Giant Isolated Attosecond Pulses from Two-Color Laser-Plasma Interactions.

A new regime in the interaction of a two-color (ω,2ω) laser with a nanometer-scale foil is identified, resulting in the emission of extremely intense, isolated attosecond pulses-even in the case of multicycle lasers. For foils irradiated by lasers exceeding the blow-out field strength (i.e., capable of fully separating electrons from the ion background), the addition of a second harmonic field results in the stabilization of the foil up to the blow-out intensity. This is then followed by a sharp transition to transparency that essentially occurs in a single optical cycle. During the transition cycle, a dense, nanometer-scale electron bunch is accelerated to relativistic velocities and emits a single, strong attosecond pulse with a peak intensity approaching that of the laser field.

Comparison of nitrogen utilization and urea kinetics between yaks (Bos grunniens) and indigenous cattle (Bos taurus).

Under traditional management on the Qinghai-Tibetan Plateau, yaks () graze only on natural pasture without supplements and are forced to cope with sparse forage of low N content, especially in winter. In contrast, indigenous Tibetan yellow cattle () require supplements during the cold season. We hypothesized that, in response to harsh conditions, yaks cope with low N intakes better than cattle. To test this hypothesis, a study of whole-body N retention and urea kinetics was conducted in 2 concurrent 4 × 4 Latin squares, with 1 square using yaks and 1 square using cattle. Four isocaloric forage-concentrate diets differing in N concentrations (10.3, 19.5, 28.5, and 37.6 g N/kg DM) were formulated, and by design, DMI were similar between species and across diets. Urea kinetics were determined with continuous intravenous infusion of NN urea for 104 h, and total urine and feces were concomitantly collected. Urea production, urea recycling to the gut, and ruminal microbial protein synthesis all linearly increased ( < 0.001) with increasing dietary N in both yaks and cattle. Urinary N excretion was less ( = 0.04) and N retention was greater ( = 0.01) in yaks than in cattle. Urea production was greater in yaks than in cattle at the 3 lowest N diets but greater in cattle than in yaks at the highest N diet (species × diet, < 0.02). Urea N recycled to the gut ( < 0.001), recycled urea N captured by ruminal bacteria ( < 0.001), and ruminal microbial protein production ( = 0.05) were greater in yaks than in cattle. No more than 12% of urea recycling was through saliva, with no difference between species ( = 0.61). Glomerular filtration rate was lower ( = 0.05) in yaks than in cattle. The higher urea recycling and greater capture of recycled urea by ruminal microbes in yaks than in cattle suggest that yaks use mechanisms to utilize dietary N more efficiently than cattle, which may partially explain the better survival of yaks than cattle when fed low-N diets.

Response characteristics of Scirpus trioueter and its rhizosphere to pyrene contaminated soils at different growth stages.

Scirpus triqueter (Triangular club-rush), a typical wetland species, is used to study the response characteristics to pyrene. A pot experiment was conducted to investigate the growth parameters (height, diameter, shoot number, total volume, underground biomass, above-ground biomass and total biomass), and enzymes (catalase and superoxide dismutase) of S. triqueter. The characteristics of soil enzymes (catalase and polyphenol oxidase) and microorganisms (bacteria and fungi) were also assessed after pyrene treatment. Elevated pyrene concentration (80 mgkg(-1)) in the soil reduced the shoot number and biomass significantly, especially at the early growth stage. In root tissue, the enzyme catalase was activated at 80 mgkg(-1) of pyrene. Compared to roots, shoots had higher enzyme activities. Catalase activities in the rhizosphere increased throughout the growth period of S. triqueter. Polyphenol oxidase activities in the rhizosphere were higher than those in the bulk soil and unplanted soil. The populations of bacteria (total bacteria, pyrene-tolerant bacteria, and actinomyces) and fungi decreased under the stress of high pyrene concentration, while that of pyrene-tolerant bacteria increased with the increasing pyrene concentration. The presence of pyrene did not benefit the growth of S. triqueter. S. triqueter and soil enzymes varied within the growth stages. The presence of S. triqueter could improve the activity of soil enzymes and facilitate the propagation of microorganisms which could help eliminate pyrene contamination.

Inhibition of spermine on calcium influx during capacitation of guinea pig spermatozoa in vitro.

