bluuebunny/crossref_metadata_2025 huggingface dataset:
Improved in vivo two‐photon imaging after blood replacement by perfluorocarbon
Authors: Haiss F. , Jolivet R. , Wyss M. T. , Reichold J. , Braham N. B. , Scheffold F. , Krafft M. P. , Weber B.
Published: April 2009

Two‐photon microscopy is a powerful method in biomedical research that allows functional and anatomical imaging at a subcellular resolution in vivo. The technique is seriously hampered by absorption and scattering of light by blood, which prevents imaging through large vessels. Here, we demonstrate in the rat cerebral cortex that blood replacement by perfluorocarbon emulsion, a compound also used in human critical care medicine, yields superior image quality, while preserving neuronal integrity. Shadows of large superficial vessels disappear completely and cells can be imaged underneath them. For the first time, it is possible to image complete populations of neurons and astrocytes in the upper layers of neocortex in vivo.
Properties of Orai1 mediated store‐operated current depend on the expression levels of STIM1 and Orai1 proteins
Authors: Scrimgeour N. , Litjens T. , Ma L. , Barritt G. J. , Rychkov G. Y.
Published: April 2009

Two cellular proteins, stromal interaction molecule 1 (STIM1) and Orai1, are recently discovered essential components of the Ca2+ release activated Ca2+ (CRAC) channel. Orai1 polypeptides form the pore of the CRAC channel, while STIM1 plays the role of the endoplasmic reticulum Ca2+ sensor required for activation of CRAC current (ICRAC) by store depletion. It is not known, however, if the role of STIM1 is limited exclusively to Ca2+ sensing, or whether interaction between Orai1 and STIM1, either direct or indirect, also defines the properties of ICRAC. In this study we investigated how the relative expression levels of ectopic Orai1 and STIM1 affect the properties of ICRAC. The results show that cells expressing low Orai1 : STIM1 ratios produce ICRAC with strong fast Ca2+‐dependent inactivation, while cells expressing high Orai1 : STIM1 ratios produce ICRAC with strong activation at negative potentials. Moreover, the expression ratio of Orai1 and STIM1 affects Ca2+, Ba2+ and Sr2+ conductance, but has no effect on the current in the absence of divalent cations. The results suggest that several key properties of Ca2+ channels formed by Orai1 depend on its interaction with STIM1, and that the stoichiometry of this interaction may vary depending on the relative expression levels of these proteins.
Heteromeric TASK‐1/TASK‐3 is the major oxygen‐sensitive background K+ channel in rat carotid body glomus cells
Authors: Kim Donghee , Cavanaugh Eric J. , Kim Insook , Carroll John L.
Published: April 2009

Carotid body (CB) glomus cells from rat express a TASK‐like background K+ channel that is believed to play a critical role in the regulation of excitability and hypoxia‐induced increase in respiration. Here we studied the kinetic behaviour of single channel openings from rat CB cells to determine the molecular identity of the ‘TASK‐like’ K+ channels. In outside‐out patches, the TASK‐like background K+ channel in CB cells was inhibited >90% by a reduction of pHo from 7.3 to 5.8. In cell‐attached patches with 140 mm KCl and 1 mm Mg2+ in the bath and pipette solutions, two main open levels with conductance levels of ∼14 pS and ∼32 pS were recorded at a membrane potential of −60 mV. The K+ channels showed kinetic properties similar to TASK‐1 (∼14 pS), TASK‐3 (∼32 pS) and TASK‐1/3 heteromer (∼32 pS). The presence of three TASK isoforms was tested by reducing [Mg2+]o to ∼0 mm, which had no effect on the conductance of TASK‐1, but increased those of TASK‐1/3 and TASK‐3 to 42 pS and 74 pS, respectively. In CB cells, the reduction of [Mg2+]o to ∼0 mm also caused the appearance of ∼42 pS (TASK‐1/3‐like) and ∼74 pS (TASK‐3‐like) channels, in addition to the ∼14 pS (TASK‐1‐like) channel. The 42 pS channel was the most abundant, contributing ∼75% of the current produced by TASK‐like channels. Ruthenium red (5 μm) had no effect on TASK‐1 and TASK‐1/3, but inhibited TASK‐3 by 87%. In CB cells, ruthenium red caused ∼12% inhibition of TASK‐like activity. Methanandamide reduced the activity of all three TASKs by 80–90%, and that of TASK‐like channels in CB cell also by ∼80%. In CB cells, hypoxia caused inhibition of TASK‐like channels, including TASK‐1/3‐like channels. These results show that TASK‐1, TASK‐1/3 and TASK‐3 are all functionally expressed in isolated CB cells, and that the TASK‐1/3 heteromer provides the major part of the oxygen‐sensitive TASK‐like background K+ conductance.
Cation currents in human airway epithelial cells induced by infection with influenza A virus
Authors: Gallacher M. , Brown S. G. , Hale B. G. , Fearns R. , Olver R. E. , Randall R. E. , Wilson S. M.
Published: April 2009

