A study was made of seasonality in twin birth rate in Denmark between 1977 and 1984. We studied all twin births (N = 45,550) in all deliveries (N = 3,679,932) during that period. Statistical analysis using a simple harmonic sinusoidal model provided no evidence for seasonality. However, sequential polynomial analysis disclosed a significant fit to a fifth order polynomial curve with peaks in tw...

Dislocation interaction with and accumulation at twin boundaries have been reported to significantly improve the strength and ductility of nanostructured face-centered cubic (fcc) metals and alloys. Here we systematically describe plausible dislocation interactions at twin boundaries. Depending on the characteristics of the dislocations and the driving stress, possible dislocation reactions at ...

We have revealed the fundamental embryonic structure of deformation twins using in situ mechanical testing of magnesium single crystals in a transmission electron microscope. This structure consists of an array of twin-related laths on the scale of several nanometers. A computational model demonstrates that this structure should be a generic feature at the incipient stage of deformation twinnin...

Copper monocrystals were subjected to shock compression at pressures of 10-60 GPa by a short (3 ns initial) duration laser pulse. Transmission electron microscopy revealed features consistent with previous observations of shock-compressed copper, albeit at pulse durations in the us regime. The results suggest that the defect structure is generated at the shock front. A mechanism for dislocation...

Conjoined twins are the most rare form of monozygotic twinning occurring when there is incomplete division of the embryonic disc after day 13 post conception. This is associated with a very high risk of perinatal morbidity and mortality. Prognosis is dependent on the site and extent of fusion and the degree of sharing of vital organs. Most conjoined twins die in utero or in the early neonatal p...

We report evidence in GaP and InP nanowires for a coherent modulation of the structure along the wire axis. By using electron diffraction, we have observed an additional series of diffraction peaks consistent with a quasiperiodic placement of twinning boundaries along the wire. This observation is indeed unexpected, as the vapor-liquid-solid growth conditions used to produce the nanowires were ...

Thin HfO2 films grown on the lightly oxidised surface of (100) Si wafers have been examined using dark-field transmission electron microscopy and selected area electron diffraction in plan view. The polycrystalline film has a grain size of the order of 100 nm and many of the grains show evidence of twinning on (110) and (001) planes. Diffraction studies showed that the film had a strong [110] o...

It is not uncommon for protein crystals to crystallize with more than a single molecule per asymmetric unit. When more than a single molecule is present in the asymmetric unit, various pathological situations such as twinning, modulated crystals and pseudo translational or rotational symmetry can arise. The presence of pseudosymmetry can lead to uncertainties about the correct space group, espe...