Spatially resolved measurements of laser filamentation in long scale length underdense plasmas with and without beam smoothing.

The onset of filamentation, following the interaction of a relatively long (τ(L)≃1 ns) and intense (I(L)≃5×10(14) W/cm(2)) laser pulse with a neopentane filled gas bag target, has been experimentally studied via the proton radiography technique, in conditions of direct relevance to the indirect drive inertial confinement fusion scheme. The density gradients associated with filamentation onset have been spatially resolved yielding direct and unambiguous evidence of filament formation and quantitative information about the filamentation mechanism in agreement with previous theoretical modelings. Experimental data confirm that, once spatially smoothed laser beams are used, filamentation is not a relevant phenomenon during the heating laser beams propagation through typical hohlraum gas fills.

Splashing of drops on shallow liquids.

The events that follow the splashing of a drop on a liquid depend on the depth of the liquid. When the depth is less than about 5 millimeters the crown that is ejected is more unstable than that from a splash on a deep liquid. As the depth is decreased from 25 to 7 millimeters, there is an increase in the maximum height to which the Rayleigh jet rises, and in the number of drops that break away from the jet. With depths less than 7 millimeters these two quantities fall off sharply, and no jet drops are produced for depths less than about 3 millimeters.

Kuwait oil fires: correction.

In our article "Airborne studies of the smoke from the Kuwait oil fires" (15 May, p. 987) (1), we stated that the depletions of sulfur dioxide (SO(2)) and nitrogen oxides (NO(x)) in the smoke plume from the Kuwait oil fires were 50 and 60% per hour, respectively. These values were derived from measurements made aboard a Convair C-131 aircraft, and measurements of CO(2) were used as a conserved tracer. Subsequent comparisons of these measurements of CO(2) (which were obtained from a continuous analyzer) with independent measurements of CO(2) (obtained from "grab" samples) revealed that the continuous CO(2) measurements were occasionally contaminated by cabin air. Recalculation of the depletion rates of SO(2) and NO(x), with the use of uncontaminated measurements of CO(2) from the "grab" sampler aboard the aircraft yielded values of 6 and 22%, respectively (2). Our conclusions with regard to the climatic effects of the Kuwait oil fires are unchanged.

Airborne studies of the smoke from the kuwait oil fires.

Airborne studies of smoke from the Kuwait oil fires were carried out in the spring of 1991 when approximately 4.6 million barrels of oil were burning per day. Emissions of sulfur dioxide were approximately 57% of that from electric utilities in the United States; emissions of carbon dioxide were approximately 2% of global emissions; emissions of soot were approximately 3400 metric tons per day. The smoke absorbed approximately 75 to 80% of the sun's radiation in regions of the Persian Gulf. However, the smoke probably had insignificant global effects because (i) particle emissions were less than expected, (ii) the smoke was not as black as expected, (iii) the smoke was not carried high in the atmosphere, and (iv) the smoke had a short atmospheric residence time.

Splashing of a water drop.

Measurements have been made of the number of spray droplets produced by the impact of a water drop on water, and of the charge to mass ratio for these droplets. For a drop 3 millimeters in diameter, the number of spray droplets increases linearly with the fall-distance of the drop over the range 10 to 200 centimeters. When the drop falls 100 centimeters, about 25 spray droplets are produced. The majority of the droplets carry a negative charge, and the ratio of the charge to the mass varies from 4 to 28 electrostatic units per gram.

Subsurface phenomena and the splashing of drops on shallow liquids.

High-speed movies have been taken of the formation of the sub-surface cavity and of the Rayleigh jet formed during the splash of a drop on a shallow liquid. They show that the initial increase and subsequent decrease in the rate of rise of the jet and the maximum jet height with decreasing depth of liquid are the result of the interaction of the subsurface cavity with the solid boundary beneath the liquid. This interaction modifies considerably the pressure gradients in the liquid during the formation and collapse of the cavity.

Cloud condensation nuclei from a simulated forest fire.

Measurements made downwind of a simulated forest fire showed that the concentration of cloud condensation nuclei active at a supersaturation of 1 percent was increased by a factor of about 2.5. Smaller increases were observed at lower supersaturations.

Atmospheric Effects of Pollutan: Pollutants which affect clouds are most likely to produce modifications in weather and climate.

We have argued that aerosols are probably the principal agents by which pollutants may affect weather and climate. They are most likely to act by influencing the structure and distribution of clouds. On the local scale, the effects of pollutants on some aspects of weather are unmistakable. The effects of man-made pollutants on global climate are a matter of debate, but they may already be significant.

Redistribution of Snowfall across a Mountain Range by Artificial Seeding: A Case Study.

Clouds over the western slopes of the Cascade Mountains were artificially seeded to reduce the riming and fall speeds of snow crystals and to divert snowfall across the crest. Aircraft observations showed that the clouds were glaciated by the seeding. The crystal habits and the degrees of riming of snow crystals reaching the target area were modified. Snowfall rates decreased at the crest and simultaneously increased 20 kilometers east of the crest.

