bluuebunny/crossref_metadata_2025 huggingface dataset:
Grid‐based versus big region approach for inverting CO emissions using Measurement of Pollution in the Troposphere (MOPITT) data
Authors: Stavrakou T. , Müller J.‐F.
Published: August 2006

The CO columns retrieved by the Measurement of Pollution in the Troposphere (MOPITT) satellite instrument between May 2000 and April 2001 are used together with the Intermediate Model for the Annual and Global Evolution of Species (IMAGES) global chemistry transport model and its adjoint to provide top‐down estimates for anthropogenic, biomass burning, and biogenic CO emissions on the global scale, as well as for the biogenic volatile organic compounds (VOC) fluxes, whose oxidation constitutes a major indirect CO source. For this purpose, the big region and grid‐based Bayesian inversion methods are presented and compared. In the former setup, the monthly emissions over large geographical regions are quantified. In the grid‐based setup, the fluxes are optimized at the spatial resolution of the model and on a monthly basis. Source‐specific spatiotemporal correlations among errors on the prior emissions are introduced in order to better constrain the inversion problem. Both inversion techniques bring the model columns much closer to the measurements at all latitudes, but the grid‐based analysis achieves a higher reduction of the overall model/data bias. Further comparisons with observed mixing ratios at NOAA Climate Monitoring and Diagnostics Laboratory and Global Atmosphere Watch sites, as well as with airborne measurements are also presented. The inferred emission estimates are weakly dependent on the prior errors and correlations. Our best estimate for the global CO source amounts to 2900 Tg CO/yr in both inversion approaches, about 5% higher than the prior. The global anthropogenic emission estimate is 18% larger than the prior, with the biggest increase for east Asia and a substantial decrease in south Asia. The vegetation fire emission estimates decrease as well, from the prior 467 Tg CO/yr to 450 Tg CO/yr in the grid‐based solution and 434 Tg CO/yr in the monthly big region setup, mainly due to a significant reduction of African savanna fire emissions. The biogenic CO/VOC flux estimates are found to be enhanced by about 15% on the global scale. The most significant error reductions concern the biogenic emissions in the tropics, the Asian anthropogenic emissions, and the vegetation fire source over Africa. Our inversion results are further compared with previously reported emission estimates.
Using geochemical fingerprinting to determine transpressive fault movement history: Application to the New Zealand Alpine Fault
Authors: Cutten H. N. C. , Korsch R. J. , Roser B. P.
Published: August 2006

Geochemical fingerprinting of conglomerate clasts from depocenters adjacent to a strike‐slip fault, and of source areas on the opposite side of the fault, provides a method of determining fault movement history in instances where potential piercing points have been removed by erosion or buried in pull‐apart or down‐warp basins. Our example demonstrating this method is the Neogene Maruia Basin adjacent to the New Zealand Alpine Fault, the on‐land Australian‐Pacific plate boundary, which shows Permian Pelorus‐Caples terrane offset by 480 km. Twenty‐six sandstone and schist conglomerate clasts from the Maruia Basin Rappahannock Group were analyzed for major elements and 18 trace elements by X‐ray fluorescence and compared to similar analyses from potential regional source areas. Significant source terranes, the Caples Group and the Torlesse terrane were identified, both located southeast of the fault. Dextral movement on the fault provided a conveyor belt of material to the Maruia Basin, first supplying (at ∼11.5 Ma) Caples sandstone, then Caples schist followed by Torlesse schist (from ∼9.5 Ma), which translates to an average Neogene movement rate of 36–37 mm yr−1. The increase in metamorphic grade reflects accelerated exhumation of source rocks as they passed through a restraining bend adjacent to the Maruia Basin and from later regional uplift from a change in the Australian Pacific plate motion vector and more transpressive movement from ∼5 Ma. This robust method of geochemical fingerprinting could be readily applied to determining movement history of transpressive faults of other regions.
Kinematic constraints on intra‐arc shear and strain partitioning in the southern Andes between 38°S and 42°S latitude
Authors: Rosenau Matthias , Melnick Daniel , Echtler Helmut
Published: August 2006

On the basis of structural field work, fault kinematic analysis, and the analysis of digital imagery, we describe the northern part of the southern Andean intra‐arc Liquiñe‐Ofqui Fault Zone (LOFZ) as an SC‐like fault zone system accommodating part of the Nazca–South American plate convergence obliquity. Kinematic modeling suggests that the LOFZ accommodated 124 (+24/−21) km of dextral displacement between 40°S and 42°S and 67 (+13/−11) km between 38°S and 40°S since the Pliocene. Associated vertical axis rotations are 31 ± 4° clockwise and 9 ± 1° counterclockwise along synthetic and antithetic faults, respectively. Mean Pliocene to recent shear rates along the LOFZ decrease northward from 32 ± 6 mm/yr to 13 ± 3 mm/yr compatible with partitioning of half of the convergence obliquity into the intra‐arc zone north of 40°S and complete partitioning to the south. The displacement gradient along the intra‐arc zone results in margin‐parallel shortening of the fore arc.
Magma supply path beneath Mt. Asama volcano, Japan
Authors: Takeo Minoru , Aoki Yosuke , Ohminato Takao , Yamamoto Maki
Published: August 2006

