Observation of Fast Current Redistribution in an Imploding Plasma Column.

Spectroscopic measurements of the magnetic field evolution in a Z-pinch throughout stagnation and with particularly high spatial resolution reveal a sudden current redistribution from the stagnating plasma (SP) to a low-density plasma (LDP) at larger radii, while the SP continues to implode. Based on the plasma parameters it is shown that the current is transferred to an increasing-conductance LDP outside the stagnation, a process likely to be induced by the large impedance of the SP. Since an LDP often exists around imploding plasmas and in various pulsed-power systems, such a fast current redistribution may dramatically affect the behavior and achievable parameters in these systems.

Self-Generated Plasma Rotation in a Z-Pinch Implosion with Preembedded Axial Magnetic Field.

Using detailed spectroscopic measurements, highly resolved in both time and space, a self-generated plasma rotation is demonstrated using a cylindrical implosion with a preembedded axial magnetic field (B_{z0}). The rotation direction is found to depend on the direction of B_{z0} and its velocity is found comparable to the peak implosion velocity, considerably affecting the force and energy balance throughout the implosion. Moreover, the evolution of the rotation is consistent with magnetic flux surface isorotation, a novel observation in a Z pinch, which is a prototypical time dependent system.

Effects of a Preembedded Axial Magnetic Field on the Current Distribution in a Z-Pinch Implosion.

The fundamental physics of the magnetic field distribution in a plasma implosion with a preembedded magnetic field is investigated within a gas-puff Z pinch. Time and space resolved spectroscopy of the polarized Zeeman effect, applied for the first time, reveals the impact of a preembedded axial field on the evolution of the current distribution driven by a pulsed-power generator. The measurements show that the azimuthal magnetic field in the imploding plasma, even in the presence of a weak axial magnetic field, is substantially smaller than expected from the ratio of the driving current to the plasma radius. Much of the current flows at large radii through a slowly imploding, low-density plasma. Previously unpredicted observations in higher-power imploding-magnetized-plasma experiments, including recent, unexplained structures observed in the magnetized liner inertial fusion experiment, may be explained by the present discovery. The development of a force-free current configuration is suggested to explain this phenomenon.

Secondary plasma formation after single pulse laser ablation underwater and its advantages for laser induced breakdown spectroscopy (LIBS).

In this work we present studies of spatial and temporal plasma evolution after single pulse ablation of an aluminium target in water. The laser ablation was performed using 20 ns long pulses emitted at 1064 nm. The plasma characterization was performed by fast photography, the Schlieren technique, shadowgraphy and optical emission spectroscopy. The experimental results indicate the existence of two distinct plasma stages: the first stage has a duration of approximately 500 ns from the laser pulse, and is followed by a new plasma growth starting from the crater center. The secondary plasma slowly evolves inside the growing vapor bubble, and its optical emission lasts over several tens of microseconds. Later, the hot glowing particles, trapped inside the vapor cavity, were detected during the whole cycle of the bubble, where the first collapse occurs after 475 µs from the laser pulse. Differences in the plasma properties during the two evolution phases are discussed, with an accent on the optical emission since its detection is of primary importance for LIBS. Here we demonstrate that the LIBS signal quality in single pulse excitation underwater can be greatly enhanced by detecting only the secondary plasma emission, and also by applying long acquisition gates (in the order of 10-100 µs). The presented results are of great importance for LIBS measurements inside a liquid environment, since they prove that a good analytical signal can be obtained by using nanosecond pulses from a single commercial laser source and by employing cost effective, not gated detectors.

p16INK4a as an adjunct test in cervical cytology.

