increased in lungs of animals exposed to SF 6:O 2 (tracheas tied), and decreased most rapidly in lungs of animals exposed to He:O 2 (tracheas tied). Our results suggest that a major part of the early gas loss from excised guinea pig lungs occurs via the trachea and may be influenced by airway foam or menisci formation. After 60 min, airways may be closed and gas loss may occur via transpleural diffusion.

New Wave Carbonate Research: What Paleontologists Can Learn from It: A Status Report from Cancun, Mexico

Carbonate research in recent years has moved a long way from the emphasis on facies and paleoecology that dominated work in the '60s and early '70sso far, indeed, that traditional paleontologists may view it as an unrelated discipline. Yet much that has been happening of late in carbonate circles has significant application to problems in the mainstream of paleontologic thought, including determination of paleosalinities, paleotemperatures, and the calibration of secular changes through Phanerozoic time. The benefits of interaction between carbonate researchers in industry and academia were crystallized at Cancun last August, as 65 geologists gathered to parade, review, and joust over current research in an SEPM Research Symposium convened by Paul Harris (Chevron Research), Lynton Land (University of Texas), and Peter Scholle (Chevron Research). The symposium title 'Spar Cements and Secondary Porosity in Carbonate Rocks' ensured strong financial support from oil companies and drew almost equal participation from geologists in industry and academia. Participants came from many countries on both sides of the Atlantic, including U.S.A., Canada, Venezuela, Belize, Great Britain, West Germany, and Poland. Four consecutive days of focussed discussion challenged brains as well as derrieres, for sessions began promptly at 8:00 a.m. each morning and continued well past 10:00 p.m. in the evenings, and opportunities were provided for informal discussion still later (should the mind, body, and soul prove capable!). Presentations were organized in four sequential sessions: (1)Surficial Processes, (2) Burial Processes, (3) Analytical Methods, and (4) Review: Comparison of Diagenetic Environments. Understandably, most of the papers were primarily oriented to carbonate petrologists, but several should be of considerable interest to PALAIOS readers for specific new data, for techniques, and for some significant theoretical implications. In the 'specific new data' category, algae were implicated as catalysts of some rather esoteric cements in two different Caribbean habitats. Brian Jones (University of Alberta) documented evidence that algae, fungi and lichen promoted the formation of 'lichen stromatolites' and microdendritic calcite growths in sinkholes on exposures of the Bluff Dolomite (Oligocene to Miocene) on Grand Cayman Island. John Kaldi (Shell Canada Limited) illustrated how algal filaments in beachrock pores of northern Jamaica have promoted the formation of low-magnesian meniscus cements by trapping fine detritus and retaining droplets of marine water in intergranular spaces.

Effect of meniscus formation and duplicate sample placement configurations on the variability of measurement by three microtiter plate photometers

Meniscus formation at the liquid/air interface of samples in microtiter wells introduced significant variability into the measurement of optical density by 3 microtiter plate photometers. Light scattering due to the diverging lens effect of the meniscus caused an increase in optical density which varied in magnitude with each of the 3 photometers. This effect was greatly reduced by first blanking on a comparable meniscus configuration. In contrast, a decrease in pathlength due to meniscus formation caused a percentage decrease in optical density when compared to samples of the same volume with no meniscus formation. Inter-row and inter-column variability, although greatly reduced by appropriate blanking, was still apparent in optical density measurements by all photometers, The averaging of optical densities from duplicate samples in specific placement configurations was an effective means of eliminating this variability.

Liquid Films Flowing Concurrently with Air in Horizontal Duct : 4th Report, Effect of the geometry of duct cross-section on liquid film flow

The effect of the aspect ratio of the duct cross-section on a liquid film flowing concurrently with an air stream was investigated using three horizontal ducts. The dimensions of the duct are 10 mm×40 mm (height×width), 40 mm×40 mm and 10 mm×80 mm. The results are summarized as follows: The boundary of flow patterns between the pebble wave flow and the disturbance wave flow strongly depends on the duct height. On the other hand, the boundary between a smooth surface flow and a two-dimensional wave flow as well as the nonwetting regime depends mainly on the duct width. The reason is that the volumetric flux of the liquid flow in the vicinity of the side walls of the duct is considerably larger than that in the central part of the duct width due to the formation of meniscus. Therefore, only the experimental values for the film parameters obtained at the central part of duct width are useful for comparison with the theoretical results obtained by the assumption that the flow is two-dimensional, even if the aspect ratio of duct seems to be sufficiently small.

Meniscus formation as a radiographic sign of colonic lesion location.