Obtaining a sharp image of magma supply path through dense geophysical observations is important for forecasting time and magnitude of hazardous future eruptions. Here we reveal a clear magma plumbing system using dense seismic and geodetic networks around Mt. Asama, central Japan. Magma intrusions occurred several times beneath the western flank of Mt. Asama, forming a WNW‐ESE directed zone with 1 km below sea level. The eastern end of this zone connects a narrow vertical pathway extending right under the summit crater, which erupted in 2004. Monitoring magmatic activity with a well‐designed observational network is vital to mitigate future volcano hazards.
A shock‐tube investigation of the dynamics of gas‐particle mixtures: Implications for explosive volcanic eruptions
Authors: Chojnicki K. , Clarke A. B. , Phillips J. C.
Published: August 2006

We use 1‐D shock‐tube experiments to investigate the dynamics of rapidly‐decompressed gas‐particle mixtures and associated shock waves, with application to the initial stages of Vulcanian and Plinian eruptions. For particle sizes 45–150 μm and pressure ratios 1–70, experimental particle Reynolds numbers reach 104 and impulsive accelerations reach 150 g. The experiments suggest that particles hinder gas motion via an interphase drag force, reducing shock strength and velocity. Gas‐particle mixture velocities decrease with increasing particle diameter for a given initial pressure ratio and are less than those predicted by pseudogas approximations and existing interphase drag relationships due to imperfect phase coupling and unsteady flow during high‐acceleration stages. We present a new analysis for predicting shock strength and velocity for gas‐particle mixtures, and apply our improved interphase drag terms to the high‐acceleration, eruption initiation stage of Vulcanian eruptions.
Changes in wind‐driven upwelling during the last three centuries: Interocean teleconnections
Authors: Goni Miguel A. , Thunell Robert C. , Woodwort Mark P. , Müller‐Karger Frank E.
Published: August 2006

Analysis of sediments from two wind‐driven upwelling systems, Guaymas and Cariaco basins, using the alkenone‐based U37K′ paleothermometer yielded high‐resolution records of sea surface temperatures (SST) from 1700 to 2000 AD. The trends in the U37K′ index reveal steady SST increases of 1 to 2°C at both sites since the end of the Little Ice Age. Higher‐frequency changes in SST indicate a decoupling in the relative intensity of wind‐driven upwelling at the two sites. Periods of enhanced upwelling in Guaymas correspond to periods of decreased upwelling in Cariaco (and vice versa). We propose that these contrasts reflect regional differences in the upwelling response of upwelling to changes in the positioning of the Inter‐Tropical Convergence Zone (ITCZ) and the Subtropical High (SH) under current climate conditions.
Tropical Atlantic sea surface temperature and heat flux simulations in a coupled GCM
Authors: Siqueira Léo , Nobre Paulo
Published: August 2006

This paper contrasts the SST and heat flux errors in the Tropical Atlantic simulated by the CPTEC Coupled ocean‐atmosphere General Circulation Model and its oceanic model forced by momentum and heat estimates. Comparisons between solar radiation estimated by satellite and measurements of PIRATA buoys have been made with the purpose of analyzing the impact of solar radiation in the simulation of SST in the tropical Atlantic. The radiative transfer model (ISCCP DX) has shown higher correlation with the buoys data than ECMWF ERA40 with larger differences over the eastern tropical Atlantic, where the numerical prediction models present difficulties in simulating the appearance of stratus clouds. The use of solar radiation based on satellite estimates and parameterized heat flux generated the best SST and surface heat fluxes. The stronger surface stresses generated by the CGCM contributed to generating an oceanic thermal structure in closer agreement with observations than the OGCM runs.
Circadian rhythms constrain leaf and canopy gas exchange in an Amazonian forest
Authors: Doughty Christopher E. , Goulden Michael L. , Miller Scott D. , da Rocha Humberto R.
Published: August 2006

We used a controlled‐environment leaf gas‐exchange system and the micrometeorological technique eddy covariance to determine whether circadian rhythms constrain the rates of leaf and canopy gas exchange in an Amazonian forest over a day. When exposed to continuous and constant light for 20 to 48 hours leaves of eleven of seventeen species reduced their photosynthetic rates and closed their stomata during the normally dark period and resumed active gas exchange during the normally light period. Similarly, the rate of whole‐forest CO2 uptake at a predetermined irradiance declined during the late afternoon and early morning and increased during the middle of the day. We attribute these cycles to circadian rhythms that are analogous to ones that have been reported for herbaceous plants in the laboratory. The importance of endogenous gas exchange rhythms presents a previously unrecognized challenge for efforts to both interpret and model land‐atmosphere energy and mass exchange.
The antiepileptic and anticancer agent, valproic acid, induces P‐glycoprotein in human tumour cell lines and in rat liver
Authors: Eyal S , Lamb J G , Smith‐Yockman M , Yagen B , Fibach E , Altschuler Y , White H S , Bialer M
Published: August 2006

Background and purpose:

The antiepileptic drug valproic acid, a histone deacetylase (HDAC) inhibitor, is currently being tested as an anticancer agent. However, HDAC inhibitors may interact with anticancer drugs through induction of P‐glycoprotein (P‐gp, MDR1) expression. In this study we assessed whether valproic acid induces P‐gp function in tumour cells. We also investigated effects of valproic acid on the mRNA for P‐gp and the cytochrome P450, CYP3A, in rat livers.