Influenza A viruses cause lung disease via an incompletely understood mechanism that involves the accumulation of liquid within the lungs. The accumulation of lung liquid is normally prevented by epithelial Na+ absorption, a transport process regulated via several pathways including phosphoinositide‐3‐kinase (PI3K). Since the influenza A virus encodes a non‐structural protein (NS1) that can activate this kinase, we now explore the effects of NS1 upon the biophysical properties of human airway epithelial cells. Transient expression of NS1 depolarized electrically isolated cells maintained in glucocorticoid‐free medium by activating a cation conductance identical to the glucocorticoid‐induced conductance seen in single cells. This response involved PI3K‐independent and PI3K‐dependent mechanisms. Infecting glucocorticoid‐deprived cells with influenza A virus disrupted the normal electrical coupling between neighbouring cells, but also activated a conductance identical to that induced by NS1. This response to virus infection was only partially dependent upon NS1‐mediated activation of PI3K. The presence of NS1 allows influenza A to modify the biophysical properties of infected cells by activating a Na+‐permeable conductance. Whilst the activation of Na+‐permeable channels may be expected to increase the rate of Na+ absorption and thus reduce the volume of liquid in the lung, liquid does normally accumulate in influenza A‐infected lungs. The overall effect of influenza A on lung liquid volume may therefore reflect a balance between the activation and inhibition of Na+‐permeable channels.
Opioid receptor mechanisms at the hypoglossal motor pool and effects on tongue muscle activityin vivo
Authors: Hajiha Mohammad , DuBord Marq‐André , Liu Hattie , Horner Richard L.
Published: April 2009

Opioids can modulate breathing and predispose to respiratory depression by actions at various central nervous system sites, but the mechanisms operating at respiratory motor nuclei have not been studied. This study tests the hypotheses that (i) local delivery of the μ‐opioid receptor agonist fentanyl into the hypoglossal motor nucleus (HMN) will suppress genioglossus activityin vivo, (ii) a component of this suppression is mediated by opioid‐induced acetylcholine release acting at muscarinic receptors, and (iii) δ‐ and κ‐opioid receptors also modulate genioglossus activity. Seventy‐two isoflurane‐anaesthetised, tracheotomised, spontaneously breathing rats were studied during microdialysis perfusion into the HMN of (i) fentanyl and naloxone (μ‐opioid receptor antagonist), (ii) fentanyl with and without co‐application of muscarinic receptor antagonists, and (iii) δ‐ and κ‐opioid receptor agonists and antagonists. The results showed (i) that fentanyl at the HMN caused a suppression of genioglossus activity (P< 0.001) that reversed with naloxone (P< 0.001), (ii) that neither atropine nor scopolamine affected the fentanyl‐induced suppression of genioglossus activity, and (iii) that δ‐, but not κ‐, opioid receptor stimulation also suppressed genioglossus activity (P= 0.036 andP= 0.402 respectively). We conclude that μ‐opioid receptor stimulation suppresses motor output from a central respiratory motoneuronal pool that activates genioglossus muscle, and this suppression does not involve muscarinic receptor‐mediated inhibition. This μ‐opioid receptor‐induced suppression of tongue muscle activity by effects at the hypoglossal motor pool may underlie the clinical concern regarding adverse upper airway function with μ‐opioid analgesics. The inhibitory effects of μ‐ and δ‐opioid receptors at the HMN also indicate an influence of endogenous enkephalins and endorphins in respiratory motor control.
Junctin and the histidine‐rich Ca2+ binding protein: potential roles in heart failure and arrhythmogenesis
Authors: Pritchard Tracy J. , Kranias Evangelia G.
Published: April 2009

Contractile dysfunction and ventricular arrhythmias associated with heart failure have been attributed to aberrant sarcoplasmic reticulum (SR) Ca2+ cycling. The study of junctin (JCN) and histidine‐rich Ca2+ binding protein (HRC) becomes of particular importance since these proteins have been shown to be critical regulators of Ca2+ cycling. Specifically, JCN is a SR membrane protein, which is part of the SR Ca2+ release quaternary structure that also includes the ryanodine receptor, triadin and calsequestrin. Functionally, JCN serves as a bridge between calsequestrin and the Ca2+ release channel, ryanodine receptor. HRC is a SR luminal Ca2+ binding protein known to associate with both triadin and the sarcoplasmic reticulum Ca2+‐ATPase, and may thus mediate the crosstalk between SR Ca2+ uptake and release. Indeed, evidence from genetic models of JCN and HRC indicate that they are important in cardiophysiology as alterations in these proteins affect SR Ca2+ handling and cardiac function. In addition, downregulation of JCN and HRC may contribute to Ca2+ cycling perturbations manifest in the failing heart, where their protein levels are significantly reduced. This review examines the roles of JCN and HRC in SR Ca2+ cycling and their potential significance in heart failure.
Developmental regulation of the intracellular Ca2+ sensitivity of vesicle fusion and Ca2+–secretion coupling at the rat calyx of Held
Authors: Kochubey Olexiy , Han Yunyun , Schneggenburger Ralf
Published: April 2009

