Novel design for transparent high-pressure fuel injector nozzles.

The efficiency and emissions of internal combustion (IC) engines are closely tied to the formation of the combustible air-fuel mixture. Direct-injection engines have become more common due to their increased practical flexibility and efficiency, and sprays dominate mixture formation in these engines. Spray formation, or rather the transition from a cylindrical liquid jet to a field of isolated droplets, is not completely understood. However, it is known that nozzle orifice flow and cavitation have an important effect on the formation of fuel injector sprays, even if the exact details of this effect remain unknown. A number of studies in recent years have used injectors with optically transparent nozzles (OTN) to allow observation of the nozzle orifice flow. Our goal in this work is to design various OTN concepts that mimic the flow inside commercial injector nozzles, at realistic fuel pressures, and yet still allow access to the very near nozzle region of the spray so that interior flow structure can be correlated with primary breakup dynamics. This goal has not been achieved until now because interior structures can be very complex, and the most appropriate optical materials are brittle and easily fractured by realistic fuel pressures. An OTN design that achieves realistic injection pressures and grants visual access to the interior flow and spray formation will be explained in detail. The design uses an acrylic nozzle, which is ideal for imaging the interior flow. This nozzle is supported from the outside with sapphire clamps, which reduces tensile stresses in the nozzle and increases the nozzle's injection pressure capacity. An ensemble of nozzles were mechanically tested to prove this design concept.

Analysis of multiple scattering suppression using structured laser illumination planar imaging in scattering and fluorescing media.

The accuracy, precision and limitations of the imaging technique named Structured Laser Illumination Planar Imaging (SLIPI) have been investigated. SLIPI, which allows multiply scattered light to be diminished, has previously demonstrated improvements in image quality and contrast for spray imaging. In the current study the method is applied to a controlled confined environment consisting of a mixture of water and monodisperse polystyrene microspheres. Elastic scattering and fluorescence are studied and the results obtained when probing different particle concentrations and diameters conclusively show the advantages of SLIPI for imaging within moderately turbid media. Although the technique presents both good repeatability and agreement with the Beer-Lambert law, discrepancies in its performance were, however, discovered. Photons undergoing scattering without changing their incident trajectory cannot be discriminated and, owing to differences in scattering phase functions, probing larger particles reduces the suppression of multiply scattered light. However, in terms of visibility such behavior is beneficial as it allows denser media to be probed. It is further demonstrated that the suppression of diffuse light performs equally well regardless of whether photons propagate along the incident direction or towards the camera. In addition, this filtering process acts independently on the spatial distribution of the multiply scattered light but is limited by the finite dynamic range and unavoidable signal noise of the camera.

Modeling of Neuronal Growth In Vitro: Comparison of Simulation Tools NETMORPH and CX3D.

We simulate the growth of neuronal networks using the two recently published tools, NETMORPH and CX3D. The goals of the work are (1) to examine and compare the simulation tools, (2) to construct a model of growth of neocortical cultures, and (3) to characterize the changes in network connectivity during growth, using standard graph theoretic methods. Parameters for the neocortical culture are chosen after consulting both the experimental and the computational work presented in the literature. The first (three) weeks in culture are known to be a time of development of extensive dendritic and axonal arbors and establishment of synaptic connections between the neurons. We simulate the growth of networks from day 1 to day 21. It is shown that for the properly selected parameters, the simulators can reproduce the experimentally obtained connectivity. The selected graph theoretic methods can capture the structural changes during growth.

[Air embolism during lumbar discal hernia repair. Retroperioneal vessels lesions have to be suspected]. / Symptomatologie d'embolie gazeuse au cours d'une chirurgie de hernie discale lombaire: suspecter une plaie vasculaire rétropéritonéale.

Occurrence of deep PETCO(2) drop during surgical lumbar disk repair is rare but dramatic. This case report leads to the diagnosis of retroperitoneal vessels lesions. We review the different diagnosis related to the drop of the PETCO(2) during surgery in the genupectoral position. We recommend that the diagnosis of retroperitoneal vessels lesion have to be suspected early if air embolism occurs during lumbar disk surgery.

Electrical detection of the contact between a microinjection pipette and cells.

This work presents the basic design and tests of a device designed for detecting the contact between a microinjection pipette and cell membrane. The device facilitates the automation of the microinjection procedure of living adherent cells. The measurement of the contact is based on measuring the resistance of the pipette. Breakage and clogging of the pipette can be detected with the same measurement.

Development of a cavity ringdown laser absorption spectrometer for detection of trace levels of mercury.

