A note on the prediction of liquid hold-up with the stratified roll wave regime for gas/liquidco-current flow in horizontal pipes.

This note presents a simple model for prediction of liquid hold-up in two-phase horizontal pipe flow for the stratified roll wave (St+RW) flow regime. Liquid hold-up data for horizontal two-phase pipe flow [1, 2, 3, 4, 5 and 6] exhibit a steady increase with liquid velocity and a more dramatic fall with increasing gas rate as shown by Hand et al. [7 and 8] for example. In addition the liquid hold-up is reported to show an additional variation with pipe diameter. Generally, if the initial liquid rate for the no-gas flow condition gives a liquid height below the pipe centre line, the flow patterns pass successively through the stratified (St), stratified ripple (St+R), stratified roll wave, film plus droplet (F+D) and finally the annular (A+D, A+RW, A+BTS) regimes as the gas rate is increased. Hand et al. [7 and 8] have given a detailed description of this progression in flow regime development and definitions of the patterns involved. Despite the fact that there are over one hundred models which have been developed to predict liquid hold-up, none have been shown to be universally useful, while only a handful have proven to be applicable to specific flow regimes [9, 10, 11 and 12]. One of the most intractable regimes to predict has been the stratified roll wave pattern where the liquid hold-up shows the most dramatic change with gas flow rate. It has been suggested that the momentum balance-type models, which give both hold-up and pressure drop prediction, can predict universally for all flow regimes but particularly in the case of the difficult stratified roll wave pattern. Donnelly [1] recently demonstrated that the momentum balance models experienced some difficulties in the prediction of this regime. Without going into lengthy details, these models differ in the assumed friction factor or shear stress on the surfaces within the pipe particularly at the liquid–gas interface. The Baker–Jardine model [13] when tested against the 0.0454 m i.d. data of Nguyen [2] exhibited a wide scatter for both liquid hold-up and pressure drop as shown in Fig. 1. The Andritsos–Hanratty model [14] gave better prediction of pressure drop but a wide scatter for liquid hold-up estimation (cf. Fig. 2) when tested against the 0.0935 m i.d. data of Hand [5]. The Spedding–Hand model [15], shown in Fig. 3 against the data of Hand [5], gave improved performance but was still unsatisfactory with the prediction of hold-up for stratified-type flows. The MARS model of Grolman [6] gave better prediction of hold-up (cf. Fig. 4) but deterioration in the estimation of pressure drop when tested against the data of Nguyen [2]. Thus no method is available that will accurately predict liquid hold-up across the whole range of flow patterns but particularly for the stratified plus roll wavy regime. The position is particularly unfortunate since the stratified-type regimes are perhaps the most predominant pattern found in multiphase lines.

Kv1.5 is a major component underlying the A-type potassium current in retinal arteriolar smooth muscle.

Little is known about the molecular characteristics of the voltage-activated K(+) (K(v)) channels that underlie the A-type K(+) current in vascular smooth muscle cells of the systemic circulation. We investigated the molecular identity of the A-type K(+) current in retinal arteriolar myocytes using patch-clamp techniques, RT-PCR, immunohistochemistry, and neutralizing antibody studies. The A-type K(+) current was resistant to the actions of specific inhibitors for K(v)3 and K(v)4 channels but was blocked by the K(v)1 antagonist correolide. No effects were observed with pharmacological agents against K(v)1.1/2/3/6 and 7 channels, but the current was partially blocked by riluzole, a K(v)1.4 and K(v)1.5 inhibitor. The current was not altered by the removal of extracellular K(+) but was abolished by flecainide, indicative of K(v)1.5 rather than K(v)1.4 channels. Transcripts encoding K(v)1.5 and not K(v)1.4 were identified in freshly isolated retinal arterioles. Immunofluorescence labeling confirmed a lack of K(v)1.4 expression and revealed K(v)1.5 to be localized to the plasma membrane of the arteriolar smooth muscle cells. Anti-K(v)1.5 antibody applied intracellularly inhibited the A-type K(+) current, whereas anti-K(v)1.4 antibody had no effect. Co-expression of K(v)1.5 with K(v)beta1 or K(v)beta3 accessory subunits is known to transform K(v)1.5 currents from delayed rectifers into A-type currents. K(v)beta1 mRNA expression was detected in retinal arterioles, but K(v)beta3 was not observed. K(v)beta1 immunofluorescence was detected on the plasma membrane of retinal arteriolar myocytes. The findings of this study suggest that K(v)1.5, most likely co-assembled with K(v)beta1 subunits, comprises a major component underlying the A-type K(+) current in retinal arteriolar smooth muscle cells

Characterization of T-type calcium current and its contribution to electrical activity in rabbit urethra.

