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F Pegoraro

Publications and source records attributed to F Pegoraro.

16 recordsLinked to original sources
PubMed2001

Three-dimensional singularities of a thin plasma slab.

The three-dimensional (3D) nonlinear development of the interchange-like (Rayleigh-Taylor) instability of a thin slab of plasma exhibits interesting features with respect to its two-dimensional (2D) limit investigated by Bulanov, Pegoraro, and Sakai [Phys. Rev. E 59, 2292 (1999)]. We show that, contrary to the 2D case, the 3D evolution equations remain nonlinear when Lagrangian variables are adopted. Explicit solutions are found by the use of a generalized hodograph transformation. Both compression and rarefaction singularities are formed. Local solutions in the neighborhood of the singular points have a generic 2D character.

Journal Article↗
PubMed2001

Fast formation of magnetic islands in a plasma in the presence of counterstreaming electrons.

With the help of 2D-3V (two dimensional in space and three dimensional in velocity) Vlasov simulations we show that the magnetic field generated by the electromagnetic current filamentation instability develops magnetic islands due to the onset of a fast reconnection process that occurs on the electron dynamical time scale. This process is relevant to magnetic channel coalescence in relativistic laser plasma interactions.

Journal Article↗
PubMed2001

Phase mixing and island saturation in Hamiltonian reconnection.

The nonlinear evolution of a Hamiltonian magnetic field line reconnection in a two-dimensional fluid plasma leads to a macroscopic equilibrium with a finite-size island and fine-scale spatial structures. The latter arise from the phase mixing of the Lagrangian invariant fields. This equilibrium is the analog of the Bernstein-Greene-Kruskal equilibrium solution for electrostatic Langmuir waves.

Journal Article↗
PubMed2001

Fast ignition by intense laser-accelerated proton beams.

The concept of fast ignition with inertial confinement fusion (ICF) is a way to reduce the energy required for ignition and burn and to maximize the gain produced by a single implosion. Based on recent experimental findings at the PETAWATT laser at Lawrence Livermore National Laboratory, an intense proton beam to achieve fast ignition is proposed. It is produced by direct laser acceleration and focused onto the pellet from the rear side of an irradiated target and can be integrated into a hohlraum for indirect drive ICF.

Journal Article↗
PubMed2000

Impact of kinetic processes on the macroscopic nonlinear evolution of the electromagnetic-beam-plasma instability

We present a new, fully kinetic mechanism of generation of spatial magnetic vortices that results from the resonant wave-particle interaction in a plasma. This phenomenon is of basic theoretical interest. It can be responsible for the magnetic vortices observed in numerical simulations in the wake of an ultrastrong, ultraintense laser pulse in an underdense plasma.

Journal Article↗
PubMed2000

Kinetic vortex chain solution in the drift-wave plasma regime

A fully nonlinear Bernstein-Greene-Kruskal stationary solution is found in the form of a quasi-three-dimensional chain of electron holes coupled to hydrodynamic vortices. This new coherent structure is enabled by the trapping and depletion of resonant particles, and the cyclotron dissipation of the singular current sheets. It is expected to play an important role in the collisionless magnetic field line reconnection in the drift-wave plasma regime, where it represents a plausible saturated state.

Journal Article↗
PubMed2000

Asymptotic evolution of nonlinear landau damping

The long-time evolution of nonlinear Landau damping in collisionless plasmas is analyzed by solving the Vlasov-Poisson system numerically. The value of the parameter marking the transition between Landau's and O'Neil's regimes is determined and compared with analytical results. The long-time evolution of a finite-amplitude electric field with wavelength lambda equal to the length of the simulation box L is given by a superposition of two counterpropagating "averaged" Bernstein-Greene-Kruskal (BGK) waves. When L>lambda and longer wavelength modes can be excited, the BGK waves correspond to an intermediate regime that is eventually modified by the excitation of the sideband instability. Ions dynamics is found not to affect these behaviors significantly.

