Implications of size dispersion on X-ray scattering of crystalline nanoparticles: CeO2 as a case study.

Controlling the shape and size dispersivity and crystallinity of nanoparticles (NPs) has been a challenge in identifying these parameters' role in the physical and chemical properties of NPs. The need for reliable quantitative tools for analyzing the dispersivity and crystallinity of NPs is a considerable problem in optimizing scalable synthesis routes capable of controlling NP properties. The most common tools are electron microscopy (EM) and X-ray scattering techniques. However, each technique has different susceptibility to these parameters, implying that more than one technique is necessary to characterize NP systems with maximum reliability. Wide-angle X-ray scattering (WAXS) is mandatory to access information on crystallinity. In contrast, EM or small-angle X-ray scattering (SAXS) is required to access information on whole NP sizes. EM provides average values on relatively small ensembles in contrast to the bulk values accessed by X-ray techniques. Besides the fact that the SAXS and WAXS techniques have different susceptibilities to size distributions, SAXS is easily affected by NP-NP interaction distances. Because of all the variables involved, there have yet to be proposed methodologies for cross-analyzing data from two techniques that can provide reliable quantitative results of dispersivity and crystallinity. In this work, a SAXS/WAXS-based methodology is proposed for simultaneously quantifying size distribution and degree of crystallinity of NPs. The most reliable easy-to-access size result for each technique is demonstrated by computer simulation. Strategies on how to compare these results and how to identify NP-NP interaction effects underneath the SAXS intensity curve are presented. Experimental results are shown for cubic-like CeO2 NPs. WAXS size results from two analytical procedures are compared, line-profile fitting of individual diffraction peaks in opposition to whole pattern fitting. The impact of shape dispersivity is also evaluated. Extension of the proposed methodology for cross-analyzing EM and WAXS data is possible.

Is the Mayfield Head Holder Obligatory for Intracranial Aneurysm Clipping?

Intracranial aneurysm surgery is commonly performed using pinned head holders, which pose a higher risk for the pediatric population. Several authors recommend avoiding the use of this device when it is not strictly necessary, and this is currently possible considering advances in anesthesiology and monitoring. As the literature on microsurgery without skull clamp use is scant, we report the case of a 15-year-old boy presenting with a subarachnoid hemorrhage after rupture of a middle cerebral artery aneurysm. Surgical treatment was performed with the head resting on a gel cushion horseshoe; aneurysm clipping was achieved without wakefulness or awareness and the patient had a good recovery.