Flow Contraction Research Articles

Effects of castration on female rabbit bladder physiology and morphology

ObjectivesTo determine the effect of ovariectomy on bladder blood flow and oxygen tension. Women are subject to bladder dysfunctions that occur less frequently in men. These include interstitial cystitis (syndrome of urgency, frequency, and pain on distension), incontinence, and bladder infections. It is believed that alterations in female sex hormones play a major role in mediating these abnormalities. We believe that alterations in estrogen can have marked effects on the blood flow to the bladder. MethodsWe divided 20 female rabbits into two equal groups: ovariectomized and sham operated. Six weeks later, the bladder of each rabbit was evaluated for bladder capacity, compliance, permeability, blood flow, tissue hypoxia, morphology, and smooth muscle contraction. ResultsOvariectomy resulted in decreased bladder compliance; decreased blood flow to the bladder mucosa and uterus, a smaller decrease in blood flow to the bladder smooth muscle, and mucosal hypoxia; and statisticallysignificant thinning of the bladder mucosa and increased mucosal permeability. ConclusionsOvariectomy resulted in decreased blood flow and hypoxia to the bladder mucosa and a mildly decreased blood flow to the smooth muscle. The decreased blood flow and hypoxia may be related to the age-related uropathologic findings in postmenopausal women.

Processes preventing nocturnal equilibration between leaf and soil water potential in tropical savanna woody species.

The impact of nocturnal water loss and recharge of stem water storage on predawn disequilibrium between leaf (psiL) and soil (psiS) water potentials was studied in three dominant tropical savanna woody species in central Brazil (Cerrado). Sap flow continued throughout the night during the dry season and contributed from 13 to 28% of total daily transpiration. During the dry season, psiL was substantially less negative in covered transpiring leaves, throughout the day and night, than in exposed leaves. Before dawn, differences in psiL between covered and exposed leaves were about 0.4 MPa. When relationships between sap flow and psiL of exposed leaves were extrapolated to zero flow, the resulting values of psiL (a proxy of weighted mean soil water potential) in two of the species were similar to predawn values of covered leaves. Consistent with substantial nocturnal sap flow, stomatal conductance (gs) never dropped below 40 mmol m(-2) s(-1) at night, and in some cases, rose to as much as 100 mmol m(-2) s(-1) before the end of the dark period. Nocturnal gs decreased linearly with increasing air saturation deficit (D), but there were species-specific differences in the slopes of the relationships between nocturnal gs and D. Withdrawal and recharge of water from stem storage compartments were assessed by monitoring diel fluctuations of stem diameter with electronic dendrometers. Stem water storage compartments tended to recharge faster when nocturnal transpiration was reduced by covering the entire plant. Water potential of covered leaves did not stabilize in any of the plants before the end of the dark period, suggesting that, even in covered plants, water storage tissues were not fully rehydrated by dawn. Patterns of sap flow and expansion and contraction of stems reflected the dynamics of water movement during utilization and recharge of stem water storage tissues. This study showed that nighttime transpiration and recharge of internal water storage contribute to predawn disequilibrium in water potential between leaves and soil in neotropical savanna woody plants.

Pressure drop caused by abrupt flow area changes in small channels

Pressure drops caused by abrupt flow area expansion and contraction in small circular channels were experimentally investigated, using air and water at room temperature and near-atmospheric pressure as the working fluids. The larger and smaller tube diameters were 1.6 and 0.84 mm, respectively. Experiments were performed with single-phase gas and liquid, and two-phase mixtures. The parameter ranges were single-phase flow Reynolds numbers in the smaller channel = 870–12,960; flow quality in two-phase flow experiments = 1.9 × 10 −3–1.6 × 10 −2. In single-phase flow experiments, the expansion and contraction loss coefficients were different for gas and liquid, and with the exception of contraction loss coefficients for water they agreed reasonably with the predictions of the commonly used prediction methods. Contraction loss coefficients for water were slightly larger than theoretical predictions. The measured total two-phase pressure changes indicated the occurrence of significant velocity slip. The assumption of a velocity slip ratio in accordance with minimum entropy production in annular flow regime led to a reasonable agreement between the data and a simple one-dimensional flow theory. An empirical correlation was developed for two-phase flow pressure drop caused by the flow area contraction.

Signaling and ligand binding by recombinant neuromedin U receptors: evidence for dual coupling to Galphaq/11 and Galphai and an irreversible ligand-receptor interaction.

