Centripetal Flow Research Articles

Lubricant Permeation From Micro Oil Pits Under Intimate Contact Condition

In the situation of serious tool-workpiece contact when a smooth surface is desired in metal forming, the lubricant is either enclosed within the micro pits or infiltrates the contact plateaus region. The evolution of surface topography and the interfacial shear stress is accordingly altered. A quantitative analysis has been developed based on a series of compression-sliding tests and three-dimensional measurements of work-piece surface. It is found that the lubricant in the oil pits seeps into the contact region under the present experimental conditions. The fractional area of oil pit is a linear function of the average surface separation. The deformation of the oil pits is in the mode of “centripetal flow” where the opening of the pit is diminished while the depth of the oil pit is basically kept constant during the deformation. The specific permeation flux, which is defined as the nondimensional permeation flux per unit relative sliding speed and width of oil pit is an important index for the tendency of permeation. The variation of the specific permeation flux reveals that the lubricant permeation increases with sliding speed and average surface separation. After adopting the permeation model, it is found that the slipping between tool surface and permeating lubricant might exist. The average film thickness of the infiltrating oil increases with increasing sliding velocity and less serious asperity contact.

Reversible Left Renal Vein Obstruction Caused by an Abdominal Aortic Aneurysm

The authors document a unique cause for left renal vein hypertension and hematuria in a 66-year-old woman presenting with abdominal pain, pulsatile mass, and hematuria. A computer tomographic scan of the abdomen revealed, in association with a 5.3-cm fusiform abdominal aortic aneurysm, a compressed left renal vein as well as dilatation of the left gonadal vein and the pelvic venous plexus. Arteriography confirmed functional occlusion of the left renal vein by the juxtarenal enlargement of the abdominal aortic aneurysm. This created centrifugal flow to the inferior vena cava through the left gonadal vein, the pelvic venous plexus, and the hypogastric veins. The patient underwent abdominal aortic aneurysm repair with complete recovery. A postoperative abdominal computer tomographic scan confirmed restored patency of the left renal vein and normalization of centripetal venous flow on the left side. While a number of mechanisms of renal vein obstruction have been reported, collateralization and hematuria secondary to stretching and compression of the left renal vein by an aortic aneurysm have not previously been described. Although left renal vein hypertension and hematuria are rarely associated with an aortic aneurysm, it should be recognized that a juxtarenal aneurysm may cause this syndrome.

Cytoplasm dynamics and cell motion: two-phase flow models

The motion of amoeboid cells is characterized by cytoplasmic streaming and by membrane protrusions and retractions which occur even in the absence of interactions with a substratum. Cell translocation requires, in addition, a transmission mechanism wherein the power produced by the cytoplasmic engine is applied to the substratum in a highly controlled fashion through specific adhesion proteins. Here we present a simple mechano-chemical model that tries to capture the physical essence of these complex biomolecular processes. Our model is based on the continuum equations for a viscous and reactive two-phase fluid model with moving boundaries, and on force balance equations that average the stochastic interactions between actin polymers and membrane proteins. In this paper we present a new derivation and analysis of these equations based on minimization of a power functional. This derivation also leads to a clear formulation and classification of the kinds of boundary conditions that should be specified at free surfaces and at the sites of interaction of the cell and the substratum. Numerical simulations of a one-dimensional lamella reveal that even this extremely simplified model is capable of producing several typical features of cell motility. These include periodic `ruffle' formation, protrusion–retraction cycles, centripetal flow and cell-substratum traction forces.

Side milling cutters with working elements made of high-speed steel powder. II. Properties of cutting materials

Investigations were carried out into the materials for blanks of side milling cutters produced from high-speed steel powder by hot upsetting ring-shaped porous blanks with the centripetal flow of the material. A method of evaluating the quality of material on the basis of the density and specific work of failure of specimens, cut from the discs in different areas and in different directions, was developed and applied for this purpose. The use in the blank of a central insert produced from rolled structural steel results in higher properties (“the head” effect). The results of testing the durability of cutters with working elements produced from high-speed steel powder show that their durability decreases less rapidly with increasing cutting speed than that of the cutters made of rolled material.