Experimental approach:

Effects of valproic acid on P‐gp were assessed in three tumour cell lines, SW620, KG1a and H4IIE. Accumulation of acetylated histone H3 in rats' livers treated for two or seven days with valproic acid was evaluated using a specific antibody. Hepatic expression of the P‐gp genes, mdr1a, mdr1b and mdr2, was determined by real‐time polymerase chain reaction. The effects of valproic acid on CYP3A were assessed by Northern blot analysis and CYP3A activity assays.

Key results:

Valproic acid (0.5–2.0 mM) induced P‐gp expression and function up to 4‐fold in vitro. The effect of a series of valproic acid derivatives on P‐gp expression in SW620 and KG1a cells correlated with their HDAC inhibition potencies. Treatment of rats with 1 mmol kg−1 valproic acid for two and seven days increased hepatic histone acetylation (1.3‐ and 3.5‐fold, respectively) and the expression of mdr1a and mdr2 (2.2–4.1‐fold). Valpromide (0.5–2.0 mM) did not increase histone acetylation or P‐gp expression in rat livers, but induced CYP3A expression.

Conclusions:

Valproic acid increased P‐gp expression and function in human tumour cell lines and in rat liver. The clinical significance of this increase merits further investigation.

British Journal of Pharmacology (2006) 149, 250–260. doi:10.1038/sj.bjp.0706830
Obesity – a risk factor or a RISK factor for myocardial infarction?
Authors: Heusch G
Published: August 2006

The detrimental actions of leptin on cardiovascular function are well established. Smith et al. report the novel finding of a reduction of infarct size by exogenous leptin when given at reperfusion. The involvement of the reperfusion injury salvage kinase (RISK) pathway in such reduction of infarct size and its relation to ischemic pre‐ and postconditioning are discussed and some methodological issues in its assessment are raised. Obesity has possibly opposite effects on the incidence and outcome of myocardial infarction.

British Journal of Pharmacology (2006) 149, 1–3. doi:10.1038/sj.bjp.0706833
Kinase‐dependent, retinoic acid receptor‐independent up‐regulation of cyclooxygenase‐2 by all‐trans retinoic acid in human mesangial cells
Authors: Alique M , Moreno V , Kitamura M , Xu Q , Lucio‐Cazana F J
Published: August 2006

Background and purpose:

Preliminary results in human mesangial cells (MC) suggested that all‐trans retinoic acid (ATRA) increased the expression of COX‐2 and the production of prostaglandin E2 (PGE2), a PG with anti‐inflammatory effects in MC. The aim of this work is to confirm that ATRA increases the expression of COX‐2 in MC and to examine the mechanisms involved.

Experimental approach:

Cultured MC were treated with ATRA. COX expression and kinase activity were analyzed by Western blot. Transcriptional mechanisms were analyzed by Northern blot, RT‐PCR and promoter assays.

Key results:

COX‐2 and COX‐1 expression and PGE2 production were increased by ATRA. COX‐2 played a role in PGE2 production as production was only partially inhibited by COX‐1 inhibitor SC‐560. COX‐2 up‐regulation by ATRA was due to transcriptional mechanisms as pre‐incubation with actinomycin D abolished it and ATRA increased the expression of COX‐2 mRNA and the activity of a human COX‐2 promoter construct, whereas post‐transcriptional mechanisms were not found. Retinoic acid receptors (RAR) were not involved in the up‐regulation of COX‐2 by ATRA since it was not inhibited by RAR‐pan‐antagonists and the RAR‐pan‐agonist TTNPB did not up‐regulate COX‐2. Instead ATRA might act through a sustained activation of extracellular signal‐regulated kinase 1/2 (ERK1/2) since up‐regulation of COX‐2 was prevented by inhibition of the activation of ERK1/2 with PD098059. Also ERK1/2, as well as downstream signalling proteins from ERK1/2, remained phosphorylated when COX‐2 increased 24 h later.

Conclusions and implications:

These results highlight the relevance of RAR‐independent mechanisms to the biological effects of ATRA.

British Journal of Pharmacology (2006) 149, 215–225. doi:10.1038/sj.bjp.0706842
Regulation of the common carotid arterial blood flow by nicotinic receptors in the medulla of cats
Authors: Gong C‐L , Chiu Y‐T , Lin N‐N , Cheng C‐C , Lin S‐Z , Lee T J‐F , Kuo J‐S
Published: August 2006

Background and purpose:

Actions of glutamate and serotonin on their respective receptors in the dorsal facial area (DFA) of the medulla are known to regulate common carotid arterial (CCA) blood flow in cats. Less is known about acetylcholine action on its nicotinic receptor (nAChR) subtypes in the DFA for regulation of CCA blood flow and this aspect was investigated.

Experimental approach:

Nicotinic and muscarinic agonists and antagonists were microinjected into the DFA through a three‐barrel tubing in anesthetized cats.

Results:

CCA blood flow was dose‐dependently increased by nicotine (a non‐selective nAChR agonist) and choline (a selectiveα7‐nAChR agonist). These effects of nicotine were attenuated byα‐bungarotoxin (anα7‐nAChR antagonist), methyllycaconitine (anα7‐nAChR antagonist), mecamylamine (a relatively selectiveα3β4‐nAChR antagonist) and dihydro‐β‐erythroidine (a relatively selectiveα4β2‐nAChR antagonist). The choline‐induced flow increase was attenuated byα‐bungarotoxin and mecamylamine, but not by dihydro‐β‐erythroidine. Muscarinic agonists (muscarine and methacholine) and antagonist (atropine) affected neither the basal nor the nicotine‐induced increase in the CCA blood flow.