The neuropeptide neuromedin U (NmU) shows considerable structural conservation across species. Within the body, it is widely distributed and in mammals has been implicated in physiological roles, including the regulation of feeding, anxiety, pain, blood flow, and smooth muscle contraction. Human NmU-25 (hNmU-25) and other NmU analogs were recently identified as ligands for two human orphan G protein-coupled receptors, subsequently named hNmU-R1 and hNmU-R2. These receptors have approximately 50% amino acid homology, and, at least in mammalian species, NmU-R1 and NmU-R2 are expressed predominantly in the periphery and central nervous system, respectively. Here, we have characterized signaling mediated by hNmU-R1 and hNmU-R2 expressed as recombinant proteins in human embryonic kidney 293 cells, particularly to define their G protein coupling and the activation and regulation of signal transduction pathways. We show that these receptors couple to both Galpha(q/11) and Galpha(i). Activation of either receptor type causes a pertussis toxin-insensitive activation of both phospholipase C and mitogen activated-protein kinase and a pertussis toxin-sensitive inhibition of adenylyl cyclase with subnanomolar potency for each. Activation of phospholipase C is sustained, but despite this capacity for prolonged receptor activation, repetitive application of hNmU-25 does not cause repetitive intracellular Ca2+ signaling by either recombinant receptors or those expressed endogenously in isolated smooth muscle cells from rat fundus. Using several strategies, we show this to be a consequence of essentially irreversible binding of hNmU-25 to its receptors and that this is followed by ligand internalization. Despite structural differences between receptors, there were no apparent differences in their activation, coupling, or regulation.

Observed and predicted bed forms and their effect on suspended sand concentrations

In this paper, we study the effect of bed forms on suspended sand concentrations and we compare three existing bed form predictors to field and laboratory measurements over a wide range of conditions and propose a new predictor that better collapses the measured bed form dimensions. We apply the different bed form predictors to estimate the suspended sediment concentration distributions based on the 1D advection diffusion equation and the bed-form-enhanced shear stress, which includes the flow contraction effect according to Nielsen [Coast. Eng. 10 (1986) 23]. Predictions of suspended sand concentration improve when including a bed form predictor. Interestingly, it does not make much difference which bed form predictor is implemented but more whether a bed form predictor is implemented. However, the choice of a particular bed form predictor is more important when the bed form effect in the sand transport model is based a roughness length scale k s and thus on η 2/ λ instead of η/ λ, where k s is Nikuradse's equivalent roughness length scale, η is the bed form height and λ is the bed form length. This is the case in the Van Rijn [Van Rijn, L.C., 2000. General view on sand transport by currents and waves: data analysis and engineering modelling for uniform and graded sand (TRANSPOR 2000 and CROSMOR 2000 models). Z2899.20 Z2099.30 Z 2824.30, WL∣Delft Hydraulics, Delft, The Netherlands] sand transport model, for example. We discuss the effect of so-called long wave ripples on the suspended sand concentrations.

An analysis of induced pressure fields in electroosmotic flows through microchannels

Induced pressure gradients are found to cause band-broadening effects which are important to the performance of microfluidic devices, such as capillary electrophoresis and capillary chromatography. An improved understanding of the underlying mechanisms causing an induced pressure gradient in electroosmotic flows is presented. The analysis shows that the induced pressure distribution is the key to understanding the experimentally observed phenomena of leakage flows. A novel way of determining the static pressures at the inlet and outlet of microchannels is also presented that takes account of the pressure losses due to flow contraction and expansion. These commonly neglected pressure losses at the channel entrance and outlet are shown to be important in accurately describing the flow. The important parameters that define the effect of induced pressure on the flows are discussed, which may facilitate the design of improved microfluidic devices. The present model clearly identifies the mechanism behind the experimentally observed leakage flows, which is further confirmed by numerical simulations. Not only can the leakage flow occur from the electric-field-free side channel to the main channel, but also the fluid in the main channel can be attracted into the side channel by the induced pressure gradient.

BRIDGE PIERS—DRAG FORCE COEFFICIENTS

ABSTRACT The rational approach for estimating afflux at bridge constrictions requires the knowledge of drag coefficient. This paper presents experimental investigations on the variation of drag coefficient with Reynolds number for piers with semicircular nose and tail and lens-shaped nose and tail considering the effects of flow contraction and length-width ratio of piers. It is observed that the drag coefficient varies directly with contraction ratio and length-width ratio of piers. A relation of the form CD1 = CRi e σj αk is also proposed for the experimental range of Rc = 7 × 104 to 5 × 105 for the two shapes of piers.