Development and movements of extraembryonic cells in the Indian meal moth, Plodia interpunctella Hübner (Lepidoptera: Pyralidae)

Summary Time-lapse video microscopy, fluorescence microscopy, and electron microscopy provide complementary perspectives on the genesis and movements of the serosa, amnion, and yolk cells of the Indian meal moth, Plodia interpunctella Hübner (Lepidoptera: Pyralidae). Prospective serosal cells undergo a nuclear division, round up and detach from the adjoining cells of the germ band. They reattach only to other serosal cells, creating a free migrating edge at the boundary between the germ band and the serosa. The serosa engages in epiboly, spreads to enclose the embryo, attaches to the vitelline envelope, and secretes materials onto the vitelline envelope on the inner side of the egg shell. The amnion derives from the dorsal edge of the germ band; at this time the germ band is a cell sheet composed of columnar cells (palisade-type). Amniotic cells change briefly into spindle-shaped, motile cells that dissociate from the germ band. They cross the dorsal rim of the germ band, then flatten and form an epithelium. The amnion engages in epiboly and spreads across most of the embryo, starting approximately 1h after the serosa does. A lamina is secreted between the amnion and the embryo. By mid-embryogenesis, the amnion reaches over the dorsal region, including some yolk cells. The lamina and amnion loosen from the embryo during blastokinesis, the stage after germ band shortening. The yolk endoplasm partitions into yolk cells between 1 to 2h after other cells appear. Yolk cells are highly motile during early embryogenesis, then gradually slow and engage in cell shape changes without locomotion. They tend to flatten and ruffle during blastokinesis. By the end of blastokinesis, they form stable membrane contacts, creating a cell sheet. These large cells exhibit fountanoid and centripetal flows when they are motile.

Die Forging Utilizing Thickening of Drawn Cup Wall. 1st Report, Feasibility of Wall Thickness Increase.

The purpose of this research is to develop a new die forging process to form machine parts which satisfy the strength requirements like a gear or a spline. The major point of this new process is the feasibility of the increase in the thickness without buckling since the initial material shape for the new process is a thick sheet and an intermediate product before die forging is a drawn cup. The new process is composed of deep drawing, redrawing with ironing, ear-trimming, and final die forging. In the redrawing, intermediate second process, the outer profile is the same to that of the final product. In the final die forging the increase in the wall thickness of the drawn cup is promoted mainly by centripetal metal flOW. The feasibility of the new plastic forming process was confirmed through a series of experimental simulation with a final product that had a wavy cross-sectional profile. As a result of an experiment the increase in the wall thickness without severe buckling has been confirmed.

Laser-induced coalescence of petroleum-in-water emulsions

A petroleum-in-water emulsion is heated by a CW He-Ne laser beam incident in the liquid free surface. The resulting temperature distribution creates a centripetal thermoconvective flow which drives the petroleum droplets to the central hot point. Coalescence of an increasing number of petroleum droplets gives rise to the formation of a homogeneous petroleum bulk. A centrifugal stress distribution now grows up in the central bulk as a result of temperature dependence of the interfacial tension of the petroleum–water interface. An equilibrium state between centrifugal and centripetal forces is finally attained and the system remains at rest. The whole sequence is visualized by observation of the light beam scattered out from the liquid volume. A theoretical model explains the main features of the thermoconvective flow.

Disassembly of actin filaments leads to increased rate and frequency of mitochondrial movement along microtubules.

In activated sea urchin coelomocytes, cytoplasmic organelles move along distinct actin and microtubule dependent pathways, actin-based motility is driven by an unconventional myosin, and microtubule disassembly does not effect actin-dependent organelle motility [D'Andrea et al., 1994: J. Cell Sci. 107:2081-2094]. Given the growing evidence for potential interactions between components of the actin and microtubule cytoskeletons, we examined the effect of actin filament disassembly on the movement of mitochondria along microtubules in activated coelomocytes. Coelomocytes treated with cytochalasin B (CB), to disrupt actin filaments, exhibited a thinning of the cytoplasm, enhanced lateral undulation of microtubules, and ceased centripetal cortical flow of actin. Interestingly, the loss of actin filaments resulted in a approximately 1.5-fold increase in the average velocity of outward and inward moving mitochondria and increased the frequency of centripetal movement. To test if enhanced motility along microtubules was a consequence of decreased actin-myosin interaction, coelomocytes were treated with 2,3-butanedione monoxime (BDM), a potent inhibitor of myosin activity [Cramer and Mitchison, 1995: J. Cell Biol. 131:179-189]. BDM inhibited all types of actin-based motility observed in these cells including retrograde cortical flow, protrusion and retraction of the cell edge, and movement of intracellular organelles. Surprisingly, BDM treatment stopped the movement of mitochondria in CB-exposed cells, suggesting that BDM can also act as an inhibitor of organelle movement along microtubules. Collectively, these data demonstrated that microtubule-dependent mitochondrial motility and microtubule movement were sensitive to changes in the assembly state of the actin cytoskeleton.