Conclusions and implications:

Functionalα7,α4β2, andα3β4 subunits of the nAChR appear to be present on the DFA neurons. Activations of these receptors increase the CCA blood flow. The present findings do not preclude the presence of other nAChRs subunits. Muscarinic receptors, if any, on the DFA are not involved in regulation of the CCA blood flow. Various subtypes of nAChRs in the DFA may mediate regulation of the CCA and cerebral blood flows.

British Journal of Pharmacology(2006)149, 206–214; doi:10.1038/sj.bjp.0706844
Mutations within the selectivity filter of the NMDA receptor‐channel influence voltage dependent block by 5‐hydroxytryptamine
Authors: Kloda A , Adams D J
Published: August 2006

Background and purpose:

Voltage‐dependent block by Mg2+is a cardinal feature of NMDA receptors which acts as a coincidence detector to prevent the receptor from over‐activation. Inhibition of NMDA receptor currents by 5‐hydroxytryptamine (5‐HT) indicated that 5‐HT, similar to Mg2+, binds within the membrane electric field. In the present study, we assessed whether point mutations of critical asparagine residues located within the selectivity filter of NR1 and NR2A subunits of NMDA receptor‐channel affect voltage‐dependent block by 5‐HT.

Experimental approach:

The mode of action of 5‐HT and Mg2+on wild‐type and mutated NMDA receptor‐channels expressed inXenopusoocytes was investigated using the two‐electrode voltage clamp recording technique.

Key results:

The mutation within the NR1 subunit NR1(N0S or N0Q) strongly reduced the voltage dependent block by 5‐HT and increased the IC50. The corresponding mutations within the NR2 subunits NR2A(N0Q or N+1Q) reduced the block by 5‐HT to a lesser extent. This is in contrast to the block produced by external Mg2+where a substitution at the NR2A(N0) and NR2A(N+1) sites but not at the NR1(N0) site significantly reduced Mg2+block.

Conclusion and implications:

The block of NMDA receptor‐channels by 5‐HT depends on the NR1‐subunit asparagine residue and to a lesser extent on the NR2A‐subunit asparagine residues. These data suggest that the interaction of 5‐HT with functionally important residues in a narrow constriction of the pore of the NMDA receptor‐channel provides a significant barrier to ionic fluxes through the open channel due to energetic factors governed by chemical properties of the binding site and the electric field.

British Journal of Pharmacology(2006)149, 163–169. doi:10.1038/sj.bjp.0706849
Muscarinic receptor‐activated cationic channels in murine ileal myocytes
Authors: Dresviannikov A V , Bolton T B , Zholos A V
Published: August 2006

Background and purpose:

There is little information about the excitatory cholinergic mechanisms of mouse small intestine although this model is important for gene knock‐out studies.

Experimental approach:

Using patch‐clamp techniques, voltage‐dependent and pharmacological properties of carbachol‐ or intracellular GTPγS‐activated cationic channels in mouse ileal myocytes were investigated.

Key results:

Three types of cation channels were identified in outside‐out patches (17, 70 and 140 pS). The voltage‐dependent behaviour of the 70 pS channel, which was also the most abundantly expressed channel (∼0.35 μ−2) was most consistent with the properties of the whole‐cell muscarinic current (half‐maximal activation at −72.3±9.3 mV, slope of −9.1±7.4 mV and mean open probability of 0.16±0.01 at −40 mV; at near maximal activation by 50 μMcarbachol). Both channel conductance and open probability depended on the permeant cation in the order: Cs+(70 pS) >Rb+(66pS) >Na+(47 pS) >Li+(30 pS). External application of divalent cations, quinine, SK&F 96365 or La3+strongly inhibited the whole‐cell current. At the single channel level the nature of the inhibitory effects appeared to be very different. Either reduction of the open probability (quinine and to some extent SK&F 96365 and La3+) or of unitary current amplitude (Ca2+, Mg2+, SK&F 96365, La3+) was observed implying significant differences in the dissociation rates of the blockers.

Conclusions and implications:

The muscarinic cation current of murine small intestine is very similar to that in guinea‐pig myocytes and murine genetic manipulation should yield important information about muscarinic receptor transduction mechanisms.

British Journal of Pharmacology(2006)149, 179–187. doi:10.1038/sj.bjp.0706852
The effects of cardamonin on lipopolysaccharide‐induced inflammatory protein production and MAP kinase and NFκB signalling pathways in monocytes/macrophages
Authors: Hatziieremia S , Gray A I , Ferro V A , Paul A , Plevin R
Published: August 2006

Background and purpose:

In this study we examined the effect of the natural product cardamonin, upon lipopolysaccharide (LPS)‐induced inflammatory gene expression in order to attempt to pinpoint the mechanism of action.

Experimental approaches:

Cardamonin was isolated from the Greek plantA. absinthiumL. Its effects were assessed on LPS‐induced nitrite release and iNOS and COX‐2 protein expression in two macrophage cell lines. Western blotting was used to investigate its effects on phosphorylation of the mitogen activated protein (MAP) kinases, ERK, JNK and p38 MAP kinase, and activation of the NFκB pathway, at the level of IκBαdegradation and phosphorylation of NFκB. Also its effects on NFκB and GAS/GAF‐DNA binding were assessed by EMSA.