Developmental refinement of synaptic transmission can occur via changes in several pre‐ and postsynaptic factors, but it has been unknown whether the intrinsic Ca2+ sensitivity of vesicle fusion in the nerve terminal can be regulated during development. Using the calyx of Held, a giant synapse in the auditory pathway, we studied the presynaptic mechanisms underlying the developmental regulation of Ca2+–secretion coupling, comparing a time period before, and shortly after the onset of hearing in rats. We found an ∼2‐fold leftward shift in the relationship between EPSC amplitude and presynaptic Ca2+ current charge (QCa), indicating that brief presynaptic Ca2+ currents become significantly more efficient in driving release. Using a Ca2+ tail current protocol, we also found that the high cooperativity between EPSC amplitude and QCa was slightly reduced with development. In contrast, in presynaptic Ca2+ uncaging experiments, the intrinsic Ca2+ cooperativity of vesicle fusion was identical, and the intrinsic Ca2+ sensitivity was slightly reduced with development. This indicates that the significantly enhanced release efficiency of brief Ca2+ currents must be caused by a tighter co‐localization of Ca2+ channels and readily releasable vesicles, but not by changes in the intrinsic properties of Ca2+‐dependent release. Using the parameters of the intrinsic Ca2+ sensitivity measured at each developmental stage, we estimate that during a presynaptic action potential (AP), a given readily releasable vesicle experiences an about 1.3‐fold higher ‘local’ intracellular Ca2+ concentration ([Ca2+]i) signal with development. Thus, the data indicate a tightening in the Ca2+ channel–vesicle co‐localization during development, without a major change in the intrinsic Ca2+ sensitivity of vesicle fusion.
NMDA potentiation by visible light in the presence of a fluorescent neurosteroid analogue
Authors: Eisenman Lawrence N. , Shu Hong‐Jin , Wang Cunde , Aizenman Elias , Covey Douglas F. , Zorumski Charles F. , Mennerick Steven
Published: April 2009

N‐Methyl‐d‐aspartate (NMDA) receptors are widely studied because of their importance in synaptic plasticity and excitotoxic cell death. Here we report a novel method of potentiating NMDA receptors with fluorescence excited by blue (480 nm) light. In the presence of 300 nmof a (7‐nitro‐2,1,3‐benzoxadiazol‐4‐yl) amino (NBD)‐tagged neuroactive steroid carrier C2‐NBD‐(3α,5α)‐3‐hydroxypregnan‐20‐one (C2‐NBD 3α5αP), responses of cultured hippocampal neurons to 10 μmNMDA were potentiated to 219.2 ± 9.2% of the baseline response (100%) by a 30 s exposure to 480 nm light. The potentiation decayed back to baseline with a time constant of 80.6 s. Responses to 1 μmand 100 μmNMDA were potentiated to 147.9 ± 9.6% and 174.1 ± 15.6% of baseline, respectively, suggesting that visible‐light potentiation is relatively insensitive to NMDA concentration. Peak autaptic NMDA responses were potentiated to 178.9 ± 22.4% of baseline. Similar potentiation was seen with 10 μmNBD‐lysine, suggesting that visible‐light potentiation is not a steroid effect. Potentiation was also seen with a steroid analogue in which the NBD was replaced with fluorescein, suggesting that NBD is not the only fluorophore capable of supporting visible‐light potentiation. UV light and redox potentiation of NMDA receptors largely occluded subsequent blue light potentiation (127.7 ± 7.4% and 120.2 ± 6.2% of baseline, respectively). The NR1a(C744A,C798A) mutant that is insensitive to redox and UV potentiation was also largely unaffected by visible‐light potentiation (135.0 ± 10.0% of baseline). Finally, we found that the singlet oxygen scavenger furfuryl alcohol decreased visible‐light potentiation. Collectively, these data suggest that visible‐light potentiation of NMDA receptors by fluorescence excitation shares mechanisms with UV and redox potentiation and may involve singlet oxygen production.
Controlling the Secondary Flow in a Turbine Cascade by Three-Dimensional Airfoil Design and Endwall Contouring
Authors: Duden A. , Raab I. , Fottner L.
Published: April 2009

A highly loaded turbine cascade has been redesigned with the objective to reduce the secondary flow by applying endwall contouring and three-dimensional airfoil design in the endwall regions. The overall loading and the axial area ratio of the cascade have been kept constant. With the tools of a three-dimensional design environment, a systematic study has been carried out regarding several features of the endwall pressure distribution and their influence on the secondary flow. Two optimized configurations have been investigated in a high-speed cascade wind tunnel. The flow field traverses showed improvements concerning the radial extent of the secondary flow and a decrease in secondary loss of 26 percent. Unfortunately this reduction was counterbalanced by increased profile losses and higher inlet losses due to increased blockage. The striking feature of the cascade with endwall contouring and three-dimensional airfoil design was a significant reduction of the exit flow angle deviations connected with the secondary flow. The predictions obtained by the three-dimensional Navier–Stokes solver TRACE_S showed a remarkable agreement with the experimental results.
The Influence of Endwall Contouring on the Performance of a Turbine Nozzle Guide Vane
Authors: Dossena V. , Perdichizzi A. , Savini M.
Published: April 2009

