bluuebunny/crossref_metadata_2025 huggingface dataset:
Resolving the Unconventional Mechanisms Underlying RXFP1 and RXFP2 Receptor Function
Authors: Hartley Brigham J. , Scott Daniel J. , Callander Gabrielle E. , Wilkinson Tracey N. , Ganella Despina E. , Kong Chze K. , Layfield Sharon , Ferraro Tania , Petrie Emma J. , Bathgate Ross A. D.
Published: April 2009

The receptors for relaxin and insulin‐like peptide 3 (INSL3) are now well‐characterized as the relaxin family peptide (RXFP) receptors RXFP1 and RXFP2, respectively. They are G‐protein‐coupled receptors (GPCRs) with closest similarity to the glycoprotein hormone receptors, with both containing large ectodomains with 10 leucine‐rich repeats (LRRs). Additionally, RXFP1 and RXFP2 are unique in the LGR family in that they contain a low‐density lipoprotein class A (LDL‐A) module at their N‐terminus. Ligand‐mediated activation of RXFP1 and RXFP2 is a complex process involving various domains of the receptors. Primary ligand binding occurs via interactions between B‐chain residues of the peptides with specific residues in the LRRs of the ectodomain. There is a secondary binding site in the transmembrane exoloops which may interact with the A chain of the peptides. Receptor signaling through cAMP then requires the unique LDL‐A module, as receptors without this domain bind ligand normally but do not signal. This is an unconventional mode of activation for a GPCR, and the precise mode of action of the LDL‐A module is currently unknown. The specific understanding of the mechanisms underlying ligand‐mediated activation of RXFP1 and RXFP2 is crucial in terms of targeting these receptors for future drug development.
Behavioral Phenotyping of Mixed Background (129S5:B6) Relaxin‐3 Knockout Mice
Authors: Smith Craig M. , Lawrence Andrew J. , Sutton Steve W. , Gundlach Andrew L.
Published: April 2009

Experimental studies in rats have revealed that the neuropeptide relaxin‐3 modulates feeding and metabolism, stress responses, arousal, and exploratory behavior. In the present study, two cohorts of mixed background (129S5:B6) relaxin‐3 knockout (KO) and wild‐type littermate mice were subjected to a series of behavioral tests. Relaxin‐3 KO mice appeared healthy and displayed no genotype differences in body weight, motor coordination (as determined via the rotarod), anxiety (light/dark box, elevated plus maze, large open field), spatial memory (Y‐maze), or sensorimotor gating (prepulse inhibition). Female KO mice did, however, display hypoactivity, reflected by significantly shorter distances traveled in the automated locomotor cell, large open field, and novel object tests, and had fewer encounters with a novel mouse in a social interaction test. Male KOs, on the other hand, displayed a “hypersensitivity” to stress, spending longer in the Porsolt posture during a repeated forced swim test and losing a significantly greater percentage of their body weight in response to an 8‐week chronic stress regimen. These findings support the hypothesis that relaxin‐3 signaling contributes to the central control of arousal, exploratory behavior and stress responses.
Distribution of Relaxin‐3 mRNA and Immunoreactivity and RXFP3‐Binding Sites in the Brain of the Macaque, Macaca fascicularis
Authors: Ma Sherie , Shen Pei‐Juan , Sang Qian , Lanciego Jose L. , Gundlach Andrew L.
Published: April 2009

This study examined the presence and distribution of relaxin‐3 (RLN3) and its receptor, RXFP3, throughout the brain of Macaca fascicularis. In perfusion‐fixed sections, RLN3 immunoreactivity (IR) was observed throughout the fore‐, mid‐, and hindbrain and was enriched in the septum, hippocampus, and interpeduncular and supramammillary nuclei. Neurons in the pontine central gray area contained RLN3‐IR and RLN3 mRNA. The distribution of RXFP3 protein, mapped by autoradiography of [125I]R3/I5‐binding sites, correlated with the distribution of RLN3‐IR. The broad distributions of RLN3‐positive neuronal axons and terminals and of RXFP3 in the brain of Macaca fascicularis are consistent with findings in the rat and with an important role for RLN3 signaling in nonhuman primate and human brain.
Structure and Activity in the Relaxin Family of Peptides
Authors: Tregear Geoffrey W. , Bathgate Ross A. D. , Hossain Mohammed Akhter , Lin Feng , Zhang Suode , Shabanpoor Fazel , Scott Daniel J. , Ma Sherie , Gundlach Andrew L. , Samuel Chrishan S. , Wade John D.
Published: April 2009

