Higher-order Kerr improve quantitative modeling of laser filamentation.

We test numerical filamentation models against experimental data about the peak intensity and electron density in laser filaments. We show that the consideration of the higher-order Kerr effect improves the quantitative agreement without the need of adjustable parameters.

Field measurements suggest the mechanism of laser-assisted water condensation.

Because of the potential impact on agriculture and other key human activities, efforts have been dedicated to the local control of precipitation. The most common approach consists of dispersing small particles of dry ice, silver iodide, or other salts in the atmosphere. Here we show, using field experiments conducted under various atmospheric conditions, that laser filaments can induce water condensation and fast droplet growth up to several µm in diameter in the atmosphere as soon as the relative humidity exceeds 70%. We propose that this effect relies mainly on photochemical formation of p.p.m.-range concentrations of hygroscopic HNO(3), allowing efficient binary HNO(3)-H(2)O condensation in the laser filaments. Thermodynamic, as well as kinetic, numerical modelling based on this scenario semiquantitatively reproduces the experimental results, suggesting that particle stabilization by HNO(3) has a substantial role in the laser-induced condensation.

Higher-order Kerr terms allow ionization-free filamentation in gases.

We show that higher-order nonlinear indices (n(4), n(6), n(8), n(10)) provide the main defocusing contribution to self-channeling of ultrashort laser pulses in air and argon at 800 nm, in contrast with the previously accepted mechanism of filamentation where plasma was considered as the dominant defocusing process. Their consideration allows us to reproduce experimentally observed intensities and plasma densities in self-guided filaments.

Complete retrieval of the field of ultrashort optical pulses using the angle-frequency spectrum.

We propose an experimental technique that allows for a complete characterization of the amplitude and phase of optical pulses in space and time. By the combination of a spatially resolved spectral measurement in the near and far fields and a frequency-resolved optical gating measurement, the electric field of the pulse is obtained through a fast, error-reduction algorithm.

Kerr-induced spontaneous Bessel beam formation in the regime of strong two-photon absorption.

We study the effect of Two-Photon Absorption (TPA) nonlinear losses on Gaussian pulses, with power that exceeds the critical power for self-focusing, propagating in bulk kerr media. Experiments performed in fused silica and silicon highlight a spontaneous reshaping of the input pulse into a pulsed Bessel beam. A filament is formed in which sub-diffractive propagation is sustained by the Bessel-nature of the pulse.

Post-natal development of amiloride sensitive sodium transport in pig distal colon.

1. Both electrophysiological properties and unidirectional Na and Cl fluxes have been determined across distal colons taken from pigs during early post-natal development. 2. The transmural potential difference (Vms) was 5 mV in the new-born and 10 mV in the 4 day old colon. The short circuit current (Scc) showed a three to sixfold increase during the first 10 days of post-natal life. The microvillar membrane potential (Vm) fell from about -45 mV in the new-born to -40 mV in the 4 day old colon. 3. Amiloride had no effect on Vms, Scc or Vm, measured in the new-born animal. It reduced Vms and Scc, caused a hyperpolarization of Vm and increased the microvillar membrane/basolateral membrane resistance ratio (Rm/Rs) in colons taken from older animals. 4. The Scc of distal colons taken from new-born and 1 day old pigs was only half that predicted from unidirectional measurements of Na flux. This discrepancy, which could not be completely accounted for by net CL absorption, disappeared in the older animals. 5. Net transport of Na doubled during the first 24 h of post-natal life. Part of this transport took place through an amiloride sensitive, non-electrogenic, pathway. 6. It is suggested that Na uses mainly a non-electrogenic pathway to cross the mucosa of the new-born pig. This pathway is replaced by an electrogenic amiloride sensitive mechanism in older animals. Aldosterone is thought to initiate these changes in Na tranport.

Stimulation by HCO3- of Na+ transport in rabbit gallbladder.

Bicarbonate presence in the bathing media doubles Na+ and fluid transepithelial transport and in parallel significantly increases Na+ and Cl- intracellular concentrations and contents, decreases K+ cell concentration without changing its amount, and causes a large cell swelling. Na+ and Cl- lumen-to-cell influxes are significantly enhanced, Na+ more so than Cl-. The stimulation does not raise any immediate change in luminal membrane potential and cannot be due to a HCO3(-)-ATPase in the brush border. The stimulation goes together with a large increase in a Na+-dependent H+ secretion into the lumen. All of these data suggests that HCO3- both activates Na+--Cl- cotransport and H+--Na+ countertransport at the luminal barrier. Thiocyanate inhibits Na+ and fluid transepithelial transport without affecting H+ secretion and HCO3(-)-dependent Na+ influx. It reduces Na+ and Cl- conentrations and contents, increases the same parameters for K+, causes a cell shrinking, and abolishes the lumen-to-cell Cl- influx. It enters the cell and is accumulated in the cytoplasm with a process which is Na+-dependent and HCO3(-)-activated. Thus SCN- is likely to compete for the Cl- site on the cotransport carrier and to be slowly transferred by the cotransport system itself.