Journal Article↗
PubMed2000

High density collimated beams of relativistic ions produced by petawatt laser pulses in plasmas

Under optimal interaction conditions ions can be accelerated up to relativistic energies by a petawatt laser pulse in both underdense and overdense plasmas. Two-dimensional particle in cell simulations show that the laser pulse drills a channel through an underdense plasma slab due to relativistic self-focusing. Both ions and electrons are accelerated in the head region of the channel. However, ion acceleration is more effective at the end of the slab. Here electrons from the channel expand in vacuum and are followed by the ions dragged by the Coulomb force arising from charge separation. A similar mechanism of ion acceleration occurs when a superintense laser pulse interacts with a thin slab of overdense plasma and the pulse ponderomotive pressure moves all the electrons away from a finite-diameter spot.

Journal Article↗
PubMed1998

Structural abnormalities and not diastolic dysfunction are the earliest left ventricular changes in hypertension. HARVEST Study Group.

It has been claimed that diastolic dysfunction is the earliest cardiac abnormality in hypertension, preceding the development of left ventricular (LV) structural abnormalities. To detect early signs of hypertensive cardiac involvement 722 subjects (533 men and 189 women), 18-45 years old, with stage I hypertension, were studied by M-mode and Doppler echocardiography. Blood pressure was measured by 24-h ambulatory monitoring. Ninety-five normotensive individuals of similar age and gender distributions were studied as controls. Significant, though modest, changes of LV mass and geometry were found in the participants in comparison with the normotensive controls. The increment was +10.4 g/m2 for LV mass index, +1.8 mm for LV wall thickness, and +0.032 for relative wall thickness. A slight increase in atrial filling peak velocity was found in the hypertensive subjects at Doppler analysis of transmitral flow, but the ratio of early to atrial velocity of LV diastolic filling did not differ between the two groups. In multiple regression analyses, which included age, body mass index, heart rate, smoking, and physical activity, 24-h mean blood pressure emerged as a significant predictor of LV mass index (men, P = .003; women, P = .04) and wall thickness (men, P = .03; women, P = .004) in the hypertensive subjects, whereas no index of diastolic filling was significantly associated with ambulatory blood pressure in either gender. The present data indicate that changes in LV anatomy are the earliest signs of hypertensive cardiac involvement. Left ventricular filling is affected only marginally in the initial phase of hypertension.

Adolescent↗
PubMed1998

The effects of alcohol consumption on ambulatory blood pressure and target organs in subjects with borderline to mild hypertension. HARVEST Study Group.

The objective of this study was to examine the relationship of alcohol consumption to target organ involvement and ambulatory blood pressure (BP) in a population of young borderline to mild hypertensive subjects. Participants were 793 male subjects, aged 18-45 years, from the HARVEST Study. The analysis was performed in three age-matched groups with similar body mass index. Casual and 24-h ambulatory BP monitoring, routine biochemistry, echocardiography, and albumin excretion rate were measured. The men were divided into three groups: 1) nondrinkers, 2) drinkers of < 50 g/day, and 3) drinkers of > or = 50 g/day. Office systolic BP was not significantly different among the three groups, whereas 24-h and daytime BPs increased progressively from the first to the third group (group 1 v 3; P = .01 for 24-h systolic BP and P = .02 for daytime systolic BP). These differences remained significant even after adjusting for smoking. Left ventricular mass index, interventricular septum thickness, and wall thickness increased progressively from group 1 to group 3; this difference also remained significant after adjusting for smoking and 24-h BPs. The albumin excretion rate was much higher in group 3 than in group 1 (P = .003), but when 24-h BP was added to the model the difference was no longer significant. These results indicate that alcohol has a detrimental effect on the heart and the kidney. Alcohol's effect on LV wall thickness appears to be direct, whereas its action on albumin excretion rate seems to be mediated mainly by its effect on BP.

Adolescent↗
PubMed1997

Target organ damage and ambulatory blood pressure in stage I hypertension. The Hypertension and Ambulatory Recording Venetia Study.