Key results:

Cardamonin concentration‐dependently inhibited both NO release and iNOS expression but had no effect on COX‐2 expression. It did not affect phosphorylation of the MAP kinases, degradation of IκBαor phosphorylation of NFκB. However, it inhibited NFκB DNA‐binding in both LPS‐stimulated cells and nuclear extracts of the cells (in vitro). It also inhibited IFNγ‐stimulated iNOS induction and GAS/GAF‐DNA binding.

Conclusions and Implications:

These results show that the inhibitory effect of cardamonin on LPS‐induced iNOS induction is not mediated via effects on the initial activation of the NFκB or MAP kinase pathways but is due to a direct effect on transcription factor binding to DNA. However, although some selectivity in cardamonin's action is implicated by its inability to affect COX‐2 expression, its exact mechanism(s) of action has yet to be identified.

British Journal of Pharmacology(2006)149, 188–198. doi:10.1038/sj.bjp.0706856
Rapamycin induces regression of endometriotic lesions by inhibiting neovascularization and cell proliferation
Authors: Laschke M W , Elitzsch A , Scheuer C , Holstein J H , Vollmar B , Menger M D
Published: August 2006

Background and purpose:

Rapamycin is a widely used drug with antifungal, immunosuppressant and antiangiogenic effects. Herein, we studied whether immunosuppressive doses of rapamycin are capable of influencing endometriotic lesions.

Experimental approach:

We tested in vitro the potential of rapamycin to inhibit endothelial cell sprouting using the aortic ring assay and we further studied its effect on the expression of proliferating cell nuclear antigen (PCNA), apoptotic cell death‐associated activated caspase‐3 and vascular endothelial growth factor (VEGF) in cultured endometrial tissue fragments. In addition, we analyzed the drug in vivo after induction of endometriotic lesions by transplanting isolated endometrial fragments into the dorsal skinfold chamber of Syrian golden hamsters. Using intravital fluorescence microscopy, we repetitively analyzed angiogenesis, neovascularization and microcirculatory parameters over a time period of 14 days in rapamycin‐treated animals and DMSO‐treated controls.

Key results:

Administration of rapamycin significantly reduced the size of the endometriotic lesions. This was associated by inhibition of VEGF‐mediated angiogenesis as indicated by a suppression of endothelial cell sprouting in vitro and a reduction of microvessel density in endometriotic lesions in vivo. Moreover, rapamycin directly inhibited cell proliferation within endometrial tissue, while manifestation of apoptotic cell death remained unaffected.

Conclusions and implications:

Our data indicate that administration of rapamycin may represent a novel therapeutic approach for an antiangiogenic treatment of endometriosis.

British Journal of Pharmacology (2006) 149, 137–144. doi:10.1038/sj.bjp.0706857
Antiangiogenic therapies in endometriosis
Authors: Ferrero S , Ragni N , Remorgida V
Published: August 2006

Oral contraceptives, androgenic agents, progestins and gonadotropin‐releasing hormone analogues have all been successfully used in the treatment of endometriosis. However, none of these drugs can eradicate the disease. It is widely accepted that the growth of newly formed blood vessels is essential for the establishment and growth of endometriotic lesions; therefore, inhibition of angiogenesis may offer a new option for treatment of this disorder. In this paper, we reviewed anti‐vascular endothelial growth factor agents and other angiostatic drugs (i.e., TNP470, endostatin, anginex, rapamycin) that have been studied in laboratory and animal models of endometriosis. Although preliminary results are interesting, further investigations are required before clinical trials can be planned in humans.

British Journal of Pharmacology (2006) 149, 133–135. doi:10.1038/sj.bjp.0706860
Eigen helicity density: A new vortex identification scheme and its application in accelerated inhomogeneous flows
Authors: Zhang Shuang , Choudhury Dipankar
Published: August 2006

Turbulence initiated by Richtmyer-Meshkov (RM) instability provides an important environment for studying three-dimensional, high-speed, compressible, and variable-density flow physics. The active baroclinic term in the vorticity evolution equation complicates the vortex dynamics and challenges existing vortex identification schemes. In this paper, we examine the insufficiency of existing vortex identification schemes when applied to a simulated RM flow [Zhang et al., J. Turbul. 6, 1 (2005)]. We propose a new scheme, eigen helicity density (He), based on the eigen analysis of the velocity gradient tensor. This Galilean invariant scheme successfully identifies vortex tubes in the same simulation.
Merger and alignment in a reduced model for three-dimensional quasigeostrophic ellipsoidal vortices
Authors: Martinsen-Burrell Neil , Julien Keith , Petersen Mark R. , Weiss Jeffrey B.
Published: August 2006