The availability of improved peptide synthesis procedures, convenient and sensitive assays for receptor binding and activation, together with advances in methods for structural characterization, has enabled the key structural features of the relaxin family of peptides responsible for biological activity to be defined. Not surprisingly, despite the similarities in primary amino acid sequences, different structural domains and residues are involved in the binding and activation at the four known relaxin family peptide receptors (RXFP1 to ‐4). Most of our knowledge on structure and function relates to the relaxin–RXFP1, insulin‐like peptide 3 (INSL3)–RXFP2, and relaxin‐3–RXFP3 systems, with information accumulating not only on the critical ligand structures but also the domains and residues on the receptor itself that are required for specificity and activation. These studies provide the framework for the design of small‐molecule mimetics. While the B‐chain cassette R‐X‐X‐X‐R‐X‐X‐I, defined by Büllesbach and Schwabe, is essential for binding and activation of RXFP1, it is now recognized that the A chain, particularly the N‐terminal domain, is also critical for receptor specificity. Studies of the various endogenous ligand–receptor pairs have led to the design of potent and specific agonists and antagonists. The relaxin‐3 A chain–INSL5 B chain chimeric peptide and analogs with C‐terminal truncations of the B chain, developed by Liu and colleagues at Johnson & Johnson, have provided selective agonist and antagonist peptides that are proving invaluable for in vivo studies of the relaxin‐3–RXFP3 system.
Relaxin Family Peptides and Receptors in Mammalian Brain
Authors: Gundlach Andrew L. , Ma Sherie , Sang Qian , Shen Pei‐Juan , Piccenna Loretta , Sedaghat Katayoun , Smith Craig M. , Bathgate Ross A. D. , Lawrence Andrew J. , Tregear Geoffrey W. , Wade John D. , Finkelstein David I. , Bonaventure Pascal , Liu Changlu , Lovenberg Timothy W. , Sutton Steve W.
Published: April 2009

As a foundation for regulatory and functional studies of central relaxin family peptide receptor systems, we are mapping the distribution of the different receptors in the brain of rat, mouse, and nonhuman primates, attempting to identify the nature of the receptor‐positive neurons in key circuits and establish the complementary distribution of the respective ligands in these species. Here we review progress in mapping RXFP1, RXFP2, and RXFP3 (mRNAs and proteins) and their respective ligands and discuss some of the putative functions for these peptides and receptors that are being explored using receptor‐selective agonist and antagonist peptides and receptor and peptide gene deletion mouse strains. Comparative studies reveal an association of RXFP1 and RXFP2 with excitatory neurons but a differential regional or cellular distribution, in contrast to the association of RXFP3 with inhibitory neurons. These studies also reveal differences in the distribution of RXFP1 and RXFP2 in rat and mouse brain, whereas the distribution of RXFP3 is more conserved across these species. Enrichment of RXFP1/2/3 in olfactory, cortical, thalamic, limbic, hypothalamic, midbrain, and pontine circuits suggests a diverse range of modulatory actions for these receptors. For example, experimental evidence in the rat reveals that RXFP1 activation in the amygdala inhibits memory consolidation, RXFP2 activation in striatum produces sniffing behavior, and RXFP3 modulation has effects on feeding and metabolism, the activity of the septohippocampal pathway, and spatial memory. Further studies are now required to reveal additional details of these and other functions linked to relaxin family peptide receptor signaling in mammalian brain and the precise mechanisms involved.
Relaxin Receptor LGR7 (RXFP1) Is Regulated by Estrogen
Authors: Maseelall Priya , Gardner Jeff , Wojtczuk Andrea , Weiss Gerson , Goldsmith Laura T.
Published: April 2009

Estrogen regulates LGR7 (RXFP1) mRNA expression in an in vitro model of human term pregnancy cervix that utilizes lower uterine segment fibroblasts. LGR7 mRNA levels were increased by estradiol to mean levels of 152%± 5.9% above those in untreated control cells. Therefore, estradiol may amplify relaxin's actions in the cervix.
A Tool for Automated Load Duration Curve Creation1
Authors: Johnson Stephanie L. , Whiteaker Timothy , Maidment David R.
Published: April 2009

Abstract:  A recent study by the Texas Bacteria Total Maximum Daily Load (TMDL) Task Force has recommended the use of load duration curves as a primary tool in calculating bacterial TMDLs. This method is attractive because it effectively integrates flow regimes into TMDL analyses, clearly communicates data through a method that is understandable to the general public, and has been successfully applied in TMDL studies in other states. To ease the creation of load duration curves, an automated load duration curve creation tool called LDCurve has been created within a Microsoft Excel framework. Web services and a webscraper are used to retrieve U.S. Geological Survey streamflow data and Texas Commission on Environmental Quality water quality data. Data are imported to the spreadsheet, combined to create flow and load duration curves, and plotted. Final steps result in a preliminary estimate of the overall load reductions needed to meet water quality standards in the modeled segment. LDCurve is currently only applicable in the state of Texas, but may be updated to model water quality throughout the nation using analogous web services from the EPA STORET database. By using automated data retrievals and computations, the LDCurve tool reduces the amount of time required to create curves and calculate load reductions to a matter of minutes. LDCurve and all supporting materials are available online for free download at: http://tools.crwr.utexas.edu/LDCurve/.
Is Denser Greener? An Evaluation of Higher Density Development as an Urban Stormwater‐Quality Best Management Practice1
Authors: Jacob John S. , Lopez Ricardo
Published: April 2009

Abstract:  A simple spreadsheet model was used to evaluate potential water quality benefits of high‐density development. The question was whether the reduced land consumed by higher density development (vs. standard suburban developments) would offset the worse water quality generated by a greater amount of impervious surface in the smaller area. Total runoff volume and per acre loadings of total phosphorous, total nitrogen, and total suspended solids increased with density as expected, but per capita loadings and runoff decreased markedly with density. For a constant or given population, then, higher density can result in dramatically lower total loadings than more diffuse suburban densities. The model showed that a simple doubling of standard suburban densities [to 8 dwelling units per acre (DUA) from about 3 to 5 DUA] in most cases could do more to reduce contaminant loadings associated with urban growth than many traditional stormwater best management practices (BMPs), and that higher densities such as those associated with transit‐oriented development could outperform almost all traditional BMPs, in terms of reduced loadings per a constant population. Because higher density is associated with vibrant urban life, building a better city may be the best BMP to mitigate the water quality damage that will accompany the massive urban growth expected for the next several decades.
Comparison of Two Regimens for the Treatment of Meningoencephalomyelitis of Unknown Etiology
Authors: Smith P.M. , Stalin C.E. , Shaw D. , Granger N. , Jeffery N.D.
Published: April 2009

Background: The optimal treatment for meningoencephalomyelitis of unknown etiology (MUE) remains unknown, despite the widespread use of a variety of immunosuppressive drugs.

