Measurement of elastic forces between iron colloidal particles in a nematic liquid crystal.

The forces that arise between two iron particles in a nematic liquid crystal with a strong homeotropic anchoring were studied. For the first time, the short range repulsive force resulting from the presence of a hedgehog defect between two particles was precisely determined thanks to application of a small magnetic field and observation of the equilibrium position resulting from the balance between the elastic and magnetic forces. Above a given threshold force, the particles stuck together whereas the hedgehog defect was expelled and transformed into a Saturn ring located between the particles. The attractive part of the interparticle force was determined with the same method on the entire range of separation distances; we found that the equilibrium distance between two particles was r = 1.19 +/- 0.05 ( was the average diameter of the pair of particles).

Neurological presentation of three patients with 22q11 deletion (CATCH 22 syndrome).

Chromosome 22q11 deletion (CATCH 22 syndrome or velocardiofacial syndrome) is one of the most frequent chromosomal syndromes. Neurological features other than cognitive disorders are probably the least-described part of the expanding phenotype of the 22q11 deletion. We report the neurological features of three unrelated children with a de novo deletion: one patient with an autistic disorder, a second patient with hypocalcaemic neonatal seizures and unusual persistent epileptic focus at electroencephalographic follow-up, and a third patient with atypical absence epilepsy. These observations enlarge the clinical and neurological spectrum of the 22q11 deletion. Awareness of such cases is necessary, and a diagnosis of the 22q11 deletion should be suspected in children with common neurological features associated with severe or mild dysmorphism. Diagnosis of the 22q11 deletion should be confirmed by fluorescence in situ hybridization analysis associated with standard chromosomal analysis.