BACKGROUND: This study investigated the correlation between cervical cytology, the expression of P16INK4a, and human papilloma virus (HPV) infection. MATERIALS AND METHODS: The study included 100 subjects with suspected pathological cervical lesions. Cervical smears were analyzed for malignancy and p16INK4a. Histological finding represented "the golden standard". RESULTS: Immunocytochemical analysis of protein p16INK4a expression on epithelial cells of cervical smear demonstrated increased p16lNK4a expression in 36.0% of subjects. There was statistically significant positive correlation (Spearman r = 0.70; p < 0.001) between the pathological findings and the intensity of p16INK4a protein expression inside the epithelial cells, as well as with the histological finding (Spearman r = 0.71; p < 0.001). The intensity of p16INK4a protein expression in cytology finding was significantly higher in HPV16 positive patients (Mann- Whitney test, p = 0.0065). CONCLUSION: Good correlation between the expression rate and the severity of lesions indicates that this test might improve the results of cytology and HPV screening, as well as the results of predicting the prognosis of the disorder of the cervix.

Azimuthal magnetic field distribution in gas-puff Z-pinch implosions with and without external magnetic stabilization.

An experimental study of the magnetic field distribution in gas-puff Z pinches with and without a preembedded axial magnetic field (B_{z0}) is presented. Spatially resolved, time-gated spectroscopic measurements were made at the Weizmann Institute of Science on a 300 kA, 1.6 µs rise time pulsed-power driver. The radial distribution of the azimuthal magnetic field, B_{θ}, during the implosion, with and without a preembedded axial magnetic field of B_{z0}=0.26T, was measured using Zeeman polarization spectroscopy. The spectroscopic measurements of B_{θ} were consistent with the corresponding values of B_{θ} inferred from current measurements made with a B-dot probe. One-dimensional magnetohydrodynamic simulations, performed with the code trac-ii, showed agreement with the experimentally measured implosion trajectory, and qualitatively reproduced the experimentally measured radial B_{θ} profiles during the implosion when B_{z0}=0.26T was applied. Simulation results of the radial profile of B_{θ} without a preembedded axial magnetic field did not qualitatively match experimental results due to magneto-Rayleigh-Taylor (MRT) instabilities. Our analysis emphasizes the importance of MRT instability mitigation when studying the magnetic field and current distributions in Z pinches. Discrepancies of the simulation results with experiment are discussed.

Single-dose concentrations of tinidazole in gingival crevicular fluid, serum, and gingival tissue in adults with periodontitis.

Previous studies have shown that metronidazole is effective in the treatment of subgingival microflora associated with destructive periodontitis. The aim of this study was to determine whether tinidazole, a close analogue of metronidazole, would reach sufficient concentrations in serum, gingival crevicular fluid, and gingival tissue, to inhibit putative periodontopathic bacteria. Ten adult patients with moderate to advanced periodontitis took a single 2-g dose of tinidazole orally. Samples were assayed by high-performance liquid chromatography. The concentrations of tinidazole in serum and GCF were in a similar range (3.2-46.5 micrograms/mL). Tinidazole was not detected in the GCF in three of the patients. The drug was found in gingival tissue obtained at two h (0.17 +/- 0.14 micrograms/mg) and six h (0.15 +/- 0.18 micrograms/mg) after oral administration. The mean concentration of tinidazole in serum at 24 h (13 +/- 3.0 micrograms/mL) is greater than the minimum inhibitory concentration for anaerobic bacteria as reported by others. The present data suggest that a single 2-g oral dose of tinidazole may lead to the presence of potentially bactericidal levels of tinidazole for up to 24 h in the periodontal pockets of some patients with periodontitis.

Disposition and metabolism of metronidazole in patients with liver failure.