Objective/Hypothesis: To compare the efficacy of prednisolone combined with either vincristine and cyclophosphamide (COP group; n= 10) or with cytosine arabinoside (AraC group; n= 9).

Animals: Nineteen dogs with neurological deficits, neuroimaging, and cerebrospinal fluid abnormalities consistent with a diagnosis of MUE.

Methods: Prospective, blinded, and randomized clinical trial. Dogs fulfilling the inclusion criteria were randomly allocated to receive 1 drug regimen.

Results: Four of 10 dogs in the COP group and 5/9 in the AraC group survived > 12 months but neither the survival time nor the time‐to‐treatment failure differed between the 2 groups. Treatment with COP resulted in an unacceptable incidence of adverse effects.

Conclusions: The adverse effects of COP make it an unsuitable treatment for MUE. Although survival of animals treated with AraC was broadly similar to that reported in recently published studies describing this treatment, it remains unclear whether it confers any benefit over using prednisolone alone.
Ca2+ sensitization via phosphorylation of myosin phosphatase targeting subunit at threonine‐855 by Rho kinase contributes to the arterial myogenic response
Authors: Johnson Rosalyn P. , El‐Yazbi Ahmed F. , Takeya Kosuke , Walsh Emma J. , Walsh Michael P. , Cole William C.
Published: April 2009

Ca2+ sensitization has been postulated to contribute to the myogenic contraction of resistance arteries evoked by elevation of transmural pressure. However, the biochemical evidence of pressure‐induced increases in phosphorylated myosin light chain phosphatase (MLCP) targeting subunit 1 (MYPT1) and/or 17 kDa protein kinase C (PKC)‐potentiated protein phosphatase 1 inhibitor protein (CPI‐17) required to sustain this view is not currently available. Here, we determined whether Ca2+ sensitization pathways involving Rho kinase (ROK)‐ and PKC‐dependent phosphorylation of MYPT1 and CPI‐17, respectively, contribute to the myogenic response of rat middle cerebral arteries. ROK inhibitors (Y27632, 0.03–10 μmol l−1; H1152, 0.001–0.3 μmol l−1) and PKC inhibitors (GF109203X, 3 μmol l−1; Gö6976; 10 μmol l−1) suppressed myogenic vasoconstriction between 40 and 120 mmHg. An improved, highly sensitive 3‐step Western blot method was developed for detection and quantification of MYPT1 and CPI‐17 phosphorylation. Increasing pressure from 10 to 60 or 100 mmHg significantly increased phosphorylation of MYPT1 at threonine‐855 (T855) and myosin light chain (LC20). Phosphorylation of MYPT1 at threonine‐697 (T697) and CPI‐17 were not affected by pressure. Pressure‐evoked elevations in MYPT1‐T855 and LC20 phosphorylation were reduced by H1152, but MYPT1‐T697 phosphorylation was unaffected. Inhibition of PKC with GF109203X did not affect MYPT1 or LC20 phosphorylation at 100 mmHg. Our findings provide the first direct, biochemical evidence that a Ca2+ sensitization pathway involving ROK‐dependent phosphorylation of MYPT1 at T855 (but not T697) and subsequent augmentation of LC20 phosphorylation contributes to myogenic control of arterial diameter in the cerebral vasculature. In contrast, suppression of the myogenic response by PKC inhibitors cannot be attributed to block of Ca2+ sensitization mediated by CPI‐17 or MYPT1 phosphorylation.
Remodelling of the respiratory network in a mouse model of Rett syndrome depends on brain‐derived neurotrophic factor regulated slow calcium buffering
Authors: Mironov S. L. , Skorova E. , Hartelt N. , Mironova L. A. , Hasan M. T. , Kügler S.
Published: April 2009

Rett syndrome caused by MeCP2 mutations is a devastating neurodevelopmental disorder accompanied by severe breathing irregularities. Using transduction of organotypic slices from model MeCP2–/y mice with neuron‐specific calcium sensor protein D3cpv, we examined the slow calcium buffering in neurons in pre‐Bötzinger complex (preBötC), a component of the complex respiratory network. Examination of wild‐type (WT) and MeCP2 null mice showed clear differences in the spatial organisations of neurons in preBötC and also in the disturbances in calcium homeostasis in mutant mice during early postnatal development. Deregulated calcium buffering in MeCP2–/y neurons was indicated by increased amplitude and kinetics of depolarisation‐induced calcium transients. Both effects were related to an insufficient calcium uptake into the endoplasmic reticulum that was restored after pretreatment with brain‐derived neurotrophic factor (BNDF). Conversely, the inhibition of BDNF signalling in WT neurons produced disturbances similar to those observed in MeCP2–/y mice. Brief hypoxia and calcium release from internal stores induced global calcium increases, after which the processes of many MeCP2–/y neurons were retracted, an effect that was also corrected by pretreatment with BDNF. The data obtained point to a tight connection between calcium homeostasis and long‐term changes in neuronal connectivity. We therefore propose that calcium‐dependent retraction of neurites in preBötC neurons can cause remodelling of the neuronal network during development and set up the conditions for appearance of breathing irregularities in Rett model mice.
Regulation of epithelial sodium channels by cGMP/PKGII
Authors: Nie Hong‐Guang , Chen Lan , Han Dong‐Yun , Li Jun , Song Wei‐Feng , Wei Shi‐Peng , Fang Xiao‐Hui , Gu Xiu , Matalon Sadis , Ji Hong‐Long
Published: April 2009

