Hydrodynamics and mixer-induced bubble formation in micro bubble columns with single and multiple-channels

A hydrodynamic characterization of an industrially used gas-liquid contacting microchannel. device is discussed, viz. the micro bubble column of IMM. Furthermore, similar characterization of a gas-liquid flow microchip of TU/e, with two tailored mixer designs, is used to solve fundamental issues on hydrodynamics, and therefore, to achieve further design and operating optimization of that chip and the IMM device. Flow pattern maps are presented in a dimensionless fashion for further predictions on new fluidic systems for optimum single-channel multiphase operation. Bubble formation was investigated in the two types of mixers and pinch-off and hydrodynamic decay mechanisms are observed. The impact of these mechanisms on bubble size, bubble size distributions, and on the corresponding flow patterns, i.e., the type of mixer design, can be decisive for the flow pattern map and thus, may be used to alter flow pattern maps. The bubble sizes and their distribution were improved for the tailored designs, i.e., smaller and more regular bubbles were generated. Finally, the impact of multi-channel distribution for gas and liquid flow is demonstrated. Intermediate flow patterns such as slug-annular flow, also found for single-phase operation, and the simultaneous coexistence of flow regimes are presented, with the latter providing evidence of flow maldistribution.

Feedback via Ca²⁺-activated ion channels modulates endothelin 1 signaling in retinal arteriolar smooth muscle

PURPOSE: To investigate the role of feedback by Ca²?-sensitive plasma-membrane ion channels in endothelin 1 (Et1) signaling in vitro and in vivo. Methods. Et1 responses were imaged from Fluo-4-loaded smooth muscle in isolated segments of rat retinal arteriole using two-dimensional (2-D) confocal laser microscopy. Vasoconstrictor responses to intravitreal injections of Et1 were recorded in the absence and presence of appropriate ion channel blockers using fluorescein angiograms imaged using a confocal scanning laser ophthalmoscope. Results. Et1 (10 nM) increased both basal [Ca²?](i) and the amplitude and frequency of Ca²?-waves in retinal arterioles. The Ca²?-activated Cl?-channel blockers DIDS and 9-anthracene carboxylic acid (9AC) blocked Et1-induced increases in wave frequency, and 9AC also inhibited the increase in amplitude. Iberiotoxin, an inhibitor of large conductance (BK) Ca²?-activated K?-channels, increased wave amplitude in the presence of Et1 but had no effect on frequency. None of these drugs affected basal [Ca²?](i). The voltage-operated Ca²?-channel inhibitor nimodipine inhibited wave frequency and amplitude and also lowered basal [Ca²?](i) in the presence of Et1. Intravitreal injection of Et1 caused retinal arteriolar vasoconstriction. This was inhibited by DIDS but not by iberiotoxin or penitrem A, another BK-channel inhibitor. Conclusions. Et1 evokes increases in the frequency of arteriolar Ca²?-waves in vitro, resulting in vasoconstriction in vivo. These responses, initiated by release of stored Ca²?, also require positive feedback via Ca²?-activated Cl?-channels and L-type Ca²?-channels.

Relativistic laser interactions with preformed plasma channels and gamma-ray measurements

The propagation of a 1-ps laser pulse at intensities exceeding 10(19) Wcm(-2) in a low-density plasma channel was experimentally tested. The channel was produced by a lower intensity preceding pulse of the same duration. Plasma electrons were accelerated during the propagation of the main pulse, and high energy gamma -ray detectors were used to detect their bremsstrahlung emission. The gamma -ray yield was studied for different channel conditions, by varying the delay between the channel forming pulse and the high intensity pulse. These results are correlated with the interferograms of the propagation region into the plasma.

Observations of collimated ionization channels in aluminum-coated glass targets irradiated by ultraintense laser pulses

Filamentary ionization tracks have been observed via optical probing inside Al-coated glass targets after the interaction of a picosecond 20-TW laser pulse at intensities above 10(19) W/cm(2). The tracks, up to 700 mu m in length and between 10 and 20 mu m in width, originate from the focal spot region of the laser beam. Simulations performed with 3D particle-in-cell and 2D Fokker-Planck hybrid codes indicate that the observations are consistent with ionization induced in the glass target by magnetized, collimated beams of high-energy electrons produced during the laser interaction.