Disassembly of actin filaments leads to increased rate and frequency of mitochondrial movement along microtubules

In activated sea urchin coelomocytes, cytoplasmic organelles move along distinct actin and microtubule dependent pathways, actin-based motility is driven by an unconventional myosin, and microtubule disassembly does not effect actin-dependent organelle motility [D'Andrea et al., 1994: J. Cell Sci. 107:2081–2094]. Given the growing evidence for potential interactions between components of the actin and microtubule cytoskeletons, we examined the effect of actin filament disassembly on the movement of mitochondria along microtubules in activated coelomocytes. Coelomocytes treated with cytochalasin B (CB), to disrupt actin filaments, exhibited a thinning of the cytoplasm, enhanced lateral undulation of microtubules, and ceased centripetal cortical flow of actin. Interestingly, the loss of actin filaments resulted in a ∼1.5-fold increase in the average velocity of outward and inward moving mitochondria and increased the frequency of centripetal movement. To test if enhanced motility along microtubules was a consequence of decreased actin-myosin interaction, coelomocytes were treated with 2,3-butanedione monoxime (BDM), a potent inhibitor of myosin activity [Cramer and Mitchison, 1995: J. Cell Biol. 131:179–189]. BDM inhibited all types of actin-based motility observed in these cells including retrograde cortical flow, protrusion and retraction of the cell edge, and movement of intracellular organelles. Surprisingly, BDM treatment stopped the movement of mitochondria in CB-exposed cells, suggesting that BDM can also act as an inhibitor of organelle movement along microtubules. Collectively, these data demonstrated that microtubule-dependent mitochondrial motility and microtubule movement were sensitive to changes in the assembly state of the actin cytoskeleton. Cell Motil. Cytoskeleton 40:368–378, 1998. © 1998 Wiley-Liss, Inc.

Radial optic flow induces vergence eye movements with ultra-short latencies.

An observer moving forwards through the environment experiences a radial pattern of image motion on each retina. Such patterns of optic flow are a potential source of information about the observer's rate of progress, direction of heading and time to reach objects that lie ahead. As the viewing distance changes there must be changes in the vergence angle between the two eyes so that both foveas remain aligned on the object of interest in the scene ahead. Here we show that radial optic flow can elicit appropriately directed (horizontal) vergence eye movements with ultra-short latencies (roughly 80 ms) in human subjects. Centrifugal flow, signalling forwards motion, increases the vergence angle, whereas centripetal flow decreases the vergence angle. These vergence eye movements are still evident when the observer's view of the flow pattern is restricted to the temporal hemifield of one eye, indicating that these responses do not result from anisotropies in motion processing but from a mechanism that senses the radial pattern of flow. We hypothesize that flow-induced vergence is but one of a family of rapid ocular reflexes, mediated by the medial superior temporal cortex, compensating for translational disturbance of the observer.

Glacial loading and unloading: a possible cause of rock salt dissolution in the Western Canada Basin