The paper presents the results of a detailed investigation of the flow field in a gas turbine linear cascade. A comparison between a contoured and a planar configuration of the same cascade has been performed, and differences in the three-dimensional flow field are here analyzed and discussed. The flow evolution downstream of the trailing edge was surveyed by means of probe traversing while a three-dimensional Navier–Stokes solver was employed to obtain information on flow structures inside the vaned passages. The experimental measurements and the numerical simulation of the three-dimensional flow field have been performed for two cascades; one with planar endwalls, and the other with one planar and one profiled endwall, so as to present a reduction of the nozzle height. The investigation was carried out at an isentropic downstream Mach number of 0.6. Airfoils of both cascades were scaled from the same high-pressure gas turbine inlet guide vane. Measurements of the three-dimensional flow field have been performed on five planes downstream of the cascades by means of a miniaturized five-hole pressure probe. The presence of endwall contouring strongly influences the secondary effects; the vortex generation and their development are inhibited by the stronger acceleration taking place throughout the cascade. The results show that the secondary effects on the contoured side of the passage are confined in the endwall region, while on the flat side the secondary vortices display characteristics similar to the ones occurring downstream of the planar cascade. The spanwise outlet angle distribution presents a linear variation for most of the nozzle height, with quite low values approaching the contoured endwall. The analysis of mass-averaged losses shows a significant performance improvement in the contoured cascade. This can be ascribed not only to lower secondary losses but also to a reduction of the profile losses.
Influence of the Hole Length-to-Diameter Ratio on Film Cooling With Cylindrical Holes
Authors: Lutum E. , Johnson B. V.
Published: April 2009

Film cooling experiments were conducted to investigate the effects of coolant hole length-to-diameter ratio on the film cooling effectiveness. The results from these experiments offer an explanation for the differences between the film cooling results for cylindrical hole injection configurations previously reported by Goldstein et al. (1974), Pedersen et al. (1977), and Sinha et al. (1991). The previously reported injection configurations differed primarily in coolant hole length-to-diameter ratio. The present experiments were conducted with a row of cylindrical holes oriented at 35 deg to a constant-velocity external flow, systematically varying the hole length-to-diameter ratios (L/D = 1.75, 3.5, 5, 7, and 18), and blowing rates (0.52 ≤ M ≤ 1.56). Results from these experiments show in a region 5 ≤ X/D ≤ 50 downstream of coolant injection that the coolant flow guiding capability in the cylindrical hole was apparently established after five hole diameters and no significant changes in the film cooling effectiveness distribution could be observed for the greater L/D. However, the film cooling effectiveness characteristics generally decreased with decreasing hole L/D ratio in the range of 1.75 ≤ L/D ≤ 5.0. This decrease in film cooling performance was attributed to (1) the undeveloped character of the flow in the coolant channels and (2) the greater effective injection angle of the coolant flow with respect to the external flow direction and surface. The lowest values of film cooling effectiveness were measured for the smallest hole length-to-diameter ratio, L/D = 1.75.
Effect of High Free-Stream Turbulence With Large Length Scale on Blade Heat/Mass Transfer
Authors: Wang H. P. , Goldstein R. J. , Olson S. J.
Published: April 2009

The naphthalene sublimation technique is used to investigate the influence of high free-stream turbulence with large length scale on the heat/mass transfer from a turbine blade in a highly accelerated linear cascade. The experiments are conducted at four exit Reynolds numbers, ranging from 2.4 × 105 to 7.8 × 105, with free-stream turbulence of 3, 8.5, and 8 percent and corresponding integral length scales of 0.9 cm, 2.6 cm, and 8 cm, respectively. On the suction surface, the heat/mass transfer rate is significantly enhanced by high free-stream turbulence due to an early boundary layer transition. By contrast, the transition occurs very late, and may not occur at very low Reynolds numbers with low free-stream turbulence. In the turbulent boundary layer, lower heat/mass transfer rates are found for the highest free-stream turbulence level with large length scale than for the moderate turbulence levels with relatively small scales. Similar phenomena also occur at the leading edge. However, the effect of turbulence is not as pronounced in the laminar boundary layer.
Film Cooling Effectiveness and Mass/Heat Transfer Coefficient Downstream of One Row of Discrete Holes
Authors: Goldstein R. J. , Jin P. , Olson R. L.
Published: April 2009

A special naphthalene sublimation technique is used to study the film cooling performance downstream of one row of holes of 35 deg inclination angle with 3d hole spacing and relatively small hole length to diameter ratio (L/d = 6.3). Both film cooling effectiveness and mass/heat transfer coefficient are determined for blowing rates from 0.5 to 2.0 with density ratio of 1.0. The mass transfer coefficient is measured using pure air film injection, while the film cooling effectiveness is derived from comparison of mass transfer coefficients obtained following injection of naphthalene-vapor-saturated air with those from pure air injection. This technique enables one to obtain detailed local information on film cooling performance. The laterally averaged and local film cooling effectiveness agree with previous experiments. The difference between mass/heat transfer coefficients and previous heat transfer results indicates that conduction error may play an important role in the earlier heat transfer measurements.
Measurements of Discharge Coefficients in Film Cooling
Authors: Burd S. W. , Simon T. W.
Published: April 2009

Measurements of discharge coefficients for several film cooling configurations having hole length-to-diameter ratios of 2.3, 4.6, 6.6, and 7.0 are presented. Recently, it was documented that the velocity distributions over the hole exit plane vary significantly with changes in hole length-to-diameter ratio. This paper documents the effects of such variations on coolant discharge coefficients. Due to the short holes, injection in engines is with a substantial amount of coolant departing the upstream portions of the hole exit plane. This results in a higher rate of momentum exchange with the free stream at that location than for longer holes, which permits more uniform exit flows. Discharge coefficient measurements are discussed in terms of this distribution of velocity. This paper also documents the effects of the hole supply plenum geometry on discharge coefficients. When the coolant flow is delivered to the holes with significant momentum either in the direction of the free stream or opposite to that direction, significant changes in discharge coefficient values are observed.
Heat Transfer Contributions of Pins and Endwall in Pin-Fin Arrays: Effects of Thermal Boundary Condition Modeling
Authors: Chyu M. K. , Hsing Y. C. , Shih T. I.-P. , Natarajan V.
Published: April 2009