Airway and alveolar fluid clearance is mainly governed by vectorial salt movement via apically located rate‐limiting Na+channels (ENaC) and basolateral Na+/K+‐ATPases. ENaC is regulated by a spectrum of protein kinases, i.e. protein kinase A (PKA), C (PKC), and G (PKG). However, the molecular mechanisms for the regulation of ENaC by cGMP/PKG remain to be elucidated. In the present study, we studied the pharmacological responses of native epithelial Na+channels in human Clara cells and human αβγδ ENaCs expressed in oocytes to cGMP. 8‐pCPT‐cGMP increased amiloride‐sensitive short‐circuit current (Isc) across H441 monolayers and heterologously expressed αβγδ ENaC activity in a dose‐dependent manner. Similarly, 8‐pCPT‐cGMP (a PKGII activator) but not 8‐Br‐cGMP (a PKGI activator) increased amiloride‐sensitive whole cell currents in H441 cells in the presence of CFTRinh‐172 and diltiazem. In all cases, the cGMP‐activated Na+channel activity was inhibited by Rp‐8‐pCPT‐cGMP, a specific PKGII inhibitor. This was substantiated by the evidence that PKGII was the sole isoform expressed in H441 cells at the protein level. Importantly, intratracheal instillation of 8‐pCPT‐cGMP in BALB/c mice increased amiloride‐sensitive alveolar fluid clearance by ∼30%, consistent with thein vitroresults. We therefore conclude that PKGII is an activator of lung epithelial Na+channels, which may expedite the resolution of oedematous fluid in alveolar sacs.
Ether‐à‐go‐go‐related gene K+ channels contribute to threshold excitability of mouse auditory brainstem neurons
Authors: Hardman Rachael M. , Forsythe Ian D.
Published: April 2009

The ionic basis of excitability requires identification and characterisation of expressed channels and their specific roles in native neurons. We have exploited principal neurons of the medial nucleus of the trapezoid body (MNTB) as a model system for examining voltage‐gated K+ channels, because of their known function and simple morphology. Here we show that channels of the ether‐à‐go‐go‐related gene family (ERG, Kv11; encoded by kcnh) complement Kv1 channels in regulating neuronal excitability around threshold voltages. Using whole‐cell patch clamp from brainstem slices, the selective ERG antagonist E‐4031 reduced action potential (AP) threshold and increased firing on depolarisation. In P12 mice, under voltage‐clamp with elevated [K+]o (20 mm), a slowly deactivating current was blocked by E‐4031 or terfenadine (V0.5,act=−58.4 ± 0.9 mV, V0.5,inact=−76.1 ± 3.6 mV). Deactivation followed a double exponential time course (τslow= 113.8 ± 6.9 ms, τfast= 33.2 ± 3.8 ms at −110 mV, τfast 46% peak amplitude). In P25 mice, deactivation was best fitted by a single exponential (τfast= 46.8 ± 5.8 ms at −110 mV). Quantitative RT‐PCR showed that ERG1 and ERG3 were the predominant mRNAs and immunohistochemistry showed expression as somatic plasma membrane puncta on principal neurons. We conclude that ERG currents complement Kv1 currents in limiting AP firing at around threshold; ERG may have a particular role during periods of high activity when [K+]o is elevated. These ERG currents suggest a potential link between auditory hyperexcitability and acoustic startle triggering of cardiac events in familial LQT2.
Network‐based activity induced by 4‐aminopyridine in rat dorsal horn in vitro is mediated by both chemical and electrical synapses
Authors: Chapman Rebecca J. , Cilia La Corte Paul F. , Asghar Aziz U. R. , King Anne E.
Published: April 2009

This study investigated the role of electrical and chemical synapses in sustaining 4‐aminopyridine (4‐AP)‐evoked network activity recorded extracellularly from substantia gelatinosa (SG) of young rat spinal cord in vitro. Superfusion of 4‐AP (50 μm) induced two types of activity, the first was observed as large amplitude field population spiking activity and the second manifested within the inter‐spike interval as low amplitude rhythmic oscillations in the 4–12 Hz frequency range (mean peak of 8.0 ± 0.1 Hz). The AMPA/kainate receptor antagonist 6‐cyano‐7‐nitroquinoxaline‐2,3‐dione (CNQX, 10 μm) abolished field population spiking and disrupted 4–12 Hz rhythmic oscillatory activity whereas the NMDA receptor antagonist d‐AP5 (50 μm) had no significant effect on either activity component. The glycine receptor antagonist strychnine (4 μm) and the GABAA receptor antagonist bicuculline (10 μm) diminished and abolished, respectively, field population spiking and both antagonists reduced the power of 4–12 Hz oscillations. The non‐specific gap junction blockers carbenoxolone (100 μm) and octanol (1 mm) attenuated both types of 4‐AP‐induced activity. By comparison, the neuronal‐specific gap junction uncouplers quinine (250 μm) and mefloquine (500 nm) both disrupted 4–12 Hz oscillations but only quinine reduced the frequency of field population spiking. These data demonstrate the existence of 4‐AP‐sensitive neuronal networks within SG that can generate rhythmic activity, are differentially modulated by excitatory and inhibitory ionotropic neurotransmission and are at least partly reliant on neuronal and/or glial‐mediated electrical connectivity. The physiological significance of these putative intrinsic SG networks and the implications in the context of processing of nociceptive inputs are discussed.
Unsteady Three-Dimensional Flow in a Single-Stage Transonic Fan: Part I—Unsteady Rotor Exit Flow Field
Authors: Cherrett M. A. , Bryce J. D. , Ginder R. B.
Published: April 2009