Each of the five main bedded Devonian rock salts in the Western Canada Basin has been leached in places more-or-less continuously since shortly after deposition. For the most part, salt dissolution has been self-sustaining and relatively slow. At various times however, leaching has been significantly accelerated by large-scale external processes such as regional uplift and erosion (during the pre-Cretaceous hiatus), and regional faulting (during the mid-Late Cretaceous). The most recent phase of accelerated leaching occurred during the Quaternary, probably as a result of glacial loading and unloading. Two principal lines of evidence support the thesis that accelerated rates of salt dissolution occurred during the Quaternary. First, there is an apparent correlation between surface drainage patterns and the active dissolution margins of the Devonian rock salts. A significant percentage of the lakes and rivers in proximity to active salt dissolution margins are situated along the near-zero edge of the respective salt bodies. Second, salt-related subsidence features at the pre-Quaternary subcrop level have been mapped on seismic data in the immediate proximity of active salt dissolution margins. The Quaternary subsidence features associated with the Prairie Formation rock salt for example, parallel the active salt margin and can be up to several kilometers wide. The areal extent of these shallow subsidence features and the high volume of rock salt dissovled at these sites suggest that accelerated rates of leaching occurred during the Quaternary (relative to the average rate of dissolution throughout the Cretaceous). The magnitude of these shallow structural features demonstrates clearly that subsidence associated with Recent salt dissolution can influence surficial drainage patterns to the extent suggested by the distribution of the lakes and rivers in proximity to the salt dissolution margins. The accelerated rates of salt dissolution during the Quaternary are attributed to glacial loading and unloading, and associated processes. Glacial loading could result in the compaction of subsurface strata, an increase in geothermal gradient, the thermal expansion of the deep aquifers, and the expulsion of interstitial water. These effects could increase both the rate of centrifugal fluid flow within a basin and the rate of salt dissolution. Glacial unloading could also affect the rate of salt dissolution. This rapid decrease in applied load is manifested as glacial rebound, a process which could increase the porosity and fracture permeability of the subsurface, and decrease the geothermal gradient. Potentially, the rate of centripetal fluid flow (at least around the basin margins) could be increased. Increased centripetal fluid flow, accompanied by an influx of understurated glacial melt waters would enhance the rate of salt dissolution.

Centripetal cholesterol flux from extrahepatic organs to the liver is independent of the concentration of high density lipoprotein-cholesterol in plasma.

High density lipoproteins (HDLs) play a role in two processes that include the amelioration of atheroma formation and the centripetal flow of cholesterol from the extrahepatic organs to the liver. This study tests the hypothesis that the flow of sterol from the peripheral organs to the liver is dependent upon circulating HDL concentrations. Transgenic C57BL/6 mice were used that expressed variable amounts of simian cholesteryl ester-transfer protein (CETP). The rate of centripetal cholesterol flux was quantitated as the sum of the rates of cholesterol synthesis and low density lipoprotein-cholesterol uptake in the extrahepatic tissues. Steady-state concentrations of cholesterol carried in HDL (HDL-C) varied from 59 to 15 mg/dl and those of apolipoprotein AI from 138 to 65 mg/dl between the control mice (CETPc) and those maximally expressing the transfer protein (CETP+). There was no difference in the size of the extrahepatic cholesterol pools in the CETPc and CETP+ animals. Similarly, the rates of cholesterol synthesis (83 and 80 mg/day per kg, respectively) and cholesterol carried in low density lipoprotein uptake (4 and 3 mg/day per kg, respectively) were virtually identical in the two groups. Thus, under circumstances where the steady-state concentration of HDL-C varied 4-fold, the centripetal flux of cholesterol from the peripheral organs to the liver was essentially constant at approximately 87 mg/day per kg. These studies demonstrate that neither the concentration of HDL-C or apolipoprotein AI nor the level of CETP activity dictates the magnitude of centripetal cholesterol flux from the extrahepatic organs to the liver, at least in the mouse.

Formation of the Female Pronucleus and Reorganization and Disassembly of the First Interphase Cytoskeleton in the Egg of the Glossiphoniid Leech Theromyzon rude

Eggs of the leech Theromyzon rude were studied under dissecting, fluorescence, light, and electron microscopes. The sperm-derived centrosome divides and separates at early first interphase. The female pronucleus forms beside the male pronucleus at the centrally located perinuclear plasm domain, by fusion and remodelling of karyomeres that have descended from the animal pole at the tip of an ooplasmic process (centripetal ooplasmic flow). Retraction of this process (centrifugal ooplasmic flow) appears to return ooplasm to the animal pole. The reversible flow of ooplasm occurs along a subset of monaster microtubules that exhibit delayed depolymerization, and organelles thus move in both directions. Depolymerization of the first interphase monaster fibers seems to occur as a regular wave, moving from the internally located perinuclear plasm to the peripherally situated egg poles. However, disassembly of the ectoplasmic monaster fibers is preceded by furrowing and reorganization of both microtubules and microfilaments along polar rings and meridional bands. Bipolar contraction of microfilaments and shortening of microtubules lead to organelle concentration at the egg poles.