We investigate the interaction of two ellipsoidal vortices in the three-dimensional quasigeostrophic fluid equations by first studying a reduced model of vortex interaction, the ellipsoidal moment model, and second by comparing the results to corresponding numerical simulations. The ellipsoidal moment model approximates the interaction of two ellipsoidal lumps of potential vorticity by a finite-degree-of-freedom Hamiltonian system. This approximation is derived explicitly in the natural moment coordinate system to first order in the ratio of the size of the vortices to their separation. Using this Hamiltonian system for the case of initially spheroidal identical vortices, the linear stability of vertically aligned vortices is analyzed. A new dynamical criterion for vortex merger and alignment is proposed and shown to give a clear and reasonable boundary for vortex merger. A similar boundary is shown to exist in the size of the largest Lyapunov exponent, although not in the chaotic region as measured by the 0-1 test of Gottwald and Melbourne [Proc. R. Soc. London, Ser. A 460, 603 (2004)]. There is no such sharp boundary for vortex alignment in this reduced model. A series of numerical experiments confirms the accuracy of the merger criterion used in the ellipsoidal moment model. The numerical simulations also suggest a mechanism for understanding the process of vortex alignment in terms of vortex Rossby waves.
Airflow velocity effects on air bearing with grooved disk surface in near-field optical disk drives
Authors: Wang H. C. , Liu T. S.
Published: August 2006

By means of an air bearing, the pickup head slider of a near-field optical disk drive flies above data tracks on a rotating disk surface to achieve a stable flying height. The influence of airflow velocities of the air bearing on lift force deserves investigation, as the airflow velocity varies during track seeking or disk speed variation. In this study, a direct simulation Monte Carlo method is used to investigate three-dimensional nanoscale gas film lubrication at the air bearing between a slider and a rotating disk. This study aims to investigate air bearing behavior at different airflow velocities. Computational results show that faster flow generates larger pressure and lift force. Lower flying height reduces force variation caused by different velocities. This study also proposes a method for maintaining the flying height within the near-field range.
A numerical study on the breakup process of laminar liquid jets into a gas
Authors: Pan Yu , Suga Kazuhiko
Published: August 2006

Surface phenomena of liquid jets into still air are numerically investigated. The liquid and air are treated as a single continuum with dynamically evolving interfaces captured by the level-set method. The jets considered are laminar: the jet exit Reynolds number ranges from 480 to 2300, with the Weber number of 3.1–28 000. The liquid/air density ratios are about 103. In comparison with an empirical correlation, the present simulations reasonably predict the breakup lengths of round liquid jets at low Weber numbers. The development of the surface wave is captured and the breakup mechanisms are discussed referring to a conventional classification chart. The breakup phenomenon at high Weber and Ohnesorge numbers is also analyzed. It is then found that large-scale longitudinal-vortex motions, which are initially generated inside the liquid core by relaxation of the axial liquid velocity profile and surface shear, are amplified by surface motions due to instability. They grow up and eventually overcome inertial and surface-tension forces leading to a sudden breakup of the liquid column.
Hydrodynamic interactions of spherical particles in Poiseuille flow between two parallel walls
Authors: Bhattacharya S. , Bławzdziewicz J. , Wajnryb E.
Published: August 2006

We study hydrodynamic interactions of spherical particles in incident Poiseuille flow in a channel with infinite planar walls. The particles are suspended in a Newtonian fluid, and creeping-flow conditions are assumed. Numerical results, obtained using our highly accurate Cartesian-representation algorithm [Physica A 356, 294 (2005)] are presented for a single sphere, two spheres, and arrays of many spheres. We consider the motion of freely suspended particles as well as the forces and torques acting on particles adsorbed at a wall. We find that the pair hydrodynamic interactions in this wall-bounded system have a complex dependence on the lateral interparticle distance due to the combined effects of the dissipation in the gap between the particle surfaces and the backflow associated with the presence of the walls. For immobile particle pairs we have examined the crossover between several far-field asymptotic regimes corresponding to different relations between the particle separation and the distances of the particles from the walls. We have also shown that the cumulative effect of the far-field flow substantially influences the force distribution in arrays of immobile spheres, and it affects trajectories of suspended particles. Therefore, the far-field contributions should be included in any reliable algorithm for evaluating many-particle hydrodynamic interactions in the parallel-wall geometry.
Linear interaction analysis for Richtmyer-Meshkov instability at low Atwood numbers
Authors: Griffond J.
Published: August 2006

A recent formulation [J. Griffond, Phys. Fluids17, 086101 (2005)] of the linear interaction analysis (LIA) for mixtures of two perfect gases is applied to a field including a sinusoidal diffuse interface between two perfect gases. It offers an original way to investigate the initial phase of the Richtmyer-Meshkov instability. The approach is valid only in the limit of gases with close molar mass and specific heat (low Atwood numbers), but it applies to interfaces of arbitrary corrugation amplitude and diffusion thickness without Mach number limitation on the shock wave. The vorticity field deduced from LIA compares favorably with two-dimensional numerical simulations. In their limit of common validity, the LIA and the formulas of Wouchuk [Phys. Rev. E63, 056303 (2001); Phys. Fluids 8, 2890 (2001)] predict close asymptotic growth rates, contrary to impulsive models. The correction for initial diffusion of the interface proposed by Brouillette and Sturtevant [J. Fluid Mech.263, 271 (1994)] shows only weak discrepancies with the present results.
Competition between axisymmetric and three-dimensional patterns between exactly counter-rotating disks
Authors: Nore C. , Martin Witkowski L. , Foucault E. , Pécheux J. , Daube O. , Le Quéré P.
Published: August 2006