Cloud condensation nuclei on the atlantic seaboard of the United States.

Concentrations of cloud condensation nuclei measured along the East Coast from Virginia to Long Island ranged from 1000 to 3500 per cubic centimeter as compared to 100 per cubic centimeter in clean maritime air and 300 per cubic centimeter in continental air. The global anthropogenic production rate of cloud condensation nuclei may be comparable to the natural production rate; in some industrial areas cloud condensation nuclei are dominated by anthropogenic sources.

Dissipation of marine stratiform clouds and collapse of the marine boundary layer due to the depletion of cloud condensation nuclei by clouds.

When the production of cloud condensation nuclei in the stratocumulus-topped marine boundary layer is low enough, droplet collisions can reduce concentrations of cloud droplet numbers to extremely low values. At low droplet concentrations a cloud layer can become so optically thin that cloud-top radiative cooling cannot drive vertical mixing. Under these conditions, model simulations indicate that the stratocumulus-topped marine boundary layer collapses to a shallow fog layer. Through this mechanism, marine stratiform clouds may limit their own lifetimes.

Eruptions of the st. Augustine volcano: airborne measurements and observations.

Airborne measurements of the effluents from the St. Augustine volcano obtained during a 10-day period of activity showed that aerosol was ejected at the rate of about 10(5) kilograms per second during brief eruptions (3 to 8 minutes). Steadier emissions contained much more water vapor and gaseous sulfur but less aerosol mass. A nuée ardente (glowing avalanche) produced by one eruption reached a maximum average speed of about 50 meters per second.

Airborne studies of the emissions from the volcanic eruptions of mount st. Helens.

The concentrations of particles less than 10 micrometers in diameter in the ash emissions from Mount St. Helens have been more than 1000 times greater than those in the ambient air. Mass loadings of particles less than 2 micrometers in diameter were generally several hundred micrograms per cubic meter. In the ash clouds, produced by the large eruption on 18 May 1980, the concentrations of several trace gases generally were low. In other emissions, significant, but variable, concentrations of sulfur gases were measured. The 18 May eruption produced nuées ardentes, lightning flashes, and volcanic hail.

Radar detection of cloud-seeding effects.

The effects on precipitation of artificially seeding clouds with Dry Ice have been monitored from cloud to ground with a radar that has a wavelength of 8.6 millimeters.

Cytochrome c release and apoptosis induced by mitochondrial targeting of nuclear orphan receptor TR3.

TR3, an immediate-early response gene and an orphan member of the steroid-thyroid hormone-retinoid receptor superfamily of transcription factors, regulates apoptosis through an unknown mechanism. In response to apoptotic stimuli, TR3 translocates from the nucleus to mitochondria to induce cytochrome c release and apoptosis. Mitochondrial targeting of TR3, but not its DNA binding and transactivation, is essential for its proapoptotic effect. Our results reveal a mechanism by which a nuclear transcription factor translocates to mitochondria to initiate apoptosis.

The receptor-DNA complex determines the retinoid response: a mechanism for the diversification of the ligand signal.

To obtain insights into the principles governing the complex biological responses to retinoids, we have analyzed the ligand sensitivities of various retinoid receptor-DNA complexes. We find that different retinoid receptor heterodimers show distinct activation patterns with various response elements while a given heterodimer can be activated at different retinoic acid concentrations on different response elements. In vitro binding experiments suggest that the same retinoic acid receptor-retinoid X receptor (RAR-RXR) heterodimer can have different ligand affinities, depending on the response element it is bound to. The differential responses of a particular receptor heterodimer with various retinoic acid responsive elements can be enhanced through the use of conformationally restricted retinoids. RAR- and RXR-selective retinoids can also synergistically activate the receptor heterodimers, indicating that both partners in the heterodimer can contribute to ligand-induced transcriptional activation. However, the relative influence of the RAR or RXR partner is specific for each response element. Together, our data demonstrate that it is the receptor-DNA complex and not the receptor alone that determines the ligand response. This flexibility allows for a highly pleiotropic retinoid response. Furthermore, conformationally restricted retinoids can accentuate the differential responses and exhibit a certain degree of gene selectivity by differentially activating the RAR or RXR component in the context of a given response element.

Inhibition of trans-retinoic acid-resistant human breast cancer cell growth by retinoid X receptor-selective retinoids.