Rabbit urethral smooth muscle cells were studied at 37 degrees C by using the amphotericin B perforated-patch configuration of the patch-clamp technique, using Cs(+)-rich pipette solutions. Two components of current, with electrophysiological and pharmacological properties typical of T- and L-type Ca(2+) currents, were recorded. Fitting steady-state inactivation curves for the L current with a Boltzmann equation yielded a V(1/2) of -41 +/- 3 mV. In contrast, the T current inactivated with a V(1/2) of -76 +/- 2 mV. The L currents were reduced by nifedipine (IC(50) = 225 +/- 84 nM), Ni(2+) (IC(50) = 324 +/- 74 microM), and mibefradil (IC(50) = 2.6 +/- 1.1 microM) but were enhanced when external Ca(2+) was substituted with Ba(2+). The T current was little affected by nifedipine at concentrations

Electrochemical Oxidation of Hydrogen Sulfide at Platinum Electrodes in Room Temperature Ionic Liquids: Evidence for Significant Accumulation of H2S at the Pt/1-Butyl-3-methylimidazolium Trifluoromethylsulfonate Interface

Electrochemical oxidation of hydrogen sulfide gas (H2S) has been studied at a platinum microelectrode (10 mu m diameter) in five room temperature ionic liquids (RTILs): [C(4)mim][OTf], [C(4)dmim][NTf2], [C(4)mim][PF6],. [C(6)mim][FAP], and [P-14,P-6,P-6,P-6][FAP] (where [C-n mim](+) = 1-alkyl-3-methylimidazolium, [C(n)dmim](+) = 1-alkyl-2,3-dimethylimidazolium, [P-14,P-6,P-6,P-6](+) = tris(p-hexyl)-tetradecylphosphonium, [OTf](-) = trifluoromethlysulfonate, [NTf2](-) = bis(trifluoromethylsulfonyl)imide, [PF6](-) = hexafluorophosphate, and [FAP](-) = trifluorotris(pentafluoroethyl)phosphate). In four of the RTILs ([C(4)dmim][NTf2], [C(4)mim][PF6], [C(6)mim][FAP], and [P-14,P-6,P-6,P-6][FAP]), no clear oxidative signal was observed. In [C(4)mim][OTf], a chemically irreversible oxidation peak was observed on the oxidative sweep with no signal seen on the reverse scan. The oxidative signal showed an adsorptive stripping peak type followed by near steady-state limiting current behavior. Potential step chronoamperometry was carried out on the reductive wave, giving a diffusion coefficient and solubility of 1.6 x 10(-11) m(2) s(-1) and 7 mM, respectively (at 25 degrees C). Using these data, we modeled the oxidation signal kinetically, assuming adsorption preceded oxidation and that adsorption was approximately Langmuirian. The oxidation step was described by an electrochemically fully irreversible Tafel law/Butler-Volmer formalism. Modeling indicated a substantial buildup of H2S in the double layer in excess of the coverage that would be expected for a monolayer of chemisorbed H2S, reflecting high solubility of the gas in [C(4)mim][OTf] and possible attractive interactions with the [OTf](-) anions accumulated at the electrode at potentials positive of the potential of zero charge. Solute enrichment of the double layer in the solution adjacent to the electrode appears a novel feature of RTIL electrochemistry.

Asymptotic layer-type model of high pressure direct current glow discharge in electronegative gases

Here a self-consistent one-dimensional continuum model is presented for a narrow gap plane-parallel dc glow discharge. The governing equations consist of continuity and momentum equations for positive and negative ions and electrons coupled with Poisson's equation. A singular perturbation method is developed for the analysis of high pressure dc glow discharge. The kinetic processes of the ionization, electron attachment, and ion-ion recombination are included in the model. Explicit results are obtained for the asymptotic limits: delta=(r(D)/L)(2)--> 0, omega=(r(S)/L)(2)--> 0, where r(D) is the Debye radius, r(S) is recombination length, and L is the gap length. The discharge gap divides naturally into four layers with multiple space scales: anode fall region, positive column, transitional region, cathode fall region and diffusion layer adjacent to the cathode surface, its formation is discussed. The effects of the gas pressure, gap spacing and dc voltage on the electrical properties of the layers and its dimension are investigated. (C) 2000 American Institute of Physics. [S0021-8979(00)00813-6].