Detailed unsteady aerodynamic measurements have been taken in a single-stage transonic fan with a very high stator-hub loading. Two-dimensional dynamic yawmeter probes, capable of measuring mean and fluctuating levels of stagnation pressure, static pressure, and yaw angle have been traversed at rotor exit, and downstream of the stator along with several types of pneumatic three-dimensional probe. Part I of this paper describes the dynamic yawmeters and their performance, and presents ensemble-averaged stagnation pressure and random stagnation pressure unsteadiness measurements taken at rotor exit. These are used to illustrate the salient features of the rotor flow field, and the effects of compressor aerodynamic loading. Part II presents measurements taken at stator exit.
Measurements of the Tip Clearance Flow for a High-Reynolds-Number Axial-Flow Rotor
Authors: Zierke W. C. , Farrell K. J. , Straka W. A.
Published: April 2009

A high-Reynolds-number pump (HIREP) facility has been used to acquire flow measurements in the rotor blade tip clearance region, with blade chord Reynolds numbers of 3,900,000 and 5,500,000. The initial experiment involved rotor blades with varying tip clearances, while a second experiment involved a more detailed investigation of a rotor blade row with a single tip clearance. The flow visualization on the blade surface and within the flow field indicate the existence of a trailing-edge separation vortex, a vortex that migrates radially upward along the trailing edge and then turns in the circumferential direction near the casing, moving in the opposite direction of blade rotation. Flow visualization also helps in establishing the trajectory of the tip leakage vortex core and shows the unsteadiness of the vortex. Detailed measurements show the effects of tip clearance size and downstream distance on the structure of the rotor tip leakage vortex. The character of the velocity profile along the vortex core changes from a jetlike profile to a wakelike profile as the tip clearance becomes smaller. Also, for small clearances, the presence and proximity of the casing endwall affects the roll-up, shape, dissipation, and unsteadiness of the tip leakage vortex. Measurements also show how much circulation is retained by the blade tip and how much is shed into the vortex, a vortex associated with high losses.
Computation of Unsteady Viscous Flow Through Turbomachinery Blade Row Due to Upstream Rotor Wakes
Authors: Ho Y.-H. , Lakshminarayana B.
Published: April 2009

A time-accurate, two-dimensional, pressure-based, Navier–Stokes solver for incompressible flow is developed and used to carry out the numerical simulation of rotor–stator interaction. A low-Reynolds-number form of the two-equation turbulence model is used to account for the turbulence effects. In order to improve the accuracy of the numerical scheme, a central differencing plus an artificial dissipation scheme is implemented to provide precise control of numerical dissipation. An inner loop iteration scheme is used at each time step to account for the nonlinear effects. The computation of unsteady flow through a flat plate cascade subjected to a transverse gust reveals that the choice of grid spacing and the amount of artificial dissipation is critical for accurate prediction of unsteady phenomena. The rotor–stator interaction problem is simulated by starting the computation upstream of the stator, and the upstream rotor wake is specified from the experimental data. The results show that the stator potential effects have appreciable influence on the upstream rotor wake. The predicted unsteady wake profiles are compared with the available experimental data and the agreement is good. The numerical results are interpreted to draw conclusions on the unsteady wake transport mechanism in the blade passage.
A Quasi-Unsteady Study on Wake Interaction of Turbine Stator and Rotor Cascades
Authors: Yamamoto A. , Murao R. , Suzuki Y. , Aoi Y.
Published: April 2009

Detailed flow measurements were made to study cascade interaction of turbine stator and rotor, using two linear cascades installed in series. The upstream cascade was moved to several places in the cascade pitchwise direction in order to change the relative location between the two cascades, and measurements were made in the downstream cascade. The result shows that the net total pressure loss generated in the downstream cascade becomes maximum when wakes of the upstream cascade pass the suction side of the downstream cascade passage, while the tip leakage loss generated in the downstream cascade does not change with the relative location of the cascades. The upstream cascade wakes interact with the secondary flows and most strongly with the endwall flow in the downstream cascade passage, making the loss distributions in the cascades fairly unsteady.
The Flow in a Second-Stage Nozzle of a Low-Speed Axial Turbine and Its Effect on Tip Clearance Loss Development
Authors: Morphis G. , Bindon J. P.
Published: April 2009