Electrical parameters in gallbladders of different species. Their contribution to the origin of the transmural potential difference.

Amphotericin B enhances Na+ conductance of the mucosal membrane of gallbladder epithelial cells and in such a way it modifies the brush border electromotive force. On this basis a method to measure cell and shunt resistances by comparing changes of the mucosal membrane potential (Vm) and of the transmural p.d. (Vms) is developed. This method is applied in gallbladders of different vertebrate species (i.e. rabbit, guinea pig, goose, tortoise, toad, trout). The two tested mammals, rabbit and guinea pig, exhibited a lower shunting percentage (89--93%) than the nonmammals (96--97%), but this fact did not bring about a homogeneous positive Vms. This means that shunting percent contributes, but it is not the only source of differences in Vms, in accordance with that reported by Gelarden and Rose (J. Membrane Biol. 19:37, 1974). Moreover, mammals exhibited a lower luminal resistance and a lower ratio between luminal and basolateral resistance than nonmammals. Possible causes of these differences are discussed.

Electrical properties of pig colonic mucosa measured during early post-natal development.

Microvillar membrane (Vm) and transmural (Vt) potential differences were measured in proximal colon taken from pigs at birth and up to 10 days of age. 2. Vm remained independent of the age of the animal provided it was measured in the absence of methionine. The over-all mean was -43-3 mV. Adding methionine to fluid bathing the mucosal surface of new-born pig colon caused a 9-8 mV depolarization of Vm and a 6-7 mV increase in Vt. These effects, which were Na+-dependent, were not seen in the 10-day-old animal. 3. Substituting SO4(2-) for Cl- in methionine-free medium caused a hyperpolarization in Vm. Increasing the concentration of K+ caused corresponding depolarization. Substituting choline for Na+ had no effect on VmCl- and K+ movement across the microvillar membrane together account for the bulk of the measured membrane potential. These results apply to all stages of development. 4. Na+ uptake across the microvillar membrane of the new-born pig colon was increased in the presence of methionine. This effect disappeared in older animals. Na+ uptake in the absence of methionine doubled during the first 24 h of post-natal life. This increase was maintained using colons taken from older animals. 5. Methionine depolarization of Vm in the new-born pig colon is probably caused by the electrogenic influx of Na+. The ability of the colon to actively concentrate methionine within tis mucosa disappears at the same time as methionine ceases to affect Vm and Vt. It is suggested that methionine and Na+ form a ternary complex with a carrier in the brush border of the new-born pig colon and that this carrier is lost or modified during early post-natal development.

Na+ and Cl- transepithelial routes in rabbit gallbladder: tracer analysis of the transports.

The reported experiments demonstrate that in rabbit gallbladder epithelium: a) the mucosa-cell Na+ and Cl- influxes (45 sec long) are reduced in Cl- -free and Na+ -free bathing solutions respectively; transconcentration effects are observed. b) Cell Cl- labelling through the luminal membrane, with 36Cl- (1 hr incubation), is nearly abolished if a Na+ -free bathing solution is used; but cell Na+ labelling with 22Na+ in the lumen (1 hr incubation) does not change if a Cl- -free bathing solution is employed. c) Cell Na+ and Cl- labelling through the basolateral membrane (1 hr incubation) is negligible; some Cl- labelling is obtained only when the intracellular electrical potential is artificially reduced. d) SO 2 4- is found to abolish net water transport, to cross the epithelium, but not to enter the cell. On the basis of these data a paracellular pathway for net Cl- transport is ruled out, a Na+ and Cl- cotransport through the cell luminal barrier and a Na+ active extrusion through the basolateral membrane are suggested. No definitive conclusion about Cl- extrusion is possible.

Transcellular ion route in rabbit gallbladder. Electric properties of the epithelial cells.

The intracellular potential in gallbladder epithelial cellsis about minus 59 mV with respects to both mucosal and serosal media. It is a diffusion potential mainly due to K+;Na+ conductance seems to be very low. Entrance of Cl- into cellsappears to be coupled with Na+ a neutral carrier and exit towards blood side seems to be due to a NaCl neutral pump.