A
bstract
The Sauter-Schwinger effect predicts the creation of electron-positron pairs out of the quantum vacuum by a strong and slowly varying electric field. This effect can be dynamically assisted ...by an additional weaker time-dependent field, which may drastically enhance the pair-creation probability. In previous studies, it has been found that the enhancement may crucially depend on the temporal shape of this weaker pulse, e.g., a Gaussian profile exp{−(ω
t
)
2
} or a Sauter pulse 1
/
cosh
2
(ω
t
) behave quite differently. In order to understand this difference, we make a perturbative expansion in terms of the weaker field while treating the strong electric field non-perturbatively. For a large class of profiles including the Sauter pulse, already the sum of the zeroth-order and the first-order amplitudes of this perturbative expansion yields good agreement. For other cases, such as a Gaussian or sinusoidal profile, this is not true in general and higher orders can yield the dominant contribution — where the dominant order depends on the chosen parameters. Our findings are confirmed by numerical simulations and help us to sort previous results into a bigger picture.
The injection and mixing of contaminant mass into the fuel in inertial confinement fusion (ICF) implosions is a primary factor preventing ignition. ICF experiments have recently achieved an ...alpha-heating regime, in which fusion self-heating is the dominant source of yield, by reducing the susceptibility of implosions to instabilities that inject this mass. We report the results of unique separated reactants implosion experiments studying pre-mixed contaminant as well as detailed high-resolution three-dimensional simulations that are in good agreement with experiments. At conditions relevant to mixing regions in high-yield implosions, we observe persistent chunks of contaminant that do not achieve thermal equilibrium with the fuel throughout the burn phase. The assumption of thermal equilibrium is made in nearly all computational ICF modeling and methods used to infer levels of contaminant from experiments. We estimate that these methods may underestimate the amount of contaminant by a factor of two or more.
Purpose
Craniopharyngiomas (CPGs) are aggressive brain tumors responsible of severe morbidity in children. The best treatment strategies are under debate. Our study evaluates surgical, pituitary, and ...hypothalamic outcomes of a tailored staged-surgical approach compared to a single-stage radical approach in children with CPGs.
Methods
Multicenter retrospective study enrolling 96 children treated for CPGs in the period 2010–2022. The surgical management was selected after a multidisciplinary evaluation. Primary endpoint includes the inter-group comparison of preservation/improvement of hypothalamic–pituitary function, the extent of resection, and progression-free survival (PFS). Secondary endpoints include overall survival (OS), morbidity, and quality of life (QoL).
Results
Gross Total Resection (GTR) was reached in 46.1% of cases in the single-stage surgery group (82 patients, age at surgery 9 ± 4.7 years) and 33.3% after the last operation in the staged surgery group (14 patients age 7.64 ± 4.57 years at first surgery and 9.36 ± 4.7 years at the last surgery). The PFS was significantly higher in patients addressed to staged- compared to single-stage surgery (93.75% vs 70.7% at 5 years, respectively,
p
= 0.03). The recurrence rate was slightly higher in the single-stage surgery group. No significant differences emerged in the endocrinological, visual, hypothalamic outcome, OS, and QoL comparing the two groups.
Conclusions
In pediatric CPGs’ surgical radicality and timing of intervention should be tailored considering both anatomical extension and hypothalamic–pituitary function. In selected patients, a staged approach offers a safer and more effective disease control, preserving psychophysical development.
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