Time-resolved turbulent dynamo in a laser plasma.

Understanding magnetic-field generation and amplification in turbulent plasma is essential to account for observations of magnetic fields in the universe. A theoretical framework attributing the origin and sustainment of these fields to the so-called fluctuation dynamo was recently validated by experiments on laser facilities in low-magnetic-Prandtl-number plasmas ([Formula: see text]). However, the same framework proposes that the fluctuation dynamo should operate differently when [Formula: see text], the regime relevant to many astrophysical environments such as the intracluster medium of galaxy clusters. This paper reports an experiment that creates a laboratory [Formula: see text] plasma dynamo. We provide a time-resolved characterization of the plasma's evolution, measuring temperatures, densities, flow velocities, and magnetic fields, which allows us to explore various stages of the fluctuation dynamo's operation on seed magnetic fields generated by the action of the Biermann-battery mechanism during the initial drive-laser target interaction. The magnetic energy in structures with characteristic scales close to the driving scale of the stochastic motions is found to increase by almost three orders of magnitude and saturate dynamically. It is shown that the initial growth of these fields occurs at a much greater rate than the turnover rate of the driving-scale stochastic motions. Our results point to the possibility that plasma turbulence produced by strong shear can generate fields more efficiently at the driving scale than anticipated by idealized magnetohydrodynamics (MHD) simulations of the nonhelical fluctuation dynamo; this finding could help explain the large-scale fields inferred from observations of astrophysical systems.

Subperiosteal midface lift: its role in static lower eyelid reconstruction after chronic facial nerve palsy.

PURPOSE: To describe the effect of subperiosteal midface lift on lower eyelid position of patients with chronic facial nerve palsy. METHODS: In an observational prospective study nine patients underwent subperiosteal midface lift. Indications for surgery were lower eyelid paralytic retraction, lagophthalmos, ocular surface disruption, reactive tearing, midface ptosis, and facial asymmetry. Exclusion criteria were previous rehabilitative oculofacial surgery, and facial nerve palsy onset less than a year. Preoperative and postoperative assessment included evaluation of lower eyelid position, lagophthalmos, midfacial ptosis and facial asymmetry. Follow-up was at 1 week, 1 month, 3, and 12 months, postoperatively. RESULTS: All patients referred improvement in their symptoms at 3 and 12 months, postoperatively: lower eyelid position (P=. 004), lagophthalmos (P=. 004), ocular surface symptoms, reactive tearing, and facial symmetry at rest. CONCLUSIONS: Subperiosteal midface lift has an effective role in the static lower eyelid malposition correction after chronic facial nerve palsy.

Inferring morphology and strength of magnetic fields from proton radiographs.

Proton radiography is an important diagnostic method for laser plasma experiments and is particularly important in the analysis of magnetized plasmas. The theory of radiographic image analysis has heretofore only permitted somewhat limited analysis of the radiographs of such plasmas. We furnish here a theory that remedies this deficiency. We show that to linear order in magnetic field gradients, proton radiographs are projection images of the MHD current along the proton trajectories. We demonstrate that in the linear regime (i.e., the small image contrast regime), the full structure of the projected perpendicular magnetic field can be reconstructed by solving a steady-state inhomogeneous 2-dimensional diffusion equation sourced by the radiograph fluence contrast data. We explore the validity of the scheme with increasing image contrast, as well as limitations of the inversion method due to the Poisson noise, discretization errors, radiograph edge effects, and obstruction by laser target structures. We also provide a separate analysis that is suited to the inference of isotropic-homogeneous magnetic turbulence spectra. Finally, we discuss extension of these results to the nonlinear regime (i.e., the order unity image contrast regime).