Short pin-fin arrays are often used for cooling turbine airfoils, particularly near the trailing edge. An accurate heat transfer estimation from a pin-fin array should account for the total heat transfer over the entire wetted surface, which includes the pin surfaces and uncovered endwalls. One design question frequently raised is the actual magnitudes of heat transfer coefficients on both pins and endwalls. Results from earlier studies have led to different and often contradicting conclusions. This variation, in part, is caused by imperfect or unrealistic thermal boundary conditions prescribed in the individual test models. Either pins or endwalls, but generally not both, were heated in those previous studies. Using a mass transfer analogy based on the naphthalene sublimation technique, the present experiment is capable of revealing the individual heat transfer contributions from pins and endwalls with the entire wetted surface thermally active. The particular pin-fin geometry investigated, S/D = X/D = 2.5 and H/D = 1.0, is considered to be one of the optimal array arrangement for turbine airfoil cooling. Both inline and staggered arrays with the identical geometric parameters are studied for 5000 ≤ Re ≤ 25,000. The present results reveal that the general trends of the row-resolved heat transfer coefficients on either pins or endwalls are somewhat insensitive to the nature of thermal boundary conditions prescribed on the test surface. However, the actual magnitudes of heat transfer coefficients can be substantially different, due to variations in the flow bulk temperature. The present study also concludes that the pins have consistently 10 to 20 percent higher heat transfer coefficient than the endwalls. However, such a difference in heat transfer coefficient imposes very insignificant influence on the overall array-averaged heat transfer, since the wetted area of the uncovered endwalls is nearly four times greater than that of the pins.
Heat Transfer and Pressure Drop in Pin-Fin Trapezoidal Ducts
Authors: Hwang J.-J. , Lai D.-Y. , Tsia Y.-P.
Published: April 2009

Experiments are conducted to determine the log-mean averaged Nusselt number and overall pressure-drop coefficient in a pin-fin trapezoidal duct that models the cooling passages in modern gas turbine blades. The effects of pin arrangement (in-line and staggered), flow Reynolds number (6,000 ≦ Re ≦ 40,000) and ratio of lateral-to-total flow rate (0 ≦ ε ≦ 1.0) are examined. The results of smooth trapezoidal ducts without pin arrays are also obtained for comparison. It is found that, for the single-outlet-flow duct, the log-mean averaged Nusselt number in the pin-fin trapezoidal duct with lateral outlet is insensitive to the pin arrangement, which is higher than that in straight-outlet-flow duct with the corresponding pin array. As for the trapezoidal ducts having both outlets, the log-mean averaged Nusselt number has a local minimum value at about ε = 0.3. After about ε ≧ 0.8, the log-mean averaged Nusselt number is nearly independent of the pin configuration. Moreover, the staggered pin array pays more pressure-drop penalty as compared with the in-line pin array in the straight-outlet-flow duct; however, in the lateral-outlet-flow duct, the in-line and staggered pin arrays yield almost the same overall pressure drop.
Heat Transfer in a Rotating Cavity With a Stationary Stepped Casing
Authors: Mirzaee I. , Quinn P. , Wilson M. , Owen J. M.
Published: April 2009

In the system considered here, corotating “turbine” disks are cooled by air supplied at the periphery of the system. The system comprises two corotating disks, connected by a rotating cylindrical hub and shrouded by a stepped, stationary cylindrical outer casing. Cooling air enters the system through holes in the periphery of one disk, and leaves through the clearances between the outer casing and the disks. The paper describes a combined computational and experimental study of the heat transfer in the above-described system. In the experiments, one rotating disk is heated, the hub and outer casing are insulated, and the other disk is quasi-adiabatic. Thermocouples and fluxmeters attached to the heated disc enable the Nusselt numbers, Nu, to be determined for a wide range of rotational speeds and coolant flow rates. Computations are carried out using an axisymmetric elliptic solver incorporating the Launder–Sharma low-Reynolds-number k–ε turbulence model. The flow structure is shown to be complex and depends strongly on the so-called turbulent flow parameter, λT, which incorporates both rotational speed and flow rate. For a given value λT, the computations show that Nu increases as Reφ, the rotational Reynolds number, increases. Despite the complexity of the flow, the agreement between the computed and measured Nusselt numbers is reasonably good.
Multistage Centrifugal Compressor Surge Analysis: Part II—Numerical Simulation and Dynamic Control Parameters Evaluation
Authors: Arnulfi G. L. , Giannattasio P. , Giusto C. , Massardo A. F. , Micheli D. , Pinamonti P.
Published: April 2009