To investigate the mechanism of action of spermine, we measured the intracellular calcium ([Ca]i) of guinea pig spermatozoa using a probe of fluorescence, Quin 2. Results showed that spermine (0.25-2.0 mmol.L-1) suppressed the membrane permeability to Ca2+ during capacitation, which was similar to that of verapamil (a Ca2+ channel blocker). Furthermore, the rapid increase of [Ca]i induced by calcimycin (A-23187) was inhibited by spermine and verapamil, whereas trifluoperazine (an inhibitor of calmodulin) had no effect on it. The inhibition of the acrosome reaction caused by verapamil (5-100 mumol.L-1) or trifluoperazine (1-60 mumol.L-1) was reversed by calcimycin and cAMP, respectively. In addition, there was no effect on the initiation of the acrosome reaction when verapamil was added to capacitated spermatozoa. This result was in agreement with that of spermine. When addition of spermine (0.5 mmol.L-1) was combined with trifluoperazine (5 mumol.L-1), the acrosome reaction decline almost to zero, indicating that spermine might inhibit Ca2+ sensitive channel during sperm capacitation.

[Spermine inhibition of in vitro fertilizing ability of human spermatozoa and its possible mode of action].

The direct effect of spermine at various concentrations (0.25-8.0 mmol/L) on in vitro fertilizing ability of human spermatozoa was evaluated by the penetration test of zona-free hamster egg. To study the effect of spermine on capacitation, as judged by the rate of penetration, spermatozoa were incubated in BWW with various concentrations of spermine for 6 h at 37 degrees C. The hyperactivated motility of spermatozoa was markedly inhibited by spermine at a concentration of 4.0 mmol/L. The penetration rate was decreased proportionally to the dose of spermine used. Spermatozoa were incubated in BWW with 0.5 mmol/L spermine for 6 h and another 4 h after spermine was washed off with spermine-free BWW. The percentage of penetration was comparable to that of the control. Therefore, spermine-mediated inhibition of capacitation was reversible. Moreover, exogenous dbcAMP (0.5-1.0 mmol/L) or caffeine (10 mmol/L) could antagonize significantly the spermine-induced inhibition of capacitation with a correlation coefficient of 0.990. The content of spermine in fertile men spermatozoa was assayed by HPLC. Before capacitation spermine in spermatozoa was 7.05 micrograms/10(7) cells, whereas after capacitation it was no longer detectable, indicating that spermine may be an inhibitor of in vitro capacitation in human sperm. To study the effect of spermine on capacitated sperm, spermine was added to the BWW medium after sperm had been preincubated in spermine-free BWW. The persistent presence of spermine could interfere with spermatozoa attachment to, binding to and penetration into zona-free hamster eggs, which was related to the concentration (r = 0.820) used.(ABSTRACT TRUNCATED AT 250 WORDS)

[Inhibition of guinea pig sperm capacitation, the acrosome reaction and sperm-egg fusion by dl-propranolol in vitro].

dl-Propranolol (Pro), known to have spermicidal effect, was evaluated for its ability to influence capacitation, the acrosome reaction (AR) and fertilization of guinea pig spermatozoa at non-spermicidal dose levels. A concentration-dependent decrease in AR and the whiplashed motility occurred in Pro as low as 0.05 mmol/L. Pro 1.0 mmol/L completely abolished AR, followed by the loss of sperm capacity to penetrate into zona-free hamster egg. Pro exerted its inhibitory effect of AR primarily by restraining the capacitation stage of sperm but at Pro 0.5 mmol/L by blocking both capacitation and AR stages. % of AR of sperm preincubated with ionophore A-23187 0.2 mumol/L was significantly higher than that of the control, but markedly lower at Pro greater than or equal to mmol/L, implying that Pro prevented sperm Ca2+ influx. Prenylamine was also found to inhibit AR potentially and enhance the action of Pro against ionophore A-23187. Furthermore, Pro inhibition of the fertilizing ability of preincubated spermatozoa was antagonized by cAMP. Pro 0.5 mmol/L even caused the egg vesiculation. The reversibility of the action depends on the dose and time of sperm exposure to Pro. These findings suggest that the inhibitory effects of Pro on guinea pig sperm capacitation, the acrosome reaction and fertilization may be the mechanisms for its antifertility action.