Recombinant alpha 2(IV)NC1 domain of type IV collagen is an effective regulator of retinal capillary endothelial cell proliferation and inhibits pre-retinal neovascularisation

Background A recombinant form of the alpha 2(IV)NC1 domain of type IV collagen has been shown to have potent anti-angiogenic activity although this peptide has not been studied in the context of proliferative retinopathies. In the current investigation we examined the potential for alpha 2(IV) NC1 to regulate retinal microvascular endothelial cell function using a range of in vitro and in vivo assay systems.

Ca(2+)-activated Cl(-) current in sheep lymphatic smooth muscle.

Freshly dispersed sheep mesenteric lymphatic smooth muscle cells were studied at 37 degrees C using the perforated patch-clamp technique with Cs(+)- and K(+)-filled pipettes. Depolarizing steps evoked currents that consisted of L-type Ca(2+) [I(Ca(L))] current and a slowly developing current. The slow current reversed at 1 +/- 1.5 mV with symmetrical Cl(-) concentrations compared with 23.2 +/- 1.2 mV (n = 5) and -34.3 +/- 3.5 mV (n = 4) when external Cl(-) was substituted with either glutamate (86 mM) or I(-) (125 mM). Nifedipine (1 microM) blocked and BAY K 8644 enhanced I(Ca(L)), the slow-developing sustained current, and the tail current. The Cl(-) channel blocker anthracene-9-carboxylic acid (9-AC) reduced only the slowly developing inward and tail currents. Application of caffeine (10 mM) to voltage-clamped cells evoked currents that reversed close to the Cl(-) equilibrium potential and were sensitive to 9-AC. Small spontaneous transient depolarizations and larger action potentials were observed in current clamp, and these were blocked by 9-AC. Evoked action potentials were triphasic and had a prominent plateau phase that was selectively blocked by 9-AC. Similarly, fluid output was reduced by 9-AC in doubly cannulated segments of spontaneously pumping sheep lymphatics, suggesting that the Ca(2+)-activated Cl(-) current plays an important role in the electrical activity underlying spontaneous activity in this tissue. PMID: 11029279 [PubMed - indexed for MEDLINE]

Ca2+ current and Ca(2+)-activated chloride current in isolated smooth muscle cells of the sheep urethra.

1. Isolated sheep urethral cells were studied using the perforated patch clamp technique (T = 37 degrees C). Depolarizing steps ranging from -40 to -10 mV evoked an inward current that peaked within 10 ms and a slower inward current. Stepping back to the holding potential of -80 mV evoked large inward tail currents. All three currents were abolished by nifedipine (1 microM). Substitution of external Ca2+ with Ba2+ resulted in potentiation of the fast inward current and blockade of the slow current and tails. 2. Changing the chloride equilibrium potential (ECl) from 0 to +27 mV shifted the reversal potential of the tail currents from 1 +/- 1 to 27 +/- 1 mV (number of cells, n = 5). Chloride channel blockers, niflumic acid (10 microM) and anthracene-9-carboxylic acid (9AC, 1 mM), reduced the slow current and tails suggesting that these were Ca(2+)-activated Cl- currents, ICl(Ca). 4. Caffeine (10 mM) induced currents that reversed at ECl and were blocked by niflumic acid (10 microM). 5. In current clamp mode, some cells developed spontaneous transient depolarizations (STDs) and action potentials. Short exposure to nifedipine blocked the action potentials and unmasked STDs. In contrast, 9AC and niflumic acid reduced the amplitude of the STDs and blocked the action potentials. 6. In conclusion, these cells have both L-type ICa and ICl(Ca). The former appears to be responsible for the upstroke of the action potential, while the latter may act as a pacemaker current.