This paper describes, from a theoretical point of view, the behavior of compression systems during surge and the effect of passive and active control devices on the instability limit of the system. A lumped parameter model is used to simulate the compression system described in Part I of this work (Arnulfi et al., 1999), based on an industrial multistage centrifugal compressor. A comparison with experimental results shows that the model is accurate enough to describe quantitatively all the features of the phenomenon. A movable wall control system is studied in order to suppress surge in the compressor. Passive and active control schemes are analyzed; they both address directly the dynamic behavior of the compression system to displace the surge line to lower flow rates. The influence of system, geometry and compressor speed is investigated: the optimum values of the control parameters and the corresponding increase in the extent of the stable operating range are presented in the paper.
Practical Use of Three-Dimensional Inverse Method for Compressor Blade Design
Authors: Damle S. , Dang T. , Stringham J. , Razinsky E.
Published: April 2009

The practical utility of a three-dimensional inverse viscous method is demonstrated by carrying out a design modification of a first-stage rotor in an industrial compressor. In this design modification study, the goal is to improve the efficiency of the original blade while retaining its overall aerodynamic, structural, and manufacturing characteristics. By employing a simple modification to the blade pressure loading distribution (which is the prescribed flow quantity in this inverse method), the modified blade geometry is predicted to perform better than the original design over a wide range of operating points, including an improvement in choke margin.
Effects of Periodic Wake Passing Upon Flat-Plate Boundary Layers Experiencing Favorable and Adverse Pressure Gradients
Authors: Funazaki K. , Koyabu E.
Published: April 2009

This paper deals with the investigation of wake-disturbed boundary layer on a flat-plate model with an elliptic leading edge. The wakes are generated by the transversely moving bars in front of the test model. The main focus of this paper is how the wake passage affects the transitional behavior of the boundary layer under the influence of favorable and adverse pressure gradients over the test surface. Detailed measurements of the boundary layer are conducted by the use of hot-wire anemometry. An ensemble-averaging technique is also employed in order to extract the periodic events associated with the wake passage from the acquired data. The previously observed dependence of wake-induced transition on the movement of the wake generating bar is confirmed. It is also found that the wake passage induces a significant change in the flow structure downstream of the flow acceleration region.
Investigation of Periodic Boundary Conditions in Multipassage Cascade Flows Using Overset Grids
Authors: Tuncer I. H. , Weber S. , Sanz W.
Published: April 2009

A Navier–Stokes solution method with overset grids is applied to unsteady multipassage cascade flows, and the unsteady blade loadings are compared against the single-passage solutions with the direct store interblade boundary condition. In the overset grid solutions, the multipassage domain is discretized with O-type grids around each blade and a rectangular background grid. Blade grids are allowed to move in time relative to the background grid, as prescribed by the oscillatory plunging motion. The overset grid method uses a simple, robust numerical algorithm to localize moving intergrid boundary points and to interpolate solution variables across grids. Computational results are presented for two and four-passage, subsonic and transonic flows through a turbine and a compressor cascade. The overset grid solutions over the multipassage periodic domains agree well with the single-passage solutions and the experimental data. It is concluded that the time linearization error introduced by the direct store approach is negligible in the range of flow conditions studied.
Vortex Simulation of Rotor/Stator Interaction in Turbomachinery
Authors: Chen M. Z. , Wu X. H.
Published: April 2009

A new numerical method is presented in this paper to simulate rotor/stator interaction in turbomachinery by means of a vortex method based on a Lagrangian frame. The algorithm takes the result from steady solution as input, which gives an initial description of the unsteady disturbance flow field. To calculate the unsteady response to these disturbances, the Lagrangian vortex method is used to capture the convective process, and the deterministic vortex scheme to approximate the viscous diffusion process. The application of Baldwin–Lomax turbulence model in wakes is developed, to overcome difficulties such as the much higher calculated viscosity in the outer region than that in the boundary regions, and the difficulty in continuously tracing moving wake centerlines encountered when other numerical methods are used. Generally the agreement between the computational and experimental results is good. The sweeping characteristic of wakes, the influence of unsteadiness on incidence, and the decaying features of unsteady velocities and pressure are studied in the paper.
Thermodynamics of Phase Transitions in Porous Media
Authors: de Boer Reint
Published: April 2009

Under certain circumstances, phase transitions can occur in porous media consisting of a porous solid saturated with liquids and gases, for example, due to a freezing process, the liquid or parts of the liquid can turn into ice, which is then connected with the porous solid, or due to a drying process, the liquid or parts of the liquid are converted to vapor, which is then a component of the gas phase. Although some special proboems of phase transitions in porous media have already been treated, a general theory on the basis of thermodynamics is still to be explored. The present paper is concerned with the development of thermodynamic restrictions for the constitutive relations of an elastic, compressible porous solid, filled with two compressible fluids, whereby it is assumed that the three phases have different temperatures. The investigations reveal that the mass changes are essentially, among others, connected to the differences of the chemical potentials and the energy transitions to the differences of the reciprocal of the temperatures, which is well-known in classical thermodynamics of gases.
Mechanical Behavior of a Non-Saturated Soil Swelling Nonhydrostatically
Authors: Karalis Theodoros K.
Published: April 2009

The effects of the external constraints on the rigidity of a non-saturated soil swelling nonhydrostatically by imbibing water are examined in some detail. The expression for the deficit of the swelling potential energy and the conjugated energy for swelling is worked out. By applying Maxwell’s relationships to these expressions, the relations between the partial derivatives of the involved intensives and extensive variables are obtained. However, the experiment does not give directly the change in the extensive variables required to calculate the change in the intensive ones. By relating intensive and extensive variables, these expressions are best approached. Some examples are given illustrating what engineers should be interested in studying swelling in the laboratory.
Ettringite-Induced Swelling in Soils: State-of-the-Art
Authors: Dermatas Dimitris
Published: April 2009