A pharmacokinetic study of metronidazole disposition was performed in 10 patients with severe liver disease, the majority of whom also had impaired renal function. Following a single intravenous dose, systemic clearance of metronidazole was decreased by 66% in patients compared with healthy controls (p less than 0.001). The apparent volume of distribution for metronidazole was also decreased in patients (by 21%), but the greater effect on clearance resulted in the elimination half-life being prolonged 152%. Total urinary excretion of unaltered metronidazole was not reduced in patients compared with controls, and systemic clearance of metronidazole did not correlate with creatinine clearance. Hepatic production of hydroxymetronidazole [1-(2-hydroxyethyl)-2-hydroxymethyl-5-nitroimidazole], the major oxidative metabolite of metronidazole, was significantly lowered in patients with liver failure. Peak plasma levels of this metabolite were lower, the time taken to achieve peak levels was longer and the area under the plasma concentration approximately time curve (AUC0-25h) was reduced in patients compared to controls (p less than 0.05). Similarly, urinary recovery of hydroxymetronidazole was lower in patients with liver disease while excretion of the other major oxymetabolite, 1-acetic acid-2-methyl-5-nitroimidazole, appeared reduced to an even greater extent. Thus, while the presence of renal function impairment in a patient with cirrhosis indicates that metronidazole elimination is likely to be abnormal, the principal mechanism for delayed elimination is impaired hepatic drug metabolism rather than reduced renal clearance of metronidazole and its major metabolites.

Pharmacokinetics of cefotaxime in neonates.

The effects of gestational age on the pharmacokinetics of cefotaxime and its desacetyl metabolite during the first days of life was investigated in a group of four full-term infants and 12 preterm infants of less than 35 weeks gestation. Half of the preterm infants had received betamethasone, a drug known to facilitate hepatic microsomal drug metabolism, whilst the others had not. No significant differences in the pharmacokinetics of cefotaxime were observed between the various groups, with elimination half-life (T 1/2 beta) of cefotaxime ranging from 4.04 +/- 1.52 to 4.56 +/- 1.31 h. The desacetyl metabolite of cefotaxime was present in all post-dose serum samples, irrespective of the gestational age of the baby. Its formation was apparently unaffected by prior exposure to betamethasone. The elimination half-life of cefotaxime is significantly longer in newborn infants than in older children or adults, this increase probably results from decreased renal excretion of the drug, rather than from immaturity in its metabolism. A dose of 50 mg/kg of cefotaxime given every 12 h is appropriate for infants of less than seven days old.

Pharmacokinetics and tissue distribution of metronidazole in the new born infant.

Metronidazole pharmacokinetics and tissue distribution were studied in 11 infants varying in gestational age from 28 to 40 weeks. Elimination half-life was inversely related to gestational age, and ranged from 22.5 to 109 hours. Hepatic hydroxylation of metronidazole was not evident in infants less than 35 weeks' gestation, unless they had been exposed prenatally to betamethasone. A dosage schedule of 15 mg/kg intravenously as an initial single dose is proposed, and will provide adequate therapeutic levels for 48 hours in the preterm infant and for 24 hours in the term infant. Subsequently a dose of 7.5 mg/kg/12 hours is suggested for the first week of life.

Theophylline metabolism in preterm neonates during the first weeks of life.

The effects of prenatal steroids on theophylline metabolism in infants of 27-32 weeks gestation was studied. Although in utero exposure to betamethasone was associated with a more mature theophylline metabolite pattern in the first days of life, initial elimination half-life (t1/2 beta) did not differ significantly between groups. By the second or third week of life the metabolite pattern was similar in all infants. The decline in t1/2 beta seen during theophylline treatment was not directly related to increased metabolite formation. These data suggest that other factors, such as renal clearance, are more important in determining the pharmacokinetics of theophylline in neonates than is hepatic metabolism.

Increased theophylline metabolism in premature infants after prenatal betamethasone administration.

The pattern of theophylline metabolites in plasma was studied in 9 preterm neonates of 28-35 weeks gestation. In infants not exposed to corticosteroids prenatally, metabolite formation was dependent on gestational age, postnatal age and/or duration of theophylline therapy. Infants prenatally exposed to betamethasone clearly showed evidence of demethylation and oxidation of theophylline during the first week of life, indicating prenatal activation of the hepatic monooxygenase enzyme system. Preliminary half-life data suggests that activation of hepatic metabolism may not affect initial elimination of theophylline.