HomeRadiologyVol. 147, No. 3 PreviousNext Meniscus formation as a radiographic sign of colonic lesion location.J R LateuladeJ R LateuladeJ R LateuladePublished Online:Jun 1 1983https://doi.org/10.1148/radiology.147.3.6844630MoreSectionsPDF ToolsImage ViewerAdd to favoritesCiteTrack CitationsPermissionsReprints ShareShare onFacebookTwitterLinked In Article HistoryPublished in print: 1983 FiguresReferencesRelatedDetailsRecommended Articles RSNA Education Exhibits RSNA Case Collection Vol. 147, No. 3 Metrics Altmetric Score PDF download

Axisymmetric meniscus formation: a viscous-fluid model for cones

The dynamics of the formation of the axisymmetric meniscus around a cone contacting a free liquid surface are discussed. An approximate phenomenological model is set up. In the case considered, where Re [Lt ] 1 and viscosity dominates the retarding forces, this leads to a differential equation relating the height of the circle of contact to time. Solutions are derived, involving one or more unknown parameters, which describe the time dependence of the height of the circle of contact.Experimental data, obtained from delayed flash photographs of the meniscus profiles of silicone fluid climbing over the surface of glass cones, provide general support for the model. The agreement between the predicted and observed height as a function of time is sufficiently close to justify the model as a useful description.

Computed tomography of the brain stem with intrathecal metrizamide. Part I: the normal brain stem.

In summary, the anatomic details of the brain stem are exquisitely demonstrated with metrizamide CT. The obex is the zone of transition from the closed medulla, which has a conical pear-shaped appearance to the quadriconcave open medulla. The pyramids and inferior olivary nuclei characterize the anterior surface of the open medulla, whereas the median sulcus and the cranial nerve nuclei constitute the floor of the fourth ventricle at the same level. The mushroomlike appearance of the pontomedullary junction is easily reproducible with the restiform bodies forming the posteriorly diverging biped. The seventh and eighth nerves are usually seen at this level or on the adjacent higher section of the low pons. The brachia pontis are well delineated in almost their entire length at the level of the low pons as they bound the fourth ventricle laterally. The trigeminal nerves are seen at the level of the midpons, which is a few millimeters lower than the isthmus. The latter constitutes the junction of the pons with the mesencephalon. The colliculi divide the midbrain into two levels of axial cross section: the inferior collicular level, which may or may not show the trochlear nerve, and the superior collicular level, which features anteriorly the suprasellar cistern and its contents. Air is an inadequate contrast agent for CT for the demonstration of the surface features of the brain stem because of partial filling of the cisterns and meniscus formation that precludes a detailed outline. Metrizamide, however, with careful technique, fills the fourth ventricle and subarachnoid space both infra- and supratentorially. High-resolution scanning using primary reconstruction, and thin tomographic sections of no more than 5 mm are a necessity for metrizamide CT. Consecutive scans should not be spaced more than 5 mm apart if all the features of the brain stem are to be evaluated. The demonstration of the various grooves and protuberances on the surface of the brain stem provides a unique opportunity for evaluating focal atrophy and focal swelling henceforth impossible to visualize consistently.

On the force acting on a horizontal cylinder withdrawn from a liquid

Analyses, reported in the literature on the capillary force resulting from the formation of a liquid meniscus, are examined in the light of a new rigorous mathematical treatment. Formal aspects are pointed out, emphasizing the consideration that surface mechanical properties should preferably be conceived as originating by virtue of the existence of a surface free energy rather than of a contractile skin.

Meniscus formation in airways of excised rat lungs

The object of this study was to determine the transpulmonary pressure at which menisci form in the airways of excisted rat lungs. The necessary geometric requirements for meniscus formation are normally met in the airways, but a meniscus is presumably prevented from forming at large lung volumes because too little fluid is present. At lower volumes a meniscus could form and easier since airway caliber is reduced and less fluid is required. a series of pressure-volume curves were recorded for lungs in which meniscus formation was inhibited by increasing the end expiratory pressure. Assuming the number of airqays containing at least one meniscus was proportional to the amount of gas trapped in the excised rat lung, it was found that the menisci were performed in 68% of the airways between positive transpulmonary pressures of 1.4 and 3.0 cm H 2O during deflation.

The Air Meniscus Sign in Sclerosing Hemangioma of the Lung

The air meniscus sign occurs in a number of lung conditions, including infection, benign and malignant tumors, and hematoma. Sclerosing hemangioma does not appear to have been implicated previously in this connection. Two such cases are described. Possible mechanisms of air meniscus formation and its diagnostic value in sclerosing hemangioma are discussed.

Adsorption systems at temperatures below the freezing point of the adsorptive

Isothermal adsorption studies and the measurement of dimensional changes below the bulk freezing point of the adsorbate indicate that substances adsorbed in porous solids are unable to freeze in situ. The difference between the vapour pressure or free energy of the unfrozen adsorbate and that of the bulk adsorptive outside of the porous system is resolved by a desorption process; the desorbed matter freezes outside of the system while the vapour pressure of the adsorbate remaining in the pores decreases through meniscus formation. Mechanical breakdown of the system occurs only then, when this process cannot be completed and an equilibrium state is not attained. This mechanism was found to be valid for porous silica glass, hydrated cement paste, bricks, and even for biological substances such as animal and plant tissue, and foodstuff. This understanding has led to the development of new methods for testing the durability of building materials, clarification of some problems of the BET surface area determination method and it suggests an explanation for the action of cryoprotective agents.