Reactions between lime, alumina released from clay during pozzolanic reactions, and sulfates present in some soils, have been responsible for the deterioration and ultimate failure, by expansion, of several lime stabilization projects, by causing the formation of the highly expansive crystalline mineral ettringite. Based on an extensive literature review, the mechanisms for these reactions were hypothesized, and a laboratory research program using both artificial and natural lime-treated soil specimens was designed and undertaken. The strength, swelling, pH, compositional, and micromorphological characteristics of the treated specimens were determined following different curing times and soaking conditions. Swell development in some of the specimens prepared, in relation with pertinent strength, pH, composition, and micromorphological data obtained, allowed the delineation of the underlying mechanisms leading to heave and deterioration. It was found that the amount of heave following ettringite hydration and growth is a function of the amount and rate of release of alumina into solution. The amount and type of sulfates present, and the amount and type of lime used are also important factors in the development of heave. Moreover, temperature and relative humidity fluctuations were also found to play an important role in the overall ettringite-related heave mechanism, as they affect reaction rates, solubilities of species, and the overall stability fields of a soil system’s components. Finally, the present study was successful in developing a soil pretreatment method that would ensure safe performance of lime-stabilization applications in sulfate-bearing soils. Pretreatment of the artificial lime-treated soil mixes with barium compounds was effective in eliminating ettringite formation. Further research is needed to assess the effectiveness and the required levels of barium pretreatment in field applications. This pretreatment method, upon appropriate modifications, could be potentially applied in other sulfate-related deterioration problems.
Mechanical Basis of Cell Morphogenesis and Volume Control
Authors: Bereiter-Hahn J. , Yastas S. , Litniewski J.
Published: April 2009

Osmotic differences between the cytoplasm and the surrounding fluid belong to the most important factors in shaping an animal tissue cell. This implies an elastic and contractile fibrillar system attached to the cell membrane which counteracts ionic imbalances and determines cell morphology. Therefore cell volume and cell shape are functionally coupled. Many cell types, epithelial cells in particular, are able to control their volume: ie, swelling (or shrinking) induced by varying the osmolarity of the surrounding fluid is compensated and the previous volume is achieved during a time interval of 10-40 min. This compensation reaction includes the opening of ion channels, activation of the Na/K/2C1 co-transport mechanism, and activities of the cytoskeleton. The changes in ion fluxes have been investigated for various cell types. The main question which is still under debate refers to the signal involved in telling a cell to have reached its appropriate volume. One of the most probable factors is the tension in the cell membrane. By action of tension-sensitive ion channels (K+, Ca++-channels) ion fluxes could be modified. Mechanical forces acting on the cell membrane always affect the cortical cytoplasm - membrane complex: In many cell types a fibrillar meshwork is closely connected to the membrane, thus determining its mechanical properties. Destruction of this complex by drugs like cytochalasins alters the mechanics of the cortex and destroys the ability of the cells for volume regulation. If mechanical forces in the cortex are involved in volume control, the loss of this ability would be a reasonable consequence of cytochalasin treatment. Measurement of the forces at the surface of cells during swelling and during the compensation phase is a direct approach to the problem of volume regulation. Scanning acoustic microscopy (SAM) is an elegant method to determine elastic properties on a subcellular level. Measuring the reflection of sound at the surface of a cell gives a good indication of local elasticity (and thus “tension at the surface”). Using the cell line HaCat which was derived from human epidermis, elasticity changes have been followed by SAM during hypotonicity-induced swelling and the subsequent compensatory volume decrease. On the basis of the present results the regulatory volume decrease (RVD) may be achieved by an increase of forces in the cortex by actomyosin-based contractions in addition to altered ion fluxes. Volume increase first results in a destruction of the actin fibrillar system which is immediately restored by stimulated actin polymerisation which strengthens the complex of the plasma membran with the cortical fibrillar layer. The results support the view that tension in the cortex may participate in RVD and be a signal for volume regulation.
Relationship of Salt Disparity and Its Consequence for Swelling in Biological Gels
Authors: Hodson Stuart , Earlam Richard
Published: April 2009

New irreversible thermodynamic relationships are derived which explain why biological tissues tend to swell. In the course of their derivation, fresh concepts arize. In particular, the relationship of salt disparity is described which forbids diffusible salt generated chemical and osmotic potentials to be simultaneously at equilibrium in the presence of ionized macromolecules. This relationship is developed to generate a new intrinsic thermodynamic property which is termed gel pressure and which drives fluid flows.
Extrudate Swelling: Physics, Models, and Computations
Authors: Papanastasiou Tasos C. , Kiriakidis Dionissios G. , Nikoleris Theodore G.
Published: April 2009