The bifurcations and the nonlinear dynamics of the von Kármán swirling flow between exactly counter-rotating disks in a stationary cylinder are numerically and experimentally investigated. The dynamics are governed by two parameters, the radius-to-height ratio A=R∕H and the Reynolds number, Re, based on disk rotation speed and cylinder height. The stability analysis performed for 2⩽A⩽20 shows that nonaxisymmetric and axisymmetric modes can be stationary or time dependent in this range. Three-dimensional modes are dominant for A⩽13.25 while axisymmetric modes are critical for A>13.25. The patterns of the dominant perturbations are analyzed. In the particular case of A=15, nonlinear computations are performed at Reynolds numbers slightly above threshold and are compared to experimental results, showing the competition between axisymmetric and three-dimensional modes.
Effects of initial radius on the propagation of premixed flame kernels in a turbulent environment
Authors: Klein M. , Chakraborty N. , Jenkins K. W. , Cant R. S.
Published: August 2006

The effects of mean curvature on the propagation of turbulent premixed flames have been investigated using three-dimensional direct numerical simulations (DNS) with single step Arrhenius-type chemistry in the thin reaction zones regime. A number of spherical flame kernels with different initial radius have been studied under identical conditions of turbulence and thermochemistry. A statistically planar turbulent back-to-back flame has been simulated as a special case of a spherical kernel in the limit of infinite kernel radius. Statistical analysis in terms of standard and joint probability density functions (pdfs) clearly indicates that the mean curvature of the flame kernel configuration has a major influence on the propagation behavior of the flame. For the planar flame configuration the density-weighted displacement speed is found to be fairly constant throughout the flame brush, in good agreement with previous DNS results. By contrast, for the flame kernel configuration the density-weighted displacement speed is found to vary strongly through the flame brush, changing from values on the order of the corresponding laminar flame speed near the fresh gas side to considerably smaller values near the burned gas side. The joint pdfs of displacement speed and its components with curvature are extensively studied, allowing for an explanation of the observed phenomena in terms of local flame geometry and its interaction with the turbulent flow field.
Evolution of finite span synthetic jets
Authors: Amitay Michael , Cannelle Florine
Published: August 2006

The streamwise and spanwise evolutions of finite span synthetic (zero net mass flux) jets were investigated experimentally using particle image velocimetry. The synthetic jet was produced over a broad range of length and time scales at Reynolds numbers from 85 to 364, stroke lengths from 16 to 50 times the slit width, and two formation frequencies, f=300 and 917Hz. The velocity and vorticity fields were measured in two planes, across the slit (i.e., along the short axis of the orifice) and along the slit (i.e., along the long axis). The paper presents the effect of the slit aspect ratio on the development of the synthetic jet, and the spatial evolution of secondary three-dimensional vortical structures in the flow field. The measurements in the plane along the slit revealed a unique flow pattern, where near the orifice the flow is two-dimensional, while farther downstream the vortex pair lines develop secondary counter-rotating structures. The streamwise and spanwise spacing between these structures vary with stroke length and formation frequency. As the orifice aspect ratio increases the effect of the slit edges decreases, thus the secondary structures are less pronounced.
Stability and transitions of hetonic quartets and baroclinic modons
Authors: Kizner Ziv
Published: August 2006

A new concept, a hetonic quartet, is presented. A hetonic quartet is a two-layer ensemble of four synchronously translating quasigeostrophic discrete vortices aligned perpendicularly to the axis of their translation. On the f-plane, a hetonic quartet is made up of conventional point vortices (confined to either the upper or the lower layer) with specially fitted circulations and distances between each other, the upper- and lower-layer vortices being opposite in sign and located symmetrically about the translation axis. On the β-plane, a two-layer version of the modulated point vortex model [Phys. Fluids 25, 2175 (1982)] is applied. A necessary and sufficient condition for the stability of f-plane hetonic quartets to perturbations that do not violate the above-mentioned symmetry is established using the analytical methods of Hamiltonian dynamics, whereas on the β-plane, a necessary (linear) stability condition is determined. As distinct from hetons, a stable hetonic quartet is not rigid: when slightly moved off equilibrium it undergoes elastic oscillations. Periodically or continuously acting small perturbations force a stable hetonic quartet to split up into two pairs of hetons, each traveling at different speeds along the same axis. The separation in the faster heton is generally greater than that between the “centers of mass” of the upper- and lower-layer vortices of the original hetonic quartet. The similarity between baroclinic modons and hetonic quartets is traced, and a plausible scenario of the transitions observed in smooth circular baroclinic modons with moderate riders [J. Fluid Mech. 468, 239 (2002)] is suggested, with the substantial stability of the ultimate elliptical modon state being attributed to the lack of overlap of the main upper and lower vorticity chunks in the modon. The splitting of finite-core hetons (two-layer f-plane vortical pairs composed of two circular patches of constant vorticity) [J. Fluid Mech. 423, 127 (2000)] is linked with the transitions in baroclinic modons and hetonic quartets.
Molecular interpretation of nonclassical gas dynamics of dense vapors under the van der Waals model
Authors: Colonna P. , Guardone A.
Published: August 2006

The van der Waals polytropic gas model is used to investigate the role of attractive and repulsive intermolecular forces and the influence of molecular complexity on the possible nonclassical gas dynamic behavior of vapors near the liquid-vapor saturation curve. The decrease of the sound speed upon isothermal compression is due to the well-known action of the van der Waals attractive forces and this effect is shown here to be comparatively larger for more complex molecules with a large number of active vibrational modes; for these fluids isentropic flows are in fact almost isothermal. Contributions to the speed of sound resulting from intermolecular forces and the role of molecular complexity are analyzed in details for both isothermal and isentropic transformations. Results of the exact solution to the problem of a finite pressure perturbation traveling in a still fluid are presented in three exemplary cases: ideal gas, dense gas and nonclassical gas behavior. A classification scheme of fluids based on the possibility of exhibiting different gas dynamic behaviors is also proposed.
Multiple solutions of gravity and surface shear driven thin film flows over a rectangular cavity
Authors: Shuaib N. H. , Power H. , Hibberd S.
Published: August 2006