A potential new laser-based air pollution measurement technique, capable of measuring ultralow concentrations of urban air toxins in the field and in real time, is examined. Cavity ringdown laser absorption spectroscopy (CRLAS) holds promise as an air pollution monitor because it is a highly sensitive species detection technique that uses either pulsed or continuous tunable laser sources. The sensitivity results from an extremely long absorption path length and the fact that the quantity measured, the cavity decay time, is unaffected by fluctuations in the laser source. In laboratory experiments, we reach detection limits for mercury of the order of 0.50 parts per trillion. We developed a CRLAS system in our laboratory and measured Hg with the system, investigating issues such as background interference. We report experimental results for mercury detection limits, the dynamic range of the sensor, detection of Hg in an absorbing background of ozone and SO(2), and detection of a mercury-containing compound (HgCl(2) in this case).

Fixed-frequency cavity ringdown diagnostic for atmospheric particulate matter.

A nonresonant cavity ringdown diagnostic to measure light attenuation from atmospheric particulate matter at 532- and 355-nm wavelengths is described. The presence of atmospheric particulate is clearly detectable with this technique, as demonstrated by experimental results. The extinction cross section is higher at 355 than at 532 nm, although we were able to purchase significantly higher-reflectivity optics at 532 nm. The expected advantage at 355 nm is thus lost. This new technique is compared with a commercially available instrument, and sensitivity limitations are discussed.

Serotonin induces inward potassium and calcium currents in rat cortical astrocytes.

Ca2+ imaging and patch-clamp techniques were used to study the effects of serotonin (5-HT) on ionic conductances in rat cortical astrocytes. 1 and 10 microM serotonin caused a transient increase in intracellular calcium (Ca(i)) levels in fura-2AM-loaded cultured astrocytes and in astrocytes acutely isolated and then cultured in horse serum-containing medium for over 24 h. However, the acutely isolated (less than 6 h from isolation) astrocytes, as well as acutely isolated astrocytes cultured in serum-free media, failed to respond to 5-HT by changes in Ca(i). Coinciding with the changes in Ca(i) levels, inward currents were activated by 10 microM 5-HT in cultured, but not in acutely isolated astrocytes. Two separate types of serotonin-induced, small-conductance inward single-channel currents were found. First, in both Ca2+-containing and Ca2+-free media serotonin transiently activated a small-conductance apamin-sensitive channel. Apamin is a specific blocker of the small-conductance Ca2+-activated K+ channel (sK(Ca)) When cells were pre-treated with phospholipase C inhibitor U73122 no 5-HT-induced sK(Ca) channel openings were seen, indicating that this channel was activated by Ca2+ released from intracellular stores via IP3. A second type of small inward channel activated later, but only in the presence of external Ca2+. It was inhibited by the L-type Ca2+ channel blockers, nimodipine and nifedipine. Both types of channel activity were inhibited by ketanserin, indicating activation of the 5-HT2A receptor.

Simultaneous detection of action potential current waveforms and single ion channel openings in rat cerebellar granule cells.

Spontaneous Action Potential Current waveforms (APCs) and single ion channel openings were recorded in cultured rat cerebellar granule cells using the cell-attached configuration of the patch-clamp technique. APCs were activated without any externally applied stimuli. Both mono- and biphasic APCs were detected with a typical amplitude (positive waveform component) of 25-60 pA. Correlation between cell APCs and inward and outward single ion channel openings immediately before and after the capacitive transients was analyzed. In a detailed analysis it was found that the opening of 1.5 pA inward channel before the waveform was associated with 16%, and the opening of 1.0 pA outward channel after the waveform with 88% of APCs (of total 327 APCs analyzed). The modulation of APC activity by bath application of the amino acid taurine was found to increase the frequency of APCs, transform the APCs from mixed monophasic/biphasic to completely biphasic, and enhance the activated inward current deflections seemingly connected to the increased firing frequency.

Picosecond degenerate four-wave mixing on potassium in a methane-air flame.

We demonstrate that picosecond mode-locked laser-based degenerate four-wave mixing can be detected with good signal-to-noise ratios in an optically thin flame and that detailed turbulence statistics can be acquired by use of this technique. A regeneratively mode-locked Ti:sapphire laser was tuned to the 4(2)S((1/2))-4(2)P degrees ((1/2)) transition in atomic potassium (which was doped into the flame) at 769.9 nm. Using the all-forward degenerate four-wave mixing geometry, we achieved signal-to-noise ratios of 70:1 without the use of a spatial filter. A sensitivity curve and a method for acquiring turbulence statistics are presented.

Length measurement and stabilization of optical substrates.

The initial work on the use of acoustic signals to feedback control the length of an optical substrate to the order of 10(-6) parts in 10(6) is described.

Pulse energy control in Q-switched, diode-pumped solid-state lasers.

This control system randomly scans a Q-switched diodepumped Nd:YLF laser from hertz to kilohertz repetition rates with less than +/-5% (3sigma) pulse-energy jitter.