H Keymeulen | PubMed Health

PubMed2003

Focusing x-ray beams to nanometer dimensions.

We address the question: what is the smallest spot size to which an x-ray beam can be focused? We show that confinement of the beam within a narrowly tapered waveguide leads to a theoretical minimum beam size of the order of 10 nm (FWHM), the exact value depending only on the electron density of the confining material. This limit appears to apply to all x-ray focusing devices. Mode mixing and interference can help to achieve this spot size without the need for ultrasmall apertures.

Journal Article↗

PubMedDate not supplied

Differentiating attention-deficit/hyperactivity disorder from pervasive developmental disorder not otherwise specified.

This study investigated early clinical differences between children with a diagnosis of pervasive developmental disorder not otherwise specified (PDD-NOS) and children with attention-deficit/hyperactivity disorder (ADHD). Differential diagnoses between the two disorders is often difficult in infancy or early childhood. Twenty-seven children with PDD-NOS were matched with 27 children with ADHD as to IQ and chronological age. Their parents were retrospectively questioned on pre-, peri-, and postnatal complications and on atypical or delayed development of the children between 0 and 4 years of age. This exploratory study revealed almost no differences between both groups with respect to pregnancy or birth complications. The results suggest that differences between the two groups become more pronounced and specific with growing age. Consequently, this investigation offers sufficient guidelines for more specific research with larger samples.

Age Factors↗