プラント流体機器の縮流部におけるスケール付着現象(発電プラントにおける非破壊検査と保守,発電プラントにおける非破壊検査と保守)

プラント流体機器の縮流部におけるスケール付着現象(発電プラントにおける非破壊検査と保守,発電プラントにおける非破壊検査と保守)

Relationship with plasma neurohormones and dyssynchrony detected by Doppler echocardiography in patients undergoing permanent pacemaker implantation

Objective — To determine whether isovolumic relaxation flow (IRF) and isovolumic contraction flow (ICF) resulted from asynchrony and asynergy due to VVI and DDD pacemakers modulated neurohormones, we measured neurohormone levels in plasma and investigated the characteristics of IRF and ICF using Doppler echocardiography.Methods and results — We studied 11 patients with dual-chamber pacemakers (DDD) and 11 patients, with ventricular inhibiting mode (VVI). All patients underwent Doppler echocardiography of the left ventricle. Atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP), renin and aldosteron were measured.The LV was scanned for the presence of intracavitary flow during the isovolumic relaxation and isovolumic contraction period. The plasma levels of BNP and ANP were significantly lower in DDD mode than in VVI mode (56±32 pg/ml vs. 94±32 pg/ml, p = 0.022 and 98 ± 20 pg/ml vs. 134 ± 17 pg/ml, p = 0.042, respectively).There were no significant differences in the plasma level of renin or aldosteron. VVI mode versus DDD mode increased isovolumic relaxation flow time (129 ± 41 vs. 111 ± 36 sec, p = 0.020) and isovolumic relaxation flow velocity (50 ± 4 vs. 37 ± 2 cm/s, p = 0.018).∞ A strong relationship between blood ANP and BNP levels and IRF velocity was found in patients with a VVI pacemaker (r: 0.632, p: 0.028; r: 0.528, p: 0.024, respectively).Conclusion — VVI mode has a longer isovolumic relaxation time, isovolumic relaxation flow velocity and has higher ANP and BNP plasma levels than DDD mode. IRF resulting from asynergy and asynchrony in VVI mode pacemakers versus DDD mode pacemakers affects the plasma levels of ANP and BNP compared to renin and aldosteron.

Silene rothmaleri P. Silva (Caryophyllaceae), a rare, fragmented but genetically diverse species

Silene rothmaleri is an endemic Portuguese species considered extinct until 1992, when it was rediscovered in the wild with a highly fragmented distribution. These rare plants occur along the southwestern Portuguese coast in small populations, which in addition to phenological differences that occur along the north–south gradient could create a pattern of genetic isolation. To evaluate the degree of genetic diversity and estimate the relationship between population fragmentation and genetic variability, we analysed the five known populations of S. rothmaleri using random amplified polymorphic DNA. Degree of polymorphism and Shannon Index of phenotypic diversity revealed high levels of diversity, found mainly within populations. PCo and cluster analysis revealed a distinct north–south cline, which was confirmed by spatial autocorrelation (Mantel) analysis. This indicates the existence of gene flow between small nearby populations and its insufficiency between widely separated populations. Levels of gene flow (Nm) estimated from the Shannon Index reveal a pattern consistent with a larger past distribution that went through a period of contraction and lack of gene flow followed by population differentiation. The central and largest population probably acts as a core of genetic variability inherited as a relict from a larger and more diverse ancestral population.

An Elliptic Grid Generation Technique for the Flow Contraction

In this paper, we determined a numerical solution of the incompressible Navier-Stokes equations for the flow inside the contraction geometry. The governing equations are written in the vorticity-stream function formulations. The numerical solution is based on a technique of automatic numerical generation of a curvilinear coordinate system by transforming the governing equation into computational plane. The transformed equations are approximated using central differences and solved simultaneously by successive over-relaxation iteration.

Coherent Structure in a Two-Dimensional Jet Passively Controled by Wake of a Cylinder Installed in Nozzle Contraction.

It is possible to control the spread of a plane jet passively by the vortices from a two-dimensional cylinder installed in the nozzle contraction. In this study, the wake characteristics of a cylinder and the coherent structure of a jet by this passive control method were examined by flow visualization and quantitative velocity measurements. In wide range of strouhal number based on vortex shedding frequency and jet exit velocity, the spreads of the jet were found to be suppressed. This suppression is caused by the high frequency vortices from the control cylinder which inhibits growth and pairing of the low frequency vortices. On the other hand, in certain cases of the strouhal number being 0.05-0.10, the spread of the jet was remarkably enhanced associated with distinctive peaks of spectrum at higher order of vortex shedding frequency caused by the deformation of the vortices in flow contraction nozzle. In the case of enhanced mode, vortex from the cylinder moves to the opposite side shear layer with the same vorticity sign as the vortex, and it enhances roll up of the shear layer.