The flow field in a one-and-a-half-stage low-speed axial turbine with varying levels of rotor tip clearance was measured in order to compare the behavior of the second nozzle with the first and to identify the manner in which the second nozzle responds to the complex tip clearance dependent flow presented to it and completes the formation of tip clearance loss. The tangentially averaged flow relative to the rotor blade in the tip clearance region was found to differ radically from that found in cascade and is not underturned with a high axial velocity. There is evidence rather of overturning caused by secondary flow. The axial velocity follows an almost normal endwall boundary layer pattern with almost no leakage jet effect. The cascade tip clearance model is therefore not accurate. The reduction in second-stage nozzle loss was shown to occur near the hub and tip, which confirms that it is probably a reduction in secondary flow loss. The nozzle exit loss contours showed that leakage suppressed the formation of the classical secondary flow pattern and that a new tip clearance related loss phenomenon exists on the suction surface. The second-stage nozzle reduced the hub endwall boundary layer below that of both the first nozzle and that behind the rotor. It also rectified secondary and tip clearance flows to such a degree that a second-stage rotor would experience no greater flow distortion than the first-stage rotor. Radial flow angles behind the second-stage nozzle were much smaller than found in a previous study with low-aspect-ratio untwisted blades.
Measurements of the Flow in an Idealized Turbine Tip Gap
Authors: Sjolander S. A. , Cao D.
Published: April 2009

To gain further insights into the details of the tip-gap flow in axial turbines, a test section has been constructed with a single idealized, large-scale tip gap. The single “blade” forms a circular arc with 90 deg of turning and has a constant thickness of 78 mm. For a plain, flat tip four clearances have been examined, varying from 0.292 to 0.667 of the blade thickness (corresponding to physical gap heights of 22.8 to 52.1 mm). The large proportions made it possible to obtain very detailed measurements inside the gap. The paper discusses the structure of the gap flow in some detail. One new feature, involving multiple vortices on the tip, probably helps to explain the “burnout” that sometimes occurs on turbine tips near the pressure side. Quantitative results are presented for the static pressures, total pressures, and velocity vectors through the gap. In addition, contraction coefficients for the flow at the separation bubble, discharge coefficients for the gap, and the gap losses have been extracted for comparison with the assumptions made in recent gap–flow models.
Experimental Investigation and Performance Analysis of Six Low Flow Coefficient Centrifugal Compressor Stages
Authors: Paroubek J. , Cyrus V. , Kyncˇl J.
Published: April 2009

Some results of a research and development program for centrifugal compressors are presented. Six-stage configurations with low flow coefficient were tested. The stages had channel width parameter b2/D2 = 0.01 and 0.03. For each value of the width parameter, three different impellers with inlet hub to outlet diameter ratio do/D2 = 0.3, 0.4, and 0.5 were designed. Test rig, instrumentation, and data analysis are described. Special attention was devoted to probe calibrations and to evaluation of the leakage, bearing, and disk friction losses. Aerodynamic performance of all tested stages is presented. Slip factors of impellers obtained experimentally and theoretically are compared. Losses in both vaneless diffuser and return channel with deswirl vanes are discussed. Rotating stall was also investigated. Criteria for stall limit were tested.
Velocity Measurements Downstream of the Impellers in a Multistage Centrifugal Blower
Authors: Arnulfi G. L. , Micheli D. , Pinamonti P.
Published: April 2009

The paper presents the results of an experimental investigation on a four-stage centrifugal blower, having the aim of obtaining an accurate description of the flow field behind the impellers in several operative conditions and for different geometric configurations. Actually, the test plant allows one to change the turbomachinery characteristics assembling one, two, three, or four stages and three different types of diffuser. In this first research step, the blower has been tested in the four-stage vaneless diffuser configuration. The unsteady flow field behind the impellers and in the diffusers has been measured by means of a hot-wire anemometer. A phase-locked ensemble-averaging technique has been utilized to obtain the relative flow field from the instantaneous signals of the stationary hot-wire probes. Several detailed measurement sets have been performed using both single and crossed hot-wire probes, to obtain the velocity vectors and turbulence trends, just behind the blower impellers and in several radial positions of the vaneless diffusers. These measurements have been done at different flow rate conditions, covering unsteady flow rate phenomena (rotating stall) also. The results obtained allowed us to get a detailed flow field analysis in the multistage centrifugal blower, in relation to the geometric configuration and to the differing operating conditions.
On Fast-Response Probes: Part 1—Technology, Calibration, and Application to Turbomachinery
Authors: Gossweiler C. R. , Kupferschmied P. , Gyarmathy G.
Published: April 2009

A system for fast-response probe measurements in turbomachine flows has been developed and tested. The system has been designed for 40 kHz bandwidth and used with various in-house built probes accommodating up to four piezoresistive pressure transducers. The present generation of probes works accurately up to several bar pressure and 120°C temperature. The probes were found to be quite robust. The use of a miniature pressure transducer placed in the head of a probe showed that a precise packaging technique and a careful compensation of errors can considerably improve the accuracy of the pressure measurement. Methods for aerodynamic probe calibration and off-line data evaluation are briefly presented. These aimed, e.g., in the case of a four-hole probe, at measuring the velocity fluctuations as characterized by yaw, pitch, total pressure, and static pressure and at deriving mean values and spectral or turbulence parameters. Applications of the measuring system to turbomachinery flow in a radial compressor and to a turbulent pipe flow demonstrate the performance of the measuring system.
A Fiber Optic Probe for Gas Total Temperature Measurement in Turbomachinery
Authors: Kidd S. R. , Barton J. S. , Meredith P. , Jones J. D. C. , Cherrett M. A. , Chana K. S.
Published: April 2009