The effect of surface shear stress on the two-dimensional flow of a thin film over a rectangular cavity is investigated by the numerical simulation of the problem in terms of its corresponding Stokes formulation. The integral representation of the problem is numerically solved by a direct boundary element method (BEM) with primitive variables of velocity and surface traction. For cases in which the applied surface shear and the gravity act in opposite directions, in such a way that the resulting flow is in the direction of the applied shear (ascending film), it is shown that more than one steady-state film profile may exist for a given flux and geometry of the cavity. An investigation into the effect of the cavity depth on these profiles is determined by separating the cavity into a step-up and a step-down flow. For the step-down flow configuration more than one film profiles exists for a given set of flux, surface shear, and inclination angle. However, for step-up flows, it is observed that for a given set of parameters, there exists a maximum ascending flux for the flow to overcome the step. For greater flux values, the solution always tends to one in which the flux is reduced to that of the maximum flux and results in a common asymptotic steady-state surface profile. For a flux lower than or equal to that of the maximum flux, more than one steady-state film profiles can exist. Based on the numerical results for the single step-up/step-down flows, feasible steady-state profiles for a film flow over a rectangular cavity are constructed.
Transition from spherical cap to toroidal bubbles
Authors: Bonometti Thomas , Magnaudet Jacques
Published: August 2006

Large gas bubbles rising under the effect of buoyancy are known to adopt either a spherical cap shape or to undergo a topological transition after which they become toroidal. We carry out an axisymmetric numerical investigation of the evolution of such large bubbles in the presence of both capillary and viscous effects. The numerical approach is of the volume of fluid type (it solves the Navier-Stokes equations on a fixed grid and transports the local volume fraction of one of the fluids), but does not involve any explicit reconstruction of the interface. The transition from spherical cap to toroidal bubbles is studied in the parameter space built on the Bond (Bo) and Archimedes (Ar) numbers, which compare the strength of inertial effects to that of capillary and viscous effects, respectively. Preliminary tests show that the position of this transition is very sensitive to the grid resolution; these tests are used to select grid characteristics that yield grid-independent results. Two markedly different transition scenarios, corresponding to the limit of large Ar and large Bo, respectively, are then identified. In the first case, the front of the bubble is pierced by an upward jet coming from the rear of the bubble. In contrast, in the limit of large Bo, a downward jet develops at the front part and pierces the rear of the bubble, unless viscous effects are sufficient to stabilize the front. We also determine the position of the transition for intermediate values of Bo and Ar and discuss the connection between present axisymmetric results and experimental situations in which the bubble is followed by a turbulent wake. We finally examine a puzzling feature of these large bubbles which is that, given an initial gas volume, the final bubble topology appears to depend dramatically on the initial conditions. Indeed, we find that initially oblate bubbles may result in stable spherical cap bubbles for values of Bo and Ar well beyond those for which initially spherical bubbles of similar volume undergo the topological transition. This remarkable influence of the initial shape is shown to be due to the influence of the oblateness on both the bubble acceleration and the hydrostatic pressure difference between the two bubble poles.
Quantitative laboratory observations of internal wave reflection on ascending slopes
Authors: Gostiaux Louis , Dauxois Thierry , Didelle Henri , Sommeria Joel , Viboud Samuel
Published: August 2006

Internal waves propagate obliquely through a stratified fluid with an angle that is fixed with respect to gravity. Upon reflection on a sloping bed, striking phenomena are expected to occur close to the slope. We present here laboratory observations at moderately large Reynolds number. A particle image velocimetry technique is used to provide time-resolved velocity fields in large volumes. Generation of the second and third harmonic frequencies is clearly demonstrated in the impact zone. The mechanism for nonlinear wavelength selection is also discussed. Evanescent waves with frequency larger than the Brunt-Väisälä frequency are detected and experimental results agree very well with theoretical predictions. The amplitude of the different harmonics after reflection is also obtained.
Nonlinear simulation of free surfaces and atomization in pressure swirl atomizers
Authors: Park Hongbok , Heister Stephen D.
Published: August 2006

A fully nonlinear boundary element method (BEM) model has been developed to simulate the pressure swirl or simplex atomizer. The free surface inside the vortex chamber and within the hollow-cone/primary atomization zone is simulated with a fourth order scheme thereby permitting investigation of highly distorted surfaces up to the point where atomization occurs. For the axisymmetric calculations, annular rings of fluid are pinched from the main liquid domain. Swirling flow is simulated via a superposition of a potential vortex with the base axial flow emanating from the nozzle in a BEM formulation. Results show good comparison to film thicknesses from test data as well as from linear one-dimensional theory. Parametric studies are conducted to assess the influence of injector geometry and flow characteristics on film thickness and spray angle produced by the atomizer. Limited results are also provided to compare droplet sizes with experimental data. In this regard, the linear stability analysis of Ponstein is used to predict the number of droplets created from each ring of fluid shed by the axisymmetric calculation.