Determining Minor Head Losses in Drip Irrigation Laterals. II: Experimental Study and Validation

Values of friction coefficient K and equivalent length le were determined for various emitter models using analytical and experimental procedures developed in the companion paper by Juana et al. in 2002. Flow contraction coefficient Cc for water jets discharging through orifices with angle α=45° is suggested when the emitters have hydrodynamic geometry at the insertion. Otherwise, α=90° or, as an extreme value, α=180° is preferred. Both criteria K and le showed a reasonable agreement for minor losses evaluation produced at emitter insertions along drip laterals. Accuracy on their determination was analyzed. Larger dispersion of K and le values was observed when lateral head losses were small. Inlet head, Reynolds number, and emitter spacing did not show a clear effect on K and le values, whereas the effect of obstruction ratio r of the pipe cross-sectional area at the emitter location was of practical significance. Parameters of the emitter discharge equation determined with lateral tests were comparable to those obtained on an emitter testing bench using the International Standard procedure.

Surface movements of emplaced lava flows measured by synthetic aperture radar interferometry

Lava flows continue to move after they have been emplaced by flow mechanisms. This movement is largely vertical and can be detected using differential synthetic aperture radar (SAR) interferometry. There are three main components to this motion: (1) movement of surface scatterers, resulting in radar phase decorrelation, (2) measurable subsidence of the flow surface due to thermal contraction and clast repacking, and (3) time‐dependent depression of the flow substrate. These effects act in proportion to the thickness of the lava flow and decay with time, although there is a time lag before the third component becomes significant. We explore these effects using SAR data from the ERS satellites over the Etna volcano, Sicily. Phase decorrelation on young, thick a'a lava flows persists for a few years and probably results from surface block rotations during flow contraction. Maximum measured subsidence rates of the 1991–1993 lava flow over a period of 70 days are about 0.7 mm day−1, but are potentially greater in areas of data decorrelation. These rates fall to <2.7 × 10−2 mm day−1 after about 20 years in flows about 50 m thick, sooner for thinner flows. Comparison with measured subsidence rates on Kilauean lava lakes suggests that thermal contraction only accounts for about one third of the observed subsidence. The remaining motion is thought to come from surface clast repacking during cooling and from creep mechanisms in the flow substrate. Measurements of postemplacement surface movement provide new constraints on the thermomechanical properties of lava flows and have cautionary implications for the interpretation of interferometric SAR data of volcanoes.

Nonlinear three-mode interactions in a developing mixing layer

A formulation based on the integral energy method is presented for the nonlinear interaction problem between three large-scale coherent modes in a developing, laminar, free shear layer. Both binary and three-mode nonlinear, modal energy and phase interactions are included. The modal evolution and the development of the mean flow are very sensitive to the initial energy contents and phases of the participating modes. A strong nonlinear coupling of the modal phase variations with the variations of the modal energies is shown to exist and is responsible for the rapid reversal of the intermodal energy interactions in favor of the occasionally declining mode. This nonlinear mechanism preserves the higher frequency modes far downstream and is shown to contribute to the appearance of mean flow contraction observed in experiments through local collective return of energy to the mean by all modes. Depending on initial conditions, our results support the arguments of R. A. Petersen and R. C. Clough [“The influence of higher harmonics on vortex pairing in an axisymmetric mixing layer,” J. Fluid Mech. 239, 81 (1992)] and M. R. Hajj, R. W. Miksad, and E. J. Powers [“Subharmonic growth by parametric resonance,” ibid. 236, 35 (1992)] according to which three-mode resonances are more efficient than the binary ones. Two cases relevant to situations where the first and second subharmonics of the most amplified mode are forced involving the 3/2 harmonic and 2/3 subharmonic, respectively, are examined. Comparisons of the calculations with experimental results indicate good qualitative agreement.