Dynamics of external ocular blood flow studied by scanning angiographic microscopy.

The scanning angiographic microscope (SAM) provides a solution to the considerable technical difficulties associated with conventional episcleral fluorescein angiography. Standardised anterior segment fluorescein videoangiograms were performed using the SAM in each episcleral quadrant of the right eye in 6 normal subjects; frame-by-frame analysis proved important. Centripetal flow was seen in all 37 scleral perforating arteries investigated. Other features were the marked individual variability, much larger vertical anterior ciliary arteries, the high frequency of arteriovenous anastomoses, the complex flow patterns, the absence of a 'watershed' zone between anterior ciliary and posterior episcleral circulations, a characteristic and discontinuous distribution of 'leaky' episcleral veins, and the primacy of venous drainage into the plexus of muscular veins. Reports of retrograde blood flow in the anterior ciliary arteries in most fluorescein angiographic studies are probably incorrect, the result of unappreciated methodological problems. The SAM is an important advance on previous anterior segment fluorescein angiography techniques.

Lamellipodia architecture: actin filament turnover and the lateral flow of actin filaments during motility

Consideration of the arrangement of actin filaments in the lamellipodia of crawling cells indicates that, in addition to a rearward flow of the actin cytoskeleton due to treadmilling, there is a lateral flow of filaments in both directions. The existence of such a lateral flow of actin filaments is supported by observation of the lateral movement of actin filament bundles in fibroblasts and by fluorescence photoactivation data. In addition to explaining the formation, dispersal and lateral movement of filament bundles, lateral filament flow could add a further velocity component to the centripetal flow of cytoplasm. As such, lateral filament flow may explain the discrepancies in the rates of the rearward flow of actin, cytoplasmic materials and dorsal particles.

An overview of some of the large scale mechanisms of salt dissolution in western Canada

Well log and seismic data indicate that the bedded rock salts (salts) of the Devonian Age Prairie Formation were widely distributed and uniformly deposited in the Lloydminster area, Western Canada (T45-65, R20W3M-R5W4M); however, as a result of extensive leaching, the distribution of these salts is not now what it once was. The Lloydminster area is now bisected by the north‐south trending main dissolutional edge of the Prairie salt. Thick salt (up to 150 m) is preserved to the west of this edge; to the east the salt is mostly absent. Analyses of remnant salt and patterns of subsurface structural relief suggests that the dissolution of the Prairie salt in the Lloydminster area was triggered and/or accentuated in part by several different large scale mechanisms including: near‐surface exposure, centripetal flow of unsaturated waters, regional faulting/fracturing, glacial loading and/or unloading, dissolution of the underlying salt, and salt creep. These mechanisms are supported by the incorporated seismic and well log control that indicate a direct relationship between the thicknesses of remnant salt and post‐salt strata. Well log and seismic data also indicate that the bedded salts of the Devonian Age Black Creek Member were uniformly deposited within the Black Creek sub‐basin, Rainbow Lake area, western Canada (T105-112, R5-R10W6M); however, as a result of extensive leaching, distribution of these salts is not now what it once was. The Black Creek salts are now preserved only as discontinuous remnants with maximum gross thicknesses on the order of 80 m. Seismic and well log control suggests that the dissolution of the Black Creek salt in the Rainbow Lake study area was triggered and/or accentuated in part by several different large scale mechanisms including: centrifugal flow of unsaturated waters, regional faulting/fracturing and salt creep. Bedded salt is preserved within five other Devonian Age evaporitic units in Alberta, Canada: the Lotsberg Formation, Cold Lake Formation, Beaverhill Lake Group, Leduc Formation, and Wabamun Group. Each of these salts has also been extensively leached in places. In the literature, dissolution is generally attributed to one or more of the previously noted large scale mechanisms. Herein we present an overview of the envisioned principal mechanisms of salt dissolution. In support of these hypothesized mechanisms, we present seismic and geologic control from both the Lloydminster and Rainbow Lake areas of western Canada, which illustrate that the dissolution of subsurface salts is accompanied by the subsidence of post‐salt strata and that the analyses of this information can be used to elucidate the timing and large scale mechanisms of salt dissolution.