Viscous, viscoelastic, or elastic normal stresses are superimposed to pressure within flowing fluids. These stresses act normal to the boundaries of the flow that may deform depending on their modulus or viscosity. At absolutely rigid boundaries of infinite modulus of elasticity any boundary deformation and therefore any fluid expansion or swelling is surpressed (eg, flow in rigid pipes, annuli, channels). Elastic boundaries (eg, flow in veins and arteries, flow by membranes, around inflating/deflating balloons) deform under the action of normal stresses, allowing expansion or swelling of fluid. The same mechanism prevails in lubrication, where pressure and superimposed normal viscoelastic stresses keep surfaces in relative motion apart, with simultaneous increase in load capacity. Viscous boundaries (eg, liquid jet in air or in immiscible liquid, slow extrusion of viscoelastic liquids from dies, expanding/collapsing air-bubbles or liquid-droplets) are displaced by flowing adjacent immiscible fluids, allowing swelling or imposing contraction depending on relative rheological characteristics. Thus, the kind of swelling examined here is independent of density, ie, incompressible, and is due to the action of normal stresses against the boundary that is imposed either by adjacent deformable obstacles or else by surface tension. The resulting swelling is dynamic (ie, it initiates, changes and ceases with the flow) and can be made permanent by solidification, crystallization or glassification. The most profound form of incompressible swelling is the extrude swelling that controls the ultimate shape of extruded parts. Incompressible swelling is enhanced by the ability of macromolecules to deform and recover (eg, viscoelastic) and by the design of flow conduits to impose sharp transitions of deformation modes (eg, singular exit flows). The same swelling is reduced by the ability of molecules (or fibers in fiber-suspensions) to align with the flow streamines, as well as any tendency of solid-like structure formulation (eg, viscoplastic).
Injection of Fluid Into a Layer of Deformable Porous Medium
Authors: Barry Steven , Aldis Geoffrey , Mercer Geoffry
Published: April 2009

The flow of fluid from a point source into a layer of deformable porous material is considered. The main applications of this work are to subcutaneous injections and subterranean soil flows. The porous material is assumed to be an isotropic, homogeneous, linearly elastic solid. The governing equations are derived for an axisymmetric geometry using linear poro-elasticity and are applied to the situation of a point source at some height z = z0 with a line sink at a distance r = ρ. These are solved analytically using Hankel transform techniques with the Hankel inversion integrals calculated numerically. Results are given for the pressure contours and the displacement of the solid matrix for a variety of source heights and elastic parameters. These indicate the swelling of the medium and subsequent deformation of the free surface. Results indicate regions where one dimensional models may be applicable.
Structural Dynamical Modeling of Step Ladders
Authors: Eisenberg Martin A.
Published: April 2009

Dynamic loads on step ladders are the result of interaction between climber and ladder. The complex dynamical behavior of the climber must be experimentally determined. An analysis of the dynamical response is presented to allow the extrapolation of experimental results to ladders of grossly different structural dynamical parameters from those on which the data are obtained. It is demonstrated that the climber characteristics dominate the dynamical response. Reliable quantitative measures of data applicability are obtained, not withstanding significant uncertainties regarding the details of the mechanics of motion.
Asymptotic Treatment of Non-Classically Damped Linear Systems
Authors: Fang W. , Tseng J.-G. , Wickert J. A.
Published: April 2009

The presence of non-classical dissipation in a general discrete dynamic system is investigated through a perturbation method for the eigenvalues and vectors. Results accurate to second-order are obtained, with corrections to the base solution being expressed in terms of readily-calculated quadratic forms. Exact solutions, and the derived asymptotic ones, are compared with the predictions of the so-called method of approximate decoupling, in which certain non-classical dissipative terms are omitted from calculations in the eigenvalue problem. The perturbation method is discussed through its application in several examples, indicating circumstances in which a non-classically damped system can be well-approximated by an “equivalent” classically damped one. Somewhat surprisingly, the addition of non-classical damping does not necessarily increase the stability of all vibration modes, and the perturbation method is shown to be useful in identifying those critical modes.
Instability Mechanisms of a Spinning Disk Under Rotating Damping Forces
Authors: Huang F. Y. , Mote C. D.
Published: April 2009

Stability of a rotating disk under rotating positive-definite damping forces is investigated analytically. The stability boundary is located exactly in parameter space by the criterion that at least one non-trivial periodic solution is necessary at every boundary point. The stable region of parameter space is identified through perturbation of a Galerkin solution. A non-trivial periodic solution is shown to exist only when damping forces are not generated with respect to that solution. Instability in the disk-damping system occurs when the wave speed of any mode in the undamped disk, when observed on the disk, is less that the speed of the damping force relative the disk. The instability occurs independent of the magnitude of the force and the definition of the positive-definite damping operator.
Influence of Loading on Mode Localization in Periodic Structures
Authors: Brasil Reyolando M. L. R. F. , Mazzilli Carlos E. N.
Published: April 2009

This paper addresses the problem of the presence of a slightly disordered loading in otherwise ordered periodic structures as an element to trigger the phenomenon of vibration mode localization due to its effect in their stiffness. The sample structures are basically cantilever columns supporting the loads due to large lumped masses in their top which may vary according to a disorder related small parameter. They are connected by very flexible springs. A first series of results deals with a two-degree-of-freedom model where localization is achieved due to loading disorder. The frequencies and displacements show very sharp and nonlinear variation when the small parameter changes slightly around its zero value. The results for this simple model compare well with those of a finite element program developed by the authors. For a more complex example, another model of a rank of six columns is analyzed by the same computer code. A pseudo-random variation of the masses is considered and the resulting vibration modes are compared to those of the ordered structure, which are global in nature and present a sinusoidal spatial distribution. Again, due to mode localization, motions in the perturbed structure are found to be restricted largely to one of the masses.