Staurolite has been long considered an enigma because of its remarkable pseudosymmetry and the frequent twinning. Staurolite gives two twins whose occurrence frequency seems to contradict the condition of lattice restoration requested by the reticular theory of twinning, in that the more frequent one (Saint Andrews cross twin) has a twin index of 12, whereas the less frequent one (Greek cross t...

We analyze the association between the rates of multiple maternities. Correlation analysis is suitable if there are at least monotonic relationships between the variables. A decreasing tendency can be observed in the rates of multiple maternities in Sweden and in its 25 counties for the period 1751-1960 and the effect of external variables can be assumed to be monotonic. After 1960, the rates o...

Twin birth rates have increased markedly in developed countries since the 1970s for two primary reasons: increasing maternal age and the advent and increasing use of fertility treatments. In addition, monozygotic (MZ) twin pregnancies have been reported to occur at a significantly higher rate following assisted reproductive technologies (ART) procedures compared with the natural incidence. Twin...

Copper with two orientations ([001] and [134]) was subjected to high intensity laser (energy levels of 40-300 J; energy densities of 15-70 MJ/m and durations below 10 ns). The defects created are characterized by transmission electron microscopy. An orientation-dependent threshold stress for twinning is observed. The results are rationalized in terms of a criterion in which slip and twinning ar...

BACKGROUND Decreased fecundity has been hypothesized as one of the causes of the widespread decline in twin rates in the 1960s and 1970s. The association between high fecundity and twinning is not, however, well documented. METHODS In the Danish National Birth Cohort, we identified 56 295 births (including 729 twin deliveries) with data on pregnancy planning and time to pregnancy (TTP) and no...

BACKGROUND It is estimated that there is at least a 2-fold rise in the incidence of monozygotic twinning after assisted reproductive technology compared with natural conception. This can result in adverse pregnancy outcomes. METHODS We searched MEDLINE, EMBASE and SCISEARCH for studies that estimated the risk of monozygotic twinning and its association with any particular assisted reproductiv...

The incidence of twin births in Accra and Kumasi, the two major cities in Ghana, was investigated. In Accra, data were collected from the Korle-Bu Teaching Hospital while data were collected and analyzed from the Komfo Anokye Teaching Hospital in Kumasi. Both hospitals are the leading teaching hospitals in Ghana. The data consisted mainly of single and twin births recorded in the hospitals over...

A comprehensive theory of quasi-phase-matched (QPM) three-wave interactions in twinned plates of q3m semiconductors is developed. The 180* phase change required by QPM is studied by treating the nonlinear polarization as a bilinear form in the applied electric field and decomposing it into invariant and sign changing parts under a 2-fold rotation of an arbitrary crystal lattice. A new 3 X 3 mat...