This paper describes the design, operation, construction, and demonstration of a new type of high-bandwidth unsteady temperature sensor based on fiber optics, and capable of operating in a high-speed multistage research compressor with flow representative of jet engine conditions. The sensing element is an optical coating of zinc selenide deposited on the end of an optical fiber. During evaluation in aerodynamic testing, a 1 K gas temperature resolution was demonstrated at 9.6 kHz and an upper bandwidth limit of 36 kHz achieved.
An Improved Aspirating Probe for Total-Temperature and Total-Pressure Measurements in Compressor Flows
Authors: Van Zante D. E. , Suder K. L. , Strazisar A. J. , Okiishi T. H.
Published: April 2009

The aspirating probe originally designed by Epstein and Ng at MIT was modified by replacing the two platinum-coated tungsten hot wires normally used with platinum–iridium alloy wires. The resulting improved unsteady total pressure and total temperature resolution of the modified probe is demonstrated. Flowfield measurements were made downstream of NASA Rotor 37 for a part-speed operating condition to test the performance of the probe. Time-resolved blade-to-blade total temperature and total pressure as calculated from the two platinum–iridium hot-wire voltages are shown. The flowfield measurements are compared with independent measurements of total pressure with high response transducers and total temperature calculated from laser anemometer measurements. Limitations of a more often used unsteady temperature data reduction method, which involves only one aspirating probe hot-wire voltage and a high-response pressure measurement, are discussed.
Darryl E. Metzger Memorial Session Paper: The Influence of Secondary Flows Near the Endwall and Boundary Layer Disturbance on Convective Transport From a Turbine Blade
Authors: Goldstein R. J. , Wang H. P. , Jabbari M. Y.
Published: April 2009

A naphthalene sublimation technique is used to investigate convective transport from a simulated turbine blade in a stationary linear cascade. In some of the tests undertaken, a trip wire is stretched along the span of the blade near the leading edge. The disturbance produced by tripping the boundary layers on the blade near the leading edge causes early boundary layer transition, creates high mass transfer rate on the pressure side and in the laminar flow region on the suction side, but lowers the transfer rate in the turbulent flow region on the suction side. Comparison is made with other heat and mass transfer studies in the two-dimensional region far from the endwall and good agreement is found. Near the endwall, flow visualization indicates a strong secondary flow pattern. The impact of vortices initiated near the endwall on the laminar–turbulent transition extends three-dimensional effects to about 0.8 chord lengths on the suction side and to about 0.2 chord lengths on the pressure side away from the endwall. The effect of the passage vortex and the new vortex induced by the passage vortex on mass transfer is clearly seen and can be traced along the suction surface of the blade. Close to the endwall the highest mass transfer rate on the suction surface is not found near the leading edge. It occurs at about 27 percent of the curvilinear distance from the stagnation line to the trailing edge where a strong main flow and the secondary passage flow from the pressure side of the adjacent blade interact. The influences of some small but very intense corner vortices and the passage vortex on mass transfer are also observed on both surfaces of the blade.
Screw System Approach to Physical Realization of Stiffness Matrix With Arbitrary Rank
Authors: Hong Man Bok , Choi Yong Je
Published: April 2009

It is possible to realize the desired compliance characteristics of a robot in a form of a passive compliance device, which demands the synthesis technique of a stiffness matrix by parallel connections of line and/or torsional springs. In this paper, the stiffness matrix is expressed in terms of the screw coordinates with respect to the basis consisting of its eigenvectors, thereby the synthesis equation is derived. Examination of the numbers of free design parameters involved in the synthesis suggests that a line or free vector for a spring can be freely selected from the induced wrench space depending on the rank of the stiffness matrix. The recursive synthesis method that allows one to select the positions or directions of the springs from the screw system spanned by the induced wrenches of the given stiffness matrix is proposed.
Heat Transfer to Supercritical Water in a Horizontal Pipe: Modeling,
New Empirical Correlation, and Comparison Against Experimental
Data
Authors: Bazargan Majid , Fraser Daniel
Published: April 2009

Enhancement of heat transfer to supercritical fluids has drawn the attentions of many researchers within the past few decades. Modeling and predicting heat transfer to turbulent flow of supercritical fluids, however, are very complicated due to severe variations of fluid properties near the critical point. Large discrepancies between available heat transfer data are greatly due to confusion of forced convection and mixed convection data. The data unaffected by buoyancy have been selected cautiously from a large database generated in this study. Such data have been used to develop a 1D numerical model as well as a semi-empirical correlation to predict forced convection heat transfer to turbulent flow of supercritical water. In the numerical model, radial variations of heat flux and shear stress are taken into account. Modifications to turbulent Prandtl number and wall shear stress formulations have been applied to a law of the wall type of model to fit supercritical conditions. The model shows good agreement with experiments. In the experimental part, the extensive database obtained on a full-scale test facility in the present study, plus a new conceptual approach, has been employed together to develop a semi-empirical heat transfer correlation. It accurately predicts the experiments.
Analysis of Viscous Effects on Cavitation
Authors: Amromin Eduard
Published: April 2009