CaIIKinterstellar observations towards early-type disc and halo stars, abundances and distances of intermediate- and high-velocity clouds

We present Ca II K (lambda(air) = 3933.661 angstrom) interstellar observations towards 20 early-type stars, to place lower distance limits to intermediate- and high-velocity clouds (IHVCs) in their lines of sight. The spectra are also employed to estimate the Ca abundance in the low-velocity gas towards these objects, when combined with Leiden-Dwingeloo 21-cm HI survey data of spatial resolution 0 degrees.5. Nine of the stars, which lie towards IHVC complexes H, K and gp, were observed with the intermediate dispersion spectrograph on the Isaac Newton Telescope at a resolution R = lambda/Delta lambda of 9000 (similar to 33 km s(-1)) and signal-to-noise ratio (S/N) per pixel of 75-140. A further nine objects were observed with the Utrecht Echelle Spectrograph on the William Herschel Telescope at R = 40 000 (similar to 7.5 km s(-1)) and S/N per pixel of 10-25. Finally, two objects were observed in both Ca II K and Na I D lines using the 2D COUDE on the McDonald 2.7-m telescope at R = 35 000 (similar to 8.5 km s(-1)). The abundance of Ca II K {log(10)(A) = log(10)[N(Ca II K)]-log(10)[N(HI)]} plotted against HI column density for the objects in the current sample with heights above the Galactic plane (z) exceeding 1000 pc is found to obey the Wakker & Mathis (2000) relation. Also, the reduced column density of Ca II K as function of z is consistent with the larger sample taken from Smoker et al. (2003). Higher S/N observations than those previously taken towards HVC complex H stars HD 13256 and HILT 190 reinforce the assertion that this lies at a distance exceeding 4000 pc. No obvious absorption is detected in observations of ALS 10407 and HD 357657 towards IVC complex gp. The latter star has a spectroscopically estimated distance of similar to 2040 pc, although this was derived assuming the star lies on the main sequence and without any reddening correction being applied. Finally, no Ca II K absorption is detected towards two stars along the line of sight to complex K, namely PG 1610+529 and PG 1710+490. The latter is at a distance of similar to 700 pc, hence placing a lower distance limit to this complex, where previously only an upper distance limit of 6800 pc was available.

Understanding B-type supergiants in the low metallicity environment of the SMC

Spectroscopic analyses of 7 SMC B-type supergiants and 1 giant have been undertaken using high resolution optical data obtained on the VLT with UVES. FASTWIND, a non-LTE, spherical, line-blanketed model atmosphere code was used to derive atmospheric and wind parameters of these stars as well as their absolute abundances. Mass-loss rates, derived from H-alpha profiles, are in poor agreement with metallicity dependent theoretical predictions. Indeed the wind-momenta of the SMC stars appear to be in good agreement with the wind-momentum luminosity relationship (WLR) of Galactic B-type stars, a puzzling result given that line-driven wind theory predicts a metallicity dependence. However the galactic stars were analysed using unblanketed model atmospheres which may mask any dependence on metallicity. A mean nitrogen enhancement of a factor of 14 is observed in the supergiants whilst only an enrichment of a factor of 4 is present in the giant, AV216. Similar excesses in nitrogen are observed in O-type dwarfs and supergiants in the same mass range, suggesting that the additional nitrogen is produced while the stars are still on the main-sequence. These nitrogen enrichments can be reproduced by current stellar evolution models, which include rotationally induced mixing, only if large initial rotational velocities of 300 kin s(-1) are invoked. Such large rotational velocities appear to be inconsistent with observed v sin i distributions for O-type stars and B-type supergiants. Hence it is suggested that the currently available stellar evolution models require more efficient mixing for lower rotational velocities.

High-density and low electron temperature direct current reflex plasma source

A new type of direct current, high-density, and low electron temperature reflex plasma source, obtained as a hybrid between a modified hollow-cathode discharge and a Penning ionization gauge discharge is presented. The plasma source was tested in argon, nitrogen, and oxygen over a range pressure of 1.0-10(-3) mbar, discharge currents 20-200 mA, and magnetic field 0-120 Gauss. Both external parameters, such as breakdown potential and the discharge voltage-current characteristic, and its internal parameters, like the electron energy distribution function, electron and ion densities, and electron temperature, were measured. Due to the enhanced hollow-cathode effect by the magnetic trapping of electrons, the density of the bulk plasma is as high as 10(18) m(-3), and the electron temperature is as low as a few tenths of electron volts. The plasma density scales with the dissipated power. Another important feature of this reflex plasma source is its high degree of uniformity, while the discharge bulk region is free of an electric field. (C) 2004 American Institute of Physics.