The Formation of Fusiform Proplatelets and their Transformation to Discoid Platelets

Blood platelets are produced in the circulation by fragmentation of long, slender processes of cytoplasm formed from the megakaryocyte, the parent cell of platelets. Fragmentation occurs at local constrictions, forming 6 to 15 µm long, fusiform fragments (elongated proplatelets). The fusiforms transform into the circular, disc-shaped mature platelet by curving into a ring, which closes by fusion at the tips. The hole in the ring is finally filled in by a centripetal flow of membrane from the periphery. It is presumed that the curving of the fusiform is mediated by curving of its contained bundle of microtubules, which becomes the marginal bundle of the disc-shaped platelet. When curving begins in the fusiform, microtubules are closely associated with a membraneous tubule that becomes the submarginal tubule of the dense tubular system.

The micocirculation of bone and marrow in the diaphysis of the rat hemopoietic long bones

The nature of the microcirculation of the diaphyseal portion of long bones and the adjacent bone marrow is poorly understood. The purpose of this study was to describe the blood supply in the diaphyseal cortex and the relationship of the bone vascular circulation to that of the bone marrow in the growing rat. India ink-gelatin was infused in the arterial system of 3-month-old rats and the vascularization was determined from histological sections. In some studies the periosteal circulation was blocked but the nutrient and metaphyseal arteriole systems were left intact. In the growing rat, most of the vascular flow appears to be centripetally through the diaphyseal cortex and this appears to be the primary blood supply for the adjacent bone marrow. The India ink traversed the cortex and entered the marrow through osteal canals at the endocortical surface. At the marrow-endocortical bone surface interface, ink exiting from the osteal canals filled the adjacent marrow sinusoids in what appeared as "bush-like" structures. From the bone marrow the ink appeared to drain into the central vein. Some arterioles from the nutrient system were found to penetrate the inner two thirds of the cortical bone and then re-enter the bone marrow. The centripetal flow of blood and the importance of the cortical flow for perfusion of the hemopoietic tissue was further documented when periosteal flow was obstructed. In this situation, the cortical bone and adjacent bone marrow were not perfused while the nutrient system and central vein were filled with ink.(ABSTRACT TRUNCATED AT 250 WORDS)

Centripetal flow and directed reassembly of the major sperm protein (MSP) cytoskeleton in the amoeboid sperm of the nematode, Ascaris suum

The cytoskeleton of the amoeboid spermatozoa of Ascaris suum consists of major sperm protein (MSP) filaments arranged into long, branched fiber complexes that span the length of the pseudopod and treadmill rearward continuously due to assembly and disassembly at opposite ends of the complexes (Sepsenwol et al., Journal of Cell Biology 108:55-66, (1989)). Examination by video-enhanced microscopy showed that this cytoskeletal flow is tightly coupled to sperm locomotion. The fiber complexes treadmilled rearward at the same rate (10-50 microns/min) as the cell crawled forward. Only fiber complexes with their plasmalemmal ends within a limited sector along the leading edge of the pseudopod underwent continuous assembly. Thus, the location of this sector, which occupies about 50% of the pseudopod perimeter, determined the direction of sperm locomotion. Treatment of sperm with agents that lower intracellular pH, such as weak acids and protonophores, caused the fiber complexes to disassemble completely in 4-5 sec. Removal of these compounds resulted in reassembly of the cytoskeleton in a pattern that mimicked treadmilling in intact sperm. The fiber complexes were reconstructed by assembly at their plasmalemmal ends so that within 30-60 sec the entire filament system reformed and the cell resumed locomotion. Both cytoskeletal reassembly and treadmilling required exogenous HCO3-. These results suggest that variation in intracellular pH may help regulate cytoskeletal treadmilling and thereby play a significant role in sperm locomotion.

Cell locomotion: New research tests old ldeas on membrane and cytoskeletal flow

Recent studies on the mobility of membrane markers on crawling cells indicate that there is no long-range centripetal flow of membrane proteins or lipids during cell locomotion. In this article we reflect on the history of ideas about membrane flow in cells, and we discuss how these new findings will shift the focus of research in cell locomotion away from the cell surface to the molecular interactions and dynamics of the actin cytoskeleton.