Mechanical engineers often are forced to be concerned with cavitation in flows near bodies or within machinery. Viscous effects on cavitation introduce difficulties in design, because these effects often are significantly different for model and full-scale conditions. Therefore, a theoretical analysis would be desirable in numerical prediction of full-scale performances and in interpretation of experimental data. Though cavitation is a very complex nonlinear phenomenon, the numerical analysis of which is difficult even approaching an ideal fluid model, recently certain successes were obtained in the examination of viscous effects on sheet cavitation and vortex cavitation. A part of the theoretical results concerning viscous effects on cavitation was provided by matches of well-known solutions for boundary layers over non-cavitating bodies and solutions for cavities in an ideal fluid. The review of theoretical methods and consideration of the best way to proceed with future research is the objective of this review article, which includes 92 references.
Contemporary Progress in Porous Media Theory
Authors: de Boer Reint
Published: April 2009

In the last decade and, in particular in recent years, the macroscopic porous media theory has made decisive progress concerning the fundamentals of the theory and the development of mathematical models in various fields of engineering and biomechanics. This progress attracted some attention and therefore conferences (colloquia, symposia, etc) devoted almost exclusively to the macroscopic porous media theory have been organized in the last three years in Cambridge, United Kingdom (1996), Prague, the Czech Republic (1997), Essen, Germany (1997), Metz, France (1999), Stuttgart, Germany (1999) and Chicago, USA (2000) in order to collect all findings, to present new results, and to discuss new trends. Also in national and international journals a great number of important contributions have been published which has brought the porous media theory, in some parts, to a close. Therefore, the time seems to be ripe to review the state of the art. The Introduction is devoted to the historical development up to the end of the 1980s and the beginning of the 1990s (readers interested in an extended description of the historical development of the porous media theory are referred to de Boer, 2000). The volume fraction concept is formulated in Section 2. An extensive review of the kinematics in porous media theory is presented in Section 3. The balance equations and the entropy inequality are discussed in Sections 4 and 5. Section 6 is devoted to the investigation of the closure problem and the saturation condition. The constitutive theory with the description of elastic, elastic-plastic, and viscous states of the porous solid as well as some reflexions on the constitutive behavior of the pore fluids are represented in Section 7. Finally, some applications of the porous media theory in various fields (soil mechanics, chemical engineering, biomechanics and building physics as well as in environmental mechanics, soil physics, the petroleum industry, and material science) will demonstrate the usefulness of the macroscopic porous media theory. This review article contains 209 references.
Possible Limitations of Probabilistic Methods in Engineering
Authors: Elishakoff Isaac
Published: April 2009

This article summarizes the thinking of researchers and engineers world-wide on possible limitations of probabilistic methods in engineering, with particular emphasis upon structural mechanics. This question was posed over a ten year period (1988-1998) to numerous experts in the field. Written responses were received from 42, and they form the main body of this article. In an extensive discussion section, the author identifies some topics, trends, and thinking which seem to be prevalent in the responses, and supplements these with numerous related observations taken from the published literature, and other experts, who were not included in the original survey. This results in a references list with 52 entries. One ultimate conclusion reached is that reliability is much less known than many think it is.
Application of Weakly Anisotropic Models of a Continuous Medium for Solving the Problems of Wave Dynamics
Authors: Rossikhin Yuriy A. , Shitikova Marina V.
Published: April 2009

A review of papers dealing with the investigation of wave phenomena occurring in weakly anisotropic elastic media is available in the present article. Several weakly anisotropic models of a continuous medium are presented and discussed which can be used to advantage both for solving the problems of wave dynamics and for carrying out comparison analysis of experimental data on measurements of elastic moduli of slightly anisotropic material by quasilongitudinal and quasitransverse waves with the results of the theoretical investigations. Based on these models, the behavior of harmonic and nonstationary bulk and surface waves and shock waves propagating in linear and nonlinear elastic isotropic and anisotropic media are examined. The problems are solved by the perturbation technique. The value characterizing the deviation of anisotropic elastic coefficients from isotropic moduli is chosen as a small parameter. Straight expansions of the desired values with respect to the small parameter are obtained, and the domains of nonuniformity of such expansions are indicated. For some of the problems under consideration, it has been possible to regularize the straight expansions of the values to be found by virtue of the especially selected manipulations of dilatation or translation of independent coordinates and to construct the uniformly valid solutions in the whole domain of wave motion existence. This review article contains 280 references.
Higher-Order Theories of Piezoelectric Plates and Applications
Authors: Wang Ji , Yang Jiashi
Published: April 2009

This review article summarizes the development of higher order theories for the dynamic analysis of piezoelectric plates, and describes their applications, especially for crystal resonators. The theories are categorized according to how the displacement components and electric potential are assumed to vary through the plate thickness. The greatest attention has been given to ordinary polynomial variations, especially the efforts of RD Mindlin and HF Tiersten and their coworkers. Considerable progress has also been made using trigonometric series representations, especially by PCY Lee and his coworkers. Legendre polynomial and normal mode expansions have also been developed. Both analytical and finite element methods of dealing with problems are described. The article contains 174 references.
On Microtransport Phenomena in Minute Droplets: A Critical Review
Authors: Aydin Orhan , Yang Wen-Jei
Published: April 2009

Liquid droplets are abundant in nature and industry. Their industrial applications are very broad. They appear in the forms of sessile, impinging, and hanging/suspending droplets, undergoing evaporation or solidification depending upon ambient conditions. In the present article, a critical review is presented for the important literature pertinent to microtransport phenomena in minute droplets. Thermocapillarity is the principal motivating force in convective heat and mass transfer, phase change, and instability inside the droplets, supplemented in part by the buoyancy force. The dimensionless governing parameters are identified and their roles in droplet transport phenomena are determined. This article includes 135 references.