All-trans-retinoic acid (trans-RA) and other retinoids exert anticancer effects through two types of retinoid receptors, the RA receptors (RARs) and retinoid X receptors (RXRs). Previous studies demonstrated that the growth-inhibitory effects of trans-RA and related retinoids are impaired in certain estrogen-independent breast cancer cell lines due to their lower levels of RAR alpha and RARbeta. In this study, we evaluated several synthetic retinoids for their ability to induce growth inhibition and apoptosis in both trans-RA-sensitive and trans-RA-resistant breast cancer cell lines. Our results demonstrate that RXR-selective retinoids, particularly in combination with RAR-selective retinoids, could significantly induce RARbeta and inhibit the growth and induce the apoptosis of trans-RA-resistant, RAR alpha-deficient MDA-MB-231 cells but had low activity against trans-RA-sensitive ZR-75-1 cells that express high levels of RAR alpha. Using gel retardation and transient transfection assays, we found that the effects of RXR-selective retinoids on MDA-MB-231 cells were most likely mediated by RXR-nur77 heterodimers that bound to the RA response element in the RARbeta promoter and activated the RARbeta promoter in response to RXR-selective retinoids. In contrast, growth inhibition by RAR-selective retinoids in trans-RA-sensitive, RAR alpha-expressing cells most probably occurred through RXR-RAR alpha heterodimers that also bound to and activated the RARbeta promoter. In MDA-MB-231 clones stably expressing RAR alpha, both RARbeta induction and growth inhibition by RXR-selective retinoids were suppressed, while the effects of RAR-selective retinoids were enhanced. Together, our results demonstrate that activation of RXR can inhibit the growth of trans-RA-resistant MDA-MB-231 breast cancer cells and suggest that low cellular RAR alpha may regulate the signaling switch from RAR-mediated to RXR-mediated growth inhibition in breast cancer cells.

Molecular determinants of AHPN (CD437)-induced growth arrest and apoptosis in human lung cancer cell lines.

6-[3-(1-Adamantyl)-4-hydroxyphenyl]-2-naphthalene carboxylic acid (AHPN or CD437), originally identified as a retinoic acid receptor gamma-selective retinoid, was previously shown to induce growth inhibition and apoptosis in human breast cancer cells. In this study, we investigated the role of AHPN/CD437 and its mechanism of action in human lung cancer cell lines. Our results demonstrated that AHPN/CD437 effectively inhibited lung cancer cell growth by inducing G0/G1 arrest and apoptosis, a process that is accompanied by rapid induction of c-Jun, nur77, and p21(WAF1/CIP1). In addition, we found that expression of p53 and Bcl-2 was differentially regulated by AHPN/CD437 in different lung cancer cell lines and may play a role in regulating AHPN/CD437-induced apoptotic process. On constitutive expression of the c-JunAla(63,73) protein, a dominant-negative inhibitor of c-Jun, in A549 cells, nur77 expression and apoptosis induction by AHPN/CD437 were impaired, whereas p21(WAF1/CIP1) induction and G0/G1 arrest were not affected. Furthermore, overexpression of antisense nur77 RNA in A549 and H460 lung cancer cell lines largely inhibited AHPN/CD437-induced apoptosis. Thus, expression of c-Jun and nur77 plays a critical role in AHPN/CD437-induced apoptosis. Together, our results reveal a novel pathway for retinoid-induced apoptosis and suggest that AHPN/CD437 or analogs may have a better therapeutic efficacy against lung cancer.

Struvite crystallisation and recovery using a stainless steel structure as a seed material.

A metallic system acting as a seed substrate has been designed and developed in order to assess its efficiency in recovering phosphorus as struvite. The device, consisting of two concentric stainless steel meshes, was immerged in the upper section of a pilot crystallisation reactor fed with synthetic liquors (MgCl(2) x 6H(2)O, NH(4)H(2)PO(4),) for 2h. Apart from soluble PO(4)-P removals which remained in the range 79-80% with or without application of the metallic system, it was found that under the specific operating conditions tested the meshes were capable of accumulating struvite at a rate of 7.6 gm(-2)h(-1), hence reducing significantly the amount of fine particles remaining in solution from 302.2 to 12 mg L(-1) when compared to trials without mesh.

Kinetics of struvite precipitation: effect of the magnesium dose on induction times and precipitation rates.

The presence of white deposits in specific areas of wastewater treatment plants is generally the consequence of the spontaneous formation of a mineral called struvite. Struvite forms when the levels of phosphate, ammonium and magnesium naturally available in wastewater effluents reach a minimum molar ratio 1:1:1 under specific conditions of pH, temperature and mixing energy. Originally regarded as a phenomenon to be controlled or eliminated, struvite has been lately identified as an alternative way of removing and recovering P from wastewater effluents and generating a product identified as an excellent base for the production of slow release fertilisers. Chemical and physical principles of struvite precipitation and the development of crystallisation technologies have been widely investigated. However, little interest has been given to kinetics of struvite precipitation. In the present work the kinetics of struvite formation have been investigated at both laboratory and pilot scale in synthetic solutions containing Mg(2+), NH4(+), and PO4(3-) ions in a molar ratio 1:2:2 at room temperature. These different tests have used pH measurements to assess the impact of water chemistry on induction times, and more precisely the influence of magnesium levels on kinetic rates. Experimental results and kinetic calculations revealed that the control of the magnesium dose initially present in solution is decisive of the speed at which struvite nucleates.