According to recent international guidelines the decision on whether to treat young subjects during the early phase of hypertension should be based not only on their office blood pressure but also on their ambulatory blood pressure and whether target organ damage has occurred. Few data on the prevalence of hypertensive complications in young subjects with mild hypertension are available. In the Hypertension and Ambulatory Recording Venetia Study (HARVEST), a multicenter trial conducted in northeast Italy, the percentage of young borderline-to-mild hypertensive subjects with echocardiographic left ventricular hypertrophy was 4.5% and the percentage with concentric remodeling was 4%. Clear differences in cardiac size and geometric adjustment to ambulatory systolic pressure between the two sexes were found. The impact of blood pressure on the walls of the left ventricle and on the left ventricular mass was remarkable in women but weak in men. The assessment of left ventricular systolic function confirmed that many young mild hypertensive subjects have an increased ejective performance. The left ventricular contractility evaluated by midwall measurement was, however, found to be depressed in 9.2% of the HARVEST participants. Their left ventricular diastolic function was similar to that of 50 normotensive controls. The prevalence of microalbuminuria [albumin excretion rate (AER) > 30 mg/24 h) was 6.1%, only slightly higher than that found by other authors among normotensive subjects and much lower than that observed among patients with more severe hypertension. For our stage I hypertensives, however, the AER was correlated to the 24 h blood pressure with high statistical significance, whereas we found no relationship between the AER and left ventricular mass index either for all of the subjects taken together or for the men and women considered separately. The results suggest that renal and cardiac involvement do not occur in parallel during the initial phase of hypertension.

Journal Article↗
PubMed1996

Prevalence and clinical correlates of microalbuminuria in stage I hypertension. Results from the Hypertension and Ambulatory Recording Venetia Study (HARVEST Study).

The objective of the present study was to examine the association between albumin excretion rate (AER) and office and ambulatory blood pressures (BP), and other recognized cardiovascular risk factors in stage I hypertension. The study was carried out in 870 never-treated 18- to 45-year-old hypertensives (628 men, 242 women). Office and ambulatory BP, 24-h urinary collection for AER assessment, and echocardiographic left ventricular mass (n = 587) were obtained. AER was similar in men and women (12.3 v 12.5 mg/24 h) and was unrelated to age and body mass index. In 85.2% of the subjects, AER was < 16 mg/24 h, in 8.3% it was between 16 and 29 mg/24 h (borderline microalbuminuria), and in 6.1% it was >or= 30 mg/24 h (overt microalbuminuria). Office systolic BP was not different in the three groups, whereas 24-h systolic BP was higher in the subjects with microalbuminuria than in those with normal AER (P < .0001) and was similar in the two microalbuminuric groups. Office and 24-h diastolic BPs were higher in the subjects with overt microalbuminuria than in those with normal AER. Left ventricular mass was correlated to systolic (P < .0001) and diastolic (P = .01) 24-h BP, but was unrelated to AER. Family history for hypertension, smoking, coffee and alcohol intake, and physical activity habits did not influence AER. In a logistic regression analysis, 24-h systolic BP emerged as the only determinant of microalbuminuria (P < .0001). In conclusion, these results indicate that borderline levels of microalbuminuria may also be clinically relevant in stage I hypertension. Overweight and lifestyle factors do not appear to influence AER in these patients. Finally, the lack of correlation between AER and left ventricular mass suggests that renal and cardiac involvement do not occur in a parallel fashion in the initial phase of hypertension.

Adolescent↗
PubMed1995

Relation between family history of hypertension, overweight and ambulatory blood pressure: the HARVEST study.

The aim of the present paper was to evaluate the influence of a family history of hypertension and the degree of obesity as indicated by tertiles of body mass index on ambulatory blood pressure (BP) values in large number (n = 406) of young mild essential hypertensives. Positive family history of hypertension was associated with a significant increase in 24h ambulatory systolic blood pressure (SBP). The difference was most pronounced in the upper tertile of body mass index with almost 6 mm Hg difference between patients with and without a family history of hypertension. Both the degree of obesity and family history of hypertension had significant effects on 24h diastolic blood pressure (DBP). Twenty four hour DBP was highest in the upper tertile of body mass index in the hypertensives with a positive family history, representing an increase of 5 mm Hg compared with patients with a negative family history in the lower tertile. We conclude that mild hypertensives with a positive family history of hypertension are characterised by higher ambulatory BP than patients without parental hypertension and similar supine BP. Furthermore, our results indicate that in mild hypertensives the increase in DBP with body mass index is underestimated by conventional sphygmomanometry.

Adult↗