Hydraulic characteristics and discharge control of sluice gates

Vertical sluice gates are widely used for flow control in irrigation and drainage channels. When the opening is smaller than the critical depth, the flow immediately downstream of the gate will be supercritical. Flows through the gate may be free or submerged depending on the tailwater depth. This paper investigates various characteristics of a vertical sluice gate in a rectangular flatbed channel. Equations for discharge coefficient, dimensionless discharge, submerged water depth, maximum allowable gate opening, and the distinguishing condition separating free flow and submerged flow were derived and plotted with consideration of flow contraction at the gate. The distinguishing condition was found to be a function of the contraction coefficient, upstream water depth and tailwater depth, and was verified through laboratory experiments.

K-1302 ノズル内の二次元物体によって励起された二次元噴流の組織構造(S15-1 噴流構造)(S15 噴流・はく離流れの計測と制御)

It is possible to control the spread of a plane jet passively by the vortices from a two-dimensional cylinder installed in the nozzle contraction. In this study, the wake characteristics of a cylinder and the coherent structure of a jet by this passive control method were examined. In wide range of strouhal number Sto based on vortex shedding frequency (fv) and jet exit velocity, the spreads of the jet were found to be suppressed. On the other hand, hi particular cases of Sto being 0.08-0.10, the spread of the jet was remarkably enhanced associated with distinctive peaks of spectrum which arose from the deformation of the vortices by flow contraction in nozzle.

Local cold stress to the soles induces retroplacental hemorrhage in rats.

The aim of this study was to investigate the effect of local cold stress to the soles on placental histology in rats. Pregnant rats were subjected to a cold provocation (0 degrees C, 12 degrees C) and room temperature (23 degrees C) for 15 and 30 minutes. During cold stimulation and at the control temperature, uterine blood flow and uterine contraction were measured simultaneously. Histological studies of the placentas of these rats were also performed. Cold stress at 0 degrees C and 12 degrees C significantly decreased uterine blood flow (P < .005, P < .02) compared with controls (23 degrees C). The decrease in uterine blood flow was greater at 0 degrees C than at 12 degrees C stress. Cold-induced stress (0 degrees C) also evoked an isometric tension with increased frequency and amplitude in the rat uterus (P < .003, P < .0002) compared with controls (23 degrees C). Stimulation at 12 degrees C did not induce any uterine contractions. Placental histology of rats stressed at 0 degreesC revealed hemorrhages into the decidua basalis. These findings suggest that local cold stress decreases uterine blood flow and increases uterine contraction, resulting in retroplacental hemorrhage in rats. This model may account for human abruptio placentae.

Effect of blood flow and muscle contraction on noradrenaline spillover in the canine gracilis muscle.

Many authors have reported that, during exercise, noradrenaline spillover increases and fractional extraction decreases. It has been suggested that the increase in blood flow to active muscles may contribute to these effects. Muscle contraction also causes changes in many factors that may affect noradrenaline spillover and fractional extraction. In this experiment, we studied the effect of muscle contraction and blood flow on noradrenaline and adrenaline spillover and fractional extraction in the in situ canine gracilis muscle. The low intensity stimulation protocol enabled us to have muscle contractions without any effect on the local concentration of noradrenaline, as measured by microdialysis, and noradrenaline spillover. Fractional extraction of both noradrenaline and adrenaline was unaffected by increasing blood flow three and four times its resting value. In addition, noradrenaline spillover was increased by the higher blood flow, from 188 to 452 pg x min(-1) at rest and from 246 to 880 pg x min(-1) during stimulation. Stimulation of muscle contraction caused a significant increase in fractional extraction of noradrenaline and a nonsignificant increase in adrenaline extraction. In addition, an adrenaline spillover was observed in certain conditions. In light of our results, it seems that blood flow may not be the main factor decreasing fractional extraction of noradrenaline during exercise. However, blood flow could contribute to the increase in noradrenaline spillover observed in the active muscles during exercise.

Slab breakoff as a mechanism for flipping of subduction polarity in Taiwan

We propose a model that involves breakoff of the east-dipping Eurasian slab beneath the Taiwan orogen to account for the flipping of subduction polarity in northern Taiwan. The breakoff was initiated in southern Ryukyu in the early Pliocene and then propagated southwestward into Taiwan, like an opening zipper. Detachment of the Eurasian slab has created a mantle window for the north-dipping Philippine Sea plate to move in laterally, causing a switch in the subduction polarity. Slab breakoff not only provides a testable model for the lithospheric structure of Taiwan, but also accounts for the high heat flow, rapid uplift, synorogenic extension, deep-focus earthquakes, and north-diminishing crustal contraction in the Taiwan mountain belt.