Ca2+-activated Cl- current in retinal arteriolar smooth muscle.

PURPOSE: To characterize the biophysical, pharmacologic, and functional properties of the Ca(2+)-activated Cl(-) current in retinal arteriolar myocytes. METHODS: Whole-cell perforated patch-clamp recordings were made from myocytes within intact isolated arteriolar segments. Arteriolar tone was assessed using pressure myography. RESULTS: Depolarizing of voltage steps to -40 mV and greater activated an L-type Ca(2+) current (I(Ca(L))) that was followed by a sustained current. Large tail currents (I(tail)) were observed on stepping back to -80 mV. The sustained current and I(tail) reversed close to 0 mV in symmetrical Cl(-) concentrations. The ion selectivity sequence for I(tail) was I(-)> Cl(-)> glucuronate. Outward I(tail) was sensitive to the Cl(-) channel blockers 9-anthracene-carboxylic acid (9-AC; 1 mM), 4-acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic acid (SITS; 1 mM), and disodium 4,4'-diisothiocyanatostilbene-2,2'-disulfonate (DIDS; 1 mM), but only DIDS produced a substantial (78%) block of inward tail currents at -100 mV. I(tail) was decreased in magnitude when the normal bathing medium was substituted with Ca(2+)-free solution or if I(Ca(L)) was inhibited by 1 microM nimodipine. Caffeine (10 mM) produced large transient currents that reversed close to the Cl(-) equilibrium potential and were blocked by 1 mM DIDS or 100 microM tetracaine. DIDS had no effect on basal vascular tone in pressurized arterioles but dramatically reduced the level of vasoconstriction observed in the presence of 10 nM endothelin-1. CONCLUSIONS: Retinal arteriolar myocytes have I(Cl(Ca)), which may be activated by Ca(2+) entry through L-type Ca(2+) channels or Ca(2+) release from intracellular stores. This current appears to contribute to agonist-induced retinal vasoconstriction.

WASP-10b: a 3M(J), gas-giant planet transiting a late-type K star

We report the discovery of WASP-10b, a new transiting extrasolar planet (ESP) discovered by the Wide Angle Search for Planets ( WASP) Consortium and confirmed using Nordic Optical Telescope FIbre-fed Echelle Spectrograph and SOPHIE radial velocity data. A 3.09-d period, 29 mmag transit depth and 2.36 h duration are derived for WASP-10b using WASP and high-precision photometric observations. Simultaneous fitting to the photometric and radial velocity data using a Markov Chain Monte Carlo procedure leads to a planet radius of 1.28R(J), a mass of 2.96M(J) and eccentricity of approximate to 0.06. WASP-10b is one of the more massive transiting ESPs, and we compare its characteristics to the current sample of transiting ESP, where there is currently little information for masses greater than approximate to 2M(J) and non-zero eccentricities. WASP-10's host star, GSC 2752-00114 (USNO-B1.0 1214-0586164) is among the fainter stars in the WASP sample, with V = 12.7 and a spectral type of K5. This result shows promise for future late-type dwarf star surveys.

Atmospheric parameters and rotational velocities for a sample of Galactic B-type supergiants

High-resolution optical spectra of 57 Galactic B-type supergiant stars have been analysed to determine their rotational and macroturbulent velocities. In addition, their atmospheric parameters (effective temperature, surface gravity and microturbulent velocity) and surface nitrogen abundances have been estimated using a non-local thermodynamic equilibrium grid of model atmospheres. Comparisons of the projected rotational velocities have been made with the predictions of stellar evolutionary models and in general good agreement was found. However, for a small number of targets, their observed rotational velocities were significantly larger than predicted, although their nitrogen abundances were consistent with the rest of the sample. We conclude that binarity may have played a role in generating their large rotational velocities. No correlation was found between nitrogen abundances and the current projected rotational velocities. However, a correlation was found with the inferred projected rotational velocities of the main-sequence precursors of our supergiant sample. This correlation is again in agreement with the predictions of single star evolutionary models that incorporate rotational mixing. The origin of the macroturbulence and microturbulent velocity fields is discussed and our results support previous theoretical studies that link the former to subphotospheric convection and the latter to non-radial gravity mode oscillations. In addition, we have attempted to identify differential rotation in our most rapidly rotating targets.