Interaction of intense laser pulses with preformed density channels

The interaction of a high-intensity laser pulse with a plasma density channel preformed in a gas jet target has been studied. At neutral densities below 3.0 X 10(19) cm(-3) a strong interaction between the pulse and the channel walls was observed, there was clear evidence of pulse confinement, and the laser irradiance was significantly increased compared to an interaction with neutral gas. At higher gas densities, however, the radial uniformity and length of the channel were both found to be adversely affected by refractive defocusing of the prepulse used to generate the channel.

Nifedipine blocks Ca2+ store refilling through a pathway not involving L-type Ca2+ channels in rabbit arteriolar smooth muscle

This study assessed the contribution of L-type Ca2+ channels and other Ca2+ entry pathways to Ca2+ store refilling in choroidal arteriolar smooth muscle. Voltage-clamp recordings were made from enzymatically isolated choroidal microvascular smooth muscle cells and from cells within vessel fragments (containing <10 cells) using the whole-cell perforated patch-clamp technique. Cell Ca2+ was estimated by fura-2 microfluorimetry. After Ca2+ store depletion with caffeine (10 mM), refilling was slower in cells held at -20 mV compared to -80 mV (refilling half-time was 38 +/- 10 and 20 +/- 6 s, respectively). To attempt faster refilling via L-type Ca2+ channels, depolarising steps from -60 to -20 mV were applied during a 30 s refilling period following caffeine depletion. Each step activated L-type Ca2+ currents and [Ca2+]i transients, but failed to accelerate refilling. At -80 mV and in 20 mM TEA, prolonged caffeine exposure produced a transient Ca2+-activated Cl- current (I(Cl)(Ca)) followed by a smaller sustained current. The sustained current was resistant to anthracene-9-carboxylic acid (1 mM; an I(Cl)(Ca) blocker) and to BAPTA AM, but was abolished by 1 microM nifedipine. This nifedipine-sensitive current reversed at +29 +/- 2 mV, which shifted to +7 +/- 5 mV in Ca2+-free solution. Cyclopiazonic acid (20 microM; an inhibitor of sarcoplasmic reticulum Ca2+-ATPase) also activated the nifedipine-sensitive sustained current. At -80 mV, a 5 s caffeine exposure emptied Ca2+ stores and elicited a transient I(Cl)(Ca). After 80 s refilling, another caffeine challenge produced a similar inward current. Nifedipine (1 microM) during refilling reduced the caffeine-activated I(Cl)(Ca) by 38 +/- 5 %. The effect was concentration dependent (1-3000 nM, EC50 64 nM). In Ca2+-free solution, store refilling was similarly depressed (by 46 +/- 6 %). Endothelin-1 (10 nM) applied at -80 mV increased [Ca2+]i, which subsided to a sustained 198 +/- 28 nM above basal. Cell Ca2+ was then lowered by 1 microM nifedipine (to 135 +/- 22 nM), which reversed on washout. These results show that L-type Ca2+ channels fail to contribute to Ca2+ store refilling in choroidal arteriolar smooth muscle. Instead, they refill via a novel non-selective store-operated cation conductance that is blocked by nifedipine.

Numbered-up gas-liquid micro/milli channels reactor with modular flow distributor

Gas-liquid processing in microreactors remains mostly restricted to the laboratory scale due to the complexity and expenditure needed for an adequate numbering-up with a uniform flow distribution. Here, the numbering-up is presented for multi-phase (gas-liquid) flow in microreactor suitable for a production capacity of kg/h. Based on the barrier channels concept, the barrier-based micro/milli reactor (BMMR) is designed and fabricated to deliver flow non-uniformity of less than 10%. The BMMR consists of eight parallel channels all operated in the Taylor flow regime and with a liquid flow rate up to 150. mL/min. The quality of the flow distribution is reported by studying two aspects. The first aspect is the influence of different viscosities, surface tensions and flow rates. The second aspect is the influence of modularity by testing three different reaction channels type: (1) square channels fabricated in a stainless steel plate, (2) square channels fabricated in a glass plate, and (3) circular channels (capillaries) made of stainless steel. Additionally, the BMMR is compared to that of a single channel regard the slug and bubble lengths and bubble generation frequency. The results pave the ground for bringing multi-phase flow in microreactor one step closer for large scale production via numbering-up. © 2012 Elsevier B.V.